Melanocyte Survival and Transformation: Hypoxia & P13 Kinase/Akt/mTOR Signaling

描述（由申请人提供）：恶性黑色素瘤是一种致命的恶性肿瘤，由于其高转移倾向和对现有治疗的耐药性。目前还没有一种治疗方法可以在出现转移性疾病时延长预期寿命。家族性和散发性黑色素瘤的分子分析已经确定了许多致癌改变，包括Ras、B-Raf、PTEN、Akt和Ink4a/Arf。尽管对Ras驱动通路的研究已经进行了多年，但我们已经观察到Ras的下游效应物和在不同生理环境下产生的复杂生物学功能存在显著差异。通过在黑素细胞中靶向表达Ras的转基因小鼠，我们通过实验验证了激活Ras的表达和下游信号通路在黑色素瘤发生和肿瘤进展中的重要性。肿瘤的微环境，特别是缺氧，已被证明是影响肿瘤进展和治疗抵抗的选择性压力。我们发现，皮肤的氧张力降低，既可以增强Ras癌基因或Akt基因活化的黑素细胞的恶性潜能，也可以通过延缓衰老来促进黑素细胞的存活。Akt3的组成激活在黑色素瘤的进展中已经被描述。Akt的激活，无论是依赖于ras还是独立的，都会导致抗凋亡信号以及帽依赖翻译的失调。利用我们开发的转基因小鼠（Akt3和Ras）和敲除小鼠（PTEN， VHL, HIF1a）和从这些小鼠培养的黑素细胞，我们提出确定在缺氧微环境（或激活的HIF1a）存在下激活pi3kinase - akt - mtor通路支持黑素细胞存活和促进黑素细胞转化的机制。我们将在小鼠系统中通过研究人类黑素细胞病变和在类似条件下培养的人类黑素细胞和黑色素瘤细胞来证实我们的观察。Akt通路中重要遗传元件的鉴定以及皮肤微环境对黑素细胞存活和转化的影响为开发有效的治疗和化学预防药物提供了重要信息。

DESCRIPTION (provided by applicant): Malignant melanoma is a deadly malignancy due to its high propensity to metastatize and its resistance to existing therapies. There are currently no treatments that increase life expectancy once metastatic disease presents. Molecular analyses of familial and sporadic melanomas have identified a number of oncogenic alterations including Ras, B-Raf, PTEN, Akt, and Ink4a/Arf. Though Ras driven pathways have been studied for a number of years, we have observed significant differences in downstream effectors of Ras and in the complex biological functions that result under different physiologic contexts. Using a transgenic mouse with targeted expression of Ras in melanocytes we have experimentally validated the importance of expression of an activated Ras and downstream signaling pathways in melanoma development and tumor progression. The microenvironment of the tumor, in particular hypoxia, has been shown to act as a selective pressure effecting tumor progression and therapeutic resistance. We have found that the skin possess reduced oxygen tension that could both enhance the malignant potential of melanocytes with an activated Ras oncogene or Akt gene and may contribute to melanocyte survival, by passing senescence. Constitutive activation of Akt3, has been described in melanoma progression. Akt activation, both Ras-dependent and independent, leads to anti-apoptotic signaling as well as dysregulation of cap dependent translation. Using transgenic mice that we developed (Akt3 and Ras) and knock out mice (PTEN, VHL, HIF1a) and melanocytes cultured from these mice, we propose to identify the mechanism by which activation of the PI3kinse-Akt-mTOR pathway in the presence of a hypoxic microenvironment (or activated HIF1a) support melanocyte survival and promote melanocyte transformation. We will substantiate our observation in the mouse systems with studies of human melanocytic lesions and cultured human melanocytes and melanoma cells under similar conditions. Identification of the essential genetic elements in Akt pathway and the impact of the microenvironment of the skin on melanocyte survival and transformation provide crucial information for the development of effective therapeutic and chemopreventive agents.