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Chromosome 11q13.5 containing RSF1 (HBXAP), a gene involved in chromatin remodelling, is amplified in several human cancers including ovarian carcinoma. Our previous studies demonstrated requirement of Rsf-1 for cell survival in cancer cells, which contributed to tumour progression; however, its role in tumourigenesis has not yet been elucidated. In this study, we co-immunoprecipitated proteins with Rsf-1 followed by nanoelectrospray mass spectrometry and identified cyclin E1, besides SNF2H, as one of the major Rsf-1 interacting proteins. Like RSF1, CCNE1 is frequently amplified in ovarian cancer, and both Rsf-1 and cyclin E1 were found co-up-regulated in ovarian cancer tissues. Ectopic expression of Rsf-1 and cyclin E1 in non-tumourigenic TP53(mut) RK3E cells led to an increase in cellular proliferation and tumour formation by activating cyclin E1-associated kinase (CDK2). Tumourigenesis was not detected if either cyclin E1 or Rsf-1 was expressed, or they were expressed in a TP53(wt) background. Domain mapping showed that cyclin E1 interacted with the first 441 amino acids of Rsf-1. Ectopic expression of this truncated domain significantly suppressed G1/S-phase transition, cellular proliferation, and tumour formation of RK3E-p53(R175H) /Rsf-1/cyclin E1 cells. The above findings suggest that Rsf-1 interacts and collaborates with cyclin E1 in neoplastic transformation and TP53 mutations are a prerequisite for tumour-promoting functions of the RSF/cyclin E1 complex., (Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)

Backgrounds: Urothelial carcinoma of the urinary bladder (UCUB) is prevalent in developed countries. It often shows genetic instability and is associated with amplification (or gain) of various oncogenic genes or suppressive genes. Rsf-1, a subunit of ATP-dependent chromatin-remodelling complexes that mediates ATPase-dependent chromatin remodelling, confers tumour aggressiveness in certain carcinomas. The authors evaluate the Rsf-1 gene and expression status and its associations with clinicopathological features and survival in their UCUB collection., Methods: Immunohistochemistry was used to assess the Rsf-1 expression profile in 295 UCUB specimens, and was found to correlate with clinicopathological data. Real-time RT-PCR and fluorescence in situ hybridisation were used to detect RSF-1 mRNA expression and gene dosage in 20 independent cases. Western blot analysis was used to evaluate Rsf-1 protein expression in human urothelial cell lines., Results: Rsf-1 overexpression was demonstrated in 101 cases (34.2%), and was significantly associated with advanced primary tumour (p<0.001), nodal metastasis (p=0.004), higher histological grades (p=0.001) and frequent mitoses (p<0.001). Moreover, it was predictive in disease-specific survival and metastasis-free survival in both univariate and multivariate analyses (p<0.0001 for both). Although RSF-1 gene amplification can be barely detected, its mRNA expression is significantly enhanced in tumours with higher primary tumour (p=0.041) and positive nodal statuses (p=0.010), respectively. Rsf-1 protein was abundant in invasive urothelial carcinoma cells but was not benign., Conclusions: Overexpression of Rsf-1 is associated with higher tumour stage and poorer clinical outcome. The current study by the authors suggests gene amplification-independent mechanisms driving Rsf-1 overexpression during UCUB tumour progression.

RSF-1, also known as hepatitis B X-antigen associated protein (HBXAP), is a subunit of an ISWI chromatin remodeling complex, remodeling and spacing factor (RSF). Recent studies have provided new evidence that chromatin remodeling participates in the pathogenesis of neoplastic diseases by altering cell cycle regulation and gene expression. In this report, we studied the biological roles of RSF-1 in oral squamous cell carcinoma (OSCC), a highly invasive neoplastic disease. Based on IHC and quantitative real-time PCR, we demonstrated that RSF-1 expression could be detected in the majority of OSCC cases, and the levels were significantly higher in OSCC cells than in their normal counterparts. Moreover, expression levels of RSF-1 significantly correlated with the presence of angiolymphatic invasion, abnormal mitoses, metastasis, tumor recurrence, and advanced stage disease at presentation. Univariate and multivariate analyses showed a significant association of RSF-1 overexpression and worse overall survival in OSCC patients. RSF-1 knockdown remarkably decreased cellular proliferation and induced apoptosis in OSCC cells with high RSF-1 expression levels, but not in those without. Taken together, our results suggest that RSF-1 up-regulation is associated with several clinicopathological features of disease aggressiveness in OSCC patients, and RSF-1 plays an important role in maintaining cellular growth and survival in OSCC., (Copyright © 2011. Published by Elsevier Inc.)

Rsf-1 (HBXAP) has been reported as an amplified gene in human cancer, including the highly aggressive ovarian serous carcinoma. Rsf-1 protein interacts with SNF2H to form an ISWI chromatin remodeling complex, RSF. In this study, we investigated the functional role of Rsf-1 by observing phenotypes after expressing it in nontransformed cells. Acute expression of Rsf-1 resulted in DNA damage as evidenced by DNA strand breaks, nuclear γH2AX foci, and activation of the ATM-CHK2-p53-p21 pathway, leading to growth arrest and apoptosis. Deletion mutation and gene knockdown assays revealed that formation of a functional RSF complex with SNF2H was required for Rsf-1 to trigger DNA damage response (DDR). Gene knock-out of TP53 alleles, TP53 mutation, or treatment with an ATM inhibitor abolished up-regulation of p53 and p21 and prevented Rsf-1-induced growth arrest. Chronic induction of Rsf-1 expression resulted in chromosomal aberration and clonal selection for cells with c-myc amplification and CDKN2A/B deletion. Co-culture assays indicated Rsf-1-induced DDR as a selecting barrier that favored outgrowth of cell clones with a TP53 mutation. The above findings suggest that increased Rsf-1 expression and thus excessive RSF activity, which occurs in tumors harboring Rsf-1 amplification, can induce chromosomal instability likely through DDR.

Recently, some studies have indicated that Rsf-1/HBXAP plays a role in chromatin remodeling and transcriptional regulation that may contribute to tumorigenesis in ovarian cancer. The present study demonstrates that using dendritic cells (DCs) from human cord blood CD34(+) cells transduced with Rsf-1/HBXAP DNA plasmids by nucleofection generate specific cytotoxic T lymphocytes (CTL) against ovarian cancer in vitro. After transfection, DCs were analyzed for Rsf-1/HBXAP mRNA expression by RT-PCR and protein expression by Western blot. Then the DC phenotypes, T-cell stimulatory capacity, endocytic activity and migration capacity were explored by flow cytometry analysis, allogeneic mixed lymphocyte reaction, endocytosis and transwell chemotaxis assay, respectively. After transfection, Rsf-1/HBXAP expression was detected at mRNA and protein levels. Allogeneic T-cell proliferation induced by transfected DCs was obviously higher than non-transfected DCs, but the endocytosis capacity and migratory ability were not different. Rsf-1/HBXAP gene-transduced DCs could induce antigen-specific CTL and generate a very potent cytotoxicity to OVCAR3 cells. These data suggest that Rsf-1/HBXAP gene-transduced DCs may be a potential adjuvant immunotherapy for ovarian cancer in clinical applications., (Copyright 2010 Elsevier Inc. All rights reserved.)

The chromosome 11q13.5 locus is frequently amplified in several types of human cancer. We have previously shown that 11q13.5 amplification was associated with significantly shorter overall survival in ovarian cancer patients, but the molecular mechanisms of how amplification of this locus contributes to disease aggressiveness remain unclear. Because ovarian cancer mortality is primarily related to resistance of chemotherapeutic agents, we screened the top six candidate genes within this amplicon for their contribution to drug resistance. Rsf-1 (also known as HBXAP) was found to be the only gene in which gene knockdown sensitized tumor cells to paclitaxel. Rsf-1 has been known to interact with hSNF2H to form an ISWI chromatin remodeling complex. We found that Rsf-1 was up-regulated in paclitaxel-resistant ovarian cancer cell lines, and Rsf-1 immunoreactivity in primary ovarian carcinoma tissues correlated with in vitro paclitaxel resistance. Ectopic expression of Rsf-1 significantly enhanced paclitaxel resistance in ovarian cancer cells. Down-regulation of hSNF2H or disruption of hSNF2H and Rsf-1 interaction enhanced paclitaxel sensitivity in tumor cells with Rsf-1 up-regulation. Rsf-1 expression altered expression in several genes and activated certain signaling pathways that may contribute to drug resistance. In conclusion, our results suggest that Rsf-1 is the major gene within the 11q13.5 amplicon that contributes to paclitaxel resistance, and the formation of the Rsf-1/hSNF2H complex is required for inducing this phenotype.

Rsf-1 interacts with human sucrose nonfermenting protein 2 homologue (hSNF2H) to form a chromatin remodeling complex that participates in several biological processes. We have previously shown that Rsf-1 gene amplification was associated with the most aggressive type of ovarian cancer and cancer cells with Rsf-1 overexpression depended on Rsf-1 to survive. In this report, we determine if formation of the Rsf-1/hSNF2H complex could be one of the mechanisms contributing to tumor cell survival and growth in ovarian carcinomas. Based on immunohistochemistry, we found that Rsf-1 and hSNF2H were co-upregulated in ovarian cancer tissues. Ectopic expression of Rsf-1 in SKOV3 ovarian cancer cells with undetectable endogenous Rsf-1 expression enhanced hSNF2H protein levels and promoted SKOV3 tumor growth in a mouse xenograft model. Our studies also indicated that induction of Rsf-1 expression affected the molecular partnership of hSNF2H and translocated hSNF2H into nuclei where it colocalized with Rsf-1. Furthermore, analysis of Rsf-1 deletion mutants showed that the Rsf-D4 fragment contained the hSNF2H binding site based on coimmunoprecipitation and in vitro competition assays. As compared with other truncated mutants, expression of Rsf-D4 resulted in remarkable growth inhibition in ovarian cancer cells with Rsf-1 gene amplification and overexpression, but not in those without detectable Rsf-1 expression. The above findings suggest that interaction between Rsf-1 and hSNF2H may define a survival signal in those tumors overexpressing Rsf-1.

Rsf-1 protein is a member of a chromatin-remodeling complex that plays an important role in regulating gene expression and cell proliferation. Our previous study showed that Rsf-1 was an amplified gene that participated in the development of ovarian serous carcinoma. To further elucidate the role of Rsf-1 in ovarian cancer, we studied Rsf-1 immunoreactivity in 294 ovarian tumors of various histologic types. Because the Rsf-1 amplicon overlaps an amplified region reported in breast cancer, we included 782 neoplastic and normal breast tissues for comparison. Immunohistochemistry was performed on tissue microarrays using a 4-tiered scoring system. Overexpression of Rsf-1 was defined as a nuclear immunointensity of 3+ to 4+ because of a strong correlation between 3+ and 4+ immunointensity and Rsf-1 gene amplification, based on our previous fluorescence in situ hybridization analysis. Rsf-1 overexpression was observed in 25% of high-grade ovarian serous carcinomas and in only rare cases (<7%) of low-grade ovarian serous, ovarian endometrioid, and invasive breast carcinomas but not in any ovarian serous borderline tumors, ovarian clear cell carcinomas, ovarian mucinous carcinomas, intraductal carcinomas of the breast, and normal ovaries and breast tissues. Thus, overexpression of Rsf-1 was significantly associated with high-grade ovarian serous carcinoma (P < .05), as compared with other types of ovarian tumors and breast carcinomas. Our results provide evidence that Rsf-1 expression is primarily confined to high-grade serous carcinoma, the most aggressive ovarian cancer. Because Rsf-1 overexpression occurs in only a small number of breast carcinomas, it is unlikely that Rsf-1 is a critical gene in the development of breast carcinoma.

A genomewide technology, digital karyotyping, was used to identify subchromosomal alterations in ovarian cancer. Amplification at 11q13.5 was found in three of seven ovarian carcinomas, and amplicon mapping delineated a 1.8-Mb core of amplification that contained 13 genes. FISH analysis demonstrated amplification of this region in 13.2% of high-grade ovarian carcinomas but not in any of low-grade carcinomas or benign ovarian tumors. Combined genetic and transcriptome analyses showed that Rsf-1 (HBXAPalpha) was the only gene that demonstrated consistent overexpression in all of the tumors harboring the 11q13.5 amplification. Patients with Rsf-1 amplification or overexpression had a significantly shorter overall survival than those without. Overexpression of Rsf-1 gene stimulated cell proliferation and transform nonneoplastic cells by conferring serum-independent and anchorage-independent growth. Furthermore, Rsf-1 gene knockdown inhibited cell growth in OVCAR3 cells, which harbor Rsf-1 amplification. Taken together, these findings indicate an important role of Rsf-1 amplification in ovarian cancer.