AJP - Gastrointestinal and Liver Physiology, Vol 271, Issue 2 293-G303, Copyright © 1996 by American Physiological Society

ARTICLES

Hepatocellular protein kinase C activation by bile acids: implications for regulation of cholesterol 7 alpha-hydroxylase

R. T. Stravitz, Y. P. Rao, Z. R. Vlahcevic, E. C. Gurley, W. D. Jarvis and P. B. Hylemon
Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond 23219, USA.

We have recently shown that taurocholate (TCA) represses the transcriptional activity of cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme of the bile acid biosynthetic pathway, through a protein kinase C (PKC)-dependent mechanism in primary cultures of rat hepatocytes. The present studies sought to determine the mechanisms by which bile acids activate hepatic PKC activity and the consequences of this activation on isoform distribution and cholesterol 7 alpha-hydroxylase mRNA levels. TCA (12.5-100 microM for 15 min) increased membrane-associated "classic" isoenzyme cPKC-alpha and "novel" isoenzymes nPKC-delta, and nPKC by two- to sixfold. Membrane-associated PKC progressively increased, and cytosolic PKC decreased, for 1 h after the addition of TCA (50 microM); after 24 h whole cell cPKC-alpha, nPKC-delta, and nPKC were downregulated by 35-55% compared with untreated controls. In a reconstituted assay system, TCA or taurodeoxycholate (10-100 microM) increased calcium-dependent and -independent PKC activity by three- and fourfold, respectively. Taurine-conjugated bile acids stimulated PKC activity in proportion to their hydrophobicity index (r = 0.99). Finally, cholesterol 7 alpha-hydroxylase mRNA was repressed > 75% by phorbol 12-myristate 13-acetate (100 nM for 3 h), a nonselective activator of PKC isoforms. In contrast, selective cPKC-alpha activation with thymeleatoxin (100 nM for 3 h) had no significant effect on cholesterol 7 alpha-hydroxylase mRNA levels. We conclude that bile acids activate hepatocellular PKC, resulting in sequential redistribution and down-regulation of calcium-dependent and -independent isoforms. The calcium-independent PKC isoforms may mediate the repression of cholesterol 7 alpha-hydroxylase mRNA by TCA.

This article has been cited by other articles:

				J. Kanchanapoo, M. Ao, R. Prasad, C. Moore, C. Kay, P. Piyachaturawat, and M. C. Rao Role of protein kinase C-{delta} in the age-dependent secretagogue action of bile acids in mammalian colon Am J Physiol Cell Physiol, December 1, 2007; 293(6): C1851 - C1861. [Abstract] [Full Text] [PDF]

				M. Le, L. Krilov, J. Meng, K. Chapin-Kennedy, S. Ceryak, and B. Bouscarel Bile acids stimulate PKC{alpha} autophosphorylation and activation: role in the attenuation of prostaglandin E1-induced cAMP production in human dermal fibroblasts Am J Physiol Gastrointest Liver Physiol, August 1, 2006; 291(2): G275 - G287. [Abstract] [Full Text] [PDF]

				P. Qin, X. Tang, M. M. Elloso, and D. C. Harnish Bile acids induce adhesion molecule expression in endothelial cells through activation of reactive oxygen species, NF-{kappa}B, and p38 Am J Physiol Heart Circ Physiol, August 1, 2006; 291(2): H741 - H747. [Abstract] [Full Text] [PDF]

				P. Qin, L. A. Borges-Marcucci, M. J. Evans, and D. C. Harnish Bile acid signaling through FXR induces intracellular adhesion molecule-1 expression in mouse liver and human hepatocytes Am J Physiol Gastrointest Liver Physiol, August 1, 2005; 289(2): G267 - G273. [Abstract] [Full Text] [PDF]

				J. Y. L. Chiang Bile Acid Regulation of Hepatic Physiology: III. Bile acids and nuclear receptors Am J Physiol Gastrointest Liver Physiol, March 1, 2003; 284(3): G349 - G356. [Abstract] [Full Text] [PDF]

				L. Qiao, E. Studer, K. Leach, R. McKinstry, S. Gupta, R. Decker, R. Kukreja, K. Valerie, P. Nagarkatti, W. E. Deiry, et al. Deoxycholic Acid (DCA) Causes Ligand-independent Activation of Epidermal Growth Factor Receptor (EGFR) and FAS Receptor in Primary Hepatocytes: Inhibition of EGFR/Mitogen-activated Protein Kinase-Signaling Module Enhances DCA-induced Apoptosis Mol. Biol. Cell, September 1, 2001; 12(9): 2629 - 2645. [Abstract] [Full Text] [PDF]

				G. J. Schroepfer Jr. Oxysterols: Modulators of Cholesterol Metabolism and Other Processes Physiol Rev, January 1, 2000; 80(1): 361 - 554. [Abstract] [Full Text] [PDF]

				S. Khare, M. Bissonnette, B. Scaglione-Sewell, R. K. Wali, M. D. Sitrin, and T. A. Brasitus 1,25-Dihydroxyvitamin D3 and TPA activate phospholipase D in Caco-2 cells: role of PKC-alpha Am J Physiol Gastrointest Liver Physiol, April 1, 1999; 276(4): G993 - G1004. [Abstract] [Full Text] [PDF]

				M. Crestani, A. Sadeghpour, D. Stroup, G. Galli, and J. Y. L. Chiang Transcriptional activation of the cholesterol 7{alpha}-hydroxylase gene (CYP7A) by nuclear hormone receptors J. Lipid Res., November 1, 1998; 39(11): 2192 - 2200. [Full Text]

				S. Gupta, R. T. Stravitz, P. Dent, and P. B. Hylemon Down-regulation of Cholesterol 7alpha -Hydroxylase (CYP7A1) Gene Expression by Bile Acids in Primary Rat Hepatocytes Is Mediated by the c-Jun N-terminal Kinase Pathway J. Biol. Chem., May 4, 2001; 276(19): 15816 - 15822. [Abstract] [Full Text] [PDF]

				E. De Fabiani, N. Mitro, A. C. Anzulovich, A. Pinelli, G. Galli, and M. Crestani The Negative Effects of Bile Acids and Tumor Necrosis Factor-alpha on the Transcription of Cholesterol 7alpha -Hydroxylase Gene (CYP7A1) Converge to Hepatic Nuclear Factor-4. A NOVEL MECHANISM OF FEEDBACK REGULATION OF BILE ACID SYNTHESIS MEDIATED BY NUCLEAR RECEPTORS J. Biol. Chem., August 10, 2001; 276(33): 30708 - 30716. [Abstract] [Full Text] [PDF]