Mechanism of Action of Retinoic Acid Using CD38

描述（由申请人提供）：这是一个多研究者的提案，旨在研究一种新的方法，通过利用视黄酸（RA）诱导的CD38受体的表达和信号传导来增强RA引起生长停滞和分化的机制。类风湿性关节炎是一种癌症化学预防剂。它是饮食中提供的一种激素原，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。拟制的研究利用未成熟的、未确定的人白血病粒细胞-单核细胞前体细胞，当分别用RA或维生素D3 （D3）治疗时，这些细胞经历G0阻滞和髓细胞或单核细胞分化。RA在诱导终末髓细胞分化/G0阻滞的过程中激活MAPK信号。我们和其他实验室对RA诱导的基因表达的调查显示，CD38是已知最早由RA诱导的受体。ra诱导的CD38表达削弱了ra诱导的分化，而CD38异位过表达增强了ra诱导的分化。CD38可能通过外酶活性或受体信号传导来支持分化：(1)外酶活性催化NAD产生ADPR；cADPR能够调动钙，一种已知的分化和增殖调节剂。(2) CD38也能够二聚化，这是另一个众所周知的MAPK信号传导的启动物。(3) CD38具有能够结合MAPK信号分子的胞质尾部，特别是c-Cbl接头。提出的研究重点是这些功能在影响RA的细胞结果（即分化和G0细胞周期阻滞）中的潜在作用。提出的目标是使用结合CD38、CD38突变体和x射线晶体学结构的小分子探针来表征CD38促进细胞分化和阻滞的机制。具体目标是：(1)确定CD38外切酶活性对ra诱导的分化的贡献；(2)确定受体二聚化和相应的细胞质MAPK信号复合物的贡献；(3)确定CD38-c-Cbl受体-接头复合物的结构，以阐明可用于合作伙伴或干预的物理接口的性质。总之，我们打算确定推动ra诱导的分化所需的CD38活性。这些研究的影响是理解RA如何工作的潜在范式转变，将指出加强其作用机制的方法。这些研究的意义在于，它们可以为增强RA的化学预防和化疗作用的新手段提供基本的机制见解。创新之处在于提出了一种基于受体表达和信号活动的新范式，作为RA恢复肿瘤转化的作用机制。因此，基本假设是RA诱导具有不同信号生成能力的CD38的早期表达，并且这些不同的能力可以被利用来增强和控制RA引起的分化/停止程序。最终目的是增强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.