Nakajima Tetsuo, Yukawa Osami, Tsuji Hideo, Ohyama Harumi, Wang Bing, Tatsumi Kouichi, Hayata Isamu, Hama-Inaba Hiroko
Research Center for Radiation Safety, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan.
Mutat Res. 2006 Mar 20;595(1-2):29-36. doi: 10.1016/j.mrfmmm.2005.10.008.
Protein kinase Cdelta (PKCdelta) has an important role in radiation-induced apoptosis. The expression and function of PKCdelta in radiation-induced apoptosis were assessed in a radiation-sensitive mouse thymic lymphoma cell line, 3SBH5, and its radioresistant variant, XR223. Rottlerin, a PKCdelta-specific inhibitor, completely abolished radiation-induced apoptosis in 3SBH5. Radiation-induced PKCdelta activation correlated with the degradation of PKCdelta, indicating that PKCdelta activation through degradation is involved in radiation-induced apoptosis in radiosensitive 3SBH5. In radioresistant XR223, radiation-induced PKCdelta activation was lower than that in radiosensitive 3SBH5. Cytosol PKCdelta levels in 3SBH5 decreased markedly after irradiation, while those in XR223 did not. There was no apparent change after irradiation in the membrane fractions of either cell type. In addition, basal cytosol PKCdelta levels in XR223 were higher than those in 3SBH5. These results suggest that the radioresistance in XR223 to radiation-induced apoptosis is due to a difference in the regulation of radiation-induced PKCdelta activation compared to that of 3SBH5. On the other hand, Atm(-/-) mouse thymic lymphoma cells were more radioresistant to radiation-induced apoptosis than wild-type mouse thymic lymphoma cells. Irradiated wild-type cells, but not Atm(-/-) cells, had decreased PKCdelta levels, indicating that the Atm protein is involved in radiation-induced apoptosis through the induction of PKCdelta degradation. The decreased Atm protein levels induced by treatment with Atm small interfering RNA had no effect on radiation-induced apoptosis in 3SBH5 cells. These results suggest that the regulation of radiation-induced PKCdelta activation, which is distinct from the Atm-mediated cascade, determines radiation sensitivity in radiosensitive 3SBH5 cells.
蛋白激酶Cδ（PKCδ）在辐射诱导的细胞凋亡中起重要作用。在辐射敏感的小鼠胸腺淋巴瘤细胞系3SBH5及其辐射抗性变体XR223中评估了PKCδ在辐射诱导的细胞凋亡中的表达和功能。PKCδ特异性抑制剂罗特勒素完全消除了3SBH5中辐射诱导的细胞凋亡。辐射诱导的PKCδ激活与PKCδ的降解相关，表明通过降解激活PKCδ参与了辐射敏感的3SBH5中辐射诱导的细胞凋亡。在辐射抗性的XR223中，辐射诱导的PKCδ激活低于辐射敏感的3SBH5。照射后3SBH5中的胞质PKCδ水平显著降低，而XR223中的则没有。两种细胞类型的膜组分在照射后均无明显变化。此外，XR223中的基础胞质PKCδ水平高于3SBH5中的。这些结果表明，XR223对辐射诱导的细胞凋亡的抗性是由于与3SBH5相比，辐射诱导的PKCδ激活的调节存在差异。另一方面，Atm（-/-）小鼠胸腺淋巴瘤细胞对辐射诱导的细胞凋亡比野生型小鼠胸腺淋巴瘤细胞更具抗性。照射的野生型细胞而非Atm（-/-）细胞的PKCδ水平降低，表明Atm蛋白通过诱导PKCδ降解参与辐射诱导的细胞凋亡。用Atm小干扰RNA处理诱导的Atm蛋白水平降低对3SBH5细胞中辐射诱导的细胞凋亡没有影响。这些结果表明，与Atm介导的级联反应不同的辐射诱导的PKCδ激活的调节决定了辐射敏感的3SBH5细胞的辐射敏感性。
