Abstract
BACKGROUND: The coiled-coil coactivator (CoCoA) enhances transcriptional activity of nuclear receptors, the xenobiotic aryl hydrocarbon receptor, and the lymphocyte enhancer factors (LEF) in the Wnt/beta-catenin signaling pathway. CoCoA is comprised of a large central coiled coil domain flanked by N-terminal and C-terminal activation domains (AD). The N-terminal AD of CoCoA is required for coactivator function with LEF and beta-catenin, while the C-terminal AD of CoCoA is required for coactivator function with nuclear receptors. We explored the role of sumoylation in regulating the activities of the two ADs and the coactivator function of CoCoA. RESULTS: The N-terminus of CoCoA is covalently modified by SUMO1 at Lys-29; both PIAS1 and ARIP3 function as E3 ligases. Fusion of SUMO1 to the N-terminus (mimicking sumoylation) reduced coactivator function of CoCoA with LEF1 and the activity of the N-terminal AD. The N- and C-termini of CoCoA can bind to each other, and C-terminal transactivation activity is attenuated in the presence of the N-terminus, indicating that the N-C interaction regulates the activity of the C-terminal AD. Fusion of SUMO1 to the N-terminal fragment of CoCoA reduced the N-C interaction and inhibition of C-terminal AD activity by the N-terminal fragment. CONCLUSION: Sumoylation of CoCoA differentially regulates the coactivator activity of CoCoA with nuclear receptors versus LEF1, by attenuating the N-terminal AD activity and enhancing the activity of the C-terminal AD.