“The {zeta} isotype of protein kinase C (PKC{zeta}) is a member of the atypical PKC subfamily and has been widely implicated in the regulation of cellular functions. Increasing evidence from studies using in vitro and in vivo systems points to PKC{zeta} as a key regulator of critical intracellular signaling pathways induced by various extracellular stimuli. The major activation pathway of PKC{zeta} depends on phosphatidylinositol (PI)-3,4,5-trisphosphate (PIP3), which is mainly produced by PI-3 kinase. 3'-PI-dependent protein kinase 1, which binds with high affinity to PIP3, phosphorylates and activates PKC{zeta}. Many studies demonstrated the involvement of PKC{zeta} in the mitogen-activated protein kinase cascade, transcriptional factor NF{kappa}B activation, ribosomal S6-protein kinase signaling, and cell polarity. An important molecular event in a cell is the association of PKC{zeta} with other signaling molecules, as well as scaffold proteins, to form large complexes that regulate their pathways. The understanding of the mechanisms underlying PKC{zeta}-mediated control of intracellular signaling is beginning to provide important insights into the roles of PKC{zeta} in various cells..” (Hirai and Chida, 2003). |