Hormonal regulation of the thyrotropin beta-subunit gene by phosphorylation of the pituitary-specific transcription factor Pit-1.
The pituitary-specific transcription factor Pit-1 is a cell-specific activator of prolactin and growth hormone gene transcription in the anterior pituitary. Pit-1 has also been shown to mediate both thyrotropin-releasing hormone (TRH) and cAMP stimulation of the prolactin and thyrotropin beta-subunit (TSH beta) genes. The molecular mechanism by which Pit-1 mediates these stimulatory effects remains unclear. At least three Pit-1-binding elements within the TSH beta gene mediate responsiveness to TRH and cAMP. The present studies were designed to test the hypothesis that phosphorylation is an important modulator of Pit-1 interaction with the TSH beta gene. TSH beta elements bind less well to nonphosphorylated Pit-1 than to phosphorylated Pit-1 and are weak activators of gene expression, unlike high-affinity Pit-1 binding sites in the prolactin and growth hormone genes. Phosphorylation by protein kinase A or C enhances Pit-1 binding to TSH beta elements 3- to 8-fold. Conversely, phosphorylation generally reduces binding of Pit-1 to elements within the prolactin and growth hormone genes. A variation within the consensus sequence for Pit-1 binding in TSH beta gene elements [A(A/T)(A/T)AATNCAT in the TSH beta gene versus A(A/T)(A/T)TATNCAT in the prolactin and growth hormone genes] could explain these differences. These elements may limit basal activation of the TSH beta gene by binding less well to nonphosphorylated Pit-1 while conferring hormonal stimulation through enhanced binding of phosphorylated Pit-1.
Steinfelder
H J
HJ
Department of Pediatrics, University Hospital, Cleveland, OH.
Radovick
S
S
Wondisford
F E
FE
D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D051381:Rats; D012045:Regulatory Sequences, Nucleic Acid; D013329:Structure-Activity Relationship; D013972:Thyrotropin / Q000235:genetics*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D050817:Transcription Factor Pit-1; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology*; D015533:Transcriptional Activation; D014162:Transfection
D004268:DNA-Binding Proteins; C494187:POU1F1 protein, human; C494186:Pou1f1 protein, rat; D050817:Transcription Factor Pit-1; D014157:Transcription Factors; D005576:Colforsin; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D000242:Cyclic AMP