Tissue-specific activity of the pro-opiomelanocortin gene promoter.

Abstract

The pro-opiomelanocortin (POMC) gene is specifically expressed in corticotroph cells of the anterior pituitary. To define the POMC promoter sequences responsible for tissue-specific expression, we assessed POMC promoter activity by gene transfer into POMC-expressing pituitary tumor cells and fibroblast L cells. The rat POMC promoter was only efficiently utilized and correctly transcribed in AtT-20 cells. 5'-End deletion analysis revealed two promoter regions required for activity in AtT-20 cells. When tested by fusion to a heterologous promoter, DNA fragments corresponding to both regions exhibited tissue-specific activity, suggesting the presence of at least two tissue-specific DNA sequence elements within the promoter. In summary, POMC promoter sequences from -480 to -34 base pairs appear sufficient to mimic the specificity of anterior pituitary expression.Control of eucaryotic transcription results from the interaction of multiple DNA sequence elements that are presumably recognized by as many trans-acting factors (reviewed in references 21 and 33). In gene transfer experiments with tissue culture cells or transgenic animals, it was shown that various DNA sequence elements are responsible for tissuespecific expression of many cellular genes (2,3,9,16,24,29,31,39,45,46). Tissue-specific sequence elements were identified in the 5'-flanking region of the genes coding for immunoglobulins (16,24,31), insulin (46), elastase (45), otl-antitrypsin (9), and many others. Some sequences conferring tissue specificity have enhancer properties and are located either upstream of the site of transcription initiation or elsewhere in the gene (1,20,37,42). In many cases, multiple DNA sequence elements are required to confer tissue specificity (8,13,16,24,31,48), includi1ag promoterproximal and -distal sequences.The pituitary gland represents an interesting system to investigate the role of tissue-specific DNA sequence elements in the expression of cell-specific genes. Pituitary hormone-secreting cells have a common embryological origin; however, each pituitary hormone gene is expressed in a distinct cell type (17). To identify DNA sequences required for tissue-specific expression in the pituitary, we studied the activity of promoter sequences present in the rat proopiomelanocortin (POMC) gene. The POMC gene is present in a single copy per haploid genome (12); it is expressed in two different pituitary cell types, the anterior pituitary corticotrophs, in which POMC is processed to adrenocorticotropin, and the pars intermedia melanotrophs, in which the same POMC protein precursor is processed to o-melanotropin (14). Regulation of POMC gene expression in these two tissues is also cell specific (18; J.-P. Gagner and J. Drouin, Mol. Endocrinol., in press), highlighting the functional and developmental differences between the two secreting cell types. MATERIALS AND METHODSPlasmid constructions. Recombinant plasmids were constructed by standard procedures (30). Plasmid DNAs used for electroporation were purified by banding twice on...

Corticotropin-releasing hormone or dexamethasone regulates rat proopiomelanocortin transcription through Tpit/Pitx-responsive element in its promoter

“…Here, we found that CRH stimulated the rat POMC promoter K480/C63 construct, while pCPT-cAMP stimulated the rat POMC promoter K480/C63 construct to a large degree. This result coincides with those of previous reports (Jeannotte et al 1987, Ray et al 1996, Kovalovsky et al 2002, Mynard et al 2004. The low promoter activation of CRH treatment might be due to low cAMP generation, because there are some reports that described low and transient cAMP accumulation on CRH stimulation in AtT-20 cells (Litvin et al 1984, Nikodemova et al 2003.…”

“…The rat POMC promoter K480/C63 construct is sufficient for corticotroph-specific POMC expression (Jeannotte et al 1987, Hammer et al 1990, and is activated by CRH and cAMP stimulation (Kovalovsky et al 2002). Here, we found that CRH stimulated the rat POMC promoter K480/C63 construct, while pCPT-cAMP stimulated the rat POMC promoter K480/C63 construct to a large degree.…”

“…Expression of the proopiomelanocortin (POMC) gene in the pituitary gland is restricted to corticotropes in the anterior lobe and melanotropes in the intermediate lobe (Jeannotte et al 1987, Drouin et al 1989b. Cell-type specific expression of the POMC gene in corticotropes and melanotropes is maintained by the expression of Tpit (also called Tbx19), a Tbox family transcription factor, and pituitary homeobox 1 (Pitx1), a homeoprotein transcription factor.…”

Analysis of the human proopiomelanocortin gene promoter in a small cell lung carcinoma cell line reveals an unusual role for E2F transcription factors

“…The activity of the POMC gene promoter in the pituitary context has been extensively studied both in the murine corticotroph cell line AtT-20 and in transgenic mice models (Hammer et al, 1990;Jeannotte et al, 1987;Tremblay et al, 1988). Multiple cis-regulatory elements have been identi®ed whose coordinate activities were required for POMC gene transcription (Therrien and Drouin, 1991).…”

60 YEARS OF POMC: Transcriptional and epigenetic regulation of POMC gene expression

“…The early studies of POMC 5′-flanking sequences indicated that these sequences exhibit cell-specific activity in cell culture experiments (Jeannotte et al 1987) and most importantly that they are sufficient to recapitulate to a large extent the unique features of POMC transcriptional regulation in transgenic mice (Tremblay et al 1988, Hammer et al 1990. Further, the transgenic data indicate that 480 bp upstream of the rat gene transcription start site (TSS) contained most of the critical targets for POMC regulation, notwithstanding the possibility that other regulatory sequences may also contribute to control of POMC transcription.…”