Toxicological Sciences 55, 97-106 (2000)
Copyright © 2000 by the Society of Toxicology
Immunotoxicology |
Low-Dose Whole-Body Irradiation (LD-WBI) Changes Protein Expression of Mouse Thymocytes: Effect of a LD-WBI-Enhanced Protein RIP10 on Cell Proliferation and Spontaneous or Radiation-Induced Thymocyte Apoptosis
,1
* Institute of Radiation Medicine, Norman Bethune University of Medical Sciences, Changchun, People's Republic of China; and
Department of Pathology, The University of Western Ontario, London, Ontario, Canada
Low-dose radiation (LDR) can potentiate cellular metabolic activities or immune functions in vivo (hormesis), and can render cells resistant to DNA or chromosome damage caused by subsequent high-dose radiation (adaptive response). Protein synthesis was required for these cellular responses to LDR. In the present study, the early expression of proteins by thymocytes in response to low-dose whole-body irradiation (LD-WBI) was investigated. The expression of novel and previously existing proteins was found in the nucleus, cytoplasm, and extracellular fluid of thymocytes at 4 hours after WBI with 75-mGy X-rays. A 10 kD protein (RIP10) was seen in the cytoplasm of thymocytes after LD-WBI was further investigated. The fraction containing RIP10 separated by Sephadex G 100 gel filtration potentiated spontaneous thymocyte, and mitogen-induced splenocyte proliferation. Western blotting demonstrated that an anti-RIP10 antibody could react with a 10-kD cytoplasm protein and also with a 13-kD nuclear protein in thymocytes at 4 h after LD-WBI. Immunocytochemical staining showed the existence of RIP10 in several immune tissues including thymus, spleen, and lymph node. RIP10 expression, as determined by immunocytochemical staining and flow cytometry, was enhanced at 4–8 h after LD-WBI. Cell-cycle arrest (G0/G1 block with decreased percentage of S-phase cells), and increased levels of spontaneous or radiation-induced apoptosis were observed in thymocytes incubated with RIP10 antibody in vitro for 4 h or 24 h. These results directly demonstrated the role of RIP10 in modulating cell proliferation and apoptosis. This finding is important to understand the mechanisms underlying LDR-induced hormesis and adaptive response.
Key Words: low-dose X-rays; whole-body irradiation; thymocytes; protein expression; RIP10.
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