ET-1 and PDGF BB induce MEK mRNA and protein expression in mesangial cells.
To evaluate a possible mechanism for the chronic regulation of MAPK/ERK kinase-1 (MEK-1) and p42 mitogen-activated protein kinase (MAPK) we studied the long-term effects of the G-protein-coupled receptor agonist endothelin-1 (ET-1) and the protein tyrosine kinase-coupled receptor agonist platelet-derived growth factor BB (PDGF BB) on MEK-1 and p42 MAPK in glomerular mesangial cells (GMCs). ET-1 and PDGF BB led to a time-dependent increase in MEK-1 mRNA expression without altering p42 MAPK mRNA levels. The effect of ET-1 and PDGF BB on MEK-1 mRNA expression was maximal after 24 h (3.3-fold) or 6 h (2.9-fold). Furthermore, the effect of ET-1 and PDGF BB on MEK-1 mRNA expression was additive (4.2-fold after 6 h) and was inhibited by actinomycin D (5 micrograms/ml). Cycloheximide (10 micrograms/ml) inhibited MEK-1 mRNA induction but stimulated p42 MAPK mRNA expression in both the absence and the presence of ET-1 and/or PDGF BB. The ET-1 and PDGF BB-induced increase in MEK-1 mRNA was accompanied by sustained enhancement of both p45 MEK protein expression after 12 h and by elevation of p42 MAPK activity for up to 24 h. We conclude that, in GMCs, MEK-1 acts like a delayed-early gene, whereas p42 MAPK resembles an immediate-early gene. MEK-1 mRNA and protein levels, as well as p42 MAPK activity, can be chronically regulated by both a seven-transmembrane domain receptor-coupled peptide such as ET-1 and by an agonist binding to a receptor with intrinsic protein tyrosine kinase activity, such as PDGF BB.
Schramek
H
H
Department of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
Sorokin
A
A
Watson
R D
RD
Dunn
M J
MJ
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D003513:Cycloheximide / Q000494:pharmacology; D016232:Endothelins / Q000494:pharmacology*; D005920:Glomerular Mesangium / Q000187:drug effects* / Q000201:enzymology; D048369:MAP Kinase Kinase 1; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D011505:Protein-Tyrosine Kinases / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley
D016232:Endothelins; D010982:Platelet-Derived Growth Factor; D012333:RNA, Messenger; D003513:Cycloheximide; 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