Lamin B autoantibodies in sera of certain patients with systemic lupus erythematosus

In vitro posttranslational modification of lamin B cloned from a human T-cell line

Autoimmune diseases are characterized by spontaneously occurring autoantibodies which have proven to be useful reagents for the characterization of specific nuclear proteins. Using a monoclonal autoantibody (72B9) derived from a murine lupus strain, we have cloned a cDNA from the human T-cell line MOLT-4, which encodes nuclear lamin B. The identity of the encoded protein as lamin B was established by both biochemical and immunological criteria. Inspection of the deduced amino acid sequence of lamin B revealed the presence in coil 1B of the alpha-helical domain of a leucine heptad repeat region. Analysis of mRNA in HL60 and MOLT-4 cells, which express only lamin B, or HeLa cells, which express all three major lamins (A, B, and C), together with the comigration of in vitro-translated product with isolated HeLa cell lamin B by two-dimensional gel electrophoresis, suggests that a single lamin B is expressed in mammalian somatic cells. In vitro translation with the cDNA clone revealed an EDTA-sensitive posttranslational modification which resulted in an increase in the apparent molecular weight to that equivalent to the native in vivo-synthesized lamin B protein. This in vitro modification included incorporation of a product of mevalonolactone and required an intact carboxy terminus.

A functionally unique anti-CD3 monoclonal antibody cross-reactive with basal keratinocytes

Monoclonal antibodies (mAb) 147, 446, and 454 each recognize different epitopes of CD3. The CD3 epitope recognized by mAb 446 is functionally unique for the T cell. In contrast to mAb 147 and 454, mAb 446 induces modulation of surface CD3 with delayed kinetics and, hence, is impaired in inducing a refractory state in the T cell to subsequent anti-CD3-induced helper function. MAb 446 (but not other anti-CD3 mAb, including mAb 147, 454, OKT3, and anti-Leu4) recognizes a cytoplasmic determinant within basal keratinocytes. Extraction of keratinocytes with nonionic detergent and 2 M NaCl abolished subsequent staining with mAb 446 but enhanced subsequent staining with anti-keratin mAb, suggesting that this cross-reactive determinant is not keratin. Immunoprecipitation of internally labeled keratinocytes with the anti-CD3 mAb 147 and 446 failed to reveal specific bands, whereas these same mAb immunoprecipitated specific bands from internally labeled CD3+ Jurkat cells corresponding to previously identified CD3 subunits, suggesting that the cross-reactive determinant in keratinocytes is also not CD3. The cross-reactivity is not species specific, in that mAb 446 stained a mouse keratinocyte line, nor is it absolutely keratinocyte specific, in that mAb 446 stained one of the two nonkeratinocyte human epithelial cell lines tested. This study raises the possibility that perturbation of unique CD3 epitopes may have unique effects on T cell surface events and subsequent activation and function.

Autoantibodies to 200 kD polypeptide(s) of the nuclear envelope: a new serologic marker of primary biliary cirrhosis

Fifty sera which gave ring-like nuclear staining in immunofluorescence on rat liver tissue sections were characterized. Using immunoprecipitation and Western blotting we showed that 10 of the sera contained antibodies to 200 kD polypeptide(s) of nuclear envelope. Clinical and biological data were available for nine of the patients. Strikingly, all of these patients suffered from primary biliary cirrhosis with eight of them having anti-mitochondrial antibodies. As no control serum displayed such a reactivity, anti-200 kD polypeptide(s) antibodies can be considered as a new marker specific of a subset of primary biliary cirrhosis, being present even when anti-mitochondrial antibodies are absent. The exact identity of the target remains to be established, since several polypeptides of similar molecular weight have been reported to belong to the nuclear envelope.

A novel autoantibody causing a peripheral fluorescent antinuclear antibody pattern is specific for nuclear pore complexes

We characterized serum from a patient with polymyositis, and found that it produced a peripheral (rim) fluorescent antinuclear antibody pattern on rat liver substrate. Indirect immunofluorescence analysis revealed a punctate pattern at the nuclear surface of PtK2, BHK-21, and HEp-2 cells. This pattern was still present after sequential extraction in situ with non-ionic detergent, DNase, RNase, and high ionic strength buffer (2M NaCl). Immunogold electron microscopic localization was specific for nuclear pore complexes. By immunoblot analysis, the antigens were polypeptides of 200 kd and 130 kd that were enriched in the nuclear fraction.

Annulate lamellae: comparison of antigenic epitopes of annulate lamellae membranes with the nuclear envelope

Annulate lamellae (AL) are a membranous structure frequently observed in differentiating gametes and tumor cells. In spite of numerous morphological studies, the function and biochemical composition of this membrane system are not well understood. In this study, we have examined the AL membrane system of vinblastine-treated mouse L cells using immunocytochemistry and Western blot analysis. Our results show that antibodies directed against nuclear envelope lamins, i.e., lamins A, B, and C, did not cross react with constituents of the AL membrane system. Furthermore an AL-specific antibody failed to react with the nuclear envelope and reacted minimally producing only a background stain over other cellular components. The data suggest that the AL membrane system has a distinct molecular make-up that is antigenically distinct from that of other subcellular structures.

Antibodies to nuclear lamins in autoimmune liver disease

Antibodies to nuclear lamins were detected in sera of patients with autoimmune liver disease. In indirect immunofluorescence tests, these sera revealed staining of the nuclear periphery. Using isolated nuclei, nuclear matrices, nuclear lamina-pore complexes, and chromatographically purified lamins as antigen source, the nuclear lamins A, B, and C were identified as reactive antigens in immunoblotting experiments. The lamins were also identified by 2-D gel electrophoresis. Antibodies to nuclear lamins occurred in 12 of 16 cases of active lupoid hepatitis, but not in 35 patients with the disease in remission. However, only 3 of 37 sera of patients with primary biliary cirrhosis contained anti-lamin antibodies. Autoimmune liver disease sera reacted preferentially with lamins A/C and less frequently with lamin B or lamins A/B/C.

Autoantibodies against nuclear envelope-associated proteins in primary biliary cirrhosis

An antinuclear immunofluorescence pattern displaying a thin ring confined to the nuclear envelope was assessed in sera from 38 patients with primary biliary cirrhosis and in sera from a control group of 277 patients with other antinuclear antibody-positive diseases. This rim-like antinuclear reactivity was present in sera from 20 primary biliary cirrhosis patients (52.6%) but in only two patients from the control group (0.7%) (p less than 0.001). Furthermore, this autoantibody was present in three of four primary biliary cirrhosis patients without antimitochondrial antibodies. Presence of this rim-like pattern in primary biliary cirrhosis did not correlate with the presence of associated autoimmune diseases nor with other clinical, biochemical, nor histological features of the disease. The antigenic specificity of sera displaying this antinuclear immunofluorescence pattern was characterized by Western blot analysis using an antigenic extract containing nuclear envelope proteins purified from rat liver. Sixteen of the 20 positive sera showed a common pattern of reactivity with a set of nuclear envelope-associated proteins approximately 200 kD in size. In conclusion, sera from primary biliary cirrhosis patients showing a rim-like fluorescent nuclear pattern have antinuclear autoantibodies that react specifically with components of the nuclear envelope. The high specificity of these new autoantibodies in primary biliary cirrhosis indicate that they might be a serological marker of the disease, particularly useful in patients without antimitochondrial antibodies.

Binding of two desmin derivatives to the plasma membrane and the nuclear envelope of avian erythrocytes: evidence for a conserved site-specificity in intermediate filament-membrane interactions

Using solution binding assays, we found that a 45-kDa fragment of desmin, lacking 67 residues from the N terminus, could specifically associate with avian erythrocyte nuclear envelopes but not with plasma membranes from the same cells. It was also observed that a 50-kDa desmin peptide, missing 27 C-terminal residues, retained the ability to bind to both membrane preparations. Displacement experiments with an excess of purified vimentin suggested that the two desmin derivatives were interacting with a previously identified vimentin receptor at the nuclear envelope, the protein lamin B [Georgatos, S. & Blobel, G. (1987) J. Cell Biol. 105, 117-127]. Additional analysis by affinity chromatography confirmed this conclusion. Employing an overlay assay, we demonstrated that the 50-kDa fragment, but not the 45-kDa desmin peptide, was capable of interacting with the plasma membrane polypeptide ankyrin (a known vimentin attachment site), as was intact vimentin. Conversely, the nuclear envelope protein lamin B was recognized by both fragments but not by a chymotryptic peptide composed solely of the helical rod domain of desmin. These data imply that the lamin B-binding site on desmin resides within the 21 residues following its helical rod domain, whereas the ankyrin-associating region is localized within its N-terminal head domain, exactly as in the case of vimentin.

Lamin B constitutes an intermediate filament attachment site at the nuclear envelope

We found that urea extraction of turkey erythrocyte nuclear envelopes abolished their ability to bind exogenous 125I-vimentin, while, at the same time, it removed the nuclear lamins from the membranes. After purification of the lamins from such urea extracts, a specific binding between isolated vimentin and lamin B, or a lamin A + B hetero-oligomer, was detected by affinity chromatography. Similar analysis revealed that the 6.6-kD vimentin tail piece was involved in this interaction. By other approaches (quantitative immunoprecipitation, rate zonal sedimentation, turbidometric assays) a substoichiometric lamin B-vimentin binding was determined under in vitro conditions. It was also observed that anti-lamin B antibodies but not other sera (anti-lamin A, anti-ankyrin, preimmune) were able to block 70% of the binding of 125I-vimentin to native, vimentin-depleted, nuclear envelopes. These data, which were confirmed by using rat liver nuclear lamins, indicate that intermediate filaments may be anchored directly to the nuclear lamina, providing a continuous network connecting the plasma membrane skeleton with the karyoskeleton of eukaryotic cells.