The Raf-1 serine-threonine kinase is a substrate for the p56lck protein tyrosine kinase in human T-cells.
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.
Laboratory of Tumor Virus Biology, National Cancer Institute, Bethesda, Maryland 20892.
P A
PA
Thompson
J A
JA
Ledbetter
U R
UR
Rapp
J B
JB
Bolen
D015496:CD4-Positive T-Lymphocytes / Q000201:enzymology*; D004789:Enzyme Activation / Q000502:physiology; D006801:Humans; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D008970:Molecular Weight; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D012016:Reference Values; D013379:Substrate Specificity
D011518:Proto-Oncogene Proteins; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D019908:Proto-Oncogene Proteins c-raf