DOK4 is rapidly and heavily phosphorylated in response to insulin and, once phosphorylated, binds a set of SH2 domain proteins, including RasGAP, CRK, and the nonreceptor tyrosine kinases SRS and FYN. DOK4 also activates MAPK in cells. In contrast, DOK5 is phosphorylated much more slowly and does not associate with this set of SH2 homology domains or activate MAPK. In addition to the PH and PTB domains, DOK4 contains a short C terminus with 5 potential sites for tyrosine phosphorylation. By RT-PCR analysis, Favre et al. (2003) detected expression of DOK4 and DOK5 in peripheral blood T cells. They noted that DOK5 is expressed in activated but not resting T cells, suggesting that the expression of DOK5 is regulated upon T cell activation.
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