Protein Kinase D Regulates Rho Gtpase Activity Through Rhotekin

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC The Protein Kinase D (PKD) family of serine / threonine kinases comprises PKD1,PKD2, and PKD3 and is grouped under the calcium / calmodulin - dependent protein kinase (CAMK) superfamily. PKDs play an important role in various biological processes including proliferation, adhesion, migration, cell shape, survival and apoptosis. Identification of the putative target substrates for this kinase family would provide a deeper insight into their role in the physiological and pathological processes. In the present study, we identified rhotekin (RTKN), an effector protein of small GTPase Rho, as a potential substrate of PKDs. Using the consensus PKD substrate sequence motif scan approach, we identified Ser435 in the C-terminal region of rhotekin as the potential phosphorylatable residue. We generated a phospho-specific antibody corresponding to Ser435 and could validate that Ser435 is indeed the critical amino acid targeted by PKD2 in vivo in HEK-293T cells. The phospho-mimecking mutant of rhotekin (Ser435Glu) when transfected into HEK-293T cells resulted in the increase of endogenous active RhoA GTPase levels, as determined from the Rho activation assay. Rho GTPases were shown to be an important upstream molecules regulating PKD activity in the process of cancer cell migration. However, our results demonstrate for the first time the role of PKDs in the regulation of RhoGTP activity levels. Considering the role of RhoGTPases in various cellular processes, our results provide a hint to the potential regulation of various cellular processes by PKDs through phosphorylation of rhotekin and thereby regulating the activity of RhoGTPases. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 296.