The Raf-1 serine-threonine kinase is a substrate for the p56lck protein tyrosine kinase in human T-cells. |
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Authors: | P A Thompson J A Ledbetter U R Rapp J B Bolen |
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Institution: | Laboratory of Tumor Virus Biology, National Cancer Institute, Bethesda, Maryland 20892. |
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Abstract: | The CD4 receptor subserves both adhesion and signal transduction functions on CD4+ T-lymphocytes. CD4 is physically associated with the src-related protein tyrosine kinase p56lck. Cell surface engagement of CD4 leads to enzymatic activation of the associated p56lck and the phosphorylation of T-cell proteins on tyrosine residues. We have identified a 72-74kD protein phosphorylated on tyrosine residues following activation of CD4-associated p56lck as the serine-threonine kinase Raf-1. The demonstration that Raf-1 is a substrate for the CD4/p56lck receptor system in normal cells suggests that receptor and nonreceptor classes of protein tyrosine kinases can independently engage functionally overlapping signal transduction pathways. |
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