Heregulin regulates cytoskeletal reorganization and increased cell migration through the p21-activated kinase (PAK)

We investigated the nature of HRG-generated signals that may potentially be involved in the regulation of cell migration by influencing the formation of motile cortical actin cytoskeleton structures. We demonstrate that HRG stimulation of non invasive breast cancer cells enhances the expression of Filamentous actin (F-actin) resulting in the formation of stress-fibers, the lateral filopodia-like structures, the tbrma.tion of membrane ruffles at the leading edge of breast cancer cells, and also increasos the ce!l migration. In HRG-stimulated cells, PAK1 is rapidly activated, and becomes redistributed into the membrane ruffles and the leading edges of motile cells. Co-IP and confocal imaging studies demonstrated that the treatment promoted physical interactions between activated PAK1. polymerized actin and HER2 receptors, and that these protein complexes are zolocalized at lhe leading edges in the activated cells. The observed tlRGqnduced stimulation of DAK 1 kinase activity was closely linked with the kinetic of PI3 kinase activation, as its inhibition prevented the activation of PAK1 kinaso, the reorgarfization of cytoskeleton structures, and cell migration in respons heregulin. Direct inhibition of PAKt flmction also blocked the ability of IIRG to induce the formation of stress-fibers, filopodia/lamellipodia and membr;me rutiting. Altogether, these findings suggest a significant role in PAK1 depends reorganization of the cortinal actin cytoskeleton in heregulinn, increased cell migration.