Mechanism of Action of Retinoic Acid Using CD38

描述(由申请人提供)：这是一项由多名研究人员提出的建议，旨在研究一种新的方法，通过利用维甲酸(RA)诱导的CD38受体的表达和信号转导来增强维甲酸(RA)导致生长停滞和分化的机制。RA是一种癌症化学预防药物。它是一种在饮食中提供的前激素，是一种常见的饮食不足。RA可以将未成熟的肿瘤转化细胞转化为成熟的分化表型。建议的研究利用了未成熟的、未确定的人类白血病粒单核细胞前体细胞，当分别用RA或维生素D3(D3)处理时，这些细胞经历了G0期停滞和髓系或单核细胞分化。RA在诱导髓系终末分化/G0期停滞的过程中引起MAPK信号的激活。我们和其他实验室对RA诱导的基因表达的调查显示，CD38是已知的最早的RA诱导的受体。抑制RA诱导的CD38表达可抑制RA诱导的分化，异位过表达CD38可增强RA诱导的分化。CD38可能通过胞外酶活性或受体信号来支持分化：(1)胞外酶活性催化NAD产生ADPR；cADPR能够动员钙，这是一种已知的分化和增殖调节因子。(2)CD38也可以二聚化，这是MAPK信号的另一个众所周知的起始者。(3)CD38有一个胞浆尾巴，能够与MAPK信号分子结合，特别是c-Cbl接头。建议的研究集中在这些功能在影响类风湿性关节炎的细胞结局中的潜在作用，即分化和G0细胞周期停滞。建议的目标是使用结合CD38、CD38突变体和X射线结晶学结构的小分子探针来表征CD38促进细胞分化和停滞的机制。其具体目的是：(1)确定CD38胞外酶活性对RA诱导分化的贡献；(2)确定受体二聚化和由此产生的胞浆MAPK信号复合体的贡献；(3)确定CD38-c-Cbl受体-适配器复合体的结构，以阐明可供合作伙伴或干预使用的物理接口的性质。总之，我们打算确定促进RA诱导分化所需的CD38活性。这些研究的影响是在理解RA如何工作方面的潜在范式转变，这将指向增强其作用机制的方法。这些研究的意义在于，它们可以为加强类风湿关节炎的化学预防和化疗效果的新方法提供基本的机制洞察。创新之处在于提出了一个基于受体表达和信号活性的新范式，作为类风湿关节炎逆转肿瘤转化的作用机制。因此，基本假设是RA诱导了CD38的早期表达，CD38具有不同的信号产生能力，这些不同的信号产生能力可以被用来增强和控制RA诱导的分化/抑制程序。最终目标是增强RA的效果。

DESCRIPTION (provided by applicant): This is a multi-investigator proposal to study a novel means of enhancing the mechanism by which retinoic acid (RA) causes growth arrest and differentiation by exploiting RA-induced expression and signaling by the CD38 receptor. RA is a cancer chemopreventive agent. It is a prohormone provided in the diet and is a common dietary insufficiency. RA can convert immature neoplastically transformed cells to a mature differentiated phenotype. The proposed studies utilize immature, uncommitted human leukemia granulocytic-monocytic precursor cells which undergo G0 arrest and either myeloid or monocytic differentiation when treated with RA or vitamin D3 (D3) respectively. RA causes activation of MAPK signaling in the process of inducing terminal myeloid differentiation/G0 arrest. Surveys of RA-induced gene expression from our and other laboratories revealed that CD38 is the earliest known receptor induced by RA. Crippling RA-induced CD38 expression cripples RA-induced differentiation, and ectopic over expression of CD38 enhances RA-induced differentiation. CD38 could potentially function through either ectoenzyme activity or receptor signaling to support differentiation: (1) The ectoenzyme activity catalyzes production of ADPR from NAD; and cADPR is able to mobilize calcium, a known regulator of differentiation and proliferation. (2) CD38 is also capable of dimerizing, which is another well known initiator of MAPK signaling. (3) CD38 has a cytosolic tail capable of binding to MAPK signaling molecules, in particular the c-Cbl adaptor. The proposed studies focus on the potential role of these functions in effecting the cellular outcome attributed to RA, namely differentiation and G0 cell cycle arrest. The proposed goals are to use small molecule probes that bind CD38, CD38 mutants, and X-ray crystallographic structures to characterize the mechanism by which CD38 promotes cell differentiation and arrest. The Specific Aims are to (1) determine the contribution of the CD38 ectoenzyme activity to RA-induced differentiation; (2) determine the contribution of receptor dimerization and the consequential cytosolic MAPK signaling complex; (3) determine the structure of the CD38-c-Cbl receptor-adaptor complex to elucidate the nature of the physical interfaces available for partners or intervention. In sum we intend to identify the CD38 activity needed to propel RA-induced differentiation. The Impact of these studies is a potential paradigm shift in understanding how RA works that will point to means of enhancing its mechanism of action. The Significance of the studies is that they could provide the basic mechanistic insight into a novel means of enhancing the chemopreventive, chemotherapeutic effects of RA. The Innovation is that a new paradigm based on receptor expression and signaling activities is proposed as a mechanism of action for RA in reverting neoplastic transformation. The basic Hypothesis is thus that RA-induces the early expression of CD38 which has different signal generating capabilities, and that these different capabilities could be exploited to enhance and control the differentiation/arrest program elicited by RA. The ultimate goal is to enhance the effects of RA.