Critical role of p42/44(MAPK) activation in anisomycin and hepatocyte growth factor-induced LDL receptor expression: activation of Raf-1/Mek-1/p42/44(MAPK) cascade alone is sufficient to induce LDL receptor expression.
The protein synthesis inhibitor anisomycin activates stress-related mitogen-activated protein kinases (MAPKs), namely, c-jun NH(2)-terminal kinase (p46/54(JNK)) and p38(MAPK) in mammalian cells. In this paper, we show that although exposure to anisomycin resulted in rapid and strong activation of p46/54(JNK) and p38(MAPK), with a delayed low level dual-phosphorylation of mitogen/extracellular protein kinase (p42/44(MAPK)), low density lipoprotein (LDL) receptor induction depends solely on the mild activation of p42/44(MAPK) signaling cascade in HepG2 cells. Unlike hepatocyte growth factor (HGF) which caused LDL receptor induction via rapid, strong, and Ras-dependent p42/44(MAPK) activation, anisomycin-induced p42/44(MAPK) activity and increased LDL receptor expression in a Ras-independent manner. Finally, we examined the role of the p42/44(MAPK) signaling cascade in LDL receptor induction by activating this kinase independently of anisomycin or HGF. By using estrogen-dependent human Raf-1 protein kinase in transient transfection assays, we show that the exclusive activation of the Raf-1/MEK-1/p42/44(MAPK) signaling cascade with antiestrogen ICI 182, 780 caused induction of LDL receptor expression to the same level as observed with either HGF or anisomycin. Consistent with the role of p42/44(MAPK), induction was strongly inhibited by pretreatment with the MEK-1/2 inhibitor PD98059. Our observation that anisomycin can use p42/44(MAPK) signaling cascade is a departure from established thinking, and the results presented shows that activation of the p42/44(MAPK) alone is sufficient to fully induce LDL receptor transcription.
Dhawan
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Department of Biochemistry and Molecular Biology, College of Medicine, University of Arkansas for Medical Sciences, 4301 West Markham, Little Rock, AR 72205, USA.
Bell
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Kumar
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Golden
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Mehta
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D000841:Anisomycin / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular; D003513:Cycloheximide / Q000494:pharmacology; D004789:Enzyme Activation; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D017228:Hepatocyte Growth Factor / Q000494:pharmacology*; D006801:Humans; D008113:Liver Neoplasms; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D011691:Puromycin / Q000494:pharmacology; D011973:Receptors, LDL / Q000235:genetics*; D014407:Tumor Cells, Cultured
D011973:Receptors, LDL; D011691:Puromycin; D017228:Hepatocyte Growth Factor; D000841:Anisomycin; D003513:Cycloheximide; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases; C482576:MAP3K1 protein, human