MiR-449a增加肺腺癌細胞對輻射線之感受性

Abstract

肺癌是所有癌症中死亡率最高的一種。輻射線常用於治療肺癌，但輻射治療常因病人體內癌細胞具有輻射線抗性而失敗，或成效不彰。因此，癌細胞調控輻射線抗性的分子機制是目前備受關注的研究議題。微小RNA (MicroRNA)已被報導具有調控輻射線感受性的能力，故其可能是一個可以改善輻射治療成效的因素。 兩株肺腺癌細胞，CL1-0及CL1-5，在過去研究中已知它們的轉移、侵襲能力有所不同；而在這份研究中，我們另外發現了這兩株細胞對輻射線的感受性亦不相同。暴露在同樣劑量的輻射線之下，CL1-0細胞的存活率高於CL1-5細胞；輻射線所導致之凋亡的細胞比例在CL1-5細胞多於CL1-0細胞；另外CL1-5細胞經過輻射處理，細胞週期將會停滯在G2/M期。為了了解這些輻射感受性差異是緣於何種調控機制，我們將這兩株細胞以10 Gy劑量輻射處理後，分別在處理之後的0、1、4、24小時收下細胞，並以這些細胞進行microRNA microarray實驗。透過這樣的篩選，其中25個microRNA的表現量因輻射處理而有顯著的變化。miR-449a是在CL1-0細胞經輻射處理後的24小時顯著被抑制的一個microRNA，因此，我們在CL1-0細胞中大量表現miR-449a，並以此細胞進行輻射處理。可發現miR-449a的存在使CL1-0細胞在輻射暴露下DNA損壞程度大增、凋亡的比例升高、並且改變了細胞週期分佈的型態，最終使得CL1-0細胞對輻射更為敏感。 總結以上所述，這份研究說明了在輻射處理之下，miR-449a可以透過增加凋亡比例，導致細胞週期停滯於G2/M期，並且降低細胞輻射後存活率以增進細胞對輻射處理之感受性。故miR-449a可能是一個可應用於臨床的輻射調控因子。

Lung cancer is the leading cause of cancer-related mortality worldwide. Radiotherapy is often applied for treating lung cancer. One of the main causes of radiotherapy failure is the relative susceptibility of cells in response to radiotherapy. Hence, understanding of the molecular mechanisms modulating radio-sensitivity has received much attention. MicroRNAs have been reported to modulate the radio-sensitivity and have the potential to improve the efficacy of radiotherapy. Here, we found that two lung adenocarcinoma cell lines (CL1-0 and CL1-5) with different metastatic ability displayed different radio-sensitivity. The cell viability and clonogenic survival of CL1-0 were higher than that of CL1-5 after radiation treatment. Irradiation induced more cell death in CL1-5 than in CL1-0, and caused the G2/M arrest in CL1-5. In order to understand the regulatory machinery of different radiosensitivity in tumor cells with isogenic background, both CL1-0 and CL1-5 were treated with 10 Gy radiations, and were harvested respectively at 0, 1, 4, and 24 h after radiation exposure. The dynamics of genomic profiling of microRNA upon irradiation was examined using Illumina Human microRNA BeadChips. Twenty-five microRNAs were identified for the differential expression post irradiation in CL1-0 or CL1-5 cells. Among these microRNAs, miR-449a, which was down-regulated in CL1-0 cells at 24 h after irradiation, was chosen for further investigation. Over-expression of miR-449a in CL1-0 cells effectively increased irradiation-induced DNA damage and apoptosis, altered the cell cycle distribution and eventually led to sensitization of CL1-0 to irradiation. Taken together, this study showed miR-449a increased radio-sensitivity by enhancing apoptosis, inducing G2/M arrest, and suppressing cell viability. MiR-449a might be a novel radio-sensitizer for clinical application.