Disease relevance of LMNA

• Here we found that rabbitpox virus CrmA/SPI-2 inhibits the cleavage of lamin A mediated by a caspase in our cell-free system of apoptosis [1].
• Ectopic expression of an A-type lamin does not interfere with differentiation of lamin A-negative embryonal carcinoma cells [2].
• A full-length chicken lamin A cDNA was also expressed in E. coli, and the recombinant protein compared with the structure and assembly properties of full-length chicken lamin B2 (E. Heitlinger et al. (1991) J. Cell Biol. 113, 485-495) [3].

High impact information on LMNA

• However, examination of apoptosis in a cell-free system revealed a block in chromatin condensation and apoptotic body formation when nuclei from HeLa cells expressing lamin A or lamin A-transfected Jurkat cells were incubated in caspase-6-deficient apoptotic extracts [4].
• In two dimensional NEPHGE gel analysis of immunoprecipitated lamin A, no detectable change in the ratio of the acidic/basic isoelectric variants of lamin A was observed during myogenesis [5].
• Expression of nuclear lamin A and muscle-specific proteins in differentiating muscle cells in ovo and in vitro [5].
• Immunofluorescence staining of chicken embryonic muscle cells in culture also indicates an accumulation of lamin A before the induction of muscle-specific proteins expression [5].
• In situ immunoelectron microscopy carried out on mitotic cells also reveals membrane association of lamin B2, whereas the distribution of lamin A is random [6].

Biological context of LMNA

• Cell fractionation experiments combined with immunoblotting show that during mitosis both chicken lamins B1 and B2 remain associated with membranes, whereas lamin A exists in a soluble form [6].
• During embryonic development, lamin A became increasingly prominent, whereas the amounts of lamin B1 decreased in many tissues [7].
• Furthermore, the accumulation of lamin A reached a plateau before the muscle-specific proteins during muscle development [5].
• In prophase cells, lamin B1 is the major component of the nuclear lamina, a filamentous network underlying the nucleoplasmic side of the nuclear membrane, whereas lamin A/C is dissociated from the scaffold [8].
• Use of a general purpose mammalian expression vector for studying intracellular protein targeting: identification of critical residues in the nuclear lamin A/C nuclear localization signal [9].

Anatomical context of LMNA

• Our results demonstrate that the P19 cells, although normally devoid of lamin A, properly incorporate and process chicken lamin A. Moreover, the stably transfected cell lines maintain the properties of undifferentiated cells, demonstrating that expression of lamin A does not directly induce differentiation [2].
• However, whereas the lamin A precursor was stable, the translation product of the lamin B2 transcript was processed in the reticulocyte lysate to a polypeptide comigrating on two-dimensional gels with authentic mature lamin B2 [10].

Associations of LMNA with chemical compounds

• Using N-(acetyltyrosinylvalinyl-Nepsilon-biotinyllysyl) aspartic acid [(2,6-dimethylbenzoyl)oxy] methyl ketone, which derivatizes the active forms of caspases, we could show that one of five caspases active in the extracts is inhibited both by CrmA/SPI-2 and by a peptide spanning the lamin A apoptotic cleavage site [1].
• Conversely, when exposed to retinoic acid, an inducer of differentiation, lamin A-expressing P19 cells are able to differentiate normally [2].
• We also report that, contrary to the predictions of previously published work, substitution of a critical residue in the nuclear lamin A/C nuclear localization signal (the equivalent of lysine 128 in the SV40 large T nuclear localization signal) retains nuclear localization, and discuss how amino acid context might affect targeting to the nucleus [9].

Analytical, diagnostic and therapeutic context of LMNA

• First, peptide mapping experiments and immunological criteria demonstrate that these two proteins are not related to each other or to lamin A via postsynthetic modifications or precursor-product relationships [11].
• Furthermore, we show that in vitro translation of transcripts derived from lamin A and lamin B2 cDNAs yielded polypeptides that were indistinguishable, by two-dimensional gel electrophoresis, from the putative in vivo precursors of lamins A and B2 respectively [10].

References