Krüger Maximilian, Pabst Andreas Max, Al-Nawas Bilal, Horke Sven, Moergel Maximilian
Department of Oral and Maxillofacial Surgery, University Medical Center of the Johannes Gutenberg-University, Augustusplatz 2, 55131, Mainz, Germany,
J Cancer Res Clin Oncol. 2015 Oct;141(10):1757-66. doi: 10.1007/s00432-015-1941-2. Epub 2015 Feb 24.
Patients with oral squamous cell carcinomas (OSCC) often receive radiotherapy to preferentially induce apoptosis of cancer cells through generation of overwhelming DNA damage. This is amplified by generation of reactive oxygen species (ROS), thereby causing oxidative stress and cell death. However, tumors resist through different mechanisms, including upregulation of anti-apoptotic factors and enhanced ROS resistance. We recently reported that the antioxidative enzyme PON2 significantly enhances cellular stress resistance by attenuating mitochondrial ROS-mediated apoptosis. Further, PON2 is often upregulated in cancer. This prompted us to investigate its yet unknown role in the protection of OSCC against irradiation-induced cell death.
PON2 expression was determined after 7 Gy singular irradiation in four OSCC cell lines (PCI-13, PCI-52, SCC-4, SCC-68) accompanied by the detection of caspase 3/7 activity. A direct role of PON2 was tested by siRNA-mediated knockdown. In vivo PON2 expression was tested in five patients with oral carcinoma and compared with healthy mucosa for the evaluation of clinical significance.
PON2 is variably expressed in OSCC in vitro and in vivo. Compared with the other cell lines, SCC-4 cells showed twofold more basal PON2 (p ≤ 0.05) and the lowest caspase 3/7 activity after singular irradiation (p ≤ 0.05). Contrarily, irradiation led to 1.2-fold induction of PON2 in PCI-13 with no effect on SCC-4 (≤0.05), suggesting that PON2 levels reflect the cells' irradiation sensitivity. In agreement, PON2 knockdown resulted in significant higher apoptosis rates (p ≤ 0.05).
Our findings give first evidence that upregulation of PON2 may protect OSCC against irradiation-induced apoptosis.
口腔鳞状细胞癌（OSCC）患者常接受放疗，通过产生大量DNA损伤优先诱导癌细胞凋亡。这会因活性氧（ROS）的产生而放大，从而导致氧化应激和细胞死亡。然而，肿瘤会通过不同机制产生抗性，包括抗凋亡因子上调和ROS抗性增强。我们最近报道，抗氧化酶PON2通过减弱线粒体ROS介导的凋亡显著增强细胞应激抗性。此外，PON2在癌症中常上调。这促使我们研究其在保护OSCC免受辐射诱导的细胞死亡中尚未明确的作用。
在四个OSCC细胞系（PCI - 13、PCI - 52、SCC - 4、SCC - 68）中进行7 Gy单次照射后测定PON2表达，并检测半胱天冬酶3/7活性。通过siRNA介导的敲低测试PON2的直接作用。在五名口腔癌患者中测试体内PON2表达，并与健康黏膜进行比较以评估临床意义。
PON2在体外和体内的OSCC中表达各异。与其他细胞系相比，SCC - 4细胞的基础PON2水平高出两倍（p≤0.05），单次照射后半胱天冬酶3/7活性最低（p≤0.05）。相反，照射导致PCI - 13中PON2诱导1.2倍，而对SCC - 4无影响（≤0.05），表明PON2水平反映细胞的辐射敏感性。一致的是，PON2敲低导致凋亡率显著升高（p≤0.05）。
我们的研究结果首次证明PON2上调可能保护OSCC免受辐射诱导的凋亡。
