Frequency of Mitochondrial DNA (mtDNA) Somatic Mutations in Oncocytic Salivary Gland Neoplasms
D Bell, MA Luna, RS Weber, AK El-Naggar. MD Anderson Cancer Center, Houston, TX
Background: Oncocytic salivary lesions comprise a spectrum of hyperplastic and neoplastic lesions. Oncocytic features are also observed in Warthin's tumors and mucoepidermoid carcinoma. These lesions share mitochondrial (mt) proliferations, with characteristic oncocytic appearance. The role and significance of this feature in these lesions remain uncertain. At issue are two fundamental questions: 1) is mt accumulations in hyperplastic and neoplastic lesions a compensatory/reactive or clonal process? 2) in neoplastic lesions, do mt alterations play a primary or a secondary role in tumorigenesis? This study focused on question 1.
Design: Mutational screening in selected regions of the mitochondrial genome in SG oncocytic lesions were performed. Tumors: 1 oncocytic hyperplasia, 2 oncocytomas, 5 Warthin's tumors (WT) and 1 malignant WT. Genomic DNA from frozen specimens was extracted, mtDNA fragments from the D-loop and COX II regions were amplified, PCR products purified and analyzed. Genetic polymorphism was identified using MITOMAP database.
Results: In D-loop , the number of point mutations varied (2-39). All of the samples had mutations in the hypervariable segment 1 (HVS 1) (2-24). The highest frequency of mutations occurred in the HVS 2 region. Of the detected point mutations, 90-100% were homoplasmic, 0-10% of the mutations heteroplasmic. Homoplasmic mtDNA mutations were G-A, C-A or G-T transitions. HVS 1 has previously been identified as a hotspot for both germline and somatic mutations, but the functional significance of mutations in this region remains unknown. In the COX II region, the homoplasmic mtDNA point mutation numbers varied between none and 11, with no heteroplasmic mutations. WT had highest frequency of mutations (5-11) compared to oncocytoma (1) and oncocytic hyperplasia (4).
Conclusions: Our analysis, limited to D-loop and COX II regions suggests that: 1) most mitochondrial mutations are homoplasmic. 2) HVS 1 and HVS 2 are the most frequent sites. 3) Mt DNA alterations of the D-loop occurred in both hyperplastic and neoplastic lesions, and may not be associated with tumorigenesis. 4) Mt DNA alterations of the COX II region were more frequent in neoplastic than in hyperplastic lesions. Further mutation analysis of other respiratory chain complex regions are ongoing in SG oncocytic lesions and cell lines developed from these neoplasms. Functional analysis of cellular O2 contents will be performed on the cell lines, at different points in culture, to assess the biological evolution of these tumors.
Category: Head & Neck
Monday, March 9, 2009 1:00 PM
Poster Session II # 159, Monday Afternoon