Protein kinase C μ is located at the Golgi compartment

Abstract

Protein kinase C μ (PKCμ) displays unusual structural features like a pleckstrin homology domain and an amino-terminal hydrophobic region with a putative leader peptide and transmembrane sequence. As a discrete location often is a direct clue to the potential biological function of a kinase, antibodies directed against unique amino- and carboxy-terminal domains of PKCμ were used to localize the protein within intracellular compartments in immunofluorescence and subcellular fractionation studies. Confocal laser scanning microscopy showed colocalization of PKCμ with the resident Golgi marker protein β1,4 galactosyltransferase in PKCμ transfectants and in the human hepatocellular carcinoma cell line HepG2, expressing endogenous PKCμ. Long-term treatment of cells with brefeldin A, which disintegrates the Golgi apparatus, disrupted PKCμ-specific staining. Cosegregation of PKCμ with β1,4 galactosyltransferase, but not with the endosomal marker rab5, upon density gradient fractionation and Western blot analysis of HepG2 cell extracts, provides independent evidence for a Golgi localization of PKCμ. Moreover, cellular sulfate uptake and Golgi-specific glycosaminoglycan sulfation was enhanced in PKCμ transfectants. Together, these data suggest that PKCμ is a resident protein kinase of the core Golgi compartment and is involved in basal transport processes.