iNOS initiates and sustains metabolic arrest in hypoxic lung adenocarcinoma cells: mechanism of cell survival in solid tumor core

Land, S.C. and Rae, C. (2005) iNOS initiates and sustains metabolic arrest in hypoxic lung adenocarcinoma cells: mechanism of cell survival in solid tumor core. American Journal of Physiology, 289(4), C918-C933. (doi: 10.1152/ajpcell.00476.2004)

Abstract

Nitric oxide (NO) modulates cellular metabolism by competitively inhibiting the reduction of O2 at respiratory complex IV. The aim of this study was to determine whether this effect could enhance cell survival in the hypoxic solid tumor core by inducing a state of metabolic arrest in cancer cells. Mitochondria from human alveolar type II-like adenocarcinoma (A549) cells showed a fourfold increase in NO-sensitive 4-amino-5-methylamino-2′,7′-difluorofluorescein (DAF-FM) fluorescence and sixfold increase in Ca2+-insensitive NO synthase (NOS) activity during equilibration from PO2s of 100→23 mmHg, which was abolished by Nω-nitro-L-arginine methyl ester-HCl (L-NAME) and the inducible NOS (iNOS) inhibitor, N6-(1-iminoethyl)-L-lysine dihydrochloride (L-NIL). Similarly, cytosolic and compartmented DAF-FM fluorescence increased in intact cells during a transition between ambient PO2 and 23 mmHg and was abolished by transfection with iNOS antisense oligonucleotides (AS-ODN). In parallel, mitochondrial membrane potential (ΔΨm), measured using 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolo-carbocyanine iodide (JC-1), decreased to a lower steady state in hypoxia without change in glycolytic rate, adenylate energy charge, or cell viability. However, L-NAME or iNOS AS-ODN treatment maintained ΔΨm at normoxic levels irrespective of hypoxia and caused a marked activation of glycolysis, destabilization energy charge, and cell death. Comparison with other cancer-derived (H441) or native tissue-derived (human bronchial epithelial; alveolar type II) lung epithelial cells revealed that the hypoxic suppression of ΔΨm was common to cells that expressed iNOS. The controlled dissipation of ΔΨm, absence of an overt glycolytic activation, and conservation of viability suggest that A549 cells enter a state of metabolic suppression in hypoxia, which inherently depends on the activation of iNOS as PO2 falls.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Rae, Dr Colin
• Authors: Land, S.C., and Rae, C.
• College/School: College of Medical Veterinary and Life Sciences > School of Cancer Sciences
• Journal Name: American Journal of Physiology
• ISSN: 0002-9513
• Published Online: 18 May 2005