Research Paper Volume 10, Issue 12 pp 4000—4023

The ER-alpha mutation Y537S confers Tamoxifen-resistance via enhanced mitochondrial metabolism, glycolysis and Rho-GDI/PTEN signaling: Implicating TIGAR in somatic resistance to endocrine therapy

Marco Fiorillo 1, 2, , Rosa Sanchez-Alvarez 3, , Federica Sotgia 1, , Michael P. Lisanti 1, ,

  • 1 Translational Medicine, School of Environment and Life Sciences, Biomedical Research Centre (BRC), University of Salford, Greater Manchester M5 4WT, United Kingdom
  • 2 The Department of Pharmacy, Health and Nutritional Sciences, The University of Calabria, Cosenza, Italy
  • 3 University of Manchester, The Paterson Institute, Manchester M1 39PL, United Kingdom

received: November 23, 2018 ; accepted: November 29, 2018 ; published: December 20, 2018 ;
How to Cite

Copyright: Fiorillo et al. This is an open‐access article distributed under the terms of the Creative Commons Attribution License (CC BY 3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Naturally-occurring somatic mutations in the estrogen receptor gene (ESR1) have been previously implicated in the clinical development of resistance to hormonal therapies, such as Tamoxifen. For example, the somatic mutation Y537S has been specifically associated with acquired endocrine resistance. Briefly, we recombinantly-transduced MCF7 cells with a lentiviral vector encoding ESR1 (Y537S). As a first step, we confirmed that MCF7-Y537S cells are indeed functionally resistant to Tamoxifen, as compared with vector alone controls. Importantly, further phenotypic characterization of Y537S cells revealed that they show increased resistance to Tamoxifen-induced apoptosis, allowing them to form mammospheres with higher efficiency, in the presence of Tamoxifen. Similarly, Y537S cells had elevated basal levels of ALDH activity, a marker of “stemness”, which was also Tamoxifen-resistant. Metabolic flux analysis of Y537S cells revealed a hyper-metabolic phenotype, with significantly increased mitochondrial respiration and high ATP production, as well as enhanced aerobic glycolysis. Finally, to understand which molecular signaling pathways that may be hyper-activated in Y537S cells, we performed unbiased label-free proteomics analysis. Our results indicate that TIGAR over-expression and the Rho-GDI/PTEN signaling pathway appear to be selectively activated by the Y537S mutation. Remarkably, this profile is nearly identical in MCF7-TAMR cells; these cells were independently-generated in vitro, suggesting a highly conserved mechanism underlying Tamoxifen-resistance. Importantly, we show that the Y537S mutation is specifically associated with the over-expression of a number of protein markers of poor clinical outcome (COL6A3, ERBB2, STAT3, AFP, TFF1, CDK4 and CD44). In summary, we have uncovered a novel metabolic mechanism leading to endocrine resistance, which may have important clinical implications for improving patient outcomes.


ESR1: estrogen receptor alpha or estrogen receptor 1; TAMR: tamoxifen resistance cell line; 4-OHT: 4-hydroxytamoxifen; ATP: adenosine triphosphate; WT: wild type; EV: empty vector; Y537S: estrogen receptor point mutation (tyrosine to serine); Y537N: estrogen receptor point mutation (tyrosine to asparagine); ERBB2: Erb-B2 receptor tyrosine kinase 2 (HER 2); CSC: cancer stem cell; OCR: oxygen consumption rate; ECAR: extracellular acidification rate; OXPHOS: oxidative phosphorylation.