Identification of Markers for Cellular S tr ess and Senescence in Laminopathic Cells by Pr oteomic Analysis

Lamins are components of the structural network in the nucleus and play a key role in nuclear or ganization and function. Mutations in the human lamin A gene cause a spectrum of genetic diseases that include muscular dystrophies, cardiomyopathy , lipodystrophy and premature ageing syndromes. Laminopathic cells display several abnormalities in nuclear morphology and function. We have carried out a comprehensive analysis of alterations in the protein profiles of HEK293T cells expressing a mutation in lamin A (Q294P) that causes Emery-Dreifuss muscular dystrophy , in comparison with cells expressing wild-type lamin A. Initially a total of 27 diferentially expressed proteins were identified by quantitative two-dimensional gel electrophoresis followed by mass spectral analysis. Importantly , a 5-fold decrease in lamin B1 levels in mutant cells was observed by quantitative two-dimensional gel electrophoresis, which was supported by immunofluorescence analysis. Changes in levels of specific heat shock proteins, hnRNPs, DNA damage response proteins, metabolic enzymes and cytoskeletal proteins were also observed. Further detailed analysis of cell lysates by one-dimensional gel electrophoresis followed by high throughput mass spectrometry revealed 650 unique proteins from wild-type cells and 1494 unique proteins from mutant cells (with two or more than two peptide hits). Alterations in a number of proteins that are involved in chromatin structure, chromosome condensation, nucleosome assembly , epigenetic modifications, centromere organization, telomere length and DNA repair were observed. These data suggest that laminopathic cells exhibit characteristics of cellular stress and senescence, and provide new insights into the cellular basis of pathologies caused by laminopathic mutations.