Synergistic interactions between Pit-1 and other elements are required for effective somatotroph rat growth hormone gene expression in transgenic mice.
The role of the pituitary-specific POU-domain protein, Pit-1, in GH gene activation has been established by in vitro analyses and by the observation that mutations affecting the Pit-1 genomic locus result in genetically transmitted dwarfism. To define the quantitative contribution of the two Pit-1 response elements and the potential role of other factors in GH gene activation, we systematically assessed the ability of a series of GH promoter regions to activate transgenes in the mouse anterior pituitary gland. These studies revealed that the two GH Pit-1 binding sites are necessary, but not sufficient, for efficient transcriptional activation. Transgenes containing information including only these cis-active regions are expressed at extremely low levels in the pituitary glands of transgenic mice. The addition of 35 base pairs of 5'-flanking information, contributing other elements including a thyroid hormone/retinoic acid response element, results in much higher levels of transgene expression. Sequences located upstream of this segment contribute a further 5- to 10-fold activation. Thus, while Pit-1 is required for GH gene activation, it alone can only direct minimal expression in transgenic animals. Rather, synergistic interactions between other promoter elements and Pit-1 appear to be required for expression of the transgenes at approximately the 100-fold higher levels that are characteristic of somatotrophs, and are therefore likely to be critical components of somatotroph-specific expression of the GH gene.
Lira
S A
SA
Eukaryotic Regulatory Biology Program, Howard Hughes Medical Institute, University of California, San Diego 92037-0648.
Kalla
K A
KA
Glass
C K
CK
Drolet
D W
DW
Rosenfeld
M G
MG
D000818:Animals; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000494:pharmacology / Q000502:physiology*; D015870:Gene Expression; D013006:Growth Hormone / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D011401:Promoter Regions, Genetic; D051381:Rats; D011988:Receptors, Thyroid Hormone / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D050817:Transcription Factor Pit-1; D014157:Transcription Factors / Q000494:pharmacology / Q000502:physiology*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; D013006:Growth Hormone; D011988:Receptors, Thyroid Hormone; D011993:Recombinant Fusion Proteins; D050817:Transcription Factor Pit-1; D014157:Transcription Factors; C494185:Pou1f1 protein, mouse; C494186:Pou1f1 protein, rat