The enhancement of PR transcriptional activity by SENP1 depends on an intact SUMO conjugation site. HeLa cells were transfected with the PRE2-Luc (A and B) or MMTV-Luc (C and D) reporter plasmids in the presence of pSV40-Renilla as internal control along with PR-B (A and C) or PR-B K388R (B and D) expressing vectors, and a Flag-SENP1 expression vector at doses of 20, 50, 100, 200 and 1000 ng of DNA or an empty vector control (-). Cells were treated without (-) or with (+) 10 nM R5020 for 24 hrs before being assayed for luciferase activity as in Figure 1. RLU of wt PR-B in the absence of hormone is set as 1. Statistical significance was computed by unpaired student's t test. *p < 0.05.