6794

STK11

We showed that the PEA3 transcriptional factor interacted with LKB1, a serine/threonine kinase, which is somatically mutated in lung cancer. This interaction occurred through the ETS domain of PEA3 and the kinase domain of LKB1. mutation of LKB1 in lung cancer cells stabilized PEA3. Reintroduction of wild-type (WT) LKB1 into cells induced down-regulation of PEA3 and subsequently resulted in reduced cyclooxygenase-2 RNA and protein expression, whereas germ-line and somatic LKB1 mutants were defective in this activity. LKB1 phosphorylated PEA3 and promoted its degradation through a proteasome-mediated mechanism. Cells expressing mutant LKB1 possessed greater invasive potential compared with cells expressing WT LKB1. Increased invasion of cells with mutant LKB1 was partly due to PEA3 expression, as RNA interference inhibition of PEA3 resulted in dramatic decrease of Matrigel invasion. However, forced expression of PEA3 resulted in down-regulation of epithelial markers and induction of mesenchymal markers. These results suggest that PEA3 stabilization due to LKB1 inactivation could lead to epithelial/mesenchymal transition and greater lung cancer invasion potential.

epithelial-mesenchymal transition (EMT) is a critical phenotypic alteration of cancer cells that triggers invasion and metastasis. Lung cancer cells often show mesenchymal phenotypes; however, a causative genetic alteration for the induction of EMT in lung cancer cells remains unknown. Recent studies have shown that the LKB1 gene is mutated in up to one-third of lung adenocarcinomas. Therefore, to pursue the possible involvement of LKB1 inactivation in the induction of EMT in lung carcinogenesis, we generated immortalized lung epithelial cells and lung adenocarcinoma cells with stable or transient LKB1 knockdown. LKB1 knockdown increased cell motility and invasiveness, and induced the expression of several mesenchymal marker proteins accompanied by the expression of ZEB1, a transcriptional repressor for E-cadherin and an EMT inducer. In agreement with the recent findings, expression of miR-200a/c was inversely correlated with that of ZEB1 in LKB1 knockdown clones with mesenchymal phenotype. Furthermore, transient knockdown of LKB1 induced ZEB1 mRNA and increased cell motility, and this motility was suppressed by ZEB1 repression. These results strongly indicate that LKB1 inactivation triggers EMT in lung cancer cells through the induction of ZEB1.CI - Copyright (c) 2010 Elsevier Ireland Ltd. All rights reserved.

Recent studies indicate that a high level of nesfatin-1/Nucleobindin-2 (NUCB-2) is associated with poor outcome and promotes cell migration in breast cancer and prostate cancer. However, the role of NUCB2 is not well known in colon cancer. In this study, NUCB-2 level in colon cancer tissue was higher than that in non-tumor tissue. Suppression of NUCB-2 in a colon cancer cell line SW620 inhibited migration and invasion. The microarray analysis showed that low expression level of transcription factor ZEB1 in NUCB-2 knockdowned SW620 cells. In addition, expression level of epithelial-mesenchymal transition (EMT)-related molecules including N-cadherin, E-cadherin, beta-catenin, Slug and Twist was affected by NUCB-2 suppression and ZEB1-denepdent pathway. The signaling pathway liver kinase B1(LKB1)/AMP-dependent protein kinase (AMPK)/target of rapamycin complex (TORC) 1 was involved in regulation of NUCB-2-mediated metastasis and EMT properties. Suppression of NUCB-2 inhibited tumor nodules formation in a murine colon tumor model as well. In summary, nesfatin-1/NUCB-2 enhanced migration, invasion and EMT in colon cancer cells through LKB1/AMPK/TORC1/ZEB1 pathways in vitro and in vivo.

During intravasation, circulating tumor cells (CTCs) detach from the epithelium of origin and begin the epithelial-to-mesenchymal transition (EMT) process, where they lose epithelial features and pass through the endothelium to enter circulation. Although detachment from the extracellular matrix is a strong source of metabolic stress, which induces anoikis, CTCs can survive. Recently, the tumor suppressor liver kinase B1 (LKB1) has gained attention for its role as a proto-oncogene in restoring the correct ATP/AMP ratio during metabolic stress. The aim of this study was to assess LKB1 expression in epithelial-negative CTCs isolated from patients with metastatic breast cancer and to characterize its possible association with EMT and stemness features. Transcriptome analysis of EpCAM-negative CTCs indicated that over 25% of patients showed enhanced LKB1 levels, while almost 20% of patients showed enhanced levels of an EMT transcription factor known as ZEB1. Transcriptome and immunofluorescence analyses showed that patients with enhanced LKB1 were correspondingly ZEB1 negative, suggesting complementary activity for the two proteins. Only ZEB1 was significantly associated with cancer stem cell (CSC) markers. Neither LKB1 nor ZEB1 upregulation showed a correlation with clinical outcome, while enhanced levels of stemness-associated CD44 correlated with a lower progression-free and overall survival. Ex vivo models showed that MDA-MB-231, a mesenchymal tumor cell line, grew in suspension only if LKB1 was upregulated, but the MCF-7 epithelial cell line lost its ability to generate spheroids and colonies when LKB1 was inhibited, supporting the idea that LKB1 might be necessary for CTCs to overcome the absence of the extracellular matrix during the early phases of intravasation. If these preliminary results are confirmed, LKB1 will become a novel therapeutic target for eradicating metastasis-initiating CTCs from patients with primary breast cancer.CI - (c) 2017 The Authors. Published by FEBS Press and John Wiley & Sons Ltd.

The AKT/PI3K/mTOR pathway is frequently altered in a range of human tumours, including bladder cancer. Here we report the phenotype of mice characterised by deletion of two key players in mTOR regulation, Pten and Lkb1, in a range of tissues including the mouse urothelium. Despite widespread recombination within the range of epithelial tissues, the primary phenotype we observe is the rapid onset of bladder tumorigenesis, with median onset of approximately 100 days. Single deletion of either Pten or Lkb1 had no effect on bladder cell proliferation or tumour formation. However, simultaneous deletion of Lkb1 and Pten led to an upregulation of the mTOR pathway and the hypoxia marker GLUT1, increased bladder epithelial cell proliferation and ultimately tumorigenesis. Bladder tissue also exhibited characteristic features of epithelial-mesenchymal transition, with loss of the epithelial markers E-cadherin and the tight junction protein ZO-1, and increases in the mesenchymal marker vimentin as well as nuclear localization of epithelial-mesenchymal transition (EMT) regulator Snail. We show that these effects were all dependent upon mTOR activity, as rapamycin treatment blocked both EMT and tumorigenesis. Our data therefore establish clear synergy between Lkb1 and Pten in controlling the mTOR pathway within bladder epithelium, and show that loss of this control leads to the disturbance of epithelial structure, EMT and ultimately tumorigenesis.