Genomic organisation and chromosomal localisation of the gene encoding human beta adducin

The Association between Gly460Trp-Polymorphism of Alpha-Adducin 1 Gene (ADD1) and Arterial Hypertension Development in Ukrainian Population

Arterial hypertension (AH) belongs to the diseases with genetic predisposition that determines the necessity of research on the genetic component's influence on this disease development. It is suggested that one of the salt-sensitive arterial hypertension potential markers may be the alpha-adducin gene because its protein product is involved in the ion transport regulation in the renal epithelium. Thus, the aim of the study was to investigate the association between ADD1 Gly460Trp-polymorphism and the AH development risk among patients with different risk factors in the Ukrainian population. The study included 232 Ukrainians: 120 patients with diagnosed arterial hypertension and 112 practically healthy individuals. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was used for ADD1 Gly460Trp-polymorphism genotyping. The ADD1 Gly460Trp-polymorphic locus is an important predictor of arterial hypertension development in the Ukrainian population, but other nongenetic factors should be considered in further studies.

A Review of the Epidemiological Evidence for Adducin Family Gene Polymorphisms and Hypertension

Hypertension is one of the most common cardiovascular diseases that seriously endangers human health and has become a significant public health problem worldwide. In the vast majority of patients, the cause of hypertension is unknown, called essential hypertension (EH), accounting for more than 95% of total hypertension. Epidemiological and genetic studies of humans and animals provide strong evidence of a causal relationship between high salt intake and hypertension. Adducin is one of the important candidate genes for essential hypertension. Adducin is a heterodimeric or heterotetrameric protein that consists of α, β, and γ subunits; the three subunits are encoded by genes (ADD1, ADD2, and ADD3) that map to three different chromosomes. Animal model experiments and clinical studies suggest that changes in single-nucleotide polymorphisms (SNPs) at part of the adducin family gene increase the Na⁺-K⁺-ATPase activity of the renal tubular basement membrane and increase the reabsorption of Na⁺ by renal tubular epithelial cells, which may cause hypertension. This review makes a summary on the structure, function, and mechanism of adducin and the role of adducin on the onset of EH, providing a basis for the early screening, prevention, and treatment of EH.

Personalized Therapy of Hypertension: the Past and the Future

During the past 20 years, the studies on genetics or pharmacogenomics of primary hypertension provided interesting results supporting the role of genetics, but no actionable finding ready to be translated into personalized medicine. Two types of approaches have been applied: a "hypothesis-driven" approach on the candidate genes, coding for proteins involved in the biochemical machinery underlying the regulation of BP, and an "unbiased hypothesis-free" approach with GWAS, based on the randomness principles of frequentist statistics. During the past 10-15 years, the application of the latter has overtaken the application of the former leading to an enlargement of the number of previously unknown candidate loci or genes but without any actionable result for the therapy of hypertension. In the present review, we summarize the results of our hypothesis-driven approach based on studies carried out in rats with genetic hypertension and in humans with essential hypertension at the pre-hypertensive and early hypertensive stages. These studies led to the identification of mutant adducin and endogenous ouabain as candidate genetic-molecular mechanisms in both species. Rostafuroxin has been developed for its ability to selectively correct Na(+) pump abnormalities sustained by the two abovementioned mechanisms and to selectively reduce BP in rats and in humans carrying the gene variants underlying the mutant adducin and endogenous ouabain (EO) effects. A clinical trial is ongoing to substantiate these findings. Future studies should apply both the candidate gene and GWAS approaches to fully exploit the potential of genetics in optimizing the personalized therapy.

The spectrin-ankyrin-4.1-adducin membrane skeleton: adapting eukaryotic cells to the demands of animal life

The cells in animals face unique demands beyond those encountered by their unicellular eukaryotic ancestors. For example, the forces engendered by the movement of animals places stresses on membranes of a different nature than those confronting free-living cells. The integration of cells into tissues, as well as the integration of tissue function into whole animal physiology, requires specialisation of membrane domains and the formation of signalling complexes. With the evolution of mammals, the specialisation of cell types has been taken to an extreme with the advent of the non-nucleated mammalian red blood cell. These and other adaptations to animal life seem to require four proteins--spectrin, ankyrin, 4.1 and adducin--which emerged during eumetazoan evolution. Spectrin, an actin cross-linking protein, was probably the earliest of these, with ankyrin, adducin and 4.1 only appearing as tissues evolved. The interaction of spectrin with ankyrin is probably a prerequisite for the formation of tissues; only with the advent of vertebrates did 4.1 acquires the ability to bind spectrin and actin. The latter activity seems to allow the spectrin complex to regulate the cell surface accumulation of a wide variety of proteins. Functionally, the spectrin-ankyrin-4.1-adducin complex is implicated in the formation of apical and basolateral domains, in aspects of membrane trafficking, in assembly of certain signalling and cell adhesion complexes and in providing stability to otherwise mechanically fragile cell membranes. Defects in this complex are manifest in a variety of hereditary diseases, including deafness, cardiac arrhythmia, spinocerebellar ataxia, as well as hereditary haemolytic anaemias. Some of these proteins also function as tumor suppressors. The spectrin-ankyrin-4.1-adducin complex represents a remarkable system that underpins animal life; it has been adapted to many different functions at different times during animal evolution.

Investigation of Adducin 2 (beta) DNA polymorphisms in genetic predisposition to diabetic nephropathy in Type 1 diabetes

AIMS

Adducin 2 (beta) (ADD2) is a biological and positional candidate gene proposed to confer genetic risk for diabetic nephropathy. This study aimed to comprehensively investigate all common and putatively functional polymorphisms in the genomic region encompassing this gene.

METHODS

Tag single nucleotide polymorphisms (n = 23) derived from phase II of the International HapMap Project and in silico functional variants (n = 2) were genotyped in 1467 White individuals from the British Isles (cases, n = 718; control subjects, n = 749) by a combination of Sequenom iPLEX and TaqMan technologies.

RESULTS

Chi(2) analysis of genotype and allele frequencies in cases vs. control subjects revealed weak evidence for association of one variant at the 5% level of significance (rs10164951, P = 0.02). Adjusting for multiple testing in the present case-control collection negated this association.

CONCLUSIONS

We selected an appropriate subset of variants suitable for genetic investigations of the ADD2 gene and report the first investigation of polymorphisms in ADD2 with diabetic nephropathy. Our results suggest that common polymorphisms and putatively functional variants in the ADD2 gene do not strongly influence genetic susceptibility to diabetic nephropathy in this White population with Type 1 diabetes.

Brain-specific promoter and polyadenylation sites of the beta-adducin pre-mRNA generate an unusually long 3'-UTR

Adducins are a family of membrane skeleton proteins composed of α-, β- and γ-subunits that promote actin and spectrin association in erythrocytes. The α- and γ-subunits are expressed ubiquitously, while the β-subunit is found in brain and erythropoietic tissues. The brain β-adducin protein is similar in size to that of spleen, but the mRNA transcript is a brain-specific one that has not been yet characterized, having an estimated length of 8–9 kb instead of the 3–4 kb of spleen mRNA. Here, we show the molecular basis for these differences by determining the structure of the brain-specific β-adducin transcript in rats, mice and humans. We identified a brain-specific promoter in rodents that, apparently, was not conserved in humans. In addition, we present evidence that the brain-mRNAs are formed by a common mechanism consisting in the tissue-specific use of alternative polyadenylation sites generating unusually long 3′-untranslated region of up to 6.6 kb. This hypothesis is supported by the presence of highly-conserved regions flanking the brain-specific polyadenylation site that suggest the involvement of these sequences in the translational regulation, stability and/or subcellular localization of the β-adducin transcript in the brain.

Role of the adducin family genes in human essential hypertension

OBJECTIVE

In both humans and rats, polymorphisms of the alpha adducin (ADD1) gene are involved in renal sodium handling, essential hypertension and some of its organ complications. Adducin functions within cells as a heterodimer composed of various combinations of three subunits that are coded by three genes (ADD1, 2, 3) each located on a different chromosome.

DESIGN

These characteristics provide the biochemical basis for investigating epistatic interactions among these loci.

METHODS

We examined the three adducin gene polymorphisms and their association with ambulatory blood pressure (ABPM) and with plasma levels of renin activity (PRA), endogenous ouabain (EO), in 512 newly discovered and never-treated hypertensive patients.

RESULTS

Relative to carriers of the wild type (Gly/Gly) ADD1 gene, patients carrying the mutated Trp ADD1 allele had higher blood pressure (systolic blood pressure (SBP) 143.2 +/- 1.0 versus 140.6 +/- 0.6 mmHg P = 0.027 and diastolic blood pressure (DBP) 94.2 +/- 0.77 versus 92.3 +/- 0.5 mmHg, P = 0.03), lower PRA and EO, consistent with the hypothesis of the renal sodium retaining effect of the Trp allele. Polymorphisms in the ADD2 and ADD3 genes taken alone were not associated with these variables. However, the differences in SBP and DBP between the two ADD1 genotypes were greatest in carriers of the ADD3 G allele (around + 8 mmHg). The significance of the interaction between ADD1 and ADD3 ranged between P = 0.020 to P = 0.006 according to the genetic model applied.

CONCLUSIONS

The interaction of ADD1 and ADD3 gene variants in humans is statistically associated with variation in blood pressure, suggesting the presence of epistatic effects among these loci.

Expression analysis of the human adducin gene family and evidence of ADD2 beta4 multiple splicing variants

Adducin is a cytoskeleton heterodimeric protein. Its subunits are encoded by three related genes (ADD1, ADD2, and ADD3) which show alternative spliced variants. Adducin polymorphisms are involved in blood pressure regulation in humans and rats. We have analyzed mRNA distribution of ADD gene family in human tissues and cells with Real-Time TaqMan RT-PCR. Whereas ADD1 is ubiquitously distributed, ADD3 is more expressed in kidney medulla and cortex than in fetal kidney, while in adult liver it is less abundant than in fetal liver. ADD2 beta1 and beta4 variants show the same pattern of distribution with the highest expression in brain, fetal liver, and kidney. Conventional RT-PCR identified new beta4 variants. Beta4a is characterized by an in-frame insertion of 21 nucleotides upstream exon 15 predicting a 7 amino acids longer protein with a similar C-terminus region. It is coexpressed with beta1 and beta4 in several tissues. Fetal kidney shows further beta4b, beta4c and beta4d variants containing internal exon deletions that enormously modify the predicted NH(2) and central regions. Our findings could help one to understand the functional role of adducin variants in specific tissues and cells.

Spectrin and ankyrin-based pathways: metazoan inventions for integrating cells into tissues

The spectrin-based membrane skeleton of the humble mammalian erythrocyte has provided biologists with a set of interacting proteins with diverse roles in organization and survival of cells in metazoan organisms. This review deals with the molecular physiology of spectrin, ankyrin, which links spectrin to the anion exchanger, and two spectrin-associated proteins that promote spectrin interactions with actin: adducin and protein 4.1. The lack of essential functions for these proteins in generic cells grown in culture and the absence of their genes in the yeast genome have, until recently, limited advances in understanding their roles outside of erythrocytes. However, completion of the genomes of simple metazoans and application of homologous recombination in mice now are providing the first glimpses of the full scope of physiological roles for spectrin, ankyrin, and their associated proteins. These functions now include targeting of ion channels and cell adhesion molecules to specialized compartments within the plasma membrane and endoplasmic reticulum of striated muscle and the nervous system, mechanical stabilization at the tissue level based on transcellular protein assemblies, participation in epithelial morphogenesis, and orientation of mitotic spindles in asymmetric cell divisions. These studies, in addition to stretching the erythrocyte paradigm beyond recognition, also are revealing novel cellular pathways essential for metazoan life. Examples are ankyrin-dependent targeting of proteins to excitable membrane domains in the plasma membrane and the Ca(2+) homeostasis compartment of the endoplasmic reticulum. Exciting questions for the future relate to the molecular basis for these pathways and their roles in a clinical context, either as the basis for disease or more positively as therapeutic targets.

Mild spherocytic hereditary elliptocytosis and altered levels of α- and γ-adducins in β-adducin-deficient mice

The membrane skeleton, a dynamic network of proteins associated with the plasma membrane, determines the shape and mechanical properties of erythrocytes. Deficiencies or defects in membrane skeletal proteins are associated with inherited disorders of erythrocyte morphology and function. Adducin is one of the proteins localized at the spectrin-actin junction of the membrane skeleton. In this work we show that deficiency of β-adducin produces an 80% decrease of -adducin and a fourfold up-regulation of γ-adducin in erythrocytes. β-Adducin or any other isoform generated by translation of abnormally spliced messenger RNAs could not be detected by our antibodies either in ghosts or in cytoplasm of −/− erythrocytes. Actin levels were diminished in mutant mice, suggesting alterations in the actin-spectrin junctional complexes due to the absence of adducin. Elliptocytes, ovalocytes, and occasionally spherocytes were found in the blood film of −/− mice. Hematological values showed an increase in reticulocyte counts and mean corpuscular hemoglobin concentration, decreased mean corpuscular volume and hematocrit, and normal erythrocyte counts that, associated to splenomegaly, indicate that the mice suffer from mild anemia with compensated hemolysis. These modifications are due to a loss of membrane surface and dehydration that result in an increase in the osmotic fragility of red blood cells. The marked alteration in osmotic fragility together with the predominant presence of elliptocytes is reminiscent of the human disorder called spherocytic hereditary elliptocytosis. Our results suggest that the amount of adducin remaining in the mutant animals (presumably γ adducin) could be functional and might account for the mild phenotype.

Mild spherocytic hereditary elliptocytosis and altered levels of α- and γ-adducins in β-adducin-deficient mice

The membrane skeleton, a dynamic network of proteins associated with the plasma membrane, determines the shape and mechanical properties of erythrocytes. Deficiencies or defects in membrane skeletal proteins are associated with inherited disorders of erythrocyte morphology and function. Adducin is one of the proteins localized at the spectrin-actin junction of the membrane skeleton. In this work we show that deficiency of β-adducin produces an 80% decrease of -adducin and a fourfold up-regulation of γ-adducin in erythrocytes. β-Adducin or any other isoform generated by translation of abnormally spliced messenger RNAs could not be detected by our antibodies either in ghosts or in cytoplasm of −/− erythrocytes. Actin levels were diminished in mutant mice, suggesting alterations in the actin-spectrin junctional complexes due to the absence of adducin. Elliptocytes, ovalocytes, and occasionally spherocytes were found in the blood film of −/− mice. Hematological values showed an increase in reticulocyte counts and mean corpuscular hemoglobin concentration, decreased mean corpuscular volume and hematocrit, and normal erythrocyte counts that, associated to splenomegaly, indicate that the mice suffer from mild anemia with compensated hemolysis. These modifications are due to a loss of membrane surface and dehydration that result in an increase in the osmotic fragility of red blood cells. The marked alteration in osmotic fragility together with the predominant presence of elliptocytes is reminiscent of the human disorder called spherocytic hereditary elliptocytosis. Our results suggest that the amount of adducin remaining in the mutant animals (presumably γ adducin) could be functional and might account for the mild phenotype.

A homeobox gene, vax2, controls the patterning of the eye dorsoventral axis

We have identified a transcription factor specifically expressed in the developing vertebrate eye. We named this gene vax2 because of the high degree of sequence similarity to the recently described vax1. Both in the human and mouse genomes, vax2 is localized in the vicinity of the emx1 gene. This mapping assignment, together with the previously reported colocalization of Vax1 and Emx2 in mouse, indicates that the vax and the emx genes may be organized in clusters. vax2 has a remarkable expression domain confined to the ventral portion of the prospective neural retina in mouse, human, and Xenopus. The overexpression of either the frog Xvax2 or the human VAX2 in Xenopus embryos leads to an aberrant eye phenotype and, in particular, determines a ventralizing effect on the developing eye. The expression domain of the transcription factor Xpax2, normally confined to the ventral developing retina, extends to the dorsal region of the retina after overexpression of vax2. On the other hand, the expression of Xvent2, a molecular marker of the dorsal retina, is strongly reduced. Furthermore, vax2 overexpression induces a striking expansion of the optic stalk, a structure deriving from the ventralmost region of the eye vesicle. Altogether, these data indicate that vax2 plays a crucial role in eye development and, in particular, in the specification of the ventral optic vesicle.

Utilization of an 86 bp exon generates a novel adducin isoform (beta 4) lacking the MARCKS homology domain

A novel isoform of beta-adducin has been amplified and characterized from a human bone marrow cDNA library (GenBank #U43959). This isoform arises from the insertion of an 86 bp alternatively spliced and previously unrecognized exon (now termed exon 15) within codon 581 of the human red blood cell beta-adducin sequence. This results in an insertion of 28 novel amino acids. The remainder of the red cell beta-adducin mRNA is then translated in a different reading frame, adding an additional 35 novel amino acids prior to the stop codon. This new isoform, thus, replaces beta 1-adducin sequence after residue 580 with a total of 63 new amino acids. Sequences from genomic clones of the human beta-adducin gene show that this alternate exon is flanked by splice consensus sequences and is appropriately located in the genomic map between exons encoding up-stream and down-stream sequences, thus defining a new exon. The COOH-terminus of this new isoform, which we designate beta 4, lacks a 22 amino acid lysine-rich sequence common to both the human red cell alpha- and beta-adducin subunits and homologous to a highly conserved region in MARCKS, a filamentous actin-cross linking protein regulated by protein kinase C and calcium/calmodulin. beta 4-adducin preserves a previously identified calmodulin binding domain. PCR analysis indicates that this new beta-adducin isoform is expressed in fetal brain and liver, bone marrow, and NT-2 (neuroepithelial) cells, but is not detected in several other tissues. We anticipate that this new beta 4 isoform of beta-adducin will display unique and tissue-specific functional properties.

Organization of the human beta-adducin gene (ADD2)

The intron-exon organization of the human beta-adducin gene (ADD2) has been determined from overlapping genomic clones. The gene spans over 100 kb on chromosome 2p13 and comprises 17 exons. Seven of the exons are identical in size to the corresponding exons of the alpha-adducin gene (4p16.3), suggesting gene duplication. A 275-bp fragment 5' to exon 1 demonstrates strong promoter activity in a transient transfection assay. Within 333 bp 5' of the first exon can be found several putative transcription factor-binding sites: three SP1 sites, one GATA site, three MZF1 sites, one p300 site, and one c-Ets site. Alternatively spliced exons in the 3' region are described and contain distinct coding regions, stop codons, and 3'UTR, corresponding to previously published beta-adducin cDNA sequences beta-1 and beta-2. The alternative splice sites for the smallest adducin isoform, beta-3, are alternative donor and acceptor sites within exons 7 and 12. The most recently described isoform, beta-4, includes an alternative exon (exon 15) that results in a frame shift and early termination. Intron-exon splice sites are presented for all 17 exons and conform to the consensus sequences for mammalian splice sites. These results will be useful in further analysis of tissue-specific expression of adducin isoforms and in analysis of DNA from patients with diseases mapping to this region of chromosome 2.

Hypertension-associated point mutations in the adducin alpha and beta subunits affect actin cytoskeleton and ion transport

The adducin heterodimer is a protein affecting the assembly of the actin-based cytoskeleton. Point mutations in rat adducin alpha (F316Y) and beta (Q529R) subunits are involved in a form of rat primary hypertension (MHS) associated with faster kidney tubular ion transport. A role for adducin in human primary hypertension has also been suggested. By studying the interaction of actin with purified normal and mutated adducin in a cell-free system and the actin assembly in rat kidney epithelial cells (NRK-52E) transfected with mutated rat adducin cDNA, we show that the adducin isoforms differentially modulate: (a) actin assembly both in a cell-free system and within transfected cells; (b) topography of alpha V integrin together with focal contact proteins; and (c) Na-K pump activity at V(max) (faster with the mutated isoforms, 1281 +/- 90 vs 841 +/- 30 nmol K/h.mg pt., P < 0.0001). This co-modulation suggests a role for adducin in the constitutive capacity of the epithelia both to transport ions and to expose adhesion molecules. These findings may also lead to the understanding of the relation between adducin polymorphism and blood pressure and to the development of new approaches to the study of hypertension-associated organ damage.

Characterisation and chromosomal localisation of the rat alpha- and beta-adducin-encoding genes

A polymorphism in the genes encoding alpha- and beta-adducin (ADD) was described as being associated with blood-pressure variation in a genetically hypertensive strain of rats (MHS). ADD is a cytoskeletal heterodimeric protein which may be involved in cellular signal transduction and interacts with other membrane skeleton proteins which affect ion transport across the cell membrane. The cDNA encoding the alpha subunit of rat ADD was isolated using PCR methods. The cDNA consists of about 3900 bp and encodes a protein of 735 amino acids (aa) which shows 91% aa identity with the human counterpart. In spleen and kidney, three alternative spliced exons were found by PCR amplification and confirmed by RNase protection analysis. 17 inbred rat strains were genotyped for the polymorphism in the alpha- and beta-ADD genes. Chromosomal localisation mapped rat alpha-ADD on chromosome 14 and rat beta-ADD on chromosome 4.