pp90RSK- and protein kinase C-dependent pathway regulates p42/44MAPK-induced LDL receptor transcription in HepG2 cells.
We have previously shown that different extracellular stimuli require signaling through the Raf/MEK/p42/44MAPK cascade to induce LDL receptor expression. The present studies were designed to delineate the molecular mechanisms underlying p42/44MAPK-induced LDL receptor transcription in HepG2-Delta Raf-1:ER cells, a modified HepG2 cell line in which the Raf-1/MEK/p42/44MAPK cascade can be specifically activated by anti-estradiol ICI182,780 in an agonist-specific manner. Using these cells, we show that: a) LDL receptor induction was reduced in reporter constructs containing mutation in either Sp1 or sterol-regulatory element-1 (SRE-1) sites, whereas inactivation of both sites abolished the induction; b) E1A, which inhibits CREB binding protein (CBP), a common activator of SRE-1 binding protein and Sp1, strongly repressed the induction; c) intracellular inhibition of the 90 kDa ribosomal S6 kinase (pp90RSK) cascade reduced LDL receptor induction; d) highly selective protein kinase C (PKC) inhibitors effectively abrogated the induction without affecting activation of pp90RSK; and e) overexpression of PKC beta significantly induced LDL receptor promoter activity. Taken together, these results demonstrate that pp90RSK and PKC beta are downstream effectors and Sp1, SRE-1 binding protein, and CBP are part of the transcriptional complex resulting in induction of LDL receptor expression in response to activation of the Raf/MEK/p42/44MAPK cascade. These findings identify for the first time a role for PKC beta in determining the specificity of p42/44MAPK signaling by participating with pp90RSK in regulating gene expression.
Kapoor
Gurpreet S
GS
Department of Molecular and Cellular Biochemistry, The Ohio State University College of Medicine and Public Health, 464 Hamilton Hall, 1645 Neil Ave., Columbus, OH 43210, USA. mehta.80@osu.edu
Golden
Carmen
C
Atkins
Brett
B
Mehta
Kamal D
KD
D050882:CREB-Binding Protein; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D064546:Protein Kinase C beta; D011973:Receptors, LDL / Q000235:genetics*; D020218:Response Elements / Q000235:genetics; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism*; D015398:Signal Transduction; D016329:Sp1 Transcription Factor / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D009687:Nuclear Proteins; D011973:Receptors, LDL; D016329:Sp1 Transcription Factor; D015534:Trans-Activators; D050882:CREB-Binding Protein; C494363:CREBBP protein, human; C069329:RPS6KA1 protein, human; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D011493:Protein Kinase C; D064546:Protein Kinase C beta; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases