Saxton T M, van Oostveen I, Bowtell D, Aebersold R, Gold M R
Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.
J Immunol. 1994 Jul 15;153(2):623-36.
Ligation of the B cell AgR activates p21ras (Ras). We have investigated the effects of AgR ligation on three proteins that have been implicated as regulators of Ras: SHC, GRB-2, and mSOS1. We show that AgR cross-linking in B cells stimulated tyrosine and serine phosphorylation of SHC. This correlated with the formation of complexes containing SHC, GRB-2, mSOS1, and an unidentified 145-kDa tyrosine-phosphorylated protein. These complexes were present in the cytosol, as well as in the membrane fraction of the cells, where Ras is located. By using a GRB-2 fusion protein to probe blots, we showed that SHC was the major protein that GRB-2 bound to in anti-Ig-stimulated B cells. This argues that SHC couples GRB-2/mSOS1 to the 145-kDa protein and that SHC is likely to be essential for mSOS1 function in B cells. Finally, we found that AgR cross-linking stimulated phosphorylation of mSOS1 and that this could be blocked by an inhibitor of protein kinase C. Thus, signaling by the B cell AgR stimulates phosphorylation of SHC and mSOS1 and induces the formation of membrane-associated complexes containing SHC, GRB-2, mSOS1, and a 145-kDa protein. These events may be important for activation of Ras by the AgR.
B细胞抗原受体（AgR）的连接可激活p21ras（Ras）。我们研究了AgR连接对三种被认为是Ras调节因子的蛋白质的影响：SHC、GRB-2和mSOS1。我们发现，B细胞中的AgR交联刺激了SHC的酪氨酸和丝氨酸磷酸化。这与包含SHC、GRB-2、mSOS1和一种未鉴定的145 kDa酪氨酸磷酸化蛋白的复合物形成相关。这些复合物存在于细胞溶质中，也存在于Ras所在的细胞的膜部分。通过使用GRB-2融合蛋白探测印迹，我们表明SHC是GRB-2在抗Ig刺激的B细胞中结合的主要蛋白质。这表明SHC将GRB-2/mSOS1与145 kDa蛋白偶联，并且SHC可能对B细胞中mSOS1的功能至关重要。最后，我们发现AgR交联刺激了mSOS1的磷酸化，并且这可以被蛋白激酶C抑制剂阻断。因此，B细胞AgR的信号传导刺激了SHC和mSOS1的磷酸化，并诱导了包含SHC、GRB-2、mSOS1和一种145 kDa蛋白的膜相关复合物的形成。这些事件可能对AgR激活Ras很重要。
