Effect of phorbol ester and platelet-derived growth factor on protein kinase C in rat hepatic stellate cells.
OBJECTIVE
Hepatic stellate cells (HSC) play a key role in hepatic fibrogenesis and thus, it is important to understand the intracellular signalling pathways that influence their behaviour. This study investigated the expression and regulation of protein kinase C (PKC) in HSC.


RESULTS
Western blot analysis indicates that rat HSC express at least four PKC isoforms, PKC-alpha, PKC-delta, PKC-epsilon and PKC-zeta. PKC-alpha and PKC-zeta were located predominantly in the cytosol and were redistributed to the membrane by the PKC agonist, phorbol 12-myristate 13-acetate (PMA), while PKC-delta and PKC-epsilon were highly membrane-bound and did not undergo translocation by PMA. PKC-alpha, PKC-delta and PKC-zeta were rapidly downregulated by PMA. However, PKC-epsilon was resistant to downregulation. We also examined phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS), a specific substrate of PKC, as another approach to assess activation of PKC. Platelet-derived growth factor (PDGF) and PMA increased the phosphorylation of MARCKS, suggesting that PDGF can induce PKC activation. PDGF-induced stimulation of extracellular signal-regulated kinase, phosphatidylinositol 3-kinase and p70-S6 kinase was not abrogated by downregulation of PKC-alpha, PKC-delta and PKC-zeta. Prolonged PKC inhibition did not inhibit the fibrogenic phenotype.


CONCLUSIONS
Multiple PKC isoforms are expressed in rat HSC and are differentially regulated by PMA. PDGF activates certain mitogenic signalling pathways independent of PKC-alpha, PKC-delta and PKC-zeta. Specific PKC isoforms may modulate different cell functions in HSC.
Kobayashi
Yoshimasa
Y
Department of Internal Medicine, Division of Gastroenterology and Hepatology, Saint Louis University Liver Center, Saint Louis University School of Medicine, St Louis, MO, USA.
Bridle
Kim R
KR
Ramm
Grant A
GA
O'neill
Rosemary
R
Britton
Robert S
RS
Bacon
Bruce R
BR
D000199:Actins / Q000378:metabolism; D000818:Animals; D000077214:Becaplermin; D002227:Carbazoles / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D008297:Male; D008301:Maleimides / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051571:Protein Kinase C-alpha / Q000378:metabolism; D051745:Protein Kinase C-delta / Q000378:metabolism; D051744:Protein Kinase C-epsilon / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D021381:Protein Transport; D020574:Proto-Oncogene Proteins c-sis; D051381:Rats; D017207:Rats, Sprague-Dawley; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D000099221:Protein Kinase C zeta
D000199:Actins; D000077214:Becaplermin; D002227:Carbazoles; D024042:Collagen Type I; D048049:Extracellular Signal-Regulated MAP Kinases; D007211:Indoles; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D008301:Maleimides; D008565:Membrane Proteins; D018832:Molecular Chaperones; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D019869:Phosphatidylinositol 3-Kinases; D010982:Platelet-Derived Growth Factor; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta; D051744:Protein Kinase C-epsilon; D047428:Protein Kinase Inhibitors; D020574:Proto-Oncogene Proteins c-sis; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D013755:Tetradecanoylphorbol Acetate; C465664:2-(1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl)-3-(1H-indol-3-yl)maleimide; C000619712:Marcks protein, rat; C490392:Prkcz protein, rat; D000099221:Protein Kinase C zeta; C498862:Acta2 protein, rat; C497260:Prkcd protein, rat; C497257:Prkce protein, rat; C088060:bisindolylmaleimide