Matsuuchi L, Gold M R, Travis A, Grosschedl R, DeFranco A L, Kelly R B
Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448.
Proc Natl Acad Sci U S A. 1992 Apr 15;89(8):3404-8. doi: 10.1073/pnas.89.8.3404.
The B-cell antigen receptors consist of membrane immunoglobulins (mIgs) noncovalently associated with two accessory proteins, MB-1 and Ig-beta. We used transfection into a nonlymphoid cell line to test whether MB-1 and Ig-beta were sufficient to promote cell surface expression of mIgM capable of signal transduction. Expression of MB-1 and Ig-beta, but not MB-1 alone, allowed high-level surface expression of mIgM in the AtT20 endocrine cell line, which presumably lacks other B-cell-specific components. The reconstituted antigen receptor was capable of mediating some of the signaling reactions characteristic of mIgM in B lymphocytes. Crosslinking mIgM on transfected AtT20 cells stimulated tyrosine phosphorylation of MB-1 and Ig-beta and also increased the amount of phosphatidylinositol 3-kinase activity that could be precipitated with anti-phosphotyrosine antibodies. When total cell lysates were analyzed by anti-phosphotyrosine immunoblotting, however, no induced phosphorylation of more abundant proteins was detected. Moreover, crosslinking of the receptor in AtT20 cells did not stimulate inositol phospholipid breakdown. Thus, the transfected B-cell antigen receptor could initiate some signal transduction events but AtT20 cells may lack components required for other signaling events associated with mIgM.
B细胞抗原受体由与两种辅助蛋白MB-1和Ig-β非共价结合的膜免疫球蛋白（mIg）组成。我们通过转染到非淋巴细胞系中，来测试MB-1和Ig-β是否足以促进能够进行信号转导的mIgM在细胞表面的表达。MB-1和Ig-β的表达，而不是单独的MB-1，能够使mIgM在可能缺乏其他B细胞特异性成分的AtT20内分泌细胞系中高水平地在细胞表面表达。重组抗原受体能够介导B淋巴细胞中mIgM的一些特征性信号反应。转染的AtT20细胞上mIgM的交联刺激了MB-1和Ig-β的酪氨酸磷酸化，并且还增加了可用抗磷酸酪氨酸抗体沉淀的磷脂酰肌醇3激酶活性的量。然而，当通过抗磷酸酪氨酸免疫印迹分析总细胞裂解物时，未检测到更丰富蛋白质的诱导磷酸化。此外，AtT20细胞中受体的交联并未刺激肌醇磷脂的分解。因此，转染的B细胞抗原受体可以启动一些信号转导事件，但AtT20细胞可能缺乏与mIgM相关的其他信号事件所需的成分。
