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Mol. Cell. Biol., Oct 1995, 5304-5311, Vol 15, No. 10
S Mahajan, J Fargnoli, AL Burkhardt, SA Kut, SJ Saouaf and JB Bolen
Bruton's tyrosine kinase (Btk) is tyrosine phosphorylated and enzymatically
activated following ligation of the B-cell antigen receptor. These events
are temporally regulated, and Btk activation follows that of various
members of the Src family of protein tyrosine kinases, thus raising the
possibility that Src kinases participate in the Btk activation process. We
have evaluated the mechanism underlying Btk enzyme activation and have
explored the potential regulatory relationship between Btk and Src protein
kinases. We demonstrate in COS transient-expression assays that Btk can be
activated through intramolecular autophosphorylation at tyrosine 551 and
that Btk autophosphorylation is required for Btk catalytic functions.
Coexpression of Btk with members of the Src family of protein tyrosine
kinases, but not Syk, led to Btk tyrosine phosphorylation and activation.
Using a series of point mutations in Blk (a representative Src protein
kinase) and Btk, we show that Src kinases activate Btk through an indirect
mechanism that requires membrane association of the Src enzymes as well as
functional Btk SH3 and SH2 domains. Our results are compatible with the
idea that Src protein tyrosine kinases contribute to Btk activation by
indirectly stimulating Btk intramolecular autophosphorylation.
Copyright © 1995, American Society for Microbiology
Src family protein tyrosine kinases induce autoactivation of Bruton's tyrosine kinase
Department of Oncology, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, New Jersey 08543, USA.
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