Isolation and characterization of the 5′-flanking region of the growth hormone secretagogue receptor gene from black seabream Acanthopagrus schlegeli

Abstract

Ghrelin, the recently discovered endogenous ligand for growth hormone secretagogue receptor (GHSR), is widely expressed and involved in regulating diverse physiological functions in addition to stimulation of growth hormone (GH) secretion. Previous studies have demonstrated the functional significance of the ghrelin/GHSR system, yet the transcriptional regulation of the ghrelin and GHSR genes are poorly understood. We have recently cloned the GHSR cDNA from the pituitary of black seabream Acanthopagrus schlegeli. In the present study, we have isolated a 2.1 kb 5′-flanking region of the GHSR gene from the same species and have investigated, for the first time, the transcriptional regulation of GHSR from a non-human species. The 5′-flanking region of the seabream GHSR gene was found to contain a number of unique putative transcription factor-binding sites different from the human counterpart. Functional characterization of the 5′-flanking region in several cell lines indicates that the region between -1423 and +19 contains sufficient elements for promoter function. Moreover, progressive 3′-deletion analysis suggests the presence of negative regulatory element(s) and essential cis-acting element(s) at -514/+19 and -928/-515, respectively. Furthermore, we have shown that the promoter activity is significantly enhanced by a GHSR agonist in a cell line stably expressing the seabream GHSR, and this stimulatory effect could be completely blocked by a GHSR antagonist. These results suggest that homologous up-regulation plays an important role in the transcriptional control of the teleostean GHSR gene. This is in big contrast to the human situation in which a homologous down-regulation of the GHSR gene transcription by its own ligand has been previously demonstrated. © 2004 Elsevier Ireland Ltd. All rights reserved.