MiT Transcription Factor Family in Pediatric Solid Tumor

描述（由申请人提供）：对儿童和成人实体瘤中染色体易位的鉴定导致了对正常和肿瘤生长重要基因的发现。透明细胞肉瘤是儿童和年轻人的一种转移性软组织肿瘤，5年总死亡率为50%，与EWS与ATF1融合的特定染色体易位有关。这种融合癌蛋白通过转录激活小眼球转录因子（MITF），该因子是黑素细胞分化、增殖和存活的主要调节因子。MITF与TFEB、TFEC和TFE3共同构成MiT家族的基本螺旋-环-螺旋亮氨酸拉链转录因子。我们已经证明，MITF在透明细胞肉瘤中的异常表达导致肿瘤的黑素细胞分化，并在其增殖和/或存活中起关键作用。此外，我们还发现了一种独特的TFEB易位参与儿童乳头状肾细胞癌的亚群。综上所述，这些结果表明，失调的MiT活性在这些肿瘤中起着关键的致癌作用。这个项目从机制上考察了MiT家族在这些肿瘤中的作用。为了了解转录失调的可能作用，将确定MiT的正常表达模式，然后将其与肿瘤细胞表达进行比较，并通过对原发肿瘤标本的类似分析来验证这些结果。MiT翻译后修饰在肿瘤发生中的作用也将被研究。将探讨视网膜母细胞瘤途径与MiT家族之间的相互作用。MiT家族成员与转录因子MYC一起，通过E-box启动子元件激活重叠的靶基因。这些肿瘤表达的特定MiT靶点将采用基于候选基因的方法进行鉴定，然后采用基于微阵列杂交的综合基因表达谱。假定的靶基因的鉴定将随后进行生物学验证，重点是治疗相关的靶标。其中一个例子是酪氨酸激酶受体MET。有趣的是，MET在家族性和一些散发性乳头状肾细胞癌中都发生突变，并且是黑色素细胞中MITF的靶点。我们将探讨这种联系及其治疗意义。通过检查MiT功能和下游靶点，对MiT家族在透明细胞肉瘤和乳头状肾细胞癌中的作用的机制理解将对这些肿瘤和其他MiT相关肿瘤（如黑色素瘤）产生影响。

DESCRIPTION (provided by applicant): The identification of chromosomal translocations in solid tumors of children and adults has led to the discovery of genes important for normal and tumor growth. Clear cell sarcoma, a metastatic soft tissue tumor of children and young adults with an overall 5-year mortality rate of 50%, is associated with a specific chromosomal translocation that fuses EWS with ATF1. This fusion oncoprotein transcriptionally activates the microphthalmia transcription factor (MITF), a master regulator of melanocyte differentiation, proliferation and survival. MITF, together with TFEB, TFEC and TFE3, comprise the MiT family of basic helix-loop-helix leucine zipper transcription factors. We have shown that the aberrant expression of MITF in clear cell sarcoma results in the melanocytic differentiation of this tumor and plays a key role in its proliferation and/or survival. Furthermore, we have discovered the involvement of a unique TFEB translocation in a subset of pediatric papillary renal cell carcinomas. Taken together, these results suggest that dysregulated MiT activity serves a critical oncogenic function in these tumors. This project mechanistically examines the role of the MiT family in these tumors. To understand the possible role of transcriptional dysregulation, the normal pattern of MiT expression will be determined then compared to tumor cell expression, validating these results with similar analyses of primary tumor specimens. The role of MiT posttranslational modification in oncogenesis will also be examined. An interaction between the retinoblastoma pathway and the MiT family will be explored. MiT family members, along with the transcription factor MYC, activate overlapping target genes through an E-box promoter element. Specific MiT targets expressed by these tumors will be identified employing a candidate gene based approach followed by comprehensive microarray hybridization-based gene expression profiling. The identification of putative target genes will be followed by biological validation with emphasis on therapeutically relevant targets. One such example is the receptor tyrosine kinase MET. Intriguingly, MET is both mutated in familial and some sporadic papillary renal cell carcinomas and a target of MITF in melanocytes. This connection and its therapeutic implications will be explored. By examining both MiT function and down-stream targets, a mechanistic understanding of the role of the MiT family in clear cell sarcoma and papillary renal cell carcinoma will emerge with implications for these and other MiT-associated tumors such as melanoma.