Low-frequency variants in HMGA1 are not associated with type 2 diabetes risk

The Role of HMGA1 and Height in Breast Cancer Risk and Prognosis: Insights from UK Biobank Data

Background/Aim

Tall women are more likely to develop breast cancer (BC). High Mobility Group AT-Hook 1 (HMGA1), an oncofetal protein, plays a role in BC progression. Variants near HMGA1 have been associated with increased height. This study examines the relationship between HMGA1, height, and BC risk and prognosis using UK Biobank data.

Patients and Methods

Data from 10,527 women with invasive BC were analyzed. Subjects were grouped by height: short (<155 cm), medium (155-175 cm), and tall (>175 cm). HMGA1 SNP rs41269028, a single nucleotide intron variant, was evaluated for its influence on height, BC risk, and survival. Statistical analysis included Fisher's exact test, regression models, and survival analysis using the log-rank test.

Results

HMGA1 SNP rs41269028 carriers (CT+TT) were taller (162.88 cm) compared to homozygotes for the major allele (162.29 cm, p=0.005). Tall women with BC showed poorer survival than short women (p=0.032). However, HMGA1 genotype did not significantly affect BC risk (p=0.602) or survival (p=0.439). Multivariate analysis confirmed an independent effect of age and HMGA1 genotype on height.

Conclusion

While HMGA1 influences height, no direct association with increased BC risk or poor prognosis in tall women was demonstrated. Nevertheless, tall women with BC had worse survival, suggesting height might be considered in treatment decisions. Future studies should explore mechanisms linking height to BC outcomes.

Tall women with breast cancer have poorer survival than short women

Background

Tall women are more likely to develop breast cancer (BC). High Mobility Group AT-Hook 1(HMGA1), an oncofetal protein, plays a role in the progression of breast cancer. Non-coding sequences proximal to HMGA1 contain variants associated with 4.83 cm taller height. In the current study, we used UK Biobank data to examine the relationship of HMGA1 to height, risk, and prognosis of women with breast cancer.

Methods

Our analysis included all subjects with invasive BC that occurred either before or after participant enrollment and were recorded in the UK Biobank database using self-reported data and the International Classification of Diseases (ICD10, ICD9). We divided the subjects into three previously described three height groups: Short (< 155 cm), Medium (155 cm to 175 cm), Tall (> 175 cm). We analyzed the HMGA1 SNP rs41269028, a single nucleotide intron variant, C > T, minor allele frequency 0.044. SNP rs41269028 was previously evaluated in subjects with diabetes.

Results

Height of 9583 women with BC homozygous for the HMGA1 SNP rs41269028 major allele was 162.29 cm ± 6.18. Height of 944 women with BC who were carriers or homozygotes (CT + TT) of the minor allele T was 162.88 cm ± 6.001. This difference was significant (p = 0.005). The effect of height group on survival was significant (p = 0.032, log rank test). Tall women had the poorest survival. The effect of HMGA1 SNP rs41269028 genotype on BC risk (p = 0.602) and survival (p = 0.439, log rank test) was insignificant.

Conclusion

We conclude that HMGA1 influences height, but we were unable to demonstrate that HMGA1 is related to increased incidence or poor prognosis of tall women with breast cancer. We did find that tall women with breast cancer have poorer survival than short women. Our finding that tall women have a worse prognosis is important because it could help the oncologist decide, along with other prognostic factors, whether adjuvant therapy is warranted.

Loss of Znt8 function in diabetes mellitus: risk or benefit?

The zinc transporter 8 (ZnT8) plays an essential role in zinc homeostasis inside pancreatic β cells, its function is related to the stabilization of insulin hexameric form. Genome-wide association studies (GWAS) have established a positive and negative relationship of ZnT8 variants with type 2 diabetes mellitus (T2DM), exposing a dual and controversial role. The first hypotheses about its role in T2DM indicated a higher risk of developing T2DM for loss of function; nevertheless, recent GWAS of ZnT8 loss-of-function mutations in humans have shown protection against T2DM. With regard to the ZnT8 role in T2DM, most studies have focused on rodent models and common high-risk variants; however, considerable differences between human and rodent models have been found and the new approaches have included lower-frequency variants as a tool to clarify gene functions, allowing a better understanding of the disease and offering possible therapeutic targets. Therefore, this review will discuss the physiological effects of the ZnT8 variants associated with a major and lower risk of T2DM, emphasizing the low- and rare-frequency variants.

HMGA1 variant IVS5-13insC is associated with insulin resistance and type 2 diabetes: an updated meta-analysis

Background

High-mobility group A1 (HMGA1) polymorphism has been suspected as a gene variant associated with type 2 diabetes (T2D). However, conflicting outcomes have been reported.

Objective

This meta-analysis aimed to predict the association between the HMGA1 variant IVS5-13insC and T2D.

Methods

Statistical analyses were performed using Stata/SE 12.0 software.

Results

A total of 11 case-control studies in 6 articles were included. Results suggested that the HMGA1 variant IVS5-13insC was associated with an increased risk of insulin resistance (OR = 0.61, 95% CI 0.56 to 0.66, P < 0.0001), T2D (OR = 0.67, 95% CI 0.61 to 0.73, P < 0.0001), particularly for Caucasians with increased risks of T2D (OR = 0.56, 95% CI 0.49 to 0.65, P < 0.0001) compared with wild-type subjects.

Conclusion

This meta-analysis indicated that the HMGA1 variant IVS5-13insC can be a risk factor of T2D development, particularly among Caucasians. Significant risks were also found (Asian: OR = 0.74, 95% CI: 0.63 to 0.86, P < 0.0001, Hispanic-American: OR = 0.81, 95% CI: 0.65 to 1.01, P < 0.0001) in non-Caucasian population. However, ethnical studies should be conducted to reveal whether the HMGA1 variant IVS5-13insC is associated with an increased risk of T2D.

Transcriptional Regulation of Glucose Metabolism: The Emerging Role of the HMGA1 Chromatin Factor

HMGA1 (high mobility group A1) is a nonhistone architectural chromosomal protein that functions mainly as a dynamic regulator of chromatin structure and gene transcription. As such, HMGA1 is involved in a variety of fundamental cellular processes, including gene expression, epigenetic regulation, cell differentiation and proliferation, as well as DNA repair. In the last years, many reports have demonstrated a role of HMGA1 in the transcriptional regulation of several genes implicated in glucose homeostasis. Initially, it was proved that HMGA1 is essential for normal expression of the insulin receptor (INSR), a critical link in insulin action and glucose homeostasis. Later, it was demonstrated that HMGA1 is also a downstream nuclear target of the INSR signaling pathway, representing a novel mediator of insulin action and function at this level. Moreover, other observations have indicated the role of HMGA1 as a positive modulator of the Forkhead box protein O1 (FoxO1), a master regulatory factor for gluconeogenesis and glycogenolysis, as well as a positive regulator of the expression of insulin and of a series of circulating proteins that are involved in glucose counterregulation, such as the insulin growth factor binding protein 1 (IGFBP1), and the retinol binding protein 4 (RBP4). Thus, several lines of evidence underscore the importance of HMGA1 in the regulation of glucose production and disposal. Consistently, lack of HMGA1 causes insulin resistance and diabetes in humans and mice, while variations in the HMGA1 gene are associated with the risk of type 2 diabetes and metabolic syndrome, two highly prevalent diseases that share insulin resistance as a common pathogenetic mechanism. This review intends to give an overview about our current knowledge on the role of HMGA1 in glucose metabolism. Although research in this field is ongoing, many aspects still remain elusive. Future directions to improve our insights into the pathophysiology of glucose homeostasis may include epigenetic studies and the use of "omics" strategies. We believe that a more comprehensive understanding of HMGA1 and its networks may reveal interesting molecular links between glucose metabolism and other biological processes, such as cell proliferation and differentiation.

IGF2 mRNA binding protein-2 is a tumor promoter that drives cancer proliferation through its client mRNAs IGF2 and HMGA1

The gene encoding the Insulin-like Growth Factor 2 mRNA binding protein 2/IMP2 is amplified and overexpressed in many human cancers, accompanied by a poorer prognosis. Mice lacking IMP2 exhibit a longer lifespan and a reduced tumor burden at old age. Herein we show in a diverse array of human cancer cells that IMP2 overexpression stimulates and IMP2 elimination diminishes proliferation by 50–80%. In addition to its known ability to promote the abundance of Insulin-like Growth Factor 2/IGF2, we find that IMP2 strongly promotes IGF action, by binding and stabilizing the mRNA encoding the DNA binding protein HMGA1, a known oncogene. HMGA1 suppresses the abundance of IGF binding protein 2/IGFBP2 and Grb14, inhibitors of IGF action. IMP2 stabilization of HMGA1 mRNA plus IMP2 stimulated IGF2 production synergistically drive cancer cell proliferation and account for IMP2’s tumor promoting action. IMP2’s ability to promote proliferation and IGF action requires IMP2 phosphorylation by mTOR.

Some types of cancers develop when genes known as oncogenes or tumor promoters become faulty, and are present at abnormally high levels or inappropriately turned on. For example, cancer cells often have extra copies of the gene IMP2 and therefore produce too much the IMP2 protein. Previous research has shown that mice that lack the IMP2 protein develop fewer cancers and live longer, while patients whose cancers make too much IMP2 have a poorer prognosis.

In healthy cells, the IMP2 protein normally helps to make new gene products by stabilising certain newly produced RNA molecules – the precursors of proteins, and in some cases by promoting the translation of these RNAs into proteins. For example, IMP2 binds to the mRNA that encodes the protein IGF2, which is a protein that helps cells to grow and is commonly produced in large quantities by cancer cells. However, until now it was not clear whether IMP2 only acts by increasing the production of IGF2 or also contributes to cancer growth in other ways.

Using a range of human cancer cell lines, and healthy mouse cells, Dai et al. first confirmed that without IMP2, cancer cells made less IGF2 and grew less quickly. When IGF2 was added to the cells lacking IMP2, it only partially restored their ability to grow. Further experiments revealed that cells without IMP2 had increased levels of proteins that counteract the effects of IGF2. Usually, IMP2 binds and stabilizes the mRNA that encodes the oncogenic protein HMGA1, which is known to regulate the number of ‘anti-IGF2 proteins’. However, without IMP2, the HMGA1 levels drop, which causes an increase of the anti-IGF2 proteins.

This indicates that IMP2 promotes cancer cell growth both by enabling cells to produce more IGF2 and by suppressing inhibitors of IGF2 action. This suggests that cancer patients whose tumors have abnormally high levels of IMP2 may be especially sensitive to drugs that target and inhibit IGF2.

Association of ICAM-1 and HMGA1 Gene Variants with Retinopathy in Type 2 Diabetes Mellitus Among Chinese Individuals

PURPOSE

To evaluate the association of intercellular cell-adhesion molecule 1 (ICAM-1) and high-mobility group A1 (HMGA1) gene variants with diabetic retinopathy (DR) in a Chinese type 2 diabetes mellitus (T2DM) cohort.

METHODS

A total of 792 patients with T2DM were enrolled and categorized into two groups: (1) the DR group consisted of 448 patients, which was further subclassified into the proliferative DR (PDR) group with 220 patients and the nonproliferative DR (NPDR) group with 228 patients; (2) the diabetes without retinopathy (DNR) group comprised 344 patients who had no signs of DR. The single-nucleotide polymorphism (SNP) rs5498 in ICAM-1 gene and IVS5-13insC variant in HMGA1 gene were genotyped.

RESULTS

No evident association was found in the allele frequencies between SNP rs5498 in ICAM-1 gene and DR patients; the combined p values for the additive, dominant, and recessive models in genotype were greater than 0.05. No significant association was identified between the IVS5-13insC variant in HMGA1 gene and DR individuals.

CONCLUSIONS

Our results revealed that SNP rs5498 in ICAM-1 gene and IVS5-13insC variant in HMGA1 gene were not associated with the susceptibility of DR in the Chinese T2DM cohort.

The Association between HMGA1 rs146052672 Variant and Type 2 Diabetes: A Transethnic Meta-Analysis

The high-mobility group A1 (HMGA1) gene has been previously identified as a potential novel candidate gene for susceptibility to insulin resistance and type 2 diabetes (T2D) mellitus. For this reason, several studies have been conducted in recent years examining the association of the HMGA1 gene variant rs146052672 (also designated IVS5-13insC) with T2D. Because of non-univocal data and non-overlapping results among laboratories, we conducted the current meta-analysis with the aim to yield a more precise and reliable conclusion for this association. Using predetermined inclusion criteria, MEDLINE, PubMed, Web of Science, Scopus, Google Scholar and Embase were searched for all relevant available literature published until November 2014. Two of the authors independently evaluated the quality of the included studies and extracted the data. Values from the single studies were combined to determine the meta-analysis pooled estimates. Heterogeneity and publication bias were also examined. Among the articles reviewed, five studies (for a total of 13,789 cases and 13,460 controls) met the predetermined criteria for inclusion in this meta-analysis. The combined adjusted odds ratio estimates revealed that the rs146052672 variant genotype had an overall statistically significant effect on increasing the risk of development of T2D. As most of the study subjects were Caucasian, further studies are needed to establish whether the association of this variant with an increased risk of T2D is generalizable to other populations. Also, in the light of this result, it would appear to be highly desirable that further in-depth investigations should be undertaken to elucidate the biological significance of the HMGA1 rs146052672 variant.

A polymorphism of HMGA1 is associated with increased risk of metabolic syndrome and related components

The metabolic syndrome (MetS) is a common disorder, where systemic insulin-resistance is associated with increased risk for type 2 diabetes (T2D) and cardiovascular disease. Identifying genetic traits influencing risk and progression of MetS is important. We and others previously reported a functional HMGA1 gene variant, rs146052672, predisposing to T2D. Here we investigated the association of rs146052672 variant with MetS and related components. In a case-control study from Italy and Turkey, increased risk of MetS was seen among carriers of the HMGA1 variant. In the larger Italian cohort, this variant positively correlated with BMI, hyperglycemia and insulin-resistance, and negatively correlated with serum HDL-cholesterol. Association between rs146052672 variant and MetS occurred independently of T2D, indicating that HMGA1 gene defects play a pathogenetic role in MetS and other insulin-resistance-related conditions. Overall, our results indicate that the rs146052672 variant represents an early predictive marker of MetS, as well as a predictive tool for therapy.

Recent advances in the molecular genetics of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a complex disease in which both genetic and environmental factors interact in determining impaired β-cell insulin secretion and peripheral insulin resistance. Insulin resistance in muscle, liver and fat is a prominent feature of most patients with T2DM and obesity, resulting in a reduced response of these tissues to insulin. Considerable evidence has been accumulated to indicate that heredity is a major determinant of insulin resistance and T2DM. It is believed that, among individuals destined to develop T2DM, hyperinsulinemia is the mechanism by which the pancreatic β-cell initially compensates for deteriorating peripheral insulin sensitivity, thus ensuring normal glucose tolerance. Most of these people will develop T2DM when β-cells fail to compensate. Despite the progress achieved in this field in recent years, the genetic causes of insulin resistance and T2DM remain elusive. Candidate gene association, linkage and genome-wide association studies have highlighted the role of genetic factors in the development of T2DM. Using these strategies, a large number of variants have been identified in many of these genes, most of which may influence both hepatic and peripheral insulin resistance, adipogenesis and β-cell mass and function. Recently, a new gene has been identified by our research group, the HMGA1 gene, whose loss of function can greatly raise the risk of developing T2DM in humans and mice. Functional genetic variants of the HMGA1 gene have been associated with insulin resistance syndromes among white Europeans, Chinese individuals and Americans of Hispanic ancestry. These findings may represent new ways to improve or even prevent T2DM.

Evidence that an HMGA1 gene variant associates with type 2 diabetes, body mass index, and high-density lipoprotein cholesterol in a Hispanic-American population

BACKGROUND

High-mobility group AT-hook 1 (HMGA1) is an important regulator of the insulin receptor gene. We have previously shown in three populations of white European ancestry that the HMGA1 gene variant rs146052672 (also designated IVS5-13insC) is associated with type 2 diabetes mellitus (T2DM). The aim of this study was to measure the frequency of this variant and to determine the degree of the association with T2DM and other features of the metabolic syndrome in a replication cohort of Hispanic Americans.

METHODS

This was a retrospective cohort study of well-characterized Hispanic-American participants analyzed in the Genomic Resource in Atherosclerosis (GRA) (Cardiovascular Research Institute, University of California, San Francisco). A total of 1144 individuals were studied, 320 of whom had T2DM. We examined associations of the rs146052672 SNP with T2DM, plasma lipids, lipoproteins, and body mass index (BMI).

RESULTS

In this Hispanic-American cohort, the HMGA1 rs146052672 minor allele (C-insertion) frequency (MAF) was 21.4% with a carrier frequency of 37.4%, considerably higher than we previously observed among GRA white Europeans (MAF 3.1%). The prevalence of the IVS5-13insC variant was significantly higher in those with T2DM compared to controls [42.2% vs. 35.5%; odds ratio (OR) 1.44 95% confidence interval (CI) 1.09-1.90, P=0.011). The variant was also associated with BMI (positively, P=0.045) and plasma high-density lipoprotein cholesterol (HDL-C) (negatively, P=0.047).

CONCLUSIONS

As we saw previously among white Europeans, a functional HMGA1 variant was associated with T2DM in individuals of Hispanic-American ethnicity and was present at a much higher frequency.

Lack of association of the HMGA1 IVS5-13insC variant with type 2 diabetes in an ethnically diverse hypertensive case control cohort

BACKGROUND

Recently, the high-mobility group A1 gene (HMGA1) variant IVS5-13insC has been associated with type 2 diabetes, but reported associations are inconsistent and data are lacking in Hispanic and African American populations. We sought to investigate the HMGA1-diabetes association and to characterize IVS5-13insC allele frequencies and linkage disequilibrium (LD) in 3,070 Caucasian, Hispanic, and African American patients from the INternational VErapamil SR-Trandolapril STudy (INVEST).

METHODS

INVEST was a randomized, multicenter trial comparing two antihypertensive treatment strategies in an ethnically diverse cohort of hypertensive, coronary artery disease patients. Controls, who were diabetes-free throughout the study, and type 2 diabetes cases, either prevalent or incident, were genotyped for IVS5-13insC using Taqman®, confirmed with Pyrosequencing and Sanger sequencing. For LD analysis, genotyping for eight additional HMGA1 single nucleotide polymorphisms (SNPs) was performed using the Illumina® HumanCVD BeadChip. We used logistic regression to test association of the HMGA1 IVS5-13insC and diabetes, adjusted for age, gender, body mass index, and percentage European, African, and Native American ancestry.

RESULTS

We observed IVS5-13insC minor allele frequencies consistent with previous literature in Caucasians and African Americans (0.03 in cases and 0.04 in controls for both race/ethnic groups), and higher frequencies in Hispanics (0.07 in cases and 0.07 in controls). The IVS5-13insC was not associated with type 2 diabetes overall (odds ratio 0.98 [0.76-1.26], p=0.88) or in any race/ethnic group. Pairwise LD (r2) of IVS5-13insC and rs9394200, a SNP previously used as a tag SNP for IVS5-13insC, was low (r2=0.47 in Caucasians, r2=0.25 in Hispanics, and r2=0.06 in African Americans). Furthermore, in silico analysis suggested a lack of functional consequences for the IVS5-13insC variant.

CONCLUSIONS

Our results suggest that IVS5-13insC is not a functional variant and not associated with type 2 diabetes in an ethnically diverse, hypertensive, coronary artery disease population. Larger, more adequately powered studies need to be performed to confirm our findings.