Abstract
BackgroundNucleolus is the most prominent mammalian organelle within the nucleus which is also the site for ribosomal biogenesis. There have been many reports indicating the involvement of nucleolus in the process of aging. Several proteins related to aging have been shown to localize in the nucleolus, which suggests the role of this organelle in senescence.ResultsIn this study, we used quantitative mass spectrometry to map the flux of proteins into and out of the nucleolus during the induction of senescence in cultured mammalian cells. Changes in the abundance of 344 nucleolar proteins in sodium butyrate-induced senescence in NIH3T3 cells were studied by SILAC (stable isotope labeling by amino acids in cell culture)-based mass spectrometry. Biochemically, we have validated the proteomic results and confirmed that B23 (nucleophosmin) protein was down-regulated, while poly (ADP-ribose) polymerase (PARP) and nuclear DNA helicase II (NDH II/DHX9/RHA) were up-regulated in the nucleolus upon treatment with sodium butyrate. Accumulation of chromatin in the nucleolus was also observed, by both proteomics and microscopy, in sodium butyrate-treated cells. Similar observations were found in other models of senescence, namely, in mitoxantrone- (MTX) treated cells and primary fibroblasts from the Lamin A knockout mice.ConclusionOur data indicate an extensive nuclear organization during senescence and suggest that the redistribution of B23 protein and chromatin can be used as an important marker for senescence.
Highlights
Nucleolus is the most prominent mammalian organelle within the nucleus which is the site for ribosomal biogenesis
Sodium butyrate induces senescence in NIH3T3 cells We used sodium butyrate treatment of NIH3T3 cells as a model system to study the effect of senescence on nucleolar proteome in mammalian cells [4]
Following treatment with 5 mM sodium butyrate for 4 days, NIH3T3 cells adopted a flattened morphology with spread-out cytoplasms, large nuclei and in many cases, the cells were multinucleated
Summary
Nucleolus is the most prominent mammalian organelle within the nucleus which is the site for ribosomal biogenesis. There have been many reports indicating the involvement of nucleolus in the process of aging. Several proteins related to aging have been shown to localize in the nucleolus, which suggests the role of this organelle in senescence. Cellular senescence is an irreversible growth-arrest programme that limits cell proliferation in an organism. This process may contribute to physiological aging, a complex phenomenon that involves the interplay of multiple genetic and environmental factors, resulting in the diminishing capacity of tissues to respond to stress and injury [1,2]. Some of the morphological and molecular events in senescence can be reproduced by the repeated passage of mammalian cells in tissue culture, possibly due to telomere deprotection. Senescence can be accelerated by subjecting cultured cells to chemical
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