Growth hormone stimulates the tyrosine phosphorylation of 42- and 45-kDa ERK-related proteins.
Growth hormone (GH) influences a number of tissue-specific biological activities in diverse cell types. However, little is known about the biochemical pathway by which the signal initiated by GH binding to its cell-surface receptor is transduced. The GH receptor has been reported to be phosphorylated on tyrosine in 3T3-F442A cells, a cell line in which GH promotes differentiation and inhibits mitogen-stimulated growth; however, it is not known whether tyrosine phosphorylation plays a role in GH signal transduction. We report that GH treatment of 3T3-F442A cells resulted in the rapid tyrosine phosphorylation of at least four proteins. These included 42- (pp42) and 45-kDa (pp45) proteins immunologically related to ERK1 (extracellular signal-regulated kinase 1), a member of a family of serine/threonine protein kinases that are phosphorylated on tyrosine in response to mitogens. Prolonged phorbol ester pretreatment attenuated the tyrosine phosphorylation of pp42 and pp45 in platelet-derived growth factor-treated cells, but not in GH-treated cells. Maximal GH-stimulated tyrosine phosphorylation of pp42 and pp45 coincided with peak levels of a 42-kDa renaturable MBP kinase activity in lysates of GH-treated cells resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The observation that multiple cellular proteins are rapidly phosphorylated on tyrosine in response to physiological concentrations of GH suggests that tyrosine phosphorylation plays a role in GH signal transduction. Moreover, the stimulation of tyrosine phosphorylation of ERK-related proteins by GH suggests that mitogens and nonmitogens may employ common phosphotyrosyl proteins in the activation of ultimately distinct cellular programs.
Winston
L A
LA
Department of Physiological Chemistry, University of Wisconsin, Madison 53706.
Bertics
P J
PJ
D016475:3T3 Cells; D000818:Animals; D001345:Autoradiography; D015153:Blotting, Western; D013006:Growth Hormone / Q000378:metabolism*; D051379:Mice; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism*
D010982:Platelet-Derived Growth Factor; D014443:Tyrosine; D013006:Growth Hormone; D011494:Protein Kinases; D011493:Protein Kinase C; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases