Hyaluronan‐CD44 interaction stimulates Rac1 signaling and PKNγ kinase activation leading to cytoskeleton function and cell migration in astrocytes

Abstract Both hyaluronan [HA, the major glycosaminoglycans in the extracellular matrix (ECM)] and CD44 (a primary HA receptor) are associated with astrocyte activation and tissue repair following central nervous system (CNS) injury. In this study we investigated the question of whether HA‐CD44 interaction influences astrocyte signaling and migration. Our data indicated that HA binding to the cultured astrocytes stimulated Rac1 signaling and cytoskeleton‐mediated migration. To determine the cellular and molecular basis of these events, we focused on PKNγ, a Rac1‐activated serine/threonine kinase in astrocytes. We determined that HA binding to astrocytes stimulated Rac1‐dependent PKNγ kinase activity which, in turn, up‐regulated the phosphorylation of the cytoskeletal protein, cortactin, and attenuated the ability of cortactin to cross‐link F‐actin. Further analyses indicated that the N‐terminal antiparallel coiled‐coil (ACC) domains of PKNγ interacted with Rac1, and transfection of astrocytes with PKNγ‐ACCcDNA inhibited PKNγ activity. Over‐expression of the PKNγ‐ACC domain also functions as a dominant‐negative mutant to block HA/CD44‐mediated PKNγ activation of cortactin and astrocyte migration. Taken together, these findings strongly suggest that hyaluronan/CD44 interaction with Rac1‐PKNγ plays a pivotal role in cytoskeleton activation and astrocyte migration. These newly discovered HA/CD44‐induced astrocyte function may provide important insight into novel therapeutic treatments for tissue repair following CNS injury.