Inhibition of integrin signaling with Arg-Gly-Asp motifs in rat hepatic stellate cells.
OBJECTIVE
Activation of hepatic stellate cells plays a key role in liver fibrogenesis. Disruption of normal hepatic stellate cell-matrix interactions may contribute to this process. However, little is known about the molecular events leading from integrin-extracellular matrix interaction to hepatic stellate cell function. Therefore, we investigated the role of integrin signaling in tyrosine phosphorylation of focal adhesion kinase and cytoskeletal assembly in rat hepatic stellate cells using soluble Arg-Gly-Asp containing peptides.


METHODS
Hepatic stellate cells were isolated from normal rat livers. Integrin alpha5beta1 expression in hepatic stellate cells was analyzed by immunoprecipitation and immunocytochemistry. The cytoskeletal assembly and tyrosine phosphorylation of focal adhesion kinase were determined by immunocytochemistry and immunoblotting. We also analyzed the effect of Arg-Gly-Asp containing peptides on the expression of smooth muscle alpha actin by immunocytochemistry and immunoblotting.


RESULTS
We identified integrin alpha5beta1 in rat hepatic stellate cells. Stress fiber formation and cell shape were different when hepatic stellate cells were plated on various extracellular matrix components. Treatment of hepatic stellate cells with soluble Arg-Gly-Asp peptides diminished the adhesion-induced tyrosine phosphorylation of focal adhesion kinase and inhibited the formation of stress fibers. The peptides also reduced the expression of smooth muscle alpha actin.


CONCLUSIONS
Our results demonstrate that adhesion to extracellular matrix induces tyrosine phosphorylation of focal adhesion kinase and promotes actin stress fiber formation and focal adhesion assembly in rat hepatic stellate cells, and that these events are disturbed by soluble Arg-Gly-Asp peptides.
Iwamoto
H
H
Third Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Sakai
H
H
Nawata
H
H
D000818:Animals; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002478:Cells, Cultured; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009842:Oligopeptides / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017469:Receptors, Fibronectin / Q000378:metabolism*; D015398:Signal Transduction; D017154:Stromal Cells / Q000378:metabolism
D015815:Cell Adhesion Molecules; D009842:Oligopeptides; D017469:Receptors, Fibronectin; C047981:arginyl-glycyl-aspartic acid; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496052:Ptk2 protein, rat