Role of CD98hc in integrin signaling

Integrin adhesion receptors regulate cellular behaviors like cell migration, proliferation, differentiation and cell survival. Most of these phenomena utilize signaling pathways initiated by activation of pp125Focal Adhesion Kinase (FAK) and src family kinases (SFK) that control the activity of Rho GTPases and downstream kinases such as AKT1,2 . CD98 heterodimers, comprised of a common heavy chain (CD98hc, SLC3A2), and one of several light chains3 , interact with integrins via the CD98hc moiety 4 . CD98hc is required for efficient adhesion-induced activation of AKT and Rac GTPase, major contributors to the integrin-dependent signals involved in cell survival 5 and cell migration 6 . Via its light chains CD98 promotes amino acid transport3 ; however, a CD98hc mutant that interacts with integrins but not CD98 light chains is sufficient for integrin-dependent signaling7 . By use of chimeric proteins, the sponsor`s lab has shown that in fibroblasts, integrin binding domain of CD98hc is required for regulation of the integrin signaling. Furthermore, chimeras that completely lack amino acid transport activity, yet retain integrin interactions can promote cell proliferation and growth in vivo 8 . I hypothesize that also in endothelial cells CD98hc interaction with integrins promotes integrin signaling, which is induced by integrin ligation with matrix proteins ("outside-in signaling"), thereby regulating angiogenesis. I aim to characterize the biochemical and functional role of CD98hc in integrin-dependent signaling events by using CD98hc-deficient cells. Since in the absence of CD98hc cell adhesion triggered SFK mediated FAK phosphorylation is lost, leading to an impaired PI3-kinase and Rac activation, I want to analyze the mechanism(s) how CD98hc/integrin interaction initiates signaling. Isolating endothelial cells from conditional CD98hc knock out mice and reconstitution of either intact or mutated forms of CD98hc will further give me the opportunity to study the role of CD98hc in angiogenic endothelial cell functions such as cell proliferation, migration, invasion and capillary-like tube formation.