The Role of RAP1 in Regulating MTORC2 Activity and Function in Cell Migration

Abstract

Directed cell migration is an important biological process that is necessary for the embryonic development, maintenance of multicellular organisms and immune response to external stimuli. Dysregulation of cell migration is implicated in the onset and progression of diseases including cardiovascular diseases and cancer metastasis. Many have identified genes and proteins that are important for directed cell migration, but the process remains incompletely understood. The mechanistic Target of Rapamycin Complex 2 (mTORC2) is a complex of proteins that has been identified as an important player in cell migration. Moreover, there is increasing evidence that shows a correlation between mTORC2 and cancer cell migration and invasion. Despite this knowledge, the role and regulation of mTORC2 is not fully understood. Recently, the Charest lab found that Rap1, a small GTPase with conserved roles in cytoskeleton remodeling and cell adhesion, is a conserved binding partner of mTORC2 component RIP3/SIN1. They also showed that Rap1 positively regulates mTORC2 activation in response to the chemoattractant cAMP in Dictyostelium discoideum. Moreover, it was recently found that expression of a constitutively active Rap1 mutant (Rap1-CA) potentiates the insulin-induced activation of mTORC2 in human HEK293T cells. I investigated if Rap1 regulation of mTORC2 is part of a mechanism involved in regulating human cell migration. I observed that basal mTORC2 activity, as well as that induced by several potential promigratory signals, including insulin, EGF, IGF-1, and LPA, was increased by the overexpression of wild-type Rap1 or Rap1CA. I also observed Rap1 colocalizing with different mTORC2 components in growth conditions and when stimulated by the same promigratory signals. Therefore, these observations suggest that Rap1 plays a role in positively regulating mTORC2 activation and controlling mTORC2 localization, in response to stimulation of promigratory signals, similar to previous observations made in Dictyostelium.