Inhibition of a signaling pathway in cardiac muscle cells by active mitogen-activated protein kinase kinase.
Signaling via the Ras pathway involves sequential activation of Ras, Raf-1, mitogen-activated protein kinase kinase (MKK), and the extracellular signal-regulated (ERK) group of mitogen-activated protein (MAP) kinases. Expression from the c-Fos, atrial natriuretic factor (ANF), and myosin light chain-2 (MLC-2) promoters during phenylephrine-induced cardiac muscle cell hypertrophy requires activation of this pathway. Furthermore, constitutively active Ras or Raf-1 can mimic the action of phenylephrine in inducing expression from these promoters. In this study, we tested whether constitutively active MKK, the molecule immediately downstream of Raf, was sufficient to induce expression. Expression of constitutively active MKK induce ERK2 kinase activity and caused expression from the c-Fos promoter, but did not significantly activate expression of reporter genes under the control of either the ANF or MLC-2 promoters. Expression of CL100, a phosphatase that inactivates ERKs, prevented expression from all of the promoters. Taken together, these data suggest that ERK activation is required for expression from the Fos, ANF, and MLC-2 promoters but MKK and ERK activation is sufficient for expression only from the Fos promoter. Constitutively active MKK synergized with phenylephrine to increase expression from a c-Fos- or an AP1-driven reporter. However, active MKK inhibited phenylephrine- and Raf-1-induced expression from the ANF and MLC-2 promoters. A DNA sequence in the MLC-2 promoter that is a target for inhibition by active MKK, but not CL100, was mapped to a previously characterized DNA element (HF1) that is responsible for cardiac specificity. Thus, activation of cardiac gene expression during phenylephrine-induced hypertrophy requires ERK activation but constitutive activation by MKK can inhibit expression by targeting a DNA element that controls the cardiac specificity of gene expression.
Thorburn
J
J
Program in Human Molecular Biology and Genetics, Eccles Institute of Human Genetics, University of Utah, Salt Lake City 84112, USA.
Carlson
M
M
Mansour
S J
SJ
Chien
K R
KR
Ahn
N G
NG
Thorburn
A
A
D000818:Animals; D000831:Animals, Newborn; D009320:Atrial Natriuretic Factor / Q000235:genetics; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000096:biosynthesis / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation; D004958:Estradiol / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles; D008156:Luciferases / Q000032:analysis / Q000096:biosynthesis; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011494:Protein Kinases / Q000096:biosynthesis / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis; D019908:Proto-Oncogene Proteins c-raf; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014162:Transfection; D018631:ras Proteins / Q000502:physiology*
D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D011994:Recombinant Proteins; D018808:Transcription Factor AP-1; D010656:Phenylephrine; D004958:Estradiol; D009320:Atrial Natriuretic Factor; D008156:Luciferases; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins