RBL1

Gene Summary

Gene:RBL1; RB transcriptional corepressor like 1
Aliases: PRB1, p107, CP107
Location:20q11.23
Summary:The protein encoded by this gene is similar in sequence and possibly function to the product of the retinoblastoma 1 (RB1) gene. The RB1 gene product is a tumor suppressor protein that appears to be involved in cell cycle regulation, as it is phosphorylated in the S to M phase transition and is dephosphorylated in the G1 phase of the cell cycle. Both the RB1 protein and the product of this gene can form a complex with adenovirus E1A protein and SV40 large T-antigen, with the SV40 large T-antigen binding only to the unphosphorylated form of each protein. In addition, both proteins can inhibit the transcription of cell cycle genes containing E2F binding sites in their promoters. Due to the sequence and biochemical similarities with the RB1 protein, it is thought that the protein encoded by this gene may also be a tumor suppressor. Two transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:retinoblastoma-like protein 1
Source:NCBIAccessed: 12 March, 2017

Ontology:

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 12 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.

  • RNA Interference
  • MicroRNAs
  • Cancer Gene Expression Regulation
  • Nuclear Proteins
  • Retinoblastoma-Like Protein p130
  • DNA-Binding Proteins
  • Neoplasm Proteins
  • Promoter Regions
  • Chromosome 20
  • Retinoblastoma
  • Transcription Factors
  • Prostate Cancer
  • Cell Cycle
  • Cyclins
  • p53 Protein
  • Mutation
  • Cancer DNA
  • Cervical Cancer
  • Tumor Suppressor Gene
  • Transcription
  • Urinary Tract
  • Phosphoproteins
  • Proteins
  • E2F Transcription Factors
  • Neoplastic Cell Transformation
  • Cell Proliferation
  • RBL1
  • Xenograft Models
  • Epigenetics
  • Genes, Retinoblastoma
  • Signal Transduction
  • Apoptosis
  • Adenovirus E1A Proteins
  • DNA Methylation
  • Base Sequence
  • Phosphorylation
  • Knockout Mice
  • RB1
  • Cell Cycle Proteins
  • Transfection
  • Cell Differentiation
Tag cloud generated 12 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (2)

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: RBL1 (cancer-related)

Moghaddaskho F, Eyvani H, Ghadami M, et al.
Demethylation and alterations in the expression level of the cell cycle-related genes as possible mechanisms in arsenic trioxide-induced cell cycle arrest in human breast cancer cells.
Tumour Biol. 2017; 39(2):1010428317692255 [PubMed] Related Publications
Arsenic trioxide (As2O3) has been used clinically as an anti-tumor agent. Its mechanisms are mostly considered to be the induction of apoptosis and cell cycle arrest. However, the detailed molecular mechanisms of its anti-cancer action through cell cycle arrest are poorly known. Furthermore, As2O3 has been shown to be a potential DNA methylation inhibitor, inducing DNA hypomethylation. We hypothesize that As2O3 may affect the expression of cell cycle regulatory genes by interfering with DNA methylation patterns. To explore this, we examined promoter methylation status of 24 cell cycle genes in breast cancer cell lines and in a normal breast tissue sample by methylation-specific polymerase chain reaction and/or restriction enzyme-based methods. Gene expression level and cell cycle distribution were quantified by real-time polymerase chain reaction and flow cytometric analyses, respectively. Our methylation analysis indicates that only promoters of RBL1 (p107), RASSF1A, and cyclin D2 were aberrantly methylated in studied breast cancer cell lines. As2O3 induced CpG island demethylation in promoter regions of these genes and restores their expression correlated with DNA methyltransferase inhibition. As2O3 also induced alterations in messenger RNA expression of several cell cycle-related genes independent of demethylation. Flow cytometric analysis revealed that the cell cycle arrest induced by As2O3 varied depending on cell lines, MCF-7 at G1 phase and both MDA-MB-231 and MDA-MB-468 cells at G2/M phase. These changes at transcriptional level of the cell cycle genes by the molecular mechanisms dependent and independent of demethylation are likely to represent the mechanisms of cell cycle redistribution in breast cancer cells, in response to As2O3 treatment.

Lee J, Jung JH, Chae YS, et al.
Long Noncoding RNA snaR Regulates Proliferation, Migration and Invasion of Triple-negative Breast Cancer Cells.
Anticancer Res. 2016; 36(12):6289-6295 [PubMed] Related Publications
AIM: We evaluated the role of long noncoding ribonucleic acid (lncRNA) in breast cancer cell lines by quantitative reverse transcription-polymerase change reaction.
MATERIALS AND METHODS: The effects of small NF90-associated RNA (snaR) with RNA interference on proliferation, migration and invasion of MDA-MB-231 cells were observed by 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide, wound healing and transwell assay.
RESULTS: Among 90 lncRNAs, E2F transcription factor 4, p107/p130-binding (E2F4) antisense, insulin-like growth factor 2 antisense (IGF2AS), snaR, and small nucleolar RNA host gene 5 (SNHG5) were up-regulated in MDA-MB-231 and 7SK, antisense noncoding RNA in the INK4 locus (ANRIL), IGF2AS, Nespas, p53 mRNA, and snaR were up-regulated in MCF-7 cells. Down-regulation of snaR inhibited the proliferation, migration, and invasion of MDA-MD-231 breast cancer cells.
CONCLUSION: LncRNA snaR was found to be up-regulated in breast cancer cells, and the cancer progression of MDA-MB-231 cells was significantly suppressed by down-regulation of snaR. Therefore, snaR knockdown has potential as a treatment modality for triple-negative breast cancer.

Eyvani H, Moghaddaskho F, Kabuli M, et al.
Arsenic trioxide induces cell cycle arrest and alters DNA methylation patterns of cell cycle regulatory genes in colorectal cancer cells.
Life Sci. 2016; 167:67-77 [PubMed] Related Publications
AIMS: Cell cycle dysregulation is important in tumorigenesis. Transcriptional silencing of cell cycle regulatory genes, due to DNA methylation, is a common epigenetic event in malignancies. As2O3 has been shown to induce cell cycle arrest and also to be a potential hypomethylating agent. Our study aimed to investigate DNA methylation patterns of cell cycle regulatory genes promoters, the effects of Arsenic trioxide (As2O3) on the methylated genes and cell cycle distribution in colorectal cancer (CRC) cell lines.
MAIN METHODS: The methylation-specific PCR (MSP) and/or restriction enzyme-based methods were used to study the promoter methylation patterns of 24 cell cycle regulatory genes in CRC cell lines. Gene expression level and cell cycle distribution were determined by Real-time PCR and flow cytometric analyses, respectively.
KEY FINDINGS: Our methylation analysis indicated that only promoters of RBL1 (p107), CHFR and p16 genes were aberrantly methylated in three cell lines. As2O3 significantly decreased DNA methylation in promoter regions of these genes and restored their expression. We found that As2O3 significantly reduced the expression of DNA methyltransferase 1 (DNMT1) and increased arsenic methyltransferase (AS3MT). Furthermore, As2O3 altered transcriptional activity of several unmethylated cell cycle regulatory genes including cyclin B1, E1, D1, GADD45A and p21. Cell cycle flow cytometry analysis showed As2O3 induced G2/M arrest in all three cell lines.
SIGNIFICANCE: These data suggest that demethylation and alteration in the expression level of the cell cycle-related genes may be possible mechanisms in As2O3-induced cell cycle arrest in colorectal cancer cells.

Li T, Zheng Q, An J, et al.
SET1A Cooperates With CUDR to Promote Liver Cancer Growth and Hepatocyte-like Stem Cell Malignant Transformation Epigenetically.
Mol Ther. 2016; 24(2):261-75 [PubMed] Free Access to Full Article Related Publications
Long noncoding RNA CUDR plays an important role during tumorigenesis. Herein, we demonstrate that SET1A cooperates with CUDR to accelerate hepatocarcinogenesis and promote malignant transformation of hepatocyte-like stem cells. Mechanistically, CUDR enhances the phosphorylation of RB1, C-myc expression, and the interplay between the SET1A and pRB1. Notably, CUDR acts as a sponge cushion that shows a link between SET1A and pRB1, producing a activated pRB1-SET1A complex. On the other hand, the pRB1-SET1A complex may carry methyls(me) to occupy the position of H3K4, resulting in specific tri-methylation of forth lysine of histone H3 (H3K4me3). Thereby, the H3K4me3 loads on the TRF2 promoter region which causes the TRF2 overexpression. Ultimately, the excessive TRF2 binds to telomere repeat DNA, prolonging the telomere length. These findings provide the first demonstration that SET1A cooperates with CUDR to play a positive potential role during hepatocarcinogenesis and hepatocyte-like stem cells' malignant transformation epigenetically.

Mileo AM, Mattarocci S, Matarrese P, et al.
Hepatitis C virus core protein modulates pRb2/p130 expression in human hepatocellular carcinoma cell lines through promoter methylation.
J Exp Clin Cancer Res. 2015; 34:140 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Hepatitis C Virus (HCV) infection is associated with chronically evolving disease and development of hepatocellular carcinoma (HCC), albeit the mechanism of HCC induction by HCV is still controversial. The nucleocapsid (core) protein of HCV has been shown to be directly implicated in cellular transformation and immortalization, enhancing the effect of oncogenes and decreasing the one of tumor suppressor genes, as RB1 and its protein product pRB. With the aim of identifying novel molecular mechanisms of hepatocyte transformation by HCV, we examined the effect of HCV core protein on the expression of the whole Retinoblastoma (RB) family of tumor and growth suppressor factors, i.e. pRb, p107 and pRb2/p130.
METHODS: We used a model system consisting of the HuH-7, HCV-free, human hepatocellular carcinoma cell line and of the HuH-7-CORE cells derived from the former and constitutively expressing the HCV core protein. We determined pRb, p107 and pRb2/p130 protein and mRNA amount of the respective genes RB1, RBL1 and RBL2, RBL2 promoter activity and methylation as well as DNA methyltransferase 1 (DNMT1) and 3b (DNMT3b) expression level. The effect of pRb2/p130 over-expression on the HCV core-expressing HuH-7-CORE cells was also evaluated.
RESULTS: We found that the HCV core protein expression down-regulated pRb2/p130 protein and mRNA levels in HuH-7-CORE cells by inducing promoter hyper-methylation with the concomitant up-regulation of DNMT1 and DNMT3b expression. When pRb2/p130 expression was artificially re-established in HuH-7-CORE cells, cell cycle analysis outlined an accumulation in the G0/G1 phase, as expected.
CONCLUSIONS: HCV core appears indeed able to significantly down-regulate the expression and the function of two out of three RB family tumor and growth suppressor factors, i.e. pRb and pRb2/p130. The functional consequences at the level of cell cycle regulation, and possibly of more complex cell homeostatic processes, may represent a plausible molecular mechanism involved in liver transformation by HCV.

Zhu S, Zhao L, Li Y, et al.
Suppression of RAD21 Induces Senescence of MDA-MB-231 Human Breast Cancer Cells Through RB1 Pathway Activation Via c-Myc Downregulation.
J Cell Biochem. 2016; 117(6):1359-69 [PubMed] Related Publications
Cellular senescence impedes cancer progression by limiting uncontrolled cell proliferation. To identify new genetic events controlling senescence, we performed a small interfering RNA screening human cancer cells and identified a number of targets potentially involved in senescence of MDA-MB-231 human breast cancer cells. Importantly, we showed that knockdown of RAD21 resulted in the appearance of several senescent markers, including enhanced senescence-associated β-galactosidase activity and heterochromatin focus formation, as well as elevated p21 protein levels and RB1 pathway activation. Further biochemical analyses revealed that RAD21 knockdown led to the downregulation of c-Myc and its targets, including CDK4, a negative regulator of RB1, and blockedRB1 phosphorylation (pRB1), and the RB1-mediated transcriptional repression of E2F. Moreover, c-Myc downregulation was partially mediated by proteasome-dependent degradation within promyelocytic leukemia (PML) nuclear bodies, which were found to be highly abundant during RAD21 knockdown-induced senescence. Exogenous c-Myc reconstitution rescued cells from RAD21 silencing-induced senescence. Altogether, data arising from this study implicate a novel function of RAD21 in cellular senescence in MDA-MB-231 cells that is mainly dependent onRB1 pathway activation via c-Myc downregulation.

Huang SJ, Gillan TL, Gerrie AS, et al.
Influence of clone and deletion size on outcome in chronic lymphocytic leukemia patients with an isolated deletion 13q in a population-based analysis in British Columbia, Canada.
Genes Chromosomes Cancer. 2016; 55(1):16-24 [PubMed] Related Publications
Deletion of the long arm of chromosome 13 (del(13q)) as the sole abnormality in chronic lymphocytic leukemia (CLL) portends a good prognosis; however, there is great outcome heterogeneity within this subgroup. The percentage of cells with a del(13q) (clone size) and the extent of the deletion are two factors that may affect outcome in CLL patients with isolated del(13q). We analyzed 248 CLL patients from the BC Provincial CLL database identified as having isolated del(13q) detected pretreatment by interphase fluorescence in situ hybridization to determine what impact clone and deletion size had on overall survival (OS) and treatment free survival (TFS). Patients with 60% or more of nuclei with a del(13q) had shorter TFS and shorter OS. A large deletion, encompassing the RB1 gene locus, was detected in half of the 90 cases with available specimens for testing, and there was no significant difference in OS and TFS between RB1-deleted and RB1-not-deleted cases. Further study in a larger sample size is required to determine the clinical interest of RB1 locus testing; however, clone size of del(13q) does predict TFS and OS and may better refine prognosis in this clinically heterogeneous population.

Zhang J, Huang JY, Chen YN, et al.
Whole genome and transcriptome sequencing of matched primary and peritoneal metastatic gastric carcinoma.
Sci Rep. 2015; 5:13750 [PubMed] Free Access to Full Article Related Publications
Gastric cancer is one of the most aggressive cancers and is the second leading cause of cancer death worldwide. Approximately 40% of global gastric cancer cases occur in China, with peritoneal metastasis being the prevalent form of recurrence and metastasis in advanced disease. Currently, there are limited clinical approaches for predicting and treatment of peritoneal metastasis, resulting in a 6-month average survival time. By comprehensive genome analysis will uncover the pathogenesis of peritoneal metastasis. Here we describe a comprehensive whole-genome and transcriptome sequencing analysis of one advanced gastric cancer case, including non-cancerous mucosa, primary cancer and matched peritoneal metastatic cancer. The peripheral blood is used as normal control. We identified 27 mutated genes, of which 19 genes are reported in COSMIC database (ZNF208, CRNN, ATXN3, DCTN1, RP1L1, PRB4, PRB1, MUC4, HS6ST3, MUC17, JAM2, ITGAD, IREB2, IQUB, CORO1B, CCDC121, AKAP2, ACAN and ACADL), and eight genes have not previously been described in gastric cancer (CCDC178, ARMC4, TUBB6, PLIN4, PKLR, PDZD2, DMBT1and DAB1).Additionally,GPX4 and MPND in 19q13.3-13.4 region, is characterized as a novel fusion-gene. This study disclosed novel biological markers and tumorigenic pathways that would predict gastric cancer occurring peritoneal metastasis.

Kumar A, Boyle EA, Tokita M, et al.
Deep sequencing of multiple regions of glial tumors reveals spatial heterogeneity for mutations in clinically relevant genes.
Genome Biol. 2014; 15(12):530 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The extent of intratumoral mutational heterogeneity remains unclear in gliomas, the most common primary brain tumors, especially with respect to point mutation. To address this, we applied single molecule molecular inversion probes targeting 33 cancer genes to assay both point mutations and gene amplifications within spatially distinct regions of 14 glial tumors.
RESULTS: We find evidence of regional mutational heterogeneity in multiple tumors, including mutations in TP53 and RB1 in an anaplastic oligodendroglioma and amplifications in PDGFRA and KIT in two glioblastomas (GBMs). Immunohistochemistry confirms heterogeneity of TP53 mutation and PDGFRA amplification. In all, 3 out of 14 glial tumors surveyed have evidence for heterogeneity for clinically relevant mutations.
CONCLUSIONS: Our results underscore the need to sample multiple regions in GBM and other glial tumors when devising personalized treatments based on genomic information, and furthermore demonstrate the importance of measuring both point mutation and copy number alteration while investigating genetic heterogeneity within cancer samples.

Vilas JM, Ferreirós A, Carneiro C, et al.
Transcriptional regulation of Sox2 by the retinoblastoma family of pocket proteins.
Oncotarget. 2015; 6(5):2992-3002 [PubMed] Free Access to Full Article Related Publications
Cellular reprogramming to iPSCs has uncovered unsuspected links between tumor suppressors and pluripotency factors. Using this system, it was possible to identify tumor suppressor p27 as a repressor of Sox2 during differentiation. This led to the demonstration that defects in the repression of Sox2 can contribute to tumor development. The members of the retinoblastoma family of pocket proteins, pRb, p107 and p130, are negative regulators of the cell cycle with tumor suppressor activity and with roles in differentiation. In this work we studied the relative contribution of the retinoblastoma family members to the regulation of Sox2 expression. We found that deletion of Rb or p130 leads to impaired repression of Sox2, a deffect amplified by inactivation of p53. We also identified binding of pRb and p130 to an enhancer with crucial regulatory activity on Sox2 expression. Using cellular reprogramming we tested the impact of the defective repression of Sox2 and confirmed that Rb deficiency allows the generation of iPSCs in the absence of exogenous Sox2. Finally, partial depletion of Sox2 positive cells reduced the pituitary tumor development initiated by Rb loss in vivo. In summary, our results show that Sox2 repression by pRb is a relevant mechanism of tumor suppression.

Wang Q, Lv H, Lv W, et al.
Genome-wide haplotype association study identifies BLM as a risk gene for prostate cancer in Chinese population.
Tumour Biol. 2015; 36(4):2703-7 [PubMed] Related Publications
Prostate cancer (PC) is a common malignant tumor that occurs in the prostate epithelial cells. It is generally considered to be caused by both genetic and environmental factors. To identify the genetic risk factors of PC in Chinese population, we carried out a genome-wide haplotype-based association study. The 33 Chinese PC cases were from the public GEO database (GSE18333), and the 139 Chinese controls (CHB) were from the HapMap project. Our analysis included three stages: (1) identifying the linkage disequilibrium (LD) blocks and performing genome-wide haplotype association scan, (2) mapping PC-risk haplotypes to PC candidate genes, and (3) prioritizing PC candidate genes based on their similarity to known PC susceptibility genes. The results showed that (1) 749 haplotypes were significantly associated with PC (P < 1E-5). (2) Then, we mapped these significant haplotypes to genes and got 454 PC candidate genes. (3) After prioritizing the candidate genes based on their similarity to known PC susceptibility genes, we found that seven novel PC susceptibility genes including BLM, RPS6KA2, FRK, ERBB4, RBL1, PAK7, and ERBB2IP. Among the seven genes, BLM gene ranked first (P = 1.89E-04). A haplotype GGTTACCCCTC (rs2270131, rs2073919, rs11073953, rs12592875, rs16944863, rs2238337, rs414634, rs401549, rs17183344, rs16944884, and rs16944888) on chromosome 15q26.1 had significant association with PC (P = 2.37E-11). To our knowledge, this is the first genetic association study to show the significant association between BLM gene and PC susceptibility in Chinese population.

Benavente CA, Finkelstein D, Johnson DA, et al.
Chromatin remodelers HELLS and UHRF1 mediate the epigenetic deregulation of genes that drive retinoblastoma tumor progression.
Oncotarget. 2014; 5(20):9594-608 [PubMed] Free Access to Full Article Related Publications
The retinoblastoma (Rb) family of proteins are key regulators of cell cycle exit during development and their deregulation is associated with cancer. Rb is critical for normal retinal development and germline mutations lead to retinoblastoma making retinae an attractive system to study Rb family signaling. Rb coordinates proliferation and differentiation through the E2f family of transcription factors, a critical interaction for the role of Rb in retinal development and tumorigenesis. However, whether the roles of the different E2fs are interchangeable in controlling development and tumorigenesis in the retina or if they have selective functions remains unknown. In this study, we found that E2f family members play distinct roles in the development and tumorigenesis. In Rb;p107-deficient retinae, E2f1 and E2f3 inactivation rescued tumor formation but only E2f1 rescued the retinal development phenotype. This allowed the identification of key target genes for Rb/E2f family signaling contributing to tumorigenesis and those contributing to developmental defects. We found that Sox4 and Sox11 genes contribute to the developmental phenotype and Hells and Uhrf1 contribute to tumorigenesis. Using orthotopic human xenografts, we validated that upregulation of HELLS and UHRF1 is essential for the tumor phenotype. Also, these epigenetic regulators are important for the regulation of SYK.

Lam SK, Li YY, Zheng CY, Ho JC
Downregulation of thymidylate synthase and E2F1 by arsenic trioxide in mesothelioma.
Int J Oncol. 2015; 46(1):113-22 [PubMed] Related Publications
Malignant pleural mesothelioma is a global health issue. Arsenic trioxide (ATO) has been shown to suppress thymidylate synthase (TYMS) in lung adenocarcinoma and colorectal cancer, and induce apoptosis in acute promyelocytic leukemia. With TYMS as a putative therapeutic target, the effect of ATO in mesothelioma was therefore studied. A panel of 5 mesothelioma cell lines was used to study the effect of ATO on cell viability, protein expression, mRNA expression and TYMS activity by MTT assay, western blot, qPCR and tritium-release assay, respectively. The knockdown of TYMS and E2F1 was performed with a specific siRNA. Phosphatidylserine externalization and mitochondrial membrane depolarization were measured by Annexin V and JC-1 staining respectively. The in vivo effect of ATO was studied using a nude mouse xenograft model. Application of ATO demonstrated anticancer effects in the cell line model with clinically achievable concentrations. Downregulation of TYMS protein (except H226 cells and 1.25 µM ATO in H2052 cells) and mRNA expression (H28 cells), pRB1 (H28 cells) and E2F1 and TYMS activity (except H226 cells) were also evident. E2F1 knockdown decreased cell viability more significantly than TYMS knockdown. In general, thymidine kinase 1, ribonucleotide reductase M1, c-myc and skp2 were downregulated by ATO. p-c-Jun was downregulated in H28 cells while upregulated in 211H cells. Phosphatidylserine externalization, mitochondrial membrane depolarization, downregulation of Bcl-2 and Bcl-xL, and upregulation of Bak and cleaved caspase-3 were observed. In the H226 xenograft model, the relative tumor growth was aborted, and E2F1 was downregulated while cleaved caspase-3 was elevated and localized to the nucleus in the ATO treatment group. ATO has potent antiproliferative and cytotoxic effects in mesothelioma in vitro and in vivo, partially mediated through E2F1 targeting (less effect through TYMS targeting). There is sound scientific evidence to support the clinical application of ATO in treatment of mesothelioma.

Xu XL, Singh HP, Wang L, et al.
Rb suppresses human cone-precursor-derived retinoblastoma tumours.
Nature. 2014; 514(7522):385-8 [PubMed] Free Access to Full Article Related Publications
Retinoblastoma is a childhood retinal tumour that initiates in response to biallelic RB1 inactivation and loss of functional retinoblastoma (Rb) protein. Although Rb has diverse tumour-suppressor functions and is inactivated in many cancers, germline RB1 mutations predispose to retinoblastoma far more strongly than to other malignancies. This tropism suggests that retinal cell-type-specific circuitry sensitizes to Rb loss, yet the nature of the circuitry and the cell type in which it operates have been unclear. Here we show that post-mitotic human cone precursors are uniquely sensitive to Rb depletion. Rb knockdown induced cone precursor proliferation in prospectively isolated populations and in intact retina. Proliferation followed the induction of E2F-regulated genes, and depended on factors having strong expression in maturing cone precursors and crucial roles in retinoblastoma cell proliferation, including MYCN and MDM2. Proliferation of Rb-depleted cones and retinoblastoma cells also depended on the Rb-related protein p107, SKP2, and a p27 downregulation associated with cone precursor maturation. Moreover, Rb-depleted cone precursors formed tumours in orthotopic xenografts with histological features and protein expression typical of human retinoblastoma. These findings provide a compelling molecular rationale for a cone precursor origin of retinoblastoma. More generally, they demonstrate that cell-type-specific circuitry can collaborate with an initiating oncogenic mutation to enable tumorigenesis.

Butcher LD, Garcia M, Arnold M, et al.
Immune response to JC virus T antigen in patients with and without colorectal neoplasia.
Gut Microbes. 2014; 5(4):468-75 [PubMed] Related Publications
JC virus (JCV) is a polyomavirus that infects approximately 75% of the population and encodes a T antigen (T-Ag) gene, which is oncogenic and inactivates the p53 and pRb/p107/p130 protein families. Previous work in our lab has identified the presence of T-Ag in colorectal neoplasms. While JCV remains in a latent state for the majority of those infected, we hypothesized that a disturbance in immunological control may permit JCV to reactivate, which may be involved in the development of colorectal neoplasia. Our aim was to determine the cell mediated immune response to JCV T-Ag, and determine if it is altered in patients with colorectal adenomatous polyps (AP) or cancers (CRC). Peripheral blood mononuclear cells (PBMCs) isolated from the blood of patients undergoing colonoscopy or colorectal surgery were stimulated by a peptide library covering the entire T-Ag protein of JCV. Cytokine production and T cell proliferation were evaluated following T-Ag stimulation using Luminex and flow cytometry assays. JCV T-Ag peptides stimulated secretion of IL-2, which induced T cell expansion in all three groups. However, stronger IL-10 and IL-13 production was seen in patients without colorectal neoplasms. IP-10 was produced at very high levels in all groups, but not significantly differently between groups. Most patients exhibited CD4(+) and CD8(+) T cells in response to stimulation by the T-Ag clusters. The combination of IL-2 and IP-10 secretion indicates the presence of T-Ag-specific Th1 cells in all patients, which is higher in patients without carcinoma.

van der Linden MH, Willekes M, van Roon E, et al.
MLL fusion-driven activation of CDK6 potentiates proliferation in MLL-rearranged infant ALL.
Cell Cycle. 2014; 13(5):834-44 [PubMed] Free Access to Full Article Related Publications
Acute lymphoblastic leukemia in infants (< 1 year-of-age) is characterized by a high incidence of MLL rearrangements. Recently, direct targets of the MLL fusion protein have been identified. However, functional validation of the identified targets remained unacknowledged. In this study, we identify CDK6 as a direct target of the MLL fusion protein and an important player in the proliferation advantage of MLL-rearranged leukemia. CDK6 mRNA was significantly higher expressed in MLL-rearranged infant ALL patients compared with MLL wild-type ALL patients (P < 0.001). Decrease of MLL-AF4 and MLL-ENL fusion mRNA expression by siRNAs resulted in downregulation of CDK6, affirming a direct relationship between the presence of the MLL fusion and CDK6 expression. Knockdown of CDK6 itself significantly inhibited proliferation in the MLL-AF4-positive cell line SEM, whereas knockdown of the highly homologous gene CDK4 had virtually no effect on the cell cycle. Furthermore, we show in vitro sensitivity of MLL-rearranged leukemia cell lines to the CDK4/6-inhibitor PD0332991, inducing a remarkable G 1 arrest, and downregulation of its downstream targets pRB1 and EZH2. We therefore conclude that CDK6 is indeed a direct target of MLL fusion proteins, playing an important role in the proliferation advantage of MLL-rearranged ALL cells.

Barh D, Jain N, Tiwari S, et al.
A novel in silico reverse-transcriptomics-based identification and blood-based validation of a panel of sub-type specific biomarkers in lung cancer.
BMC Genomics. 2013; 14 Suppl 6:S5 [PubMed] Free Access to Full Article Related Publications
Lung cancer accounts for the highest number of cancer-related deaths worldwide. Early diagnosis significantly increases the disease-free survival rate and a large amount of effort has been expended in screening trials and the development of early molecular diagnostics. However, a gold standard diagnostic strategy is not yet available. Here, based on miRNA expression profile in lung cancer and using a novel in silico reverse-transcriptomics approach, followed by analysis of the interactome; we have identified potential transcription factor (TF) markers that would facilitate diagnosis of subtype specific lung cancer. A subset of seven TF markers has been used in a microarray screen and was then validated by blood-based qPCR using stage-II and IV non-small cell lung carcinomas (NSCLC). Our results suggest that overexpression of HMGA1, E2F6, IRF1, and TFDP1 and downregulation or no expression of SUV39H1, RBL1, and HNRPD in blood is suitable for diagnosis of lung adenocarcinoma and squamous cell carcinoma sub-types of NSCLC. Here, E2F6 was, for the first time, found to be upregulated in NSCLC blood samples. The miRNA-TF-miRNA interaction based molecular mechanisms of these seven markers in NSCLC revealed that HMGA1 and TFDP1 play vital roles in lung cancer tumorigenesis. The strategy developed in this work is applicable to any other cancer or disease and can assist in the identification of potential biomarkers.

Gala MK, Mizukami Y, Le LP, et al.
Germline mutations in oncogene-induced senescence pathways are associated with multiple sessile serrated adenomas.
Gastroenterology. 2014; 146(2):520-9 [PubMed] Free Access to Full Article Related Publications
BACKGROUND & AIMS: Little is known about the genetic factors that contribute to the development of sessile serrated adenomas (SSAs). SSAs contain somatic mutations in BRAF or KRAS early in development. However, evidence from humans and mouse models indicates that these mutations result in oncogene-induced senescence (OIS) of intestinal crypt cells. Progression to serrated neoplasia requires cells to escape OIS via inactivation of tumor suppressor pathways. We investigated whether subjects with multiple SSAs carry germline loss-of function mutations (nonsense and splice site) in genes that regulate OIS: the p16-Rb and ATM-ATR DNA damage response pathways.
METHODS: Through a bioinformatic analysis of the literature, we identified a set of genes that function at the main nodes of the p16-Rb and ATM-ATR DNA damage response pathways. We performed whole-exome sequencing of 20 unrelated subjects with multiple SSAs; most had features of serrated polyposis. We compared sequences with those from 4300 subjects matched for ethnicity (controls). We also used an integrative genomics approach to identify additional genes involved in senescence mechanisms.
RESULTS: We identified mutations in genes that regulate senescence (ATM, PIF1, TELO2,XAF1, and RBL1) in 5 of 20 subjects with multiple SSAs (odds ratio, 3.0; 95% confidence interval, 0.9–8.9; P =.04). In 2 subjects,we found nonsense mutations in RNF43, indicating that it is also associated with multiple serrated polyps (odds ratio, 460; 95% confidence interval, 23.1–16,384; P = 6.8 x 10(-5)). In knockdown experiments with pancreatic duct cells exposed to UV light, RNF43 appeared to function as a regulator of ATMATRDNA damage response.
CONCLUSIONS: We associated germline loss-of-function variants in genes that regulate senescence pathways with the development of multiple SSAs.We identified RNF43 as a regulator of the DNA damage response and associated nonsense variants in this gene with a high risk of developing SSAs.

Mui MZ, Kucharski M, Miron MJ, et al.
Identification of the adenovirus E4orf4 protein binding site on the B55α and Cdc55 regulatory subunits of PP2A: Implications for PP2A function, tumor cell killing and viral replication.
PLoS Pathog. 2013; 9(11):e1003742 [PubMed] Free Access to Full Article Related Publications
Adenovirus E4orf4 protein induces the death of human cancer cells and Saccharomyces cerevisiae. Binding of E4orf4 to the B/B55/Cdc55 regulatory subunit of protein phosphatase 2A (PP2A) is required, and such binding inhibits PP2A(B55) activity leading to dose-dependent cell death. We found that E4orf4 binds across the putative substrate binding groove predicted from the crystal structure of B55α such that the substrate p107 can no longer interact with PP2A(B55α). We propose that E4orf4 inhibits PP2A(B55) activity by preventing access of substrates and that at high E4orf4 levels this inhibition results in cell death through the failure to dephosphorylate substrates required for cell cycle progression. However, E4orf4 is expressed at much lower and less toxic levels during a normal adenovirus infection. We suggest that in this context E4orf4 largely serves to recruit novel substrates such as ASF/SF2/SRSF1 to PP2A(B55) to enhance adenovirus replication. Thus E4orf4 toxicity probably represents an artifact of overexpression and does not reflect the evolutionary function of this viral product.

Lewis H, Lance R, Troyer D, et al.
miR-888 is an expressed prostatic secretions-derived microRNA that promotes prostate cell growth and migration.
Cell Cycle. 2014; 13(2):227-39 [PubMed] Free Access to Full Article Related Publications
MicroRNAs (MiRNAs) are a growing class of small non-coding RNAs that exhibit widespread dysregulation in prostate cancer. We profiled miRNA expression in syngeneic human prostate cancer cell lines that differed in their metastatic potential in order to determine their role in aggressive prostate cancer. miR-888 was the most differentially expressed miRNA observed in human metastatic PC3-ML cells relative to non-invasive PC3-N cells, and its levels were higher in primary prostate tumors from cancer patients, particularly those with seminal vesicle invasion. We also examined a novel miRNA-based biomarker source called expressed prostatic secretions in urine (EPS urine) for miR-888 expression and found that its levels were preferentially elevated in prostate cancer patients with high-grade disease. These expression studies indicated a correlation for miR-888 in disease progression. We next tested how miR-888 regulated cancer-related pathways in vitro using human prostate cancer cell lines. Overexpression of miR-888 increased proliferation and migration, and conversely inhibition of miR-888 activity blocked these processes. miR-888 also increased colony formation in PC3-N and LNCaP cells, supporting an oncogenic role for this miRNA in the prostate. Our data indicates that miR-888 functions to promote prostate cancer progression and can suppress protein levels of the tumor suppressor genes RBL1 and SMAD4. This miRNA holds promise as a diagnostic tool using an innovative prostatic fluid source as well as a therapeutic target for aggressive prostate cancer.

Liu F, Gong J, Huang W, et al.
MicroRNA-106b-5p boosts glioma tumorigensis by targeting multiple tumor suppressor genes.
Oncogene. 2014; 33(40):4813-22 [PubMed] Related Publications
Aberrant expression of microRNAs (miRNAs) has been implicated in cancer initiation and progression. However, little is known about the potential role of miRNAs in glioma tumorigenesis. In this study, we found that miRNA-106b-5p was significantly upregulated in glioma tumor samples and cell lines compared with normal brain tissues, and its expression level correlated with the pathological grading. Overexpression of miR-106b-5p in glioma tumor cells significantly promoted cell proliferation, although inhibited cell apoptosis in vitro and in vivo. In contrast, knockdown of miR-106b-5p significantly inhibited cell proliferation, although enhanced cell apoptosis. Mechanistic study revealed that two target genes, retinoblastoma-like 1 (RBL1) and RBL2, were involved in miR-106b-5p's regulation of cell proliferation and one target gene, caspase-8 (CASP8), mediated miR-106b-5p's regulation of apoptosis. We also investigated the function of the three targets in glioma tumorigenesis by RNA interference manipulation and demonstrated that knockdown of these target genes led to cell proliferation enhancement or cell apoptosis inhibition in vitro. More interestingly, the expression levels of these targets were significantly downregulated in glioma samples and knockdown of these targets in glioma cells inhibited the xenograft tumor formation in vivo. Moreover, we verified the regulation function of miR-106b-5p and its targets on cell proliferation and apoptosis of the primary cultured astrocytes isolated from glioma tumor samples and healthy controls. Collectively, our findings show the critical roles of miR-106b-5p and its targets, RBL1, RBL2 and CASP8, in glioma tumorigenesis and provide potential candidates for malignant glioma therapy.

Su S, Minges JT, Grossman G, et al.
Proto-oncogene activity of melanoma antigen-A11 (MAGE-A11) regulates retinoblastoma-related p107 and E2F1 proteins.
J Biol Chem. 2013; 288(34):24809-24 [PubMed] Free Access to Full Article Related Publications
Melanoma antigen-A11 (MAGE-A11) is a low-abundance, primate-specific steroid receptor coregulator in normal tissues of the human reproductive tract that is expressed at higher levels in prostate cancer. Increased expression of MAGE-A11 enhances androgen receptor transcriptional activity and promotes prostate cancer cell growth. Further investigation into the mechanisms of MAGE-A11 function in prostate cancer demonstrated interactions with the retinoblastoma-related protein p107 and Rb tumor suppressor but no interaction with p130 of the Rb family. MAGE-A11 interaction with p107 was associated with transcriptional repression in cells with low MAGE-A11 and transcriptional activation in cells with higher MAGE-A11. Selective interaction of MAGE-A11 with retinoblastoma family members suggested the regulation of E2F transcription factors. MAGE-A11 stabilized p107 by inhibition of ubiquitination and linked p107 to hypophosphorylated E2F1 in association with the stabilization and activation of E2F1. The androgen receptor and MAGE-A11 modulated endogenous expression of the E2F1-regulated cyclin-dependent kinase inhibitor p27(Kip1). The ability of MAGE-A11 to increase E2F1 transcriptional activity was similar to the activity of adenovirus early oncoprotein E1A and depended on MAGE-A11 interactions with p107 and p300. The immunoreactivity of p107 and MAGE-A11 was greater in advanced prostate cancer than in benign prostate, and knockdown with small inhibitory RNA showed that p107 is a transcriptional activator in prostate cancer cells. These results suggest that MAGE-A11 is a proto-oncogene whose increased expression in prostate cancer reverses retinoblastoma-related protein p107 from a transcriptional repressor to a transcriptional activator of the androgen receptor and E2F1.

Sadasivam S, DeCaprio JA
The DREAM complex: master coordinator of cell cycle-dependent gene expression.
Nat Rev Cancer. 2013; 13(8):585-95 [PubMed] Free Access to Full Article Related Publications
The dimerization partner, RB-like, E2F and multi-vulval class B (DREAM) complex provides a previously unsuspected unifying role in the cell cycle by directly linking p130, p107, E2F, BMYB and forkhead box protein M1. DREAM mediates gene repression during the G0 phase and coordinates periodic gene expression with peaks during the G1/S and G2/M phases. Perturbations in DREAM complex regulation shift the balance from quiescence towards proliferation and contribute to the increased mitotic gene expression levels that are frequently observed in cancers with a poor prognosis.

Kurimchak A, Haines DS, Garriga J, et al.
Activation of p107 by fibroblast growth factor, which is essential for chondrocyte cell cycle exit, is mediated by the protein phosphatase 2A/B55α holoenzyme.
Mol Cell Biol. 2013; 33(16):3330-42 [PubMed] Free Access to Full Article Related Publications
The phosphorylation state of pocket proteins during the cell cycle is determined at least in part by an equilibrium between inducible cyclin-dependent kinases (CDKs) and serine/threonine protein phosphatase 2A (PP2A). Two trimeric holoenzymes consisting of the core PP2A catalytic/scaffold dimer and either the B55α or PR70 regulatory subunit have been implicated in the activation of p107/p130 and pRB, respectively. While the phosphorylation state of p107 is very sensitive to forced changes of B55α levels in human cell lines, regulation of p107 in response to physiological modulation of PP2A/B55α has not been elucidated. Here we show that fibroblast growth factor 1 (FGF1), which induces maturation and cell cycle exit in chondrocytes, triggers rapid accumulation of p107-PP2A/B55α complexes coinciding with p107 dephosphorylation. Reciprocal solution-based mass spectrometric analysis identified the PP2A/B55α complex as a major component in p107 complexes, which also contain E2F/DPs, DREAM subunits, and/or cyclin/CDK complexes. Of note, p107 is one of the preferred partners of B55α, which also associates with pRB in RCS cells. FGF1-induced dephosphorylation of p107 results in its rapid accumulation in the nucleus and formation of larger complexes containing p107 and enhances its interaction with E2F4 and other p107 partners. Consistent with a key role of B55α in the rapid activation of p107 in chondrocytes, limited ectopic expression of B55α results in marked dephosphorylation of p107 while B55α knockdown results in hyperphosphorylation. More importantly, knockdown of B55α dramatically delays FGF1-induced dephosphorylation of p107 and slows down cell cycle exit. Moreover, dephosphorylation of p107 in response to FGF1 treatment results in early recruitment of p107 to the MYC promoter, an FGF1/E2F-regulated gene. Our results suggest a model in which FGF1 mediates rapid dephosphorylation and activation of p107 independently of the CDK activities that maintain p130 and pRB hyperphosphorylation for several hours after p107 dephosphorylation in maturing chondrocytes.

Pomerantz JH, Blau HM
Tumor suppressors: enhancers or suppressors of regeneration?
Development. 2013; 140(12):2502-12 [PubMed] Free Access to Full Article Related Publications
Tumor suppressors are so named because cancers occur in their absence, but these genes also have important functions in development, metabolism and tissue homeostasis. Here, we discuss known and potential functions of tumor suppressor genes during tissue regeneration, focusing on the evolutionarily conserved tumor suppressors pRb1, p53, Pten and Hippo. We propose that their activity is essential for tissue regeneration. This is in contrast to suggestions that tumor suppression is a trade-off for regenerative capacity. We also hypothesize that certain aspects of tumor suppressor pathways inhibit regenerative processes in mammals, and that transient targeted modification of these pathways could be fruitfully exploited to enhance processes that are important to regenerative medicine.

López-Díaz FJ, Gascard P, Balakrishnan SK, et al.
Coordinate transcriptional and translational repression of p53 by TGF-β1 impairs the stress response.
Mol Cell. 2013; 50(4):552-64 [PubMed] Free Access to Full Article Related Publications
Cellular stress results in profound changes in RNA and protein synthesis. How cells integrate this intrinsic, p53-centered program with extracellular signals is largely unknown. We demonstrate that TGF-β1 signaling interferes with the stress response through coordinate transcriptional and translational repression of p53 levels, which reduces p53-activated transcription, and apoptosis in precancerous cells. Mechanistically, E2F-4 binds constitutively to the TP53 gene and induces transcription. TGF-β1-activated Smads are recruited to a composite Smad/E2F-4 element by an E2F-4/p107 complex that switches to a Smad corepressor, which represses TP53 transcription. TGF-β1 also causes dissociation of ribosomal protein RPL26 and elongation factor eEF1A from p53 mRNA, thereby reducing p53 mRNA association with polyribosomes and p53 translation. TGF-β1 signaling is dominant over stress-induced transcription and translation of p53 and prevents stress-imposed downregulation of Smad proteins. Thus, crosstalk between the TGF-β and p53 pathways defines a major node of regulation in the cellular stress response, enhancing drug resistance.

Agrelo R, Kishimoto H, Novatchkova M, et al.
SATB1 collaborates with loss of p16 in cellular transformation.
Oncogene. 2013; 32(48):5492-500 [PubMed] Free Access to Full Article Related Publications
Tumor progression is associated with invasiveness and metastatic potential. The special AT-rich binding protein 1 (SATB1) has been identified as a key factor in the progression of breast cancer cells to a malignant phenotype and is associated with progression of human tumors. In normal development, SATB1 coordinates gene expression of progenitor cells by functioning as a genome organizer. In contrast to progenitor and tumor cells, SATB1 expression in nontransformed cells is not compatible with proliferation. Here we show that SATB1 expression in mouse embryonic fibroblasts induces cell cycle arrest and senescence that is associated with elevated p16 protein levels. Deletion of p16 overcomes the SATB1-induced senescence. We further provide evidence for an interaction of SATB1 with the retinoblastoma (RB)/E2F pathway downstream of p16. A combined deletion of the RB proteins, RB, p107 and p130 (triple-mutant; TM), prevents SATB1-induced G1 arrest, which is restored upon the reintroduction of RB into SATB1-expressing TM fibroblasts. SATB1 interacts with the E2F/RB complex and regulates the cyclin E promoter in an E2F-dependent manner. These findings demonstrate that p16 and the RB/E2F pathway are critical for SATB1-induced cell cycle arrest. In the absence of p16, SATB1 causes anchorage-independent growth and invasive phenotype in fibroblasts. Our data illustrate that p16 mutations collaborate with the oncogenic activity of SATB1. Consistent with our finding, a literature survey shows that deletion of p16 is generally associated with SATB1 expressing human cell lines and tumors.

Ito K, Maruyama Z, Sakai A, et al.
Overexpression of Cdk6 and Ccnd1 in chondrocytes inhibited chondrocyte maturation and caused p53-dependent apoptosis without enhancing proliferation.
Oncogene. 2014; 33(14):1862-71 [PubMed] Related Publications
Cell proliferation and differentiation are closely coupled. However, we previously showed that overexpression of cyclin-dependent kinase (Cdk6) blocks chondrocyte differentiation without affecting cell-cycle progression in vitro. To investigate whether Cdk6 inhibits chondrocyte differentiation in vivo, we generated chondrocyte-specific Cdk6 transgenic mice using Col2a1 promoter. Unexpectedly, differentiation and cell-cycle progression of chondrocytes in the Cdk6 transgenic mice were similar to those in wild-type mice. Then, we generated chondrocyte-specific Ccnd1 transgenic mice and Cdk6/Ccnd1 double transgenic mice to investigate the possibility that Cdk6 inhibits chondrocyte differentiation through E2f activation. Bromodeoxyuridine (BrdU)-positive chondrocytes and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive chondrocytes were increased in number, and chondrocyte maturation was inhibited only in Cdk6/Ccnd1 transgenic mice (K6(H)/D1(H) mice), which showed dwarfism. Retinoblastoma protein (pRb) was highly phosphorylated but p107 was upregulated, and the expression of E2f target genes was dysregulated as shown by upregulation of Cdc6 but downregulation of cyclin E, dihydrofolate reductase (dhfr), Cdc25a and B-Myb in chondrocytes of K6(H)/D1(H) mice. Similarly, overexpression of Cdk6/Ccnd1 in a chondrogenic cell line ATDC5 highly phosphorylated pRb, upregulated p107, induced apoptosis, upregulated Cdc6 and downregulated cyclin E, dhfr and B-Myb and p107 small interfering RNA reversed the expression of downregulated genes. Further, introduction of kinase-negative Cdk6 and cyclin D1 abolished all effects by Cdk6/cyclin D1 in ATDC5 cells, indicating the requirement of the kinase activity on these effects. p53 deletion partially restored the size of the skeleton and almost completely rescued chondrocyte apoptosis, but failed to enhance chondrocyte proliferation in K6(H)/D1(H) mice. These findings indicated that Cdk6/Ccnd1 overexpression inhibited chondrocyte maturation and enhanced G1/S cell-cycle transition by phosphorylating pRb, but the chondrocytes failed to accomplish the cell cycle, and underwent p53-dependent apoptosis probably due to the dysregulation of E2f target genes. Our findings also indicated that p53 deletion in addition to the inactivation of Rb was not sufficient to accelerate chondrocyte proliferation, suggesting the resistance of chondrocytes to sarcomagenesis.

Zhang A, Hao J, Wang K, et al.
Down-regulation of miR-106b suppresses the growth of human glioma cells.
J Neurooncol. 2013; 112(2):179-89 [PubMed] Related Publications
Recently, many studies have found that the miR-106b ~25 cluster plays an oncogenic role in tumor progression. However, the precise role of each microRNAs (miRNAs) in the cluster is not yet clear. In the present study, we examined the expression of miR-106b in glioma samples and a tissue microarray by real-time PCR and in situ hybridization (ISH), respectively, finding that miR-106b is overexpressed in the majority of gliomas. Meanwhile, the expression of miR-106b was positively correlated with tumor grade (p < 0.05). The transfection of a miR-106b anti-sense oligonucleotide (ASON) into three human glioma cell lines (U251, LN229 and TJ905) suppressed the proliferation of these cells. Moreover, the growth of xenograft tumors in nude mice treated with miR-106b ASON was significantly impaired. A bioinformatics analysis predicted that RBL2 may be the target of miR-106b, and dual-luciferase reporter assays identified RBL2, but not RB1 or RBL1, as a target of miR-106b. These results suggest that miR-106b facilitates glioma cell growth by promoting cell cycle progression through the negative regulation of RBL2.

Di Fiore R, D'Anneo A, Tesoriere G, Vento R
RB1 in cancer: different mechanisms of RB1 inactivation and alterations of pRb pathway in tumorigenesis.
J Cell Physiol. 2013; 228(8):1676-87 [PubMed] Related Publications
Loss of RB1 gene is considered either a causal or an accelerating event in retinoblastoma. A variety of mechanisms inactivates RB1 gene, including intragenic mutations, loss of expression by methylation and chromosomal deletions, with effects which are species-and cell type-specific. RB1 deletion can even lead to aneuploidy thus greatly increasing cancer risk. The RB1gene is part of a larger gene family that includes RBL1 and RBL2, each of the three encoding structurally related proteins indicated as pRb, p107, and p130, respectively. The great interest in these genes and proteins springs from their ability to slow down neoplastic growth. pRb can associate with various proteins by which it can regulate a great number of cellular activities. In particular, its association with the E2F transcription factor family allows the control of the main pRb functions, while the loss of these interactions greatly enhances cancer development. As RB1 gene, also pRb can be functionally inactivated through disparate mechanisms which are often tissue specific and dependent on the scenario of the involved tumor suppressors and oncogenes. The critical role of the context is complicated by the different functions played by the RB proteins and the E2F family members. In this review, we want to emphasize the importance of the mechanisms of RB1/pRb inactivation in inducing cancer cell development. The review is divided in three chapters describing in succession the mechanisms of RB1 inactivation in cancer cells, the alterations of pRb pathway in tumorigenesis and the RB protein and E2F family in cancer.

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