Implication of SUMO-1 modification in synergistic transcription mediated by Ad4BP/SF-1 Implication of SUMO-1 Modification in Synergistic Transcription Mediated by Ad4BP/SF-1
Implication of SUMO-1 modification in synergistic transcription mediated by Ad4BP/SF-1
Implication of SUMO-1 Modification in Synergistic Transcription Mediated by Ad4BP/SF-1
An orphan nuclear receptor, Ad4BP/SF-1, is essential for the development and function of steroidogenic tissues. To examine the transcriptional regulation of Ad4BP/SF-1, two-hybrid screening was performed and the sumoylation (conjugation of a small ubiqutin-like modifier, SUMO) components Ubc9, PIAS1, and PIAS3 were isolated. Sumoylation is a novel posttranslational modification and has been reported to play a crucial role in a variety of cellular processes. Cultured cell and in vitro studies revealed that Ad4BP/SF-1 is sumoylated at K119 and K194. PIAS3 and PIAS1 promoted conjugation of SUMO to Ad4BP/SF-1 as E3 ligases. Since K194 lies within the synergy control (SC) motif defined to repress synergistic transcription from promoters containing multiple binding sites, correlation between the functions of the SC motif and sumoylation was investigated. The K194R mutant of Ad4BP/SF-1, which cannot be sumoylated, showed enhanced synergistic transcription from a promoter containing multiple Ad4/SF-1 sites, suggesting that sumoylation is necessary for repression of transcriptional synergy through the SC motif. It has been established that the Müllerian inhibiting substance (Mis) gene is transcribed predominantly under the control of Ad4BP/SF-1 and, moreover, its transcription is regulated synergistically with Sox9, Gata4, and Wt1. Interestingly, it was found that all of these factors are sumoylated, and these sumoylation sites occur within SC motifs. Based on the observation that SC motif mutants of Ad4BP/SF-1 and Sox9 resulted in the enhancement of their synergistic transcription, it was concluded that the SC motif regulates synergistic transcription even between distinct types of transcription factors. Considering that both mutants cannot be sumoylated, it is likely that sumoylation is implicated in this regulation. Since it was revealed with an in vitro sumoylated Ad4BP/SF-1 that DNA binding activity and interaction with Sox9 were unaffected, the transcriptional suppression by SUMO is suggested to be mediated by other unknown factors. Thus, sumoylation may regulate transcription through affecting selective and cooperative interaction among factors constituting transcriptional complexes.