Mitochondrial DNA mutations in oral squamous cell carcinoma

Abstract

It has previously been demonstrated that mitochondrial DNA (mtDNA) mutations within the ND2 gene of histologically normal parotid salivary gland tissue of smokers may be molecular biomarkers for smoking-induced mtDNA damage. Oral squamous cell carcinoma (SCC) is strongly related to cigarette smoking; therefore, we used PCR and direct sequencing to establish whether mtDNA mutations were also present in oral SCC which could be used as additional biomarkers for smoking-associated DNA damage. In addition to searching for mutations in the ND2 gene, the mitochondrial D-Loop was also analysed. Three mutation hotspots were observed in the D-Loop at nt 146, 152 and 186, two of which (nt 146 and 152) have also been implicated in oesophageal SCC, another smoking-related cancer. The mutation hotspot observed at nt 186 has not previously been reported in other tumours. Furthermore, we show that the mutations previously reported within the ND2 gene in normal parotid tissue of smokers were not evident in these samples, but that a mutation hotspot occurs at nucleotide 4917 in oral SCC. We also show that D-Loop mutations occur predominantly in male smokers and female non-smokers and that this association with gender is statistically significant (P = 0.003). We conclude that the mtDNA mutation hotspots found in this study, in particular nt 186, are potential biomarkers for oral SCC. However, owing to gender-specific differences in occurrence in smokers and non-smokers, and a lack of environmental smoking history, in general, it is difficult to associate these mutations with mtDNA damage induced by smoking. If the mutations observed in the subset of male patients are smoking induced, given our previous findings, mutation hotspots in the ND2 gene may be tissue specific suggesting the causative mutagens for mtDNA damage within these tissues are likely to be different.

Mitochondrial DNA: The Alternative Molecular Marker for Cancer Detection and Treatment

“…9 Head and neck squamous cell carcinomas arise through premalignant intermediates and may be merely morphologic manifestations of accumulated genetic alterations. 20 In keeping with this molecular tumour progression model, studies have shown that mtDNA increases according to histopathologygrade, a phenomenon that may be a feedback mechanism that compensates for a generalised decline in respiratory chain function. Therefore, high mtDNA content may be another marker of genetic alteration, a measure of relative DNA injury, and a surrogate measure of histopathology grade.…”

“…They found that both tumours and saliva from head and neck cancer patients contained an increased amount of mitochondrial DNA content. [19][20][21][22] It has been shown that mitochondrial mutations result in an increase in mitochondrial mass which could be due to nuclear encoded factors that are translocated into mitochondria resulting in proliferation. 19,21 It was found that the in vitro effect of tobacco smoke extract and tobacco smoke exposure and its effect on mitochondrial function and mitochondrial contents in both acute and chronic setting.…”

“…There is no apoptotic response which there obviouslyshould be despite release of commonly known apoptotic inducing factors into cytosol. 19,20 Mitochondrial DNA (mtDNA) mutations within ND 2 gene of histological normal parotid salivary gland tissue of smokers has been demonstrated as molecular biomarkers for smoking induced mt DNA damage by Lewis et al According to them mtDNA mutations are present in oncocytes within Warthin's tumour. In addition, Warthin's tumours contain morphologically abnormal and respiratory deficient mitochondria.…”

“…Furthermore it is shown that the mutations previously reported within the ND2 gene in normal parotid tissue of smokers were not evident in these samples, but that a mutation hotspot occurs at nucleotide 4917 in oral SCC.It is concluded that the mtDNAmutations hotspot found in this study in particular nt186 are potential biomarkers for oral SCC. 20,26,27 D-loop mutations should be considered as a cancer biomarker that may be useful for the early detection of HNSCC in individuals at risk of this cancer. The presence of these mutations in saliva and serum of tobacco and alcohol consumers' should be investigated in further studies in order to evaluate their relevance in the screening of these cancers in association with other tumour specific molecular alterations.…”

Mitochondrial Mutations Are a Late Event in the Progression of Head and Neck Squamous Cell Cancer

“…The timing of other mitochondrial mutations in the progression from normal mucosa to invasive tumor has not been well established (18,19). The D-loop, which has propensity for mutation, was found to carry mutations in 21% to 53% of HNSCC (20,21). Sequencing of 80% of the mitochondrial genome using conventional methods has revealed mutation in 46% in a limited cohort of HNSCC (2).…”