Activation of apoptosis in NAF-1-deficient human epithelial breast cancer cells.

Sarah H Holt,Luhua Song,Merav Darash-Yahana,Ioav Z Cabantchik,Rachel Nechushtai,Yuting Luo,Ron Mittler,Mark L Paddock,Dorit Michaeli,Ola Karmi,Eli Pikarsky,Rajeev K Azad,Patricia A Jennings,Yang Sung Sohn,Sagi Tamir,José N Onuchic

doi:10.1242/jcs.178293

Abstract

ABSTRACTMaintaining iron (Fe) ion and reactive oxygen species homeostasis is essential for cellular function, mitochondrial integrity and the regulation of cell death pathways, and is recognized as a key process underlying the molecular basis of aging and various diseases, such as diabetes, neurodegenerative diseases and cancer. Nutrient-deprivation autophagy factor 1 (NAF-1; also known as CISD2) belongs to a newly discovered class of Fe-sulfur proteins that are localized to the outer mitochondrial membrane and the endoplasmic reticulum. It has been implicated in regulating homeostasis of Fe ions, as well as the activation of autophagy through interaction with BCL-2. Here we show that small hairpin (sh)RNA-mediated suppression of NAF-1 results in the activation of apoptosis in epithelial breast cancer cells and xenograft tumors. Suppression of NAF-1 resulted in increased uptake of Fe ions into cells, a metabolic shift that rendered cells more susceptible to a glycolysis inhibitor, and the activation of cellular stress pathways that are associated with HIF1α. Our studies suggest that NAF-1 is a major player in the metabolic regulation of breast cancer cells through its effects on cellular Fe ion distribution, mitochondrial metabolism and the induction of apoptosis.

Highlights

Iron (Fe) ions are essential for many cellular processes, including energy metabolism, DNA synthesis and cell cycle progression (Crichton, 2009)
Suppression of Nutrient-deprivation autophagy factor 1 (NAF-1) in MDA-MB-231 and MCF-7 cells resulted in increased uptake of Fe ions into cells and mitochondria, as well as enhanced mitochondrial reactive oxygen species (ROS) production To explore the potential of NAF-1 to affect Fe ion and ROS metabolism in cancer cells (Tamir et al, 2015), we examined the level of expression of transferrin receptors and the site of ROS accumulation in breast cancer cells with suppressed NAF-1 expression
We show that NAF-1 deficiency results in an increased expression of transferrin receptor protein (TfR) at the plasma membrane, an increased uptake of transferrin-bound Fe into cells and an increased production of ROS in the mitochondria (Figs 3, 4; Figs S1, S2)

Summary

Introduction

Iron (Fe) ions (which can exist in multiple oxidations states, most commonly Fe2+ and Fe3+) are essential for many cellular processes, including energy metabolism, DNA synthesis and cell cycle progression (Crichton, 2009). An important physiological contribution of Fe ions is associated with the formation of ironsulfur (Fe-S) clusters (Lill, 2009), a process that takes place initially and predominantly in mitochondria but comprises obligatory. The binding of NAF-1 to BCL-2 has been mapped in a recent study (Tamir et al, 2014), the potential of NAF1 to activate apoptosis is unclear

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