title: Sustained ERK-2 activation in rat glomerular mesangial cells: differential regulation by protein phosphatases.
abstract: The duration of extracellular signal-regulated protein kinase (ERK) activation is critical for cell signaling decisions and probably determines whether a stimulus elicits proliferation or differentiation. We studied the intracellular signals regulating sustained ERK-2 activity in glomerular mesangial cells (GMC), utilizing combination of GMC mitogens of different potency. Incubation of GMC with both endothelin-1 (ET-1) and platelet-derived growth factor BB (PDGF-BB) led to a long-lasting, monophasic increase in ERK-2 activity. In contrast, when ET-1 was administered together with epidermal growth factor (EGF), a less pronounced and shorter activation occurred. Long-term stimulation of ERK-2 was accompanied by an increase in p45 MEK activity, which again was more pronounced when ET-1 was administered together with PDGF-BB compared with EGF. In the presence of actinomycin D (Act D), an inhibitor of RNA synthesis, ERK-2 activity induced by ET-1 and PDGF-BB but not by ET-1 and EGF remained elevated more than sixfold throughout the whole incubation period of 6 h. The effect of Act D on ET-1- and PDGF-BB-induced ERK-2 activation was mimicked by the protein phosphatase inhibitor sodium orthovanadate. In addition, vanadate also unmarked an ET-1- and EGF-induced ERK-2 activity after 6 h. The serine/threonine phosphatase inhibitor okadaic acid (OA) did neither alter agonist-induced ERK-2 activity after 6 h (0.5 nM OA) nor after 10 min or 1 h (250 nM). Together these results suggest that, in GMC, long-term activation of the mitogen-activated protein kinase ERK-2 is differentially regulated, depending on the combination of agonists administered. ET-1- and PDGF-BB-induced long-term activation of ERK-2 is regulated by a vanadate-sensitive protein phosphatase(s) and by a transcriptionally regulated protein(s). In contrast, ET-1- and EGF-induced sustained ERK-2 stimulation is regulated by a vanadate-sensitive protein phosphatase(s) but not by a transcriptionally regulated protein. Agonist-specific and time-dependent stimulation of ERK-2-regulating protein phosphatases may be critical for the length of ERK-2 activation in GMC and could thus be of pathophysiological significance in glomerular diseases associated with alterations in cell proliferation or cell differentiation.
authors.affiliation: Department of Physiology, University of Innsbruck, Austria.
authors.forename: H
authors.initials: H
authors.lastname: Schramek
authors.forename: M
authors.initials: M
authors.lastname: Schumacher
authors.forename: W
authors.initials: W
authors.lastname: Pfaller
mesh_terms: D000818:Animals; D000077214:Becaplermin; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D003609:Dactinomycin / Q000494:pharmacology; D004338:Drug Combinations; D019332:Endothelin-1 / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005920:Glomerular Mesangium / Q000166:cytology / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000502:physiology*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D020574:Proto-Oncogene Proteins c-sis; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins; D013997:Time Factors; D014638:Vanadates / Q000494:pharmacology
chemical_list: D004338:Drug Combinations; D019332:Endothelin-1; D004791:Enzyme Inhibitors; D010982:Platelet-Derived Growth Factor; D011500:Protein Synthesis Inhibitors; D020574:Proto-Oncogene Proteins c-sis; D011994:Recombinant Proteins; D000077214:Becaplermin; D003609:Dactinomycin; D019319:Okadaic Acid; D014638:Vanadates; D004815:Epidermal Growth Factor; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D010749:Phosphoprotein Phosphatases