Characterisation of a functional intronic polymorphism in the human growth hormone (gh1) gene

Abstract

The th1169A allele of the A/T single nucleotide polymorphism (SNP; rs2665802), located within intron 4 of the human growth hormone 1 (GH1) gene, has been associated with reduced levels of circulating GH and insulin-like growth factor 1, a reduced risk of colorectal cancer and a predisposition to osteoporosis. Whether this intronic SNP is itself the functional polymorphism responsible for exerting a direct effect on GH1 gene expression, however, or whether it is instead in linkage disequilibrium with the functional SNP, has been an open question. The evolutionary conservation of the th1169T allele (and the surrounding intronic sequence) in the bovine genome, as well as in primate genomes, is, however, suggestive of its functionality. Although a potential alternative splice site spans the location of the th1169 SNP, polymerase chain reaction-based assays failed to yield any evidence for alternative splicing associated with either allele. To determine whether the th1169 SNP, in different allelic combinations with SNPs at-278 (G/T),-57 (T/G) and th2103 (C/T), exerts a direct effect on gene expression and/or GH secretion, we performed a series of transfections of various GH1 haplotype-expressing constructs into rat GC (somatotroph) cells. The results obtained provided evidence to support the contention that the th1169A allele contributes directly to the observed reduction in both GH1 gene expression and GHsecretion. Part of the apparent influence of the th1169A-bearing allele on GH1 gene expression and GH secretion may still, however, be attributable to alleles of additional SNPs in cis to th1169A and located within either the promoter or the 30-flanking region.