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。目前没有治疗方法可以增加转移性疾病出现后的预期寿命。家族性和散发性黑色素瘤的分子分析已经鉴定了许多致癌改变，包括Ras、B-Raf、PTEN、Akt和Ink 4a/Arf。虽然Ras驱动的通路已经研究了许多年，但我们已经观察到Ras下游效应子的显著差异以及在不同生理背景下产生的复杂生物学功能。使用在黑素细胞中具有Ras靶向表达的转基因小鼠，我们已经通过实验验证了激活的Ras和下游信号传导途径在黑色素瘤发展和肿瘤进展中的表达的重要性。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抗性的选择性压力。我们已经发现，皮肤具有降低的氧张力，这既可以增强具有激活的Ras癌基因或Akt基因的黑素细胞的恶性潜能，又可以通过衰老促进黑素细胞存活。Akt 3的组成性激活已在黑色素瘤进展中描述。Ras依赖性和非依赖性的Akt活化导致抗凋亡信号传导以及帽依赖性翻译的失调。使用我们开发的转基因小鼠（Akt 3和Ras）和敲除小鼠（PTEN，VHL，HIF 1a）以及从这些小鼠中培养的黑素细胞，我们建议确定在缺氧微环境（或激活的HIF 1a）存在下PI 3激酶-Akt-mTOR通路的激活支持黑素细胞存活并促进黑素细胞转化的机制。我们将证实我们在小鼠系统中的观察与人类黑素细胞病变和培养的人类黑素细胞和黑色素瘤细胞在类似的条件下的研究。Akt通路中的关键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剂提供了重要信息。

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.