Calphostin-C stimulates epidermal growth factor receptor phosphorylation and internalization via light-dependent mechanism.
Calphostin-C with perylenequinone structure is known to bind the regulatory domain of protein kinase C (PKC) and to inhibit kinase activity in vitro in a light-dependent fashion. We have found that calphostin-C induces substantial serine and threonine phosphorylation of the epidermal growth factor (EGF) receptor in a light-dependent fashion in the EGF receptor-hyperproducing squamous carcinoma cell line NA. Tryptic phospho-peptide mapping and phospho-amino acid analysis revealed that calphostin-C-enhanced phosphorylation was on threonine 669, serine 671, serine 1046/1047, and serine 1166. However, calphostin-C did not inhibit phosphorylation of the 80 K protein, a cytosolic major substrate of PKC (MARCKS). Staurosporine, a potent PKC inhibitor with affinity for the catalytic domain of PKC, inhibited phosphorylation of the 80 K protein and 12-O-tetradecanoyl-13-phorbol acetate induction of EGF receptor phosphorylation but did not inhibit the calphostin-C induction of the EGF receptor phosphorylation. These results suggest that the target of calphostin-C in vivo is different from that of staurosporine and thus calphostin-C in vivo does not inhibit PKC. Furthermore, calphostin-C enhanced the internalization of phosphorylated EGF receptor. Thus, calphostin-C apparently activates a novel signal transduction pathway which involves phosphorylation and internalization of the EGF receptor via light-dependent mechanism.
Gamou
S
S
Department of Molecular Biology, Keio University School of Medicine, Tokyo, Japan.
Shimizu
N
N
D000470:Alkaloids / Q000494:pharmacology; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008027:Light; D008565:Membrane Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D009281:Naphthalenes; D010449:Peptide Mapping; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D011083:Polycyclic Compounds / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011506:Proteins / Q000378:metabolism; D019311:Staurosporine; D014357:Trypsin; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
D000470:Alkaloids; D047908:Intracellular Signaling Peptides and Proteins; C000619710:MARCKS protein, human; D008565:Membrane Proteins; D009281:Naphthalenes; D011083:Polycyclic Compounds; D011506:Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D014443:Tyrosine; D066246:ErbB Receptors; D011493:Protein Kinase C; D014357:Trypsin; D019311:Staurosporine; C058819:calphostin C