Phosphatidylinositol 3-kinase is required for platelet-derived growth factor's actions on hepatic stellate cells.
OBJECTIVE
Platelet-derived growth factor (PDGF) is the most potent mitogen for hepatic stellate cells (HSCs) in vitro. The aim of this study was to investigate the role of phosphatidylinositol 3-kinase (PI 3-K) activation in mediating the biological effects of PDGF on cultured HSCs and its involvement in vivo.


METHODS
HSCs were isolated from normal human livers. PI 3-K was assayed on phosphotyrosine or PDGF-receptor immunoprecipitates by in vitro kinase assay.


RESULTS
Incubation of HSCs with PDGF caused a time-dependent increase in PI 3-K activity. Immunoprecipitation of PDGF-alpha and -beta receptors showed that both subunits associate with active PI 3-K in PDGF-stimulated HSCs. Wortmannin, a specific PI 3-K inhibitor, dose-dependently blocked PI 3-K activity induced by PDGF and inhibited DNA synthesis. PDGF (homodimer)-BB also stimulated HSC chemotaxis, which was inhibited by pretreatment with wortmannin. To explore the potential role of PI 3-K in vivo, liver homogenates from rats treated with CCl4 and from control rats were immunoprecipitated with anti-PDGF-beta-receptor antibodies. Liver injury was associated with increased PDGF-beta-receptor autophosphorylation, and greater PI 3-K activity associated with the receptor itself.


CONCLUSIONS
This study shows that in cultured HSCs, PI 3-K activation is necessary for both mitogenesis and chemotaxis induced by PDGF and that this pathway is up-regulated during liver injury in vivo.
Marra
F
F
Istituto di Medicina Interna, Universita di Firenze, Florence, Italy.
Gentilini
A
A
Pinzani
M
M
Choudhury
G G
GG
Parola
M
M
Herbst
H
H
Dianzani
M U
MU
Laffi
G
G
Abboud
H E
HE
Gentilini
P
P
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D002630:Chemotactic Factors / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D008107:Liver Diseases / Q000201:enzymology; D008297:Male; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D000077191:Wortmannin
D000730:Androstadienes; D002630:Chemotactic Factors; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D010982:Platelet-Derived Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D020794:Receptor Protein-Tyrosine Kinases; D000077191:Wortmannin