Repression of the prolactin promoter: a functional consequence of the heterodimerization between Pit-1 and Pit-1 beta.
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.
Sporici
R A
RA
Department of Physiology, University of Kentucky College of Medicine, 800 Rose Street, Lexington, KY 40536, USA.
Hodskins
J S
JS
Locasto
D M
DM
Meszaros
L B
LB
Ferry
A L
AL
Weidner
A M
AM
Rinehart
C A
CA
Bailey
J C
JC
Mains
I M
IM
Diamond
S E
SE
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*
D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D050817:Transcription Factor Pit-1; D011388:Prolactin; D050882:CREB-Binding Protein