Lenticular intermediate-sized filaments: biosynthesis and interaction with plasma membrane

The binding of vimentin to human erythrocyte membranes: a model system for the study of intermediate filament-membrane interactions

We have characterized the association of the intermediate filament protein, vimentin, with the plasma membrane, using radioiodinated lens vimentin and various preparations of human erythrocyte membrane vesicles. Inside-out membrane vesicles (IOVs), depleted of spectrin and actin, bind I125-vimentin in a saturable manner unlike resealed, right-side-out membranes which bind negligible amounts of vimentin in an unsaturable fashion. The binding of vimentin to IOVs is abolished by trypsin or acid treatment of the vesicles. Extraction of protein 4.1 or reconstitution of the membranes with purified spectrin do not basically affect the association. However, removal of ankyrin (band 2.1) significantly lowers the binding. Upon reconstitution of depleted vesicles with purified ankyrin, the vimentin binding function is restored. If ankyrin is added in excess the binding of vimentin to IOVs is quantitatively inhibited, whereas protein 4.1, the cytoplasmic fragment of band 3, band 6, band 4.5 (catalase), or bovine serum albumin do not influence it. Preincubation of the IOVs with a polyclonal anti-ankyrin antibody blocks 90% of the binding. Preimmune sera and antibodies against spectrin, protein 4.1, glycophorin A, and band 3 exhibit no effect. On the basis of these data, we propose that vimentin is able to associate specifically with the erythrocyte membrane skeleton and that ankyrin constitutes its major attachment site.

Interaction of crystallins with the cytoskeletal-plasma membrane complex of the bovine lens

The isolated lenticular plasma membrane-cytoskeleton complex, when analysed by sodium dodecylsulphate-polyacrylamide gel electrophoresis, shows reproducibly a significant amount of crystallins, mainly alpha-crystallin. Evidence is provided that purified plasma membranes from the bovine lens also associate selectively with a limited number of newly synthesized polypeptides on cell-free translation of calf lens polyribosomes and addition of the membranes to the incubation medium. This capability is retained by purified lens membrane junctions. The polypeptides that are selected comprise alpha-crystallin chains (in particular alpha A2-crystallin), actin, vimentin and beta B1a-crystallin. Sequence analysis revealed that the latter has in its N-terminal extension a characteristic Pro-Ala track. The designation 'PAPA-arm' is proposed for this N-terminal region, comprising the alternating Pro-Ala sequence, that has previously also been found in rabbit myosin and might be responsible for anchoring beta B1a-crystallin to lens membranes.

Sequence analysis of peptide fragments from the intrinsic membrane protein of calf lens fibers MP26 and its natural maturation product MP22

Calf lens fiber plasma membranes, containing only the intrinsic membrane protein MP26 and its maturation product MP22 were treated with proteolytic enzymes such as trypsin, protease V8 from S. aureus or with chemical agents as CNBr in formic acid. The cleavage products, purified by electrophoresis, were analysed for their amino acid composition and N-terminal sequences. Proteolysis gave rise to peptides which were mainly shortened at the C-terminal end of the molecules. While the V8 protease produced a fragment with a similar N-terminal sequence as the maturation product MP22, trypsin yielded another cleavage product. Chemical hydrolysis yielded large fragments (11-15 kDa) with hydrophobic N-terminal sequences. Our results suggest that MP26 is characterised by an N-terminal signal sequence and possesses other hydrophobic domains which could function as untranslocated insertion sequences.

Isolation of the intermediate filament protein vimentin by chromatofocusing

A novel, simple and relatively rapid method is described for the isolation of the intermediate-sized filament protein vimentin from eye lens tissue. Chromatofocusing is applied as the sole purification step. The apparent isoelectric point of the protein in 6 M urea and at 22 degrees C is 4.9. Electrophoretic mobility on one- and two-dimensional polyacrylamide gels, solubility in 6 M urea and amino acid composition were used for identification.

Expression of the intermediate-filament-associated protein synemin in chicken lens cells

Synemin, a 230-kilodalton polypeptide component of avian muscle and erythrocyte intermediate filaments, is also found in association with the vimentin filaments of lens tissue. In chicken lens cells, synemin is bound to the core vimentin polymer with the same 180-nm periodicity that it exhibits in erythrocytes. Its solubility properties are characteristic of those of intermediate filaments in general and similar to those of synemin in muscle cells and erythrocytes. Synemin appears at an early stage of lens development and undergoes a dramatic accumulation as the epithelial cells elongate and differentiate into fiber cells. In contrast to synemin in cultured skeletal muscle, lens synemin is not confined to postmitotic, terminally differentiating cells but is present in proliferative cells as well. It is lost from the fibers near the center of the lens, as are many other cellular structures including intermediate filaments. These findings provide new information about the occurrence and expression of avian synemin and new insight regarding its presumptive role as a modulator of intermediate-filament function.

Expression of the intermediate-filament-associated protein synemin in chicken lens cells

Synemin, a 230-kilodalton polypeptide component of avian muscle and erythrocyte intermediate filaments, is also found in association with the vimentin filaments of lens tissue. In chicken lens cells, synemin is bound to the core vimentin polymer with the same 180-nm periodicity that it exhibits in erythrocytes. Its solubility properties are characteristic of those of intermediate filaments in general and similar to those of synemin in muscle cells and erythrocytes. Synemin appears at an early stage of lens development and undergoes a dramatic accumulation as the epithelial cells elongate and differentiate into fiber cells. In contrast to synemin in cultured skeletal muscle, lens synemin is not confined to postmitotic, terminally differentiating cells but is present in proliferative cells as well. It is lost from the fibers near the center of the lens, as are many other cellular structures including intermediate filaments. These findings provide new information about the occurrence and expression of avian synemin and new insight regarding its presumptive role as a modulator of intermediate-filament function.

Vimentin intermediate filaments in cultures of human meningiomas

Monolayer cultures of six human meningiomas and meningeal cells from a human foetus were examined by indirect immunofluorescence with a human autoantibody to intermediate filaments and with a monoclonal antibody to vimentin intermediate filaments. No difference could be demonstrated in the staining of an intricate fibrillar network in cultures of transitional, fibroblastic, psammomatous and sarcomatous meningiomas compared to those of human foetal meninges. Many meningotheliomatous meningioma cells showed staining of distinctive 'whorls' of intermediate filaments, an observation less frequently seen in fetal meningeal cells or in meningiomas of other histological types. Meningioma cells, pretreated with vinblastine, showed staining of rearranged filaments whose conformation and compactness varied from cell to cell. A striking observation frequently seen in transitional and psammomatous meningiomas was the staining of thick intermediate filament 'bands' bridging two contiguous meningioma cells. Immunoblotting experiments confirmed the presence of vimentin intermediate filaments in the cultured meningioma cells.

Avian lens spectrin: subunit composition compared with erythrocyte and brain spectrin

Chicken lens spectrin is composed predominantly of equimolar amounts of two polypeptides with solubility properties similar, but not identical, to erythrocyte spectrin. The larger polypeptide, Mr 240,000 (lens alpha-spectrin), co-migrates with erythrocyte and brain alpha-spectrin on one- and two-dimensional SDS polyacrylamide gels and cross-reacts with antibodies specific for chicken erythrocyte alpha-spectrin; the smaller polypeptide, Mr 235,000 (lens gamma-spectrin), co-migrates with brain gamma-spectrin and does not cross-react with either the alpha-spectrin antibodies specific for chicken erythrocyte beta-spectrin. Minor amounts of polypeptides antigenically related to erythrocyte beta-spectrin with a greater electrophoretic mobility than lens gamma-spectrin are also detected in lens. The equimolar ratio of lens alpha- and gamma-spectrin is invariantly maintained during the extraction of lens plasma membranes under different conditions, or after immunoprecipitation of whole extracts of lens with erythrocyte alpha-spectrin antibodies. Two-dimensional peptide mapping reveals that whereas alpha-spectrins from chicken erythrocytes, brain, and lens are highly homologous, the gamma-spectrins, although related, have some cell-type-specific peptides and are substantially different from erythrocyte beta-spectrin. Thus, the expression of cell-type-specific gamma- and beta-spectrins may be the basis for the assembly of a spectrin-plasma membrane complex whose molecular composition is tailored to the functional requirements of the particular cell-type.

Antibodies to intermediate filament proteins in the immunohistochemical identification of human tumours: an overview

Intermediate-sized filament proteins (IFP) are tissue specific in that antibodies to keratin, vimentin, desmin, glial fibrillary acidic protein (GFAP) and the neurofilament proteins can distinguish between cells of epithelial and mesenchymal origin as well as of myogenic and neural origin respectively. Malignant cells retain their tissue-specific IFP, which makes it possible to use these antibodies in tumour diagnosis. Carcinomas are exclusively detected by antibodies to keratin. Monoclonal antibodies to keratin have allowed the differentiation between subgroups of epithelial tumours until now between adenocarcinomas and squamous cell carcinomas. Lymphomas, melanomas and several soft tissue tumours are distinctly recognized by antibodies to vimentin. On the other hand, rhabdomyosarcomas and leiomyosarcomas are positive for desmin, while astrocytomas give a strong reaction with GFAP antibodies. Thus, antibodies to IFP are useful tools for differential diagnosis in surgical pathology.

Functional changes of intermediate filaments in fibroblastic cells revealed by a monoclonal antibody

We describe reversible changes of intermediate filaments of fibroblastic cells associated with changes in the functional state of the cells. The changes are revealed by comparing the immunofluorescence patterns given by a monoclonal antibody and a polyclonal serum, both recognizing vimentin. The state of the filaments depends on culture density; this effect cannot be attributed to the nutritional state of the cells, their growth rate, or substances released into the medium. It seems to depend mainly on the aggregation of filaments during strong cell movements. The possible significance of these findings for the functional role of intermediate filaments is discussed.

The role of cytoskeletal and cytocontractile elements in pathologic processes

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Immunolocalization of a novel, cytoskeleton-associated polypeptide of Mr 230,000 daltons (p230)

Antibodies were raised against a cytoskeleton-associated, nonphosphorylated, 230,000-dalton bovine lens polypeptide (designated p230), and rendered monospecific by using a novel immunoaffinity technique. In immunofluorescence and electron microscopy of cultured fibroblasts, as well as of various other cells (endothelial, epithelial, lenticular, monocytes, neuroblastoma cells) and tissues (human kidney and liver), p230 was localized as a distinct subplasmalemmal layer in the peripheral cytoplasm of the cells. It constituted less than 0.3% of the total cellular protein in cultured fibroblasts and was not extractable with Triton X-100. In detergent-extracted cytoskeletal preparations of cultured fibroblasts, p230 remained as an elaborate peripheral network that showed a distribution distinctly different from that of the major cytoskeletal structures, stress fibers, cortical myosin, vinculin, and intermediate filaments (IF). The distribution was not dependent on the presence of intact stress fibers or microtubules, as shown by double-fluorescence microscopy of cells exposed to cytochalasin B or cultured in the presence of monensin and of cold-treated cells. Upon demecolcine-induced reorganization of intermediate filaments, however, the localization of p230 was rapidly altered to a dense plaque underneath the perinuclear aggregate of intermediate filaments. On the other hand, p230 seemed to colocalize with the detergent-resistant cell surface lamina, visualized in fluorescence microscopy with fluorochrome-coupled wheat germ agglutinin-lectin. The results suggest that p230 is part of a cell surface- and cytoskeleton-associated subplasmalemmal structure that may play an important role in cell surface-cytoskeleton interaction in various cells both in vitro and in vivo.

One of the protein components of lens fiber membranes is glyceraldehyde 3-phosphate dehydrogenase

The eye lens membrane component 'MP34' [Exp. Eye Res. 24 (1977) 413-415] has been resolved into three protein components and in a revised nomenclature designated MP35, MP36.5 and MP37, respectively. MP37 has been identified as the enzyme glyceraldehyde 3-phosphate dehydrogenase, which is one of the major components of membranes both from cultured hamster lens cells and from HeLa cells.

Squid lens cytoskeleton and membrane proteins

Cytoskeletal and membrane proteins were isolated from respectively the urea-soluble and urea-insoluble fractions of the squid lens. The main cytoskeletal polypeptide has a molecular weight (63000) and an amino acid composition similar to those of vertebrate intermediate filament proteins, including mammalian lens vimentins. Intermediate filaments, and bundles thereof, were regenerated from the squid lens urea-soluble fraction upon removal of urea. The main membrane polypeptide of 140000 Mr has an amino acid composition entirely different from that of the main intrinsic membrane protein of 26000 Mr which is found in all vertebrates. Although non-EDTA-extractable, the 140000 Mr squid membrane polypeptide is best classified as extrinsic, since it has a high polarity (mainly acidic residues) and can be degraded completely upon trypsin treatment of squid lens membranes.