2006 Fiscal Year Final Research Report Summary
Elucidation of the mechanisms of okadaic acid-induced apoptosis and cleavage of nucleolar proteins in osteoblasts
| Project/Area Number |
17591915
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Morphological basic dentistry
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| Research Institution | The University of Tokushima |
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Principal Investigator |
HANEJI Tatsuji Institute of Health Bioscience, Professor, 大学院ヘルスバイオサイエンス研究部, 教授 (50156379)
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| Co-Investigator(Kenkyū-buntansha) |
MORIMOTO Hiroyuki University of Occupational and environmental Health, School of Medicine, Associate professor, 医学部, 助教授 (30335806)
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| Project Period (FY) |
2005 – 2006
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| Keywords | apoptosis / osteoblasts / nucleolar proteins / okadaic acid / calyculin A / nucleorin / protein phosphorylation / protein dephosphorylation |
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| Research Abstract |
Protein phosphorylation and dephosphorylation has been recognized as a key mechanism in cell function. Okadaic acid (OA) is a potent inhibitor of protein phosphatases and induces apoptosis in human osteoblasts. Nuclear factor-kappa B (NF-κB) is an essential transcription factor in the control of expression of genes involved in cell growth and differentiation. Treatment of human osteoblastic MG63 cells with OA enhanced the phosphorylation level of NF-κB on serine 536, as judged from the results of Western analysis and a k protein phosphatase dephosphorylation assay. OA stimulated the transcriptional activity of NF-κB in MG63 cells by a luciferase assay. These findings indicate that OA elicit phosphorylation of NF-κB on serine 536 in MG63 cells, resulting in the translocation of phospho-NF-κB to the nucleus, thereby promoting transcriptional activity of genes.
Nucleolin is an abundantly expressed nucleolar phosphoprotein and is located mainly in the nucleolus. The staining pattern of nucleolin in cultured cells is similar to that of protein phosphatase1δ. (PP1δ). Nucleolin was demonstrated to bind to PP1δ in nucleolus in human osteoblasts by using immunocytochemical and immunoprecipitation methods. AgNORs and nucleolin disappeared from the nuclei of the osteoblasts treated with OA. A major band, 110 kDa, was detected in the proteins obtained from osteoblastic cells. The level of the 110 kDa protein decreased in the apoptotic osteoblasts, whereas an additional band, 80 kDa, appeared and the level of this protein increased in the proteins prepared from OA-induced apoptotic osteoblasts. The present results indicate that PP18 directly binds to nucleolin in the nucleolus of osteoblasts and that nucleolin is cleaved during apoptosis in osteoblasts.
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