Molecular mechanism of oncogenesis by translcated genes encoding chromath remodelhg factors fused to a nucleoporin

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The ultimate goal of this study is to clarify the molecular and cellular mechanism of oncogenesis by chromatin remodeling factor-nucleoporin fusion genes such as TAF-I (Template Activating Factor-I) β/SET-CAN and DEK-CAN associated with myeloid leukemia. TAF-Iβ/SET is a histone chaperone and DEK is identified as a factor involved in regulation of the chromatin structure, while CAN, alternatively designated Nup214, is one of components of nuclear pore complexes.Introduction of TAF-Iβ/SET-CAN into normal cells, for instance, NIH3T3 cells resulted in cell transformation and tumor formation in nude mice. TAF-Iβ-CAN was found to be present in the nucleus as distinct dots. hCRM1, an exportin that binds to CAN bound to TAF-Iβ-CAN, so that NES proteins, molecular targets of hCRM1, were found accumulated in the nucleus. Knock-down of expression of TAF-Iβ-CAN in TAF-Iβ-CAN-transformed cells with specific si RNA cancelled some of the cell transformation properties, suggesting that TAF-Iβ/SET-CAN is involved in cell transformation through at least two independent mechanisms. Studies on parts of the fusion gene products revealed several novel findings: TAF-Iβ/SET bound to MLL, a trxG family member, and was found to be involved in expression regulation of MLL target genes with MLL. TAF-II/NAP-1, a structural and functional homologue of TAF-Iβ/SET, regulated the mitotic progression through its nuclear export. It was found that TAF-III, a histone chaperone consists of nucleophosmin/B23 and RNA molecules. Experiments using dominant-negative mutants for the TAF-III activity showed that TAF-III is involved in regulation of rRNA synthesis through its chromatin regulation activity and thereby in cell growth rate control.