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  • 标题:Both p21ras and pp60v-src are required, but neither alone is sufficient, to activate the Raf-1 kinase
  • 本地全文:下载
  • 作者:N G Williams ; T M Roberts ; P Li
  • 期刊名称:Proceedings of the National Academy of Sciences
  • 印刷版ISSN:0027-8424
  • 电子版ISSN:1091-6490
  • 出版年度:1992
  • 卷号:89
  • 期号:7
  • 页码:2922-2926
  • DOI:10.1073/pnas.89.7.2922
  • 语种:English
  • 出版社:The National Academy of Sciences of the United States of America
  • 摘要:The raf genes encode a family of cytoplasmic proteins with intrinsic protein-serine/threonine kinase activity. The c-raf gene is the cellular homolog of v-raf, the transforming gene of murine sarcoma virus 3611. The constitutive kinase activity of the v-Raf protein has been implicated in transformation and mitogenesis. The activity of Raf-1, the protein product of the c-raf gene, is normally suppressed by a regulatory N-terminal domain. Activation of various tyrosine-kinase growth factor receptors results in activation of Raf-1 and its hyperphosphorylation. Further, Raf-1 has been shown to act either downstream or independently of the p21ras protein, as indicated by experiments involving microinjection of anti-Ras antibodies. To investigate the potential role of p21ras in the activation of Raf-1 by tyrosine kinases, we have used the baculovirus/Sf9 cell system to overproduce various wild-type and mutant forms of pp60src, p21ras, and Raf-1 proteins. We show that either pp60v-src or p21c-ras can independently activate the autokinase activity of Raf-1, but only to a limited extent. Surprisingly, both pp60v-src and p21c-ras are required to fully activate Raf-1. Analysis of the Raf-1 autokinase activity in vitro shows that Raf-1 autophosphorylation sites are distributed equally on serine and threonine residues. When Raf-1 is analyzed by immunoblotting, as previously reported for mammalian cell experiments, a marked increase in the apparent molecular weight of Raf-1 is seen only when it is coexpressed with both pp60v-src and p21ras.
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