Intact LKB1 activity is required for survival of dormant ovarian cancer spheroids.

Teresa Peart,Akira Sugimoto,Yudith Ramos Valdes,Elena Fazio,Rohann J M Correa,Trevor G Shepherd,Michel Préfontaine,Monique Bertrand,Gabriel E Dimattia,Jacob Mcgee

doi:10.18632/oncotarget.4211

Abstract

Metastatic epithelial ovarian cancer (EOC) cells can form multicellular spheroids while in suspension and disperse directly throughout the peritoneum to seed secondary lesions. There is growing evidence that EOC spheroids are key mediators of metastasis, and they use specific intracellular signalling pathways to control cancer cell growth and metabolism for increased survival. Our laboratory discovered that AKT signalling is reduced during spheroid formation leading to cellular quiescence and autophagy, and these may be defining features of tumour cell dormancy. To further define the phenotype of EOC spheroids, we have initiated studies of the Liver kinase B1 (LKB1)-5'-AMP-activated protein kinase (AMPK) pathway as a master controller of the metabolic stress response. We demonstrate that activity of AMPK and its upstream kinase LKB1 are increased in quiescent EOC spheroids as compared with proliferating adherent EOC cells. We also show elevated AMPK activity in spheroids isolated directly from patient ascites. Functional studies reveal that treatment with the AMP mimetic AICAR or allosteric AMPK activator A-769662 led to a cytostatic response in proliferative adherent ovarian cancer cells, but they fail to elicit an effect in spheroids. Targeted knockdown of STK11 by RNAi to reduce LKB1 expression led to reduced viability and increased sensitivity to carboplatin treatment in spheroids only, a phenomenon which was AMPK-independent. Thus, our results demonstrate a direct impact of altered LKB1-AMPK signalling function in EOC. In addition, this is the first evidence in cancer cells demonstrating a pro-survival function for LKB1, a kinase traditionally thought to act as a tumour suppressor.

Highlights

Ovarian cancer is the most lethal gynecologic malignancy in the developed world, and the overall survival for women diagnosed with late-stage disease has remained largely unchanged for more than 25 years [1, 2]
In order to examine the status of STK11 (LKB1) and PRKAA1 (AMPKα1) in serous ovarian tumours, we analyzed the gene copy number and reverse phase protein array (RPPA) data available from The Cancer Genome Atlas (TCGA) datasets using cBioPortal [31, 32]
Despite single allele loss of STK11, Liver kinase B1 (LKB1) protein expression is maintained in metastatic ovarian cancer cells and may serve an important function in late-stage disease

Summary

Introduction

Ovarian cancer is the most lethal gynecologic malignancy in the developed world, and the overall survival for women diagnosed with late-stage disease has remained largely unchanged for more than 25 years [1, 2]. Intraperitoneal implants identified in these patients with advanced-stage disease are the result of single cells and multicellular aggregates, or spheroids, that adhere to the mesothelial lining of various abdominal organs to establish secondary lesions [4,5,6]. This is often accompanied by accumulation of ascites fluid within the peritoneal cavity, where cells in suspension are exposed www.impactjournals.com/oncotarget to a unique set of microenvironmental cues, allowing this population of cells to form secondary metastases [7]. Ovarian cancer cells that are able to resist anoikis, and survive within peritoneal or ascitic fluid, have likely adapted key survival pathways to meet the nutrient and energy demands of this particular microenvironment

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Conclusion