PHLPP regulates hexokinase 2-dependent glucose metabolism in colon cancer cells

Xiaopeng Xiong,Shigeki Miyamoto,Yang-An Wen,Mary C Oaks,Mihail I Mitov,Tianyan Gao

doi:10.1038/cddiscovery.2016.103

Abstract

Increased glucose metabolism is considered as one of the most important metabolic alterations adapted by cancer cells in order to generate energy as well as high levels of glycolytic intermediates to support rapid proliferation. PH domain leucine-rich repeat protein phosphatase (PHLPP) belongs to a novel family of Ser/Thr protein phosphatases that function as tumor suppressors in various types of human cancer. Here we determined the role of PHLPP in regulating glucose metabolism in colon cancer cells. Knockdown of PHLPP increased the rate of glucose consumption and lactate production, whereas overexpression of PHLPP had the opposite effect. Bioenergetic analysis using Seahorse Extracelluar Flux Analyzer revealed that silencing PHLPP expression induced a glycolytic shift in colon cancer cells. Mechanistically, we found that PHLPP formed a complex with Akt and hexokinase 2 (HK2) in the mitochondrial fraction of colon cancer cells and knockdown of PHLPP enhanced Akt-mediated phosphorylation and mitochondrial localization of HK2. Depletion of HK2 expression or treating cells with Akt and HK2 inhibitors reversed PHLPP loss-induced increase in glycolysis. Furthermore, PHLPP knockdown cells became addicted to glucose as a major energy source in that glucose starvation significantly decreased cancer cell survival. As HK2 is the key enzyme that determines the direction and magnitude of glucose flux, our study identified PHLPP as a novel regulator of glucose metabolism by controlling HK2 activity in colon cancer cells.

Highlights

Deregulation of cell proliferation in cancer often requires corresponding modifications in the cellular metabolism in order to fuel the increasing need for the biosynthesis of macromolecules including nucleotides, proteins and lipids.[1,2,3] Glucose is one of the major carbon sources for many types of cancers
We show that loss of PH domain leucine-rich repeat protein phosphatase (PHLPP) expression promotes glycolysis and mitochondrial respiration by upregulating Akt-dependent phosphorylation and mitochondrial translocation of hexokinase 2 (HK2)
Phosphorylation of HK2 at T473 site promotes mitochondrial binding of HK2, which facilitates the coupling of glycolysis and oxidative phosphorylation through preferential access of HK2 to ATP generated by mitochondria.[39]

Summary

Introduction

Deregulation of cell proliferation in cancer often requires corresponding modifications in the cellular metabolism in order to fuel the increasing need for the biosynthesis of macromolecules including nucleotides, proteins and lipids.[1,2,3] Glucose is one of the major carbon sources for many types of cancers. To adapt to the increased demand for the production of energy and metabolic intermediates, cancer cells often upregulate aerobic glycolysis,[4,5,6] a phenomenon that was first described by Otto Warburg in 1920s.7. The increased glycolytic phenotype associated with cancer cells enables the detection of tumor lesions by FDGPET imaging.[8] In addition, accumulating evidence has suggested that mitochondrial metabolism is essential for tumor growth and progression. It has been shown that the mitochondrial function is tightly coupled with increased glucose metabolism in order to produce metabolites as building blocks for cell proliferation and as signaling molecules to control cell signaling (Danvers, MA, USA).[9,10] For example, Tan et al.[11] reported recently that cancer cells with defected mitochondria show delayed tumor growth in primary lesion and impaired metastatic potential

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