Functional characterization of a haplotype in the AKT1 gene associated with glucose homeostasis and metabolic syndrome

Abstract

A small 12-kb haplotype upstream of the AKT1 gene has been found to be associated with insulin resistance phenotypes. We sought to define the functional consequences of the three component polymorphic loci (rs1130214, rs10141867, rs33925946) on AKT1 and the upstream ZBTB42 gene. 5′ RACE analysis of AKT1 transcripts in human skeletal muscle biopsies showed the predominant promoter to be 2.5 kb upstream of exon 2, and distinct from those promoters previously reported in rat. We then studied the effect of each of the three haplotype polymorphisms in transcriptional reporter assays in muscle, bone, and fat cell culture models, and found that each modulated enhancer and repressor activity are in a cell-specific and differentiation-specific manner. Our results in promoter assays are consistent with the human phenotype data; we found an anabolic effect on muscle and bone with increased mRNA expression of AKT1, and catabolic effect on fat with decreased expression. To test the hypothesis that rs10141867 affects transcription levels of the novel zinc finger protein ZBTB42 in vivo, we developed the allele-specific expression assay using Taqman technology to test for allelic differences within heterozygotes. The allele containing the derived polymorphism (haplotype H2) showed a 1.75-fold increase in expression in human skeletal muscle. Our data show a particularly complex effect of the component polymorphisms of a single haplotype on cells and tissues, suggesting that the coordination of different tissue-specific effects may have driven selection for the H2 haplotype. In light of the recent abundance of SNP association studies, our approach can serve as a method for exploring the biological function of polymorphisms that show significant genotype/phenotype associations.

Genetic variants in AKT1 gene were associated with risk and survival of OSCC in Chinese Han Population

“…In the current study, variant genotype and allele of rs1130214 was related to increased risk of OSCC, which was in accordance with the findings in non‐small cell lung cancer and prostate cancer in previous studies . Despite human cancer, polymorphism rs1130214 was also found to contribute to glucose/obesity‐related metabolism disturbance , Parkinson's disease , and schizophrenia , implying rs1130214 might be an important functional SNP with a major impact on various human diseases. In addition, patients with variant genotypes and allele of rs3803300 also had a higher risk of OSCC.…”

AKT1G205T genotype influences obesity-related metabolic phenotypes and their responses to aerobic exercise training in older Caucasians

“…Furthermore, the G205T polymorphism may have a functional effect (Thiselton et al 2008). Recently, Harmon et al (2010) reported that the T allele was part of an AKT1 haplotype that resulted in enhanced transcription in muscle and decreased transcription in fat. In keeping with these findings, we found that several obesity‐related metabolic variables differed prior to exercise training by the AKT1 G205T genotype in generally healthy, older men.…”

“…Although speculative, sex‐specific physiological differences in hormone levels or body composition may influence AKT1 genotype associations with obesity‐related metabolic variables. This is an interesting avenue for further research, since AKT1 variants appear to have tissue‐specific effects (Harmon et al 2010). In contrast, in the present study, these sex differences may be due in part to a statistical power issue resulting from the inclusion of HRT usage in the analyses involving women.…”

Genes thatAKTto determine physiological heterogeneity in response to exercise

“…McKenzie et al (2011) studied the impact of the AKT1 G205T (rs1130214) polymorphism on these physiological parameters and the response to exercise training. The G205T single nucleotide polymorphism is not in a protein‐coding region, and it has recently been shown to have a cell‐type‐specific impact on transcriptional activity (Harmon et al 2010). In particular, the T allele appears to enhance transcription in muscle cells, while inhibiting transcription in adipocytes (Harmon et al 2010), albeit the human sequence studied in murine cells.…”

“…The G205T single nucleotide polymorphism is not in a protein‐coding region, and it has recently been shown to have a cell‐type‐specific impact on transcriptional activity (Harmon et al 2010). In particular, the T allele appears to enhance transcription in muscle cells, while inhibiting transcription in adipocytes (Harmon et al 2010), albeit the human sequence studied in murine cells. Thus, it could be expected that McKenzie et al (2011) would find a complex in vivo phenotype for the AKT1 G205T (rs1130214) polymorphism.…”