Leprince C, Draves K E, Geahlen R L, Ledbetter J A, Clark E A
Department of Microbiology, University of Washington, Seattle 98195.
Proc Natl Acad Sci U S A. 1993 Apr 15;90(8):3236-40. doi: 10.1073/pnas.90.8.3236.
The B-cell surface molecule CD22, when cross-linked, modulates signaling through the surface IgM (sIgM)-B-cell receptor (BCR) complex. Here we analyzed the basis of this interaction between CD22 and the human sIgM complex. After lysis of B cells or B-cell lines in digitonin, CD22 coimmunoprecipitated a kinase activity that in vitro-phosphorylated two polypeptides of 150 and 130 kDa on tyrosine residues. By immunoblot analysis with a rabbit anti-serum specific for a synthetic peptide of CD22, we found these proteins to be CD22 itself. Furthermore, the phosphorylated 150-kDa CD22 was found in the sIgM-BCR complex maintained by digitonin, along with Ig alpha/mb-1, Ig beta/B29, and a 75-kDa polypeptide precipitated by an antiserum specific to protein-tyrosine kinase PTK72. CD22 is likely to be an important signaling partner in the sIgM-BCR complex since it is very rapidly and strikingly phosphorylated after sIgM is cross-linked and since it contains the antigen recognition homology I (ARHI) motif, present in other antigen receptor molecules.
B细胞表面分子CD22在交联后，可调节通过表面IgM（sIgM）-B细胞受体（BCR）复合物的信号传导。在此，我们分析了CD22与人sIgM复合物之间这种相互作用的基础。在用洋地黄皂苷裂解B细胞或B细胞系后，CD22通过免疫共沉淀得到一种激酶活性，该活性在体外可使两条分别为150 kDa和130 kDa的多肽在酪氨酸残基上发生磷酸化。通过用针对CD22合成肽的兔抗血清进行免疫印迹分析，我们发现这些蛋白就是CD22本身。此外，在由洋地黄皂苷维持的sIgM-BCR复合物中发现了磷酸化的150 kDa CD22，同时还有Igα/mb-1、Igβ/B29以及由针对蛋白酪氨酸激酶PTK72的抗血清沉淀出的一条75 kDa多肽。CD22可能是sIgM-BCR复合物中一个重要的信号传导伙伴，因为在sIgM交联后它会非常迅速且显著地发生磷酸化，并且它含有存在于其他抗原受体分子中的抗原识别同源性I（ARHI）基序。
