Differential splicing of the GHF1 primary transcript gives rise to two functionally distinct homeodomain proteins.

Abstract

The POU domain protein GHF‐1 has a critical role in generation, proliferation and phenotypic expression of three pituitary cell types. GHF‐1 functions in part by binding to and transactivating the promoters of both the growth hormone (GH) and prolactin (PRL) genes and that of the GHF1 gene itself. We describe a naturally occurring isoform of GHF‐1, GHF‐2, in which an additional 26 amino acids are inserted into the activation domain of the protein as a result of alternative splicing. GHF‐2 retains the DNA binding activity of GHF‐1 and can activate the GH promoter but has lost the ability to activate the PRL and GHF1 promoters. These results suggest that GHF‐2 may function in differential target gene activation during differentiation of the somatotrophic lineage. Both GHF‐1 and GHF‐2 transcripts are specifically expressed in the anterior pituitary. Analysis of the genomic GHF1 gene shows that most of the distinct functional domains of GHF‐1 (and GHF‐2) are encoded by separate exons. Gene segment duplication and exon shuffling may have contributed to the evolution of this cell type‐specific transcriptional regulatory gene.

Identification and characterization of four splicing variants of ovine POU1F1 gene

“…The function of POU1F1-β variant has been analysed by other authors. Morris et al (1992), Konzak and Moore (1992) and Theill et al (1992) agreed that, similarly to our results, the rat β variant has only 5 to 10% of the Wt capacity to trans-activate the PRL promoter. In agreement with our results, Haugen et al (1994) observed that, in HeLa cells, the β variant stimulated GH promoter but had almost no effect on PRL promoter.…”

“…In agreement with our results, Haugen et al (1994) observed that, in HeLa cells, the β variant stimulated GH promoter but had almost no effect on PRL promoter. When both isoforms are co-expressed, contradictory results were described: Theill et al (1992) and Vila et al (1993) observed a dominant negative repressor effect of the β variant, while Konzak and Moore (1992) observed that Wt and β are not antagonists, they can function together and interact in the activation of the rat PRL promoter when co-expressed, in agreement with the results of the present work. Diamond and Gutierrez-Hartmann (2000) stated that, in pituitary cell lines, POU1F1-β represses PRL promoter, but in non-pituitary cells, like HeLa cells, the rat β variant presented a higher capacity to activate PRL promoter.…”

“…The POU1F1 gene, as described by Theill et al (1989Theill et al ( , 1992, contains six exons and five introns and encodes a protein with 33 kDa. This transcription factor contains two important regions for the transcriptional regulation of target promoters: a N-terminal trans-activation domain (TAD) spanning amino acids 1 to 80 and a C-terminal DNA-binding and dimerization domain that consists of a POU-specific domain (POU S from aa 128 to 198) and a POU homeodomain (POU HD from aa 214 to 273).…”

“…Theill et al (1992), Konzak and Moore (1992) and Morris et al (1992) published independent results showing an alternative transcript in this gene, with different nomenclatures: GHF2, Pit-1β and Pit-1a, respectively. This POU1F1 alternative form arises from the use of an alternative 3′ splice acceptor at the end of the first intron and contains an insertion of 78 bp downstream the nucleotide 142 relatively to the initiation ATG codon, giving rise to a 26 aa insertion at position 48 of the TAD domain.…”

Increase in Pit-1 mRNA Is Not Required for the Estrogen-Induced Expression of Prolactin Gene and Lactotroph Proliferation.

“…Recently an alternative splicing variant of Pit-1 called Pit-1a, Pit-1/3, or GHF-2 has been reported [24][25][26]. This splicing variant has 26 amino acid insertions in the transactivation domain of the original Pit-1.…”