Rapid phosphorylation of the L-myc protein induced by phorbol ester tumor promoters and serum.
We have examined post-translational modification of the L-myc protein using polyclonal and monoclonal antibodies against a peptide well conserved in the predicted amino acid sequences of the c-myc, N-myc and L-myc genes. These antibodies precipitate three polypeptides of Mr 60-66,000 from [35S]methionine or [32P]orthophosphate-labelled human small cell lung cancer cell lines expressing amplified L-myc genes, but not the other myc genes. Treatment of the L-myc immunoprecipitates with alkaline phosphatase prior to electrophoresis converts the three methionine-labelled polypeptides into a single band migrating at Mr 59,000, and efficiently removes radioactivity from the 32P-labelled L-myc protein, suggesting that, in contrast to the c-myc and N-myc proteins, the L-myc polypeptide heterogeneity is due to differential phosphorylation of a common precursor. When the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or serum is added to cultures of U-1690 cells the Mr 66,000 polypeptide is rapidly enriched while the Mr 60,000 form is decreased in the L-myc immunoprecipitates. This effect is correlated with the ability of phorbol ester and diacylglycerol analogues to activate protein kinase C. The TPA-induced phosphorylation of the L-myc protein occurs in a protein synthesis-independent manner as it is not inhibited by cycloheximide or anisomycin. These data indicate that the phosphorylation of the L-myc nuclear oncoprotein is modulated in response to TPA via a rapid signal transduction system involving protein kinase C. This mechanism could play an important role in the response of lung cells to e.g. bombesin-related growth factors.
Saksela
K
K
Department of Virology and Pathology, University of Helsinki, Finland.
Mäkelä
T P
TP
Evan
G
G
Alitalo
K
K
D000911:Antibodies, Monoclonal / Q000276:immunology; D001790:Blood Physiological Phenomena; D018288:Carcinoma, Small Cell / Q000473:pathology; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology; D009363:Neoplasm Proteins / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate