Differential regulation of mitogen-activated protein/ERK kinase (MEK)1 and MEK2 and activation by a Ras-independent mechanism.
Mitogen-activated protein (MAP)/ERK kinase (MEK)1 and MEK2 are the upstream activators of the MAP kinases, ERK1 and ERK2. MEK1 and MEK2 are approximately 85% identical in sequence but have unique inserts in their C-terminal domains. MEK isoform-specific antibodies were used to examine expression and regulation of each enzyme. MEK1 and MEK2 were expressed in approximately equal amounts in several cell lines; in some, MEK1 was present in slight excess. Activation of tyrosine kinase-containing receptors, heterotrimeric G proteins, and protein kinase C enhanced the activities of both MEK isoforms in 293 and PC12 cells. AIF4-stimulated both MEK1 and MEK2 in PC12 cells expressing a dominant interfering Ras mutant that prevents nerve growth factor-dependent activation of the cascade. Carbachol also stimulated the pathway in these cells. Thus, in addition to their ability to activate Ras/Raf and the downstream ERK pathway, heterotrimeric G proteins also appear to trigger a Ras-independent mechanism to regulate this kinase cascade. In U373, Chinese hamster ovary (CHO), and INS-1 cells, MEK1 was activated by regulators of ERKs, while MEK2 was not. These data suggest that, like the MAP kinases ERK1 and ERK2, in some cell settings the two similar MEK isoforms are differentially regulated.
Xu
S
S
University of Texas Southwestern Medical Center, Department of Pharmacology, Dallas 75235-9041, USA.
Khoo
S
S
Dang
A
A
Witt
S
S
Do
V
V
Zhen
E
E
Schaefer
E M
EM
Cobb
M H
MH
D016475:3T3 Cells / Q000187:drug effects / Q000378:metabolism; D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism; D016466:CHO Cells; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D004622:Embryo, Mammalian; D004789:Enzyme Activation; D004790:Enzyme Induction; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007340:Insulinoma / Q000378:metabolism / Q000473:pathology; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases; D016716:PC12 Cells / Q000201:enzymology; D010190:Pancreatic Neoplasms / Q000378:metabolism / Q000473:pathology; D010673:Pheochromocytoma / Q000473:pathology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects* / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D017607:Aluminum Compounds; D000911:Antibodies, Monoclonal; D007328:Insulin; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; D005576:Colforsin; C050992:tetrafluoroaluminate; D002217:Carbachol; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D019204:GTP-Binding Proteins; D005947:Glucose; D005459:Fluorides