Proteomic and phosphoproteomic reprogramming in epithelial ovarian cancer metastasis

Epithelial ovarian cancer (EOC) is a high-risk cancer presenting with heterogeneous tumors. The high incidence of EOC metastasis from primary tumors to nearby tissues and organs is a major driver of EOC lethality. We used cellular models of spheroid formation and re-adherence to investigate cellular signaling dynamics in each step toward EOC metastasis. In our system, adherent cells model primary tumors, spheroids formation represents the initiation of metastatic spread, while re-adherent spheroid cells represent secondary tumors. Proteomic and phosphoproteomic analyses show that spheroid cells are hypoxic and show markers for cell cycle arrest. Aurora kinase B (AURKB) abundance and downstream substrate phosphorylation are significantly reduced in spheroids and re-adherent cells, explaining their cell cycle arrest phenotype. The proteome of re-adherent cells is most similar to spheroids, yet greater changes in the phosphoproteome show that spheroid cells stimulate Rho-associated kinase 1 (ROCK1) mediated signaling, which controls cytoskeletal organization. In spheroids, we found significant phosphorylation of ROCK1 substrates that were reduced in both adherent and re-adherent cells. Application of the ROCK1-specific inhibitor Y-27632 to spheroids increased the rate of re-adherence and spheroid density. The data suggest ROCK1 inhibition increases EOC metastatic potential. We identified novel pathways controlled by AURKB and ROCK1 as major drivers of metastatic behavior in EOC cells. Our data show that phosphoproteomic reprogramming precedes proteomic changes that characterize spheroid re-adherence in EOC metastasis.