title: Selective modulation of MAP kinase in embryonic palate cells.
abstract: Murine embryonic palate mesenchyme (MEPM) cells are responsive to a number of endogenous factors found in the local embryonic tissue environment. Recently, it was shown that activation of the cyclic AMP (cAMP) or the transforming growth factor beta (TGFbeta) signal transduction pathways modulates the proliferative response of MEPM cells to epidermal growth factor (EGF). Since the mitogen-activated protein kinase (MAPK) cascade is a signal transduction pathway that mediates cellular responsiveness to EGF, we examined the possibility that several signaling pathways which abrogate EGF-stimulated proliferation do so via the p42/p44 MAPK signaling pathway. We demonstrate that EGF stimulates MAPK phosphorylation and activity in MEPM cells maximally at 5 minutes. Tyrosine phosphorylation and activation of MAPK was unaffected by treatment of MEPM cells with TGFbeta or cholera toxin. Similarly, TGFbeta altered neither EGF-induced MAPK tyrosine phosphorylation nor activity. However, the calcium ionophore, A23187, significantly increased MAPK phosphorylation which was further increased in the presence of EGF, although calcium mobilization reduced EGF-induced proliferation. Despite the increase in phosphorylation, we could not demonstrate induction of MAPK activity by A23187. Like EGF, phorbol ester, under conditions which activate PKC isozymes in MEPM cells, increased MAPK phosphorylation and activity but was also growth inhibitory to MEPM cells. The MEK inhibitor, PD098059, only partially abrogated EGF-induced phosphorylation. Likewise, depletion of PKC isozymes partially abrogated EGF-induced MAPK phosphorylation. Inhibition of both MEK and PKC isozymes resulted in a marked decrease in MAPK activity, confirming that EGF uses multiple pathways to stimulate MAPK activity. These data indicate that the MAPK cascade does not mediate signal transduction of several agents that inhibit growth in MEPM cells, and that there is a dissociation of the proliferative response and MAP kinase activation. Furthermore, other signaling pathways known to play significant roles in differentiation of palatal tissue converge with the MAPK cascade and may use this pathway in the regulation of alternative cellular processes.
authors.affiliation: Department of Pathology, Anatomy & Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Potchinsky
authors.forename: M R
authors.initials: MR
authors.lastname: Lloyd
authors.forename: W M
authors.initials: WM
authors.lastname: Weston
authors.forename: R M
authors.initials: RM
authors.lastname: Greene
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002273:Carcinogens / Q000494:pharmacology; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D016228:Endothelial Growth Factors / Q000494:pharmacology / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005333:Fetus / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D005419:Flavonoids / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D051379:Mice; D008813:Mice, Inbred ICR; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases; D010159:Palate / Q000166:cytology* / Q000201:enzymology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013449:Sulfonamides; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000494:pharmacology
chemical_list: D002273:Carcinogens; D016228:Endothelial Growth Factors; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007476:Ionophores; D007546:Isoquinolines; D013449:Sulfonamides; D016212:Transforming Growth Factor beta; D000001:Calcimycin; D002772:Cholera Toxin; D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D013755:Tetradecanoylphorbol Acetate; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one