Regulation of tumor promotion by RasGRP1

描述（由申请人提供）：肿瘤促进是癌变过程中一个可逆且无基因毒性的阶段，因此，该过程的各个组成部分是开发基于机制的抗癌和化学预防药物的中心目标。在化学诱导癌变的小鼠皮肤模型中，肿瘤促进是通过将致癌物处理过的表皮暴露于佛波酯中实现的，佛波酯诱导携带致癌物诱导的H-Ras基因激活突变的角质形成细胞克隆扩增。佛波酯和Ras信号在肿瘤促进中的相互作用的性质尚未明确。虽然蛋白激酶C （PKC）一直被认为是所有磷酯作用的原因，但非PKC受体的发现对PKC介导的唯一作用的假设提出了质疑。我们最近将新型Ras激活因子RasGRP1描述为一种高亲和力的磷酸酯受体，我们的初步数据表明，RasGRP1在表皮角化细胞中表达，这是化学致癌的靶细胞。这些数据表明，RasGRP1可能代表了表皮中Ras和磷酯信号之间的一种新的直接联系。本提案将处理这种可能性。我们假设磷酸酯可以调节角质形成细胞中的RasGRP1活性，并且这种调节有助于在癌症形成过程中促进肿瘤激活的机制。验证该假设的具体目的是：(1)明确RasGRP1在角化细胞中phorbol酯诱导的反应中的功能作用，包括生长停滞、分化和凋亡；(2)确定启动的（h - ras突变的）角质形成细胞中RasGRP1信号是否发生改变，通过改变RasGRP1的表达水平，改变底物亲和力，或两者兼有；(3)建立体内模型，研究RasGRP1在皮肤致癌和促瘤中的作用（敲除和转基因RasGRP1动物）。综上所述，本研究的结果有可能揭示参与癌变过程的磷酯信号传递的新分子靶点。这一信息可能导致未来开发针对肿瘤促进事件的新型化学预防化合物的方法。

DESCRIPTION (provided by applicant): Tumor promotion is a reversible and non-genotoxic stage in carcinogenesis and, as a consequence, the various components of this process are central targets for the development of mechanism-based anticancer and chemopreventive drugs. In the mouse skin model of chemical-induced carcinogenesis, tumor promotion is achieved by exposure of carcinogen-treated epidermis to phorbol esters, which induce the clonal expansion of those keratinocytes carrying the carcinogen-induced activating mutation in the H-Ras gene. The nature of the interaction between phorbol esters and Ras signaling in tumor promotion has not been defined yet. Although protein kinase C (PKC) has historically been considered responsible for all phorbol ester actions, the discovery of non-PKC receptors casts doubts on the assumption of an exclusive PKC-mediated effect. We have recently characterized the novel Ras activator RasGRP1 as a high affinity receptor for phorbol esters, and our preliminary data indicate that RasGRP1 is expressed in the epidermal keratinocyte, the target cell in chemical carcinogenesis. These data suggest that RasGRP1 may represent a novel and direct link between Ras and phorbol ester signaling in the epidermis. The present proposal will address this possibility. We hypothesize that phorbol esters can modulate RasGRP1 activity in keratinocytes, and that this modulation contributes to the mechanisms activated by tumor promotion during cancer formation. The specific aims to test the hypothesis are: (1) to define the functional role of RasGRP1 on the responses induced by phorbol esters in keratinocytes, including growth arrest, differentiation, and apoptosis; (2) to determine if RasGRP1 signaling is altered in initiated (H-Ras-mutated) keratinocytes, either by changes in the level of expression of RasGRP1, changes in substrate affinity, or both; and (3) to establish in vivo models to investigate the role of RasGRP1 in skin carcinogenesis and tumor promotion (knockout and transgenic animals for RasGRP1). Taken together, the results of this study have the potential to unravel a new molecular target for the transmission of phorbol ester-signals involved in carcinogenesis. This information could lead to future approaches for developing novel chemopreventive compounds targeted to tumor promotion events.