A possible role for D8/PSF-A-like sequences in lactotroph versus somatotroph expression of the human prolactin gene.
The transcription factor GHF-1/Pit-1 is essential for the expression of GH and prolactin (PRL) by somatotrophs and lactotrophs respectively. However, PRL is not expressed in mature somatotrophs despite the presence of GHF-1/Pit-1. A possible mechanism is the presence of a somatotroph-specific repressor in the 5'-flanking sequences of the PRL gene. The region -3500/-1750 of the human (h) PRL gene is associated with negative regulatory activity and contains an element, designated D8, that resembles repressor PSF-A sequences which are located in the distal upstream region of placental members of the human GH family. An internal deletion of D8 sequences resulted in a significant stimulation of promoter activity in somatotroph GC (P < 0.005) and somatolactotroph-like GH3 and GH4C1 cells (P < 0.05), but not lactotroph-like 235-1 cells after gene transfer. However, D8 binding was observed by nuclease protection with lactotroph- as well as somatotroph-like cell nuclear protein. Although proteins that bind to the D8 element appear ubiquitous, this element does yield tissue-specific complexes in mobility shift assays. Further, competition studies do not suggest an interaction between GHF-1/Pit-1 and D8 proteins. The hPRL D8 element was inserted upstream of a thymidine kinase promoter and used to transfect pituitary and non-pituitary HeLa cells, to assess intrinsic repressor activity and/or promoter specificity. Although no repression was observed, a significant ninefold increase in expression was observed in HeLa cells (P < 0.001) which was at least twofold greater than observed in any of the pituitary cell lines tested. These results implicate D8 in the somatotroph-specific repression of hPRL; however, they also suggest that D8 can act as a stimulator as well as a repressor, depending on the interaction of a ubiquitous D8 factor forming promoter and cell-specific complexes with other elements/factors.
Leite
V
V
Department of Physiology, University of Manitoba, Winnipeg, Canada.
Cardoso
E A
EA
Bock
M E
ME
Sobrinho
L G
LG
Cattini
P A
PA
D001483:Base Sequence; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation; D018014:Gene Transfer Techniques; D013006:Growth Hormone / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D011388:Prolactin / Q000235:genetics* / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D050817:Transcription Factor Pit-1; D014157:Transcription Factors / Q000378:metabolism
D004268:DNA-Binding Proteins; C494187:POU1F1 protein, human; D012097:Repressor Proteins; D050817:Transcription Factor Pit-1; D014157:Transcription Factors; D011388:Prolactin; D013006:Growth Hormone