Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Lamin Type A”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1990

Characterization of a second highly conserved B-type lamin present in cells previously thought to contain only a single B-type lamin.

Previous analyses of the nuclear lamina of mammalian cells have revealed three major protein components (lamins A, B and C) that have been identified by protein sequence homology as members of the intermediate filament (IF) protein family. It has been claimed that mammalian cells contain either all three lamins or lamin B alone. Using monoclonal antibodies specific for B-type lamins and cDNA cloning we identified a second major mammalian B-type lamin (murine lamin B2), thus showing that lamin composition in mammals is more complex than previously thought. Lamin B2 is coexpressed with lamin B1 (formerly termed lamin B) in all somatic cells and mammalian species that we analysed, including a variety of cells currently believed to contain only a single lamin. This suggests that two B-type lamins are necessary to form a functional lamina in mammalian somatic cells. By cDNA cloning we found that Xenopus laevis lamin LII is the amphibian homolog of mammalian lamin B2. Lamin expression during embryogenesis of amphibians and mammals shows striking similarities. The first lamins expressed in the early embryo are the two B-type lamins, while A-type lamins are only detected much later in development. These findings indicate that the genomic differentiation into two B-type lamins occurred early in vertebrate evolution and has been maintained in both their primary structure and pattern of expression.

Amino Acid Sequence↗
PubMed1995

Genomic structure of the mouse A-type lamin gene locus encoding somatic and germ cell-specific lamins.

Mouse A-type lamin genes were isolated. Structural analyses revealed that all the three known mouse A-type lamins (A, C and C2) were coded in a single genomic locus in a 22 kilobase DNA segment. The three lamins were coded in 12, 10 and 10 exons for A, C and C2, respectively, and shared 8 exons among them. Primer extension analyses identified possible transcription start sites for both A/C and C2 genes suggesting that the locus is under the control of two separate promoters, that is a somatic cell-acting promoter (for A and C) and a testis-specific promoter (for C2) which resides in the first intron of the A/C gene. Sequence characteristics of the possible promoter regions are discussed. Divergence of the two somatic cell-type lamins (A and C) is formally accounted for by differential selection of poly(A) sites together with lamin A-specific splicing.

Animals↗
PubMed2006

A-type lamin networks in light of laminopathic diseases.

Lamins are major structural components of the lamina providing mechanical support for the nuclear envelope in vertebrates. A subgroup of lamins, the A-type lamins, are only expressed in differentiated cells and serve important functions both at the nuclear envelope and in the nucleoplasm in higher order chromatin organization and gene regulation. Mutations in A-type lamins cause a variety of diseases from muscular dystrophy and lipodystrophy to systemic diseases such as premature ageing syndromes. The molecular basis of these diseases is still unknown. Here we summarize known interactions of A-type lamins with components of the nuclear envelope and the nucleoplasm and discuss their potential involvement in the etiology and molecular mechanisms of the diseases. Lamin binding partners involve chromatin proteins potentially involved in higher order chromatin organization, transcriptional regulators controlling gene expression during cell cycle progression, differentiation and senescence, and several enzymes involved in a multitude of functions.

Chromatin↗
PubMed1997

A- and B-type lamins are differentially expressed in normal human tissues.

A selection of normal human tissues was investigated for the presence of lamins B1, B2, and A-type lamins, using a panel of antibodies specific for the individual lamin subtypes. By use of immunoprecipitation and two-dimensional immunoblotting techniques we demonstrated that these antibodies do not cross-react with other lamin subtypes and that a range of different phosphorylation isoforms is recognized by each antibody. The lamin B2 antibodies appeared to decorate the nuclear lamina in all tissues examined, except hepatocytes, in which very little lamin B2 expression was observed. In contrast to previous studies, which suggested the ubiquitous expression of lamin B1 in mammalian tissues, we show that lamin B1 is not as universally distributed throughout normal human tissues as was to be expected from previous studies. Muscle and connective tissues are negative, while in epithelial cells lamin B1 seemed to be preferentially detected in proliferating cells. These results correspond well with those obtained for lamin B1 in chicken tissues. The expression of A-type lamins is most prominent in well-differentiated epithelial cells. Relatively undifferentiated and proliferating cells in epithelia showed a clearly reduced expression of A-type lamins. Furthermore, most cells of neuroendocrine origin as well as most hematopoietic cells were negative for A-type lamin antibodies.

Antibodies, Monoclonal↗
PubMed1997

Assembly of A- and B-type lamins studied in vivo with the baculovirus system.

We have expressed an A-type lamin (Xenopus lamin A), a probable A-type lamin (Drosophila lamin C), two B-type lamins (Xenopus lamin LI, Drosophila lamin Dmo), and two mutants of Xenopus lamin A in Sf9 cells. All proteins were synthesized at high levels resulting in formation of paracrystals with an axial repeat of 18.5-20.0 nm by A-type lamins; in contrast B-type lamins assembled into aggregates with a fibrillar ultrastructure. Of the four wild-type proteins analyzed only lamin Dmo was found in the nuclear compartment of Sf9 cells in association with the lamina whereas the three other lamins assembled into polymers localized in the cytoplasm as well as the nucleoplasm. The Xenopus lamin A mutant lacking the complete carboxy-terminal tail assembled in the cytoplasm into long filament bundles consisting of fibrils of less than 6 nm diameter. In vitro the non-helical amino-terminal head domain of lamins is required for the formation of 'head-to-tail' polymers. A lamin A mutant lacking this domain could be efficiently extracted from Sf9 cells with physiological buffers containing Triton X-100, demonstrating the importance of this domain for lamin assembly in vivo.

Animals↗
PubMed1997

Comparison of A and B-type lamin expression in reactive lymph nodes and nodular sclerosing Hodgkin's disease.

AIMS: In order to clarify the differentiation and proliferation status of the Reed-Sternberg and Hodgkin cells we studied A and B-type lamin expression with specific monoclonal antibodies in nodular sclerosing Hodgkin's disease. Its normal counterpart, the reactive lymph node, was also examined for lamin subtype expression. METHODS AND RESULTS: The CD20 positive centrocytes and centroblasts of the follicle centre in the reactive lymph nodes expressed lamin B1, but were not or only very weakly positive for lamin B2 or A-type lamin antibodies. Mantle zone lymphocytes displayed lamins B1 and B2, but were negative for A-type lamins. Furthermore, CD3- and CD20-positive lymphocytes in the medulla and paracortex lacked A-type lamins, but were positive for both B-type lamins. Finally, the proliferation marker Ki67 was mainly detected in the centroblasts, but also in a fraction of the A-type lamin negative cells in the paracortex and medulla. In Hodgkin's disease, all cells expressed lamins B1 and B2, whereas A-type lamins were primarily observed in CD30-positive Reed-Sternberg and Hodgkin cells. About 20% of the Reed-Sternberg and Hodgkin cells expressed Ki67, with co-expression of lamin A in most of these cells. CONCLUSIONS: Ki67 and A-type lamin staining were in general mutually exclusive in lymph nodes, indicating that A-type lamin positive cells are not proliferative. This suggests also that the A-type lamin expression in Reed-Sternberg and Hodgkin cells is correlated with a relatively mature phenotype of these malignant cells. However, some of these differentiated malignant cells still have a capacity to proliferate as indicated by Ki67 positivity. Our observation that lamin B2 expression in the follicle centre cells of the reactive lymph node is low or absent indicates that this lamin subtype is not always expressed in nucleated cells, which is in clear contrast to the results obtained in previous studies in other diseases and in normal tissues. Absence of lamin B2 expression may be associated with the follicle centre stage of B-cells.

Fluorescent Antibody Technique, Indirect↗
PubMed1993

Nuclear A-type lamins are differentially expressed in human lung cancer subtypes.

Nuclear A-type and B-type lamin expression was investigated in the major human lung cancer subtypes: small cell lung cancer (SCLC), squamous cell carcinomas, and adenocarcinomas (both non-SCLC). Twenty-two human lung cancer cell lines and 46 fresh frozen human lung cancer specimens were examined. Expression of B-type lamins was found in all the different cell lines. A-type lamins were expressed in all non-SCLC cell lines but were absent or only weakly expressed in 14 out of 16 SCLC cell lines. The immunocytochemical results were confirmed by immunoblotting and Northern blot analyses. In sections of SCLCs and non-SCLCs, B-type lamins were found to be expressed in all tumors. However, in some non-SCLCs, particularly in adenocarcinomas, a considerable proportion of the tumor cells were negative for B-type lamins. A-type lamin expression in SCLCs was weakly positive or negative in 14 out of 15 cases. In contrast, all non-SCLCs displayed A-type lamins, but in several of these samples, both cytoplasmic and nuclear staining was observed.

Adenocarcinoma↗
PubMed1995

Abnormal A-type lamin organization in a human lung carcinoma cell line.

We have studied the expression of lamins A and C (A-type lamins) in a lung carcinoma cell line using type-specific monoclonal antibodies. Using immunofluorescence and immunoblotting studies it was noted that several irregularities in lamin expression exist in the cell line GLC-A1, derived from an adenocarcinoma. First, the expression of the A-type lamins was lower than in other adenocarcinoma cell lines of the lung. Also the ratio between lamins A and C proteins was 1:8 instead of the 1:1 ratio seen in the other cell lines. Northern blotting confirmed the altered level of A-type lamin expression. Secondly, an abnormal localization of lamin A was observed. Intensely fluorescing lamin A aggregates were observed in the nucleus, rather than the typical perinuclear staining pattern. Confocal scanning laser microscopy revealed that the lamin A aggregates were indeed present throughout the internal nucleus. When these cells were extracted with Triton X-100 the nucleoplasmic aggregates disappeared, which indicates that the A-type lamins are not properly incorporated into the lamina. The A-type lamins in other cell lines derived from adenocarcinomas remained present in the nuclear periphery after extraction with the non-ionic detergent. Immunoblotting studies of the Triton X-100 soluble and insoluble fractions showed that lamin A and an apparently truncated product, which was detected with the lamin A antibody, were present in the insoluble fraction of GLC-A1. This truncated product is partly Triton X-100 soluble since it was also detected in the detergent soluble fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenocarcinoma↗
PubMed1999

Loss of A-type lamin expression compromises nuclear envelope integrity leading to muscular dystrophy.

The nuclear lamina is a protein meshwork lining the nucleoplasmic face of the inner nuclear membrane and represents an important determinant of interphase nuclear architecture. Its major components are the A- and B-type lamins. Whereas B-type lamins are found in all mammalian cells, A-type lamin expression is developmentally regulated. In the mouse, A-type lamins do not appear until midway through embryonic development, suggesting that these proteins may be involved in the regulation of terminal differentiation. Here we show that mice lacking A-type lamins develop to term with no overt abnormalities. However, their postnatal growth is severely retarded and is characterized by the appearance of muscular dystrophy. This phenotype is associated with ultrastructural perturbations to the nuclear envelope. These include the mislocalization of emerin, an inner nuclear membrane protein, defects in which are implicated in Emery-Dreifuss muscular dystrophy (EDMD), one of the three major X-linked dystrophies. Mice lacking the A-type lamins exhibit tissue-specific alterations to their nuclear envelope integrity and emerin distribution. In skeletal and cardiac muscles, this is manifest as a dystrophic condition related to EDMD.

Animals↗
PubMed1992

The gene structure of Xenopus nuclear lamin A: a model for the evolution of A-type from B-type lamins by exon shuffling.

Nuclear lamins are intermediate filament (IF) type proteins that form a fibrillar network underlying the inner nuclear membrane. The existence of multiple subtypes of lamins in vertebrates has been interpreted in terms of functional specialization during cell division and differentiation. The structure of a gene encoding an A-type lamin of Xenopus laevis was analysed. Comparison with that of a B-type lamin of the same species shows remarkable conservation of the exon/intron pattern. In both genes the last exon, only 9-12 amino acids in length, encodes the complete information necessary for membrane targeting of lamins, i.e. a ras-related CaaX motif. The lamin A specific extension of the tail domain is encoded by a single additional exon. The 5' boundary of this exon coincides with the sequence divergence between human lamins A and C, for which an alternative splice mechanism had previously been suggested. Arguments are presented suggesting that B-type lamins represent the ancestral type of lamins and that A-type lamins derived there from by exon shuffling. The acquisition of the new exon might explain the different fates of A- and B-types lamins during cell division.

Amino Acid Sequence↗
PubMed2006

Adhesive strength and its improvement referring to the laminated-type mouthguard.

The manufacture of laminated-type mouthguards requires skill in fusing sheets of mouthguard materials together. Adequate adhesive strength is required to use mouthguards in a stable condition for a long time. Therefore, in this study, the exfoliation test was applied and some treating techniques and conditions that improve the adhesive strength on a laminated surface were examined. Samples were laminated with two pieces of mouthguard material (3 mm thickness) having an adhesive area of 5 x 5 mm2, and whose other end was the holding part. The experimental factors used were as follows: heating time, use of solvent, elimination and direct heating of the laminate surface, colour of materials and water sorption. The result was measured at the time of breakage of the maximum load (N) and the form of destruction was examined. At 165 s of heating time, material failure was shown at under a load exceeding 5.0 N when compared to an untreated condition. Material failure was measured when a solvent was used and during the elimination of the laminated surface at a heating time of 150 s, which is 15 s lesser than in an untreated condition. Material failure was also measured by direct heating on the bonding surface of a second sheet of material at a heating time of 135 s, which is 30 s lesser than in an untreated condition. The differences in colour of the materials influence adhesion. Clear and light coloured materials showed higher adhesion ability. One-way analysis of variance confirmed a statistically significant difference in heating time differences, usage of solvent, elimination, direct heating on bonding surface and colour (P < 0.05). The decrease of adhesive strength by water sorption at 23 degrees and 37 degrees C was not observed significantly. Maximal laminated bond strength can be obtained by minimal heating time and proper treatment with the use of solvent, elimination and direct heating on bonding surface. The differences in the colour of the materials influenced adhesion. Clear and light coloured materials showed higher adhesive ability. Water sorption did not affect the adhesive strength. Therefore, if laminated-type mouthguards were manufactured properly, it can be used for a longer time and in a good condition.

Adhesiveness↗
PubMed1993

Identification of novel phosphorylation sites in murine A-type lamins.

We report the distribution of phosphorylation sites in murine lamins A and C (A-type lamins) in vitro and in vivo followed by reverse-phase high-performance liquid chromatography and microsequencing of peptides spanning the almost complete lamin sequence. We show that two distinct protein kinases, cell-division-cycle-2 kinase (cdc2 kinase) and protein kinase C (PKC), phosphorylate murine A-type lamins at the non-alpha-helical amino- and carboxy-terminal domains in vitro and in vivo. Cdc2 kinase, but not PKC, is capable of inducing depolymerization of the nuclear lamina in permeabilized cells. Accordingly, lamins were proposed to be direct in vivo substrates of cdc2 kinase and PKC with different effects on the lamina dynamics. Analysis of the original A-type lamins revealed phosphorylation of residues Ser5 and Ser392. Residue Ser392 was substoichiometrically phosphorylated in the substrate and by cdc2 kinase in vitro. PKC phosphorylated peptides with its kinase-specific motifs surrounding Ser5, Thr199, Thr416, Thr480 and Ser625. In vivo, a mitosis-specific phosphorylation at the cdc2-kinase-specific phosphoacceptor site Ser392 and of the N-terminal peptide was identified. An interphase-specific phosphorylation at Ser525 matching the PKC consensus sequence and of peptides phosphorylated by unknown kinases was determined. The results lead us to propose that different cyclin-dependent kinase activities act as lamin kinases in mitosis and in interphase. Other kinases may cooperate with cdc2 kinase during reversible disassembly in mitosis and may modulate the supramolecular assembly of lamin filaments.

Amino Acid Sequence↗
PubMed2001

Mistargeting of B-type lamins at the end of mitosis: implications on cell survival and regulation of lamins A/C expression.

We previously showed that targeting of protein phosphatase 1 (PP1) to the nuclear envelope (NE) by the A-kinase anchoring protein, AKAP149, correlates with nuclear assembly of B-type lamins in vitro. We demonstrate here that failure of AKAP149-mediated assembly of B-type lamins into the nuclear lamina at the end of mitosis is followed by apoptosis, and induces expression of the gene encoding A-type lamins in cells that normally do not express lamins A/C. In HeLa cells, inhibition of PP1 association with the NE mediated by a peptide containing the PP1-binding domain of AKAP149 results in failure of B-type lamins to assemble, and in their rapid caspase-dependent proteolysis. However, assembly of lamins A/C is not affected. Nonetheless, apoptosis follows within hours of nuclear reformation after mitosis. In lymphoid KE37 cells, which do not express lamins A/C, inhibition of B-type lamin assembly triggers rapid synthesis and nuclear assembly of both lamins A and C before apoptosis takes place. The results indicate that nuclear assembly of B-type lamins is essential for cell survival. They also suggest that mistargeting of B-type lamins at the end of mitosis elicits a tentative rescue process to assemble a nuclear lamina in lymphoid cells that normally do not express lamins A/C.

A Kinase Anchor Proteins↗
PubMed1999

Dynamics of the nuclear lamina as monitored by GFP-tagged A-type lamins.

The behavior of chimeric proteins consisting of A-type lamins and green fluorescent protein (GFP) was studied to investigate the localization and dynamics of nuclear lamins in living cells. Cell line CHO-K1 was transfected with cDNA constructs encoding fusion proteins of lamin A-GFP, lamin Adelta10-GFP, or lamin C-GFP. In the interphase nucleus lamin-GFP fluorescence showed a perinuclear localization and incorporation into the lamina for all three constructs. Our findings show for the first time that the newly discovered lamin A 10 protein is localized to the nuclear membrane. The GFP-tagged lamins were processed and behaved similarly to the endogenous lamin molecules, at least in cells that expressed physiological levels of the GFP-lamins. In addition to the typical perinuclear localization, in the majority of transfected cells each individual A-type lamin-GFP revealed an extensive collection of branching intra- and trans-nuclear tubular structures, which showed a clear preference for a vertical orientation. Time-lapse studies of 3-D reconstructed interphase cells showed a remarkable stability in both number and location of these structures over time, while the lamina showed considerable dynamic movements, consisting of folding and indentation of large parts of the lamina. Fluorescence recovery after bleaching studies revealed a low protein turnover of both tubular and lamina-associated lamins. Repetitive bleaching of intranuclear areas revealed the presence of an insoluble intranuclear fraction of A-type lamins. Time-lapse studies of mitotic cells showed that reformation of the lamina and the tubular structures consisting of A-type lamins did not occur until after cytokinesis was completed.

Animals↗
PubMed2000

Lamina-associated polypeptide 2alpha binds intranuclear A-type lamins.

The nucleoskeletal protein lamina-associated polypeptide 2(&agr;) (LAP2*) contains a large, unique C terminus and differs significantly from its alternatively spliced, mostly membrane-integrated isoforms, such as LAP2beta. Unlike lamin B-binding LAP2beta, LAP2alpha was found by confocal immunofluorescence microscopy to colocalize preferentially with A-type lamins in the newly formed nuclei assembled after mitosis. While only a subfraction of lamins A and C (lamin A/C) was associated with the predominantly nuclear LAP2alpha in telophase, the majority of lamin A/C colocalized with LAP2alpha in G(1)-phase nuclei. Furthermore, selective disruption of A-type lamin structures by overexpression of lamin mutants in HeLa cells caused a redistribution of LAP2alpha. Coimmunoprecipitation experiments revealed that a fraction of lamin A/C formed a stable, SDS-resistant complex with LAP2alpha in interphase cells and in postmetaphase cell extracts. Blot overlay binding studies revealed a direct binding of LAP2alpha to exclusively A-type lamins and located the interaction domains to the C-terminal 78 amino acids of LAP2alpha and to residues 319-566 in lamin A/C, which include the C terminus of the rod and the entire tail common to lamin A/C. These findings suggest that LAP2alpha and A-type lamins cooperate in the organization of internal nuclear structures.

Amino Acid Motifs↗
PubMed1997

Cell cycle changes in A-type lamin associations detected in human dermal fibroblasts using monoclonal antibodies.

A new panel of anti-A-type lamin monoclonal antibodies was generated. Epitope mapping was performed by immunoblotting against GST-lamin fusion peptides. Epitopes were mapped to four different regions of human lamin A and three different regions of human lamin C. The distribution of A-type lamins was compared with the distribution of the proliferation marker Ki67 in proliferating and quiescent cultures of human dermal fibroblasts (HDFs) using a double indirect immunofluorescence assay. Antibodies that had been mapped to a region of the lamin C tail stained the nuclear envelope of proliferating and quiescent cells equally brightly. In contrast, antibodies recognizing epitopes in the head domain and rod domain of lamins A and C and the tail domain of lamin A stained the nuclear envelope of quiescent cells strongly but reacted poorly or not at all with the nuclear envelope of proliferating cells. Changes in the level of expression of lamins A and C were not detected in immunoblotting assays. However, epitope masking was revealed, and this occurred by two distinct mechanisms. Epitope masking in the head domain of lamins A and C occurred as a result of protein phosphorylation. Epitope masking in the rod domain of lamins A and C and in the tail domain of lamin A occurred through a physical association between the lamin and chromatin and/or other nuclear proteins. The cell cycle timing of epitope masking was investigated in HDFs that had been restimulated after serum starvation. Extensive epitope masking in restimulated cells only occurred after cells had passed through mitosis. These results are consistent with the hypothesis that rearrangement of A-type lamin filaments, as cells progress from a quiescent to a proliferating state, results in altered lamina associations.

Animals↗
PubMed2002

Partial cleavage of A-type lamins concurs with their total disintegration from the nuclear lamina during apoptosis.

Although activated caspase 6 is capable of cleaving both A- and B-type lamins during apoptosis, the higher-order structure of the nuclear lamina may cause a differential breakdown of these two types of lamins. In order to obtain a better understanding of the dynamics and the consequences of the rapid, coordinated breakdown of the lamina complex, we applied the green fluorescent protein (GFP) technology in living cells, in which the fate of individual caspase cleavage fragments of A- and B-type lamins was examined. CHO-K1 cells were stably transfected with cDNA constructs encoding N-terminally GFP-labelled hybrids of lamin A, lamin Adelta10, lamin C or lamin B1. The course of the apoptotic process, induced by the kinase inhibitor staurosporine or by the proteasome inhibitor MG132, was monitored by digital imaging microscopy or confocal microscopy. Time-lapse recordings showed that parallel to DNA condensation N-terminally GFP-tagged A-type lamins became diffusely dispersed throughout the nucleoplasm and rapidly translocated to the cytoplasm. In contrast, the majority of GFP-lamin B1 signal remained localised at the nuclear periphery, even after extensive DNA condensation. Comparison of lamin B1-GFP signal with A-type lamin antibody staining in the same apoptotic cells confirmed the temporal differences between A- and B-type lamina dispersal. Immunoblotting revealed only a partial cleavage of A-type lamins and an almost complete cleavage of lamin B1 during apoptosis. In contrast to lamin B1 in normal cells, this cleaved lamin B1, which is apparently still associated with the nuclear membrane, can be completely extracted by methanol or ethanol. Fluorescence loss of intensity after photobleaching experiments showed that in apoptotic cells A-type lamin-GFP molecules diffuse almost freely in both nucleoplasm and cytoplasm, while the lamin B1-GFP fragments remain more stably associated with the nuclear membrane, which is confirmed by co-localisation immunofluorescence studies with a nucleoporin p62 antibody. Our results therefore clearly show a differential behaviour of A- and B-type lamins during apoptosis, suggesting not only distinct differences in the organisation of the lamina filaments, but also that caspase cleavage of only a small fraction of A-type lamins is needed for its complete disintegration.

Active Transport, Cell Nucleus↗