Protein Kinase N (PKN) and PKN-Related Protein Rhophilin as Targets of Small GTPase Rho

TLDR

The Rho GTPase cycles between GTP‑bound and GDP‑bound states to regulate cell adhesion and cytokinesis, yet the mechanisms of these actions remain unknown. This study aims to identify a serine‑threonine protein kinase as a Rho effector and to characterize a conserved motif for GTP‑Rho binding shared by Rho target proteins. Using a yeast two‑hybrid screen, the authors cloned Rhophilin, a protein that specifically binds GTP‑Rho. The results show that PKN, a serine‑threonine kinase, binds GTP‑Rho, is activated by this interaction in vitro and in vivo, and possesses a 40‑percent identical Rho‑binding domain to Rhophilin, indicating a shared binding motif among Rho effectors.

Abstract

The Rho guanosine 5′-triphosphatase (GTPase) cycles between the active guanosine triphosphate (GTP)-bound form and the inactive guanosine diphosphate-bound form and regulates cell adhesion and cytokinesis, but how it exerts these actions is unknown. The yeast two-hybrid system was used to clone a complementary DNA for a protein (designated Rhophilin) that specifically bound to GTP-Rho. The Rho-binding domain of this protein has 40 percent identity with a putative regulatory domain of a protein kinase, PKN. PKN itself bound to GTP-Rho and was activated by this binding both in vitro and in vivo. This study indicates that a serine-threonine protein kinase is a Rho effector and presents an amino acid sequence motif for binding to GTP-Rho that may be shared by a family of Rho target proteins.