TGFβ-induced changes in membrane curvature influence Ras oncoprotein membrane localization

In the course of cancer progression tumor cells undergo morphological changes that lead to increased motility and invasiveness thus promoting formation of metastases. This process called epithelial to mesenchymal transition (EMT) is triggered by transforming growth factor (TGF beta) but for gaining the full invasive potential an interplay between signaling of TGF beta and Ras GTPases is required. Ras proteins possess a lipidated domain that mediates Ras association with the plasma membrane, which is essential for Ras biological functions. Type and number of the lipid anchors are the main difference among three Ras variants-H-ras, N-ras and K-ras. The lipid anchors determine membrane partitioning of lipidated proteins into membrane areas of specific physico-chemical properties and curvature. In this study, we investigated the effect of TGF beta treatment on the subcellular localization of H-ras and K-ras. We show that TGF beta increases positive plasma membrane curvature, which is subsequently sensed by H-ras, leading to its elevated plasma membrane localization and activation. This observation suggests the existence of a novel positive feedback loop whereby the increased level of plasma membrane curvature during TGF beta induced EMT attracts more Ras molecules to the plasma membrane resulting in increased Ras activity which in turn promotes further EMT and thus ultimately enables the acquisition of full invasive potential.