Hofmeister J K, Cooney D, Coggeshall K M
Ohio State University Comprehensive Cancer Center, 300 West 12th Avenue, Columbus, Ohio 43210, USA.
Blood Cells Mol Dis. 2000 Apr;26(2):133-43. doi: 10.1006/bcmd.2000.0287.
Anti-CD20 antibodies may reduce or eliminate non-Hodgkin's lymphoma B cells in patients, although the mechanism of action is not clear. To explore mechanism(s), we examined the induction of signal transduction events using anti-CD20 monoclonal antibodies (mAb) in the human non-Hodgkin's lymphoma Ramos B cell line. We found that while Rituximab (a human-mouse hybrid mAb) alone induced apoptotic cell death, other murine anti-CD20 mAbs induced apoptosis of Ramos B cells only upon clustering with a secondary antibody. CD20 clustering was accompanied by activation of tyrosine protein kinase activity, PLCgamma2 phosphorylation, influx of Ca(2+), and activation of caspase 3. All signaling events, as well as the subsequent apoptosis, were blocked by PP2, a selective inhibitor of Src-family kinases. Treatment of Ramos with EGTA and BAPTA to block changes in cytoplasmic Ca(2+) likewise prevented CD20-induced apoptosis. Our findings support a model in which CD20 clustering activates members of the Src family of protein tyrosine kinases, leading to phosphorylation of PLCgamma2 and increased cytoplasmic Ca(2+). These early signal transduction events activate caspase 3 to promote apoptotic cell death of NHL B cells.
抗CD20抗体可能会减少或消除患者体内的非霍奇金淋巴瘤B细胞，尽管其作用机制尚不清楚。为了探究其机制，我们使用抗CD20单克隆抗体（mAb）在人非霍奇金淋巴瘤Ramos B细胞系中检测了信号转导事件的诱导情况。我们发现，虽然利妥昔单抗（一种人鼠嵌合mAb）单独就能诱导凋亡性细胞死亡，但其他鼠源性抗CD20 mAb只有在与二抗聚集时才会诱导Ramos B细胞凋亡。CD20聚集伴随着酪氨酸蛋白激酶活性的激活、PLCγ2的磷酸化、Ca(2+)内流以及caspase 3的激活。所有这些信号事件以及随后的凋亡都被PP2（一种Src家族激酶的选择性抑制剂）阻断。用EGTA和BAPTA处理Ramos以阻断细胞质Ca(2+)的变化同样可防止CD20诱导的凋亡。我们的研究结果支持这样一种模型，即CD20聚集激活了蛋白酪氨酸激酶Src家族的成员，导致PLCγ2磷酸化并使细胞质Ca(2+)增加。这些早期信号转导事件激活caspase 3，从而促进非霍奇金淋巴瘤B细胞的凋亡性细胞死亡。
