Loss of Complex I due to Mitochondrial DNA Mutations in Renal Oncocytoma

Abstract

Purpose: Many solid tumors exhibit abnormal aerobic metabolism characterized by increased glycolytic capacity and decreased cellular respiration. Recently, mutations in the nuclear encoded mitochondrial enzymes fumarate hydratase and succinate dehydrogenase have been identified in certain tumor types, thus demonstrating a direct link between mitochondrial energy metabolism and tumorigenesis. Although mutations in the mitochondrial genome (mitochondrial DNA, mtDNA) also can affect aerobic metabolism and mtDNA alterations are frequently observed in tumor cells, evidence linking respiratory chain deficiency in a specific tumor type to a specific mtDNA mutation has been lacking. Experimental Design: To identify mitochondrial alterations in oncocytomas, we investigated the activities of respiratory chain enzymes and sequenced mtDNA in 15 renal oncocytoma tissues.Results: Here, we show that loss of respiratory chain complex I (NADH/ubiquinone oxidoreductase) is associated with renal oncocytoma. Enzymatic activity of complex I was undetectable or greatly reduced in the tumor samples (n = 15). Blue Native gel electrophoresis of the multisubunit enzyme complex revealed a lack of assembled complex I. Mutation analysis of the mtDNA showed frame-shift mutations in the genes of either subunit ND1, ND4, or ND5 of complex I in 9 of the 15 tumors. Conclusion: Our data indicate that isolated loss of complex I is a specific feature of renal oncocytoma and that this deficiency is frequently caused by somatic mtDNA mutations.A shift in cellular energy production from aerobic oxidation in mitochondria to anaerobic glycolysis is a fundamental property of cancer cells, also called the Warburg effect (1, 2). Otto Warburg postulated that damage of the aerobic energy metabolism is a primary and irreversible event in tumor formation (2). Recently, this hypothesis has been supported by the demonstration that mutations of single enzymes of the mitochondrial energy metabolism are associated with tumorigenesis (3, 4). Germline mutations in distinct subunits of succinate dehydrogenase predispose to hereditary paragangliomas and pheochromocytomas (4, 5). Germline mutations in the fumarate hydratase gene can either cause leiomyoma, leiomyosarcoma, and renal cell carcinoma (3) or Leydig cell tumor (6). Therefore, succinate dehydrogenase and fumarate hydratase are regarded as mitochondrial tumor suppressors for these types of tumors (5).Mitochondrial DNA (mtDNA), the small genome of the mitochondrion, is essential for aerobic energy metabolism and encodes some of the subunits of respiratory chain complexes I, III, and IV, as well as the F 1 F 0 -ATP synthase. Complex I consists of 46 different subunits, with a molecular mass totaling 980 kDa. Seven of these subunits (ND1 -ND6 and ND4L) are encoded by mtDNA; the other complex I genes are located on nuclear chromosomes.Because of its essential role in energy metabolism, the mitochondrial genome has long been suspected of contributing to metabolic alterations in tumors. Such investigations d...

Prognostic implications and molecular associations of NADH dehydrogenase subunit 4 (ND4) mutations in acute myeloid leukemia

“…Supporting this hypothesis, others have shown that cells harboring one of the ND4 mutations we observed, the somatic 1-base-pair deletion resulting in early translation termination (UPN12 , Table 1), had markedly reduced Complex I activity. 40 Furthermore, the 11 predicted TMDs of ND4 may be important for mitochondrial proton transport and 47% of the mutations we detected are within these domains (Figure 1). The S407P ND4 mutation discovered by others in an AML sample 6 is predicted to reside in the same ND4 transmembrane domain as the four additional mutations (I391V, A404T, L405P, Y409H) that we identified.…”

Lack of complex I is associated with oncocytic thyroid tumours

“…All investigated thyroid oncocytomas showed complex I deficiency and most had a benign clinical course; however, 2 of the 19 tumours in this study were carcinomas. Renal oncocytoma, another type of oncocytic tumour with a benign course, was recently found to be associated with complex I deficiency (Gasparre et al, 2008;Mayr et al, 2008). The oncocytic tumour cell line XTC.UC1, which is derived from a metastasis of a Hürthle cell carcinoma, shows both an insertion mutation in the gene encoding ND1 subunit of complex I and a reduction in complex I activity (Bonora et al, 2006).…”

“…However, the effects of the observed mutations on complex I enzyme activity and protein content have not been shown particularly for the remaining cases in which clear evidence for complex I deficiency could not be shown. In contrast, we identified a loss of complex I enzyme activity and protein in 100% of renal oncocytomas (Mayr et al, 2008). We hypothesised that thyroid oncocytomas would exhibit a similar deficiency.…”

“…After evaporation of ethanol, tissues were treated with 200 ml of PCRK (2 mg ml À1 Proteinase K, 75 mM Tris-HCl pH 8.8, 20 mM (NH 4 ) 2 SO 4 , 0.01% Tween 20) at 601C for 24 h followed by 951C for 10 min. Sequence analysis of the mtDNA was carried out as described previously (Mayr et al, 2008).…”

Mitochondrial Dysfunction Impairs Tumor Suppressor p53 Expression/Function

“…Mutations in both mtDNA and nuclear genes encoding OxPhos complexes are associated with almost all types of cancers (1,3). Somatic mutations in complex I subunit-encoding genes are frequently associated with oncocytomas (5,6). A recent study with head and neck cancers suggests that there are no mutational hot spots in the mtDNA (7).…”