Regulation of Btk Function by a Major Autophosphorylation Site Within the SH3 Domain

Department of Microbiology and Molecular Genetics, University of California, Los Angeles 90095-1662, USA.
Immunity (Impact Factor: 21.56). 06/1996; 4(5):515-25. DOI: 10.1016/S1074-7613(00)80417-3
Source: PubMed


Bruton's tyrosine kinase (Btk) plays a crucial role in B cell development. Overexpression of Btk with a Src family kinase increases tyrosine phosphorylation and catalytic activity of Btk. This occurs by transphosphorylation at Y551 in the Btk catalytic domain and the enhancement of Btk autophosphorylation at a second site. A gain-of-function mutant called Btk* containing E41 to K change within the pleckstrin homology domain induces fibroblast transformation. Btk* enhances the transphosphorylation of Y551 by endogenous Src family tyrosine kinases and autophosphorylation at the second site. We mapped the major Btk autophosphorylation site to Y223 within the SH3 domain. Mutation of Y223 to F blocks Btk autophosphorylation and dramatically potentiates the transforming activity of Btk* in fibroblasts. The location of Y223 in a potential ligand-binding pocket suggests that autophosphorylation regulates SH3-mediated signaling by Btk.

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Available from: Jean-Pierre Kinet, Feb 04, 2015
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    • "The TH domain houses conserved regions designated as BTK motif (zinc cofactor binding site) and proline-rich stretch [21], and serves as a major determinant binding site for protein kinase C-beta (PKC-β) [22]. Initial activation (trans-phosphorylation) of BTK takes place in the activation loop located in the SH1/TK domain; however further activation occurs within the SH3 and SH2 domains, which contains major autophosphorylation sites [23,24]. These Src homologous domains also contain the nuclear localization signals (NLS) and nuclear export sequence (NES) required for nucleocytoplasmic shuttling of BTK [25]. "
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    • "Specifically, Btk plays an essential role in the B cell receptor (BCR) signaling pathway. Antigen binding to the BCR results in B cell receptor oligomerization, Syk and Lyn kinase activation (Gauld et al., 2002), followed by Btk kinase activation (Park et al., 1996; Rawlings et al., 1996; Baba et al., 2001). Once activated, Btk forms a signaling complex with proteins such as BLNK, Lyn, and Syk and phosphorylates phospholipase C (PLC)g2 (Baba et al., 2001; Tsukada et al., 2001). "
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    • "To test whether Btk is part of the signaling cascade that is induced in macrophages upon Lm infection, wt and Btk−/− BMMs were infected with Lm for different time points. Subsequently, the phosphorylation status of the Btk autophosphorylation site Y223 was determined to assess Btk activity [31]. This revealed that Btk was activated approximately 30 min after Lm infection (Fig. 1C and 1D), indicating that Btk is part of the signaling network induced by Lm. "
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