Determining the role of the Ras family GTPase Rap1 in regulating mTORC2 activity and function in cell migration.

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 studies 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 have been identified as important players in cell migration. mTORC2 is known to have a role in regulating F-actin organization and actomyosin (MyoII). 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, we found that Rap1, a member of the Ras superfamily of small GTPases with conserved roles in cytoskeleton remodeling and cell adhesion, is a conserved binding partner of mTORC2 component RIP3/SIN1. We previously showed that Rap1 positively regulates mTORC2 activation in response to the chemoattractant cAMP in the model organism Dictyostelium discoideum. Moreover, we recently found that expression of a constitutively active Rap1 mutant (Rap1CA) potentiates the insulin-induced activation of mTORC2 in human HEK293 cells. We then undertook a study to investigate if Rap1 regulation of mTORC2 is part of a mechanism involved in regulating human cell migration. We observed that basal mTORC2 activity, as well as that induced by several potential promigratory signals, including insulin, epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), and lysophosphatidic acid (LPA), was increased by the overexpression of wild-type Rap1 or Rap1CA. Therefore, these observations suggest that Rap1 plays a role in positively regulating mTORC2 activation in HEK293 cells in response to stimulation of promigratory signals, similar to our previous observations made in Dictyostelium. Ongoing studies now aim at determining how Rap1 regulates the function of mTORC2 in cell migration.