P21-activated kinases in cell-cell and cell-matrix adhesion signaling ABSTRACT The development and functioning of multicellular organisms, tissue formation, and responses to injury and infection rely on tightly coordinated adhesion of cells to one another, and of cells to the extracellular matrix. These processes are mediated in large part through the action of two families of adhesion receptors: the integrins which are principally responsible for cell-matrix adhesion, and the cadherins which are central to cell-cell adhesion. Our preliminary data suggest that the type-II p21-activated kinases (PAKs), a group of serine- threonine kinases, use a range of mechanisms to influence cell-matrix adhesion and cell-cell adhesion. The ability to regulate both adhesion systems places the PAKs as central players in coordination of cell adhesion dynamics. This proposal aims to understand the functional, cellular and molecular basis for this regulation. To address how they control cell-matrix and cell-cell adhesions we propose a combination of structural, biochemical and cellular approaches. In Aim 1 we test the hypothesis that Direct binding of PAK to cytoplasmic tails of integrin adhesion receptors regulates matrix adhesion and/or PAK signaling. We will conduct an extensive study employing structural, biophysical, biochemical and cell biological approaches. This will allow us to comprehensively understand how integrin adhesion receptors bind PAK serine-threonine kinases, and the functional consequences of such interactions on cell signaling, adhesion, motility and invasion. In Aim 2 we test the hypothesis that PAK targeted to cell-cell contacts phosphorylates b-catenin, triggering adhesion turnover and escape of individual cells from epithelial islands. We will determine the mechanisms by which PAKs drive colony escape, and the structural basis for PAK regulation of β-catenin. Finally, we will test whether the roles of PAKs in cell-cell and cell-ECM adhesion are linked. Our proposed work will define how PAKs regulate both integrin- mediated cell-matrix adhesion, and β-catenin-associated cell-cell adhesion, and therefore will provide new understanding of interconnections between cell-matrix and cell-cell adhesion via the type-II PAKs.