Abstract
Forkhead box (FOX) protein A1 has been dubbed a pioneer transcription factor because it binds target sites in DNA, thereby displacing nucleosomes to loosen chromatin and facilitating steroid receptor DNA binding nearby. FOXA1 is an important regulator of prostate development, collaborating with androgen receptor (AR). Post-translational modifications regulating FOXA1 are thus far poorly understood. SUMOylation, post-translational modification of proteins by small ubiquitin-like modifier (SUMO) proteins, has emerged as an important regulatory mechanism in transcriptional regulation. In this work, we show by SUMOylation assays in COS-1 cells that the FOXA1 is modified at least in two of its three lysines embedded in SUMOylation consensus, K6 and K389, in proximity to its transactivation domains and K267 proximal to its DNA-binding domain. We also provide evidence for SUMO-2/3 modification of endogenous FOXA1 in LNCaP prostate cancer cells. Based on fluorescence recovery after photobleaching assays with mCherry-fused FOXA1 and EGFP-fused AR in HEK293 cells, the presence of FOXA1 retards the nuclear mobility of agonist-bound AR. Interestingly, mutation of the FOXA1 SUMOylation sites slows down the mobility of the pioneer factor, further retarding the nuclear mobility of the AR. Chromatin immunoprecipitation and gene expression assays suggest that the mutation enhances FOXA1's chromatin occupancy as well as its activity on AR-regulated prostate-specific antigen (PSA) locus in LNCaP cells. Moreover, the mutation altered the ability of FOXA1 to influence proliferation of LNCaP cells. Taken together, these results strongly suggest that the SUMOylation can regulate the transcriptional activity of FOXA1 with the AR.