Hypoxic repression of pyruvate dehydrogenase activity is necessary for metabolic reprogramming and growth of model tumours.

Tereza Golias,Quynh-Thu Le,Nicholas C Denko,Benjamin J Swanson,Ioanna Papandreou,Ramon Sun,Diego Jaitin,Reetesh Pai,Bhavna Kumar,Theodoros N Teknos,Nicole V Brown

doi:10.1038/srep31146

Abstract

Tumour cells fulfil the bioenergetic and biosynthetic needs of proliferation using the available environmental metabolites. Metabolic adaptation to hypoxia causes decreased mitochondrial function and increased lactate production. This work examines the biological importance of the hypoxia-inducible inhibitory phosphorylations on the pyruvate dehydrogenase E1α subunit. Pancreatic cancer cell lines were genetically manipulated to alter the net phosphorylation of PDH E1α through reduced kinase expression or enhanced phosphatase expression. The modified cells were tested for hypoxic changes in phosphorylated E1α, mitochondrial metabolism and growth as xenografted tumours. Even though there are four PDHK genes, PDHK1 is essential for inhibitory PDH phosphorylation of E1α at serine 232, is partially responsible for modification of serines 293 and 300, and these phosphorylations are necessary for model tumour growth. In order to determine the clinical relevance, a cohort of head and neck cancer patient biopsies was examined for phosphorylated E1α and expression of PDHK1. Patients with detectable 232 phosphorylation or expression of PDHK1 tend to have worse clinical outcome. These data show that PDHK1 activity is unique and non-redundant in the family of PHDK enzymes and a PDHK1 specific inhibitor would therefore have anti-cancer activity with reduced chance of side effects from inhibition of other PDHKs.

Highlights

How tumour cells have decreased oxidative function, and as a result produce increased amounts of acidic lactate, even when oxygen is present[5]
We show for the first time in vivo that phosphorylation of serine 232 is absolutely dependent on PDHK1, and the expression of PDHK1 and presence of phosphorylated serine 232 on E1αshows trends of poor outcome in patients with head and neck squamous cell carcinoma
In low glucose there is the decrease in oxygen consumption rate (OCR), but in these conditions we detect a significant increase in extracellular acidification rate (ECAR) (Supplementary Fig. S1)

Summary

Introduction

How tumour cells have decreased oxidative function, and as a result produce increased amounts of acidic lactate, even when oxygen is present[5]. One mechanism by which tumour cells have reduced mitochondrial oxidation is presumed to be through hypoxic reduction in pyruvate dehydrogenase (PDH) activity[6,7]. In vitro work on purified proteins has shown that PDHK1 is unique in its ability to phosphorylate the E1αserine at 232, in vivo data has not been reported. This suggests a unique relationship between hypoxia, PDHK1, pSer232-E1α,and regulation of mitochondrial function. We generate functional data that show how pancreatic cancer cells induce PDHK1 in hypoxia, increase phosphorylation at all three phosphorylation sites, reduce PDH activity, and reduce mitochondrial oxygen consumption. We show for the first time in vivo that phosphorylation of serine 232 is absolutely dependent on PDHK1, and the expression of PDHK1 and presence of phosphorylated serine 232 on E1αshows trends of poor outcome in patients with head and neck squamous cell carcinoma

Methods

Results

Conclusion