The syndrome of apparent mineralocorticoid excess (AME) is an inherited form of human hypertension thought to result from a deficiency of 11 beta-hydroxysteroid dehydrogenase (11 beta HSD). This enzyme normally converts cortisol to inactive cortisone and is postulated to thus confer specificity for aldosterone upon the mineralocorticoid receptor. We have analysed the gene encoding the kidney isozyme of 11 beta HSD and found mutations on both alleles in nine of 11 AME patients (eight of nine kindreds). These mutations markedly affect enzymatic activity. They thus permit cortisol to occupy the renal mineralocorticoid receptor and thereby cause sodium retention and hypertension.
Genetic variations in or near the aldosterone synthase (CYP11B2) gene strongly affect left ventricular size and mass in young adults free of clinical heart disease. These polymorphisms may also influence the response of the left ventricle to increases in dietary salt.
Polymorphisms in or near the aldosterone synthase gene are associated with variations in aldosterone and 11-deoxycortisol production in males. This may modulate the activity of the renin-angiotensin system and thereby contribute to blood pressure regulation.
Abstract-Mutations in the HSD11B2 gene encoding the kidney (11-HSD2) isozyme of 11-hydroxysteroid dehydrogenase cause apparent mineralocorticoid excess, a form of familial hypertension. Because the hypertension associated with AME is of the salt-sensitive type, it seemed possible that decreases in 11-HSD2 activity might be associated with salt sensitivity. To examine this, Italians with mild hypertension underwent a protocol consisting of a rapid intravenous saline infusion and subsequent furosemide diuresis. To determine whether there were genetic associations between HSD11B2 and salt sensitivity, 198 Italians were genotyped for a CA repeat polymorphism (11 alleles) in the first intron. Increased differences in mean arterial pressure between the sodium loaded and depleted states were correlated with shorter CA repeat length (Rϭ0.214, Pϭ0.0025). The effect behaved as a recessive trait. This suggested that decreased HSD11B2 expression was associated with shorter CA repeat length. Furthermore, activity of renal 11-HSD2 as measured by an increase in the ratio of urinary-free cortisol/urinary-free cortisone was lower in 33 salt-sensitive subjects (urinary-free cortisol/urinary-free cortisone 0.89Ϯ0.04 [meanϮSE]) compared with 34 salt-resistant subjects (0.71Ϯ0.04, PϽ0.001). However, when minigenes containing either 14 or 23 CA repeats were transfected into rabbit or human kidney cortical collecting duct cells, the construct with 14 repeats was instead expressed at levels 50% higher than those of the construct with 23 repeats, as determined by reverse transcription-polymerase chain reaction. We conclude that polymorphisms in HSD11B2 and decreased 11-HSD2 activity are associated with sensitivity to sodium loading, but a functional explanation for these associations remains to be elucidated. Key Words: polymorphism Ⅲ gene expression Ⅲ hypertension, genetic Ⅲ dehydrogenases Ⅲ dinucleotide repeat T he syndrome of apparent mineralocorticoid excess (AME) is an autosomal recessive form of salt-sensitive hypertension caused by deficiency of the kidney isozyme of 11-hydroxysteroid dehydrogenase (11-HSD2). In this disorder, cortisol is not inactivated to cortisone. As a result, cortisol, which is usually a weak mineralocorticoid in vivo, occupies the mineralocorticoid receptor in target tissues such as the distal nephron and causes excessive sodium retention and potassium excretion. The disease is caused by mutations in the HSD11B2 gene encoding the enzyme, most of which severely affect its activity. 1 AME is a rare disorder, but mutations or polymorphisms with milder effects on activity might occur more frequently and could be a significant cause of hypertension in the general population. Although mutations that produce very mild effects on enzymatic activity have been identified in relatively mildly affected patients with AME, 2,3 such mutations seem to be rare in the general population. Other polymorphisms have been sought but have not been associated with variations in blood pressure. 4 Because the hypertension associate...
The gene for the soluble cytochrome b562 from Escherichia coli B has been cloned on a SalI fragment. The analysis of the gene reveals the presence of a leader sequence in front of the sequence encoding the mature protein. Expression of cytochrome b562 using the lac‐promoter produced the protein to a level of 3–5% of total protein. This over‐production enables employment of a simple, high‐yield purification protocol to obtain homogeneous cytochrome b562. Spectroscopic and N‐terminal sequence analyses of the purified protein demonstrate that it is identical to the chromosomally expressed cytochrome b562 purified and characterized from E. coli B [Itagaki, E. & Hager, L. P. (1966) J. Biol. Chem. 241, 3687–3695]. It is demonstrated that the genomic sequence codes for a classic N‐terminal signal sequence and that mature cytochrome b562 is translocated to the periplasmic space.
A full-length hemopexin cDNA was isolated from a rat liver cDNA library and the derived amino acid sequence was obtained. Rat hemopexin shows a 76% amino acid homology with human hemopexin. The amino-terminal domain of rat hemopexin contains two histidine residues that are conserved in the human and rat sequences and are the most likely heme axial ligands. Analogous to human hemopexin, the rat hemopexin consists of 10 internal repeating peptide motifs characteristic of the pexin gene family. A complete conservation of cysteine residues is seen between the human and rat sequences suggesting an identical disulfide bridge structure in both proteins. Our analysis of the primary structure of rat hemopexin reveals characteristics typical for members of the pexin gene family and suggests a conserved evolutionary role for the C-terminal (non-heme-binding) domain of this protein. The full-length rat hemopexin cDNA was used to analyze changes in hemopexin gene expression during development and experimental inflammation. RNA blot analysis showed a single 2.0-kb hemopexin mRNA present in fetal liver at day 14. Hemopexin-specific mRNA was not detected in embryonic or fetal tissues at earlier stages of development and was confined to the liver throughout fetal, newborn, and adult life. The abundance of hemopexin mRNA was found to increase throughout gestation, with a sharp increase in the first postnatal weeks, reaching maximum levels in adult animals. Endotoxin-induced inflammation resulted in a 5-fold increase in hepatic hemopexin mRNA content within 48 h without associated changes in hemopexin transcript size. Adult animals exposed to hyperoxia (95% oxygen) showed a 3-fold increase in hepatic hemopexin mRNA content.(ABSTRACT TRUNCATED AT 250 WORDS)
cDNA clones encoding a novel putative G protein-coupled receptor have been characterized. The receptor is widely expressed in normal solid tissues. Consisting of 1967 amino acid residues, this receptor is one of the largest known and is therefore referred to as a very large G protein-coupled receptor, or VLGR1. It is most closely related to the secretin family of G protein-coupled receptors based on similarity of the sequences of its transmembrane segments. As demonstrated by cell surface labeling with a biotin derivative, the recombinant protein is expressed on the surface of transfected mammalian cells. Whereas several other recently described receptors in this family also have large extracellular domains, the large extracellular domain of VLGR1 has a unique structure. It has nine imperfectly repeated units that are rich in acidic residues and are spaced at intervals of approximately 120 amino acid residues. These repeats resemble the regulatory domains of Na+/Ca2+ exchangers as well as a component of an extracellular aggregation factor of marine sponges. Bacterial fusion proteins containing two or four repeats specifically bind 45Ca in overlay experiments; binding is competed poorly by Mg2+ but competed well by neomycin, Al3+, and Gd3+. These results define a consensus cation binding motif employed in several widely divergent types of proteins. The ligand for VLGR1, its function, and the signaling pathway(s) it employs remain to be defined.
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