pp60c-src in human melanocytes and melanoma cells exhibits elevated specific activity and reduced tyrosine 530 phosphorylation compared to human fibroblast pp60c-src.
Elevated levels of pp60c-src tyrosine kinase activity have been implicated in both tumorigenesis and cell differentiation. We have found a 2- to 4-fold elevation in pp60c-src specific activity in certain human melanoma cell lines compared to human foreskin fibroblasts. This activation of pp60c-src did not appear to be related to melanoma tumor progression, because when normal human epidermal melanocytes were examined, it was found that they contained pp60c-src having a 7-fold elevation in specific activity compared to pp60c-src from human fibroblasts. It was determined that pp60c-src from melanocytes was not the neuronal form, pp60c-src+. Melanocyte pp60c-src exhibited a reduced level of phosphorylation on its carboxyl-terminal regulatory site, tyrosine 530, which might be responsible for its elevated specific activity. These results suggest that, in melanocytes, regulation of tyrosine 530 phosphorylation-dephosphorylation favors activation of pp60c-src. This activation may be involved in the growth, differentiation, or function of human melanocytes.
O'Connor
T J
TJ
Department of Medical Biochemistry, University of Calgary, Health Sciences Center, Alberta, Canada.
Neufeld
E
E
Bechberger
J
J
Fujita
D J
DJ
D002478:Cells, Cultured; D005134:Eye Neoplasms / Q000201:enzymology; D005347:Fibroblasts / Q000201:enzymology*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D008297:Male; D008544:Melanocytes / Q000201:enzymology*; D008545:Melanoma / Q000201:enzymology / Q000473:pathology*; D009363:Neoplasm Proteins / Q000378:metabolism*; D009474:Neurons / Q000201:enzymology; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D012175:Retinoblastoma / Q000201:enzymology; D014407:Tumor Cells, Cultured / Q000201:enzymology
D007527:Isoenzymes; D009363:Neoplasm Proteins; D016392:Proto-Oncogene Proteins pp60(c-src)