CD98 modulates integrin beta1 function in polarized epithelial cells

The type II transmembrane protein CD98, best known as the heavy chain of the heterodimeric amino acid transporters (HAT), is required for the surface expression and basolateral localization of this transporter complex in polarized epithelial cells. CD98 also interacts with beta1 integrins resulting in an increase in their affinity for ligand. In this study we explored the role of the transmembrane and cytoplasmic domains of CD98 on integrin-dependent cell adhesion and migration in polarized renal epithelial cells. We demonstrate that the transmembrane domain of CD98 was sufficient, whereas the five N-terminal amino acids of this domain were required for CD98 interactions with beta1 integrins. Overexpression of either full-length CD98 or CD98 lacking its cytoplasmic tail increased cell adhesion and migration, whereas deletion of the five N-terminal amino acids of the transmembrane domain of CD98 abrogated this effect. CD98 and mutants that interacted with beta1 integrins increased both focal adhesion formation and FAK and AKT phosphorylation. CD98-induced cell adhesion and migration was inhibited by addition of phosphoinositol 3-OH kinase (PI3-K) inhibitors suggesting these cell functions are PI3-K-dependent. Finally, CD98 and mutants that interacted with beta1, induced marked changes in polarized renal epithelial cell branching morphogenesis in collagen gels. Thus, in polarized renal epithelial cells, CD98 might be viewed as a scaffolding protein that interacts with basolaterally expressed amino acid transporters and beta1 integrins and can alter diverse cellular functions such as amino acid transport as well as cell adhesion, migration and branching morphogenesis.