Proteomic analysis of high NaCl-induced changes in abundance of nuclear proteins.

Mammalian cells are normally stressed by high interstitial NaCl in the renal medulla and by lesser elevation of NaCl in several other tissues. High NaCl damages proteins and DNA and can kill cells. Known protective responses include nuclear translocation of the transcription factor NFAT5 and other proteins. In order better to understand the extent and significance of changes in nuclear protein abundance, we extracted nuclear and cytoplasmic proteins separately from HEK293 cells and measured by LC-MS/MS (iTRAQ) changes of abundance of proteins in the extracts in response to high NaCl at three time points: 1 h, 8 h, and adapted for two passages. We confidently identified a total of 3,190 proteins; 163 proteins changed significantly at least at one time point in the nucleus. We discerned the biological significance of the changes by Gene Ontology and protein network analysis. Proteins that change in the nucleus include ones involved in protein folding and localization, microtubule-based process, regulation of cell death, cytoskeleton organization, DNA metabolic process, RNA processing, and cell cycle. Among striking changes in the nucleus, we found a decrease of all six 14-3-3 isoforms; dynamic changes of "cytoskeletal" proteins, suggestive of nucleoskeletal reorganization; rapid decrease of tubulins; and dynamic changes of heat shock proteins. Identification of these changes of nuclear protein abundance enhances our understanding of high NaCl-induced cellular stress, and provides leads to previously unknown damages and protective responses.