LKB1轉錄層次缺失促進結直腸癌腫瘤惡化和較差之臨床預後

LKB1 Loss at transcriptional level Promotes Tumor Malignancy and Poor Patient Outcomes in Colorectal Cancer

何宗殷(Tsung-Ying He)

指導教授 ： 李輝 ； 周明智

中山醫學大學/醫學院/醫學研究所/博士(2016年)

摘要

LKB1 會調控細胞代謝, 細胞分裂和細胞增生，做為抑癌基因的角色抑制腫瘤的生長與侵襲。 過去的研究指出LKB1 基因突變會導致 Peutz-Jeghers 症候群以及促進腫瘤之發展。LKB1基因突變、染色體異質和啟動子甲基化是主要造成 LKB1 缺失的分子機制, 但LKB1由以上三種機制引起缺失，很少發生在結腸直腸癌。因此本研究假設LKB1轉錄層次缺失是否與結腸直腸癌腫瘤惡化和患者有較差之臨床預後有關。本研究以兩株p53野生型（HCT116和LoVo）和兩株p53突變型 (SW480和HT29）的結腸癌細胞，探討LKB1缺失是否會經由NKX2-1媒介的p53路徑失常所致。本研究使用免疫組織化學染色法分析 LKB1 和NKX2-1 在結腸癌細胞之表現。採用Kaplan-Meier和Cox回歸統計模式評估LKB1 和NKX2-1的表現是否與患者overall survival (OS)和relapse free survival (RFS)之臨床預後有關? 由於NKX2-1媒介的p53途徑的失常，會造成LKB1在轉錄層次之缺失，促進結腸癌細胞之侵襲能力。LKB1轉錄層次缺失引起的癌細胞侵襲能力幾乎可以完全被 mTOR抑製劑 （Rapamycin 和 Everolimus）和mTOR /AKT雙重抑製劑Palomid529（P529）所抑制。發現腫瘤組織有較低 LKB1 mRNA表現的結直腸患者相較於LKB1 mRNA表現較高者，有較差的OS和RFS。若將患者以p53基因突變與否，分為p53野生型和突變型兩類。在p53野生型，LKB1 mRNA表現較低，同時又NKX2-1表現較低之患者，在p53突變型，LKB1 mrNA表現較低，但NKX2-1表現較高之患者，在OS和RFS上都有較高之風險比值 (hazard ratio)。 因此經由NKX2-1/p53 axis引起LKB1在轉錄層次之缺失，會促進腫瘤細胞之侵襲能力，以致結直腸患者有較差之臨床預後。

關鍵字

LKB1 ； NKX2-1 ； 結直腸癌

並列摘要

LKB1 loss by gene mutation, loss of heterozygosity, and promoter methylation was rarely occurred in colorectal cancer. The intracellular LKB1 kinase is implicated in regulating polarity, metabolism, cell differentiation, and proliferation – all functions potentially contributing to tumor suppression. Germ-line mutations at LKB1 result in the Peutz-Jeghers syndrome and an increased risk of cancer found in previous studies. LKB1 gene was also found to be mutated in lung cancer of sporadic origin, predominantly adenocarcinomas. We asked whether LKB1 loss could be deregulated at transcriptional level to promote tumor progression and poor outcome in colorectal cancer. Mechanistic studies were performed in two each of p53 wild-type (HCT116, LoVo) and p53 mutated (SW480, HT29) colon cancer cells to explore whether LKB1 loss could be deregulated by NKX2-1-mediated p53 pathway. LKB1 and NKX2-1 expressions in colorectal tumors were determined by immunohistochemistry and the prognostic value of both molecules was assessed using Kaplan-Meier and Cox-regression model. Mechanistically, LKB1 loss at transcriptional level due to alteration of the NKX2-1-mediated p53 pathway promotes invasiveness in colon cancer cells. The cancer cell invasiveness induced by LKB1 loss was nearly suppressed by mTOR inhibitor (Rapamycin and Everolimus) and mTOR/AKT dual inhibitor Palomid 529 (P529). Among patients, low LKB1 tumors exhibited shorter overall survival (OS) and relapse free survival (RFS) periods than high LKB1 tumors. The highest hazard ratio (HR) value for OS and RFS was observed in p53 wild-type patients with low LKB1/low NKX2-1 tumors and in p53 mutated patients with low LKB1/high NKX2-1 tumors when p53 wild-type patients with high LKB1/high NKX2-1 and p53 mutated patients with high LKB1/low NKX2-1 tumors were as references. In conclusion, LKB1 loss at transcriptional level via alteration of the NKX2-1/p53 axis promotes cancer cell invasion and consequently resulting in poor outcome in colorectal cancer patients.

並列關鍵字

LKB1 ； NKX2-1 ； colorectal cancer

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