Regulation of tumor promotion by RasGRP1

描述(申请人提供)：促癌是致癌过程中一个可逆和非遗传毒性的阶段，因此，这一过程的各个组成部分是基于机制的抗癌和化学预防药物开发的中心目标。在化学致癌的小鼠皮肤模型中，致癌物处理的表皮暴露在佛波酯中，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性扩张，从而实现促癌作用。佛波醇酯和RAS信号在肿瘤促进中的相互作用的性质尚未确定。虽然蛋白激酶C(PKC)历来被认为负责佛波酯的所有作用，但非PKC受体的发现使人们对PKC独有的作用的假设产生了怀疑。我们最近鉴定了新的RAS激活剂RASGRP1是佛波酯的高亲和力受体，我们的初步数据表明RASGRP1表达于表皮角质形成细胞，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和佛波酯信号之间的一种新的直接联系。本提案将解决这一可能性。我们假设佛波酯可以调节角质形成细胞中RASGRP1的活性，这种调节作用与癌症形成过程中肿瘤促进激活的机制有关。该假说的具体目的是：(1)确定RASGRP1在佛波酯诱导的角质形成细胞反应中的功能作用，包括生长停滞、分化和凋亡；(2)确定在启动(H-RAS突变的)角质形成细胞中，RASGRP1信号是否因RASGRP1表达水平的变化、底物亲和力的变化或两者兼而有之而改变；以及(3)建立体内模型，以研究RASGRP1在皮肤癌和肿瘤促进(RASGRP1基因敲除和转基因动物)中的作用。综上所述，这项研究的结果有可能揭开一个新的分子靶点，传递佛波酯-参与致癌的信号。这些信息可能导致未来开发针对肿瘤促进活动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.