The Role of AP-1 and Other Transcription Factors in Cancer Cause and Prevention

AP-1转录因子是Jun和Fos家族蛋白的异源二聚体，与某些基因转录启动子上的特定序列结合并驱动其转录。AP-1活性在几个人类癌症部位的肿瘤进展过程中升高。在与人类致癌相关的多种小鼠模型中，转基因小鼠中显性负性Jun的角质形成细胞特异性表达抑制了AP-1诱导的AP-1和肿瘤的形成，而不抑制细胞增殖或细胞存活(Young等人，PNAS，1999)。其中包括因人类乳头瘤病毒E7的表达而提高皮肤肿瘤促进反应的小鼠(Young等人Molec Carc 2002)和通过反复暴露于UVB而诱导形成鳞癌的小鼠(Cooper等人Molec癌症RES 2003)。四环素调控的67的表达最近在合作者鲍威尔·布朗的实验室中被定向到乳腺上皮细胞(Shenet al Dev Biol，2006)，并正在测试其在预防HER2/Neu诱导的乳腺癌发生中的有效性。转录因子NFkappa B与AP-1协调调节，表明这两种因子在转化中可能具有重要作用(Li et，Cancer res 1997)。最近的观察发现，NFkB无反应性是JB6模型中转化无反应性的一个解释(Hsu等人，癌症RES 2001，Hu等人癌症发生2004年)。转化抵抗细胞由于不能激活NFkappa B p65蛋白而无反应。S536处的p65磷酸化对于DNA结合、泛素化和抑制物IkappaBα的降解是重要的(Hu等人Molec癌症2005年)。靶向AP-1和NFkB上调可防止肿瘤的推进和进展的观察已从小鼠JB6模型扩展到小鼠和人类角质形成细胞进展模型，以及转基因小鼠模型。表达AP-1/NFkB抑制因子67的转基因小鼠为鉴定AP-1或NFkB在肿瘤转化中起关键作用的靶基因提供了一个有价值的机会。表达芯片分析揭示了TAM67靶基因在驱动癌症发生中的功能意义。这样的靶基因可能是癌症预防的新的分子靶点(Young等人在2003年的Molec医学趋势中)。最近的研究已经确定染色质结构蛋白HMGA1(Dhar等人癌基因2004)、COX-2和骨桥蛋白(Matthews等人癌症RES 2007)作为TAM67的重要功能靶点的重要性。与分子靶标开发计划合作的一个有前途的药物发现项目旨在识别模仿TAM67特异性的化合物，即在不抑制细胞增殖或细胞存活的情况下防止肿瘤发生。对300,000种合成和天然产物进行的初步高通量筛选与细胞增殖(XTT)分析相结合，产生了一组小的命中结果(Ruocco等人J Biomolec Screen 2007)。二次检测是评估对NFkB的抑制作用。对遗传性肥胖小鼠的新干预研究采用了豆类饮食，测试了暴露于偶氮甲烷后对结肠癌的缓解作用。在最近完成的息肉预防试验中，以豆类为基础的饮食被选为模拟条件，在该试验中，食用最高四分之一豆类(海军、利马、肾脏、黑色等)的人类受试者显示，晚期腺瘤(E.Lanza和同事)的发病率降低了3%。整个豆类和两个豆类部分显示出降低肿瘤多样性的效果(Bobe等人，提交)。目前的研究目的是在有效条件下确定豆类饮食的重要分子靶标以及预测生物标记物。

The AP-1 transcription factor is a heterodimer of Jun and Fos family proteins that binds to a specific sequence on the transcriptional promoter of certain genes and drives their transcription. AP-1 activity is elevated during tumor progression in several human cancer sites. Keratinocyte-specific expression of Dominant Negative Jun in transgenic mice inhibits induced AP-1 and tumorigenesis without inhibiting cell proliferation or cell survival in multiple mouse models relevant to human carcinogenesis (Young et al., PNAS, 1999). Among these are mice whose skin tumor promotion response is elevated by expression of Human Papilloma Virus E7 (Young et al Molec Carc 2002) and mice induced to form squamous carcinomas by repeated exposure to UVB (Cooper et al Molec Cancer Res 2003). Tetracycline regulated expression of TAM 67 has recently been directed to mammary epithelia in the laboratory of collaborator Powel Brown (Shen et al Dev Biol 2006) and is being tested for efficacy in preventing HER2/Neu induced mammary carcinogenesis. The transcription factor NFkappa B is coordinately regulated with AP-1, suggesting the possible importance of both factors in transformation (Li et, Cancer Res 1997). Recent observations have identified NFkB non-responsiveness as an explanation for transformation non-responsiveness in the JB6 model (Hsu et al, Cancer Res 2001, Hu et al Carcinogenesis 2004). Transformation resistant cells owe their nonresponsiveness to an inability to activate NFkappa B p65 protein. p65 phosphorylation at S536 is important for DNA binding and for ubiquitination and degradation of inhibitor IkappaB alpha (Hu et al Molec Carcinog 2005). The observation that targeting AP-1 and NFkB elevation prevents tumor promotion and progression has been extended from the mouse JB6 model to mouse and human keratinocyte progression models, and to transgenic mouse models. Transgenic mice expressing AP-1/ NFkB inhibitor TAM 67 present a valuable opportunity to identify AP-1 or NFkB target genes whose expression is critical to neoplastic transformation. Expression microarray analysis has revealed TAM67 target genes that are being queried for functional significance in driving carcinogenesis. Such target genes may be promising new molecular targets for cancer prevention (Young et al Trends in Molec Medicine 2003). Recent studies have established the importance of chromatin architectural protein HMGA1 (Dhar et al Oncogene 2004), COX-2, and osteopontin (Matthews et al Cancer Res 2007) as functionally significant TAM67 targets. A promising drug discovery project in collaboration with the Molecular Targets Development Program aims to identify compounds that mimic the specificity of TAM67, i.e. that prevent tumorigenesis without inhibiting cell proliferation or cell survival. The primary high throughput screen of 300,000 synthetic and natural products coupled to a cell proliferation (XTT) assay yielded a small set of hits (Ruocco et al J Biomolec Screening 2007). The secondary assay is assessing inhibition of NFkB. New intervention studies in genetically obese mice employ a bean-based diet being tested for attenuation of colon carcinogenesis following exposure to azoxymethane. The bean-based diet was chosen to mimic conditions in the recently completed polyp prevention trial in which human subjects consuming the highest quartile of beans (navy, lima, kidney, black etc) showed a 3-fold reduction in ocurrence of advanced adenoma (E. Lanza and coworkers). The whole beans and two bean fractions showed efficacy in attenuating tumor multiplicity (Bobe et al, submitted). Current studies are aimed at identifying funtionally significant molecular targets of the bean diets under conditions of efficacy as well as predictive biomarkers.