PROTEIN-KINASE-C-MU IS LOCATED AT THE GOLGI COMPARTMENT

Protein kinase C mu (PKC mu) 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 discr ete location often is a direct clue to the potential biological functi on of a kinase, antibodies directed against unique amino- and carboxy- terminal domains of PKC mu were used to localize the protein within in tracellular compartments in immunofluorescence and subcellular fractio nation studies. Confocal laser scanning microscopy showed colocalizati on of PKC mu with the resident Golgi marker protein beta 1,4 galactosy ltransferase in PKC mu transfectants and in the human hepatocellular c arcinoma cell line HepG2. expressing endogenous PKC mu. Long-term trea tment of cells with brefeldin A, which disintegrates the Golgi apparat us, disrupted PKC mu-specific staining. Cosegregation of PKC mu with b eta 1,4 galactosyltransferase, but not with the endosomal marker rab5, upon density gradient fractionation and Western blot analysis of HepG 2 cell extracts, provides independent evidence for a Golgi localizatio n of PKC mu. Moreover, cellular sulfate uptake and Golgi-specific glyc osaminoglycan sulfation was enhanced in PKC mu transfectants. Together , these data suggest that PKC mu is a resident protein kinase of the c ore Golgi compartment and is involved in basal transport processes.