UCLA

The initial molecular events that lead to malignant transformation of the fimbria of the fallopian tube (FT) through high-grade serous ovarian carcinoma (HGSC) remain poorly understood. In this study, we report that increased expression of signal transducer and activator of transcription 3 (pSTAT3 Tyr705) and suppression or loss of protein inhibitor of activated STAT3 (PIAS3) in FT likely drive HGSC. We evaluated human tissues-benign normal FT, tubal-peritoneal junction (TPJ), p53 signature FT tissue, tubal intraepithelial lesion in transition (TILT), serous tubal intraepithelial carcinoma (STIC) without ovarian cancer, and HGSC for expression of STAT3/PIAS3 (compared with their known TP53 signature) and their target proliferation genes. We observed constitutive activation of STAT3 and low levels or loss of PIAS3 in the TPJ, p53 signature, TILT, and STIC through advanced stage IV (HGSC) tissues. Elevated expression of pSTAT3 Tyr705 and decreased levels of PIAS3 appeared as early as TPJ and the trend continued until very advanced stage HGSC (compared with high PIAS3 and low pSTAT3 expression in normal benign FT). Exogenous expression of STAT3 in FT cells mediated translocation of pSTAT3 and c-Myc into the nucleus. In vivo experiments demonstrated that overexpression of STAT3 in FT secretory epithelial cells promoted tumor progression and metastasis, mimicking the clinical disease observed in patients with HGSC. Thus, we conclude that the STAT3 pathway plays a role in the development and progression of HGSC from its earliest premalignant states.Significance: Concomitant gain of pSTAT3 Tyr705 and loss of PIAS3 appear critical for initiation and development of high-grade serous carcinoma. Cancer Res; 78(7); 1739-50. ©2018 AACR.