Mechanism of Action of Retinoic Acid Using CD38

描述（由申请人提供）：这是一项多研究者建议，旨在研究一种新的方法，通过利用维甲酸（RA）诱导的CD 38受体表达和信号传导来增强RA引起生长停滞和分化的机制。RA是一种癌症化学预防剂。它是一种在饮食中提供的激素原，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。所提出的研究利用未成熟的未定型的人白血病粒细胞-单核细胞前体细胞，当分别用RA或维生素D3（D3）处理时，所述粒细胞-单核细胞前体细胞经历G 0停滞和髓样或单核细胞分化。RA在诱导终末髓样分化/G 0阻滞的过程中引起MAPK信号转导的激活。我们和其他实验室对RA诱导的基因表达的调查显示，CD 38是已知最早由RA诱导的受体。削弱RA诱导的CD 38表达削弱了RA诱导的分化，并且CD 38的异位过度表达增强了RA诱导的分化。CD 38可能通过胞外酶活性或受体信号传导发挥作用以支持分化：（1）胞外酶活性催化NAD产生ADPR;并且cADPR能够动员钙，钙是分化和增殖的已知调节剂。(2)CD 38还能够二聚化，这是另一种众所周知的MAPK信号传导起始剂。(3)CD 38具有能够结合MAPK信号传导分子，特别是c-Cbl衔接子的胞质尾部。拟议的研究集中在这些功能的潜在作用，影响细胞的结果归因于RA，即分化和G 0细胞周期阻滞。提出的目标是使用结合CD 38、CD 38突变体和X射线晶体学结构的小分子探针来表征CD 38促进细胞分化和停滞的机制。具体目的是（1）确定CD 38胞外酶活性对RA诱导分化的贡献;（2）确定受体二聚化和随后的胞质MAPK信号传导复合物的贡献;（3）确定CD 38-c-Cbl受体-接头复合物的结构，以阐明可用于伴侣或干预的物理界面的性质。总之，我们打算确定所需的CD 38活性，以推动RA诱导的分化。这些研究的影响是理解RA如何工作的潜在范式转变，这将指向增强其作用机制的方法。这些研究的意义在于，它们可以为增强RA的化学预防、化学治疗效果的新方法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传导活性的新范式，作为RA逆转肿瘤转化的作用机制。因此，基本假设是RA诱导具有不同信号产生能力的CD 38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由RA引起的分化/停滞程序。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.