Underexpression of LKB1 tumor suppressor is associated with enhanced Wnt signaling and malignant characteristics of human intrahepatic cholangiocarcinoma.

Jinghan Wang,Bing Mu,Xiaoqing Jiang,Peiguo Chu,Baihe Zhang,Keqiang Zhang,Lu Yang,Jinhui Wang,Shuya Hu,Qi Liu,Yan Zhu,Zhenli Hu,Mengchao Wu,Chao Guo,Yun Yen,Xiwei Wu,Jie Li,Xiyong Liu,Qiang Cheng ,Li B ,Vincent H.s Chang ,Chun‐Hao Tsai ,Yang Yu ,D Lynne Smith

doi:10.18632/oncotarget.4305

Abstract

Intrahepatic cholangiocarcinoma (ICC) is a rare and highly aggressive malignancy. In this study, we identified the presence of gene deletion and missense mutation leading to inactivation or underexpression of liver kinase B1 (LKB1) tumor suppressor and excluded the involvement of LKB1 gene hypermethylation in ICC tissues. Immunohistochemical analysis showed that LKB1 was underexpressed in a portion of 326 ICC tissues compared to their adjacent normal tissues. By statistical analysis underexpression of LKB1 in ICC tissues significantly correlated with poor survival and malignant disease characteristics in ICC patients. Moreover, we showed that knockdown of LKB1 significantly enhanced growth, migration, and invasion of three LKB1-competent ICC cell lines. Global transcriptional profiling analysis identified multiple malignancy-promoting genes, such as HIF-1α, CD24, Talin1, Vinculin, Wnt5, and signaling pathways including Hedgehog, Wnt/β-catenin, and cell adhesion as novel targets of LKB1 underexpression in ICC cells. Furthermore, knockdown of LKB1 gene expression dramatically enhanced Wnt/β-catenin signaling in ICC cells, while an inverse correlation between LKB1 and nuclear β-catenin was observed in ICC tissues. Our findings suggest a novel mechanism for ICC carcinogenesis in which LKB1 underexpression enhances multiple signaling pathways including Wnt/β-catenin to promote disease progression.

Highlights

Intrahepatic cholangiocarcinoma (ICC) is the second most common hepatic malignancy and is highly aggressive [1, 2]
We have for the first time identified liver kinase B1 (LKB1) underexpression was inversely associated with malignancy and poor survival of ICC patients, and suggested a novel mechanism for ICC carcinogenesis in which LKB1 underexpression enhances multiple signaling pathways including Wnt/β-catenin to promote disease progression
We first found LKB1 gene deletions and missense mutations including the well-characterized loss-of-function mutation of c.C1062G, p.F354L in ICC tissue samples [24], albeit in low frequency. These genetic alterations lead to complete inactivation or haploinsufficiency of LKB1 tumor suppressor in ICC tissues

Summary

INTRODUCTION

Intrahepatic cholangiocarcinoma (ICC) is the second most common hepatic malignancy and is highly aggressive [1, 2]. Liver kinase B1 (LKB1) is a serine/threonine kinase ( named STK11) which plays essential roles in development and cell polarity [11] It was first recognized as a tumor suppressor gene from germ-line mutations that cause Peutz–Jeghers syndrome, which is characterized by gastrointestinal hamartoma with an increased risk of various cancers [12]. We investigated the cross-talk between the Wnt/β-catenin pathway, which in ICC is aberrantly activated in the absence of APC and E-Cad mutations [7, 8], and LKB1 dysregulation in ICC cells using LKB1 knockdown. We discovered an inverse correlation between LKB1 and nuclear β-catenin in our ICC cohort This suggests that LKB1 underexpression may partially enhance activation of the WNT/β-catenin pathway and contribute to the malignancy and progression of ICC

RESULTS

DISCUSSION

MATERIALS AND METHODS