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Tyrosine phosphorylation of focal adhesion kinase by PDGF is dependent on Ras in human hepatic stellate cells
Author(s) -
Carloni Vinicio,
Pinzani Massimo,
Giusti Sabrina,
Romanelli Roberto G.,
Parola Maurizio,
Bellomo Giorgio,
Failli Paola,
Hamilton Andrew D.,
Sebti Said M.,
Laffi Giacomo,
Gentilini Paolo
Publication year - 2000
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.510310121
Subject(s) - platelet derived growth factor receptor , tyrosine phosphorylation , microbiology and biotechnology , focal adhesion , farnesyltransferase , ptk2 , receptor tyrosine kinase , cancer research , phosphorylation , tyrosine kinase , hepatic stellate cell , signal transduction , biology , proto oncogene tyrosine protein kinase src , platelet derived growth factor , growth factor , protein kinase a , biochemistry , receptor , prenylation , endocrinology , mitogen activated protein kinase kinase , enzyme
Focal adhesion kinase (FAK) is a widely expressed nonreceptor tyrosine kinase found in focal adhesions. FAK has been indicated as a point of convergence of other signaling pathways including platelet‐derived growth factor (PDGF) receptors, and recently, FAK tyrosine phosphorylation has been shown to be stimulated by PDGF. In the present study we assessed the role of Ras as a possible intermediate protein regulating PDGF‐induced FAK tyrosine phosphorylation in human hepatic stellate cells (HSCs), liver‐specific pericytes primarily involved in the pathogenesis of liver fibrosis. For this purpose, cells were first subjected to retroviral‐mediated gene transfer with a dominant‐negative mutant of Ras (N17Ras). This resulted in a marked inhibition of PDGF‐induced FAK tyrosine phosphorylation together with the expected reduction of PDGF‐induced extracellular signal‐regulated kinase activity (ERK). Afterward, the effects of pharmacological agents potentially affecting Ras isoprenylation were evaluated. PDGF‐induced FAK tyrosine phosphorylation, ERK activity and intracellular calcium increase, as well as the biological effects of this growth factor, ( i.e. , mitogenesis and cell migration) were effectively blocked by GGTI‐298, an inhibitor of geranylgeranyltransferase I. Inhibition of Ras processing obtained with FTI‐277, an inhibitor of farnesyltransferase, resulted in detectable effects only at high doses. Taken together, these results establish that Ras operates as a protein‐linking PDGF‐β receptor to FAK in human HSCs, and that signaling molecules requiring geranylgeranylation may also be involved in this process.