Prognostic Significance of S100A4 in Ovarian Clear Cell Carcinoma: Its Relation to Tumor Progression and Chemoresistance.

Background/objectives: S100A4, a small calcium-binding protein, promotes metastasis in a variety of human malignancies, but little is known about its involvement in ovarian clear cell carcinoma (OCCC). Herein, we characterized the functional role of S100A4 in this tumor type.

Methods: We analyzed immunohistochemical sections from 120 OCCC patients. OCCC cell lines in which S100A4 was knocked out (KO) or overexpressed were also used to study the protein's effects.

Results: Stable overexpression of S100A4 decreased the proliferation of OCCC cell lines (concomitant with more cells in G1 and fewer in the G2/M phase of the cell cycle). S100A4 overexpression also reduced susceptibility to cisplatin-induced apoptosis (probably due to an increased BCL2: BAX ratio), accelerated epithelial-mesenchymal transition (EMT)-related cell mobility, and enhanced cancer stem cell (CSC) properties (including increases in both spheroid formation and in the aldehyde dehydrogenase 1 (ALDH1) population). In contrast, S100A4 KO generally induced the opposite phenotypes, although it did not affect migration capability. In clinical OCCC samples, high S100A4 expression was associated with a low frequency of cleaved poly-(ADP-ribose) polymerase 1-positive apoptotic cells, a reduced proliferative rate, and expression of high ALDH1 and vimentin levels. In addition, a high S100A4 score was a significant (but not independent) prognostic factor in OCCC.

Conclusions: Our findings suggest that S100A4 may be an unfavorable prognostic factor in OCCC, as it accelerates tumor progression and promotes chemoresistance through the modulation of proliferation, susceptibility to apoptosis, and EMT/CSC properties.