CK1δ kinase activity is modulated by protein kinase C α (PKCα)-mediated site-specific phosphorylation

Cellular signal transduction components are usually regulated not only on transcriptional or translational level, but also by posttranslational modifications. Among these, reversible phosphorylation represents the most abundant modification. In general, phosphorylation events are essential for regulating the activity of central signal transduction proteins, also including kinases itself. Members of the CK1 family can be found as central signal transduction proteins in numerous cellular pathways. Due to its wide variety of cellular functions the activity of CK1 family members has to be tightly regulated. We previously reported that PKA and Chk1 are able to phosphorylate CK1δ within its C-terminal regulatory domain, consequently resulting in altered CK1 kinase activity. In the present study, we show by several methods that protein kinase C α (PKCα) as well is able to phosphorylate CK1δ at its C-terminally located residues S328, T329, and S370. Furthermore, we analyze the functional consequences of PKCα-mediated phosphorylation on CK1δ kinase activity. Mutation of S328, T329, or S370 to alanine dramatically alters the kinetic parameters of CK1δ. By using the PKCα-specific inhibitor Go-6983 in a selected cell culture model, we finally show that the in vitro detected regulatory connection between PKCα and CK1δ is also relevant in the cellular context. Taken together, these data contribute to a deeper understanding of cellular signal transduction networks thereby helping to form a basis for the development of future therapeutic concepts.