Although bystin has been identified as a protein potentially involved in embryo implantation (a process unique to mammals) in humans, the bystin gene is evolutionarily conserved from yeast to humans. DNA microarray data indicates that bystin is overexpressed in human cancers, suggesting that it promotes cell growth. We undertook RT (reverse transcription)–PCR and immunoblotting, and confirmed that bystin mRNA and protein respectively are expressed in human cancer cell lines, including HeLa. Subcellular fractionation identified bystin protein as nuclear and cytoplasmic, and immunofluorescence showed that nuclear bystin localizes mainly in the nucleolus. Sucrose gradient ultracentrifugation of total cytoplasmic ribosomes revealed preferential association of bystin with the 40S subunit fractions. To analyse its function, bystin expression in cells was suppressed by RNAi (RNA interference). Pulse–chase analysis of ribosomal RNA processing suggested that bystin knockdown delays processing of 18S ribosomal RNA, a component of the 40S subunit. Furthermore, this knockdown significantly inhibited cell proliferation. Our findings suggest that bystin may promote cell proliferation by facilitating ribosome biogenesis, specifically in the production of the 40S subunit. Localization of bystin to the nucleolus, the site of ribosome biogenesis, was blocked by low concentrations of actinomycin D, a reagent that causes nucleolar stress. When bystin was transiently overexpressed in HeLa cells subjected to nucleolar stress, nuclear bystin was included in particles different from the nuclear stress granules induced by heat shock. In contrast, cytoplasmic bystin was barely affected by nucleolar stress. These results suggest that, while bystin may play multiple roles in mammalian cells, a conserved function is to facilitate ribosome biogenesis required for cell growth.
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June 2007
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Research Article|
May 29 2007
Bystin in human cancer cells: intracellular localization and function in ribosome biogenesis
Masaya Miyoshi
;
Masaya Miyoshi
*Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
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Tetsuya Okajima
;
Tetsuya Okajima
*Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
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Tsukasa Matsuda
;
Tsukasa Matsuda
*Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
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Michiko N. Fukuda
;
Michiko N. Fukuda
†Burnham Institute for Medical Research, North Torrey Pines Road, La Jolla, CA 92037, U.S.A.
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Daita Nadano
Daita Nadano
1
*Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
1To whom correspondence should be addressed (email nadano@agr.nagoya-u.ac.jp).
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Biochem J (2007) 404 (3): 373–381.
Article history
Received:
October 23 2006
Revision Received:
February 15 2007
Accepted:
March 23 2007
Accepted Manuscript online:
March 23 2007
Citation
Masaya Miyoshi, Tetsuya Okajima, Tsukasa Matsuda, Michiko N. Fukuda, Daita Nadano; Bystin in human cancer cells: intracellular localization and function in ribosome biogenesis. Biochem J 15 June 2007; 404 (3): 373–381. doi: https://doi.org/10.1042/BJ20061597
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