Valentine M A, Bursten S L, Harris W E, Draves K E, Pollok B A, Ostrowski J, Bomsztyk K, Clark E A
Department of Microbiology, University of Washington, Seattle 98195.
Cell Immunol. 1992 May;141(2):373-87. doi: 10.1016/0008-8749(92)90156-j.
We have examined signal transduction via membrane IgM (mIgM) in resting and cycling human B cells. Crosslinking mIgM on all of the cell types studied transduced a signal through the phosphatidylinositol pathway, producing inositol 1,4,5-trisphosphate and release of intracellular free calcium. These second messengers were formed regardless of quantitative or qualitative differences in the surface expression of mIgM: cells that had low levels of surface IgM (T-51) or had no light chain associated with surface heavy chain (DB) signaled phosphatidylinositol pathway activation after mIgM crosslinking. Production of specific lipid products in nonquiescent B cells differed from that in normal resting cells. Ligation of surface immunoglobulin on resting B cells resulted in sustained increases of both diacylglycerol and phosphatidic acid, two lipids that can influence PKC activation. Whereas PKC was strongly activated in normal tonsillar B cells, several cell lines had reduced PKC activation following crosslinking of mIgM. The reduction in protein kinase C activation correlated with the absence or reduced levels of phosphatidic acid or diacylglycerol following stimulation: protein kinase C translocated and was activated only in cells that had elevated levels of both diacylglycerides and phosphatidic acid. Anti-IgM-induced phosphorylation of a protein kinase C substrate protein CD20, also increased in those cells having PKC activation and not in cells in which kinase activity was reduced. CD20 phosphorylation also increased following the direct addition of exogenous phosphatidic acid to resting B cells. Together, these observations show that the generation of lipid products following mIgM crosslinking in resting cells can vary from that in cycling cells and may relate to the different levels of PKC activation. In a companion study we report that ligation of surface IgM activates both an acyltransferase and phospholipase D to form phosphatidic acid.
我们研究了静息和循环中的人B细胞通过膜免疫球蛋白M（mIgM）进行的信号转导。在所研究的所有细胞类型上交联mIgM均可通过磷脂酰肌醇途径转导信号，产生肌醇1,4,5-三磷酸并释放细胞内游离钙。无论mIgM的表面表达在数量或质量上存在何种差异，均可形成这些第二信使：表面IgM水平较低的细胞（T-51）或表面重链未与轻链相关联的细胞（DB）在mIgM交联后均表明磷脂酰肌醇途径被激活。非静止B细胞中特定脂质产物的产生与正常静息细胞不同。静息B细胞表面免疫球蛋白的连接导致二酰基甘油和磷脂酸这两种可影响蛋白激酶C（PKC）激活的脂质持续增加。虽然PKC在正常扁桃体B细胞中被强烈激活，但几种细胞系在mIgM交联后PKC激活有所降低。蛋白激酶C激活的降低与刺激后磷脂酸或二酰基甘油的缺失或水平降低相关：蛋白激酶C仅在二酰基甘油和磷脂酸水平均升高的细胞中发生易位并被激活。抗IgM诱导的蛋白激酶C底物蛋白CD20的磷酸化在具有PKC激活的细胞中也增加，而在激酶活性降低的细胞中则没有增加。在静息B细胞中直接添加外源性磷脂酸后，CD20磷酸化也增加。总之，这些观察结果表明，静息细胞中mIgM交联后脂质产物的产生可能与循环细胞不同，并且可能与PKC激活的不同水平有关。在一项配套研究中，我们报告表面IgM的连接可激活酰基转移酶和磷脂酶D以形成磷脂酸。
