T-box1 (TBX1) has been identified as a candidate disease-causing gene in DiGeorge syndrome/conotruncal anomaly face syndrome (DGS/CAFS). Tbx1 can function as a transcriptional transactivator as well as a transrepressor. Although the transactivating role of Tbx1 has been the focus of a number of published studies, its transrepression activity has been largely unexplored. Thus, this study centers on the identification of potential transrepressed targets of Tbx1. By subtractive hybridization, we compared the expression profiles of control mouse P19 cells and P19 cells depleted of Tbx1 via RNA interference. We identified 127 genes that were potentially transrepressed by Tbx1. Of the transrepressed genes, we focused on Ywhae and C1qbp and carried out promoter assays. The results showed that Tbx1 potentially transrepresses the promoter activities of these genes via palindromic sequences, including 5'-CCACAG-3' and 5'-(C/G)TGTG(C/G)-3', harbored within the promoters. Electromobility shift assays also showed that Tbx1 specifically interacts with certain portions of these promoter sequences. Moreover, the construction of Tbx1 mutants containing known human TBX1 mutations showed that these mutations result in the loss of Tbx1 transrepression activity. These results indicate that Tbx1 functions as a transrepressor in a gene regulation network, wherein Ywhae and C1qbp are 2 of the targets transrepressed by Tbx1 via T-box binding elements. Hence, the loss of TBX1 transrepression activity could be associated with the disease phenotypes of patients with DGS/CAFS.
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