Signaling Pathway Dissection After Progesterone Receptor Enhancement in an Immortalized Pre-Cancer Fallopian Tube Epithelial Cell Line

Ovarian cancer remains the most lethal gynecologic malignancy, with the majority of patients presenting at advanced stages and exhibiting poor long-term survival. High-grade serous carcinoma (HGSC), the predominant subtype, likely originates from fallopian tube epithelial cells (FTECs), whose biology is strongly influenced by hormonal signaling. Progesterone receptor (PR) expression, particularly of the PR-B isoform, is associated with improved prognosis in HGSC; however, the isoform-specific molecular mechanisms in precancerous FTECs remain unclear. This study investigated the distinct biological and transcriptomic effects of PR-A and PR-B in p53- and Rb-defective FE25 FTEC-derived cells. Stable overexpression of PR-A suppressed cell proliferation, enhanced apoptosis, and induced robust senescence, whereas PR-B promoted proliferation and activated JNK/c-Jun signaling. Upon progesterone (P4) treatment, both isoforms mediated cell-cycle arrest and apoptosis, with PR-A exhibiting stronger Sub-G1 induction. PR-A and PR-B differentially regulated cell-cycle inhibitors, senescence markers, and downstream pathways, including the PI3K-Akt and MAPK pathways, while RNA sequencing analyses revealed broader P4-induced transcriptomic changes in PR-B than in PR-A, involving immune, angiogenic, and proliferative programs. Collectively, these findings demonstrate that PR-A and PR-B exert distinct yet complementary regulatory roles in FTEC biology and progesterone responsiveness. The observed PR isoform-dependent effects in FE25 cells should be interpreted as context-specific mechanistic insights rather than direct predictors of clinical prognosis or treatment response.