Bouillie S, Barel M, Drane P, Cassinat B, Balbo M, Holers V M, Frade R
Immunochimie des Régulations Cellulaires et des Interactions Virales, INSERM U.354, Centre INSERM, Hôpital Saint-Antoine, Paris, France.
Eur J Immunol. 1995 Sep;25(9):2661-7. doi: 10.1002/eji.1830250939.
We previously demonstrated that human C3d or pep16, a 16-amino acid synthetic peptide derived from human C3d, induced in vivo and in vitro tyrosine phosphorylation of pp105, an intracellular component found only in human cells that express CR2 at their surface. To determine the contribution of CR2 molecules to this enzymatic regulation, we first analyzed whether activation of CR2 by other extracellular CR2 ligands could trigger such regulation in cell extracts. Subsequently, we used cell extracts of either CR2-positive cells depleted in CR2 molecules by absorption with anti-CR2 antibodies or CR2-negative cells transfected with CR2 cDNA. We demonstrate here that pp105 phosphorylation was induced when CR2 was activated by C3d and pep16 as well as by gp350, the Epstein-Barr virus capsid protein or OKB7, an anti-CR2 monoclonal antibody (mAb). HB5, another anti-CR2 mAb, which did not activate B lymphocytes through CR2, did not induce pp105 phosphorylation. Thus, C3d, pep16, gp350, and OKB7 presented similar properties in activating CR2 to trigger pp105 phosphorylation and in regulating B lymphocyte proliferation, while HB-5 had no effect on either assays. Furthermore, our data demonstrate that the presence of CR2 activated by its extracellular ligands regulates pp105 phosphorylation through two distinct pathways: one which also requires the presence of non-activated CD19, and one which is independent of CD19. The involvement of CD19 in the first pathway was not due to the formation of putative CR2-CD19 complexes. Both pathways were TAPA-1 independent. This is the first demonstration that activated CR2 molecules can play a regulatory role in enzymatic function, such as phosphorylation, despite the absence of CD19 and TAPA-1.
我们先前证明，人C3d或pep16（一种源自人C3d的16个氨基酸的合成肽）可在体内和体外诱导pp105的酪氨酸磷酸化，pp105是一种仅在表面表达CR2的人细胞中发现的细胞内成分。为了确定CR2分子对这种酶调节的作用，我们首先分析了其他细胞外CR2配体对CR2的激活是否能在细胞提取物中触发这种调节。随后，我们使用了通过抗CR2抗体吸收而使CR2分子缺失的CR2阳性细胞的细胞提取物，或用CR2 cDNA转染的CR2阴性细胞的细胞提取物。我们在此证明，当CR2被C3d、pep16以及gp350（爱泼斯坦-巴尔病毒衣壳蛋白）或OKB7（一种抗CR2单克隆抗体）激活时，pp105会发生磷酸化。另一种抗CR2单克隆抗体HB5不能通过CR2激活B淋巴细胞，也不会诱导pp105磷酸化。因此，C3d、pep16、gp350和OKB7在激活CR2以触发pp105磷酸化以及调节B淋巴细胞增殖方面具有相似的特性，而HB - 5对这两种检测均无影响。此外，我们的数据表明，被其细胞外配体激活的CR2的存在通过两条不同途径调节pp105磷酸化：一条途径还需要未激活的CD19的存在，另一条途径则不依赖于CD19。CD19在第一条途径中的参与并非由于假定的CR2 - CD19复合物的形成。两条途径均不依赖于TAPA - 1。这是首次证明，尽管不存在CD19和TAPA - 1，但激活的CR2分子仍可在诸如磷酸化等酶功能中发挥调节作用。
