title: Repression of the prolactin promoter: a functional consequence of the heterodimerization between Pit-1 and Pit-1 beta.
abstract: The POU-homeodomain transcription factor Pit-1 is required for the differentiation of the anterior pituitary cells and the expression of their hormone products. Pit-1beta, an alternate splicing isoform, has diametrically different outcomes when it is expressed in different cell types. Pit-1beta acts as a transcriptional repressor of prolactin (PRL) and growth hormone genes in pituitary cells, and as a transcriptional activator in non-pituitary cells. In order to explore these differences, we: (1) identified the transcriptional cofactors necessary for reconstitution of repression in non-pituitary cells; (2) tested the effect of the beta-domain on heterodimerization with Pit-1 and physical interaction with the co-activator CREB binding protein (CBP); and (3) determined the beta-domain sidechain chemistry requirements for repression. Co-expression of both Pit-1 isoforms reconstituted the repression of the PRL promoter in non-pituitary cells. The beta-domain allowed heterodimerization with Pit-1 but blocked physical interaction with CBP, and specific chemical properties of the beta-domain beyond hydrophobicity were dispensable. These data strongly suggest that Pit-1beta represses hormone gene expression by heterodimerizing with Pit-1 and interfering with the assembly of the Pit-1-CBP complex required for PRL promoter activity in pituitary cells.
authors.affiliation: Department of Physiology, University of Kentucky College of Medicine, 800 Rose Street, Lexington, KY 40536, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Sporici
authors.forename: J S
authors.initials: JS
authors.lastname: Hodskins
authors.forename: D M
authors.initials: DM
authors.lastname: Locasto
authors.forename: L B
authors.initials: LB
authors.lastname: Meszaros
authors.forename: A L
authors.initials: AL
authors.lastname: Ferry
authors.forename: A M
authors.initials: AM
authors.lastname: Weidner
authors.forename: C A
authors.initials: CA
authors.lastname: Rinehart
authors.forename: J C
authors.initials: JC
authors.lastname: Bailey
authors.forename: I M
authors.initials: IM
authors.lastname: Mains
authors.forename: S E
authors.initials: SE
authors.lastname: Diamond
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D050882:CREB-Binding Protein / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism; D011388:Prolactin / Q000235:genetics* / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D050817:Transcription Factor Pit-1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D050817:Transcription Factor Pit-1; D011388:Prolactin; D050882:CREB-Binding Protein