Protein Kinase A Activity In The Leading Edge Of Migrating Cells Is Dependent On The Activity Of Focal Adhesion Kinase

Abstract

Protein Kinase A (PKA) is a pleiotropic serine/threonine kinase whose localized and dynamic activity is required for cellular migration. Several cell types have shown robust PKA activity in the leading edge during migration. This activity is regulated by changes in actomyosin contractility, but the mechanism of the mechanochemical regulation of PKA remains unclear. Our ongoing investigation into this mechanism led us to discover a novel relationship between PKA and the non-receptor tyrosine kinase Focal Adhesion Kinase (FAK). Here, we find that while inhibition of actomyosin contractility leads to a relatively slow decrease in total cellular levels of phosphorylated FAK over tens of minutes, it decreases the focal adhesion-associated pool of both phospho-FAK and phospho-paxillin within two minutes, similar to the timing of the effect of inhibition of contractility on leading edge PKA activity. We then show that pharmacologic inhibition of FAK rapidly decreases leading edge PKA activity. Additionally, leading edge PKA activity is significantly reduced in FAK-null mouse embryonic fibroblasts and essentially eliminated by also silencing expression of the closely-related kinase Pyk2 in these cells. Importantly, leading edge PKA activity in FAK-null cells is rescued by re-expression of wild-type but not kinase-dead FAK. Taken together, these observations show that FAK activity is required for localized regulation of PKA during cell migration and, in so doing, establish a novel and unexpected connection between an adhesion-regulated tyrosine kinase and a serine/threonine kinase canonically downstream of G-protein coupled receptor and second-messenger signaling.