Phospholipase D1-regulated autophagy supplies free fatty acids to counter nutrient stress in cancer cells.

Ming Cai,Li Wei Rachel Tay,Guobin Wang,Jian Xiong,Michael Zhu,Jingshu Wang,Feng Li,Yoshiko Banno,Jingquan He,Colin Rog,Ziqing Wang,Yizhao Xie,Guangwei Du

doi:10.1038/cddis.2016.355

Abstract

Cancer cells utilize flexible metabolic programs to maintain viability and proliferation under stress conditions including nutrient deprivation. Here we report that phospholipase D1 (PLD1) participates in the regulation of metabolic plasticity in cancer cells. PLD1 activity is required for cancer cell survival during prolonged glucose deprivation. Blocking PLD1 sensitizes cancer cells to glycolysis inhibition by 2-deoxy-D-glucose (2-DG) and results in decreased autophagic flux, enlarged lysosomes, and increased lysosomal pH. Mechanistically, PLD1-regulated autophagy hydrolyzes bulk membrane phospholipids to supply fatty acids (FAs) for oxidation in mitochondria. In low glucose cultures, the blockade of fatty acid oxidation (FAO) by PLD1 inhibition suppresses adenosine triphosphate (ATP) production and increases reactive oxygen species (ROS), leading to cancer cell death. In summary, our findings reveal a novel role of PLD1 in sustaining cancer cell survival during metabolic stress, and suggest PLD1 as a potential target for anticancer metabolism therapy.

Highlights

We report that the activity of phospholipase D1 (PLD1) is required for metabolic reprogramming of cancer cells enduring prolonged glucose deprivation
PLD1 is required for cancer cell survival during prolonged glucose deprivation
PLD1i caused some moderate reduction in viable MCF-7 and RCC4 cells in high glucose (Supplementary Figure S2), it robustly inhibited the growth of all three cell types starting from day 3 in low glucose (Figure 1d)

Summary

Introduction

One hallmark of cancer cells is increased aerobic glycolysis, widely known as the Warburg effect, that maintains cell growth and proliferation through the generation of adenosine triphosphate (ATP) and precursors for macromolecular synthesis.[1,2] the Warburg effect empowers cells to proliferate rapidly when glucose is abundant, a flexible and alternative metabolic program must be available for cancer cells to respond readily to conditions leading to metabolic stresses, for example, rapid tumor growth and exposure to therapy.[2,3] This metabolic plasticity explains why, in theory, therapies aimed at inhibiting glucose utilization in ‘glucose-addicted’ cancer cells should be efficacious at eliminating tumors, but in practice, cancer cells often resist to approaches that target glycolysis alone.[2,3] One major mechanism by which cancer cells adapt to nutrient scarcity is to shift their dependence on glycolysis to mitochondrial fatty acid oxidation (FAO) that serves to sustain ATP levels and counter oxidative stress.[4,5,6] The biochemical basis for this metabolic reprogramming under metabolic stress is largely known.[4,5] how fatty acids (FAs) are generated, mobilized, and transferred into mitochondria for subsequent utilization remains unclear. It is generally accepted that autophagy suppresses tumor initiation at the early stages of cancer but promotes tumor growth by providing a source of nutrients during rapid tumor growth.[7,8] in many tumor cells, autophagy activation is required for proliferation and survival, as well as the development of resistance to the treatment.[7,8] inhibiting autophagy may be beneficial for cancer therapy. We report that the activity of phospholipase D1 (PLD1) is required for metabolic reprogramming of cancer cells enduring prolonged glucose deprivation. PLD1 inhibition blocks autophagic flux and free FA production from bulk membrane phospholipids that in turn limits FAO in mitochondria. This results in a decrease in cytosolic ATP level and an increase in mitochondrial reactive oxygen species (ROS) production, promoting cancer cell death during glucose deprivation

Methods

Results

Conclusion