An increase in DNA copy number at the chromosome 11q13.5 locus containing Rsf-1
) is detected in several types of human cancer including ovarian high-grade serous carcinoma. Rsf-1
) encodes for a cellular nuclear protein that binds to hSNF2H (18
), forming a chromatin remodeling protein complex called RSF (Remodeling and Spacing Factor) (19
). Rsf-1 (HBXAP) has been shown to function as a histone chaperone in the nuclei while its binding partner, hSNF2H, possesses nucleosome-dependent ATPase activity (21
). The Rsf-1/hSNF2H complex (RSF complex) mediates ATP-dependent chromatin remodeling, which alters the chromatin structure or positioning of nucleosomes (20
). At the cellular level, RSF participates in chromatin remodeling in response to a variety of growth signals and environmental cues. Such nucleosome remodeling is required for transcriptional activation or repression (22
), DNA replication (25
), and cell cycle progression (26
In this study, we used a well characterized anti-Rsf-1 antibody to study the expression pattern of Rsf-1 in CCC, and provided new evidence that expression of Rsf-1 was associated with advanced clinical stages and with the status of lymph node metastasis in CCC. The findings suggest a biological role for Rsf-1 in disease aggressiveness in this type of ovarian carcinoma. Interestingly, we have previously reported that chromosome 11q13.5 amplification and overexpression in cases of ovarian high-grade serous carcinoma contributes to shorter overall survival compared to cases without amplification. A possible mechanism was thought to be related to the de novo paclitaxel resistance rendered by Rsf-1 overexpression (27
). Although Kaplan-Meier survival analysis did not show statistically significant difference between Rsf-1 positive CCC cases and Rsf-1 negative CCC cases, long-term prognosis of Rsf-1 positive cases appears to be slightly worse than Rsf-1 negative cases. However, the number of Rsf-1 negative CCC cases in our series was relatively small, and we believe that analysis in larger series on CCCs is required to conclude if Rsf-1 overexpression predicts worse overall survival in CCCs. Furthermore, our study suggests a potential use of Rsf-1 immunoreactivity as a biomarker that may prove useful for predicting clinical outcomes in primary CCC, including higher clinical stages, and for predicting the risk of developing lymph node metastasis. To this end, several proteins including IGF2BP3 (IMP3) (11
) and annexin A4 (12
) have been reported as new markers associated with treatment outcomes in CCC. Thus, a panel of different markers including Rsf-1 could be tested in future clinical trials to determine their potential to be used in the management of CCC patients.
In the current report, we observed that, with a single exception, the immunostaining intensity score of Rsf-1 was less than 3+ in all cases analyzed. This finding provides an independent confirmation of our previous observation in another, smaller set of CCC samples in which we demonstrated that the majority of CCCs showed an immunostaining intensity score of 1+ or 2+ (14
). In fact, the percentage of Rsf-1 positive and negative cases is very similar between the current and previous reports. Moreover, analysis of SNP arrays performed on affinity-purified CCC specimens did not show an increase in DNA copy number at chromosome 11q13.5, indicating that Rsf-1
is rarely amplified in CCC (28
). The above findings in CCC are in sharp contrast to those in high-grade serous carcinoma (14
), and underscore the distinct molecular pathways in developing CCC and high-grade serous carcinoma (reviewed in (29
)). It is also noteworthy that endometrioid and mucinous carcinomas of the ovary express Rsf-1 much less frequently as compared to CCCs and high-grade serous carcinoma. Only 49% of endometrioid carcinomas and 48% of mucinous carcinomas were Rsf-1 positive, and the intensity scores of positive cases were mostly 1+ and 2+.
In conclusion, using immunohistochemistry with an Rsf-1 specific antibody we demonstrated that the presence of Rsf-1 immunoreactivity is significantly associated with advanced stage and lymph node metastasis in primary CCCs. Our findings suggest Rsf-1 expression may contribute to disease aggressiveness in CCC, and warrant further study of the biological role of Rsf-1 in progression of CCC.