E2F1 mediates competition, proliferation and drug sensitivity of co-cultured resistant and sensitive ovarian cancer cells.
Background: Tumor heterogeneity is one of the key factors leading to chemo-resistance relapse. It remains unknown how resistant cancer cells influence sensitive cells during cohabitation and growth within a heterogenous tumors. The goal of our study was to identify driving factors that mediate the interactions between resistant and sensitive cancer cells and to determine the effects of cohabitation on both phenotypes. Methods: We used isogenic ovarian cancer cell (OC) lines pairs, sensitive and resistant to platinum: OVCAR5 vs. OVCAR5 CisR and PEO1 vs. PEO4, respectively, to perform long term direct culture and to study the phenotypical changes of the interaction of these cells. Results: Long term direct co-culture of sensitive and resistant OC cells promoted proliferation (p < 0.001) of sensitive cells and increased the proportion of cells in the G1 and S cell cycle phase in both PEO1 and OVCAR5 cells. Direct co-culture led to a decrease in the IC50 to platinum in the cisplatin-sensitive cells (5.92 µM to 2.79 µM for PEO1, and from 2.05 µM to 1.51 µM for OVCAR5). RNAseq analysis of co-cultured cells showed enrichment of Cell Cycle Control, Cyclins and Cell Cycle Regulation pathways. The transcription factor E2F1 was predicted as the main effector responsible for the transcriptomic changes in sensitive cells. Western blot and qRT-PCR confirmed upregulation of E2F1 in co-cultured vs monoculture. Furthermore, an E2F1 inhibitor reverted the increase in proliferation rate induced by co-culture to baseline levels. Conclusions: Our data suggest that long term cohabitation of platinum-sensitive and -resistant cancer cells drive sensitive cells to a higher proliferative state, more responsive to platinum. Our results reveal an unexpected effect caused by direct interactions between cancer cells with different proliferative rates and levels of platinum resistance, modelling competition between cells in heterogeneous tumors. Overall design: To study the interaction between platinum resistant (PEO4) and platinum sensitive (PEO1) ovarian cancer cells, we perform RNAseq analysis of co-cultures. We co-culture PEO1 cells with PEO4 cells in a proportion of 1:7 respectively for 14 days. Cells then were separated using FACS sorting, and RNA was extracted for RNAseq analysis. We compared PEO1 co-cultured vs PEO1 on monoculture (n=2). Later we compared PEO1 cultured on regular media vs PEO1 cultured with conditioned media of PEO4 (n=2) to study the influence of the conditioned media on the sensitive cells.