Fig. 5. Endogenous GNL3L suppresses transcriptional activity of ERR family genes. (A) To confirm the GNL3L-mediated negative regulation of ERR activities from a loss-of-function angle, a small interfering RNA (siRNA) approach was used to knock down the endogenous expression of GNL3L. Compared to the control knockdown sample (siNEG), the protein knockdown efficiencies of GNL3L-specific siRNA duplexes (siGNL3L-1 and siGNL3L-2) in HEK293 cells stably expressing HA-tagged GNL3L are estimated to be 83% and 84%, respectively. (B) Consistent with our overexpression data, the transcriptional activity of ERR is increased 2.5 times by siGNL3L-1 and siGNL3L-2 treatment as compared with the siNEG-treated sample. (C,D) GNL3L knockdown has the same effect on the ERR- and ERR-mediated transactivation, although their increase is less dramatic than the increase in the ERR-mediated transactivation. Error bars represent the standard error of the mean (± s.e.m.). ^**P<0.001; ^***P<0.0001.