Role of SIRT1 in melanocyte biology and melanocyte transformation

描述（由申请人提供）：遗传解剖的一个复杂的过程，如黑素细胞转化是一项艰巨的任务。事实上，人类黑素细胞的不同分化阶段，例如代表疾病进展不同阶段的正常黑素细胞、痣和黑素瘤，反映了不同的基因表达模式。深入了解细胞增殖和细胞周期进程的遗传和表观遗传控制，可以提供有关正常黑素细胞转化为肿瘤表型的关键信息。SIRT 1是SIR 2家族中的一个成员，在肿瘤的发生、发展过程中发挥着重要的作用。许多关键蛋白质，包括p53和FoxO转录因子，已被确定为SIRT 1底物。SIRT 1在癌症中的作用和功能已经变得非常复杂，并且还没有得到很好的理解。尽管大量研究表明SIRT 1具有肿瘤促进功能，但许多研究都主张其肿瘤抑制作用。SIRT 1在不同的组织环境中发挥双重功能，这取决于不同SIRT 1下游靶点和调节SIRT 1的因子的时空分布和丰度。SIRT 1在黑素细胞生物学、黑素细胞转化和进展中的作用和功能意义尚不清楚。在我们的初步数据中，我们发现i）SIRT 1在黑素瘤细胞和组织中以高得多的水平表达，和ii）SIRT 1的抑制导致黑素瘤细胞中显著的抗增殖反应。此外，观察到的SIRT 1抑制作用伴随着p53的转录激活。这是特别令人感兴趣的，因为黑色素瘤是少数几种很少具有p53突变的癌症之一，这可能为改变p53调节而没有实际突变提供替代途径。因此，基于现有的文献和我们令人兴奋的初步数据，在这项研究中，我们建议测试的假设，SIRT 1通过调节其下游调控的p53，FoxO和E2 F1转录因子在黑素细胞转化和黑色素瘤生存中起着至关重要的作用。本研究的主要目的是：1）研究SIRT 1的表达谱及其与下游调控因子的特异性相关性（即黑色素瘤发生过程中的p53、FoxO和E2 F1），并确定SIRT 1是否参与体外模型中的黑色素细胞转化; 2）将p53、FoxO和E2 F1转录因子的参与定义为黑色素细胞中SIRT 1的下游决定子;和3）确定SIRT 1抑制在植入黑素瘤细胞的无胸腺裸鼠体内的治疗意义。我们期望本申请中提出的研究结果可以定义SIRT 1在黑素细胞生物学、黑素细胞转化和黑色素瘤进展中的作用和机制。这最终可能具有治疗意义。

DESCRIPTION (provided by applicant): The genetic dissection of a complex process such as melanocytic transformation is a daunting task. Indeed, different stages of differentiation of human melanocytic cells, such as normal melanocytes, nevi and melanomas representing different stages of disease progression, reflect distinct gene expression patterns. An in-depth knowledge of the genetic and epigenetic controls of cellular proliferation and cell cycle progression may provide critical information regarding the conversion of a normal melanocyte to its neoplastic phenotype. Over the past decade, SIRT1, a member of SIR2 family of sirtuin class III histone deacetylases, has garnered tremendous attention in neoplastic transformation and progression. A number of critical proteins, including p53 and FoxO transcription factors, have been identified as SIRT1 substrates. The roles and functions of SIRT1 in cancer have become extremely complex and are not well understood. Whereas a plethora of studies have shown a tumor promoter function of SIRT1, a number of studies have advocated its tumor suppressor role. It appears that SIRT1 plays dual functions in different tissue contexts depending on the spatial and temporal distribution and abundance of different SIRT1 downstream targets and factors that regulate SIRT1. The role and functional significance of SIRT1 in melanocyte biology, melanocytic transformation and progression is not clear. In our preliminary data, we have found that i) SIRT1 is expressed at much higher levels in melanoma cells and tissues, and ii) inhibition of SIRT1 results in a significant anti-proliferative response in melanoma cells. Further, the observed effects of SIRT1 inhibition were accompanied with transcriptional activation of p53. This is of particular interest because melanoma is one of the few cancers which rarely possess p53 mutations and this may provide an alternative route for altered p53 regulation without actual mutations. Thus, based on available literature and our exciting preliminary data, in this study we propose to test the hypothesis that SIRT1 plays a critical role in melanocytic transformation and melanoma survival via modulating its downstream regulation of p53, FoxO, and E2F1 transcription factors. The following aims are proposed: 1) to evaluate the expression profile of SIRT1 and its specific correlations with downstream regulators (viz. p53, FoxOs and E2F1 during melanomagenesis), and to determine if SIRT1 is involved in melanocytic transformation in an in vitro model; 2) to define the involvement of p53, FoxO and E2F1 transcription factors as downstream determinants of SIRT1 in melanocytic cells; and 3) to determine the therapeutic significance of SIRT1 inhibition in vivo in athymic nude mice implanted with melanoma cells. We expect that the outcome of studies proposed in this application may define the role and mechanism of SIRT1 in melanocyte biology, melanocytic transformation and melanoma progression. This may ultimately have therapeutic implications.