Transcript Variants Have Distinct Roles in Ovarian Carcinoma and Differently Influence Platinum Sensitivity and Angiogenesis.

The prognosis of late-stage epithelial ovarian cancer (EOC) patients is affected by chemotherapy response and the malignant potential of the tumor cells. In earlier work, we identified hypermethylation of the gene () as a prognostic biomarker and contrary functions of transcript variants (TV1 and TV2) in A2780 and SKOV3 cells. The aim of the study was to further validate these results and to increase the knowledge about function in EOC. New overexpression models of high-grade serous ovarian cancer (HGSOC) were established and analyzed for phenotypic (IC determination, migration, proliferation and angiogenesis assay, DNA damage analysis) and transcriptomic consequences (NGS) of TV1 and TV2 overexpression. Platinum sensitivity was affected by a specific transcript variant depending on BRCA background. TV2 induced an increased sensitivity in BRCA1 cells (OVCAR3), whereas TV1 increased the sensitivity and induced a G2/M arrest under treatment in cells (A13-2-12). These different phenotypes relate to differences in DNA repair: homologous recombination deficient A13-2-12 cells show less γH2AX foci despite higher levels of Pt-DNA adducts. RNA-Seq analyses prove transcript variant and cell-line-specific effects. Pathway analyses revealed another clinically important function of RUNX3-regulation of angiogenesis. This was confirmed by thrombospondin1 analyses, HUVEC spheroid sprouting assays and proteomic profiling. Importantly, conditioned media (CM) from TV1 overexpressing A13-2-12 cells induced an increased HUVEC sprouting. Altogether, the presented data support the hypothesis of different functions of transcript variants related to the clinically relevant processes-platinum resistance and angiogenesis.