Hypoxia-inducible factors enhance glutamate signaling in cancer cells.

Hongxia Hu,Lisha Xiang,Weibo Luo,Gregg L Semenza,Daniele M Gilkes,Naoharu Takano

doi:10.18632/oncotarget.2593

Hongxia Hu, Lisha Xiang + Show 4 more

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https://doi.org/10.18632/oncotarget.2593

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Abstract

Signaling through glutamate receptors has been reported in human cancers, but the molecular mechanisms are not fully delineated. We report that in hepatocellular carcinoma and clear cell renal carcinoma cells, increased activity of hypoxia-inducible factors (HIFs) due to hypoxia or VHL loss-of-function, respectively, augmented release of glutamate, which was mediated by HIF-dependent expression of the SLC1A1 and SLC1A3 genes encoding glutamate transporters. In addition, HIFs coordinately regulated expression of the GRIA2 and GRIA3 genes, which encode glutamate receptors. Binding of glutamate to its receptors activated SRC family kinases and downstream pathways, which stimulated cancer cell proliferation, apoptosis resistance, migration and invasion in different cancer cell lines. Thus, coordinate regulation of glutamate transporters and receptors by HIFs was sufficient to activate key signal transduction pathways that promote cancer progression.

Highlights

Hypoxia-inducible factors (HIFs) are transcription factors that mediate adaptive responses to reduced oxygen availability
We demonstrated that HIF activity, induced by hypoxia or von Hippel-Lindau tumor suppressor protein (VHL) loss-of-function in hepatocellular and renal carcinoma cells, respectively, mediated the coordinate transcription of multiple genes encoding glutamate transporters and glutamate receptors, which resulted in activation of signal transduction pathways that stimulated cancer cell proliferation, survival, or migration and invasion
Reverse transcription and quantitative real-time PCR (RT-qPCR) analysis of Hep3B cells exposed to 20% or 1% O2 for 24 h revealed that the abundance of SLC1A1 and SLC1A3 mRNA, but not that of mRNAs encoding other glutamate transporters, was significantly induced by hypoxia (Fig. 1B and Fig. S1A)

Summary

Introduction

Hypoxia-inducible factors (HIFs) are transcription factors that mediate adaptive responses to reduced oxygen availability. HIFs are heterodimers, composed of an oxygen-regulated HIF-1α or HIF-2α subunit and a constitutively expressed HIF-1β subunit, that bind to the consensus DNA sequence 5’-RCGTG-3’, which is embedded within hypoxia response elements (HREs) in target genes [1]. Proline residues Pro402 and Pro564 of human HIF-1α (Pro405 and Pro531 of HIF-2α) are subjected to O2 dependent hydroxylation by prolyl hydroxylase domain proteins (PHDs) [2,3,4]. This modification is required for interaction with the von Hippel-Lindau tumor suppressor protein (VHL), which is the substratespecific component of an E3 ubiquitin ligase that targets hydroxylated HIF-1α or HIF-2α for ubiquitination and subsequent proteasomal degradation [4]. High HIF-1α or HIF-2α abundance in the diagnostic biopsy is associated with metastasis, treatment failure, and patient mortality in many types of cancer [7, 9]

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