Impact of Mitochondrial DNA Haplogroups on Cancer Gene Expression

Abstract

PurposeThe objective of this study is to investigate the effects of mitochondrial (mt) DNA haplogroups on expression of cancer genes, and the role that mtDNA plays in retrograde signaling between the mitochondria and nucleus. The present study tests the hypothesis that mtDNA haplogroups (H versus K) can differentially modulate cancer gene expression through the STING (Stimulator of Interferon Genes) pathway in response to unique DNA fragments.MethodsThis study uses “personalized” transmitochondrial cybrids that are cell lines with identical nuclei that contain mitochondria from either H haplogroup mtDNA (Common European) or K haplogroup mtDNA (Ashkenazi Jewish) individuals.Cybrids were generated by fusing platelets from either H or K haplogroup subjects with Rho0 (lacking mtDNA) human retinal ARPE‐19 cells. Haplogroups were verified by mtDNA sequencing. STING gene expression was knocked down in H cybrids (n=5) and K cybrids (n=5) by transfection with STING siRNA or negative control. Gene expression was measured by qRT‐PCR. Statistical analyses performed using unpaired t‐test.ResultsUntreated K cybrids had significantly lower expression levels of four cancer related genes (BRCA1, 51.6% ± 9.9%, p = 0.007; EGFR, 73.9% ± 6.9%, p = 0.05; ALK, 22.6% ± 5.9%, p = 0.003 and PD1, 40.5% ± 12.6%, p = 0.03) compare to untreated H cybrids. STING knockdown decreased expression of EGFR in both H and K cybrids (73.2% ± 6.7%, p=0.05, and 44.8% ± 7.2% p=0.02). STING knockdown decreased expression of BRCA1 in H cybrids (66.2% ± 8.2%, p=0.02) but had no effect on the already lower levels of BRCA1 in K cybrids. Untreated H and K cybrids showed no difference in the level of STING expression. However, Untreated K cybrids exhibited altered levels of key genes involved in the STING signalling pathway. This included increased levels of IkBa (194.0% ± 30.2%, p = 0.05) and NFKB2 (145.1% ± 11.9%, p = 0.026) as well as lower expression of IRF3 (67.9% ± 5.1%, p = 0.009).ConclusionsThe Ashkenazi Jewish population is well characterized and at higher risk for a variety of diseases. Previous data has shown that K haplogroup cybrids differentially expressed genes associated with epigenetics and inflammation. Our findings show that although all cybrid cells have identical nuclei, those with K haplogroup mtDNA show dramatically altered expression of cancer related genes. STING is involved in sensing DNA fragments, including mitochondrial DNA, and driving type I interferon expression. K haplogroup cybrids exhibit altered expression of several genes involved in the STING pathway. This suggests that mitochondrial haplogroup can impact the way a cell responds to DNA fragmentation, which is seen in a wide variety of diseases. This study suggests that mtDNA haplogroups could potentially play a role in cancer susceptibility, through altered gene expression and differential response to DNA fragments.Support or Funding InformationFunding Supported by Discovery Eye Foundation, Polly and Michael Smith, Iris and B. Gerald Cantor Foundation, Roy and Edith Carver Foundation, Max Factor Family Foundation. Supported by an RPB Unrestricted Grant. Kevin Schneider, PhD holds a Mabel and Arnold Beckman Foundation Fellowship. We acknowledge support from the Institute for Clinical and Translational Science (ICTS) at University of California IrvineThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.