Genetic and functional assessment of the role of the rs13431652-A and rs573225-A alleles in the G6PC2 promoter that are strongly associated with elevated fasting glucose levels.
OBJECTIVE
Genome-wide association studies have identified a single nucleotide polymorphism (SNP), rs560887, located in a G6PC2 intron that is highly correlated with variations in fasting plasma glucose (FPG). G6PC2 encodes an islet-specific glucose-6-phosphatase catalytic subunit. This study examines the contribution of two G6PC2 promoter SNPs, rs13431652 and rs573225, to the association signal.


METHODS
We genotyped 9,532 normal FPG participants (FPG <6.1 mmol/l) for three G6PC2 SNPs, rs13431652 (distal promoter), rs573225 (proximal promoter), rs560887 (3rd intron). We used regression analyses adjusted for age, sex, and BMI to assess the association with FPG and haplotype analyses to assess comparative SNP contributions. Fusion gene and gel retardation analyses characterized the effect of rs13431652 and rs573225 on G6PC2 promoter activity and transcription factor binding.


RESULTS
Genetic analyses provide evidence for a strong contribution of the promoter SNPs to FPG variability at the G6PC2 locus (rs13431652: β = 0.075, P = 3.6 × 10(-35); rs573225 β = 0.073 P = 3.6 × 10(-34)), in addition to rs560887 (β = 0.071, P = 1.2 × 10(-31)). The rs13431652-A and rs573225-A alleles promote increased NF-Y and Foxa2 binding, respectively. The rs13431652-A allele is associated with increased FPG and elevated promoter activity, consistent with the function of G6PC2 in pancreatic islets. In contrast, the rs573225-A allele is associated with elevated FPG but reduced promoter activity.


CONCLUSIONS
Genetic and in situ functional data support a potential role for rs13431652, but not rs573225, as a causative SNP linking G6PC2 to variations in FPG, though a causative role for rs573225 in vivo cannot be ruled out.
Bouatia-Naji
Nabila
N
CNRS-UMR-8199, Institut Pasteur de Lille, Lille, France.
Bonnefond
Amélie
A
Baerenwald
Devin A
DA
Marchand
Marion
M
Bugliani
Marco
M
Marchetti
Piero
P
Pattou
François
F
Printz
Richard L
RL
Flemming
Brian P
BP
Umunakwe
Obi C
OC
Conley
Nicholas L
NL
Vaxillaire
Martine
M
Lantieri
Olivier
O
Balkau
Beverley
B
Marre
Michel
M
Lévy-Marchal
Claire
C
Elliott
Paul
P
Jarvelin
Marjo-Riitta
MR
Meyre
David
D
Dina
Christian
C
Oeser
James K
JK
Froguel
Philippe
P
O'Brien
Richard M
RM
D000328:Adult; D001786:Blood Glucose / Q000235:genetics; D002648:Child; D015331:Cohort Studies; D017931:DNA Primers; D005215:Fasting; D005260:Female; D005387:Finland / Q000453:epidemiology; D005786:Gene Expression Regulation; D014644:Genetic Variation; D005952:Glucose-6-Phosphatase / Q000235:genetics*; D006801:Humans; D007333:Insulin Resistance / Q000235:genetics; D007438:Introns / Q000235:genetics; D024821:Metabolic Syndrome / Q000235:genetics*; D009035:Mothers; D009928:Organ Specificity; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012016:Reference Values; D044465:White People / Q000235:genetics
D001786:Blood Glucose; D017931:DNA Primers; D012313:RNA; D005952:Glucose-6-Phosphatase; C492194:G6PC2 protein, human