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

• Published in: Human genomics Vol. 4; no. 5; pp. 289 - 301
• Main Authors: Millar, David S, Horan, Martin, Chuzhanova, Nadia A, Cooper, David N
• Format: Journal Article
• Language: English
• Published: England BioMed Central 01.06.2010; BioMed Central Ltd; BMC
• Subjects: 3' Flanking Region - genetics; Alleles; alternative splicing; Alternative Splicing - genetics; Animals; Base Sequence; Cell Line; Conserved Sequence - genetics; European Continental Ancestry Group - genetics; Evolution, Molecular; gene expression; Gene Expression Regulation; growth hormone (GHI) gene; Haplotypes - genetics; Human Growth Hormone - genetics; Humans; intronic functional polymorphism; Introns - genetics; Linkage Disequilibrium - genetics; Molecular Sequence Data; Polymorphism, Single Nucleotide - genetics; Primary Research; Promoter Regions, Genetic - genetics; protein secretion; Rats; RNA Splice Sites - genetics; Sequence Homology, Nucleic Acid; Somatotrophs - metabolism
• DOI: 10.1186/1479-7364-4-5-289
• ISSN: 1479-7364; 1473-9542

The +1169A 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 +1169T 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 +1169 SNP, polymerase chain reaction-based assays failed to yield any evidence for alternative splicing associated with either allele. To determine whether the +1169 SNP, in different allelic combinations with SNPs at -278 (G/T), -57 (T/G) and +2103 (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 +1169A allele contributes directly to the observed reduction in both GH1 gene expression and GH secretion. Part of the apparent influence of the +1169A-bearing allele on GH1 gene expression and GH secretion may still, however, be attributable to alleles of additional SNPs in cis to +1169A and located within either the promoter or the 3'-flanking region.