MECHANISMS OF DMBA INDUCED BONE MARROW TOXICITY

产品说明：（改编自研究者摘要）7，12-二甲基苯并[a]蒽已被广泛研究作为致癌和免疫抑制多环芳烃的模型。DMBA的大多数生物效应需要细胞色素P450家族的一些成员激活。DMBA对免疫系统最显著的影响之一是骨髓毒性，导致祖B-淋巴细胞严重耗竭。该项目的长期目标是确定DMBA骨髓毒性的机制。在初步研究中，研究人员发现骨髓基质细胞具有高组成水平的细胞色素P450 IB 1（CYP 1B 1），其在体外将DMBA代谢为致癌代谢物。研究人员还观察到，祖B-淋巴细胞在体外与DMBA和骨髓基质细胞共培养时发生凋亡，但在单独与DMBA孵育时不发生凋亡。中心假设是骨髓基质细胞中CYP 1B 1代谢DMBA导致代谢物释放，直接或间接导致祖B淋巴细胞凋亡。本研究的基本原理是基于：i）基质细胞-B细胞相互作用在正常B细胞发育中的关键重要性; ii）基质细胞中CYP 1B 1的高组成性水平及其在前B细胞中的缺失;和iii）DMBA仅在与骨髓基质细胞共培养时才能在前B细胞中引起细胞凋亡。祖B细胞的死亡可能是由于：前B细胞中DMBA-DNA加合物的形成; DMBA处理的骨髓基质细胞的专性生长信号的丢失;或DMBA处理的骨髓基质细胞释放前B细胞的毒性部分。为了解决这些可能性，研究者将致力于以下三个具体目标：1）使用基因敲除小鼠在一系列体内和体外实验中描述CYP 1B 1和AhR在DMBA诱导的前B细胞凋亡中的作用。2)区分可能的机制（即，DNA加合物的形成、生长信号的丢失、Fas配体或其他介质的释放），这些可能是DMBA处理的骨髓基质细胞引起前B细胞凋亡的能力的原因; 3）鉴定影响骨髓基质细胞中CYP 1B 1表达的生长因子和相关调节机制。在这个项目完成时，研究者期望已经评估了骨髓基质细胞CYP 1B 1的作用，以及由此产生的效应机制，在祖B细胞中DMBA介导的凋亡。这些发现可能导致对有毒物质引起骨髓毒性的机制的新见解。

DESCRIPTION: (Adapted from the Investigator's Abstract) 7,12-Dimethylbenzo[a]anthracene has been studied extensively as a model for carcinogenic and immuno-suppressive polycyclic aromatic hydrocarbons. Most of the biological effects of DMBA require activation by some member of the cytochrome P450 family. One of the most striking effects of DMBA on the immune system is bone marrow toxicity, resulting in severe depletion of progenitor B- lymphocytes. The long-term goal of this project is to identify the mechanisms involved in the bone marrow toxicity of DMBA. In preliminary studies, the investigators found that bone marrow stromal cells have high constitutive levels of cytochrome P450lBl (CYPlBl) that metabolizes DMBA to carcinogenic metabolites in vitro. The investigators also observed that progenitor B- lymphocytes undergo apoptosis when co-cultured with DMBA and bone marrow stromal cells in vitro, but not when incubated with DMBA alone. The central hypothesis is that DMBA metabolism by CYP1B1 in bone marrow stromal cells results in release of metabolites that, directly or indirectly, cause apoptosis in progenitor B- lymphocytes. The rationale for this study is based on: i) the critical importance of stromal cell-B cell interactions in normal B cell development; ii) the high constitutive levels of CYPlBl in stromal cells and its absence in pre B cells; and iii) the ability of DMBA to cause apoptosis in pre-B cells only when co-cultured with bone marrow stromal cells. Death of progenitor B cells might result from: DMBA-DNA adduct formation in pre B cells; loss of an obligatory growth signal from DMBA-treated bone marrow stromal cells; or the release of a toxic moiety for pre B cells by DMBA- treated bone marrow stromal cells. To resolve these possibilities, the investigators will pursue to following three specific aims: 1) Use gene knockout mice in a series of in vivo and in vitro experiments to delineate the roles of CYP1B1, and the AhR, in DMBA-induced pre B cell apoptosis. 2) Distinguish possible mechanisms (i.e., DNA-adduct formation, loss of growth signals, release of Fas ligand or other mediators) that could be responsible for the ability of DMBA-treated bone marrow stromal cells to cause apoptosis in pre-B cells; 3) Identify growth factors and associated regulatory mechanisms that affect CYP1B1 expression in bone marrow stromal cells. At the completion of this project, the investigators expect to have evaluated the role of bone marrow stromal cell CYP1B1, and resulting effector mechanisms, in DMBA-mediated apoptosis in progenitor B cells. These findings could lead to new insights into the mechanisms by which the toxicants cause bone marrow toxicity.