Glucose transporter GLUT12-functional characterization in Xenopus laevis oocytes

We have recently identified and cloned the cDNA of a new member of the glucose transporter family that has been designated GLUT12. GLUT12 possesses the structural features critical to facilitative transport of glucose but the key to understanding the possible physiological roles of this novel protein requires analysis of functional glucose transport. In the current study, we have utilized the Xenopus laevis oocyte expression system to assay transport of the glucose analog 2-deoxy-D-glucose and characterize the glucose transport properties and hexose affinities of GLUT12. Our results demonstrate that GLUT12 facilitates transport of glucose with an apparent preferential substrate affinity for glucose over other hexoses assayed. The results are significant to understanding the potential role and importance of GLUT12 in insulin-sensitive tissues and also cells with high glucose utilization such as cancer cells.

Paraoxonase and other coronary risk factors in a community-based cohort

Oxidative damage to circulating lipids and vascular tissues contributes to the initiation and progression of atherosclerosis. High density lipoprotein provides protection from atherosclerosis and the enzyme paraoxonase may contribute to this effect. The aim of the present study was to examine the trends in paraoxonase activity during the course of a community-directed life-style intervention, and relationships of paraoxonase activity to other coronary heart disease risk factors, in a cohort of Australian Aboriginal people.

Inflammation and vascular endothelial activation in an Aboriginal population: relationships to coronary disease risk factors and nutritional markers

OBJECTIVE

To describe the levels of inflammation and vascular endothelial activation in an Aboriginal community, and the relationship of these factors to coronary heart disease (CHD) risk factors and markers of nutritional quality.

DESIGN AND PARTICIPANTS

A cross-sectional survey of 95 women and 76 men participating in a chronic-disease prevention program.

SETTING

A remote Aboriginal community in Western Australia in 1996.

MAIN OUTCOME MEASURES

Concentrations of markers of inflammation (C-reactive protein [CRP]) and vascular endothelial activation (soluble E-selectin [sE-selectin]); presence of metabolic syndrome; concentrations of diet-derived antioxidants.

RESULTS

Participants exhibited very high plasma concentrations of CRP (mean, 5.4 mg/L; 95% CI, 4.6-6.3 mg/L) and sE-selectin (mean, 119 ng/mL; 95% CI, 111-128 ng/mL). Both CRP and sE-selectin concentrations were significantly higher in the presence of the metabolic syndrome. There were significant inverse linear relationships between concentrations of CRP and plasma concentrations of the antioxidants lycopene, beta-carotene, cryptoxanthin and retinol. Even stronger inverse associations were evident between concentrations of sE-selectin and lycopene, beta-carotene, cryptoxanthin and lutein.

CONCLUSIONS

Vascular inflammation and endothelial activation may be important mediators of elevated CHD risk in Aboriginal people. Inadequate nutrition and physical inactivity may contribute to this process.

GLUT12 expression in human placenta in first trimester and term

The aim of this study was to characterize the expression of a novel glucose transporter protein GLUT12 in human placenta. GLUT12 mRNA expression was identified by RT-PCR in extracts from five normal term placentae and in extracts from cultured cells of the JAR, JEG-3 and HTR-8Svneo cell lines. In further studies, paraffin sections of first trimester tissue from chorionic villus sampling and term tissue obtained after delivery were analysed by immunohistology with a GLUT12 specific polyclonal antibody. GLUT12 immunoreactivity was expressed predominantly in the syncytiotrophoblast and in extra-villous trophoblast cells in first trimester tissues at 10, 11 and 12 weeks' gestation. In term tissue, however, GLUT12 staining was not detected in syncytiotrophoblast and was found predominantly in villous vascular smooth muscle cells and villous stromal cells. These results suggest that there is a dynamic spatial and temporal expression pattern for the novel glucose transporter GLUT12 in human placenta.

Differential expression of GLUT12 in breast cancer and normal breast tissue

Increased and deregulated expression of glucose transporters is a characteristic of cancer cells. We previously identified a novel glucose transporter protein, GLUT12, in the MCF7 malignant breast epithelial cell line. Here we present the first demonstration of GLUT12 expression in human breast tumours. Using immunohistochemistry and reverse transcription polymerase chain reaction, GLUT12 was detected in eight of ten invasive tumours. Ductal cell carcinoma in situ cells also stained strongly for GLUT12. Immunohistochemical staining for GLUT12 in benign ducts was less intense, with few positively stained cells. GLUT12 may have a role in hexose supply to breast cancer cells.

Expression and localization of GLUT1 and GLUT12 in prostate carcinoma

BACKGROUND

Increased glucose consumption is a characteristic of malignant cells and in prostate carcinoma is associated with the proliferation of both androgen-dependent and independent cells. Transport of polar glucose across the nonpolar membrane relies on glucose transporter proteins, known as GLUTs. Increased expression of GLUT1 is a characteristic of many malignant cells. The authors characterized and cloned the cDNA for a novel glucose transporter, GLUT12, which was identified initially in malignant breast epithelial cells. To the authors' knowledge, there have been no reports on the expression of glucose transporters in the human prostate or human prostate carcinoma cells. The authors evaluated GLUT1 and GLUT12 expression in human prostate carcinoma cells.

METHODS

Reverse transcription-polymerase chain reaction was performed on total RNA extracted from cultured prostate carcinoma cells LNCaP, C4, C4-2, and C4-2B using primers to amplify GLUT1, GLUT12, or the housekeeping gene, 36B4. Total protein extracted from prostate carcinoma cell lines was assessed for GLUT12 protein by Western blot analysis. Cultured cell monolayers were incubated with antibodies to GLUT1 or GLUT12 and a peripheral Golgi protein, Golgi 58K, for detection by immunofluorescent confocal microscopy. Sections of benign prostatic hyperplasia and human prostate carcinoma were stained for immunohistochemical detection of GLUT1 and GLUT12.

RESULTS

GLUT1 and GLUT12 mRNA and protein were detected in all cell lines evaluated. Immunofluorescence staining demonstrated both GLUT1 and GLUT12 on the plasma membrane and in the cytoplasm in all cultured prostate carcinoma cell lines, with GLUT1 but not GLUT12 appearing to colocalize with the Golgi. Immunohistochemical staining of benign prostatic hyperplasia indicated expression of GLUT1 but not GLUT12. Malignant tissue stained for GLUT12 but was negative for GLUT1.

CONCLUSIONS

GLUT1 and GLUT12 are expressed in human prostate carcinoma cells. One possible rationale for the GLUT1 Golgi association is that it may supply glucose to the Golgi for byproduct incorporation into the prostatic secretory fluid. Further work will investigate the importance of glucose transport and GLUT1 and GLUT12 in prostate carcinoma cell growth.

Association of albuminuria and the metabolic syndrome

Microalbuminuria clusters with the metabolic syndrome, and both conditions predict cardiovascular disease mortality. The reported relationships of microalbuminuria with the individual components of the metabolic syndrome (i.e., hyperglycemia, insulin resistance, hypertension, dyslipidemia, abdominal obesity) are variable. Each of these components, as well as intrauterine effects and diet and other lifestyle factors, may contribute to elevated risk of microalbuminuria in certain population groups. Recent evidence indicates a role for oxidation and inflammation in cardiovascular disease, and endothelial dysfunction (exacerbated by factors such as dyslipidemia) may be the mediator of this relationship. Because endothelial dysfunction can also be manifested as microalbuminuria, this provides a potential explanation of the observed association of the metabolic syndrome, chronic inflammation, and microalbuminuria.

Expression and localisation of GLUT1 and GLUT12 glucose transporters in the pregnant and lactating rat mammary gland

Glucose plays a major role in mammary gland function during lactation as it is used both as a fuel and as a precursor of milk components. In rats, previous studies have shown that the facilitative glucose transporter GLUT1 is expressed in mammary epithelial cells. We have used confocal immunofluorescence to localise GLUT1 and GLUT12, a recently identified member of the sugar transporter family, in pregnant and lactating rat mammary gland. GLUT12 staining was observed in the cytoplasm of mammary epithelial cells at day 20 of pregnancy, and at 1 and 6 days postpartum. Furthermore, GLUT12 staining was present at the apical plasma membrane of epithelial cells during lactation. In contrast, GLUT1 protein localised to the cytoplasm and basolateral surface of mammary epithelial cells. Forced weaning resulted in decreased cytoplasmic GLUT1 staining intensity, but no change in GLUT12 staining. The results suggest a possible role for GLUT12 in the metabolism of mammary epithelial cells during pregnancy and lactation.

A cross-sectional study of the effects of type 2 diabetes and other cardiovascular risk factors on structure and function of nonstenotic arteries of the lower limb

OBJECTIVE

To compare intimal-medial thickness (IMT) and pulse wave conduction velocity (PWCV) in unstenosed arteries of the lower limb in subjects with and without type 2 diabetes and to determine the contribution of a range of cardiovascular risk factors.

RESEARCH DESIGN AND METHODS

IMT and PWCV were determined in lower-limb arteries of 79 subjects with diabetes and 77 euglycemic subjects. Plasma lipids were determined by enzymatic assays, and LDL particle size was measured by gradient gel electrophoresis. Lag time for copper-induced oxidation of LDL was determined. alpha-Tocopherol, retinol, and ascorbate levels were determined by high-performance liquid chromatography, soluble E-selectin by enzyme-linked immunosorbent assay, and fibrinogen and factor VII by automated assays.

RESULTS

Subjects with diabetes had greater superficial femoral artery (SFA) IMT, popliteal artery (PA) IMT, and SFA PWCV (all P < 0.0001). In univariate analysis, IMT and PWCV correlated with increased waist-to-hip ratio, triglycerides, and fibrinogen and inversely with HDL cholesterol and LDL size. Ascorbate was inversely associated with IMT, and LDL lag time was inversely correlated with PWCV. Subjects with the greatest number of features of the metabolic syndrome had the highest IMT and PWCV.

CONCLUSIONS

Adverse changes in the structure and function of unstenosed lower-limb arteries are present in type 2 diabetes and are associated with features of the metabolic syndrome.

Expression during rat fetal development of GLUT12--a member of the class III hexose transporter family

Glucose is an essential molecule for most mammalian cells, and is particularly important during fetal development, when cells are rapidly dividing and differentiating. In rats, GLUT1 is present at high levels in most fetal tissues, with levels decreasing after birth. We used immunohistochemistry to localise GLUT12 protein, a recently identified member of the sugar transporter family, and GLUT1 during rat fetal development. GLUT12 staining was observed in heart muscle from gestational days 15 to 21. GLUT12 staining in skeletal muscle increased from gestational days 17 to 21, and GLUT12 was also detected in brown adipose tissue. The expression of GLUT12 in insulin-responsive tissues supports a potential role for GLUT12 in the provision of glucose to these tissues before the appearance of GLUT4. GLUT12 protein was also expressed in fetal chondrocytes from gestational day 15 onward, in kidney distal tubules and collecting ducts from day 19, and in lung bronchioles from day 19. The specific pattern of expression observed in the rat fetus suggests that GLUT12 may be important in hexose delivery to developing tissues.

Obesity, diabetes and associated cardiovascular risk factors among Torres Strait Islander people

OBJECTIVE

To describe the lifestyle-related chronic disease and risk factor prevalence among Torres Strait Islander people of the Torres Strait and Northern Peninsula Area Health Service District and to compare this information with that available for the general Australian population.

METHODS

Voluntary community-based screening for persons aged 15 years and older, including oral glucose tolerance test, anthropometry, health questionnaire, measurement of lipids and lipoprotein levels, blood pressure and urinary albumin to creatinine ratio.

RESULTS

Nine communities participated in screening between 1993 and 1997. Five hundred and ninety-two participants (286 male and 306 female) identified as Torres Strait Islander. There were high prevalences of overweight (30%), obesity (51%), abdominal obesity (70%), diabetes (26%), hypercholesterolaemia (33%), albuminuria (28%), hypertension (32%) and tobacco smoking (45%). Only 8.5% of men and 6.5% of women were free of any cardiovascular risk factors (abdominal obesity, hypercholesterolaemia, hypertension, dyslipidaemia, smoking, diabetes, albuminuria). Comparisons of this information for Torres Strait Islander people with results from the AusDiab survey show rates of obesity three times higher and diabetes six times higher than for other Australians.

CONCLUSIONS

There is a very high prevalence of preventable chronic disease and associated risk factors among Torres Strait Islander people of the Torres Strait and Northern Peninsula Area.

IMPLICATIONS

Effective interventions to prevent and manage obesity, diabetes and associated cardiovascular risk factors are essential if the health of the Torres Strait Islander people is to improve. Such interventions could inform initiatives to stem the burgeoning epidemic of obesity and diabetes among all Australians.

Nomenclature of the GLUT/SLC2A family of sugar/polyol transport facilitators

The recent identification of several additional members of the family of sugar transport facilitators (gene symbol SLC2A, protein symbol GLUT) has created a heterogeneous and, in part, confusing nomenclature. Therefore, this letter provides a summary of the family members and suggests a systematic nomenclature for SLC2A and GLUT symbols.

How many patients with coronary heart disease are not achieving their risk-factor targets? Experience in Victoria 1996-1998 versus 1999-2000

OBJECTIVES

To determine the proportion of patients with established coronary heart disease (CHD) in two Australian studies (VIC-I in 1996-1998, and VIC-II in 1999-2000) who achieved their risk-factor targets as recommended by the National Heart Foundation of Australia, and to compare this proportion with those in studies from the United Kingdom (ASPIRE), Europe (EUROASPIRE I and II) and the United States (L-TAP).

DESIGN AND SETTING

Prospective cohort study with VIC-I set in a single Melbourne university teaching hospital and VIC-II set in six university teaching hospitals in Melbourne, Victoria.

PARTICIPANTS

460 patients (112 in VIC-I, 348 in VIC-II) who completed follow-up in the control groups of two randomised controlled trials of a coaching intervention in patients with established CHD.

MAIN OUTCOME MEASURES

The treatment gap (100%, minus the percentage of patients achieving the target level for a particular modifiable risk factor) at six months after hospitalisation.

RESULTS

The treatment gap declined from 96.4% (95% CI, 91%-99%) to 74.1% (95% CI, 69%-79%) for total cholesterol concentration (TC) < 4.0 mmol/L (P = 0.0001) and from 90.2% (95% CI, 83%-95%) to 54.0% (95% CI, 49%-59%) for TC < 4.5 mmol/L (P = 0.0001). This reduction in the treatment gap between VIC-I and VIC-II appears to be entirely explained by an increase in the number of patients prescribed lipid-lowering drugs. The treatment gaps in the UK and two European studies were substantially greater. The treatment gap for blood pressure (systolic > or = 140 mmHg and/or diastolic > or = 90 mmHg) in VIC-II was 39.5%, again less than corresponding European data. There were 8.1% of patients who had unrecognised diabetes in VIC-II (fasting glucose level > or = 7 mmol/L), making a total of 25.6% of VIC-II patients with diabetes, self-reported or unrecognised. The proportion of patients in VIC-II who were obese (body mass index > or = 30 kg/m2) was similar to the overseas studies, while fewer patients in VIC-II smoked compared with those in the UK and European studies.

CONCLUSIONS

A substantial treatment gap exists in Victorian patients with established CHD. The treatment gap compares well with international surveys and, at least in the lipid area, is diminishing.

Coaching patients with coronary heart disease to achieve the target cholesterol: a method to bridge the gap between evidence-based medicine and the "real world"--randomized controlled trial

Community studies have demonstrated suboptimal achievement of lipid targets in the management of patients with coronary heart disease (CHD). An effective strategy is required for the application of evidence-based prevention therapy for CHD. The objective of this study was to test coaching as a technique to assist patients in achieving the target cholesterol level of <4.5 mmol/L. Patients with established CHD (n = 245) underwent a stratified randomization by cardiac procedure (coronary artery bypass graft surgery or percutaneous coronary intervention) to receive either the coaching intervention (n = 121) or usual medical care (n = 124). The primary outcome measure was fasting serum total cholesterol (TC), serum triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), and calculated low-density lipoprotein cholesterol (LDL-C) level, measured at 6 months post-randomization. At 6 months, the serum TC and LDL-C levels were significantly lower in the coaching intervention group (n = 107) than the usual care group (n = 112): mean TC (95%CI) 5.00 (4.82-5.17) mmol/L versus 5.54 (5.36-5.72) mmol/L (P <.0001); mean LDL-C (95%CI) 3.11 (2.94-3.29) mmol/L versus 3.57 (3.39-3.75) mmol/L (P <.0004), respectively. Coaching had no impact on TG or on HDL-C levels. Multivariate analysis showed that being coached (P <.001) had an effect of equal magnitude to being prescribed lipid-lowering drug therapy (P <.001). The effectiveness of the coaching intervention is best explained by both adherence to drug therapy and to dietary advice given. Coaching may be an appropriate method to reduce the treatment gap in applying evidence-based medicine to the "real world."

Identification of a novel glucose transporter-like protein-GLUT-12

Facilitative glucose transporters exhibit variable hexose affinity and tissue-specific expression. These characteristics contribute to specialized metabolic properties of cells. Here we describe the characterization of a novel glucose transporter-like molecule, GLUT-12. GLUT-12 was identified in MCF-7 breast cancer cells by homology to the insulin-regulatable glucose transporter GLUT-4. The GLUT-12 cDNA encodes 617 amino acids, which possess features essential for sugar transport. Di-leucine motifs are present in NH(2) and COOH termini at positions similar to the GLUT-4 FQQI and LL targeting motifs. GLUT-12 exhibits 29% amino acid identity with GLUT-4 and 40% to the recently described GLUT-10. Like GLUT-10, a large extracellular domain is predicted between transmembrane domains 9 and 10. Genomic organization of GLUT-12 is highly conserved with GLUT-10 but distinct from GLUTs 1-5. Immunofluorescence showed that, in the absence of insulin, GLUT-12 is localized to the perinuclear region in MCF-7 cells. Immunoblotting demonstrated GLUT-12 expression in skeletal muscle, adipose tissue, and small intestine. Thus GLUT-12 is potentially part of a second insulin-responsive glucose transport system.