Regulation of glucose transporter SGLT1 by ubiquitin ligase Nedd4-2 and kinases SGK1, SGK3, and PKB

Objectives: Serum- and glucocorticoid-inducible kinase 1 (SGK1) inhibits the ubiquitin ligase neuronal cell expressed developmentally downregulated 4-2 (Nedd4-2), which retards the retrieval of the epithelial Na+ channel ENaC. Accordingly, SGK1 enhances ENaC abundance in the cell membrane. The significance of this effect is shown by an association of an E8CC/CT;I6CC polymorphism in the SGK1 gene with increased blood pressure. However, strong expression of SGK1 in enterocytes not expressing ENaC points to further functions of SGK1. This study was performed to test for regulation of Na+-coupled glucose transporter 1 (SGLT1) by Nedd4-2, SGK1, and/or the related kinases SGK3 and PKB. Additional studies searched for an association of the SGK1 gene with BMI. Research Methods and Procedures: mRNA encoding SGLT1, wild-type Nedd4-2, inactive (C938S)Nedd4-2, wild type SGK1, constitutively active (S422D)SGK1 or inactive (K127N)SGK1, wild-type SGK3, and constitutively active (T308DS473D)PKB or inactive (T308AS473A)PKB were injected into Xenopus oocytes, and glucose transport was quantified from glucose-induced current (Iglc). BMI was determined in individuals with or without the E8CC/CT;I6CC polymorphism. Results: Iglc was significantly decreased by coexpression of Nedd4-2 but not of (C938S)Nedd4-2. Coexpression of SGK1, (S422D)SGK1, SGK3, or (T308DS473D)PKB, but not of (K127N)SGK1 or (T308AS473A)PKB, enhanced Iglc and reversed the effect of Nedd4-2. SGK1 and SGK3 phosphorylated Nedd4-2. Deletion of the SGK/PKB phosphorylation sites in Nedd4-2 blunted the kinase effects. BMI was significantly (p < 0.008) greater in individuals with the E8CC/CT;I6CC polymorphism than in individuals without. Discussion: Overactivity of SGK1 may lead not only to excessive ENaC activity and hypertension but also to enhanced SGLT1 activity and obesity

β‐2 adrenergic receptor gene variations and blood pressure under stress in normal twins

We tested the hypothesis that blood pressure (BP) responses to physical and mental stress are associated with polymorphisms in the β‐2 adrenergic receptor (AR) gene. We studied normotensive, young, monozygotic (MZ) and dizygotic (DZ) twins. The subjects underwent automated BP measurements at the brachial and digital arteries and were subjected to mental arithmetic and cold pressor stress. We used allele‐specific PCR to genotype four single nucleotide polymorphisms in the β‐2 AR gene. The most functionally relevant polymorphism in the β‐2 AR gene, Arg16/Gly, was associated with systolic and diastolic BP under resting conditions, during mental arithmetic, and during the cold pressor test, as well as with the increase in diastolic BP during both forms of stress. These findings support a role for the β‐2 AR gene in BP regulation. They also indicate that the β‐2 AR gene influences the level of not only resting but also stress‐related BP.Peer Reviewe

Beta-2 Adrenergic receptor gene variations and coping styles in twins

We tested the hypothesis that the beta-2 adrenergic receptor (beta-2 AR) gene locus, with known effects on blood pressure regulation, is also involved in psychological coping styles. 166 pairs of monozygotic (MZ) and dizygotic (DZ) twins and DZ twin parents were investigated. We found common genetic variance for the coping factor Emotional Coping and blood pressure. Using three microsatellites we found linkage between the beta-2 AR gene locus and the coping factor Active Coping. Using allele-specific PCR of all the single nucleotide polymorphisms (SNPs) in the gene causing amino acid substitutions we identified associations between the +491 G/A SNP and various coping factors. We conclude that the beta-2 AR gene is relevant to coping. These preliminary findings suggest a molecular genetic underpinning of the relationship between psychological and physiological phenotypes important to cardiovascular risk