Abstract B60: Pro-HGF and its activator confer a sustained transformation activity in ovulatory follicular fluid

Abstract

Abstract The etiology of ovarian high-grade serous ovarian cancers (HGSC) originating from the epithelium of fallopian tube fimbriae is elusive. Based on the incessant ovulation hypothesis, our previous studies found that ROS released during ovulation, collaborated with hemoglobin from retrograde menstruation, caused oxidative damage and DNA breaks to the fimbrial epithelial cells. Repeated exposures of ovulatory follicular fluid could induce tumorigenesis of in Trp53-null mice and transform human fimbrial epithelial cells (FE25) immortalized by E6/E7. In addition to mutagenic ROS, we later identified IGF-axis proteins abundantly present in follicular fluid (FF) are largely responsible for the stemness activation and transformation of FE25 cells. However, FF-IGF signal does not confer other key phenotypes induced by FF, such as mitogenesis and cell migration. In this study, we further clarified the role of HGF, another growth factor abundantly present in FF. Treating FE25 cells with pure HGF and IGF2 could fully recapitulate the anchorage-independent growth (AIG) activity of FF with equal colony number of 55±12 and 60±6, respectively. Inhibitor of HGF cMET receptor, AMG337, greatly reduced the AIG activity to 8±5 colonies. HGF is known to be activated by a cascade of activation by cleavage of its precursor pro-HGF and the precursor (pro-HGFA) of its activating protein HGFA. We found FF contains a high level of these pro-form proteins and a low amount of the cleaved active forms. Interestingly, these pro-form HGF axis proteins are extremely stable in FF. After one-month incubation at 37 degrees Celsius, they could still be activated and exerted AIG of FE25 cells. Once encountering the cell surface, protease cleavage is initiated to activated pro-HGFA to HGFA, which then cleaves pro-HGF to HGF. Via the c-MET/AKT/ERK signaling, the activated HGF confers the mitogenic and transformation activity of FF. In FF, HGF seems to cooperate with IGF2 to sustain a long-term proliferation of fimbrial epithelial cells initiated by ROS-induced mutagenesis and clonally expanded by IGF axis signaling. A reservoir of durable pro-forms of HGFA and HGF are responsible for this sustained transformation activity. Thus, the mutagenic, clonogenic, and sustained mitogenic activities in FF strongly support the incessant ovulation theory with ovulatory carcinogens to be the culprit. Citation Format: Hsuan Shun Huang, Tang-Yuan Chu. Pro-HGF and its activator confer a sustained transformation activity in ovulatory follicular fluid [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr B60.