TAF1, From a General Transcription Factor to Modulator of Androgen Receptor in Prostate Cancer
Annual summary rept. 15 Jan 2007-14 Jan 2008
BRITISH COLUMBIA UNIV VANCOUVER
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The androgen receptor AR is a ligand-activated transcription factor that binds androgen response elements ARE in the promoters of target genes. When bound to AREs, the receptor recruits chromatin-remodeling complexes, components of the general transcription machinery, and coregulator proteins. Using the N-terminus of AR as bait in the repressed transactivator yeast two-hybrid system, TATA binding protein-associated factor 1 TAF1 was identified. TAF1, a multifunctional protein that contains acetylation, ubiquitin activating and kinase domains, can interact with several proteins to promote or suppress gene transcription. We showed that AR and TAF1 co-immunoprecipitated in nuclear extracts from LNCaP cells, an AR-containing prostate cancer cell line. Furthermore, using ChIP assays with LNCaP cells, we found that both AR and TAF1 associated with an ARE in the proximal promoter of the PSA gene. To assess if TAF1 can modulate AR transcription, we performed transfection assays with androgen responsive luciferase reporters. Our results indicate that overexpression of TAF1 enhances AR activity several fold in LNCaP cells, whereas siRNA knockdown of TAF1 decreases AR transactivation. To differentiate between the direct effects of TAF1 on AR activity from general effects on transcription and to determine which TAF1 domains are involved in AR transactivation, we cloned and tested various functional domains of TAF1. Comparing AR-regulated and generic promoters, our results indicate that both the ubiquitin activating and the N-terminal kinase domains of TAF1 differentially enhance AR activity, but unlike full-length TAF1, have no effect on general gene transcriptional activity.
- Medicine and Medical Research