Time-Dependent Stabilization of Hypoxia Inducible Factor-1α by Different Intracellular Sources of Reactive Oxygen Species

Maura Calvani,Elisa Giannoni,Giuseppina Comito,Paola Chiarugi,Andrzej T Slominski

doi:10.1371/journal.pone.0038388

Abstract

Intratumoral hypoxia is a major obstacle in the development of effective cancer chemotherapy, decreasing the efficacy of anti-neoplastic drugs in several solid tumours. The hypoxic environment, through its master regulator hypoxia inducible factor-1 (HIF-1), is able to maintain an anti-apoptotic potential through activation of critical genes associated with drug resistance. Besides affecting metabolism and motility of tumour cells, hypoxia also paradoxically increases production of reactive oxygen species (ROS), which contribute to stabilize HIF-1 through a redox-mediated inhibition of its proteolysis. Here we reported that 1% O2 hypoxia increases the resistance of human metastatic melanoma cells to conventional chemotherapy with etoposide, and that the increase in chemoresistance strongly depends on ROS delivery due to hypoxia. We reported a biphasic redox-dependent role of HIF-1, involving mitochondrial complex III and NADPH oxidase as oxidants sources, synergising in enhancing survival to chemotherapy. The feed-forward loop engaged by hypoxia involves first an HIF-1-dependent vascular endothelial growth factor-A (VEGF-A) autocrine production and, in the later phase, activation of NADPH oxidase from VEGF/VEGFR2 interaction, finally leading to a further redox-dependent long lasting stabilization of HIF-1. We therefore identified a redox-dependent circuitry linking hypoxia-driven ROS to VEGF-A secretion and to enhanced melanoma cell survival to etoposide chemotherapy.

Highlights

Melanoma is the most aggressive form of skin cancer and its advanced stages are inevitably associated with a poor prognosis, due to their resistance to conventional therapeutic agents
Using HS29-4T human metastatic melanoma cells treated with etoposide, we proved that hypoxia-driven reactive oxygen species (ROS) orchestrate a biphasic redox-dependent cellular response that leads cells to escape apoptosis induced by both etoposide and hypoxic hostile environment
We found that mitochondrial ROS and NADPH oxidase ROS cooperate in HIF1 stabilization, with a different time course

Summary

Introduction

Melanoma is the most aggressive form of skin cancer and its advanced stages are inevitably associated with a poor prognosis, due to their resistance to conventional therapeutic agents. The resistance to undergo apoptosis in response to chemotherapy and other environmental cues gives rise in aggressive melanoma to a selective advantage for tumour progression, metastasis formation as well as for resistance to therapy [1,2]. Tumour microenvironment is known to contribute in different ways to drug resistance essentially through increasing cancer mutation rate or creating a selective pressure favouring resistant and aggressive populations [3]. Stabilization of HIF-1a is influenced by genetic alterations, as well as by growth factors, hormones and cytokines produced by both tumour and stromal cells [10]. Under hypoxic condition HIF-1 coordinates the expression of many genes that orchestrate angiogenesis and cancer cell metabolism reprogramming, including GLUT1 and GLUT3, glycolytic enzymes, vascular endothelial growth factor (VEGF), erythropoietin (EPO), heme oxygenase-1 (HO-1), etc [11]

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