Abstract TMEM-026: ZEB1–MEDIATED NNMT EXPRESSION ELICITS PHENOTYPIC AND METABOLIC PLASTICITY OF OVARIAN CANCER CELLS UNDER NUTRITIONAL STRESS
Authors: Kanska Justyna , Taylor-Harding Barbie , Aspuria Paul-Joseph , Karlan Beth Y. , Gayther Simon , Wiedemeyer W. Ruprecht 
Published: June 2017

Glucose is considered the primary energy source for all cells, and some cancers are addicted to glucose. However, poorly vascularized regions of advanced human cancers, such as high grade serous ovarian cancers (HGSC), may have limited glucose access and suffer from nutritional stress. Here, we investigated the functional consequences of chronic glucose deprivation in serous ovarian cancer cell lines (OVCAR3, OVCAR4 and OAW28).

Cells selected for resistance to glucose deprivation (glucose-independent sublines) demonstrated increased metabolic plasticity in utilization of additional energy sources compared to glucose-dependent precursor cells. Furthermore, some cells acquired mesenchymal gene expression and functional characteristics of EMT, such as increased migration efficiency; however classic EMT was not a prerequisite for glucose independence as majority of sublines retained their epithelial-like morphology. Instead, we identified the metabolic enzyme Nicotinamide N-methyltransferase (NNMT) to be commonly upregulated in all glucose-independent sublines. NNMT catalyzes methylation reactions that may alter histones and DNA methylation status. Also, NNMT expression is enriched in the mesenchymal subtype of HGSC and correlates with an invasive phenotype in vitro. We showed that NNMT overexpression in glucose-independent cells is mediated by genetic changes (genomic gain of NNMT), as well as transcriptional changes, such as induction of ZEB1. Ectopic expression of ZEB1 in ovarian cancer cell lines strongly induced NNMT, rendered cells more resistant to glucose deprivation and recapitulated many of the metabolic adaptations and mesenchymal gene expression observed in glucose-independent sublines. We further showed that ZEB1-driven glucose independence was mediated by NNMT because depletion of NNMT via shRNA or CRISPR/Cas9 reversed the metabolic plasticity of these cells and significantly impaired proliferation and de novo formation of glucose-independent colonies in the absence of glucose. In addition to its role in glucose independence, we found that NNMT was required for other ZEB1-induced phenotypes, such as increased migration.

Our analysis also showed that increased NNMT expression correlated with worse overall and progression-free survival in patients. In line with these results, our tissue microarray data demonstrated that NNMT protein levels were elevated in metastatic and recurrent tumors compared to matched primary carcinomas, while normal ovary and fallopian tube tissue had no detectable NNMT expression.

Our studies define a novel ZEB1/NNMT signaling axis, which elicits phenotypic and metabolic plasticity of ovarian cancer cells upon chronic glucose starvation. Understanding the causes of cancer cell plasticity is crucial for the development of therapeutic strategies to counter intratumoral heterogeneity, acquired drug resistance and recurrence in HGSC.

Citation Format: Justyna Kanska, Barbie Taylor-Harding, Paul-Joseph Aspuria, Beth Y. Karlan, Simon Gayther and W. Ruprecht Wiedemeyer. ZEB1–MEDIATED NNMT EXPRESSION ELICITS PHENOTYPIC AND METABOLIC PLASTICITY OF OVARIAN CANCER CELLS UNDER NUTRITIONAL STRESS [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr TMEM-026.