Role of SIRT1 in melanocyte biology and melanocyte transformation

描述（由申请人提供）：黑素细胞转化等复杂过程的遗传解剖是一项艰巨的任务。事实上，人类黑素细胞分化的不同阶段，如正常黑素细胞、痣和黑素瘤代表疾病进展的不同阶段，反映了不同的基因表达模式。对细胞增殖和细胞周期进程的遗传和表观遗传控制的深入了解可能为正常黑素细胞向肿瘤表型的转化提供关键信息。在过去的十年中，SIRT1作为sirtuin III类组蛋白去乙酰化酶SIR2家族的一员，在肿瘤的转化和进展中受到了极大的关注。许多关键蛋白，包括p53和FoxO转录因子，已被确定为SIRT1底物。SIRT1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SIRT1具有肿瘤启动子功能，但也有一些研究主张SIRT1具有肿瘤抑制作用。SIRT1似乎在不同的组织环境中发挥双重功能，这取决于不同SIRT1下游靶点和调节SIRT1的因子的时空分布和丰度。SIRT1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) SIRT1在黑色素瘤细胞和组织中的表达水平要高得多，ii)抑制SIRT1会导致黑色素瘤细胞中显著的抗增殖反应。此外，观察到的SIRT1抑制效应伴随着p53的转录激活。这是特别有趣的，因为黑色素瘤是少数几种很少有p53突变的癌症之一，这可能为p53调节的改变提供了一种没有实际突变的替代途径。因此，基于现有文献和我们令人兴奋的初步数据，在本研究中，我们提出验证SIRT1通过调节其下游p53， FoxO和E2F1转录因子在黑素细胞转化和黑色素瘤存活中起关键作用的假设。提出以下目标：1)在体外模型中评估SIRT1的表达谱及其与下游调节因子（即黑色素瘤形成过程中的p53、FoxOs和E2F1）的特定相关性，并确定SIRT1是否参与黑色素细胞转化；2)确定p53、FoxO和E2F1转录因子参与黑素细胞SIRT1的下游决定因素；3)确定体内SIRT1抑制对植入黑色素瘤细胞的胸腺裸鼠的治疗意义。我们期望在本应用中提出的研究结果可以确定SIRT1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。这可能最终具有治疗意义。

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.