Marches R, Scheuermann R H, Uhr J W
Cancer Immunobiology Center and Department of Microbiology, University of Texas Southwestern Medical Center at Dallas, 75235-8576, USA.
Cancer Res. 1998 Feb 15;58(4):691-7.
Anti-idiotype (anti-Id) antibody can induce tumor dormancy in a murine B lymphoma, BCL1, by its ability to induce cell cycle arrest and apoptosis (negative signaling). In human B lymphoma, there is accumulating evidence that the antitumor effect of anti-Id or several other B cell-reactive antibodies relates to their ability to act as agonists rather than conventional effector antibodies. In this study, we sought to elucidate the role of cyclins, cyclin-dependent kinases (CDKs), and their inhibitors in anti-IgM-induced cell cycle arrest to better understand the mechanisms underlying cancer dormancy. To accomplish this, we have performed in vitro studies with a human lymphoma cell line (Daudi) because its response to anti-Id (or anti-IgM) is similar to that of a BCL1 cell line, more reagents are available, and the results would be particularly pertinent to therapy of human B cell lymphomas. Our results show that cross-linking of membrane IgM on Daudi cells induces an arrest late in G1 and prevents pRb from becoming phosphorylated. The G1 arrest is correlated with an induction of the CDK inhibitor p21 and reduced CDK2 activity, although the level of CDK2 protein was not changed. Coprecipitation of CDK2 with p21 in anti-IgM-treated cells and the unchanged level of cyclin E suggest that p21 is responsible for the reduction of CDK2 activity and therefore blockade of the cell cycle. The induction of p21 was not accompanied by changes in p53 levels. As a result of the G1 block, cyclin A levels sharply declined by 24 h after anti-IgM treatment. There was no evidence for involvement of CDK4 or CDK6 in the blockade. These results provide evidence that membrane IgM cross-linking on Daudi cells induces expression of p21 and a subsequent inhibition of the cyclin E-CDK2 kinase complex resulting in a block to pRb phosphorylation and cell cycle arrest late in G1.
抗独特型（抗Id）抗体能够通过诱导细胞周期停滞和凋亡（负向信号传导），使小鼠B淋巴瘤BCL1进入肿瘤休眠状态。在人类B淋巴瘤中，越来越多的证据表明，抗Id或其他几种B细胞反应性抗体的抗肿瘤作用与其作为激动剂而非传统效应抗体的能力有关。在本研究中，我们试图阐明细胞周期蛋白、细胞周期蛋白依赖性激酶（CDK）及其抑制剂在抗IgM诱导的细胞周期停滞中的作用，以便更好地理解癌症休眠的潜在机制。为实现这一目标，我们使用了一种人类淋巴瘤细胞系（Daudi）进行体外研究，因为其对抗Id（或抗IgM）的反应与BCL1细胞系相似，有更多试剂可供使用，且研究结果对人类B细胞淋巴瘤的治疗尤为相关。我们的结果表明，Daudi细胞膜上IgM的交联诱导了G1期晚期停滞，并阻止pRb磷酸化。G1期停滞与CDK抑制剂p21的诱导及CDK2活性降低相关，尽管CDK2蛋白水平未改变。抗IgM处理的细胞中，CDK2与p21共沉淀以及细胞周期蛋白E水平不变，表明p21是CDK2活性降低以及细胞周期阻滞的原因。p21的诱导并未伴随p53水平的变化。由于G1期阻滞，抗IgM处理24小时后细胞周期蛋白A水平急剧下降。没有证据表明CDK4或CDK6参与了这种阻滞。这些结果证明，Daudi细胞膜上IgM的交联诱导了p21的表达，随后抑制了细胞周期蛋白E-CDK2激酶复合物，导致pRb磷酸化受阻以及G1期晚期细胞周期停滞。
