RASSF1C oncogene elicits amoeboid invasion, cancer stemness and invasive EVs via a novel SRC/Rho axis

Cell plasticity is a crucial hallmark leading to cancer metastasis. Upregulation of Rho/ROCK pathway drives actomyosin contractility, protrusive forces and contributes to the occurrence of highly invasive amoeboid cells in tumors. Cancer stem cells are similarly associated with metastasis, but how these populations arise in tumors is not fully understood. Here we show that the novel oncogene RASSF1C drives mesenchymal to amoeboid transition and stem cell attributes in breast cancer cells. Mechanistically, RASSF1C activates Rho/ROCK via SRC mediated RhoGDI inhibition, resulting in generation of actomyosin contractility. Moreover, we demonstrate that amoeboid cells display the cancer stem cell markers CD133, ALDH1 and the pluripotent marker Nanog; are accompanied by higher invasive potential in vitro and in vivo; and employ extracellular vesicles to transfer the invasive phenotype to target cells and tissue. Importantly, the underlying RASSF1C driven biological processes concur to explain clinical data: namely, methylation of the RASSF1C promoter correlates with better survival in early stage breast cancer patients. Therefore, we propose the use of RASSF1 gene promoter methylation status as a biomarker for patient stratification.