A Common Functional Regulatory Variant at a Type 2 Diabetes Locus Upregulates ARAP1 Expression in the Pancreatic Beta Cell

Am J Hum Genet. 2014 Feb 6;94(2):186-97. doi: 10.1016/j.ajhg.2013.12.011. Epub 2014 Jan 16.

Abstract

Genome-wide association studies (GWASs) have identified more than 70 loci associated with type 2 diabetes (T2D), but for most, the underlying causal variants, associated genes, and functional mechanisms remain unknown. At a T2D- and fasting-proinsulin-associated locus on 11q13.4, we have identified a functional regulatory DNA variant, a candidate target gene, and a plausible underlying molecular mechanism. Fine mapping, conditional analyses, and exome array genotyping in 8,635 individuals from the Metabolic Syndrome in Men study confirmed a single major association signal between fasting proinsulin and noncoding variants (p = 7.4 × 10(-50)). Measurement of allele-specific mRNA levels in human pancreatic islet samples heterozygous for rs11603334 showed that the T2D-risk and proinsulin-decreasing allele (C) is associated with increased ARAP1 expression (p < 0.02). We evaluated four candidate functional SNPs for allelic effects on transcriptional activity by performing reporter assays in rodent pancreatic beta cell lines. The C allele of rs11603334, located near one of the ARAP1 promoters, exhibited 2-fold higher transcriptional activity than did the T allele (p < 0.0001); three other candidate SNPs showed no allelic differences. Electrophoretic mobility shift assays demonstrated decreased binding of pancreatic beta cell transcriptional regulators PAX6 and PAX4 to the rs11603334 C allele. Collectively, these data suggest that the T2D-risk allele of rs11603334 could abrogate binding of a complex containing PAX6 and PAX4 and thus lead to increased promoter activity and ARAP1 expression in human pancreatic islets. This work suggests that increased ARAP1 expression might contribute to T2D susceptibility at this GWAS locus.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics*
  • Adaptor Proteins, Signal Transducing / metabolism
  • Aged
  • Alleles
  • Animals
  • Cell Line
  • Diabetes Mellitus, Type 2 / genetics*
  • Diabetes Mellitus, Type 2 / metabolism
  • Eye Proteins / genetics
  • Eye Proteins / metabolism
  • Genetic Loci*
  • Genetic Predisposition to Disease
  • Genome-Wide Association Study
  • Homeodomain Proteins / genetics
  • Homeodomain Proteins / metabolism
  • Humans
  • Insulin-Secreting Cells / cytology
  • Insulin-Secreting Cells / metabolism*
  • Male
  • Mice
  • Middle Aged
  • PAX6 Transcription Factor
  • Paired Box Transcription Factors / genetics
  • Paired Box Transcription Factors / metabolism
  • Polymorphism, Single Nucleotide
  • Promoter Regions, Genetic
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Up-Regulation*

Substances

  • Adaptor Proteins, Signal Transducing
  • Agtrap protein, mouse
  • Eye Proteins
  • Homeodomain Proteins
  • PAX6 Transcription Factor
  • PAX6 protein, human
  • Paired Box Transcription Factors
  • Pax4 protein, mouse
  • Pax6 protein, mouse
  • Repressor Proteins