Cardiac muscle cell cytoskeletal protein 4.1: Analysis of transcripts and subcellular location?relevance to membrane integrity, microstructure, and possible role in heart failure

4.1N-Mediated Interactions and Functions in Nerve System and Cancer

Scaffolding protein 4.1N is a neuron-enriched 4.1 homologue. 4.1N contains three conserved domains, including the N-terminal 4.1-ezrin-radixin-moesin (FERM) domain, internal spectrin–actin–binding (SAB) domain, and C-terminal domain (CTD). Interspersed between the three domains are nonconserved domains, including U1, U2, and U3. The role of 4.1N was first reported in the nerve system. Then, extensive studies reported the role of 4.1N in cancers and other diseases. 4.1N performs numerous vital functions in signaling transduction by interacting, locating, supporting, and coordinating different partners and is involved in the molecular pathogenesis of various diseases. In this review, recent studies on the interactions between 4.1N and its contactors (including the α7AChr, IP3R1, GluR1/4, GluK1/2/3, mGluR8, KCC2, D2/3Rs, CASK, NuMA, PIKE, IP6K2, CAM 1/3, βII spectrin, flotillin-1, pp1, and 14-3-3) and the 4.1N-related biological functions in the nerve system and cancers are specifically and comprehensively discussed. This review provides critical detailed mechanistic insights into the role of 4.1N in disease relationships.

Protein 4.1 family and ion channel proteins interact to regulate the process of heart failure in rats

Heart failure (HF) is a major cause of death in cardiovascular diseases worldwide, and its molecular mechanisms and effective prevention strategies remain to be further studied. The myocardial cytoskeleton plays a pivotal role in many heart diseases. However, little is known about the function of the membrane cytoskeleton 4.1 protein family and related regulatory mechanisms in the pathogenesis of HF. In this study, we detected the localization and expression of the protein 4.1 family and ion channel proteins in a rat HF model induced by doxorubicin (DOX), and studied the interactions between them. Our results showed that compared with the control group, the HF group displayed an increased expression level of protein 4.1R and decreased levels of protein 4.1 G and 4.1 N. The Nav1.5 protein levels were significantly increased, while the SERCA2a and Cav1.2 protein levels were significantly decreased in the HF group. Furthermore, there is co-localization and interaction between protein 4.1R and Nav1.5, protein 4.1 G and SERCA2a, protein 4.1 N and Cav1.2, respectively. Taken together, the results indicated that the protein 4.1 family might be involved in the occurrence and development of HF through its interaction with ion channel proteins, suggesting that 4.1 proteins may serve as a novel therapeutic target for HF.

Supporting the heart: Functions of the cardiomyocyte's non-sarcomeric cytoskeleton

The non-contractile cytoskeleton in cardiomyocytes is comprised of cytoplasmic actin, microtubules, and intermediate filaments. In addition to providing mechanical support to these cells, these structures are important effectors of tension-sensing and signal transduction and also provide networks for the transport of proteins and organelles. The majority of our knowledge on the function and structure of these cytoskeletal networks comes from research on proliferative cell types. However, in recent years, researchers have begun to show that there are important cardiomyocyte-specific functions of the cytoskeleton. Here we will discuss the current state of cytoskeletal biology in cardiomyocytes, as well as research from other cell types, that together suggest there is a wealth of knowledge on cardiac health and disease waiting to be uncovered through exploration of the complex signaling networks of cardiomyocyte non-sarcomeric cytoskeletal proteins.

Thick Filament Protein Network, Functions, and Disease Association

Sarcomeres consist of highly ordered arrays of thick myosin and thin actin filaments along with accessory proteins. Thick filaments occupy the center of sarcomeres where they partially overlap with thin filaments. The sliding of thick filaments past thin filaments is a highly regulated process that occurs in an ATP-dependent manner driving muscle contraction. In addition to myosin that makes up the backbone of the thick filament, four other proteins which are intimately bound to the thick filament, myosin binding protein-C, titin, myomesin, and obscurin play important structural and regulatory roles. Consistent with this, mutations in the respective genes have been associated with idiopathic and congenital forms of skeletal and cardiac myopathies. In this review, we aim to summarize our current knowledge on the molecular structure, subcellular localization, interacting partners, function, modulation via posttranslational modifications, and disease involvement of these five major proteins that comprise the thick filament of striated muscle cells. © 2018 American Physiological Society. Compr Physiol 8:631-709, 2018.

Protein 4.1R Influences Myogenin Protein Stability and Skeletal Muscle Differentiation

Protein 4.1R (4.1R) isoforms are expressed in both cardiac and skeletal muscle. 4.1R is a component of the contractile apparatus. It is also associated with dystrophin at the sarcolemma in skeletal myofibers. However, the expression and function of 4.1R during myogenesis have not been characterized. We now report that 4.1R expression increases during C2C12 myoblast differentiation into myotubes. Depletion of 4.1R impairs skeletal muscle differentiation and is accompanied by a decrease in the levels of myosin heavy and light chains and caveolin-3. Furthermore, the expression of myogenin at the protein, but not mRNA, level is drastically decreased in 4.1R knockdown myocytes. Similar results were obtained using MyoD-induced differentiation of 4.1R^-/- mouse embryonic fibroblast cells. von Hippel-Lindau (VHL) protein is known to destabilize myogenin via the ubiquitin-proteasome pathway. We show that 4.1R associates with VHL and, when overexpressed, reverses myogenin ubiquitination and stability. This suggests that 4.1R may influence myogenesis by preventing VHL-mediated myogenin degradation. Together, our results define a novel biological function for 4.1R in muscle differentiation and provide a molecular mechanism by which 4.1R promotes myogenic differentiation.

Whole-exome sequencing analysis in twin sibling males with an anterior cruciate ligament rupture

Familial predisposition is among the major genetic risk factors for non-contact musculoskeletal tissue injuries. Personal genome sequence shows that different polymorphism profiles may account for the number and the degree of injuries and the recovery time. Genotyping studies allow investigation into genome factors with potential impact on pathogenesis of non-contact ligament injuries. We have studied a family with twin sibling males surgically diagnosed of an anterior cruciate ligament non-contact rupture and non-affected progenitors (father and mother) were subjected to whole exome sequencing (WES) analysis. WES analysis previously carried out on 16 individuals, without ACL injury medical records, were also included in this study for single nucleotide variants (SNVs) and small insertions and deletions detection (indels), variant filtering and to prioritize variants relative to the disease. WES analysis to identify SNVs and indels was performed using open web-based bioinformatics tools. A set of 11 new variants shared by family members can be associated to ACL non-contact injury, including SerpinA11, ARSI, NOCHT4, EPB41, FDFT1, POMC, KIF26A, OLFML2B, ATG7, FAH and WDR6. All of them, except ATG7 and WDR6, have shown a damaging predictive pattern by combinatorial standard predictive scores. In combination to the identified SNVs of EPB41 and SerpinA11 genes, ACTL7A gene showed a predicted deleterious variant reinforcing the idea these variants impact on of fibroblast-like cells deformability and ECM misbalance, Differential gene expression and RNA sequencing analysis will help to understand the combined participation of these protein coding genes in ACL non-contact injuries.

Comprehensive characterization of protein 4.1 expression in epithelium of large intestine

The protein 4.1 family consists of four members, 4.1R, 4.1N, 4.1B and 4.1G, each encoded by a distinct gene. All 4.1 mRNAs undergo extensive alternative splicing. Functionally, they usually serve as adapters that link actin-based cytoskeleton to plasma membrane proteins. It has been reported that 4.1 proteins are expressed in most animal cell types and tissues including epithelial cells and epithelial tissues. However, the expression of 4.1 proteins in large intestine has not been well characterized. In the present study, we performed RT-PCR, western blot and immunohistochemistry analysis to characterize the transcripts, the protein expression and cellular localization of 4.1 proteins in the epithelia of mouse large intestine. We show that multiple transcripts derive from each gene, including eight 4.1R isoforms, four 4.1N isoforms, four 4.1B isoforms and six 4.1G isoforms. However, at the protein level, only one or two major bands were detected, implying that not all transcripts are translated and/or the proteins do not accumulate at detectable levels. Immunohistochemistry revealed that 4.1R, 4.1N and 4.1B are all expressed at the lateral membrane as well as cytoplasm of epithelial cells, suggesting a potentially redundant role of these proteins. Our findings not only provide new insights into the structure of protein 4.1 genes but also lay the foundation for future functional studies.

The Protein 4.1 family: hub proteins in animals for organizing membrane proteins

Proteins of the 4.1 family are characteristic of eumetazoan organisms. Invertebrates contain single 4.1 genes and the Drosophila model suggests that 4.1 is essential for animal life. Vertebrates have four paralogues, known as 4.1R, 4.1N, 4.1G and 4.1B, which are additionally duplicated in the ray-finned fish. Protein 4.1R was the first to be discovered: it is a major mammalian erythrocyte cytoskeletal protein, essential to the mechanochemical properties of red cell membranes because it promotes the interaction between spectrin and actin in the membrane cytoskeleton. 4.1R also binds certain phospholipids and is required for the stable cell surface accumulation of a number of erythrocyte transmembrane proteins that span multiple functional classes; these include cell adhesion molecules, transporters and a chemokine receptor. The vertebrate 4.1 proteins are expressed in most tissues, and they are required for the correct cell surface accumulation of a very wide variety of membrane proteins including G-Protein coupled receptors, voltage-gated and ligand-gated channels, as well as the classes identified in erythrocytes. Indeed, such large numbers of protein interactions have been mapped for mammalian 4.1 proteins, most especially 4.1R, that it appears that they can act as hubs for membrane protein organization. The range of critical interactions of 4.1 proteins is reflected in disease relationships that include hereditary anaemias, tumour suppression, control of heartbeat and nervous system function. The 4.1 proteins are defined by their domain structure: apart from the spectrin/actin-binding domain they have FERM and FERM-adjacent domains and a unique C-terminal domain. Both the FERM and C-terminal domains can bind transmembrane proteins, thus they have the potential to be cross-linkers for membrane proteins. The activity of the FERM domain is subject to multiple modes of regulation via binding of regulatory ligands, phosphorylation of the FERM associated domain and differential mRNA splicing. Finally, the spectrum of interactions of the 4.1 proteins overlaps with that of another membrane-cytoskeleton linker, ankyrin. Both ankyrin and 4.1 link to the actin cytoskeleton via spectrin, and we hypothesize that differential regulation of 4.1 proteins and ankyrins allows highly selective control of cell surface protein accumulation and, hence, function. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé

Functional characterization of protein 4.1 homolog in amphioxus: defining a cryptic spectrin-actin-binding site

Vertebrate 4.1 proteins have a spectrin-actin-binding (SAB) domain, which is lacking in all the invertebrate 4.1 proteins indentified so far, and it was therefore proposed that the SAB domain emerged with the advent of vertebrates during evolution. Here we demonstrated for the first time that amphioxus (an invertebrate chordate) protein 4.1, though lacking a recognizable SAB, was able to bind both spectrin and actin, with a binding capacity comparable to that of human protein 4.1. Detailed structure-activity analyses revealed that the unique domain U2/3 was a newly identified SAB-like domain capable of interacting with spectrin and actin, suggesting the presence of a “cryptic” SAB domain in amphioxus 4.1 protein. We also showed that amphioxus 4.1 protein gene was the common ancestor of vertebrate 4.1 protein genes, from which 4.1R, 4.1N, 4.1G, and 4.1B genes originated. This work will encourage further study on the structure-activity of invertebrate 4.1 protein and its interacting proteins.

Cardiomyocyte growth and sarcomerogenesis at the intercalated disc

Cardiomyocytes grow during heart maturation or disease-related cardiac remodeling. We present evidence that the intercalated disc (ID) is integral to both longitudinal and lateral growth: increases in width are accommodated by lateral extension of the plicate tread regions and increases in length by sarcomere insertion within the ID. At the margin between myofibril and the folded membrane of the ID lies a transitional junction through which the thin filaments from the last sarcomere run to the ID membrane and it has been suggested that this junction acts as a proto Z-disc for sarcomere addition. In support of this hypothesis, we have investigated the ultrastructure of the ID in mouse hearts from control and dilated cardiomyopathy (DCM) models, the MLP-null and a cardiac-specific β-catenin mutant, cΔex3, as well as in human left ventricle from normal and DCM samples. We find that the ID amplitude can vary tenfold from 0.2 μm up to a maximum of ~2 μm allowing gradual expansion during heart growth. At the greatest amplitude, equivalent to a sarcomere length, A-bands and thick filaments are found within the ID membrane loops together with a Z-disc, which develops at the transitional junction position. Here, also, the tops of the membrane folds, which are rich in αII spectrin, become enlarged and associated with junctional sarcoplasmic reticulum. Systematically larger ID amplitudes are found in DCM samples. Other morphological differences between mouse DCM and normal hearts suggest that sarcomere inclusion is compromised in the diseased hearts.

Isoforms of protein 4.1 are differentially distributed in heart muscle cells: relation of 4.1R and 4.1G to components of the Ca2+ homeostasis system

The 4.1 proteins are cytoskeletal adaptor proteins that are linked to the control of mechanical stability of certain membranes and to the cellular accumulation and cell surface display of diverse transmembrane proteins. One of the four mammalian 4.1 proteins, 4.1R (80 kDa/120 kDa isoforms), has recently been shown to be required for the normal operation of several ion transporters in the heart (Stagg MA et al. Circ Res, 2008; 103: 855-863). The other three (4.1G, 4.1N and 4.1B) are largely uncharacterised in the heart. Here, we use specific antibodies to characterise their expression, distribution and novel activities in the left ventricle. We detected 4.1R, 4.1G and 4.1N by immunofluorescence and immunoblotting, but not 4.1B. Only one splice variant of 4.1N and 4.1G was seen whereas there are several forms of 4.1R. 4.1N, like 4.1R, was present in intercalated discs, but unlike 4.1R, it was not localised at the lateral plasma membrane. Both 4.1R and 4.1N were in internal structures that, at the level of resolution of the light microscope, were close to the Z-disc (possibly T-tubules). 4.1G was also in intracellular structures, some of which were coincident with sarcoplasmic reticulum. 4.1G existed in an immunoprecipitable complex with spectrin and SERCA2. 80 kDa 4.1R was present in subcellular fractions enriched in intercalated discs, in a complex resistant to solubilization under non-denaturing conditions. At the intercalated disc 4.1R does not colocalise with the adherens junction protein, β-catenin, but does overlap with the other plasma membrane signalling proteins, the Na/K-ATPase and the Na/Ca exchanger NCX1. We conclude that isoforms of 4.1 proteins are differentially compartmentalised in the heart, and that they form specific complexes with proteins central to cardiomyocyte Ca(2+) metabolism.

Protein 4.1R regulates cell adhesion, spreading, migration and motility of mouse keratinocytes by modulating surface expression of beta1 integrin

Protein 4.1R is a membrane-cytoskeleton adaptor protein that has diverse roles in controlling the cell surface expression and/or function of transmembrane proteins, and in organizing F-actin. 4.1R is expressed in keratinocytes, but its role in these cells has not been explored. Here, we have investigated the role of 4.1R in skin using 4.1R(-/-) mice. Cell adhesion, spreading, migration and motility were significantly impaired in 4.1R(-/-) keratinocytes, and 4.1R(-/-) mice exhibited defective epidermal wound healing. Cultured 4.1R(-/-) keratinocytes on fibronectin failed to form actin stress fibres and focal adhesions. Furthermore, in the absence of 4.1R, the surface expression, and consequently the activity of β1 integrin were reduced. These data enabled the identification of a functional role for protein 4.1R in keratinocytes by modulating the surface expression of β1 integrin, possibly through a direct association between 4.1R and β1 integrin.

Lack of protein 4.1G causes altered expression and localization of the cell adhesion molecule nectin-like 4 in testis and can cause male infertility

Protein 4.1G is a member of the protein 4.1 family, which in general serves as adaptors linking transmembrane proteins to the cytoskeleton. 4.1G is thought to be widely expressed in many cells and tissues, but its function remains largely unknown. To explore the function of 4.1G in vivo, we generated 4.1G(-/-) mice and bred the mice in two backgrounds: C57BL/6 (B6) and 129/Sv (129) hybrids (B6-129) and inbred B6. Although the B6 4.1G(-/-) mice showed no obvious abnormalities, deficiency of 4.1G in B6-129 hybrids was associated with male infertility. Histological examinations of these 4.1G(-/-) mice revealed atrophy, impaired cell-cell contact and sloughing off of spermatogenic cells in seminiferous epithelium, and lack of mature spermatids in the epididymis. Ultrastructural examination revealed enlarged intercellular spaces between spermatogenic and Sertoli cells as well as the spermatid deformities. At the molecular level, 4.1G is associated with the nectin-like 4 (NECL4) adhesion molecule. Importantly, the expression of NECL4 was decreased, and the localization of NECL4 was altered in 4.1G(-/-) testis. Thus, our findings imply that 4.1G plays a role in spermatogenesis by mediating cell-cell adhesion between spermatogenic and Sertoli cells through its interaction with NECL4 on Sertoli cells. Additionally, the finding that infertility is present in B6-129 but not on the B6 background suggests the presence of a major modifier gene(s) that influences 4.1G function and is associated with male infertility.

Comprehensive characterization of expression patterns of protein 4.1 family members in mouse adrenal gland: implications for functions

The members of the protein 4.1 family, 4.1R, 4.1G, 4.1N, and 4.1B, are encoded by four genes, all of which undergo complex alternative splicing. It is well established that 4.1R, the prototypical member of the family, serves as an adapter that links the spectrin-actin based cytoskeleton to the plasma membrane in red cells. It is required for mechanical resilience of the membrane, and it ensures the cell surface accumulation of selected membrane proteins. However, the function of 4.1 proteins outside erythrocytes remains under-explored, especially in endocrine tissues. Transcripts of all 4.1 homologs have previously been documented to be abundantly expressed in adrenal gland. In order to begin to decipher the function of 4.1 proteins in adrenal gland, we performed a detailed characterization of the expression pattern of various 4.1 proteins and their cellular localization. We show that 4.1R (~80 and ~135 kDa) splice forms are expressed on the membrane of all cells, while a ~160 kDa 4.1G splice form is distributed in the cytoplasm and the membrane of zona glomerulosa and of medullary cells. Two 4.1N splice forms, ~135 and ~95 kDa, are present in the peri-nuclear region of both zona glomerulosa and medullary cells, while a single ~130 kDa 4.1B splice form, is detected in all layers of adrenal gland in both the cytoplasm and the membrane. The characterization of distinct splice forms of various 4.1 proteins with diverse cellular and sub-cellular localization indicates multiple functions for this family of proteins in endocrine functions of adrenal gland.

Identification of SNP markers on 1p36 and association analysis of EPB41 with mandibular prognathism in a Chinese population

OBJECTIVE

The results of a genome-wide scan suggested that chromosome locus 1p36 might be linked to the etiology of mandibular prognathism (MP) amongst Asian ethnicities. In this study, we performed a two-stage case-control association study to determine whether one or more genes that confer susceptibility to MP are located within this genomic region.

DESIGN

In the first stage of the study, we examined 103 single nucleotide polymorphisms (SNPs) on 1p36 across an 8.6Mb critical region and within four candidate genes in 158 cases and 147 controls to identify genes associated with MP. In the second stage of the study, we examined an additional 23 SNPs within the erythrocyte membrane protein band 4.1 (EPB41) gene in 211 cases and 224 controls.

RESULTS

Four SNPs located in the EPB41 gene showed possible allelic and genotypic associations with MP (P<0.03 and P<0.05, respectively) in the first stage. In the analysis of single SNPs in the second stage, the allele of rs4654388 showed the strongest significant association with MP (P=0.008) and the rs4654388 G-allele was associated with a significantly increased risk of MP (OR: 1.78, 95% CI: 1.16-2.74). Haplotype analysis revealed that MP was associated significantly with haplotype GTTCAGGT (P(corrected)=0.031), which included the rs4654388 G-allele.

CONCLUSIONS

An association between genetic polymorphisms in the EPB41 gene and MP has been observed. Although the polymorphisms which may contribute to MP have not been determined, the results of our study suggest that the EPB41 gene could confer susceptibility to MP.

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.

Protein 4.1 and the control of ion channels

The classical function of 4.1R in red blood cells is to contribute to the mechanochemical properties of the membrane by promoting the interaction between spectrin and actin. More recently, it has been recognized that 4.1R is required for the stable cell surface accumulation of a number of erythrocyte membrane proteins. 4.1R is one member of the mammalian 4.1 family - the others being 4.1N, 4.1G and 4.1B - and is expressed in many cell types other than erythrocytes. Recently we have examined the phenotype of hearts from 4.1R knockout mice. Although they had a generally normal morphology, these hearts exhibited bradycardia, and prolongation of both action potentials and QT intervals. Electrophysiological analysis revealed anomalies in a range of ion channel activities. In addition, the immunoreactivity of voltage-gated Na(+) channel NaV1.5 was reduced, indicating a role for 4.1R in the cellular accumulation of this ion channel. 4.1 proteins also have roles in the accumulation of at least two other classes of ion channel. In epithelia, 4.1 interacts with the store-operated channel TRPC4. In neurons, the ligand-gated channels GluR1 and GluR4 require 4.1 proteins for cell surface accumulation. The spectrum of transmembrane proteins that bind to 4.1 proteins overlaps with that of ankyrin. A hypothesis to investigate in the future is that differential regulation of 4.1 and ankyrins (e.g. by PIP(2)) allows highly selective control of cell surface accumulation and transport activity of a specific range of ion channels.

Cytoskeletal protein 4.1R affects repolarization and regulates calcium handling in the heart

The 4.1 proteins are a family of multifunctional adaptor proteins. They promote the mechanical stability of plasma membranes by interaction with the cytoskeletal proteins spectrin and actin and are required for the cell surface expression of a number of transmembrane proteins. Protein 4.1R is expressed in heart and upregulated in deteriorating human heart failure, but its functional role in myocardium is unknown. To investigate the role of protein 4.1R on myocardial contractility and electrophysiology, we studied 4.1R-deficient (knockout) mice (4.1R KO). ECG analysis revealed reduced heart rate with prolonged Q-T interval in 4.1R KO. No changes in ejection fraction and fractional shortening, assessed by echocardiography, were found. The action potential duration in isolated ventricular myocytes was prolonged in 4.1R KO. Ca(2+) transients were larger and slower to decay in 4.1R KO. The sarcoplasmic reticulum Ca(2+) content and Ca(2+) sparks frequency were increased. The Na(+)/Ca(2+) exchanger current density was reduced in 4.1R KO. The transient inward current inactivation was faster and the persistent Na(+) current density was increased in the 4.1R KO group, with possible effects on action potential duration. Although no major morphological changes were noted, 4.1R KO hearts showed reduced expression of NaV1.5alpha and increased expression of protein 4.1G. Our data indicate an unexpected and novel role for the cytoskeletal protein 4.1R in modulating the functional properties of several cardiac ion transporters with consequences on cardiac electrophysiology and with possible significant roles during normal cardiac function and disease.

Neuroacanthocytosis associated with a defect of the 4.1R membrane protein

Background

Neuroacanthocytosis (NA) denotes a heterogeneous group of diseases that are characterized by nervous system abnormalities in association with acanthocytosis in the patients' blood. The 4.1R protein of the erythrocyte membrane is critical for the membrane-associated cytoskeleton structure and in central neurons it regulates the stabilization of AMPA receptors on the neuronal surface at the postsynaptic density. We report clinical, biochemical, and genetic features in four patients from four unrelated families with NA in order to explain the cause of morphological abnormalities and the relationship with neurodegenerative processes.

Case presentation

All patients were characterised by atypical NA with a novel alteration of the erythrocyte membrane: a 4.1R protein deficiency. The 4.1R protein content was significantly lower in patients (3.40 ± 0.42) than in controls (4.41 ± 0.40, P < 0.0001), reflecting weakened interactions of the cytoskeleton with the membrane. In patients IV:1 (RM23), IV:3 (RM15), and IV:6 (RM16) the 4.1 deficiency seemed to affect the horizontal interactions of spectrin and an impairment of the dimer self-association into tetramers was detected. In patient IV:1 (RM16) the 4.1 deficiency seemed to affect the skeletal attachment to membrane and the protein band 3 was partially reduced.

Conclusion

A decreased expression pattern of the 4.1R protein was observed in the erythrocytes from patients with atypical NA, which might reflect the expression pattern in the central nervous system, especially basal ganglia, and might lead to dysfunction of AMPA-mediated glutamate transmission.