Abstract
Pit-1 stimulates the expression of growth hormone, prolactin, and thyrotropin beta subunit genes. Consequently, abnormality of the Pit-1 gene results in combined pituitary hormone deficiency (CPHD). In this study, we analyzed the function of Pit-1 with a mutation (proline to leucine at codon 24) in the transactivation domain, P24L, which has a normal POU domain important for binding to DNA, because this mutation had been reported in a patient with CPHD. We found that codon 24 proline in the transactivation domain as well as the POU domain of Pit-1 was crucial to recruit coactivator CREB-binding protein (CBP) in the cultured cells. P24L completely lost the responsiveness to cAMP to stimulate the expression of the Pit-1-targeted genes. Furthermore, CBP and Pit-1, but not P24L, markedly enhanced the expression of the Pit-1-targeted gene to cAMP, and adenovirus E1a that binds to CBP and abrogates its function blocked the induction by cAMP of Pit-1-stimulated gene transcription in the pituitary-derived GH3 cells. These results suggest that CBP and proline at codon 24 in the transactivation domain of Pit-1 are important for the cAMP-induced activation of Pit-1-targeted genes. However, P24L maintained basal transcriptional activity, suggesting that CBP is unlikely to be an essential coactivator for Pit-1.
Highlights
A pituitary-specific transcription factor, Pit-1, known as GHF-1, is a member of the homeobox POU family of DNAbinding proteins (1, 2)
Because the patients with these mutations were both heterozygous for the mutation, it is believed that P14L and P24L may dominantly inhibit the transcriptional activity of the wild type Pit-1 (21– 23)
Reduced Ability of P24L, but Not P14L, to Activate growth hormone (GH) and PRL Genes—Transcriptional activity of P14L and P24L for the expression of GH and PRL genes was investigated in COS7 cells (Pit-1 deficient)
Summary
A pituitary-specific transcription factor, Pit-1, known as GHF-1, is a member of the homeobox POU family of DNAbinding proteins (1, 2). To compare the function of P24L to activate Pit-1-targeted genes in response to cAMP with that of wild type Pit-1, 2 g of PRL-Luc or 1P-Luc, which contains seven Pit-1-responsive elements derived from a Pit-1-binding DNA element, 1P, of the rat PRL gene, was transfected into the COS7 cells with 0.3 g of empty expression vector (pcDNA3.1), pcDNA3.1-wild type-Pit-1, or pcDNA3.1-P24L.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
