Nuclear receptor (NR) transactivation involves multiple coactivators, and the molecular basis for how these are functionally integrated needs to be determined to fully understand the NR action. Activating signal cointegrator-2 (ASC-2), a transcriptional coactivator of many NRs and transcription factors, forms a steady-state complex, ASCOM (for ASC-2 complex), which contains histone H3-lysine-4 (H3K4) methyltransferase MLL3 or its paralog MLL4. Here, we show that ASCOM requires a functional cross talk with the ATPase-dependent chromatin remodeling complex Swi/ Snf for efficient NR transactivation. Our results reveal that ASCOM and Swi/Snf are tightly colo- calized in the nucleus and that ASCOM and Swi/Snf promote each other's binding to NR target genes. We further show that the C-terminal SET domain of MLL3 and MLL4 directly interacts with INI1, an integral subunit of Swi/Snf. Our mutational analysis demonstrates that this interaction underlies the mutual facilitation of ASCOM and Swi/Snf recruitment to NR target genes. Importantly, this study uncovers a specific protein-protein interaction as a novel venue to couple two distinct enzymatic coactivator complexes during NR transactivation.
ASJC Scopus subject areas
- Molecular Biology