Abstract 431: Mitochondrial-nuclear crosstalk influences accumulation of mitochondrial DNA mutations in mammary tumor progression
Authors: Brewer Takae M. , Brinker Amanda E. , Manley Sharon , Vivian Carolyn J. , Welch Danny R. 
Published: August 2018

Introduction: Previous studies demonstrated that mitochondrial inheritance may contribute to aggressiveness of metastatic disease. Accumulating evidence suggests the mitochondrial genetic background may influence how certain cancers behave. We utilized Mitochondrial-Nuclear eXchange (MNX) female mice crossed with transgenic mice over-expressing the Her-2 gene and showed mitochondrial DNA (mtDNA)-dependent differences in tumor latency, lung metastasis number and lung metastasis size. We hypothesized that mtDNA mutations accumulate as mammary tumors progress and that the evolution is associated with mtDNA-nuclear DNA cross-talk. To test this hypothesis, we conducted next generation sequencing analyses to examine the spectra of mutations in the mitochondrial genome.

Methods: Normal mammary gland, primary tumor and lung metastases [n=5 each] were obtained from FVB/NJ mice with FVB/NJ (designated FF), C57BL/6J (designated FC) or BALB/cJ mtDNA (designated FB). Epithelial cells from mammary gland or tumor cells were carefully isolated by laser capture microdissection in order to minimize contamination from surrounding stromal cell mtDNA. mtDNA was deep sequenced using three pools totaling 182 overlapping primers spanning the whole mitochondrial genome using the Ion TorrentTM PGM System. Sequences were compared to an FVB mtDNA reference sequence to detect variants.

Results: Significant differences in the total number of mtDNA mutations were observed between the wild-type and MNX mice. Both FB and FC MNX cohorts exhibited increased mtDNA mutations compared to the wild-type (FF). As tumor progressed, the numbers of and distribution of mutations across the mitochondrial genome increased. ‘Hotspots' were observed in FB mice (S12 rRNA, COX I, ND4, CYTB) that were distinct from common mutations in the FC mice (16S rRNA, COX I).

Discussion: As predicted, tumor cells accumulated more mutations in mtDNA as neoplastic cells from the primary tumor progressed to metastasis. Surprisingly, wild-type (FF) mice, even though more clinically aggressive (i.e., more metastases), accumulated fewer mtDNA mutations than tumors arising in the MNX mice. The mutations appear to occur in different sites, depending upon the nuclear-mitochondrial combination. Whether the mtDNA mutations function as contributors to metastatic efficiency has not yet been determined. Nonetheless, the data imply that nuclear-mitochondrial cross-talk influences mtDNA mutational spectra and metastasis and that defining the critical mtDNA genes most commonly involved may eventually be used to predict patient prognosis.

Citation Format: Takae M. Brewer, Amanda E. Brinker, Sharon Manley, Carolyn J. Vivian, Danny R. Welch. Mitochondrial-nuclear crosstalk influences accumulation of mitochondrial DNA mutations in mammary tumor progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 431.