RETINOID RECEPTOR FUNCTION IN SKIN CANCER PROGRESSION

鳞状细胞癌（SCC）是临床上最具侵袭性的形式， 非黑色素瘤皮肤癌，尽管积极治疗， 浸润性SCC病变复发率很高（30%）。 因而 迫切需要开发改进的治疗和 预防性治疗这种疾病。 维甲酸很重要 上皮分化和增殖的调节剂。 类视黄醇 有效治疗和预防上皮癌， 包括皮肤SCC。 然而，这种效应的机制不是 很好理解。 为了更好地设计化学预防疗法 对于皮肤SCC，更多关于维甲酸机制的信息 需要在这个系统中采取行动。 类维生素A发挥作用 主要通过核受体，视黄酸受体（RAR α， β和γ）和类维生素A X受体（RXR α、β和γ）， 类固醇激素受体超家族的成员。 类视黄醇受体 在几个系统中，损失与恶性肿瘤相关， 最近的研究表明，抑制RAR α，RAR γ和 患者SCC中RXR α的表达。 本研究基于 假设类维生素A受体丢失有助于恶性肿瘤的发生， 表型通过使上皮细胞对类维生素A具有抗性， 通常抑制致癌作用。 为了验证这一假设，HaCaT 细胞，一种自发永生化的，非肿瘤性的角质形成细胞， 选择衍生的细胞系。 这些细胞表达两种主要的 通常在皮肤中发现的类维生素A受体，RAR γ和RXR α，以及 保持相同的分化特征和反应， 类维生素A作为正常角质形成细胞。 HaCaT细胞是一种 对于癌前细胞，将用于完成以下任务 具体目标：1.）要创建RAR gamma null、RXT alpha null和 同源重组介导的RAR γ/RXR α双无效细胞 基因靶向2.）为了确定受体表达的缺失 导致改变的细胞表型，特别是关于 致瘤潜力、分化能力和对 维甲酸（RA）水平的变化。3.）第三章重新表达思念 受体（RAR γ或RXR α）在敲除细胞系中的稳定表达 转染以确定推定的表型是否 这是遗传病的直接结果。 体细胞 基因打靶方法已经成功地通过原理 研究人员分析F9胚胎中类维生素A受体功能 癌细胞 预期受体无效的产生 HaCaT细胞将提供一个同样强大的工具来了解 类维生素A受体在皮肤SCC发展中的作用，以及 在表皮分化中的作用。

Squamous cell carcinoma (SCC) is the most clinically aggressive form of non-melanoma skin cancer and in spite of aggressive treatment, deeply invasive SCC lesions recur at a high rate (30 percent). Therefore there is an urgent need for the development of improved therapeutic and preventive treatments for this disease. Retinoids are important modulators of epithelial differentiation and proliferation. Retinoids are effective in the treatment and prevention of epithelial cancers, including cutaneous SCC. However the mechanism for this effect is not well understood. In order to better design chemopreventive therapies for cutaneous SCC, more information about the mechanism of retinoid action in this system is needed. Retinoids exert their effects primarily through nuclear receptors, retinoic acid receptors (RARalpha, beta and gamma) and retinoid X receptors (RXRalpha, beta and gamma), members of the steroid hormone receptor superfamily. Retinoid receptor loss has been correlated with malignancy in several systems, and one recent study has demonstrated a suppression of RARalpha, RARgamma and RXRalpha expression in SCCs of patients. This study is based on the hypothesis that retinoid receptor loss contributes to the malignant phenotype by rendering epithelial cells resistant to retinoids, which wold normally suppress carcinogenesis. To test this hypothesis, HaCaT cells, a spontaneously immortalized, nontumorigenic, keratinocyte- derived cell line was chose. These cells express the two predominant retinoid receptors normally found in skin, RARgamma and RXRalpha, and retain the same differentiation characteristics and response to retinoids as normal keratinocytes. The HaCaT cells, which are a model for premalignant cells, will be used to accomplish the following specific aims: 1.) To create RARgamma null, RXTalpha null and RARgamma/RXRalpha double null cells by homologous recombination-mediated gene targeting. 2.) To determine whether loss of receptor expression results in an altered cell phenotype, specifically with regard to tumorigenic potential, differentiation capacity and response to alterations in retinoic acid (RA) levels. 3.) To reexpress the missing receptor (RARgamma or RXRalpha) in the knockout cell lines by stable transfection in order to determine whether the putative phenotype observed is the direct result of the genetic lesion. A somatic cell gene targeting approach has been successfully by the principle investigator to analyze retinoid receptor function in F9 embryonal carcinoma cells. It is expected that the generation of receptor null HaCaT cells will provide an equally powerful tool for understanding the role of retinoid receptors in the development of cutaneous SCC, as well as their role in epidermal differentiation.