Mitochondrial microsatellite instability in colorectal carcinomas—frequency and association with nuclear microsatellite instability
Introduction
In 1976, Nowell suggested genetic instability as a basis for clonal evolution of tumours through selection of cellular subpopulations [1]. Later, Vogelstein proposed a genetic model for development of colorectal tumours [2]. The knowledge about genetic characteristics of this disease has expanded further. However, most of the investigational efforts have been made on genetic changes in nuclear DNA (nDNA).
Recently, much attention has been paid to genetic changes in mitochondrial DNA (mtDNA). Due to generation of reactive oxygen species as a by-product of oxidative phosphorylation [3], poor protection of mtDNA because of the lack of histones and limited mtDNA repair mechanisms [4], [5], [6], mtDNA mutation rates are several times greater than nuclear mutation rates [4], [5], [7]. Alterations in mtDNA have been identified in conditions such as aging [5], [8], [9], [10], as well as in degenerative and metabolic disorders [4], [5]. Several studies have reported that mtDNA mutations are also common in cancer [11], [12], among them colorectal cancer [13], [14], [15]. However, the significance of these mutations is still unclear.
Mitochondrial microsatellite instability (mtMSI) has been defined as change in length in short base-repetitive sequences of mtDNA. An association between mtDNA microsatellite instability (mtMSI) and nuclear DNA instability (nMSI) has been sought for in different tumour types and discussed, so far without consent [13], [15], [16], [17].
The purpose of the present study was to investigate a possible relationship between microsatellite instability in nuclear DNA and in mitochondrial DNA. Four mononucleotide repeats in mtDNA were analyzed in 95 colorectal carcinomas previously stratified by nMSI status [18], [19], [20]. In addition, we have correlated our findings with the occurrence of alterations in the same homopolymeric tracts in 95 healthy controls. The presence of mtDNA mutations was also related to clinicopathological variables, and to nuclear genetic characteristics of the tumours.
Section snippets
Patients
Blood and tissue samples were obtained from 95 patients with colorectal carcinomas removed during laparotomy. Median age was 70 years (range 26–95). Table 1 provides a further description of the patient material. The tumour samples were mechanically minced in phosphate-buffered saline, filtered through a nylon mesh (pore size 70 μm), fixed in 70% ethanol and stored at 4 °C. To evaluate contamination of normal cells in the tumour cell suspensions, cytospin preparations were made and examined as
Alterations in the D310 mononucleotide repeat in D-loop
Fragment analysis showed D310 alterations in 35 of the 95 colorectal carcinomas, as compared with the blood sample from the patient. In three carcinomas DNA sequencing could not confirm the alteration, and these were considered to have no changes. Thus, 32 of 95 (34%) carcinomas had changes in the D310 region. An example of the DNA fragment and sequencing analysis is shown in Fig. 1. In contrast, two of the 95 controls (2%) had D310 alterations, the frequency being significantly lower than in
Discussion
In this study, we found that 34% of the colorectal cancer patients had alterations in the D310 poly-C tract in the D-loop. This suggests D310 as a hotspot for alterations in colorectal tumours when concerning frequency. However, the mtMSI was not significantly associated with nMSI or other clinicopathological variables.
The incidence of 34% D310 alterations is in general agreement with previous studies, reporting a frequency of 44% in 45 colorectal carcinomas [13], 28% in 103 colon tumours [16]
Acknowledgements
The study was supported by grants form The Norwegian Cancer Society and the Norwegian Foundation for Health and Rehabilitation.
References (44)
- et al.
A genetic model for colorectal tumorigenesis
Cell
(1990) - et al.
Mitochondrial DNA repair and aging
Mutat. Res.
(2002) - et al.
Mitochondrial DNA in human malignancy
Mutat. Res.
(2001) - et al.
Mitochondrial DNA mutations as an important contributor to ageing and degenerative diseases
Lancet
(1989) Mitochondrial genome instability in human cancers
Mutat. Res.
(2001)- et al.
Microsatellite instability and mutation of mitochondrial and nuclear DNA in gastric carcinoma
Gastroenterology
(2000) - et al.
WNT1 inducible signaling pathway protein 3, WISP3, a novel target gene in colorectal carcinomas with microsatellite instability
Gastroenterology
(2001) The mitochondrial genome: structure, transcription, translation and replication
Biochim. Biophys. Acta
(1999)- et al.
Hypermutability and mismatch repair deficiency in RER+tumor cells
Cell
(1993) Repair of oxidative DNA damage in nuclear and mitochondrial DNA, and some changes with aging in mammalian cells
Free Radic. Biol. Med.
(2002)
Two distinct types of mitochondrial DNA segregation in mouse-rat hybrid cells. Stochastic segregation and chromosome-dependent segregation
Exp. Cell Res.
Accumulation of mitochondrial DNA mutations in ageing, cancer, and mitochondrial disease: is there a common mechanism?
Lancet
The clonal evolution of tumor cell populations
Science
Diseases of the mitochondrial DNA
Annu. Rev. Biochem.
Mitochondrial DNA sequence variation in human evolution and disease
Proc. Natl Acad. Sci. USA
Mitochondrial mutational spectra in human cells and tissues
Proc. Natl Acad. Sci. USA
Oxidative damage and mitochondrial decay in aging
Proc. Natl Acad. Sci. USA
Aging-dependent large accumulation of point mutations in the human mtDNA control region for replication [see comments]
Science
Mitochondrial defects in cancer
Mol. Cancer
Microsatellite instability in the mitochondrial DNA of colorectal carcinomas: evidence for mismatch repair systems in mitochondrial genome
Oncogene
Somatic mutations of the mitochondrial genome in human colorectal tumours
Nat. Genet.
Mitochondrial gene mutation, but not large-scale deletion, is a feature of colorectal carcinomas with mitochondrial microsatellite instability
Int. J. Cancer
Cited by (27)
Mitochondrial C150T polymorphism increases the risk of cervical cancer and HPV infection
2011, MitochondrionCitation Excerpt :Parrella et al. (2001) found that D310 was a hot spot for mutations in breast tumors. D310 alterations were found in 34% of total colorectal cancers but only in 2% of the control group (Guleng et al., 2005). The D514 dinucleotide repeat was reported in ovarian (Liu et al., 2001), thyroid (Maximo et al., 2005), and gastric cancers (Zhao et al., 2005).
Mitochondrial genome alterations in rectal and sigmoid carcinomas
2009, Cancer LettersCitation Excerpt :All mutations detected are frameshift, possibly resulting in non-functional proteins and respiratory chain alteration. These findings are in agreement with those obtained by Habano et al. [7] in CRC, who detected mutation frequencies of 2.2% and 4.4% for ND1 and ND5, respectively, but not with those of Guleng et al. [8] and Lièvre et al. [9], who found no mutations in RC. In fact, we describe here for the first time ND1 and ND5 mutations in RC or SC.