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.
