Organization of the human FK506-binding immunophilin FKBP52 protein gene (FKBP4).

FKBP52 is a widely expressed FK506-binding immunophilin that possesses peptidylprolyl isomerase activity and a tetratricopeptide repeat involved in protein-protein interaction. FKBP52 plays an important role in steroid receptor function and is implicated in other diverse processes, including regulation of transcription, cation channel activity, and gene transfer efficiency. Reported here is the genomic organization of the human FKBP52 gene (FKBP4), which shares all but one of the same exon-intron boundaries as the structurally related immunophilin FKBP51 gene (FKBP5). Approximately 3.5 kb of 5'-flanking DNA of FKBP4 was subcloned into a luciferase reporter vector and was found to exhibit robust activity in T-47D, MCF7, and COS-7 cells. Promoter constructs with only 143 bp of upstream sequence maintained high activity. This region contains a CAAT motif sequence and consensus binding sites for Sp1, heat-shock factor, and MYC-MAX, which are conserved in the rabbit FKBP4 promoter and, when deleted, dramatically reduced promoter activity in T-47D cells.

The FK506-binding immunophilin FKBP51 is transcriptionally regulated by progestin and attenuates progestin responsiveness.

FKBP51 and FKBP52 are large molecular weight FK506-binding immunophilins that have diverse biochemical functions. Best studied is the role that they play as components of steroid hormone receptors. Differential display and gene array screens have identified FKBP51 as a progestin-inducible gene. Here we demonstrate progestin enhancement of FKBP51 mRNA and protein in T-47D cells. FKBP51 mRNA and protein levels were increased 3-fold by 20 nM R5020. Induction of FKBP51 mRNA was unaffected by 1 micro g/ml cycloheximide but was blocked by the progestin receptor (PR) antagonist RU486 (1 micro M). Reporter plasmids containing 3.4 kb and 427 bp of 5'-flanking sequences of the human FKBP51 protein gene (FKBP5) exhibited regulation by progestin in T-47D cells. A construct containing 19 bp of upstream sequence demonstrated diminished basal activity and no stimulation by R5020. To test whether elevated FKBP51 affects progestin responsiveness, HepG2 cells were transfected with human FKBP51, PR, and mouse mammary tumor virus-luciferase plasmids, and treated with R5020 (0.03-10 nM). Expression of FKBP51 increased the EC(50) for PR transactivation by 3.2-fold. Expression of FKBP51 from squirrel monkey, a New World primate with naturally occurring progestin resistance, increased the EC(50) more dramatically (11.7-fold vs. control). Expression of FKBP51 bearing a double-point mutation in the tetratricopeptide repeat domain had no effect on PR transactivation. These results suggest that increased expression of FKBP51 by progestin may attenuate progestin responsiveness in hormone-conditioned cells. Furthermore, overexpression of FKBP51 in the squirrel monkey may be a contributing cause of progesterone resistance in this species.