Inhibition of cell growth and spreading by stomach cancer-associated protein-tyrosine phosphatase-1 (SAP-1) through dephosphorylation of p130cas.
SAP-1 (stomach cancer-associated protein-tyrosine phosphatase-1) is a transmembrane-type protein-tyrosine phosphatase that is abundant in the brain and certain cancer cell lines. With the use of a "substrate-trapping" approach, p130(cas), a major focal adhesion-associated phosphotyrosyl protein, has now been identified as a likely physiological substrate of SAP-1. Expression of recombinant SAP-1 induced the dephosphorylation of p130(cas) as well as that of two other components of the integrin-signaling pathway (focal adhesion kinase and p62(dok)) in intact cells. In contrast, expression of a substrate-trapping mutant of SAP-1 induced the hyperphosphorylation of these proteins, indicating a dominant negative effect of this mutant. Overexpression of SAP-1 induced disruption of the actin-based cytoskeleton as well as inhibited various cellular responses promoted by integrin-mediated cell adhesion, including cell spreading on fibronectin, growth factor-induced activation of extracellular signal-regulated kinase 2, and colony formation. Finally, the enzymatic activity of SAP-1, measured with an immunocomplex phosphatase assay, was substantially increased by cell-cell adhesion. These results suggest that SAP-1, by mediating the dephosphorylation of focal adhesion-associated substrates, negatively regulates integrin-promoted signaling processes and, thus, may contribute to contact inhibition of cell growth and motility.
Second Department of Internal Medicine, Kobe University School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan. noguchi@med.kobe-u.ac.jp
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T
Noguchi
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M
Tsuda
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H
Takeda
T
T
Takada
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K
Inagaki
T
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Yamao
K
K
Fukunaga
T
T
Matozaki
M
M
Kasuga
D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D002448:Cell Adhesion; D002455:Cell Division; D006224:Cricetinae; D050719:Crk-Associated Substrate Protein; D017931:DNA Primers; D004789:Enzyme Activation; D005353:Fibronectins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011506:Proteins; D054631:Receptor-Like Protein Tyrosine Phosphatases, Class 3; D011956:Receptors, Cell Surface; D050717:Retinoblastoma-Like Protein p130; D013274:Stomach Neoplasms / Q000201:enzymology*; D013379:Substrate Specificity; D014443:Tyrosine / Q000378:metabolism
D050719:Crk-Associated Substrate Protein; D017931:DNA Primers; D005353:Fibronectins; D010750:Phosphoproteins; D011506:Proteins; D011956:Receptors, Cell Surface; D050717:Retinoblastoma-Like Protein p130; D014443:Tyrosine; D054645:Protein Phosphatase 1; C431695:PTPRH protein, human; D017027:Protein Tyrosine Phosphatases; D054631:Receptor-Like Protein Tyrosine Phosphatases, Class 3