Abstract TMIM-075: MUTANT P53 PROMOTES THE INITIATION OF HIGH-GRADE SEROUS OVARIAN CARCINOMA FROM FALLOPIAN TUBE TUMOR PRECURSORS THROUGH ENHANCING TYROSINE RECEPTOR KINASE B SIGNALING
Authors: Kang Min , Chong Kay Y. , Hartwich Tobias MP. , Cady Sarah , Ncci Jonah , Yang-Hartwich Yang 
Published: June 2021

Abstract
Lesions in the fallopian tube (FT) fimbriae are hypothesized to be the precursors of high-grade serous ovarian carcinomas (HGSOC). Immunohistalchemical and sequencing analyses demonstrated that FT lesions shared the same TP53 mutation as the surrounding carcinomas. Analyses of mutations and chromosomal alterations in FT lesions, ovarian cancers, and metastases also revealed that the mutation of TP53 is an early event that might drive tumor initiation. Our study focuses on understanding the molecular mechanisms of mutant p53 promoting tumor initiation from the FT.
Our previous data showed that the FT epithelial cells expressed TrkB. The ligand of TrkB, brain-derived neurotrophic factor (BDNF), is secreted by the ovary, omental adipocytes, peritoneal visceral epithelial cells, and immune cells in the omentum and peritoneum. BDNF suppresses anoikis, the apoptosis induced by lack of proper cell to extra-cellular matrix (ECM) attachment. BDNF/TrkB signaling has been associated to tumor progression. We hypothesize that mutant p53 enhances tyrosine receptor kinase B (TrkB) signaling in FT tumor precursors, which promotes tumor precursors to spread towards the ovary and peritoneal sites.
We used two immortalized human FT cell lines, in which p53 was knocked down by shRNA. Mutant p53 or a control vector were introduced to these cell lines via a lentiviral expression system. The expression level of TrkB protein in FT cells expressing mutant p53 or a control vector was evaluated using Western blot and flow cytometry. CellTiter luminescent cell viability assays were performed to assess the effects of BDNF on the survival of FT cells with or without p53 mutation in 3D culture. Cellmate hydrogel was used as scaffold to support FT cells. And the cells migrated outside the hydrogel were quantified using CellTiter assay. Collagen I-coated beads were used in a 3D cell adhesion model to quantify the ability of FT cells to adhere to ECM and evaluate the effects of BDNF on the cell adhesion. The activation of TrkB downstream proteins was assessed using western blot.
Our data demonstrated that the protein level of TrkB was higher in FT cells expressing mutant p53 (R175H, R248W, and R273H) compared to the control FT cells. Mutant p53 significantly enhanced the survival of FT cells in the serum-free 3D culture condition in the presence of BDNF. BDNF increased the ability of FT cells to migrate outside the hydrogel, and mutant p53 further enhance their migration. Mutant p53 also accelerated the BDNF-mediated attachment of FT cells to collagen I-coated beads. Western blot results showed that the BDNF-activated phosphorylations of TrkB, AKT, ERK, PLC-gamma1 CREB were all increased in the FT cells expressing mutant p53 comparing to the control cells without mutant p53.
These results suggest the role of mutant p53 in promoting the initiation of HGSOC from FT tumor precursors. Through enhancing BDNF/TrkB signaling, mutant p53 can enhance the ability of FT tumor precursors to overcome anoikis and spread towards the ovary, peritoneum, and omentum. A better understanding of the underlying mechanisms will contribute to the development of new treatment and detection markers for HGSOC initiated from the FT.
Citation Format: Min Kang, Kay Y. Chong, Tobias MP. Hartwich, Sarah Cady, Jonah Ncci, Yang Yang-Hartwich. MUTANT P53 PROMOTES THE INITIATION OF HIGH-GRADE SEROUS OVARIAN CARCINOMA FROM FALLOPIAN TUBE TUMOR PRECURSORS THROUGH ENHANCING TYROSINE RECEPTOR KINASE B SIGNALING [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr TMIM-075.