Mitochondrial DNA damage in non-melanoma skin cancer
aDermatology, University of Newcastle, Newcastle upon Tyne, United Kingdom, bGenesis Genomics Inc, Thunder Bay, ON, Canada
AIM: Mitochondrial DNA (mtDNA) damage, predominantly encompassing point mutations, has been reported in a variety of cancers (reviewed in Penta et al., (2001). Mutat Res 488: 119-133). Our aim was perform in human skin, the first detailed study of the distribution of multiple forms of mtDNA damage in non-melanoma skin cancer compared to histologically normal perilesional dermis and epidermis. METHODS: included long range PCR, 3-primer PCR, back to back primer PCR and automated sequencing. RESULTS: We present the first entire spectrum of deletions found between different types of skin tumours and perilesional skin (n=30). Twenty different deletion species were observed in the major deletion arc and four species were observed in the minor deletion arc. Our data clearly shows that more deletions occur in the skin from BCC rather than SCC patients. In addition, we provide the first quantitative data for the incidence of the common deletion as well as the first report of specific tandem duplications in tumours from any tissue. Importantly, this work shows that there are clear differences in the distribution of deletions between the tumour and the histologically normal perilesional skin. Furthermore, DNA sequencing of four mutation "hotspot" regions of the mitochondrial genome identified heteroplasmic changes, which were present in the tumour alone (i.e. somatic) or at least with a greater incidence compared to the surrounding perilesional skin. For example, we identified a previously unreported somatic C to T heteroplasmic mutation at np438 in the non-coding D-loop. There were two further heteroplasmic changes, a T to C transition at np16093 in the non-coding D-loop and an A to G transition at np215 in the coding region, in the tumour of an 88-year-old BCC patient which were absent in the perilesional dermis and barely detectable in the associated epidermis. In addition, 81 unreported and reported homoplasmic single base changes were identified in the other NMSC patients. Unlike the distribution of deletions and the heteroplasmic mutations, these homoplasmic mutations were present in both tumour and perilesional skin. CONCLUSION: This suggests that for some genetic studies, the traditional use of histologically normal perilesional skin from NMSC patients may be limited. Currently from this data, it is unclear whether mtDNA damage has a direct causal link to skin cancer or it may simply reflect an underlying nuclear DNA instability. It is clear however from our data and from cancer studies of other tissues, that mtDNA damage is likely to provide a potentially powerful tool in cancer diagnosis.
Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in oral session 797 (Manifestations of cancer).