Human anticentriole autoantibody in patients with scleroderma and Raynaud's phenomenon

Clinical features of Japanese systemic sclerosis (SSc) patients negative for SSc-related autoantibodies: A single-center retrospective study

OBJECTIVE

To examine the clinical features of systemic sclerosis (SSc) patients negative for SSc-related autoantibodies (autoAbs).

METHODS

Serum samples were collected from 546 SSc patients. The presence of antinuclear antibody (ANA) was screened by indirect immunofluorescence (IIF) staining using HEp-2 cells. SSc-related autoantibodies were identified by specific IIF staining, enzyme-linked immunosorbent assay, or immunoprecipitation assay. Clinical features were analyzed among patients negative for ANA/SSc-related autoAbs, anticentromere Abs (ACA), anti-topoisomerase I (anti-topo I) Abs, and anti-RNA polymerase (anti-RNAP) Abs.

RESULTS

Of the 546 SSc patients, 26 (4.8%) were negative for ANA and 29 (5.3%) were ANA-positive but negative for SSc-related autoAbs. Regarding clinical features, patients negative for ANA/SSc-related autoAbs (n = 55) had a significantly shorter disease duration, higher proportion of the diffuse type, contracture of phalanges, diffuse pigmentation, higher modified Rodnan total skin thickness score (mRSS), and lower incidence of telangiectasia than those with ACA (n = 224). On the other hand, younger disease onset, lower mRSS, and lower incidence of scleroderma renal crisis were observed in patients negative for ANA/SSc-related autoAbs than in those with anti-RNAP Abs (n = 52). Although pitting scars were less common in patients negative for ANA/SSc-related autoAbs than in those with anti-topo I Abs (n = 144), their clinical features were similar.

CONCLUSION

Patients negative for ANA/SSc-related autoAbs form a clinically distinct subset among SSc patients.

Characteristics of Pulmonary Arterial Hypertension in Patients with Systemic Sclerosis and Anticentriole Autoantibodies

Anticentriole autoantibodies-positive systemic sclerosis (SSc) has been reported to develop pulmonary arterial hypertension (PAH) at a high rate. In this report, we describe two patients with anticentriole antibodies-positive SSc-PAH who were treated with pulmonary vasodilators. Both cases were elderly women with poor physical conditions and clinical findings of SSc. Case 1 was resistant to combination therapy with pulmonary vasodilators; in Case 2, hemodynamic improvement was obtained by upfront combination therapy at an early stage. Because anticentriole antibodies-positive SSc-PAH rapidly deteriorates, careful hemodynamic observation and timely aggressive use of pulmonary vasodilators should be considered.

Successful Treatment of Pulmonary Arterial Hypertension in Systemic Sclerosis with Anticentriole Antibody

Systemic sclerosis (SSc) is characterized by skin sclerosis and multiple organ damages which may cause mortality and is usually accompanied with several specific autoantibodies, each of which is associated with characteristic complications. Among them, anticentriole antibody is recently reported to be highly associated with SSc-associated pulmonary arterial hypertension (SSc-PAH). In general, several vasodilators are used as therapeutic drugs for SSc-PAH, whereas immunosuppressive therapies are not. Here, we report the case of a 62-year-old female with anticentriole antibody-positive SSc-PAH treated with immunosuppressants and vasodilators. She presented with two-year exertional dyspnea and was diagnosed with PAH and SSc owing to the centriole staining pattern and other symptoms without digital sclerosis. Oral vasodilators were initially administered but were not sufficiently effective on dyspnea. Immunosuppressants such as prednisolone and cyclophosphamide were started. Both of them improved mean pulmonary arterial pressure and 6-minute walk distance, and the anticentriole antibody also disappeared. In this case, SSc-PAH with anticentriole antibody was properly diagnosed and immunosuppressants and vasodilators improved the hemodynamics of PAH with anticentriole antibody and stably maintained it and, in addition, reduced the titer of anticentriole antibody. This indicates that anticentriole antibody might represent a good responsive group to therapies among subgroups of patients with SSc-PAH.

Anti-centrosome antibodies: Prevalence and disease association in Chinese population

Anti-centrosome antibodies are rare findings with undefined clinical significance in clinical research. We aimed at investigating the prevalence and clinical significance of anti-centrosome antibodies in Chinese population. Testing results of total of 281,230 ANA-positive sera were retrospectively obtained from West China Hospital Sichuan University in China between 2008 and 2017. We retrospectively collected and analysed the clinical and laboratory data of the patients with positive anti-centrosome antibody. Of the 356 453 patients tested, 281 230 patients had positive antinuclear antibodies (ANAs, 78.9%), but only 78 patients with positive anti-centrosome antibodies (0.022%), of which 74.4% are females. Diagnoses were established in 69 of 78 patients: 37 cases were autoimmune diseases, mainly including undifferentiated connective tissue diseases (UCTD, 9/37), rheumatoid arthritis (RA, 6/37), Sjögren's syndrome (SS, 5/37) and primary biliary cirrhosis (PBC, 5/37), and the remaining were other autoimmune conditions. The most frequent clinical symptoms of the anti-centrosome-positive patients were arthralgia and eyes and mouth drying. Additionally, 86.7% of anti-centrosome antibodies were not associated with other ANA profiles; however, when associated, the most frequent ANA was anti-U1RNP. Anti-centrosome antibodies are featured by a low prevalence and female gender predominance. They are correlated with some specific diseases, both autoimmune diseases, especially UCTD, RA, SS and PBC, and non-autoimmune diseases, such as infection and cancer, which suggests that they might be potential supporting serological markers of these diseases.

Anti-nuclear autoantibodies in systemic sclerosis : News and perspectives

Systemic sclerosis is a connective tissue disorder characterized by microvascular damage and excessive fibrosis of the skin and internal organs. One hallmark of the immunological abnormalities in systemic sclerosis is the presence of anti-nuclear antibodies, which are detected in more than 90% of patients with systemic sclerosis. Anti-centromere antibodies, anti-DNA topoisomerase I antibodies, and anti-RNA polymerase III antibodies are the predominant anti-nuclear antibodies found in systemic sclerosis patients. Other systemic sclerosis-related anti-nuclear antibodies include those targeted against U3 ribonucleoprotein, Th/To, U11/U12 ribonucleoprotein, and eukaryotic initiation factor 2B. Anti-U1 ribonucleoprotein, anti-Ku antibodies, anti-PM-Scl, and anti-RuvBL1/2 antibodies are associated with systemic sclerosis overlap syndrome. Anti-human upstream binding factor, anti-Ro52/TRIM21, anti-B23, and anti-centriole antibodies do not have specificity to systemic sclerosis, but are sometimes detected in sera from patients with systemic sclerosis. Identification of each systemic sclerosis-related antibody is useful to diagnose and predict organ involvement, since the particular type of systemic sclerosis-related antibodies is often predictive of clinical features, severity, and prognosis. The clinical phenotypes are largely influenced by ethnicity. Currently, an immunoprecipitation assay is necessary to detect most systemic sclerosis-related antibodies; therefore, the establishment of an easy, reliable, and simple screening system is warranted.

Spectrum of centrosome autoantibodies in childhood varicella and post-varicella acute cerebellar ataxia

BACKGROUND

Sera from children with post-varicella infections have autoantibodies that react with centrosomes in brain and tissue culture cells. We investigated the sera of children with infections and post-varicella ataxia and related conditions for reactivity to five recombinant centrosome proteins: gammagamma-enolase, pericentrin, ninein, PCM-1, and Mob1.

METHODS

Sera from 12 patients with acute post-varicella ataxia, 1 with post-Epstein Barr virus (EBV) ataxia, 5 with uncomplicated varicella infections, and other conditions were tested for reactivity to cryopreserved cerebellum tissue and recombinant centrosome proteins. The distribution of pericentrin in the cerebellum was studied by indirect immunofluorescence (IIF) using rabbit antibodies to the recombinant protein. Antibodies to phospholipids (APL) were detected by ELISA.

RESULTS

Eleven of 12 children with post-varicella ataxia, 4/5 children with uncomplicated varicella infections, 1/1 with post-EBV ataxia, 2/2 with ADEM, 1/2 with neuroblastoma and ataxia, and 2/2 with cerebellitis had antibodies directed against 1 or more recombinant centrosome antigens. Antibodies to pericentrin were seen in 5/12 children with post-varicella ataxia but not in any of the other sera tested. IIF demonstrated that pericentrin is located in axons and centrosomes of cerebellar cells. APL were detected in 75% of the sera from children with post-varicella ataxia and 50% of children with varicella without ataxia and in none of the controls.

CONCLUSION

This is the first study to show the antigen specificity of anti-centrosome antibodies in children with varicella. Our data suggest that children with post-varicella ataxia have unique autoantibody reactivity to pericentrin.

The clinical relevance of autoantibodies in scleroderma

Scleroderma (systemic sclerosis) is associated with several autoantibodies, each of which is useful in the diagnosis of affected patients and in determining their prognosis. Anti-centromere antibodies (ACA) and anti-Scl-70 antibodies are very useful in distinguishing patients with systemic sclerosis (SSc) from healthy controls, from patients with other connective tissue disease, and from unaffected family members. Whereas ACA often predict a limited skin involvement and the absence of pulmonary involvement, the presence of anti-Scl-70 antibodies increases the risk for diffuse skin involvement and scleroderma lung disease. Anti-fibrillarin autoantibodies (which share significant serologic overlap with anti-U3-ribonucleoprotein antibodies) and anti-RNA-polymerase autoantibodies occur less frequently and are also predictive of diffuse skin involvement and systemic disease. Anti-Th/To and PM-Scl, in contrast, are associated with limited skin disease, but anti-Th/To might be a marker for the development of pulmonary hypertension. Other autoantibodies against extractable nuclear antigens have less specificity for SSc, including anti-Ro, which is a risk factor for sicca symptoms in patients with SSc, and anti-U1-ribonucleoprotein, which in high titer is seen in patients with SSc/systemic lupus erythematosus/polymyositis overlap syndromes. Limited reports of other autoantibodies (anti-Ku, antiphospholipid) have not established them as being clinically useful in following patients with SSc.

Quantitative genetic variation in CD19 expression correlates with autoimmunity

Signaling thresholds influence the balance between humoral immunity and autoimmunity. Cell surface CD19 regulates intrinsic and Ag receptor-induced B lymphocyte signaling thresholds, and transgenic mice that overexpress CD19 by 3-fold generate spontaneous autoantibodies in a genetic background not associated with autoimmunity. To quantify the extent that genetically determined differences in expression of a single cell surface molecule can influence autoantibody production, we have assessed autoimmunity in a C57BL/6-transgenic mouse line with subtle 15-29% increases in CD19 cell surface expression (CD19 transgenic). Antinuclear Abs, especially anti-spindle pole Abs, rheumatoid factor, and autoantibodies for ssDNA, dsDNA, and histone were produced in these transgenic mice, but not littermate controls. This demonstrates that small changes in CD19 expression can induce autoantibody production. Remarkably, similar changes in CD19 expression were found on B cells from patients with systemic sclerosis, a multisystem disorder of connective tissue with autoantibody production. CD19 density on blood B cells from systemic sclerosis patients was significantly ( approximately 20%) higher compared with normal individuals, whereas CD20, CD22, and CD40 expression were normal. These results suggest that modest changes in the expression or function of regulatory molecules such as CD19 may shift the balance between tolerance and immunity to autoimmunity. Thereby autoimmune disease may result from a collection of subtle multigenic alterations that could include incremental density changes in cell surface signaling molecules.

Autoantibodies to components of the mitotic apparatus

Autoantibodies directed to a variety of cellular antigens and organelles are a feature of autoimmune diseases. They have proven useful in a clinical setting to establish diagnosis, estimate prognosis, follow disease progression, alter therapy, and initiate new investigations. Cellular and molecular biologists have used autoantibodies as probes to identify molecules involved in key cellular processes. One of the most interesting sets of autoantibodies are those that target antigens within the mitotic apparatus (MA). The MA includes chromosomes, spindle microtubules and centrosomes. The identification, localization, function, and clinical relevance of MA autoantigens is the focus of this review.

Localization of autoepitopes on the PCM-1 autoantigen using scleroderma sera with autoantibodies against the centrosome

Characterization of epitope domains of autoantigens is important for deducing the cellular functions of autoantigens and may be important for understanding the autoimmune response. In the reported studies, epitope analysis of the centrosome autoantigen PCM-1 was performed. For these investigations, portion of the PCM-1 cDNA were subcloned into the pMAL expression plasmid, fusion proteins were induced, and aliquots of the extracts were probed by immunoblot analysis using two human autoimmune anticentrosome autoantisera. Immunoblotting identified three individual autoepitopes of 26-40 amino acid residues, amino acids 506-545, 1434-1465, and 1661-1686, within the PCM-1 protein. ELISA assays using non-denatured proteins did not identity any additional autoepitopes in the remainder of the PCM-1 molecule. To analyze the identified autoepitopes further, synthetic peptides were generated that covered each of the three autoepitopes and the synthetic peptides then were probed using the scleroderma sera. Peptides that covered the antigenic regions from amino acids 506-545 and 1434-1465 failed to react with the anticentrosome autoantisera suggesting that overall protein conformation may be important for the formation of those two autoepitopes. Peptides derived from the sequence of the third autoepitope were recognized by autoantibodies present in the anticentrosome autoantisera allowing the identification of the tripeptide KDC as the autoepitope in this region of the PCM-1 molecule. These studies lay the foundation for future investigations of the autoimmune response in scleroderma patients that are producing anticentrosome autoantibodies and should allow an investigation of the cellular role of the PCM-1 protein.

The centrosome in animal cells and its functional homologs in plant and yeast cells

The centrosome is the principal microtubule-organizing center in mammalian cells. Until recently, the centrosome could only be studied at the ultrastructural level and defined as a functional entity. However, during the past decade a number of clever experimental strategies have been used to identify numerous molecular components of the centrosome. The identification of biochemical subunits of the centrosome complex has allowed the centrosome to be investigated in much more detail, resulting in important advances being made in our understanding of microtubule nucleation events, spindle formation, the assembly and replication of the centrosome, and the nature of the microtubule-organizing centers in plant cells and lower eukaryotes. The next several years should see additional rapid progress in our understanding of the microtubule cytoskeleton as investigators begin to assign functions to the centrosome proteins that have already been reported and as additional centrosome components are discovered.

Polarity orientation and assembly process of microtubule bundles in nocodazole-treated, MAP2c-transfected COS cells

Microtubule bundles reminiscent of those found in neuronal processes are formed in fibroblasts and Sf9 cells that are transfected with the microtubule-associated proteins tau, MAP2, or MAP2c. To analyze the assembly process of these bundles and its relation to the microtubule polarity, we depolymerized the bundles formed in MAP2c-transfected COS cells using nocodazole, and observed the process of assembly of microtubule bundles after removal of the drug in cells microinjected with rhodamine-labeled tubulin. Within minutes of its removal, numerous short microtubule fragments were observed throughout the cytoplasm. These short fragments were randomly oriented and were already bundled. Somewhat longer, but still short bundles, were then found in the peripheral cytoplasm. These bundles became the primordium of the larger bundles, and gradually grew in length and width. The polarity orientation of microtubules in the reformed bundle as determined by "hook" procedure using electron microscope was uniform with the plus end distal to the cell nucleus. The results suggest that some mechanism(s) exists to orient the polarity of microtubules, which are not in direct continuity with the centrosome, during the formation of large bundles. The observed process presents a useful model system for studying the organization of microtubules that are not directly associated with the centrosomes, such as those observed in axons.

Autoepitope mapping of the centrosome autoantigen PCM-1 using scleroderma sera with anticentrosome autoantibodies

We previously characterized a scleroderma serum (serum 1) containing autoantibodies against centrosome autoantigens that have been named PCM-1, PCM-2 and PCM-3. In this study, we analyzed another scleroderma serum (serum 2) reactive with centrosome autoantigens of identical molecular weights to those recognized by serum 1. To further analyze the autoepitope domains in PCM-1 recognized by the autoantibodies present in scleroderma sera, cDNAs encoding different portions of the PCM-1 autoantigen were expressed in bacteria as fusion proteins. The immunoreactivity of the fusion proteins to the scleroderma sera was assayed by immunoblot analysis. Two regions containing autoepitope domains reactive with both sera were identified in the PCM-1 molecule. One is between amino acids 312-706 of the PCM-1 autoantigen, and the other is localized between amino acids 1,433-1,787, indicating that the immune response is oligoclonal. The results are important to clarify the mechanism of induction of anticentrosome autoantibodies. The potential diagnostic and prognostic significance of the autoantibodies for subgroups of scleroderma is discussed.

Human autoimmune sera recognize a conserved 26 kD protein associated with mammalian heterochromatin that is homologous to heterochromatin protein 1 of Drosophila

Immunofluorescence indicated that autoimmune sera from certain scleroderma/CREST patients, in addition to binding to the primary constrictions or centromeres, also labelled pericentromeric heterochromatin in mouse and human metaphase chromosomes. Immunoblotting has revealed that two conserved nuclear antigens are recognized by this CREST subgroup, one of mol. wt 26 kD (p26), and the other of mol. wt 23 kD (p23). In situ immunolabelling with affinity purified antibodies demonstrated that p26, but not p23, is concentrated in pericentromeric heterochromatin. Further studies have shown that both p26 and p23 are immunologically related to the Drosophila heterochromatin-associated protein HP1, and to other chromodomain proteins.

Autoantibodies in scleroderma

Autoantibodies directed against nuclear, nucleolar, and a number of cytoplasmic components are described in the sera of scleroderma patients. Early studies of autoantibodies that relied on cryopreserved sections of rodent organ substrates showed that approximately 50% of scleroderma patients had anti-nuclear antibodies (ANA). More recent studies that have used tissue culture cell substrates have shown that up to 98% of scleroderma patients have a positive ANA. In all of these studies, the presence of different patterns of staining have suggested that scleroderma sera reacted with a variety of intracellular antigens. The use of molecular and immunochemical techniques has now shown that over 20 intracellular autoantigens are targets of autoantibodies in scleroderma sera. Clinical studies have shown that these autoantibodies are important diagnostic and prognostic markers in scleroderma. In the future, autoantibody testing may be used to monitor the patient's response to immunological therapies.

Microtubule nucleating activity of centrosomes in cell-free extracts from Xenopus eggs: involvement of phosphorylation and accumulation of pericentriolar material

We have studied the regulation of microtubule nucleating activity of the centrosome using cell-free extracts from Xenopus eggs. We found that the number of microtubules per centrosome increases dramatically with time during incubation of isolated centrosomes in interphasic egg extracts prepared 20–30 minutes after electric activation of cytostatic factor (CSF)-arrested eggs. The increase in microtubule nucleation was still conspicuous even when KCl-treated centrosomes (centrosomes stripped of their microtubule nucleating activity by 1 M KCl treatment) were incubated in interphasic extracts. Electron microscopy and immunostaining by anti-gamma-tubulin and 5051 human anti-centrosome antibodies revealed that pericentriolar material (PCM) was accumulated during the increase in microtubule nucleation from centrosomes in interphasic extracts, suggesting regulation of centrosomal activity by PCM accumulation. The ability of egg extracts to activate microtubule nucleation from centrosomes was also assumed to be regulated by phosphorylation, since addition of protein kinase inhibitors into interphasic extracts totally blocked the increase in microtubule nucleation from the KCl-treated centrosome. The ability of CSF-arrested mitotic extracts to increase microtubule nucleation from KCl-treated centrosomes was 3.5- to 5-fold higher than that of interphasic extracts, while PCM accumulation in mitotic extracts seemed to be similar to that in interphasic extracts. The increase in microtubule nucleation from KCl-treated centrosomes was strikingly enhanced by the addition of purified p34cdc2/cyclin B complex to interphasic extracts, but not by MAP kinase, which is activated downstream of p34cdc2/cyclin B. These results suggest two pathways activating centrosomal activity in egg extracts: accumulation of PCM and phosphorylation mediated by p34cdc2/cyclin B.

Enolase is present at the centrosome of HeLa cells

Antibodies raised against the C-terminus and N-terminus region of gamma gamma enolase, as well as a polyclonal antibody raised against bovine brain gamma gamma enolase, were used to study the distribution of this glycolytic enzyme during the cell cycle in HeLa cells. Enolase was found to be present throughout the cytoplasm of both interphase and dividing cells. In addition, a portion of cellular enolase was detected at the centrosome throughout the cell cycle. The capacity of glycolytic enzymes to play a structural as well as a glycolytic role suggests that the presence of enolase at the centrosome may be correlated with the organization of both the interphase cytoskeleton and the mitotic spindle.

MSA-36: a chromosomal and mitotic spindle-associated protein

We have identified a novel M(r) 36,000 protein (MSA-36) that has a complex cell cycle dependent distribution. This protein is first detected in interphase nuclei just prior to the onset of chromosome condensation. MSA-36 is found along condensing chromosomes and is a component of the centromere through metaphase. At anaphase, this protein is no longer detected in association with the chromosomes but appears at the forming stembodies and subsequently within the intercellular bridge at either side of the midbody. At the completion of cell division, the amount of MSA-36 in the bridge appears to decline concurrent with the appearance of this protein briefly within the reforming nucleus. To investigate whether MSA-36 is an active component of the chromosome or a passive passenger protein, we studied the behaviour of this protein in cells exhibiting premature chromosome condensation and in cells during and following recovery from mitotic arrest. These studies suggest that MSA-36 is not essential for a variety of major chromosome-associated events.

Gamma-tubulin is a highly conserved component of the centrosome

We have cloned and characterized gamma-tubulin genes from both X. laevis and S. pombe, and partial genes from maize, diatom, and a budding yeast. The proteins encoded by these genes are very similar to each other and to the original Aspergillus protein, indicating that gamma-tubulins are an ubiquitous and highly conserved subfamily of the tubulin family. A null mutation of the S. pombe gene is lethal. gamma-tubulin is a minor protein, present at less than 1% the level of alpha- and beta-tubulin, and is limited to the centrosome. In particular, gamma-tubulin is associated with the pericentriolar material, the microtubule-nucleating material of the centrosome. gamma-Tubulin remains associated with the centrosome when microtubules are depolymerized, suggesting that it is an integral component that might play a role in microtubule organization.

The identification of mammalian centrosomal antigens using human autoimmune anticentrosome antisera

Human autoimmune sera were screened for the presence of anticentrosome autoantibodies. Two high titer sera were identified that reacted with HeLa, CHO, and PtK2 centrosomes by immunofluorescence, although the fluorescent patterns that were obtained using the two antisera were separate and distinct. Serum obtained from patient IJ contained antibodies that reacted with epitopes present only in mitotic centrosomes; staining of interphase centrosomes was never detected uing IJ antiserum. Immunoblot analysis demonstrated that antibodies present in IJ antiserum reacted with a 190 kD spindle pole antigen. Immunofluorescent staining of cultured mammalian cells demonstrated that antibodies present in serum obtained from patient SPJ reacted with both interphase and mitotic centrosomes. Characterization of SPJ antiserum by immunoblotting demonstrated that antibodies present in the SPJ serum recognized proteins of Mrs of 39, 185, and 220 kD, although the possibility that the 185 kD polypeptide was a proteolytic breakdown product of the 220 kD protein has not been eliminated. Neither antiserum was able to inhibit microtubule nucleation from centrosomes in a lysed cell system in which pure 6S tubulin was added to permeabilized cells following pretreatment of the cells with either SPJ or IJ antiserum. These antisera should be useful probes for studying the biochemistry of the mammalian centrosome.

Identification of microtubule-associated proteins in the centrosome, spindle, and kinetochore of the early Drosophila embryo

We have developed affinity chromatography methods for the isolation of microtubule-associated proteins (MAPs) from soluble cytoplasmic extracts and have used them to analyze the cytoskeleton of the early Drosophila embryo. More than 50 Drosophila embryo proteins bind to microtubule affinity columns. To begin to characterize these proteins, we have generated individual mouse polyclonal antibodies that specifically recognize 24 of them. As judged by immunofluorescence, some of the antigens localize to the mitotic spindle in the early Drosophila embryo, while others are present in centrosomes, kinetochores, subsets of microtubules, or a combination of these structures. Since 20 of the 24 antibodies stain microtubule structures, it is likely that most of the proteins that bind to our columns are associated with microtubules in vivo. Very few MAPS seem to be identically localized in the cell, indicating that the microtubule cytoskeleton is remarkably complex.

Anticytoskeletal autoantibody to microfilament anchorage sites recognizes novel focal contact proteins

Actin microfilaments are anchored to the plasma membrane at focal contacts. Using an indirect immunofluorescence method, we detected an autoantibody reactive with focal contacts in PtK2, HEp-2, and BHK-21 cells in serum from two patients with early systemic sclerosis. With double immunofluorescence, using the actin-binding drug phalloidin, we localized the plaques decorated by these sera specifically at the termini of microfilament bundles. The reactive antigens were identified by immunoblotting as proteins of 80,000- and 75,300-mol wt in PtK2, and of 53,500-mol wt in HEp-2 and BHK-21 cells. The 53,500-mol wt protein was also identified in rat skeletal, myocardial, and smooth muscle tissues. The detergent solubility of these proteins suggested that they may be linked to the plasma membrane. The autoantigens were immunologically distinct from vinculin and alpha-actinin, two major proteins also known to be concentrated at the ends of microfilament bundles. Our observations suggest that this novel anticytoskeletal autoantibody may identify a novel family of vertebrate cell proteins involved in the linkage of microfilaments to the plasma membrane at focal contacts.

Centrosomal proteins and lactate dehydrogenase possess a common epitope in human cell lines

A spontaneously arising rabbit anti-centrosome serum with strong human specificity, used to identify specific antigens in isolated centrosomes, was shown to react with several noncentrosomal proteins including a 36-kDa protein that appeared to be the major cellular antigen. To explore the immunological relationship between noncentrosomal and centrosomal antigens, immunoglobulins were affinity purified using the individual noncentrosomal antigens (from lymphoblastoma KE37 cells) and were tested for their capacity to bind to human centrosomes in situ and to proteins from isolated centrosomes. In this way, the 36-kDa antigen, an abundant cytosolic protein, was shown to share at least one antigenic determinant with high molecular weight centrosomal proteins. This antigen was further identified by mild proteolysis as the glycolytic enzyme lactate dehydrogenase. In all the analyzed human cell lines, the centrosomal staining in situ was correlated with a strong labeling of purified lactate dehydrogenase in immunoblots. Conversely, the absence of centrosomal staining in rodent cells was always correlated with the absence of lactate dehydrogenase labeling. These data suggest an evolutionary relationship between centrosomal proteins and this "housekeeping" enzyme.

Identification of centrosomal proteins in a human lymphoblastic cell line

Highly enriched preparations of centrosomes from human T-lymphoblasts KE 37 were analyzed for their protein content. The specific pattern of polypeptides was characterized by an abundant subset of high mol. wt proteins and a major group of proteins with mol. wt ranging from 50 to 65 kd. Several immunoreactive proteins were identified, using a rabbit serum spontaneously reacting with human centrosomes. They include a family of high mol. wt ranging from 180 to 250 kd, a 130-kd protein and a 60-65 kd doublet. These antigens have the following properties: they are localized within the pericentriolar material; their abundance, as judged by centrosome labelling, changes significantly during the cell cycle, the maximum being observed at the pole of the metaphasic spindle; in Taxol-treated cells where the centrosome is no longer acting as a nucleating center, they redistribute at one end of the microtubule arrays in both mitotic and interphasic cells, as expected for nucleating, or capping, proteins. All these properties are compatible with their involvement in microtubule nucleation.