Li Z, Wahl M I, Eguinoa A, Stephens L R, Hawkins P T, Witte O N
Department of Microbiology and Molecular Genetics, University of California, Los Angeles, CA 90095-1662, USA.
Proc Natl Acad Sci U S A. 1997 Dec 9;94(25):13820-5. doi: 10.1073/pnas.94.25.13820.
Bruton's tyrosine kinase (Btk) is essential for normal B lymphocyte development and function. The activity of Btk is partially regulated by transphosphorylation within its kinase domain by Src family kinases at residue Tyr-551 and subsequent autophosphorylation at Tyr-223. Activation correlates with Btk association with cellular membranes. Based on specific loss of function mutations, the Btk pleckstrin homology (PH) domain plays an essential role in this activation process. The Btk PH domain can bind in vitro to several lipid end products of the phosphatidylinositol 3-kinase (PI 3-kinase) family including phosphatidylinositol 3,4,5-trisphosphate. Activation of Btk as monitored by elevation of phosphotyrosine content and a cellular transformation response was dramatically enhanced by coexpressing a weakly activated allele of Src (E378G) and the two subunits of PI 3-kinase-gamma. This activation correlates with new sites of phosphorylation on Btk identified by two-dimensional phosphopeptide mapping. Activation of Btk was dependent on the catalytic activity of all three enzymes and an intact Btk PH domain and Src transphosphorylation site. These combined data define Btk as a downstream target of PI 3-kinase-gamma and Src family kinases.
布鲁顿酪氨酸激酶（Btk）对于正常B淋巴细胞的发育和功能至关重要。Btk的活性部分受Src家族激酶在其激酶结构域内对酪氨酸551位点的转磷酸化以及随后酪氨酸223位点的自身磷酸化调控。激活与Btk与细胞膜的结合相关。基于功能丧失特异性突变，Btk普列克底物蛋白同源（PH）结构域在这一激活过程中起关键作用。Btk PH结构域在体外可与磷脂酰肌醇3激酶（PI 3激酶）家族的几种脂质终产物结合，包括磷脂酰肌醇3,4,5三磷酸。通过共表达Src的弱激活等位基因（E378G）和PI 3激酶γ的两个亚基，酪氨酸磷酸化含量升高及细胞转化反应所监测到的Btk激活显著增强。这种激活与二维磷酸肽图谱鉴定出的Btk上新的磷酸化位点相关。Btk的激活依赖于所有三种酶的催化活性以及完整的Btk PH结构域和Src转磷酸化位点。这些综合数据将Btk定义为PI 3激酶γ和Src家族激酶的下游靶点。
