Gene Summary

Gene:SIX1; SIX homeobox 1
Aliases: BOS3, TIP39, DFNA23
Summary:The protein encoded by this gene is a homeobox protein that is similar to the Drosophila 'sine oculis' gene product. This gene is found in a cluster of related genes on chromosome 14 and is thought to be involved in limb development. Defects in this gene are a cause of autosomal dominant deafness type 23 (DFNA23) and branchiootic syndrome type 3 (BOS3). [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:homeobox protein SIX1
Source:NCBIAccessed: 11 March, 2017


What does this gene/protein do?
Show (49)

Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 11 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.

  • Signal Transduction
  • Cell Movement
  • Protein Tyrosine Phosphatases
  • Transforming Growth Factor beta Receptors
  • Breast Cancer
  • Messenger RNA
  • Mesoderm
  • Homeodomain Proteins
  • Gene Expression Profiling
  • Cell Proliferation
  • RNA Interference
  • Chromosome 14
  • Epithelial-Mesenchymal Transition
  • Trans-Activators
  • Apoptosis
  • Cervical Cancer
  • Nerve Tissue Proteins
  • MicroRNAs
  • Cell Cycle
  • siRNA
  • Homeobox Genes
  • Cancer Gene Expression Regulation
  • Neoplastic Cell Transformation
  • Transcription Factors
  • Western Blotting
  • Immunohistochemistry
  • Tumor Burden
  • Intracellular Signaling Peptides and Proteins
  • Neoplasm Metastasis
  • Wilms Tumour
  • Down-Regulation
  • Mutation
  • Transcription Factor AP-1
  • Biomarkers, Tumor
  • Oligonucleotide Array Sequence Analysis
  • Mice, Inbred NOD
  • Epithelium
  • Transforming Growth Factor beta
  • Up-Regulation
  • Gene Expression
  • Nuclear Proteins
Tag cloud generated 11 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (3)

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: SIX1 (cancer-related)

Xu HX, Wu KJ, Tian YJ, et al.
Expression profile of SIX family members correlates with clinic-pathological features and prognosis of breast cancer: A systematic review and meta-analysis.
Medicine (Baltimore). 2016; 95(27):e4085 [PubMed] Free Access to Full Article Related Publications
Sineoculis homeobox homolog (SIX) family proteins, including SIX1, SIX2, SIX3, SIX4, SIX5, and SIX6, have been implicated in the initiation and progression of breast cancer, but the role of each member in breast tumor is not fully understood. We conducted a systematic review and meta-analysis to evaluate the association between the mRNA levels of all 6 members and clinic-pathological characteristics and clinical outcome of breast cancer patients based on the PRISMA statement criteria.ArrayExpress and Oncomine were searched for eligible databases published up to December 10, 2015. The association between the mRNA expression of SIX family members and clinic-pathological features and prognosis was measured by the odds ratio (OR), hazard ratio (HR), and the corresponding 95% confidence interval (CI), respectively. All statistical analyses were performed using STATA software.In total, 20 published Gene Expression Omnibus (GEO) databases with 3555 patients were analyzed. Our analysis revealed that patients with SIX1 overexpression had worse overall survival (OS) (HR: 1.28, 95% CI: 1.03-1.58) and shorter relapse-free survival (RFS) (HR: 1.28, 95% CI: 1.05-1.56), and much worse prognosis for luminal breast cancer patients with SIX1 overexpression (OS: HR: 1.64, 95% CI: 1.13-2.39; RFS: HR: 1.43, 95% CI: 1.06-1.93). We found that patients with higher SIX2 level had shorter time to both relapse and metastasis. However, high SIX3 mRNA level was a protective factor for OS and RFS of basal-like breast cancer patients.Our study suggested that members of SIX family played distinct roles in breast cancer. Detailed analysis of the expression of the SIX family members might provide useful information to predict breast cancer progression and prognosis.

Armat M, Ramezani F, Molavi O, et al.
Six family of homeobox genes and related mechanisms in tumorigenesis protocols.
Tumori. 2016; 2016(3):236-43 [PubMed] Related Publications
In recent years, the homeobox gene superfamily has been introduced as a master regulator in downstream target genes related to cell development and proliferation. An indispensable role of this family involved in organogenesis development has been widely demonstrated since expression of Six family led to a distinct increase in development of various organs. These functions of Six family genes are primarily based on structure as well as regulatory role in response to external or internal stimuli. In addition to these roles, mutation or aberrant expression of Six family plays a fundamental role in initiation of carcinogenesis, a multistep process including transformation, proliferation, angiogenesis, migration, and metastasis. This suggests that the Six superfamily members can be considered as novel target molecules to inhibit tumor growth and progression. This review focuses on the structure, function, and mechanisms of the Six family in cancer processes and possible strategies to apply these family members for diagnostic, prognostic, and therapeutic purposes.

Spreafico F, Ciceri S, Gamba B, et al.
Chromosomal anomalies at 1q, 3, 16q, and mutations of SIX1 and DROSHA genes underlie Wilms tumor recurrences.
Oncotarget. 2016; 7(8):8908-15 [PubMed] Free Access to Full Article Related Publications
Approximately half of children suffering from recurrent Wilms tumor (WT) develop resistance to salvage therapies. Hence the importance to disclose events driving tumor progression/recurrence. Future therapeutic trials, conducted in the setting of relapsing patients, will need to prioritize targets present in the recurrent lesions. Different studies identified primary tumor-specific signatures associated with poor prognosis. However, given the difficulty in recruiting specimens from recurrent WTs, little work has been done to compare the molecular profile of paired primary/recurrent diseases. We studied the genomic profile of a cohort of eight pairs of primary/recurrent WTs through whole-genome SNP arrays, and investigated known WT-associated genes, including SIX1, SIX2 and micro RNA processor genes, whose mutations have been recently proposed as associated with worse outcome. Through this approach, we sought to uncover anomalies characterizing tumor recurrence, either acquired de novo or already present in the primary disease, and to investigate whether they overlapped with known molecular prognostic signatures. Among the aberrations that we disclosed as potentially acquired de novo in recurrences, some had been already recognized in primary tumors as associated with a higher risk of relapse. These included allelic imbalances of chromosome 1q and of chromosome 3, and CN losses on chromosome 16q. In addition, we found that SIX1 and DROSHA mutations can be heterogeneous events (both spatially and temporally) within primary tumors, and that their co-occurrence might be positively selected in the progression to recurrent disease. Overall, these results provide new insights into genomic and genetic events underlying WT progression/recurrence.

Armat M, Oghabi Bakhshaiesh T, Sabzichi M, et al.
The role of Six1 signaling in paclitaxel-dependent apoptosis in MCF-7 cell line.
Bosn J Basic Med Sci. 2016; 16(1):28-34 [PubMed] Free Access to Full Article Related Publications
The resistance of cancer cells to chemotherapeutic agents represents the main problem in cancer treatment. Despite intensive research, mechanisms of resistance have not yet been fully elucidated. Six1 signaling has an important role in the expansion of progenitor cell populations during early embryogenesis. Six1 gene overexpression has been strongly associated with aggressiveness, invasiveness, and poor prognosis of different cancers. In this study, we investigated the role of Six1 signaling in resistance of MCF-7 breast cancer cells to taxanes. We first established in vitro paclitaxel-resistant MCF-7 breast cancer cells. Morphological modifications in paclitaxel-resistant cells were examined via light microscopic images and fluorescence-activated cell sorting analysis. Applying quantitative real-time polymerase chain reaction, we measured Six1, B-cell lymphoma/leukemia(BCL-2), BAX, and P53 mRNA expression levels in both non-resistant and resistant cells. Resistant cells were developed from the parent MCF-7 cells by applying increasing concentrations of paclitaxel up to 64 nM. The inhibitory concentration 50% value in resistant cells increased from 3.5 ± 0.03 to 511 ± 10.22 nM (p = 0.015). In paclitaxel-resistant cells, there was a significant increase in Six1 and BCL-2 mRNA levels (p = 0.0007) with a marked decrease in pro-apoptotic Bax mRNA expression level (p = 0.03); however, there was no significant change in P53 expression (p = 0.025). Our results suggest that identifying cancer patients with high Six1 expression and then inhibition of Six1 signaling can improve the efficiency of chemotherapeutic agents in the induction of apoptosis.

Towers CG, Guarnieri AL, Micalizzi DS, et al.
The Six1 oncoprotein downregulates p53 via concomitant regulation of RPL26 and microRNA-27a-3p.
Nat Commun. 2015; 6:10077 [PubMed] Free Access to Full Article Related Publications
TP53 is mutated in 50% of all cancers, and its function is often compromised in cancers where it is not mutated. Here we demonstrate that the pro-tumorigenic/metastatic Six1 homeoprotein decreases p53 levels through a mechanism that does not involve the negative regulator of p53, MDM2. Instead, Six1 regulates p53 via a dual mechanism involving upregulation of microRNA-27a and downregulation of ribosomal protein L26 (RPL26). Mutation analysis confirms that RPL26 inhibits miR-27a binding and prevents microRNA-mediated downregulation of p53. The clinical relevance of this interaction is underscored by the finding that Six1 expression strongly correlates with decreased RPL26 across numerous tumour types. Importantly, we find that Six1 expression leads to marked resistance to therapies targeting the p53-MDM2 interaction. Thus, we identify a competitive mechanism of p53 regulation, which may have consequences for drugs aimed at reinstating p53 function in tumours.

Zakrzewski K, Jarząb M, Pfeifer A, et al.
Transcriptional profiles of pilocytic astrocytoma are related to their three different locations, but not to radiological tumor features.
BMC Cancer. 2015; 15:778 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Pilocytic astrocytoma is the most common type of brain tumor in the pediatric population, with a generally favorable prognosis, although recurrences or leptomeningeal dissemination are sometimes also observed. For tumors originating in the supra-or infratentorial location, a different molecular background was suggested, but plausible correlations between the transcriptional profile and radiological features and/or clinical course are still undefined. The purpose of this study was to identify gene expression profiles related to the most frequent locations of this tumor, subtypes based on various radiological features, and the clinical pattern of the disease.
METHODS: Eighty six children (55 males and 31 females) with histologically verified pilocytic astrocytoma were included in this study. Their age at the time of diagnosis ranged from fourteen months to seventeen years, with a mean age of seven years. There were 40 cerebellar, 23 optic tract/hypothalamic, 21 cerebral hemispheric, and two brainstem tumors. According to the radiological features presented on MRI, all cases were divided into four subtypes: cystic tumor with a non-enhancing cyst wall; cystic tumor with an enhancing cyst wall; solid tumor with central necrosis; and solid or mainly solid tumor. In 81 cases primary surgical resection was the only and curative treatment, and in five cases progression of the disease was observed. In 47 cases the analysis was done by using high density oligonucleotide microarrays (Affymetrix HG-U133 Plus 2.0) with subsequent bioinformatic analyses and confirmation of the results by independent RT-qPCR (on 39 samples).
RESULTS: Bioinformatic analyses showed that the gene expression profile of pilocytic astrocytoma is highly dependent on the tumor location. The most prominent differences were noted for IRX2, PAX3, CXCL14, LHX2, SIX6, CNTN1 and SIX1 genes expression even within different compartments of the supratentorial region. Analysis of the genes potentially associated with radiological features showed much weaker transcriptome differences. Single genes showed association with the tendency to progression.
CONCLUSIONS: Here we have shown that pilocytic astrocytomas of three different locations can be precisely differentiated on the basis of their gene expression level, but their transcriptional profiles does not strongly reflect the radiological appearance of the tumor or the course of the disease.

Wang L, Liu H
microRNA-188 is downregulated in oral squamous cell carcinoma and inhibits proliferation and invasion by targeting SIX1.
Tumour Biol. 2016; 37(3):4105-13 [PubMed] Related Publications
microRNA-188 expression is downregulated in several tumors. However, its function and mechanism in human oral squamous cell carcinoma (OSCC) remains obscure. The present study aims to identify the expression pattern, biological roles, and potential mechanism by which miR-188 dysregulation is associated with oral squamous cell carcinoma. Significant downregulation of miR-188 was observed in OSCC tissues compared with paired normal tissues. In vitro, gain-of-function, loss-of-function experiments were performed to examine the impact of miR-188 on cancer cell proliferation, invasion, and cell cycle progression. Transfection of miR-188 mimics suppressed Detroit 562 cell proliferation, cell cycle progression and invasion, with downregulation of cyclin D1, MMP9, and p-ERK. Transfection of miR-188 inhibitor in FaDu cell line with high endogenous expression exhibited the opposite effects. Using fluorescence reporter assays, we confirmed that SIX1 was a direct target of miR-188 in OSCC cells. Transfection of miR-188 mimics downregulated SIX1 expression. SIX1 siRNA treatment abrogated miR-188 inhibitor-induced cyclin D1 and MMP9 upregulation. In addition, we found that SIX1 was overexpressed in 32 of 80 OSCC tissues. In conclusion, this study indicates that miR-188 downregulation might be associated with oral squamous cell carcinoma progression. miR-188 suppresses proliferation and invasion by targeting SIX1 in oral squamous cell carcinoma cells.

Nagel S, Meyer C, Kaufmann M, et al.
Aberrant expression of homeobox gene SIX1 in Hodgkin lymphoma.
Oncotarget. 2015; 6(37):40112-26 [PubMed] Free Access to Full Article Related Publications
In Hodgkin lymphoma (HL) we recently identified deregulated expression of homeobox genes MSX1 and OTX2 which are physiologically involved in development of the embryonal neural plate border region. Here, we examined in HL homeobox gene SIX1 an additional regulator of this embryonal region mediating differentiation of placodal precursors. SIX1 was aberrantly activated in 12 % of HL patient samples in silico, indicating a pathological role in a subset of this B-cell malignancy. In addition, SIX1 expression was detected in HL cell lines which were used as models to reveal upstream factors and target genes of this basic developmental regulator. We detected increased copy numbers of the SIX1 locus at chromosome 14q23 correlating with enhanced expression while chromosomal translocations were absent. Moreover, comparative expression profiling data and pertinent gene modulation experiments indicated that the WNT-signalling pathway and transcription factor MEF2C regulate SIX1 expression. Genes encoding the transcription factors GATA2, GATA3, MSX1 and SPIB - all basic lymphoid regulators - were identified as targets of SIX1 in HL. In addition, cofactors EYA1 and TLE4, respectively, contrastingly mediated activation and suppression of SIX1 target gene expression. Thus, the protein domain interfaces may represent therapeutic targets in SIX1-positive HL subsets. Collectively, our data reveal a gene regulatory network with SIX1 centrally deregulating lymphoid differentiation and support concordance of lymphopoiesis/lymphomagenesis and developmental processes in the neural plate border region.

Zeng J, Wei M, Shi R, et al.
MiR-204-5p/Six1 feedback loop promotes epithelial-mesenchymal transition in breast cancer.
Tumour Biol. 2016; 37(2):2729-35 [PubMed] Related Publications
Epithelial-mesenchymal transition (EMT) is a vital process in epithelial cancer invasion and metastasis. The induction of EMT by Six1 has been described as a common mode of cancer progression, which could promote breast cancer migration and invasion. In the study, we found that miR-204-5p could suppress the migration and invasion of breast cancer cell lines. Since overexpression of Six1 promote EMT, we identified a mechanism by which miR-204-5p inhibited the EMT by downregulating the Six1, which was mediated by a conserved miR-204-5p seed-matching sequence in the 3'-UTR of Six1 mRNA. We also identified that upregulation of Six1 could downregulate miR-204-5p expression, affecting the migration and invasion of breast cancer cell lines. In conclusion, the frequent upregulation of Six1 and/or downregulation of miR-204-5p in breast cancer may shift the equilibrium of these reciprocal regulations and lock breast cancer cells in the mesenchymal state.

Liu Y, Han N, Zhou S, et al.
The DACH/EYA/SIX gene network and its role in tumor initiation and progression.
Int J Cancer. 2016; 138(5):1067-75 [PubMed] Related Publications
The functional abnormality of developmental genes is a common phenomenon in cancer initiation and progression. The retinal determination gene network (RDGN) is a key signal in Drosophila eye specification, and this conservative pathway is also required for the development of multiple organs in mammalian species. Recent studies demonstrated that aberrant expressions of RDGN components in vertebrates, mainly Dach, Six, and Eya, represent a novel tumor signal. RDGN regulates proliferation, apoptosis, tumor growth and metastasis through interactions with multiple signaling pathways in a co-ordinated fashion; Dach acts as a tumor suppressor, whereas Six and Eya function as oncogenes. Clinical analyses demonstrated that the expression levels of RDGN correlate with tumor stage, metastasis and survival, suggesting that combinational detection of this pathway might be used as a promising biomarker for the stratification of therapy and for the prediction of the prognosis of cancer patients.

Kahlert C, Lerbs T, Pecqueux M, et al.
Overexpression of SIX1 is an independent prognostic marker in stage I-III colorectal cancer.
Int J Cancer. 2015; 137(9):2104-13 [PubMed] Related Publications
Epithelial-to-mesenchymal transition (EMT) contributes significantly to tumor progression and metastasis. The assessment of EMT-associated transcription factors could be a promising approach to identify biomarkers and potential therapeutic targets in colorectal cancer. In our study, we focused on the transcription factor "Sine oculis homeobox" (SIX) 1, which is a member of the superfamily of the homeobox genes and has been described to promote EMT in different types of tumors. Immunohistochemistry against SIX1 was performed on colorectal mucosa, adenomas, carcinomas-in situ and primary adenocarcinomas. An expression score was developed and subsequently assessed for its prognostic value in two independent cohorts. Cohort 1 consisted of 128 patients with stage I-III colorectal cancer; cohort 2 included 817 patients with stage I-III colorectal cancer who had participated in the DACHS study. HCT-116 cells were transfected with SIX1 plasmids and subjected to migration and colony formation assays. The expression of SIX1 increases gradually from mucosa to colorectal adenocarcinomas (p > 0.0001). Univariate and multivariate analyses reveal that high expression of SIX1 is associated with decreased overall survival (cohort 1: HR: 4.01, CI: 1.20-14.07, p = 0.025; cohort 2: HR: 1.43, CI: 1.014-2.02, p = 0.047). Overexpression of SIX1 induces a more mesenchymal-like phenotype in HCT-116 cells and enhances tumor migration. High expression of SIX1 is an independent prognostic marker in colorectal cancer. It might be a promising biomarker to stratify patients into different risk groups. Moreover, targeting SIX1 might be a novel therapeutic approach in patients with colorectal cancer.

Eisner A, Pazyra-Murphy MF, Durresi E, et al.
The Eya1 phosphatase promotes Shh signaling during hindbrain development and oncogenesis.
Dev Cell. 2015; 33(1):22-35 [PubMed] Free Access to Full Article Related Publications
Sonic hedgehog (Shh) signaling is critical in development and oncogenesis, but the mechanisms regulating this pathway remain unclear. Although protein phosphorylation clearly affects Shh signaling, little is known about phosphatases governing the pathway. Here, we conducted a small hairpin RNA (shRNA) screen of the phosphatome and identified Eya1 as a positive regulator of Shh signaling. We find that the catalytically active phosphatase Eya1 cooperates with the DNA-binding protein Six1 to promote gene induction in response to Shh and that Eya1/Six1 together regulate Gli transcriptional activators. We show that Eya1, which is mutated in a human deafness disorder, branchio-oto-renal syndrome, is critical for Shh-dependent hindbrain growth and development. Moreover, Eya1 drives the growth of medulloblastoma, a Shh-dependent hindbrain tumor. Together, these results identify Eya1 and Six1 as key components of the Shh transcriptional network in normal development and in oncogenesis.

Wegert J, Ishaque N, Vardapour R, et al.
Mutations in the SIX1/2 pathway and the DROSHA/DGCR8 miRNA microprocessor complex underlie high-risk blastemal type Wilms tumors.
Cancer Cell. 2015; 27(2):298-311 [PubMed] Related Publications
Blastemal histology in chemotherapy-treated pediatric Wilms tumors (nephroblastoma) is associated with adverse prognosis. To uncover the underlying tumor biology and find therapeutic leads for this subgroup, we analyzed 58 blastemal type Wilms tumors by exome and transcriptome sequencing and validated our findings in a large replication cohort. Recurrent mutations included a hotspot mutation (Q177R) in the homeo-domain of SIX1 and SIX2 in tumors with high proliferative potential (18.1% of blastemal cases); mutations in the DROSHA/DGCR8 microprocessor genes (18.2% of blastemal cases); mutations in DICER1 and DIS3L2; and alterations in IGF2, MYCN, and TP53, the latter being strongly associated with dismal outcome. DROSHA and DGCR8 mutations strongly altered miRNA expression patterns in tumors, which was functionally validated in cell lines expressing mutant DROSHA.

Walz AL, Ooms A, Gadd S, et al.
Recurrent DGCR8, DROSHA, and SIX homeodomain mutations in favorable histology Wilms tumors.
Cancer Cell. 2015; 27(2):286-97 [PubMed] Free Access to Full Article Related Publications
We report the most common single-nucleotide substitution/deletion mutations in favorable histology Wilms tumors (FHWTs) to occur within SIX1/2 (7% of 534 tumors) and microRNA processing genes (miRNAPGs) DGCR8 and DROSHA (15% of 534 tumors). Comprehensive analysis of 77 FHWTs indicates that tumors with SIX1/2 and/or miRNAPG mutations show a pre-induction metanephric mesenchyme gene expression pattern and are significantly associated with both perilobar nephrogenic rests and 11p15 imprinting aberrations. Significantly decreased expression of mature Let-7a and the miR-200 family (responsible for mesenchymal-to-epithelial transition) in miRNAPG mutant tumors is associated with an undifferentiated blastemal histology. The combination of SIX and miRNAPG mutations in the same tumor is associated with evidence of RAS activation and a higher rate of relapse and death.

Blevins MA, Towers CG, Patrick AN, et al.
The SIX1-EYA transcriptional complex as a therapeutic target in cancer.
Expert Opin Ther Targets. 2015; 19(2):213-25 [PubMed] Free Access to Full Article Related Publications
INTRODUCTION: The SIX homeodomain proteins and the eyes absent (EYA) family of co-activators form a bipartite transcription factor complex that promotes the proliferation and survival of progenitor cells during organogenesis and is down-regulated in most adult tissues. Abnormal over-expression of SIX1 and EYA in adult tissue is associated with the initiation and progression of diverse tumor types. Importantly, SIX1 and EYA are often co-overexpressed in tumors, and the SIX1-EYA2 interaction has been shown to be critical for metastasis in a breast cancer model. The EYA proteins also contain protein tyrosine phosphatase activity, which plays an important role in breast cancer growth and metastasis as well as directing cells to the repair pathway upon DNA damage.
AREAS COVERED: This review provides a summary of the SIX1/EYA complex as it relates to development and disease and the current efforts to therapeutically target this complex.
EXPERT OPINION: Recently, there have been an increasing number of studies suggesting that targeting the SIX1/EYA transcriptional complex will potently inhibit tumor progression. Although current attempts to develop inhibitors targeting this complex are still in the early stages, continued efforts toward developing better compounds may ultimately result in effective anti-cancer therapies.

Xia Y, Zhu Y, Ma T, et al.
miR-204 functions as a tumor suppressor by regulating SIX1 in NSCLC.
FEBS Lett. 2014; 588(20):3703-12 [PubMed] Related Publications
The involvement of miR-204 in lung cancer development is unclear. In our study, we analyzed the expression of miR-204 in tumor- and adjacent-tissue samples from 141 patients with non-small cell lung cancer (NSCLC). MiR-204 expression was decreased in tumor samples compared with non-cancerous tissue-derived controls. Moreover, miR-204 expression negatively correlated with homeobox protein SIX1 expression, tumor size and metastasis. MiR-204 silencing in miR-204-positive NSCLC cell lines promoted cell invasion and proliferation. Concomitantly, MiR-204 overexpression resulted in reduced cell proliferation and invasion, upregulated E-cadherin and downregulated N-cadherin and Vimentin expression. SIX1 was identified as a potential target of miR-204, and SIX1 silencing partially compromised the invasive and proliferative capacity of miR-204-deficient cells. Thus, miR-204 may be involved in the NSCLC development.

Kong J, Zhou X, Liu S, et al.
Overexpression of sineoculis homeobox homolog 1 predicts poor prognosis of hepatocellular carcinoma.
Int J Clin Exp Pathol. 2014; 7(6):3018-27 [PubMed] Free Access to Full Article Related Publications
High expression levels of the human sineoculis homeobox homolog 1 (SIX1) gene have been correlated with numerous human malignancies. The SIX1 protein is involved in chromatin reconstruction and gene transcription, and plays an important role in cell apoptosis. This study explores the role of SIX1 in tumor progression and in the prognostic evaluation of hepatocellular carcinoma (HCC). Real-time PCR, Western blotting analysis, immunofluorescence (IF) staining, and immunohistochemistry (IHC) were performed to examine SIX1 expression in HCC cell line/tissues compared with adjacent non-tumor and normal liver tissues. Statistical analysis was applied to evaluate the correlation between SIX1 overexpression and the clinicopathological features of HCC. Survival rates were calculated using the Kaplan-Meier method, and the relationship between prognostic factors and patient survival was analyzed using the Cox proportional hazard models. The SIX1 protein was detected in 80.9% of HCCs, which was significantly higher than that in either adjacent non tumor liver or normal liver tissues (P < 0.01). SIX1 overexpression was positively correlated with tumor size, pTNM stage and venous infiltration. Moreover, the 5-year survival rate of patients with high expression of SIX1 was significantly lower than that of patients with low SIX1 expression. Multivariate analysis suggested that pTNM stage and SIX1 protein expression were independent risk factors for survival in HCC. In conclusion, SIX1 plays an important role in the progression of HCC. High level expression of SIX1 is an independent poor prognostic factor of HCC.

Liu D, Zhang XX, Xi BX, et al.
Sine oculis homeobox homolog 1 promotes DNA replication and cell proliferation in cervical cancer.
Int J Oncol. 2014; 45(3):1232-40 [PubMed] Related Publications
Malignant proliferation is the fundamental trait of tumor cells. The initiation of DNA replication represents a key process for cell proliferation, and has a marked impact on tumorigenesis and progression. Here we report that Sine oculis homeobox homolog 1 (SIX1) functions as a master regulator in DNA replication of cervical cancer cells. The expression of SIX1 was induced by the E7 oncoprotein of human papillomaviruses in cervical intraepithelial neoplasia and cervical cancer. The increase of SIX1 expression resulted in the upregulation of multiple genes related to the initiation of DNA replication, including the genes coding for the proteins in minichromosome maintenance complex (MCM2, MCM3, MCM6), DNA polymerase α-primase complex (POLA1, PRIM1, PRIM2), clamp loader (RFC3, RFC4, RFC5), DNA polymerase δ complex (POLD3) and DNA polymerase ε complex (POLE2). In line with this, the increase of SIX1 expression enhanced DNA synthesis, accelerated G1 to S phase progression, and promoted the proliferation of cervical cancer cells and the growth of cervical cancer. Consistently, knockdown of SIX1 could hamper DNA synthesis, slow down G1 to S phase progression, and suppress tumor cell proliferation and tumor growth. Importantly, SIX1 could more efficiently promote anchorage-independent cell growth. These results suggest that the increase of SIX1 expression could promote tumorigenesis, progression and invasive growth of cervical cancer by promoting DNA replication, and that targeting SIX1 may have significant therapeutic value in cervical cancer treatment.

Lv H, Cui A, Sun F, et al.
Sineoculis homeobox homolog 1 protein as an independent biomarker for gastric adenocarcinoma.
Exp Mol Pathol. 2014; 97(1):74-80 [PubMed] Related Publications
Sine oculis homeobox homolog 1 (SIX1) protein is a member of the homeobox transcription factor family. Overexpression of SIX1 contributes to cancer progression and is associated with adverse outcomes in various cancer types including breast, ovarian, uterine cervical and liver. To investigate the clinicopathological significance of SIX1 protein expression in gastric adenocarcinomas (GAC), localization of the SIX1 protein was determined in MKN-1, a gastric cancer cell line, using immunofluorescence (IF) staining; SIX1 mRNA level was detected in fresh tissues of GAC and normal gastric mucosa using quantitative real-time polymerase chain reaction (qRT-PCR); and SIX1 protein expression was assessed in 163 GAC, 35 gastric dysplasia and 26 normal gastric mucosa using immunohistochemical (IHC) staining. Correlations between SIX1 protein expression and pathological parameters of GAC were analyzed using Chi-square tests, differences in survival curves were analyzed using log-rank tests, and multivariate survival analysis was performed using the Cox proportional hazards regression model. SIX1 protein showed a mainly cytoplasmic staining pattern in GAC using IF and IHC staining. The positive SIX1 protein expression rate was 80.4% in GAC, which was significantly higher than in either gastric dysplasia (45.7%) or normal gastric mucosa (26.9%) (P<0.01). qRT-PCR data also confirmed increased levels of SIX1 mRNA expression in GAC compared with the normal gastric mucosa in fresh tissues. In addition, the strongly positive SIX1 protein expression rate was significantly correlated with clinical stage, lymph node metastasis and serosal invasion of GAC (P<0.01 or P<0.05), while there was no association with gender, age, tumor size, Lauren classification or histological types of GAC. Notably, strongly positive signals were frequently observed in tumor blood vessels and/or lymphatic vessels. GAC patients with high expression of the SIX1 had shorter overall and disease-free survival rates than those with low SIX1 protein expression (P<0.01). Furthermore, using multivariate analysis, SIX1 protein expression was found to be an independent risk factor for survival in patients with GAC along with clinical stage and serosal invasion (P<0.01). In conclusion, SIX1 protein expression status may be an independent biomarker for prognostic evaluation of GAC.

Sehic D, Ciornei CD, Gisselsson D
Evaluation of CITED1, SIX1, and CD56 protein expression for identification of blastemal elements in Wilms tumor.
Am J Clin Pathol. 2014; 141(6):828-33 [PubMed] Related Publications
OBJECTIVES: Successful further treatment of Wilms tumors (WTs) after preoperative chemotherapy and surgery depends on correct histopathologic risk stratification, including quantification of remaining blastemal elements. In the present study, we assessed the usefulness of protein markers for the detection of WT blastema.
METHODS: Expression of the candidate blastemal protein markers CITED1, SIX1, and CD56 was evaluated by immunofluorescence regarding sensitivity and specificity for staining blastema in a tissue microarray containing cores from 30 WTs, a small number of rarer pediatric renal neoplasms, and normal postnatal kidney.
RESULTS: CITED1, SIX1, and CD56 were expressed in blastema in 100%, 89%, and 74%, respectively, of the WTs with this component present. However, they were also expressed in 64%, 25%, and 79%, respectively, of epithelial WT elements and 48%, 52%, and 62%, respectively, of stromal WT elements.
CONCLUSIONS: SIX1 showed the highest specificity, CITED1 the highest sensitivity, and CD56 low specificity and sensitivity for detection of postchemotherapy WT blastema. Cytokeratin staining proved to be a useful way to determine rudimentary tubular elements not readily recognized by routine staining.

Feng GW, Dong LD, Shang WJ, et al.
HDAC5 promotes cell proliferation in human hepatocellular carcinoma by up-regulating Six1 expression.
Eur Rev Med Pharmacol Sci. 2014; 18(6):811-6 [PubMed] Related Publications
OBJECTIVES: Histone deacetylases (HDACs) plays important roles in the regulation of genes expression and contribute to the growth of cancer cells. The present study aimed to investigate the function of HDAC5 in human hepatocellular carcinoma (HCC).
PATIENTS AND METHODS: The expression of HDAC5 in human hepatocellular carcinoma tissues and cells was detected. MTT assay was used to measure the proliferation of HCC cell lines. siRNA technology was employed to down-regulate the protein expression of HDAC5 and Six1.
RESULTS: Western blot showed that the HDAC5 expression was increased in human HCC tissues. The mRNA and protein levels of HDAC5 were up-regulated in human HCC cell lines. MTT assay showed that over-expression of HDAC5 promoted cell proliferation in human HCC cell lines. Down-regulation of HDAC5 caused a significantly inhibition of liver cancer cells proliferation. Furthermore, we found that HDAC5 promoted the Six1 expression both at the mRNA and protein levels in HCC cell lines.
CONCLUSIONS: The current study demonstrated for the first time that HDAC5 promoted HCC cell proliferation through up-regulation of Six1 expression and might provide novel therapeutic targets in the treatment of HCC.

Liu D, Zhang XX, Wan DY, et al.
Sine oculis homeobox homolog 1 promotes α5β1-mediated invasive migration and metastasis of cervical cancer cells.
Biochem Biophys Res Commun. 2014; 446(2):549-54 [PubMed] Related Publications
Sine oculis homeobox homolog 1 (SIX1) has been supposed to be correlated with the metastasis and poor prognosis of several malignancies. However, the effect of SIX1 on the metastatic phenotype of tumor cells and the underlying mechanisms were still unclear to date. Here we report that SIX1 can promote α5β1-mediated metastatic capability of cervical cancer cells. SIX1 promoted the expression of α5β1 integrin to enhance the adhesion capacity of tumor cells in vitro and tumor cell arrest in circulation in vivo. Moreover, higher expression of SIX1 in tumor cells resulted in the increased production of active MMP-2 and MMP-9, up-regulation of anti-apoptotic genes (BCL-XL and BCL2) and down-regulation of pro-apoptotic genes (BIM and BAX), thus promoting the invasive migration and anoikis-resistance of tumor cells. Importantly, blocking α5β1 abrogated the regulatory effect of SIX1 on the expression of these genes, and also abolished the promotional effect of SIX1 on invasive capability of tumor cells. Furthermore, knock-down of α5 could abolish the promoting effect of SIX1 on the development of metastatic lesions in both experimental and spontaneous metastasis model. Therefore, by up-regulating α5β1 expression, SIX1 not only promoted the adhesion capacity, but also augmented ECM-α5β1-mediated regulation of gene expression to enhance the metastatic potential of cervical cancer cells. These results suggest that SIX1/α5β1 might be considered as valuable marker for metastatic potential of cervical cancer cells, or a therapeutic target in cervical cancer treatment.

Zhao H, Xu Z, Qin H, et al.
miR-30b regulates migration and invasion of human colorectal cancer via SIX1.
Biochem J. 2014; 460(1):117-25 [PubMed] Related Publications
CRC (colorectal cancer) is one of the most malignant tumours in both developing and developed countries. It is estimated that 60% of CRC patients have liver metastasis. In the present study, we show that miR-30b is an important regulator in human CRC migration and invasion, which are vital steps in CRC liver metastasis. miR-30b was significantly down-regulated in primary CRC specimens compared with normal tissues. Furthermore, miR-30b was much lower in liver metastasis tissues than in CRCs. We validated SIX1 (SIX homeobox 1), a member of the SIX homeodomain family of transcription factors and an EMT (epithelial-mesenchymal transition)-promoting gene, as the direct target of miR-30b. Forced expression of miR-30b inhibited CRC cell migration and invasion in vitro via its target gene SIX1. Furthermore, an inverse correlation between expression of SIX1 and miR-30b has been observed both in primary CRC specimens and liver metastasis. Taken together, miR-30b plays an important role in mediating metastatic related behaviour in CRC. miR-30b may serve as a potential diagnostic marker and therapeutic target for patients with CRC in the future.

Xu H, Zhang Y, Altomare D, et al.
Six1 promotes epithelial-mesenchymal transition and malignant conversion in human papillomavirus type 16-immortalized human keratinocytes.
Carcinogenesis. 2014; 35(6):1379-88 [PubMed] Free Access to Full Article Related Publications
Six1, a member of the Six family of homeodomain transcription factors, is overexpressed in various human cancers, and SIX1 overexpression is associated with tumor progression and metastasis. Six1 messenger RNA levels increase during in vitro progression of human papillomavirus type 16 (HPV16)-immortalized human keratinocytes (HKc/HPV16) toward a differentiation-resistant (HKc/DR) phenotype. In this study, we show that HKc/DR-overexpressing Six1 exhibited a more mesenchymal phenotype, as characterized by a fibroblastic appearance and increased invasion. We utilized Whole Human Genome Microarrays to explore the gene expression changes associated with Six1 overexpression in HKc/DR. We found that overexpression of Six1 downregulated epithelial-related genes and upregulated mesenchymal-related genes, which suggests that Six1 overexpression induces epithelial-mesenchymal transition (EMT). Pathway analysis of the microarray data showed alterations in the transforming growth factor-beta (TGF-β) pathway, including enhanced expression of the TGF-β receptor type II (TβRII), and activation of the mitogen-activated protein kinase (MAPK) pathway in HKc/DR-overexpressing Six1, suggesting that Smad-independent pathways of TGF-β signaling may be involved in Six1-mediated EMT. p38 MAPK activation was required for sustained Six1-induced EMT and TβRII overexpression. Finally, we determined that Six1 overexpression in HKc/DR resulted in malignant conversion and increased the cancer stem cell (CSC)-like population. Thus, Six1 overexpression promotes EMT, CSCs properties and malignant conversion in HKc/DR through MAPK activation, which supports the possible use of p38-TβRII inhibitors for the treatment of cancers overexpressing Six1.

Li Z, Tian T, Hu X, et al.
Targeting Six1 by lentivirus-mediated RNA interference inhibits colorectal cancer cell growth and invasion.
Int J Clin Exp Pathol. 2014; 7(2):631-9 [PubMed] Free Access to Full Article Related Publications
The Six1 homeodomain protein is a developmental transcription factor that has been implicated in tumor onset and progression. Recently, it's reported that overexpression of Six1 is sufficient to induce epithelial-to-mesenchymal transition (EMT) and metastasis of colorectal cancer. Moreover, its expression is significantly associated with poorer overall survival probability in advanced-stage colorectal cancer. To address whether Six1 could serve as a therapeutic target for human colorectal cancer, we used a lentivirus-mediated short hairpin RNA (shRNA) gene knockdown method to suppress the expression of Six1 in colorectal cancer cells. We showed that lentivirusmediated shRNA targeted to Six1 gene efficiently reduced its expression in colorectal cancer cells at both mRNA and protein levels. In vitro functional assays revealed that knockdown of Six1 significantly suppressed cell proliferation, and inhibited cell migration and invasion of colorectal cancer cells. Furthermore, tumor xenograft model demonstrated that downregulation of Six1 dramatically inhibited colorectal cancer growth in vivo. In conclusion, these findings suggest that lentivirus-mediated Six1 inhibition may represent a novel therapeutic approach for treatment of colorectal cancer.

Wu W, Ren Z, Li P, et al.
Six1: a critical transcription factor in tumorigenesis.
Int J Cancer. 2015; 136(6):1245-53 [PubMed] Related Publications
In the past two decades, many studies have shown that sine oculis homeobox 1 (Six1) is a powerful regulator of organogenesis and disease, with important roles in tumorigenesis; therefore, it is important to review the biology of Six1 gene comprehensively. This review describes the function of Six1 in normal organ development, summarizes its role in several diseases, including cancer. The review will extend our understanding about the functional roles of Six1 and suggests opportunities to target Six1 for diagnostic, prognostic, and therapeutic purposes.

Jin A, Xu Y, Liu S, et al.
Sineoculis homeobox homolog 1 protein overexpression as an independent biomarker for pancreatic ductal adenocarcinoma.
Exp Mol Pathol. 2014; 96(1):54-60 [PubMed] Related Publications
Sineoculis homeobox homolog 1 (SIX1) is a member of the SIX gene family. It is highly expressed in cancers derived from tissues that play a fundamental role during embryogenesis. Recent studies suggest that inappropriate expression of SIX1 can both initiate tumorigenesis and promote metastasis. To investigate the clinicopathological significance of SIX1 expression in pancreatic ductal adenocarcinoma (PDAC), and to further identify its role as a potential biomarker and therapeutic target in PDAC, 103 PDAC tissue samples and 45 normal pancreatic tissue samples were immunohistochemically stained for SIX1 protein. The localization of SIX1 protein was detected in Panc-1 cancer cells using immunofluorescence staining. Correlations between SIX1 overexpression and the clinicopathological features of pancreatic cancer were evaluated using Chi-square (χ(2)) tests, differences in survival curves were analyzed using log-rank tests, and multivariate survival analysis was performed using the Cox proportional hazard regression model. In results, SIX1 protein showed mainly cytoplasmic/perinuclear staining pattern in PDAC with immunohistochemistry. The strongly positive rate of SIX1 protein was 60.2% (62/103) in PDAC, which was significantly higher than normal pancreatic tissue (6.7%, 3/45). SIX1 overexpression was positively correlated with tumor size, TNM stage, lymph node metastasis, and grade of PDAC (P < 0.001). SIX1 high expression levels influenced overall survival rates in G1, G2, stage I-II and stage III-IV groups of PDAC; and high expression levels had significantly lower overall survival rates than SIX1 low expression levels. In conclusion, SIX1 emerged as a significant independent prognostic factor in PDAC. SIX1 overexpression appears to be associated with PDAC, and may be a potential biomarker for early diagnosis and prognostic evaluation of PDAC.

Li Z, Tian T, Hu X, et al.
Six1 mediates resistance to paclitaxel in breast cancer cells.
Biochem Biophys Res Commun. 2013; 441(3):538-43 [PubMed] Related Publications
Paclitaxel resistance remains a major challenge in the treatment of breast cancer. Six1 is a homeodomain-containing transcription factor invloved in the initiation, progression and metastasis of breast cancer. We herein investigate the relationship between Six1 and resistance of paclitaxel in this study. The results indicate that six1 is a mediator of the paclitaxel resistance in breast cancer. The expression level of Six1 in breast cancer cells correlates with their resistance to paclitaxel. On the one hand, forced overexpression of Six1 in Six1-low/paclitaxel-sensitive MCF-7 or HS578T breast cancer cells induce their resistance to paclitaxel treatment directly; On the other hand, knockdown of endogenous Six1 in Six1-high/drug-resistant BT-474 breast cancer cells sensitized these cells to paclitaxel treatment. Besides, Six1 overexpression confers resistance to paclitaxel-mediated apoptosis in breast cancer cells. Furthermore, clinical data and the publicly available breast cancer gene expression datasets display that the association of Six1 expression with paclitaxel sensitivity is clinically relevant. In conclusion, these data suggest that Six1 may function as an important modifier of the paclitaxel response in breast cancer cells, and serve as a potential target for overcoming paclitaxel resistance in breast cancer.

Hua L, Fan L, Aichun W, et al.
Inhibition of Six1 promotes apoptosis, suppresses proliferation, and migration of osteosarcoma cells.
Tumour Biol. 2014; 35(3):1925-31 [PubMed] Related Publications
Sineoculis homeobox homolog 1 (Six1) is one of the transcription factors that act as master regulators of development and is frequently dysregulated in cancers. However, the biological role of Six1 is not clear in osteosarcoma. To address the expression of Six1 in osteosarcoma cells, three osteosarcoma cell lines (U2OS, SaOS-2, and MG63) and a human osteoblastic cell line (hFOB1.19) were used to detect the expression of Six1 by quantitative real-time polymerase chain reaction and western blotting. The results showed that Six1 was upregulated in osteosarcoma cell lines compared to human osteoblastic cell line hFOB1.19. To investigate the role of Six1 in osteosarcoma cells, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, flow cytometry analysis, and transwell chamber assays were used to determine the effects of Six1 on the cell viability, cycle, apoptosis, and migration properties in U2OS cells. The results showed that Six1 could promote U2OS cell proliferation and migration, and suppress U2OS cell apoptosis. In addition, we investigated the effects of Six1 on the expression of following proteins (cyclin D1, caspase-3, and vascular endothelial growth factor-C (VEGF-C)). Results showed that Six1 could increase the expression of cyclin D1 and VEGF-C, and decrease the expression of caspase-3. All these data suggested that Six1 might be involved in the promotion of growth, proliferation, and migration of U2OS cells, as well as the inhibition of apoptosis of U2OS cells. These data might provide information for the prediction of osteosarcoma prognosis and potential targets for therapy of osteosarcoma.

DeInnocentes P, Perry AL, Graff EC, et al.
Characterization of HOX gene expression in canine mammary tumour cell lines from spontaneous tumours.
Vet Comp Oncol. 2015; 13(3):322-36 [PubMed] Related Publications
Spatial/temporal controls of development are regulated by the homeotic (HOX) gene complex and require integration with oncogenes and tumour suppressors regulating cell cycle exit. Spontaneously derived neoplastic canine mammary carcinoma cell models were investigated to determine if HOX expression profiles were associated with neoplasia as HOX genes promote neoplastic potential in human cancers. Comparative assessment of human and canine breast cancer expression profiles revealed remarkable similarity for all four paralogous HOX gene clusters and several unlinked HOX genes. Five canine HOX genes were overexpressed with expression profiles consistent with oncogene-like character (HOXA1, HOXA13, HOXD4, HOXD9 and SIX1) and three HOX genes with underexpressed profiles (HOXA11, HOXC8 and HOXC9) were also identified as was an apparent nonsense mutation in HOXC6. This data, as well as a comparative analysis of similar data from human breast cancers suggested expression of selected HOX genes in canine mammary carcinoma could be contributing to the neoplastic phenotype.

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