title: Decreased Mitochondrial Mutagenesis during Transformation of Human Breast Stem Cells into Tumorigenic Cells.
abstract: Rare stochastic mutations may accumulate during dormancy of stem-like cells, but technical limitations in DNA sequencing have limited exploring this possibility. In this study, we employed a recently established deep-sequencing method termed Duplex Sequencing to conduct a genome-wide analysis of mitochondrial (mt) DNA mutations in a human breast stem cell model that recapitulates the sequential stages of breast carcinogenesis. Using this method, we found significant differences in mtDNA among normal stem cells, immortal/preneoplastic cells, and tumorigenic cells. Putative cancer stem-like cell (CSC) populations and mtDNA copy numbers increased as normal stem cells become tumorigenic cells. Transformed cells exhibited lower rare mutation frequencies of whole mtDNA than did normal stem cells. The predicted mtDNA rare mutation pathogenicity was significantly lower in tumorigenic cells than normal stem cells. Major rare mutation types in normal stem cells are C>T/G>A and T>C/A>G transitions, while only C>T/G>A are major types in transformed cells. We detected a total of 1,220 rare point mutations, 678 of which were unreported previously. With only one possible exception (m10342T>C), we did not find specific mutations characterizing mtDNA in human breast CSCs; rather, the mitochondrial genome of CSCs displayed an overall decrease in rare mutations. On the basis of our work, we suggest that this decrease (in particular T>C/A>G transitions), rather than the presence of specific mitochondrial mutations, may constitute an early biomarker for breast cancer detection. Our findings support the hypothesis that the mitochondrial genome is altered greatly as a result of the transformation of normal stem cells to CSCs, and that mtDNA mutation signatures may aid in delineating normal stem cells from CSCs. Cancer Res; 76(15); 4569-78. ©2016 AACR.
authors.affiliation: Department of Pathology, University of Washington, Seattle, Washington. Institute of Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington.
authors.forename: Eun Hyun
authors.initials: EH
authors.lastname: Ahn
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, Washington.
authors.forename: Seung Hyuk
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, Washington.
authors.forename: Joon Yup
authors.initials: JY
authors.lastname: Kim
authors.affiliation: Department of Pediatrics and Human Development, Michigan State University, East Lansing, Michigan.
authors.forename: Chia-Cheng
authors.initials: CC
authors.lastname: Chang
authors.affiliation: Department of Pathology, University of Washington, Seattle, Washington. Department of Biochemistry, University of Washington, Seattle, Washington. laloeb@uw.edu.
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Loeb
mesh_terms: D001940:Breast / Q000473:pathology*; D001943:Breast Neoplasms / Q000235:genetics*; D063646:Carcinogenesis / Q000235:genetics; D005260:Female; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D016296:Mutagenesis