Proto-Oncogene Products Vav and c-Cbl are Involved in the Signal Transduction Through Grb2/Ash in Hematopoietic Cells
Grb2/Ash is composed of one SH2 and two SH3 domains and functions as an adapter linking tyrosine-kinase receptors and Ras in fibroblasts. We have investigated the nature of proteins interacting with Grb2/Ash in hematopoietic cells.
The product of the vav proto-oncogene (Vav) is exclusively expressed in hematopoietic cells and has the guanine nucleotide exchange activity. Here we report that granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and erythropoietin (EPO) induce rapid and transient tyrosine phosphorylation of Vav and that Vav is constitutively associated with the SH3 domain of Grb2/Ash in a human leukemia cell line UT-7. These data suggest that Vav is implicated in a signaling pathway leading to activation of Ras or Ras-related proteins in hematopoietic cells.
Furthermore, we have shown that the proto-oncogene c-cblc product (c-Cbl) is also tyrosine-phosphorylated by stimulation with GM-CSF or EPO and is constitutively associated with the SH3 domain of Grb2/Ash in UT-7. However, we could not find the homologous regions with guanine nucleotide exchange factors or GTPase-activating proteins in the c-cbl gene. Therefore, Grb2/Ash might also transduce a signal that is different from the signal leading to the small-G protein regulation.
KeywordsTyrosine Phosphorylation Guanine Nucleotide Exchange Factor Normal Rabbit Serum Lx107 Cell Kirin Brewery
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