SOX17 expression in ovarian clear cell carcinoma

Recent studies have revealed that the Sry-related HMG box gene 17 (SOX17) plays an important role in ovarian carcinogenesis. Unlike other types of ovarian cancer, ovarian clear cell carcinoma (OCCC) has a distinct pathobiological phenotype, often harboring an AT-rich interaction domain 1 A (ARID1A) mutation. In the present study, to determine the SOX17 in OCCC cells, we immunohistochemically examined SOX17 expression in 47 whole-tissue specimens of OCCC. Although not statistically significant, SOX17-high immunoreactivity tended to be related to unfavorable patient outcomes. We also aimed to determine the relationship of SOX17 with ARID1A. Double immunofluorescence staining demonstrated that SOX17 immunoreactivity was not associated with ARID1A immunoreactivity. Immunoblotting revealed that SOX17 was abundantly expressed in cultured OVISE and RMG-V OCCC cells, but not in OVTOKO OCCC cells. Polyubiquitinated bands of SOX17 were observed in MG132 treated OVTOKO, but not in OVISE or RMG-V OCCC cells. Notably, si-RNA-mediated knockdown of a deubiquitinase enzyme, ubiquitin C-terminal hydrolase L1, increased polyubiquitination followed by proteasome degradation of SOX17 in OVISE. These findings indicate that SOX17 is not uniformly and heterogeneously expressed in OCCCs, independent of ARID1A deficiency. Impaired ubiquitin-mediated proteasome degradation may stabilize SOX17 in some OCCC cells.