Csk enhances insulin-stimulated dephosphorylation of focal adhesion proteins.
Insulin has pleiotropic effects on the regulation of cell physiology through binding to its receptor. The wide variety of tyrosine phosphorylation motifs of insulin receptor substrate 1 (IRS-1), a substrate for the activated insulin receptor tyrosine kinase, may account for the multiple functions of insulin. Recent studies have shown that activation of the insulin receptor leads to the regulation of focal adhesion proteins, such as a dephosphorylation of focal adhesion kinase (pp125FAK). We show here that C-terminal Src kinase (Csk), which phosphorylates C-terminal tyrosine residues of Src family protein tyrosine kinases and suppresses their kinase activities, is involved in this insulin-stimulated dephosphorylation of focal adhesion proteins. We demonstrated that the overexpression of Csk enhanced and prolonged the insulin-induced dephosphorylation of pp125FAK. Another focal adhesion protein, paxillin, was also dephosphorylated upon insulin stimulation, and a kinase-negative mutant of Csk was able to inhibit the insulin-induced dephosphorylation of pp125FAK and paxillin. Although we have shown that the Csk Src homology 2 domain can bind to several tyrosine-phosphorylated proteins, including pp125FAK and paxillin, a majority of protein which bound to Csk was IRS-1 when cells were stimulated by insulin. Our data also indicated that tyrosine phosphorylation levels of IRS-1 appear to be paralleled by the dephosphorylation of the focal adhesion proteins. We therefore propose that the kinase activity of Csk, through the insulin-induced complex formation of Csk with IRS-1, is involved in insulin's regulation of the phosphorylation levels of the focal adhesion proteins, possibly through inactivation of the kinase activity of c-Src family kinases.
Tobe
K
K
Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Sabe
H
H
Yamamoto
T
T
Yamauchi
T
T
Asai
S
S
Kaburagi
Y
Y
Tamemoto
H
H
Ueki
K
K
Kimura
H
H
Akanuma
Y
Y
Yazaki
Y
Y
Hanafusa
H
H
Kadowaki
T
T
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D000081247:CSK Tyrosine-Protein Kinase; D002417:Cattle; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D051419:Paxillin; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D011972:Receptor, Insulin / Q000187:drug effects / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D019061:src-Family Kinases / Q000378:metabolism
D015815:Cell Adhesion Molecules; D003598:Cytoskeletal Proteins; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D046911:Macromolecular Substances; D051419:Paxillin; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D000081247:CSK Tyrosine-Protein Kinase; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D019061:src-Family Kinases; D010749:Phosphoprotein Phosphatases