The Rho GTPase regulates protein kinase activity

Rho, a member of the Ras superfamily of small GTPases, has multiple biological roles: it regulates signal trasduction pathways linking extracellular growth factors to the assembly of actin stress fibres and focal adhesion complexes; it is required for G₁ progression and activates the SRF transcription factor when quiescent fibroblasts are stimulated to grow; and it plays a role later in the cell cycle during cytokinesis. Two groups have recently succeeded in identifying downstream effectors of Rho that may mediate some of these biological effects. One protein identified by both groups is protein kinase N (PKN), a serine/threonine kinase whose catalytic domain is closely related to that of protein kinase C^(1,2).