| Research Abstract |
A number of chimeric transcription factors due to tumor-specific chromosomal translocation have been reported in human sarcomas. In order to understand fundamental function of the chimeric transcription factors we have isolated target genes for EWS-ATF1 and EWS-FLI1 in clear cell sarcoma and Ewing sarcoma, respectively, by using a DNA-protein crosslinking/immunopurification/GFP reporter assay (DIGR). Expression of candidate target genes was examined in original tumor cells, and difference of expression induction by chimeric and wild type transcription factors was compared. We have identified POSH, ATM, ARNT2, GPP34, NKX6.1 and NYD-SP28 as target genes for EWS-ATF1 in clear cell sarcoma. EWS-ATF1 repressed POSH expression while it upregulated the other targets. Endogenous POSH expression was suppressed in the clear cell sarcoma cell line, and induction of POSH brought apoptotic cell death to the same cell, suggesting that repressed expression of POSH in clear cell sarcoma may be relevant to the normal signaling pathway in apoptosis. Moreover, BCAR3, RPS18 and p29 have been identified as EWS-FLI1 targets in Ewing sarcoma, indicating that the DIGR method could be applied to broad range of transcription factors. Recently, we have identified a novel chimera in Ewing Sarcoma with t(4;19) translocation. The chimera consists of the HMG box gene CIC and the double homeobox gene DUX4, and it exemplifies the EWS-ETS independent molecular pathway in Ewing sarcoma.
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