ACTIVATION OF THE PP60C-SRC KINASE BY MIDDLE ANTIGEN-T BINDING OR BY DEPHOSPHORYLATION
ACTIVATION OF THE PP60C-SRC KINASE BY MIDDLE ANTIGEN-T BINDING OR BY DEPHOSPHORYLATION
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DOI：
10.1002/j.1460-2075.1985.tb03805.x
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发表时间：
1985-01-01
期刊：
影响因子：
11.4
通讯作者：
COURTNEIDGE, SA
中科院分区：
文献类型：
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作者：
COURTNEIDGE, SA
多瘤病毒的转化蛋白，中间T抗原，与蛋白酪氨酸激酶pp 60 c-src，和中间T的突变体的分析表明，该复合物在多瘤病毒的转化中起着重要的作用。最近有报道，从多瘤病毒转化的细胞pp 60 c-src在体外具有增强的酪氨酸连接酶活性。本文提供的数据证实了这些发现，并表明pp 60 c-src的增强的激酶活性是由于该酶的Vmax增加。蔗糖密度梯度分析表明，只有与中间T抗原结合的pp 60 c-src形式被激活。当从含有磷酸酪氨酸蛋白磷酸酶抑制剂原钒酸钠的裂解物制备酶时，来自正常和中间T转化细胞的pp 60 c-src之间的酶活性差异更加显著。来自中间T转化细胞的pp 60 c-src不受影响，但如果去磷酸化被阻止，来自正常细胞的pp 60 c-src具有降低的激酶活性。因此，pp 60 c-src的激酶活性似乎受其酪氨酸磷酸化程度的调节，并提供了支持这一假设的数据。pp 60 c-src是蛋白酪氨酸激酶的第一个例子，其活性被酪氨酸磷酸化抑制。中T抗原可能通过阻止该调节位点的磷酸化而增加pp 60 c-src的激酶活性。
The transforming protein of polyoma virus, middle T antigen, associates with the protein tyrosine kinase pp60c-src, and analysis of mutants of middle T suggests that this complex plays an important role in transformation by polyoma. It was recently reported that pp60c-src from polyma virus-transformed cells has enhanced tyrosine linase activity in vitro. The data presented here confirm these findings and show that the enhanced kinase activity of pp60c-src is due to an increase in the Vmax of the enzyme. Sucrose density gradient analysis demonstrates that only the form of pp60c-src which is bound to middle T antigen is activated. The difference in enzyme activity between pp60c-src from normal and middle T transformed cells is more marked when the enzyme is prepared from lysates containing the phosphotyrosine protein phosphatase inhibitor, sodium orthovanadate. pp60c-src from middle T transformed cells is unaffected, but pp60c-src from normal cells has reduced kinase activity if dephosphorylation is prevented. The kinase activity of pp60c-src thus appears to be regulated by its degree of phosphorylation at tyrosine, and data are presented which support this hypothesis. pp60c-src is the 1st example of a protein tyrosine kinase whose activity is inhibited by phosphorylation at tyrosine. Middle T antigen may increase the kinase activity of pp60c-src by preventing phosphorylation at this regulatory site.