Sabe H, Hata A, Okada M, Nakagawa H, Hanafusa H
Laboratory of Molecular Oncology, Rockefeller University, New York, NY 10021.
Proc Natl Acad Sci U S A. 1994 Apr 26;91(9):3984-8. doi: 10.1073/pnas.91.9.3984.
Csk (C-terminal Src kinase), a protein-tyrosine kinase, bearing the Src homology 2 and 3 (SH2 and SH3) domains, has been implicated in phosphorylation of c-Src Tyr-527, resulting in suppression of c-Src kinase activity. We found that mutations in the SH2 or SH3 domain of Csk, though they did not affect its kinase activity, resulted in a loss of suppression of c-Src activity in fibroblasts. In normal fibroblasts, tyrosine-phosphorylated paxillin and focal adhesion kinase pp125FAK, which colocalize at focal adhesion plaques, were the major proteins to which the Csk SH2 domain bound. Loss of binding to these proteins by the Csk SH2 mutants correlated with loss of the activity to suppress c-Src. Consistent with this observation, the levels of tyrosine phosphorylation of paxillin and pp125FAK were greatly reduced during mitosis, whereas the kinase activity of c-Src was elevated. We suggest that the SH2 domain is required for Csk to suppress c-Src, perhaps in combination with the SH3 domain, by anchoring Csk to a particular subcellular location where c-Src may exist. Our data also indicate that a certain fraction of the Csk and Src family kinases function at the focal adhesion plaques. The activity of the c-Src kinase localized at the focal adhesion plaques appears to be regulated by cell adhesion to the extracellular matrix.
Csk（C末端Src激酶）是一种蛋白酪氨酸激酶，带有Src同源2和3（SH2和SH3）结构域，参与c-Src酪氨酸527位点的磷酸化，从而抑制c-Src激酶活性。我们发现，Csk的SH2或SH3结构域发生突变，尽管不影响其激酶活性，但会导致成纤维细胞中c-Src活性抑制的丧失。在正常成纤维细胞中，在粘着斑共定位的酪氨酸磷酸化桩蛋白和粘着斑激酶pp125FAK是Csk SH2结构域结合的主要蛋白。Csk SH2突变体与这些蛋白结合的丧失与抑制c-Src活性的丧失相关。与这一观察结果一致，在有丝分裂期间桩蛋白和pp125FAK的酪氨酸磷酸化水平大大降低，而c-Src的激酶活性升高。我们认为，SH2结构域是Csk抑制c-Src所必需的，可能与SH3结构域协同作用，通过将Csk锚定到c-Src可能存在的特定亚细胞位置。我们的数据还表明，一定比例的Csk和Src家族激酶在粘着斑发挥作用。定位于粘着斑的c-Src激酶活性似乎受细胞与细胞外基质粘附的调节。
