P160 RHOA-BINDING KINASE ROK-ALPHA INDUCES NEURITE RETRACTION

We previously reported that the activation of prostaglandin E receptor EP3 subtype caused neurite retraction via small GTPase Rho in the EP3 B receptor-expressing PC12 cells (Katoh, H., Negishi, M., and Ichikawa , A. (1996) J. Biol. Chem. 271, 29780-29784). However, a potential dow nstream effector of Rho that induces neurite retraction was not identi fied, Here we examined the morphological effect of p160 RhoA-binding k inase ROK alpha, a target for RhoA recently identified, on the nerve g rowth factor-differentiated PC12 cells. Microinjection of the catalyti c domain of ROK alpha rapidly induced neurite retraction similar to th at induced by microinjection of a constitutively active Rho, Rho(V14) whereas microinjection of the kinase-deficient catalytic domain of ROK alpha did not induce neurite retraction. This morphological change wa s observed even though C3 exoenzyme, which was known to inactivate Rho , had been preinjected. On the other hand, microinjection of the Rho-b inding domain or the pleckstrin homology domain of ROK alpha inhibited the EP3 receptor-induced neurite retraction, These results demonstrat e that ROK alpha induces neurite retraction acting downstream of Rho i n neuronal cells.