p53-dependent accelerated senescence induced by ionizing radiation in breast tumour cells
p53-dependent accelerated senescence induced by ionizing radiation in breast tumour cells
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DOI：
10.1080/09553000500168549
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发表时间：
2005-06-01
影响因子：
2.6
通讯作者：
Gewirtz, DA
中科院分区：
文献类型：
--
作者：
Jones, KR;Elmore, LW;Gewirtz, DA
据报道，电离辐射会促进正常细胞系和肿瘤细胞系加速或过早衰老。目前的研究旨在表征乳腺肿瘤细胞对辐射的加速衰老反应，包括其对功能性p53的依赖性及其与端粒酶活性、端粒长度、人端粒酶逆转录酶（hTERT，端粒酶催化亚基）和人端粒酶RNA（hTR，端粒酶RNA亚基）表达的关系，以及细胞遗传学畸变的诱导。在p53野生型MCF-7细胞、p53功能减弱的MCF-7/E6细胞、具有突变p53的MDA-MB231细胞和具有hTERT组成型表达的MCF-7/hTERT细胞中进行了研究。通过端粒重复扩增方案（TRAP 测定）测定端粒酶活性，通过末端限制性片段（TRF）测定测定端粒长度，通过逆转录酶聚合酶链式反应（RT-PCR）测定hTR和hTERT表达，通过β-半乳糖苷酶染色测定衰老，通过TdT介导的d-UTP-X缺口末端标记（TUNEL测定）测定细胞凋亡。暴露于 10 Gy 电离辐射后，MCF-7 乳腺肿瘤细胞中明显存在 β-半乳糖苷酶（细胞衰老标志物）的广泛表达。辐射不会抑制 hTERT 或 hTR 的表达，不会改变端粒酶活性或诱导端粒缩短。在受辐射的 MCF-7/hTERT 细胞中也观察到衰老停滞，由于端粒酶催化成分的异位表达，这些细胞的端粒延长。与 MCF-7 细胞相反，受辐射的 MDA-MB231 乳腺肿瘤细胞和 MCF-7/E6 细胞未能衰老，而是表现出延迟的细胞凋亡。辐射产生了染色体末端相关异常，包括 MCF-7 细胞、MCF-7/hTERT 细胞以及 MCF-7/E6 细胞中的端对端融合（端粒功能障碍的指标）。当细胞在辐射后维持在培养物中时，增殖恢复仅在衰老后明显，而通过凋亡响应辐射的细胞系的细胞数量继续下降。电离辐射引起的加速衰老是 p53 依赖性的，并与端粒功能障碍相关，但与端粒酶活性或端粒长度、hTERT 和 hTR 表达的变化无关。在缺乏功能性 p53 的情况下，细胞无法长时间停滞，导致细胞凋亡，而表达 p53 的细胞则加速衰老并随后通过增殖恢复来实现。
Ionizing radiation has been reported to promote accelerated or premature senescence in both normal and tumour cell lines. The current studies were designed to characterize the accelerated senescence response to radiation in the breast tumour cell in terms of its dependence on functional p53 and its relationship to telomerase activity, telomere lengths, expression of human telomerase reverse transcriptase (hTERT, the catalytic subunit of telomerase) and human telomerase RNA (hTR, the RNA subunit of telomerase), as well as the induction of cytogenetic aberrations. Studies were performed in p53 wild-type MCF-7 cells, MCF-7/E6 cells with attenuated p53 function, MDA-MB231 cells with mutant p53 and MCF-7/hTERT cells with constitutive expression of hTERT. Telomerase activity was measured by the telomeric repeat amplification protocol (TRAP assay), telomere lengths by the terminal restriction fragment (TRF) assay, hTR and hTERT expression by reverse transcriptase-polymerase chain reaction (RT-PCR), senescence by beta-galactosidase staining, and apoptosis by TdT-mediated d-UTP-X nick-end labelling (TUNEL assay). Widespread and extensive expression of beta-galactosidase, a marker of cellular senescence, was evident in MCF-7 breast tumour cells following exposure to 10 Gy of ionizing radiation. Radiation did not suppress expression of either hTERT or hTR, alter telomerase activity or induce telomere shortening. Senescence arrest was also observed in irradiated MCF-7/hTERT cells, which have elongated telomeres due to the ectopic expression of the catalytic component of telomerase. In contrast to MCF-7 cells, irradiated MDA-MB231 breast tumour cells and MCF-7/E6 cells failed to senesce and instead demonstrated a delayed apoptotic cell death. Irradiation produced chromosome end associated abnormalities, including end-to-end fusions (an indicator of telomere dysfunction) in MCF-7 cells, MCF-7/hTERT cells, as well as in MCF-7/E6 cells. When cells were maintained in culture following irradiation, proliferative recovery was evident exclusively after senescence while the cell lines which responded to radiation by apoptosis continued to decline in cell number. Accelerated senescence in response to ionizing radiation is p53 dependent and associated with telomer dysfunction but is unrelated to changes in telomerase activity or telomere lengths, expression of hTERT and hTR. In the absence of functional p53, cells are unable to arrest for an extended period, resulting in apoptotic cell death while accelerated senescence in cells expressing p53 is succeeded by proliferative recovery.