Gene Summary

Gene:PPIA; peptidylprolyl isomerase A
Aliases: CYPA, CYPH, HEL-S-69p
Summary:This gene encodes a member of the peptidyl-prolyl cis-trans isomerase (PPIase) family. PPIases catalyze the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and accelerate the folding of proteins. The encoded protein is a cyclosporin binding-protein and may play a role in cyclosporin A-mediated immunosuppression. The protein can also interact with several HIV proteins, including p55 gag, Vpr, and capsid protein, and has been shown to be necessary for the formation of infectious HIV virions. Multiple pseudogenes that map to different chromosomes have been reported. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:peptidyl-prolyl cis-trans isomerase A
Source:NCBIAccessed: 15 March, 2017


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 15 March 2017 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

Tag cloud generated 15 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (6)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: PPIA (cancer-related)

Cheng S, Luo M, Ding C, et al.
Downregulation of Peptidylprolyl isomerase A promotes cell death and enhances doxorubicin-induced apoptosis in hepatocellular carcinoma.
Gene. 2016; 591(1):236-44 [PubMed] Related Publications
Peptidylprolyl isomerase A (PPIA) is a peptidyl-prolyl cis-trans isomerase that is known to play a critical role in the development of many human cancers. However, the precise biological function of PPIA in hepatocellular carcinoma (HCC) remains largely unclear. In this study, lentiviral overexpression vectors and small interfering RNA knockdown methods were employed to investigate the biological effects of PPIA in HCC. PPIA levels in HCC tissues and peritumoral tissues were detected by real-time Polymerase Chain Reaction (RT-PCR), Western blotting, and immunohistochemistry. Our results indicate that PPIA levels were significantly higher in the HCC tissues compared to the matched peritumoral tissues. Moreover, PPIA expression was significantly associated with tumor size in these tissues. Interestingly, serum PPIA (sPPIA) levels were significantly higher in healthy controls compared to the HCC patients. Knockdown or overexpression of PPIA was shown to downregulate and upregulate cell growth, respectively. Moreover, PPIA siRNA knockdown appears to promote doxorubicin-induced apoptosis in HCC cells, altering the expression of downstream apoptotic factors. In summary, our results indicate that PPIA may play a pivotal role in HCC by regulating cell growth and could serve as a novel marker and therapeutic molecular target for HCC patients.

Wu R, Nijland M, Rutgers B, et al.
Proteomics Based Identification of Proteins with Deregulated Expression in B Cell Lymphomas.
PLoS One. 2016; 11(1):e0146624 [PubMed] Free Access to Full Article Related Publications
Follicular lymphoma and diffuse large B cell lymphomas comprise the main entities of adult B cell malignancies. Although multiple disease driving gene aberrations have been identified by gene expression and genomic studies, only a few studies focused at the protein level. We applied 2 dimensional gel electrophoresis to compare seven GC B cell non Hodgkin lymphoma (NHL) cell lines with a lymphoblastoid cell line (LCL). An average of 130 spots were at least two folds different in intensity between NHL cell lines and the LCL. We selected approximately 38 protein spots per NHL cell line and linked them to 145 unique spots based on the location in the gel. 34 spots that were found altered in at least three NHL cell lines when compared to LCL, were submitted for LC-MS/MS. This resulted in 28 unique proteins, a substantial proportion of these proteins were involved in cell motility and cell metabolism. Loss of expression of B2M, and gain of expression of PRDX1 and PPIA was confirmed in the cell lines and primary lymphoma tissue. Moreover, inhibition of PPIA with cyclosporine A blocked cell growth of the cell lines, the effect size was associated with the PPIA expression levels. In conclusion, we identified multiple differentially expressed proteins by 2-D proteomics, and showed that some of these proteins might play a role in the pathogenesis of NHL.

Sharan RN, Vaiphei ST, Nongrum S, et al.
Consensus reference gene(s) for gene expression studies in human cancers: end of the tunnel visible?
Cell Oncol (Dordr). 2015; 38(6):419-31 [PubMed] Related Publications
BACKGROUND: Gene expression studies are increasingly used to provide valuable information on the diagnosis and prognosis of human cancers. Also, for in vitro and in vivo experimental cancer models gene expression studies are widely used. The complex algorithms of differential gene expression analyses require normalization of data against a reference or normalizer gene, or a set of such genes. For this purpose, mostly invariant housekeeping genes are used. Unfortunately, however, there are no consensus (housekeeping) genes that serve as reference or normalizer for different human cancers. In fact, scientists have employed a wide range of reference genes across different types of cancer for normalization of gene expression data. As a consequence, comparisons of these data and/or data harmonizations are difficult to perform and challenging. In addition, an inadequate choice for a reference gene may obscure genuine changes and/or result in erroneous gene expression data comparisons.
METHODS: In our effort to highlight the importance of selecting the most appropriate reference gene(s), we have screened the literature for gene expression studies published since the turn of the century on thirteen of the most prevalent human cancers worldwide.
CONCLUSIONS: Based on the analysis of the data at hand, we firstly recommend that in each study the suitability of candidate reference gene(s) should carefully be evaluated in order to yield reliable differential gene expression data. Secondly, we recommend that a combination of PPIA and either GAPDH, ACTB, HPRT and TBP, or appropriate combinations of two or three of these genes, should be employed in future studies, to ensure that results from different studies on different human cancers can be harmonized. This approach will ultimately increase the depth of our understanding of gene expression signatures across human cancers.

Ayakannu T, Taylor AH, Willets JM, et al.
Validation of endogenous control reference genes for normalizing gene expression studies in endometrial carcinoma.
Mol Hum Reprod. 2015; 21(9):723-35 [PubMed] Related Publications
Real-time quantitative RT-PCR (qRT-PCR) is a powerful technique used for the relative quantification of target genes, using reference (housekeeping) genes for normalization to ensure the generation of accurate and robust data. A systematic examination of the suitability of endogenous reference genes for gene expression studies in endometrial cancer tissues is absent. The aims of this study were therefore to identify and evaluate from the thirty-two possible reference genes from a TaqMan(®) array panel their suitability as an internal control gene. The mathematical software packages geNorm qBasePLUS identified Pumilio homolog 1 (Drosophila) (PUM1), ubiquitin C (UBC), phosphoglycerate kinase (PGK1), mitochondrial ribosomal protein L19 (MRPL19) and peptidylpropyl isomerase A (cyclophilin A) (PPIA) as the best reference gene combination, whilst NormFinder identified MRPL19 as the best single reference gene, with importin 8 (IPO8) and PPIA being the best combination of two reference genes. BestKeeper ranked MRPL19 as the most stably expressed gene. In addition, the study was validated by examining the relative expression of a test gene, which encodes the cannabinoid receptor 1 (CB1). A significant difference in CB1 mRNA expression between malignant and normal endometrium using MRPL19, PPIA, and IP08 in combination was observed. The use of MRPL19, IPO8 and PPIA was identified as the best reference gene combination for the normalization of gene expression levels in endometrial carcinoma. This study demonstrates that the arbitrary selection of endogenous control reference genes for normalization in qRT-PCR studies of endometrial carcinoma, without validation, risks the production of inaccurate data and should therefore be discouraged.

Xin J, Ren X, Chen L, Wang Y
Identifying network biomarkers based on protein-protein interactions and expression data.
BMC Med Genomics. 2015; 8 Suppl 2:S11 [PubMed] Free Access to Full Article Related Publications
Identifying effective biomarkers to battle complex diseases is an important but challenging task in biomedical research today. Molecular data of complex diseases is increasingly abundant due to the rapid advance of high throughput technologies. However, a great gap remains in identifying the massive molecular data to phenotypic changes, in particular, at a network level, i.e., a novel method for identifying network biomarkers is in pressing need to accurately classify and diagnose diseases from molecular data and shed light on the mechanisms of disease pathogenesis. Rather than seeking differential genes at an individual-molecule level, here we propose a novel method for identifying network biomarkers based on protein-protein interaction affinity (PPIA), which identify the differential interactions at a network level. Specifically, we firstly define PPIAs by estimating the concentrations of protein complexes based on the law of mass action upon gene expression data. Then we select a small and non-redundant group of protein-protein interactions and single proteins according to the PPIAs, that maximizes the discerning ability of cases from controls. This method is mathematically formulated as a linear programming, which can be efficiently solved and guarantees a globally optimal solution. Extensive results on experimental data in breast cancer demonstrate the effectiveness and efficiency of the proposed method for identifying network biomarkers, which not only can accurately distinguish the phenotypes but also provides significant biological insights at a network or pathway level. In addition, our method provides a new way to integrate static protein-protein interaction information with dynamical gene expression data.

Feng W, Xin Y, Xiao Y, et al.
Cyclophilin A Enhances Cell Proliferation and Xenografted Tumor Growth of Early Gastric Cancer.
Dig Dis Sci. 2015; 60(9):2700-11 [PubMed] Related Publications
BACKGROUND: Recently Cyclophilin A (CypA) was identified as a candidate target protein in gastric carcinoma. However, the role of CypA in gastric cancer (GC) has not been investigated extensively so far.
AIM: The purpose of this study was to determine the expression pattern of CypA in human GC, and to explore the effects of suppressed CypA expression on cell proliferation and xenografted tumor growth of gastric cancer.
METHODS: In the present study, we detected the expression pattern of CypA in human GC by immunohistochemistry analysis. Further, the RNAi method was used to silence CypA, and colony formation assay, growth curves, cell cycle and mouse xenograft were analysed.
RESULTS: An elevated expression of CypA in GC tissues compared with normal gastric mucosa was observed, especially in TNM stage-I and intestinal type of tumor. CypA was overexpressed in most GC cell lines and endogenous expression of CypA correlated with cell growth phenotypes. Transient suppression of CypA reduced the proliferation of BGC-823 and SGC-7901 GC cell lines. Exogenous CypA promoted the proliferation of NCI-N87 GC cells in a concentration dependent manner. Further study revealed that stable CypA silencing inhibited the proliferation, prevented cell cycle and reduced autophagy of BGC-823 GC cells in vitro through suppressing the ERK1/2 signal pathway. Stable CypA silencing also inhibited the growth of xenografted tumor of BGC-823 GC cell in nude mice.
CONCLUSIONS: These results indicate a special function mode for CypA of playing more important roles in the early stage of gastric tumorigenesis and suggest CypA as a new molecular target of diagnosis and treatment for GC patients.

Zhu D, Wang Z, Zhao JJ, et al.
The Cyclophilin A-CD147 complex promotes the proliferation and homing of multiple myeloma cells.
Nat Med. 2015; 21(6):572-80 [PubMed] Free Access to Full Article Related Publications
B cell malignancies frequently colonize the bone marrow. The mechanisms responsible for this preferential homing are incompletely understood. Here we studied multiple myeloma (MM) as a model of a terminally differentiated B cell malignancy that selectively colonizes the bone marrow. We found that extracellular CyPA (eCyPA), secreted by bone marrow endothelial cells (BMECs), promoted the colonization and proliferation of MM cells in an in vivo scaffold system via binding to its receptor, CD147, on MM cells. The expression and secretion of eCyPA by BMECs was enhanced by BCL9, a Wnt-β-catenin transcriptional coactivator that is selectively expressed by these cells. eCyPA levels were higher in bone marrow serum than in peripheral blood in individuals with MM, and eCyPA-CD147 blockade suppressed MM colonization and tumor growth in the in vivo scaffold system. eCyPA also promoted the migration of chronic lymphocytic leukemia and lymphoplasmacytic lymphoma cells, two other B cell malignancies that colonize the bone marrow and express CD147. These findings suggest that eCyPA-CD147 signaling promotes the bone marrow homing of B cell malignancies and offer a compelling rationale for exploring this axis as a therapeutic target for these malignancies.

Qu X, Wang C, Zhang J, et al.
The roles of CD147 and/or cyclophilin A in kidney diseases.
Mediators Inflamm. 2014; 2014:728673 [PubMed] Free Access to Full Article Related Publications
CD147 is a widely expressed integral plasma membrane glycoprotein and has been involved in a variety of physiological and pathological activities in combination with different partners, including cyclophilins, caveolin-1, monocarboxylate transporters, and integrins. Recent data demonstrate that both CyPA and CD147 significantly contribute to renal inflammation, acute kidney injury, renal fibrosis, and renal cell carcinoma. Here we review the current understanding of cyclophilin A and CD147 expression and functions in kidney diseases and potential implications for treatment of kidney diseases.

Ali H, Du Z, Li X, et al.
Identification of suitable reference genes for gene expression studies using quantitative polymerase chain reaction in lung cancer in vitro.
Mol Med Rep. 2015; 11(5):3767-73 [PubMed] Related Publications
The present study aimed to examine 10 housekeeping genes (HKGs), including 18s ribosomal RNA (18S), glyceraldehyde‑3‑phosphate dehydrogenase (GAPDH), ribosomal protein large P0 (RPLP0), β‑actin (ACTB), peptidylprolyl isomerase A (PPIA), phosphoglycerate kinase‑1 (PGK1), β‑2‑microglobulin (B2M), ribosomal protein LI3a (RPL13A), hypoxanthine phosphoribosyl transferase‑1 (HPRT1) and TATA box binding protein (TBP) in order to identify the most stable and suitable reference genes for use in expression studies in non‑small cell lung cancer. The mRNA expression encoding the panel of the 10 HKGs was determined using reverse transcription‑quantitative PCR (RT‑qPCR) in human lung cancer cell lines. Three software programs, BestKeeper, NormFinder and geNorm, were used to ascertain the most suitable reference genes to normalize the RNA input. The present study examined three lung cancer cell lines (A549, NCI‑H446 and NCI‑H460). The analysis of the experimental data using BestKeeper software revealed that all 10 HKGs were stable, with GADPH, followed by 18S being the most stable genes and PPIA and HPRT1 being the least stable genes. The NormFinder software results demonstrated that PPIA followed by ACTB were the most stable and B2M and RPLP0 were the least stable. The geNorm software results revealed that ACTB and PGK1, followed by PPIA were the most stable genes and B2M and RPLP0 were identified as the least stable genes. Due to discrepancies in the ranking orders of the reference genes obtained by different analyzing software programs, it was not possible to determine a single universal reference gene. The suitability of selected reference genes requires unconditional validation prior to each study. Based on the three analyzing programs, ACTB, PPIA and PGK1 were the most stable reference genes in lung cancer cell lines.

Romani C, Calza S, Todeschini P, et al.
Identification of optimal reference genes for gene expression normalization in a wide cohort of endometrioid endometrial carcinoma tissues.
PLoS One. 2014; 9(12):e113781 [PubMed] Free Access to Full Article Related Publications
Accurate normalization is a primary component of a reliable gene expression analysis based on qRT-PCR technique. While the use of one or more reference genes as internal controls is commonly accepted as the most appropriate normalization strategy, many qPCR-based published studies still contain data poorly normalized and reference genes arbitrarily chosen irrespective of the particular tissue and the specific experimental design. To date, no validated reference genes have been identified for endometrial cancer tissues. In this study, 10 normalization genes (GAPDH, B2M, ACTB, POLR2A, UBC, PPIA, HPRT1, GUSB, TBP, H3F3A) belonging to different functional and abundance classes in various tissues and used in different studies, were analyzed to determine their applicability. In total, 100 endometrioid endometrial cancer samples, which were carefully balanced according to their tumor grade, and 29 normal endometrial tissues were examined using SYBR Green Real-Time RT-PCR. The expression stability of candidate reference genes was determined and compared by means of geNorm and NormFinder softwares. Both algorithms were in agreement in identifying GAPDH, H3F3A, PPIA, and HPRT1 as the most stably expressed genes, only differing in their ranking order. Analysis performed on the expression levels of all candidate genes confirm HPRT1 and PPIA as the most stably expressed in the study groups regardless of sample type, to be used alone or better in combination. As the stable expression of HPRT1 and PPIA between normal and tumor endometrial samples fulfill the basic requirement of a reference gene to be used for normalization purposes, HPRT1 expression showed significant differences between samples from low-grade and high-grade tumors. In conclusion, our results recommend the use of PPIA as a single reference gene to be considered for improved reliability of normalization in gene expression studies involving endometrial tumor samples at different tumor degrees.

Coumans JV, Gau D, Poljak A, et al.
Profilin-1 overexpression in MDA-MB-231 breast cancer cells is associated with alterations in proteomics biomarkers of cell proliferation, survival, and motility as revealed by global proteomics analyses.
OMICS. 2014; 18(12):778-91 [PubMed] Free Access to Full Article Related Publications
Despite early screening programs and new therapeutic strategies, metastatic breast cancer is still the leading cause of cancer death in women in industrialized countries and regions. There is a need for novel biomarkers of susceptibility, progression, and therapeutic response. Global analyses or systems science approaches with omics technologies offer concrete ways forward in biomarker discovery for breast cancer. Previous studies have shown that expression of profilin-1 (PFN1), a ubiquitously expressed actin-binding protein, is downregulated in invasive and metastatic breast cancer. It has also been reported that PFN1 overexpression can suppress tumorigenic ability and motility/invasiveness of breast cancer cells. To obtain insights into the underlying molecular mechanisms of how elevating PFN1 level induces these phenotypic changes in breast cancer cells, we investigated the alteration in global protein expression profiles of breast cancer cells upon stable overexpression of PFN1 by a combination of three different proteome analysis methods (2-DE, iTRAQ, label-free). Using MDA-MB-231 as a model breast cancer cell line, we provide evidence that PFN1 overexpression is associated with alterations in the expression of proteins that have been functionally linked to cell proliferation (FKPB1A, HDGF, MIF, PRDX1, TXNRD1, LGALS1, STMN1, LASP1, S100A11, S100A6), survival (HSPE1, HSPB1, HSPD1, HSPA5 and PPIA, YWHAZ, CFL1, NME1) and motility (CFL1, CORO1B, PFN2, PLS3, FLNA, FLNB, NME2, ARHGDIB). In view of the pleotropic effects of PFN1 overexpression in breast cancer cells as suggested by these new findings, we propose that PFN1-induced phenotypic changes in cancer cells involve multiple mechanisms. Our data reported here might also offer innovative strategies for identification and validation of novel therapeutic targets and companion diagnostics for persons with, or susceptibility to, breast cancer.

Yu S, Yang Q, Yang JH, et al.
Identification of suitable reference genes for investigating gene expression in human gallbladder carcinoma using reverse transcription quantitative polymerase chain reaction.
Mol Med Rep. 2015; 11(4):2967-74 [PubMed] Related Publications
Reverse transcription quantitative polymerase chain reaction (RT‑qPCR) has become a frequently used strategy in gene expression studies. The relative quantification method is an important and commonly used method for the evaluation of RT‑qPCR data. The key aim of this method is to identify an applicable internal reference gene, however, there are currently no suitable reference genes for gene analysis in gallbladder carcinoma. In the present study, screening was performed using 12 common reference genes, which were selected in order to provide an experimental basis for the investigation of gene expression in gallbladder carcinoma. A total of 16 tissue samples of gallbladder carcinoma and their matched normal gallbladder tissues were used. The gene expression stability and applicability of the 12 reference gene candidates were determined using the geNorm, NormFinder and BestKeeper software programs. Following comparison of the results of the three software programs, HPRT1 was identified as the most stably expressed reference gene. In the normal gallbladder group, the relative stably expressed reference gene was PPIA and in the entire sample group, the relatively stably expressed reference gene was PPIA. The present study also demonstrated that the combination of the three reference genes was the most appropriate. The recommended combinations were PPIA + PUM1 + ACTB for the total sample group, GAPDH + PBGD + ALAS1 for the gallbladder carcinoma group and PPIA + PUM1 + TBP for the paired normal gallbladder group.

Feng MX, Li JP, Wang H, et al.
Clinical significance of cyclophilin a expression in esophageal squamous cell carcinoma.
Genet Test Mol Biomarkers. 2015; 19(4):182-6 [PubMed] Related Publications
OBJECTIVE: To explore the expression of cyclophilin A (CypA) in esophageal tissues and its clinical significance.
METHOD: Expression of CypA was detected in 236 esophageal cancer tissues and 236 normal tissues by using an immunohistochemical method, and the relationship between CypA expression and clinical outcomes was observed.
RESULTS: There were 166 patients with high expression of CypA (70.23%) and a higher expression in 69.3% of males and 73.3% in females. The CypA expression was irrelevant to age, tumor location, lymph node metastasis, and tumor differentiation degree. The Kaplan-Meier survival curve analysis showed that the expression of CypA was associated with the prognosis of patients with esophageal squamous cell carcinoma.
CONCLUSION: The poor prognosis of esophageal cancer patients was associated with high expression of CypA.

Obchoei S, Sawanyawisuth K, Wongkham C, et al.
Secreted cyclophilin A mediates G1/S phase transition of cholangiocarcinoma cells via CD147/ERK1/2 pathway.
Tumour Biol. 2015; 36(2):849-59 [PubMed] Related Publications
Cyclophilin A (CypA) was shown to be upregulated in human cholangiocarcinoma (CCA) tissues. Suppression of intracellular CypA (inCypA) significantly reduces cell proliferation in vitro and tumor growth in nude mice. In the present study, the effect and potential mechanism of secreted CypA (sCypA) on cell proliferation of CCA cell lines were further investigated. CCA cells were treated with sCypA-containing conditioned media (CM) or with purified recombinant human CypA (rhCypA). Cell proliferation, cell cycle, ERK1/2, p38 MAPK, NF-κB, and STAT3 activities were examined by MTS assay, flow cytometry, and Western blot. sCypA was detected in CM from MMNK1 (an immortalized human cholangiocyte cell line) and six CCA cell lines. The sCypA levels corresponded to the inCypA levels indicating the intracellular origin of sCypA. Both sCypA-containing CM and rhCypA significantly increased proliferation of CCA cells. CD147 depletion by shRNA-knockdown or neutralizing with a CD147-monoclonal antibody significantly reduced sCypA-, and rhCypA-mediated cell proliferation. Upon rhCypA treatment, ERK1/2 was rapidly phosphorylated; whereas neutralizing CD147 inhibited ERK1/2 phosphorylation. Cell cycle analysis showed a significant increase in S phase and decrease in G1 population in rhCypA-treated cells. The expression levels of cyclin D1 and phosphorylated-retinoblastoma protein in the rhCypA-treated cells were increased compared with those in the non-treated control cells. p38 MAPK pathway was shown to be suppressed in siCypA-treated cells. In summary, CypA is secreted from CCA cells and enhances cell proliferation in an autocrine/paracrine manner, at least via direct binding with CD147, which may activate the ERK1/2 and p38 MAPK signaling pathways.

Zhang F, Li C, Liu H, et al.
The functional proteomics analysis of VEGF-treated human epithelial ovarian cancer cells.
Tumour Biol. 2014; 35(12):12379-87 [PubMed] Related Publications
Vascular endothelial growth factor (VEGF), one of the most important angiogenic factor, can impact the tumor cell proliferation and invasion, but the mechanism remains unclear. This study is to investigate the key proteins which may play an important role in the VEGF-induced progress of ovarian cancer cells. The total protein from HO-8910 cells was separated by two-dimensional electrophoresis (2-DE), and differentially expressed proteins were identified by matrix-assisted laser desorption and ionization time-of-flight tandem mass spectrometry (MALDI-TOF MS) and PDQuest image analysis software. Furthermore, real-time PCR, Western blot, and immunocytochemistry were also used to confirm different expression levels of differential proteins. Morphological changes and invasion capability were evaluated by electron microscope and Matrigel invasion assay, respectively. The highly reproducible and well-resolved 2-DE patterns of both HO-8910/VEGF and HO-8910 cells were acquired. A total of 17 expressed differential proteins were identified, 8 proteins were upregulated (ACTB, TIM, PDIA3, PDIA1, DCTN2, KIC17, SIAS, and KIC10) and 9 downregulated (KIC18, GRP78, CAPG, PPIA, ROA2, LMNA, EZRI, ADRM1, and ENOA). Ultrastructure of VEGF-treated group showed more malignant characteristic compared with control group, an obvious increase in the number of cells penetrating the Matrigel membrane in VEGF-treated group (P < 0.05). These results suggested that VEGF could impact ovarian cancer's malignant progression by regulating expression of associated proteins.

Dupasquier S, Delmarcelle AS, Marbaix E, et al.
Validation of housekeeping gene and impact on normalized gene expression in clear cell renal cell carcinoma: critical reassessment of YBX3/ZONAB/CSDA expression.
BMC Mol Biol. 2014; 15:9 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: YBX3/ZONAB/CSDA is an epithelial-specific transcription factor acting in the density-based switch between proliferation and differentiation. Our laboratory reported overexpression of YBX3 in clear cell renal cell arcinoma (ccRCC), as part of a wide study of YBX3 regulation in vitro and in vivo. The preliminary data was limited to 5 cases, of which only 3 could be compared to paired normal tissue, and beta-Actin was used as sole reference to normalize gene expression. We thus decided to re-evaluate YBX3 expression by real-time-PCR in a larger panel of ccRCC samples, and their paired healthy tissue, with special attention on experimental biases such as inter-individual variations, primer specificity, and reference gene for normalization.
RESULTS: Gene expression was measured by RT-qPCR in 16 ccRCC samples, each compared to corresponding healthy tissue to minimize inter-individual variations. Eight potential housekeeping genes were evaluated for expression level and stability among the 16-paired samples. Among tested housekeeping genes, PPIA and RPS13, especially in combination, proved best suitable to normalize gene expression in ccRCC tissues as compared to classical reference genes such as beta-Actin, GAPDH, 18S or B2M. Using this pair as reference, YBX3 expression level among a collection of 16 ccRCC tumors was not significantly increased as compared to normal adjacent tissues. However, stratification according to Fuhrman grade disclosed higher YBX3 expression levels in low-grade tumors and lower in high-grade tumors. Immunoperoxidase confirmed homogeneous nuclear staining for YBX3 in low-grade but revealed nuclear heterogeneity in high-grade tumors.
CONCLUSIONS: This paper underlines that special attention to reference gene products in the design of real-time PCR analysis of tumoral tissue is crucial to avoid misleading conclusions. Furthermore, we found that global YBX3/ZONAB/CSDA mRNA expression level may be considered within a "signature" of RCC grading.

Krzystek-Korpacka M, Diakowska D, Bania J, Gamian A
Expression stability of common housekeeping genes is differently affected by bowel inflammation and cancer: implications for finding suitable normalizers for inflammatory bowel disease studies.
Inflamm Bowel Dis. 2014; 20(7):1147-56 [PubMed] Related Publications
Instability of housekeeping genes (HKG), supposedly unregulated and hence used as normalizers, may dramatically change conclusions of quantitative PCR experiments. The effect of bowel inflammation on HKG remains unknown. Expression stability of 15 HKG (ACTB, B2M, GAPDH, GUSB, HPRT1, IPO8, MRPL19, PGK1, PPIA, RPLP0, RPS23, SDHA, TBP, UBC, and YWHAZ) in 166 bowel specimens (91 normal, 35 cancerous, and 40 inflamed) was ranked by coefficients of variation (CV%) or using dedicated software: geNorm and NormFinder. The RPS23, PPIA, and RPLP0 were top-ranked, whereas IPO8, UBC and TBP were the lowest-ranked HKG across inflamed/cancerous/normal colonic tissues. The pairs RPS23/RPLP0, PGK1/MRPL19, or PPIA/RPLP0 were optimal reference by CV%, NormFinder, and geNorm, respectively. Colon inflammation affected HKG more pronouncedly than cancer with ACTB significantly down- and B2M upregulated. In inflammatory bowel disease (IBD), different genes were top-ranked in a large and small bowel, whereas TBP, UBC, and IPO8 were lowest-ranked in both. For patients with IBD at large, RPS23/PPIA, PGK1/MRPL19, and PPIA/RPLP0 were found optimal by CV%, NormFinder, and geNorm, respectively. ACTB and B2M expression was related to CRC stage and positively correlated with clinical activity of IBD. Although GAPDH was upregulated neither in CRC nor IBD, it tended to positively correlate with tumor depth and Crohn's disease activity index. Normalizing against GAPDH affected experimental conclusions in a small but not large bowel. Bowel inflammation significantly affects several classic HKG. The pair PPIA/RPLP0 is a common optimal reference for studies encompassing tissues sampled from colorectal cancer and IBD patients. Using ACTB or B2M is not recommended.

Cai J, Li T, Huang B, et al.
The use of laser microdissection in the identification of suitable reference genes for normalization of quantitative real-time PCR in human FFPE epithelial ovarian tissue samples.
PLoS One. 2014; 9(4):e95974 [PubMed] Free Access to Full Article Related Publications
Quantitative real-time PCR (qPCR) is a powerful and reproducible method of gene expression analysis in which expression levels are quantified by normalization against reference genes. Therefore, to investigate the potential biomarkers and therapeutic targets for epithelial ovarian cancer by qPCR, it is critical to identify stable reference genes. In this study, twelve housekeeping genes (ACTB, GAPDH, 18S rRNA, GUSB, PPIA, PBGD, PUM1, TBP, HRPT1, RPLP0, RPL13A, and B2M) were analyzed in 50 ovarian samples from normal, benign, borderline, and malignant tissues. For reliable results, laser microdissection (LMD), an effective technique used to prepare homogeneous starting material, was utilized to precisely excise target tissues or cells. One-way analysis of variance (ANOVA) and nonparametric (Kruskal-Wallis) tests were used to compare the expression differences. NormFinder and geNorm software were employed to further validate the suitability and stability of the candidate genes. Results showed that epithelial cells occupied a small percentage of the normal ovary indeed. The expression of ACTB, PPIA, RPL13A, RPLP0, and TBP were stable independent of the disease progression. In addition, NormFinder and geNorm identified the most stable combination (ACTB, PPIA, RPLP0, and TBP) and the relatively unstable reference gene GAPDH from the twelve commonly used housekeeping genes. Our results highlight the use of homogeneous ovarian tissues and multiple-reference normalization strategy, e.g. the combination of ACTB, PPIA, RPLP0, and TBP, for qPCR in epithelial ovarian tissues, whereas GAPDH, the most commonly used reference gene, is not recommended, especially as a single reference gene.

Zhang H, Chen J, Liu F, et al.
CypA, a gene downstream of HIF-1α, promotes the development of PDAC.
PLoS One. 2014; 9(3):e92824 [PubMed] Free Access to Full Article Related Publications
Hypoxia-inducible factor-1α (HIF-1α) is a highly important transcription factor involved in cell metabolism. HIF-1α promotes glycolysis and inhibits of mitochondrial respiration in pancreatic ductal adenocarcinoma (PDAC). In response to tumor hypoxia, cyclophilin A (CypA) is over-expressed in various cancer types, and is associated with cell apoptosis, tumor invasion, metastasis, and chemoresistance in PDAC. In this study, we showed that both HIF-1α and CypA expression were significantly associated with lymph node metastasis and tumor stage. The expression of CypA was correlated with HIF-1α. Moreover, the mRNA and protein expression of CypA markedly decreased or increased following the suppression or over-expression of HIF-1α in vitro. Chromatin immunoprecipitation analysis showed that HIF-1α could directly bind to the hypoxia response element (HRE) in the CypA promoter regions and regulated CypA expression. Consistent with other studies, HIF-1α and CypA promoted PDAC cell proliferation and invasion, and suppressed apoptosis in vitro. Furthermore, we proved the combination effect of 2-methoxyestradiol and cyclosporin A both in vitro and in vivo. These results suggested that,CypA, a gene downstream of HIF-1α, could promote the development of PDAC. Thus, CypA might serve as a potential therapeutic target for PDAC.

Zhan C, Zhang Y, Ma J, et al.
Identification of reference genes for qRT-PCR in human lung squamous-cell carcinoma by RNA-Seq.
Acta Biochim Biophys Sin (Shanghai). 2014; 46(4):330-7 [PubMed] Related Publications
Although the accuracy of quantitative real-time polymerase chain reaction (qRT-PCR) is highly dependent on the reliable reference genes, many commonly used reference genes are not stably expressed and as such are not suitable for quantification and normalization of qRT-PCR data. The aim of this study was to identify novel reliable reference genes in lung squamous-cell carcinoma. We used RNA sequencing (RNA-Seq) to survey the whole genome expression in 5 lung normal samples and 44 lung squamous-cell carcinoma samples. We evaluated the expression profiles of 15 commonly used reference genes and identified five additional candidate reference genes. To validate the RNA-Seq dataset, we used qRT-PCR to verify the expression levels of these 20 genes in a separate set of 100 pairs of normal lung tissue and lung squamous-cell carcinoma samples, and then analyzed these results using geNorm and NormFinder. With respect to 14 of the 15 common reference genes (B2M, GAPDH, GUSB, HMBS, HPRT1, IPO8, PGK1, POLR2A, PPIA, RPLP0, TBP, TFRC, UBC, and YWHAZ), the expression levels were either too low to be easily detected, or exhibited a high degree of variability either between lung normal and squamous-cell carcinoma samples, or even among samples of the same tissue type. In contrast, 1 of the 15 common reference genes (ACTB) and the 5 additional candidate reference genes (EEF1A1, FAU, RPS9, RPS11, and RPS14) were stably and constitutively expressed at high levels in all the samples tested. ACTB, EEF1A1, FAU, RPS9, RPS11, and RPS14 are ideal reference genes for qRT-PCR analysis of lung squamous-cell carcinoma, while 14 commonly used qRT-PCR reference genes are less appropriate in this context.

Huang CF, Zhang L, Ma SR, et al.
Clinical significance of Keap1 and Nrf2 in oral squamous cell carcinoma.
PLoS One. 2013; 8(12):e83479 [PubMed] Free Access to Full Article Related Publications
Oxidative stress has been reported to play an important role in progression and prognostication in various kinds of cancers. However, the role and clinical significance of oxidative stress markers Keap1 and Nrf2 in oral squamous cell carcinoma (OSCC) has not been elucidated. This study aimed to investigate the correlation of oxidative stress markers Keap1 and Nrf2 expression and pathological features in OSCC by using tissue microarray. Tissue microarrays containing 17 normal oral mucosa, 7 oral epithelial dysplasia and 43 OSCC specimens were studied by immunohistochemistry. The association among these proteins and pathological features were analyzed. Expression of oxidative stress markers Keap1, Nrf2, and antioxidants PPIA, Prdx6, as well as CD147 was found to increase consecutively from normal oral mucosa to OSCC, and the Keap1, Nrf2, PPIA, Prdx6, CD147 expression in OSCC were significantly higher when compared to normal oral mucosa. Expression of Keap1, Nrf2 in tumors was not found to be significantly associated with T category, lymph node metastases, and pathological grade. Furthermore, we checked the relationship among these oxidative stress markers and found that Keap1 was significantly correlated with Nrf2, Prdx6 and CD147. Significant relationship between Nrf2 and Prdx6 was also detected. Finally, we found patients with overexpression of Keap1 and Nrf2 had not significantly worse overall survival by Kaplan-Meier analysis. These findings suggest that ROS markers are associated with carcinogenesis and progression of OSCC, which may have prognostic value and could be regarded as potential therapeutic targets in OSCC.

Li Y, Guo H, Dong D, et al.
Expression and prognostic relevance of cyclophilin A and matrix metalloproteinase 9 in esophageal squamous cell carcinoma.
Diagn Pathol. 2013; 8:207 [PubMed] Free Access to Full Article Related Publications
AIMS: To guide clinicians in selecting treatment options for esophageal squamous cell carcinoma (ESCC) patients, reliable markers predictive of clinical outcome are desirable. This study analyzed the correlation of cyclophilin A (CypA) and matrix metalloproteinase 9 (MMP9) in ESCC and their relationships to clinicopathological features and survival.
METHODS: We immunohistochemically investigated 70 specimens of ESCC tissues using CypA and MMP9 antibodies. Then, the correlations between CypA and MMP9 expression and clinicopathological features and its prognostic relevance were determined.
RESULTS: Significant correlations were only found in high level of CypA and MMP9 expression with tumor differentiation and lymph node status. Significant positive correlations were found between the expression status of CypA and that of MMP9. Overexpression of CypA and metastasis were significantly associated with shorter progression free survival times in univariate analysis. Multivariate analysis confirmed that CypA expression was an independent prognostic factor.
CONCLUSIONS: CypA might be correlated with the differentiation, and its elevated expression may be an adverse prognostic indicator for the patients of ESCC. CypA/MMP9 signal pathway may be attributed to the malignant transformation of ESCC, and attention should be paid to a possible target for therapy.
VIRTUAL SLIDES: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1166551968105508.

Li L, Tang W, Wu X, et al.
HAb18G/CD147 promotes pSTAT3-mediated pancreatic cancer development via CD44s.
Clin Cancer Res. 2013; 19(24):6703-15 [PubMed] Free Access to Full Article Related Publications
PURPOSE: Signal transducer and activator of transcription 3 (STAT3) plays a critical role in initiation and progression of pancreatic cancer. However, therapeutically targeting STAT3 has failed clinically. We previously identified HAb18G/CD147 as an effective target for cancer treatment. In this study, we aimed to investigate the potential role of HAb18G/CD147 in STAT3-involved pancreatic tumorigenesis in vitro and in vivo.
EXPERIMENTAL DESIGN: The expression of HAb18G/CD147, pSTAT3, and CD44s was determined in tissue microarrays. The tumorigenic function and molecular signaling mechanism of HAb18G/CD147 were assessed by in vitro cellular and clonogenic growth, reporter assay, immunoblot assay, immunofluorescence staining, immunoprecipitation, and in vivo tumor formation using loss or gain-of-function strategies.
RESULTS: Highly expressed HAb18G/CD147 promoted cellular and clonogenic growth in vitro and tumorigenicity in vivo. Cyclophilin A (CyPA), a ligand of CD147, stimulated STAT3 phosphorylation and its downstream genes cyclin D1/survivin through HAb18G/CD147-dependent mechanisms. HAb18G/CD147 was associated and colocalized with cancer stem cell marker CD44s in lipid rafts. The inhibitors of STAT3 and survivin, as well as CD44s neutralizing antibodies suppressed the HAb18G/CD147-induced cell growth. High HAb18G/CD147 expression in pancreatic cancer was significantly correlated with the poor tumor differentiation, and the high coexpression of HAb18G/CD147-CD44s-STAT3 associated with poor survival of patients with pancreatic cancer.
CONCLUSIONS: We identified HAb18G/CD147 as a novel upstream activator of STAT3, which interacts with CD44s and plays a critical role in the development of pancreatic cancer. The data suggest that HAb18G/CD147 could be a promising therapeutic target for highly aggressive pancreatic cancer and a surrogate marker in the STAT3-targeted molecular therapies.

Duechler M, Peczek L, Zuk K, et al.
The heterogeneous immune microenvironment in breast cancer is affected by hypoxia-related genes.
Immunobiology. 2014; 219(2):158-65 [PubMed] Related Publications
The immune system constitutes an important first-line defence against malignant transformation. However, cancer mediated immunosuppression inactivates the mechanisms of host immune surveillance. Cancer cells shut down anti-cancer immunity through direct cell-cell interactions with leukocytes and through soluble factors, establishing an immunosuppressive environment for unimpeded cancer growth. The composition of the immunosuppressive microenvironment in breast tumours is not well documented. To address this question, selected immunosuppressive factors were analyzed in tumour specimens from 33 breast cancer patients after surgery. The mRNA expression of selected genes was quantified in fresh tumour samples. Tumour infiltrating leukocytes were characterized by flow cytometry to identify regulatory T cells, myeloid derived suppressor cells, and type 2 macrophages. Statistical analysis revealed several interesting correlations between the studied parameters and clinical features. Overall, a surprisingly high degree of heterogeneity in the composition of the immunosuppressive environment was found across all breast cancer samples which adds to the complexity of this disease. The influence of the hypoxia inducible factors (HIFs) on the immune microenvironment was also addressed. The level of HIFs correlated with hormone receptor status and the expression of several immunosuppressive molecules. Targeting HIFs might not only sensitize breast tumours for radiation and chemotherapies but also interfere with cancer immunosuppression.

Li Z, Gou J, Xu J
Down-regulation of focal adhesion signaling in response to cyclophilin A knockdown in human endometrial cancer cells, implicated by cDNA microarray analysis.
Gynecol Oncol. 2013; 131(1):191-7 [PubMed] Related Publications
OBJECTIVE: CypA had been identified as a potential therapeutic target to endometrial cancer in our previous research. Herein, we aimed to further elucidate the underlying comprehensive mechanisms of CypA knockdown-associated anticancer effects by cDNA microarray-based approach.
METHODS: LV-shCypA was constructed and transfected into HEC-1-B cells. The efficiency of CypA knockdown was determined by qRT-PCR and Western blotting. The migratory/invasive capacity was examined by transwell assay. CypA knockdown-induced comprehensive gene expression alterations were analyzed using NimbleGen Human Gene Expression Microarray consisting of 45,033 probes for human genes. Functional analysis of the microarray data was performed using KEGG and Gene Ontology analyses. The selected differentially expressed genes were validated by qRT-PCR.
RESULTS: Knockdown of CypA by LV-shCypA led to a significant decrease of migratory/invasive cell proportions in HEC-1-B cells. Microarray analysis showed 3533 and 2772 genes to be up-regulated and down-regulated in CypA-knockdown cells, respectively. Functional analysis showed 50 up-regulated pathways and 14 down-regulated pathways in CypA-knockdown cells, and focal adhesion signaling was one of the most enriched down-regulated pathways. The expression patterns of 16 genes in focal adhesion signaling, which encoded MAPK kinases, focal adhesion kinase (FAK), integrin subunits and laminin subunits, were validated by qRT-PCR and the consistency percentage with microarray data reached 100%.
CONCLUSIONS: Suppression of migratory/invasive capacity by CypA knockdown is likely associated with the down-regulation of focal adhesion signaling, which may contribute to the understanding of the role of CypA as a potential therapeutic target for endometrial cancer.

Ye Y, Huang A, Huang C, et al.
Comparative mitochondrial proteomic analysis of hepatocellular carcinoma from patients.
Proteomics Clin Appl. 2013; 7(5-6):403-15 [PubMed] Related Publications
PURPOSE: To define mitochondrial protein markers related to liver cancer.
EXPERIMENTAL DESIGN: Mitochondrial subproteomes of 20 patient-derived liver carcinoma and tumor-free control tissues were performed by 2DE coupled with MALDI-TOF/TOF. The altered patterns of three identified proteins were validated by Western blot and immunohistochemistry.
RESULTS: The results showed that compared with tumor-free control samples, nine proteins were downregulated and six proteins were upregulated in carcinoma samples. The increased expression of Arg1 mRNA and protein was validated by Western blot, Q-RT-PCR, paraffin tissue microarray and immunohistochemistry. Furthermore, a literature review shows that Heat shock protein 10 (Hsp10), single-stranded DNA-binding protein (SSBP1), and peptidyl-prolyl cis-trans isomerase A (PPIA), which were identified as being increased in the tumor samples in this study, may be closely related to protein folding and translation.
CONCLUSIONS AND CLINICAL RELEVANCE: These results show that in addition to changes in the signaling pathways, such as the Ras-Raf-MEK-ERK pathway, altered mitochondrial DNA replication and protein folding in liver cancer are also worth studying further. Collectively, these results suggest that specific mitochondrial proteins are uniquely susceptible to alterations in expression and carry implications for the investigation of their potential as therapeutic and prognostic markers. Further studies focusing on these proteins will be used to predict treatment response and reverse the apoptosis resistance.

Qian Z, Zhao X, Jiang M, et al.
Downregulation of cyclophilin A by siRNA diminishes non-small cell lung cancer cell growth and metastasis via the regulation of matrix metallopeptidase 9.
BMC Cancer. 2012; 12:442 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Cyclophilin A (CypA) is a cytosolic protein possessing peptidyl-prolyl isomerase activity that was recently reported to be overexpressed in several cancers. Here, we explored the biology and molecular mechanism of CypA in non-small cell lung cancer (NSCLC).
METHODS: The expression of CypA in human NSCLC cell lines was detected by real-time reverse transcription PCR. The RNA interference-mediated knockdown of CypA was established in two NSCLC cell lines (95C and A549). 239836 CypA inhibitor was also used to suppress CypA activity. Tumorigenesis was assessed based on cellular proliferation, colony formation assays, and anchorage-independent growth assays; metastasis was assessed based on wound healing and transwell assays.
RESULTS: Suppression of CypA expression inhibited the cell growth and colony formation of A549 and 95C cells. CypA knockdown resulted in the inhibition of cell motility and invasion. Significantly, we show for the first time that CypA increased NSCLC cell invasion by regulating the activity of secreted matrix metallopeptidase 9 (MMP9). Likewise, suppression of CypA with 239836 CypA inhibitor decreased cell proliferation and MMP9 activity.
CONCLUSIONS: The suppression of CypA expression was correlated with decreased NSCLC cell tumorigenesis and metastasis.

Vajda A, Marignol L, Barrett C, et al.
Gene expression analysis in prostate cancer: the importance of the endogenous control.
Prostate. 2013; 73(4):382-90 [PubMed] Related Publications
BACKGROUND: Aberrant gene expression is a hallmark of cancer. Quantitative reverse-transcription PCR (qRT-PCR) is the gold-standard for quantifying gene expression, and commonly employs a house-keeping gene (HKG) as an endogenous control to normalize results; the choice of which is critical for accurate data interpretation. Many factors, including sample type, pathological state, and oxygen levels influence gene expression including putative HKGs. The aim of this study was to determine the suitability of commonly used HKGs for qRT-PCR in prostate cancer.
METHODS: Prostate cancer (LNCaP, 22Rv1, PC3, and DU145) and normal (PWR1E and RWPE1) cell lines were cultured in air and hypoxia. The performance of 16 HKGs was assessed using Normfinder and coefficient of variation. In silico promoter analysis was performed to identify putative hypoxia response elements (HREs). The impact of the endogenous control on expression levels of HIF1A and GSTP1 was investigated by qRT-PCR in cell lines and tissue specimens respectively.
RESULTS: Hypoxia altered expression of several HKGs: IPO8, B2M, and PGK1. The most stably expressed HKGs were ACTB, PPIA, and UBC. Both UBC and ACTB showed constitutive expression of HIF1A in air and hypoxia, while PGK1 falsely implied a sixfold hypoxia-induced down-regulation. In prostate tumors, UBC and PGK1 both revealed down-regulation of GSTP1 relative to matched benign, whereas ACTB showed variability.
CONCLUSIONS: This study demonstrates that no universal endogenous control exists for gene expression studies, even within one disease type. It highlights the importance of validating expression of intended HKGs between different sample types and environmental exposures.

Rienzo M, Schiano C, Casamassimi A, et al.
Identification of valid reference housekeeping genes for gene expression analysis in tumor neovascularization studies.
Clin Transl Oncol. 2013; 15(3):211-8 [PubMed] Related Publications
INTRODUCTION: Real time RT-PCR is a widely used technique to evaluate and confirm gene expression data obtained in different cell systems and experimental conditions. However, there are many conflicting reports about the same gene or sets of gene expression. A common method is to report the interest gene expression relative to an internal control, usually a housekeeping gene (HKG), which should be constant in cells independently of experimental conditions.
MATERIALS AND METHODS: In this study, the expression stability of ten HKGs was considered in parallel in two cell systems (endothelial and osteosarcoma cells): beta actin (ACTB), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), TATA box binding protein (TBP), hypoxanthine phosphoribosyl-transferase 1 (HPRT1), Cyclophilin A (PPIA), beta-2-microglobulin (B2M), glucuronidase beta (GUSB), eukaryotic translation elongation factor 1 alpha1 (EEF1A1), transferrin receptor (TFRC), ribosomal protein S18 (RPS18). In order to study the stability of candidate reference genes, data have been also analyzed by several algorithms (geNorm, NormFinder, BestKeeper and delta-Ct method).
RESULTS AND CONCLUSIONS: The overall analysis obtained by the comprehensive ranking showed that RPS18 and PPIA are appropriate internal reference genes for tumor neovascularization studies where it is necessary to analyze both systems at the same time.

Ma Y, Dai H, Kong X, Wang L
Impact of thawing on reference gene expression stability in renal cell carcinoma samples.
Diagn Mol Pathol. 2012; 21(3):157-63 [PubMed] Related Publications
More and more samples are obtained from biobanks for biomedical research; however, some of these samples may undergo thawing before processing. We aim to evaluate the reference gene expression stability in thawed renal cell carcinoma samples. Sixteen matched malignant and nonmalignant renal tissue samples were obtained and each sample was divided into 4 aliquots before being snap frozen and stored at -80°C. By quantitative real-time polymerase chain reaction, a time-course study was conducted on the thawed tissue to evaluate the expression stability of a panel of the 10 most frequently used reference genes in renal cell carcinom samples: ACTB, ALAS1, B2M, GAPDH, HMBS, HPRT, PPIA, RPLP0,TBP, and TUBB. As shown by geNorm M values, PPIA was the most stable gene at the 0-, 15-, and 30-minute time points (M=0.82, 0.85, and 0.76, respectively), whereas GAPDH was ranked last at the 5-, 15-, and 30-minute time points (M=1.38, 1.44, and 1.39, respectively). A positive correlation was found by linear regression between the thawing time and 2 to the power of crossing point values of all candidate reference genes (P<0.05). The mean coefficient of variance of all reference genes increased significantly at time points 5, 15, and 30 minutes compared with 0 minutes (P<0.01). In conclusion, using the geNorm algorithm, PPIA was identified as the most stably expressed gene between malignant and nonmalignant renal tissue samples that were thawed for similar time periods. All the reference genes showed high variations along with the thawing time; it should be recommended to use a combination of several candidate reference genes when comparing samples thawed for different time periods.

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