APOE genotype-function relationship: evidence of -491 A/T promoter polymorphism modifying transcription control but not type 2 diabetes risk.
BACKGROUND
The apolipoprotein E gene (APOE) coding polymorphism modifies the risks of Alzheimer's disease, type 2 diabetes, and coronary heart disease. Aside from the coding variants, single nucleotide polymorphism (SNP) of the APOE promoter has also been shown to modify the risk of Alzheimer's disease.


RESULTS
In this study we investigate the genotype-function relationship of APOE promoter polymorphism at molecular level and at physiological level: i.e., in transcription control of the gene and in the risk of type 2 diabetes. In molecular studies, the effect of the APOE -491A/T (rs449647) polymorphism on gene transcription was accessed by dual-luciferase reporter gene assays. The -491 A to T substitution decreased the activity (p<0.05) of the cloned APOE promoter (-1017 to +406). Using the -501 to -481 nucleotide sequence of the APOE promoter as a 'bait' to screen the human brain cDNA library by yeast one-hybrid system yielded ATF4, an endoplasmic reticulum stress response gene, as one of the interacting factors. Electrophoretic-mobility-shift assays (EMSA) and chromatin immuno-precipitation (ChIP) analyses further substantiated the physical interaction between ATF4 and the APOE promoter. Over-expression of ATF4 stimulated APOE expression whereas siRNA against ATF4 suppressed the expression of the gene. However, interaction between APOE promoter and ATF4 was not -491A/T-specific. At physiological level, the genotype-function relationship of APOE promoter polymorphism was studied in type 2 diabetes. In 630 cases and 595 controls, three APOE promoter SNPs -491A/T, -219G/T (rs405509), and +113G/C (rs440446) were genotyped and tested for association with type 2 diabetes in Hong Kong Chinese. No SNP or haplotype association with type 2 diabetes was detected.


CONCLUSIONS
At molecular level, polymorphism -491A/T and ATF4 elicit independent control of APOE gene expression. At physiological level, no genotype-risk association was detected between the studied APOE promoter SNPs and type 2 diabetes in Hong Kong Chinese.
Department of Biochemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, China.
Hua
H
Geng
Peggy P Y
PP
Law
Maggie C Y
MC
Ng
Ting
T
Li
Li-Yun
LY
Liang
Tian-Fang
TF
Ge
Kam-Bo
KB
Wong
Chun
C
Liang
Ronald C
RC
Ma
Wing-Yee
WY
So
Juliana C N
JC
Chan
Yuan-Yuan
YY
Ho
D051701:Activating Transcription Factor 4 / Q000378:metabolism; D000328:Adult; D001057:Apolipoproteins E / Q000235:genetics* / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics; D059865:Endoplasmic Reticulum Stress / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation / Q000235:genetics*; D020022:Genetic Predisposition to Disease / Q000235:genetics; D005838:Genotype; D005947:Glucose / Q000378:metabolism; D057809:HEK293 Cells; D006706:Homeostasis / Q000235:genetics; D006801:Humans; D050356:Lipid Metabolism / Q000235:genetics; D008297:Male; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D014158:Transcription, Genetic / Q000235:genetics*
C497109:ATF4 protein, human; D001057:Apolipoproteins E; D051701:Activating Transcription Factor 4; D005947:Glucose