Spratley, Samantha J.

PAKs (p21-activated kinases) are effectors of RhoGTPases. PAK4 contributes to regulation of cofilin at the leading edge of migrating cells through activation of LIMK (Lin-11/Isl-1/Mec-3 kinase). PAK4 activity is regulated by an autoinhibitory domain that is released upon RhoGTPase binding as well as phosphorylation at Ser474 in the activation loop of the kinase domain. In the present study, we add another level of complexity to PAK4 regulation by showing that phosphorylation at Ser99 is required for its targeting to the leading edge. This phosphorylation is mediated by PKD1 (protein kinase D1). Phosphorylation of PAK4 at Ser99 also mediates binding to 14-3-3 protein, and is required for the formation of a PAK4–LIMK–PKD1 complex that regulates cofilin activity and directed cell migration.

Abstract During early metastatic events in cancer, reorganization of the actin cytoskeleton must occur to allow for cell invasion and migration. A key enzyme initiating actin remodeling at the leading edge is Cofilin, a small actin binding protein of the ADF/cofilin family with actin severing activities. Cofilin activity is tightly regulated by phosphorylation and dephosphorylation events that are mediated by LIM Kinase (LIMK) and the phosphatase Slingshot (SSH), respectively. Protein kinase D (PKD) is a serine/threonine kinase that has previously been shown to regulate actin driven directed cell migration through phosphorylation and thus inactivation of Slingshot. Here we show that PKD can also regulate cofilin activity via activation of LIMK. We further show that PKD-induced regulation of LIMK and the resulting diminished cofilin activity translates to altered cell motility. Our data suggest that PKD inactivates Cofilin through modulation of both of its regulatory pathways. Further elucidation of the mechanisms by which PKD regulates directed cell migration could enable development of a potential treatment strategy for invasive cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2364. doi:10.1158/1538-7445.AM2011-2364