Variants in the Human Insulin Gene That Affect Pre-mRNA Splicing: Is -23HphI a Functional Single Nucleotide Polymorphism at IDDM2?

J. Kralovicova, T. R. Gaunt, S. Rodriguez, P. J. Wood, I. N.M. Day, I. Vorechovsky
2005 Diabetes  
Predisposition to type 1 diabetes and juvenile obesity is influenced by the susceptibility locus IDDM2 that includes the insulin gene (INS). Although the risk conferred by IDDM2 has been attributed to a minisatellite upstream of INS, intragenic variants have not been ruled out. We examined whether INS polymorphisms affect pre-mRNA splicing and proinsulin secretion using minigene reporter assays. We show that IVS1-6A/T (؊23HphI؉/؊) is a key INS variant that influences alternative splicing of
more » ... ive splicing of intron 1 through differential recognition of its 3 splice site. The A allele resulted in an increased production of mature transcripts with a long 5 leader in several cell lines, and the extended mRNAs generated more proinsulin in culture supernatants than natural transcripts. The longer mRNAs were significantly overrepresented among ␤-cellexpressed sequenced tags containing the A allele as compared with those with T alleles. In addition, we show that a rare insertion/deletion polymorphism IVS1؉5insTTGC (IVS-69), which is exclusively present in Africans, activated a downstream cryptic 5 splice site, extending the 5 leader by 30 bp. These results indicate that ؊23HphI and IVS-69 are the most important INS variants affecting pre-mRNA splicing and suggest that -23HphI؉/؊ is a common functional single nucleotide polymorphism at IDDM2. Diabetes
doi:10.2337/diabetes.55.01.06.db05-0773 pmid:16380501 fatcat:bgw2tcklcrbfnfxyyzvm6qo2km