The PLZF BTB/POZ domain is necessary but not sufficient for repression of VDR-mediated transactivation.

(A) Deletion of the PLZF BTB/POZ domain relieves repression mediated by PLZF of 1,25(OH)₂D₃-dependent activation. U937 cells were transfected with the indicated amounts of either PLZF (lanes 2 and 3) or PLZF(ΔBTB/POZ) (lanes 4 and 5). Levels of expression of each protein in transfected extracts were similar (data not shown). (B) Expression of the BTB/POZ domain alone is not sufficient to repress 1,25(OH)₂D₃-dependent activation. A construct containing an epitope (flag)-tagged version of the PLZF BTB/POZ domain was cotransfected with VDR in U937 cells in the indicated DNA amounts. The fBTB/POZ protein was detectable in transfected extracts (data not shown). U937 cells were transfected as described previously and treated with ligand for 24 hours before harvesting. (C) Deletion of the 9 carboxyl zinc fingers in PLZF (PLZFΔZF1-9]) partly relieves PLZF-mediated repression of 1,25(OH)₂D₃-dependent activation. Protein amounts determined by Western blotting were similar for PLZF and PLZFΔZF1-9 (data not shown). (D) Deletion of the central RD2 domain of PLZF does not affect the ability of PLZF to repress 1,25(OH)₂D₃-dependent activation. All experiments shown are representative and were done in triplicate.