Cyclin D1 Associates with the TBP-associated factor TAFII250 to regulate Sp1-mediated transcription

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Abstract
We have previously shown that Sp1-mediated transcription is stimulated by Rb and repressed by cyclin D1. The stimulation of Sp1 transcriptional activity by Rb is conferred, in part, through a direct interaction with the TBP-associated factor TAFII250. Here we investigated the mechanism(s) through which cyclin D1 represses Sp1. We examined the ability of cyclin D1 to regulate transcription mediated by Gal4-Sp1 fusion proteins, which contain the Gal4 DNA-binding domain and Sp1 trans-activation domain(s). The domain of Sp1 sufficient to confer repression by cyclin D1 was mapped to a region important for interaction with TAFII110. We further demonstrate that TAFII250-cyclin D1 complexes can be immunoprecipitated from mammalian and baculovirus-infected insect cells and that recombinant GST-TAFII250 (amino acids 1 – 434) associates with cyclin D1 in vitro. Moreover, the overexpression of Rb or CDK4 reduced the level of TAFII250-cyclin D1 complex. The amino terminus of cyclin D1 (amino acids 1 – 100) was sufficient for association with TAFII250 and for repressing Sp1-mediated transcription. Taken together, the results suggest that cyclin D1 may regulate transcription by interacting directly or indirectly with TAFII250.