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，其与某些基因的转录启动子上的特定序列结合并驱动其转录。虽然正常功能需要基础AP-1活性，但AP-1活性升高会驱动几个人类癌症部位的肿瘤进展。转基因小鼠中显性阴性Jun的角质细胞特异性表达抑制诱导的AP-1和肿瘤发生，而不抑制与人类致癌相关的多种小鼠模型中的细胞增殖或细胞存活（Young等人，PNAS，1999）。其中包括皮肤肿瘤促进反应因人乳头瘤病毒E7的表达而升高的小鼠（Young等Molec Carc 2002）和通过反复暴露于UVB而诱导形成鳞状细胞癌的小鼠（库珀等Molec Cancer Res 2003）。与Powel Brown（Shen et al Dev Biol 2006）合作，已将四环素调节的TAM 67表达导向乳腺上皮细胞，最近已检测其在预防HER 2/Neu诱导的乳腺癌发生中的疗效。结果显示AP-1阻滞剂对肿瘤前以及早期和晚期肿瘤发展具有显著抑制作用（Shen et al Ca Prev Res 2008）。重要的是，TAM 67表达在发生的乳腺肿瘤中沉默。与Jay Tichelaar的实验室合作，还发现诱导型TAM 67抑制化学诱导的肺癌发生（Cancer Prev Research 2010）。转录因子NF κ B与AP-1协同调节，表明两种因子在转化中的可能重要性（Li et，Cancer Res 1997）。最近的观察已经将NFkB无应答性鉴定为JB 6模型中转化无应答性的解释（Hsu等，Cancer Res 2001，Hu等Carcinogenesis 2004）。转化抗性细胞的无应答性归因于不能激活NF κ B p65蛋白。在S536处的p65磷酸化对于DNA结合以及抑制剂IkappaB α的泛素化和降解是重要的（Hu et al Molec Carcinog 2005）。靶向AP-1和NFkB升高可预防肿瘤促进和进展的观察结果已从小鼠JB 6模型扩展到小鼠和人角质形成细胞进展模型以及转基因小鼠模型。表达AP-1/ NFkB抑制剂TAM 67的转基因小鼠提供了鉴定AP-1或NFkB靶基因的宝贵机会，所述靶基因的表达对于肿瘤转化是关键的。表达微阵列分析揭示了TAM 67靶基因，这些靶基因正在被质疑在驱动癌发生中的功能意义。这样的靶基因可能是用于癌症预防的有希望的新分子靶标（Young等Trends in Molec Medicine 2003）。最近的研究已经确定了染色质结构蛋白HMGA 1（达尔等人Oncogene 2004）、考克斯-2、骨桥蛋白、尿激酶纤溶酶原激活剂、Cxcl 1和MMP-10（马修斯等人Cancer Res 2007）作为功能上重要的TAM 67靶标的重要性。最近发现的TAM 67/AP-1靶基因是硫氧还蛋白（sulfiredoxin），其是一种氧化还原酶，在肿瘤促进和侵袭以及在人类癌症中升高两者中具有重要功能（Wei Q等人，PNAS 2008和PNAS 2011）。与分子靶标实验室合作的药物发现项目已经鉴定出模拟TAM 67特异性的化合物，即抑制AP-1和/或NFkB并防止致癌而不抑制细胞增殖或细胞存活。与细胞增殖（XTT）测定偶联的300，000种合成和天然产物的初级AP-1高通量筛选产生了一小组AP-1命中（Ruocco等人J Biomolec Screening 2007）。二次试验评估了NF κ B的抑制作用，并鉴定了对NF κ B活性更高的AP-1抑制剂（Kang et al Mol Ca Ther，2009）。新的化学生物学实验室CCR正在生产这种NF κ B抑制剂的类似物。总之，该项目最近的成就包括1）发现新的AP-1调节基因，其衰减负责AP-1阻断剂TAM 67（特别是Sulfiredoxin和Wnt 5a）的致癌抑制活性，以及2）发现靶向AP-1或NF κ B而不抑制细胞活力的新的小分子。

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. Although basal AP-1 activity is needed for normal function, elevated AP-1 activity drives 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 been directed to mammary epithelia in collaboration with Powel Brown (Shen et al Dev Biol 2006) and has recently been tested for efficacy in preventing HER2/Neu induced mammary carcinogenesis. The results show substantial inhibition by the AP-1 blocker of preneoplastic as well as early and later stage tumor development (Shen et al Ca Prev Res 2008). Importantly, TAM67 expression was silenced in mammary tumors that developed. Inducible TAM67 has been found also to inhibit chemically induced lung carcinogenesis in collaboration with the laboratory of Jay Tichelaar (Cancer Prev Research 2010). 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, osteopontin, urokinase plasminogen activator, Cxcl1 and MMP-10 (Matthews et al Cancer Res 2007) as functionally significant TAM67 targets. The most recently discovered TAM67/AP-1 target gene is sulfiredoxin, a redox enzyme that is functionally significant both in tumor promotion and invasion as well as elevated in human cancer (Wei Q, et al, PNAS 2008 and PNAS 2011). A drug discovery project in collaboration with the Molecular Targets Laboratory has identified compounds that mimic the specificity of TAM67, i.e. that inhibit AP-1 and/or NFkB and prevent carcinogenesis without inhibiting cell proliferation or cell survival. The primary AP-1 high throughput screen of 300,000 synthetic and natural products coupled to a cell proliferation (XTT) assay yielded a small set of AP-1 hits(Ruocco et al J Biomolec Screening 2007). The secondary assay has assessed inhibition of NFkB and identified an AP-1 inhibitor that is even more active against NFkappa B (Kang et al Mol Ca Ther, 2009). The new Chemical Biology Laboratory, CCR is generating analogs of this NFkappaB inhibitor. In summary, recent accomplishments for this Project include 1) the discovery of new AP-1 regulated genes whose attenuation is responsible for the carcingenesis suppressing activity of AP-1 blocker TAM67, notably Sulfiredoxin and Wnt5a, and 2) the discovery of new small molecules that target AP-1 or NFkappaB without inhibiting cell viability.