Transcriptional regulation of urate transportosome member SLC2A9 by nuclear receptor HNF4α.

Renal tubular handling of urate is realized by a network of uptake and efflux transporters, including members of drug transporter families such as solute carrier proteins and ATP-binding cassette transporters. Solute carrier family 2, member 9 (SLC2A9), is one key factor of this so called "urate transportosome." The aim of the present study was to understand the transcriptional regulation of SLC2A9 and to test whether identified factors might contribute to a coordinated transcriptional regulation of the transporters involved in urate handling. In silico analysis and cell-based reporter gene assays identified a hepatocyte nuclear factor (HNF)4α-binding site in the promoter of SLC2A9 isoform 1, whose activity was enhanced by transient HNF4α overexpression, whereas mutation of the binding site diminished activation. HNF4α overexpression induced endogenous SLC2A9 expression in vitro. The in vivo role of HNF4α in the modulation of renal SLC2A9 gene expression was supported by findings of quantitative real-time RT-PCR analyses and chromatin immunoprecipitation assays. Indeed, mRNA expression of SLC2A9 and HNF4α in human kidney samples was significantly correlated. We also showed that in renal clear cell carcinoma, downregulation of HNF4α mRNA and protein expression was associated with a significant decline in expression of the transporter. Taken together, our data suggest that nuclear receptor family member HNF4α contributes to the transcriptional regulation of SLC2A9 isoform 1. Since HNF4α has previously been assumed to be a modulator of several urate transporters, our findings support the notion that there could be a transcriptional network providing synchronized regulation of the functional network of the urate transportosome.

Influence of DRD2 and ANKK1 genotypes on apomorphine-induced growth hormone (GH) response in alcohol-dependent patients.

BACKGROUND: D(2) receptor function can be assessed by growth hormone (GH) response to apomorphine. Several association studies between dopamine receptor polymorphisms and results of the apomorphine challenge test with normal and alcohol-dependent subjects yielded inconsistent results. In this pilot study, we tested polymorphisms from the DRD2 region for GH response to apomorphine challenge in more detail. METHODS: Apomorphine challenge tests measuring GH responses on 5 time points were performed on day 1 of alcohol detoxification in 43 patients with alcohol dependence; patients were genotyped for 11 polymorphisms including DRD2, ANKK1, NCAM1 and TTC12. RESULTS: Associations (p<0.05) were found for ANKK1 (rs11604671, rs1800497) and DRD2 (rs6276, rs1076560), which are located on adjacent chromosomal positions. Consistent with PET studies suggesting a reduced D(2) receptor availability in patients carrying the ANKK1 rs1800497 T polymorphism (formerly known as DRD2 TaqI A1) we found a reduced GH response to apomorphine in those subjects. CONCLUSION: This has been the first study showing significant associations between apomorphine-induced GH response and SNPs in DRD2 and ANKK1 in alcohol-dependent patients. In this respect, our preliminary results are in line with other reports which suggested that DRD2 and ANKK1 polymorphisms influence D(2) receptor availability and signal transduction in the dopaminergic pathways. Small sample size in our study limits the generalizability of our results.

Common variants in the G protein beta3 subunit gene and thyroid disorders in a formerly iodine-deficient population.

BACKGROUND: Heterotrimeric G proteins are key mediators of signals from membrane receptors-including the thyroid-stimulating hormone (TSH) receptor-to cellular effectors. Gain-of-function mutations in the TSH receptor and the Galpha(S) subunit occur frequently in hyperfunctioning thyroid nodules and differentiated thyroid carcinomas, whereby the T allele of a common polymorphism (825C>T, rs5443) in the G protein beta3 subunit gene (GNB3) is associated with increased G protein-mediated signal transduction and a complex phenotype. The aim of this study was to investigate whether this common polymorphism affects key parameters of thyroid function and morphology and influences the pathogenesis of thyroid diseases in the general population. METHODS: The population-based cross-sectional Study of Health in Pomerania is a general health survey with focus on thyroid diseases in northeast Germany, a formerly iodine-deficient area. Data from 3428 subjects (1800 men and 1628 women) were analyzed for an association of the GNB3 genotype with TSH, free triiodothyronine and thyroxine levels, urine iodine and thiocyanate excretion, and thyroid ultrasound morphology including thyroid volume, presence of goiter, and thyroid nodules. RESULTS: There was no association between GNB3 genotype status and the functional or morphological thyroid parameters investigated, neither in crude analyses nor upon multivariable analyses including known confounders of thyroid disorders. CONCLUSIONS: Based on the data from this large population-based survey, we conclude that the GNB3 825C>T polymorphism does not affect key parameters of thyroid function and morphology in the general population of a formerly iodine-deficient area.

Comment on "A common genetic variant is associated with adult and childhood obesity".

Contrary to the findings of Herbert et al. (Reports, 14 April 2006, p. 279), homozygous carriers of the C allele of the rs7566605 variant near the INSIG2 gene did not exhibit a significantly increased risk for obesity in a large population-based cross-sectional German study. A subgroup analysis, however, revealed that this allele significantly increased the risk for obesity in already overweight individuals.

Association between migraine and the G1246A polymorphism in the hypocretin receptor 2 gene.

BACKGROUND: The hypocretin receptor 2 (HCRTR2) G1246A polymorphism has been associated with the risk for cluster headache. Since the hypothalamic hypocretin/orexin system projects throughout the nervous system and affects multiple vegetative functions including generation of rhythmicity, vasomotion, autonomic symptoms as well as modulation of nociception, it may also be linked with migraine. OBJECTIVE: We thus sought to evaluate whether the HCRTR2 G1246A polymorphism is associated with the risk for migraine. METHODS: We prospectively established a cohort of 146 unrelated patients with migraine. The control group consisted of 279 healthy volunteers. We genotyped patients and controls for the HCRTR2 G1246A polymorphism and examined an association with presence or absence of migraine. RESULTS: Genotype and allele frequencies were not significantly different between migraine patients and controls (genotype distribution: chi(2)= 4.13, 2 df, P= .13; allele distribution: chi(2)= 0.9, 1 df, P= .34). CONCLUSION: Our study does not support a major contribution of the HCRTR2 G1246A polymorphism to the pathogenesis of migraine in contrast to its effects in cluster headache.