TSA downregulates Wilms tumor gene 1 (Wt1) expression at multiple levels

The Wilms tumor gene WT1 encodes a zinc-finger transcription factor that is inactivated in a subset of pediatric kidney cancers. During embryogenesis, WT1 is expressed in a time- and tissue-specific manner in various organs including gonads and kidney but also in the hematopoietic system. Although widely regarded as a tumor suppressor gene, wild-type WT1 is overexpressed in a variety of hematologic malignancies, most notably in acute lymphoblastic leukemia as well as myelodysplastic syndromes. Reduction of WT1 expression levels leads to decrease of proliferation and apoptosis of leukemic cells, suggesting that in certain contexts WT1 might act as an oncogene. We show here that histone deacetylase inhibitors like Trichostatin A (TSA) can promptly and dramatically downregulate Wt1 expression levels in different cell lines. This effect was mostly due to the cessation of transcription and was mediated by sequences located in intron 3 of Wt1. In addition, TSA also caused enhanced degradation of the Wt1 protein by the proteasome. This was at least in part due to induction of the ubiquitin-conjugating enzyme UBCH8. Thus, downregulation of Wt1 expression might contribute to the beneficial effects of histone deacetylase inhibitors that are currently used in clinical trials as cancer therapeutics.