Human alpha B-crystallin (CRYA2) gene mapped to chromosome 11q12-q23

αB-Crystallin R120G variant causes cardiac arrhythmias and alterations in the expression of Ca(2+) -handling proteins and endoplasmic reticulum stress in mice

Mutations of αB-crystallin (CryαB), a small heat shock protein abundantly expressed in cardiac and skeletal muscles, are known to cause desmin-related myopathies. The CryαB R120G allele has been linked to a familial desminopathy and, in transgenic mice, causes a sudden death at about 28 weeks of age. To investigate the mechanisms of the sudden cardiac arrest of CryαB R120G transgenic mice, we prepared protein samples from left ventricular tissues of two different age groups (10 and 28 weeks) and examined Ca(2+) -handling proteins. Expression of sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) 2, phospholamban, ryanodine receptor 2 and calsequestrin 2 was significantly decreased in 28- versus 10-week-old CryαB R120G transgenic mice. In addition, low heart rate variability, including heart rate, total power and low frequency, was observed and continuous electrocardiogram monitoring revealed cardiac arrhythmias, such as ventricular tachycardia, atrioventricular block and atrial flutter, in 28-week-old CryαB R120G transgenic mice. In contrast, expression of endoplasmic reticulum (ER) degradation enhancing α-mannosidase-like protein, inositol requirement 1 and X-box binding protein 1 were increased significantly in 28- versus 10-week-old CryαBR120G transgenic mice, suggesting that the CryαBR120G transgenic mice exhibit increased ER stress compared with wild-type mice. Together, the data suggest that the CryαB R120G dominant variant induces ER stress and impairs Ca(2+) regulation, leading to ageing-related cardiac dysfunction, arrhythmias and decreased autonomic tone with shortened lifespan.

Desmin-related myopathy

Desmin-related myopathy (DRM) is an autosomally inherited skeletal and cardiac myopathy, mainly caused by dominant mutations in the desmin gene (DES). We provide (i) a literature review on DRM, including clinical manifestations, inheritance, molecular genetics, myopathology and management and (ii) a meta-analysis of reported DES mutation carriers, focusing on their clinical characteristics and potential genotype-phenotype correlations. Meta-analysis: DES mutation carriers (n = 159) with 40 different mutations were included. Neurological signs were present in 74% and cardiological signs in 74% of carriers (both neurological and cardiological signs in 49%, isolated neurological signs in 22%, and isolated cardiological signs in 22%). More than 70% of carriers exhibited myopathy or muscular weakness, with normal creatine kinase levels present in one third of them. Up to 50% of carriers had cardiomyopathy and around 60% had cardiac conduction disease or arrhythmias, with atrioventricular block as an important hallmark. Symptoms generally started during the 30s; a quarter of carriers died at a mean age of 49 years. Sudden cardiac death occurred in two patients with a pacemaker, suggesting a ventricular tachyarrhythmia as cause of death. The majority of DES mutations were missense mutations, mostly located in the 2B domain. Mutations in the 2B domain were predominant in patients with an isolated neurological phenotype, whereas head and tail domain mutations were predominant in patients with an isolated cardiological phenotype.

Tragedy in a heartbeat: malfunctioning desmin causes skeletal and cardiac muscle disease

Muscle fiber deterioration resulting in progressive skeletal muscle weakness, heart failure, and respiratory distress occurs in more than 20 inherited myopathies. As discussed in this Review, one of the newly identified myopathies is desminopathy, a disease caused by dysfunctional mutations in desmin, a type III intermediate filament protein, or alphaB-crystallin, a chaperone for desmin. The range of clinical manifestations in patients with desminopathy is wide and may overlap with those observed in individuals with other myopathies. Awareness of this disease needs to be heightened, diagnostic criteria reliably outlined, and molecular testing readily available; this would ensure prevention of sudden death from cardiac arrhythmias and other complications.

Molecular pathology of myofibrillar myopathies

Myofibrillar myopathies (MFMs) are clinically and genetically heterogeneous muscle disorders that are defined morphologically by the presence of foci of myofibril dissolution, accumulation of myofibrillar degradation products, and ectopic expression of multiple proteins. MFMs are the paradigm of conformational protein diseases of the skeletal (and cardiac) muscles characterised by intracellular protein accumulation in muscle cells. Understanding of this group of disorders has advanced in recent years through the identification of causative mutations in various genes, most of which encode proteins of the sarcomeric Z-disc, including desmin, alphaB-crystallin, myotilin, ZASP and filamin C. This review focuses on the MFMs arising from defects in these proteins, summarising genetic and clinical features of the disorders and then discussing emerging understanding of the molecular pathogenic mechanisms leading to muscle fibre degeneration. Defective extralysosomal degradation of proteins is now recognised as an important element in this process. Several factors--including mutant proteins, a defective ubiquitin-proteasome system, aggresome formation, mutant ubiquitin, p62, oxidative stress and abnormal regulation of some transcription factors--are thought to participate in the cascade of events occurring in muscle fibres in MFMs.

Intermediate filament diseases: desminopathy

Desminopathy is one of the most common intermediate filament human disorders associated with mutations in closely interacting proteins, desmin and alphaB-crystallin. The inheritance pattern in familial desminopathy is characterized as autosomal dominant or autosomal recessive, but many cases have no family history. At least some and likely most sporadic desminopathy cases are associated with de novo DES mutations. The age of disease onset and rate of progression may vary depending on the type of inheritance and location of the causative mutation. Typically, the illness presents with lower and later upper limb muscle weakness slowly spreading to involve truncal, neck-flexor, facial and bulbar muscles. Skeletal myopathy is often combined with cardiomyopathy manifested by conduction blocks, arrhythmias and chronic heart failure resulting in premature sudden death. Respiratory muscle weakness is a major complication in some patients. Sections of the affected skeletal and cardiac muscles show abnormal fibre areas containing chimeric aggregates consisting of desmin and other cytoskeletal proteins. Various DES gene mutations: point mutations, an insertion, small in-frame deletions and a larger exon-skipping deletion, have been identified in desminopathy patients. The majority of these mutations are located in conserved alpha-helical segments, but additional mutations have recently been identified in the tail domain. Filament and network assembly studies indicate that most but not all disease-causing mutations make desmin assembly-incompetent and able to disrupt a pre-existing filamentous network in dominant-negative fashion. AlphaB-crystallin serves as a chaperone for desmin preventing its aggregation under various forms of stress; mutant CRYAB causes cardiac and skeletal myopathies identical to those resulting from DES mutations.

The human E48 antigen, highly homologous to the murine Ly-6 antigen ThB, is a GPI-anchored molecule apparently involved in keratinocyte cell-cell adhesion

The E48 antigen, a putative human homologue of the 20-kD protein present in desmosomal preparations of bovine muzzle, and formerly called desmoglein III (dg4), is a promising target antigen for antibody-based therapy of squamous cell carcinoma in man. To anticipate the effect of high antibody dose treatment, and to evaluate the possible biological involvement of the antigen in carcinogenesis, we set out to molecularly characterize the antigen. A cDNA clone encoding the E48 antigen was isolated by expression cloning in COS cells. Sequence analysis revealed that the clone contained an open reading frame of 128 amino acids, encoding a core protein of 13,286 kD. Database searching showed that the E48 antigen has a high level of sequence similarity with the mouse ThB antigen, a member of the Ly-6 antigen family. Phosphatidylinositol-specific (PI-specific) phospholipase-C treatment indicated that the E48 antigen is glycosylphosphatidylinositol-anchored (GPI-anchored) to the plasma membrane. The gene encoding the E48 antigen is a single copy gene, located on human chromosome 8 in the 8q24-qter region. The expression of the gene is confined to keratinocytes and squamous tumor cells. The putative mouse homologue, the ThB antigen, originally identified as an antigen on cells of the lymphocyte lineage, was shown to be highly expressed in squamous mouse epithelia. Moreover, the ThB expression level is in keratinocytes, in contrast to that in lymphocytes, not mouse strain related. Transfection of mouse SV40-polyoma transformed mouse NIH/3T3 cells with the E48 cDNA confirmed that the antigen is likely to be involved in cell-cell adhesion.

Construction and characterization of the chimeric monoclonal antibody E48 for therapy of head and neck cancer

Data from an ongoing clinical radioimmunoscintigraphy trial indicate that 99mTc-labeled monoclonal antibody (mAb) E48 is highly capable of selectively targeting squamous cell carcinoma of the head and neck (HNSCC). The percentage of the injected dose per gram of tumor tissue was found to be high, rendering mAb E48 a promising candidate mAb for therapeutic purposes. We now describe the construction of a chimeric (mouse/human) mAb E48 by recombinant DNA technology. The genes encoding the variable domains of the heavy and light chain were cloned and ligated into expression vectors containing the human gamma 1 heavy-chain gene and the human kappa light-chain gene respectively. Biological properties of the resulting chimeric mAb E48 were compared to the murine form in vitro and in vivo. The reactivities of chimeric (c)mAb and murine (m)mAb E48 with HNSCC, as assessed by immunohistochemical staining as well as immuno-blotting were shown to be similar. The affinity constant appeared to be 0.9 x 10(10) M-1 and 1.6 x 10(10) M-1 for the mmAb and cmAb respectively. The biodistribution of both antibodies was tested by simultaneous injection into nude mice bearing human HNSCC xenografts. cmAb E48 was found to be cleared more rapidly from the blood than mmAb E48, resulting in a 30% lower tumor uptake but similar tumor to non-tumor ratios, 3 days after injection. Moreover, it was shown that cmAb E48 is highly capable of lysing HNSCC targets in ADCC assays in vitro, whereas the mmAb appeared to be almost inactive. These data indicate that cmAb E48 has potential as a targeting agent for the eradication of HNSCC in man.

Structure and modifications of the junior chaperone alpha-crystallin. From lens transparency to molecular pathology

alpha-Crystallin is a high-molecular-mass protein that for many decades was thought to be one of the rare real organ-specific proteins. This protein exists as an aggregate of about 800 kDa, but its composition is simple. Only two closely related subunits termed alpha A- and alpha B-crystallin, with molecular masses of approximately 20 kDa, form the building blocks of the aggregate. The idea of organ-specificity had to be abandoned when it was discovered that alpha-crystallin occurs in a great variety of nonlenticular tissues, notably heart, kidney, striated muscle and several tumors. Moreover alpha B-crystallin is a major component of ubiquinated inclusion bodies in human degenerative diseases. An earlier excitement arose when it was found that alpha B-crystallin, due to its very similar structural and functional properties, belongs to the heat-shock protein family. Eventually the chaperone nature of alpha-crystallin could be demonstrated unequivocally. All these unexpected findings make alpha-crystallin a subject of great interest far beyond the lens research field. A survey of structural data about alpha-crystallin is presented here. Since alpha-crystallin has resisted crystallization, only theoretical models of its three-dimensional structure are available. Due to its long life in the eye lens, alpha-crystallin is one of the best studied proteins with respect to post-translational modifications, including age-induced alterations. Because of its similarities with the small heat-shock proteins, the findings about alpha-crystallin are illuminative for the latter proteins as well. This review deals with: structural aspects, post-translational modifications (including deamidation, racemization, phosphorylation, acetylation, glycation, age-dependent truncation), the occurrence outside of the eye lens, the heat-shock relation and the chaperone activity of alpha-crystallin.

Identification of a lens-specific regulatory region (LSR) of the murine alpha B-crystallin gene

Previous studies have shown that the -661/+44 sequence of the murine alpha B-crystallin gene contains a muscle-preferred enhancer (-426/-257) and can drive the bacterial chloramphenicol acetyltransferase (CAT) gene in the lens, skeletal muscle and heart of transgenic mice. Here we show that transgenic mice carrying a truncated -164/+44 fragment of the alpha B-crystallin gene fused to the CAT gene expressed exclusively in the lens; by contrast mice carrying a -426/+44 fragment of the alpha B gene fused to CAT expressed highly in the lens, skeletal muscle and heart, and slightly in the lung, brain, kidney, spleen and liver. DNase I protection experiments indicated that the -147/-118 sequence is protected by nuclear proteins from alpha TN4-1 lens cell line, but not by nuclear proteins from myotubes of the C2C12 cell line. Site directed mutagenesis of this sequence decreased promoter activity in transiently-transfected lens cells, consistent with this sequence being a lens-specific regulatory region (LSR). We conclude that the -426/-257 enhancer is required for expression in skeletal muscle, heart and possibly other tissues, and that the -164/+44 sequence of the alpha B-crystallin gene is sufficient for expression in the lens of transgenic mice.

Subregional physical mapping of an alpha B-crystallin sequence and of a new expressed sequence D11S877E to human 11q

We report the regional assignment on Chromosome (Chr) 11q of two cDNA clones selected as sequences expressed in mature kidney and not expressed in Wilms' tumor. Clone T70 was identified as an alpha B-crystallin sequence (CRYA2). CRYA2 has previously been mapped to 11q22.3-23.1 by in situ hybridization. Clone 6.2 represents a new gene expressed in adult and fetal kidney, pancreas, and liver. In order to map sequences corresponding to clone 6.2 and to physically define the boundaries of the localization of CRYA2, we used somatic cell hybrids carrying either different human chromosomes or Chr 11 segments and a cell line established from a patient with an interstitial deletion of region 11q14.3-q22.1. We showed that CRYA2 lies proximal to the 11q23.2 breakpoint defined by the constitutional t(11;22) and distal to the 11q22.1 breakpoint (between D11S388 and D11S35) of a constitutional interstitial deletion. This is in agreement with previous data obtained by in situ hybridization and provides proximal and distal physical benchmarks for this localization. Clone 6.2-related sequence (D11S877E) was assigned to region 11q23.2-q24.2 defined by the breakpoints of the constitutional t(11;22) and of the Ewing's sarcoma neuroepithelioma t(11;22).

Immunoreactive alpha A crystallin in rat non-lenticular tissues detected with a sensitive immunoassay method

For the quantitative analysis of the A subunit of alpha crystallin (alpha A) in the lens and for the survey of possible existence of alpha A in the non-lenticular tissues, we have established a highly sensitive and specific immunoassay method for alpha A. Antisera to alpha A were raised in rabbits with alpha A purified from bovine lens, or the C-terminal decapeptide (EEKPSSAPSS) of alpha A (alpha Apep). The antibodies to alpha A and alpha Apep were purified by the use of an alpha A-coupled Sepharose 4B column. The F(ab')2 fragments of purified anti-alpha A IgG were immobilized on polystyrene balls and the Fab' fragments of purified anti-alpha Apep IgG were labeled with beta-D-galactosidase from Escherichia coli. The minimum detection limit of the sandwich-type immunoassay using the two antibody preparations was less than 10 pg alpha A without any cross-reactivity with alpha B. By employing the present methods, it was found that a significant amount of immunoreactive alpha A was present in rat spleen and thymus. Very low levels of immunoreactive alpha A were detected in the rectum, caecum, liver, kidney, adrenal, cerebellum and brainstem. The immunoreactive alpha A in the spleen extract was purified partially (about 50% purity) by the use of anti-alpha Apep-coupled Sepharose. The concentration of alpha A in the spleen was less than 1 ng/mg protein before 3 weeks of age. After 5 weeks of age, however, it increased lineally reaching about 20 ng/mg protein by 18 weeks of age. Immunohistochemically, the alpha A was localized in the reticular cells in the spleen and thymus.

Tissue distribution and developmental profiles of immunoreactive alpha B crystallin in the rat determined with a sensitive immunoassay system

In order to determine the quantitative distribution of alpha B crystallin (alpha B) in non-lenticular tissues, we have established a sensitive immunoassay system for specific measurement of alpha B. Antisera were raised in rabbits by injecting alpha B purified from bovine lenses, or C-terminal decapeptide (KPAVTAAPKK) of alpha B (alpha Bpep). The antibodies to alpha B and alpha Bpep were purified by the use of alpha B-coupled Sepharose column. The F(ab')2 fragments of antibody IgG to alpha B were immobilized on polystyrene balls and the Fab' fragments of antibody IgG to alpha Bpep were labeled with beta-D-galactosidase from Escherichia coli. The sandwich-type enzyme immunoassay consisted of the above two antibodies was sensitive, and the minimum detection limit of the assay was 10 pg alpha B without any crossreactivity with alpha A. By using the assay method, it is revealed that the alpha B was distributed in most of the tissues examined. Among the non-lenticular tissues, alpha B was present at high levels in the heart and striated muscles, especially in the soleus muscle, and kidney. High levels of alpha B in the muscle tissues were also seen in various animals. Developmental increases of alpha B in rat muscle tissues and kidney were observed from 16 days of gestational age to 1 or 5 weeks of postnatal age. In contrast, the alpha B in the brain kept a low level during the same period. After 5 weeks of age, alpha B concentrations in the brain increased sharply, reaching the adult levels at 9 weeks of age. Immunohistochemical staining with anti-alpha Bpep revealed that alpha B was positive not only in glial cells, in the central nervous tissues, but also in some neurons of spinal cord, brainstem, hippocampus, and olfactory bulb. Spermatocytes in the testis were also immunopositive for alpha B.