Activation of the prolactin gene by peroxisome proliferator-activated receptor-alpha appears to be DNA binding-independent.
Although the effects of the peroxisome proliferator-activated receptors (PPARs) have been studied primarily in adipocytes and liver, the wide distribution of these receptors suggests that they might also play a role in other cell types. We present evidence that PPAR activators stimulate the expression of the prolactin gene in pituitary GH4C1 cells. Transfection assays in non-pituitary HeLa cells showed that stimulation of the prolactin promoter by PPARalpha requires the presence of the transcription factor GHF-1 (or Pit-1). Proximal promoter sequences confer responsiveness to PPARalpha, and activation by this receptor is lost concomitantly with the response to GHF-1. Surprisingly, expression of the retinoid X receptor (RXR) abolishes stimulation by PPARalpha. Furthermore, the promoter region that confers PPARalpha responsiveness does not contain a PPAR response element. This suggests that the transcriptional effect of PPARalpha might be mediated by protein-protein interactions rather than by binding of PPAR/RXR to the promoter. A direct interaction between PPARalpha and GHF-1 was confirmed by in vitro binding studies. Expression of the coactivators SRC-1 and CREB-binding protein, which bind to PPAR, also enhanced the responsiveness of the prolactin promoter to PPARalpha. Furthermore, CREB-binding protein also significantly increased activation by GHF-1, and both proteins associated in vitro. Thus, PPARalpha, a receptor that normally acts as a ligand-dependent transcription factor by binding to specific DNA sequences in one context, can also stimulate the prolactin promoter by association with GHF-1 and coactivator proteins.
Tolón
R M
RM
Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Científicas, 28029 Madrid, Spain.
Castillo
A I
AI
Aranda
A
A
D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D017931:DNA Primers; D005786:Gene Expression Regulation / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D011388:Prolactin / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism / Q000502:physiology*; D011960:Receptors, Estrogen / Q000502:physiology; D018168:Receptors, Retinoic Acid / Q000502:physiology; D047488:Retinoid X Receptors; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*
D017931:DNA Primers; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D011960:Receptors, Estrogen; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D015534:Trans-Activators; D014157:Transcription Factors; D011388:Prolactin; D015500:Chloramphenicol O-Acetyltransferase