Differential modulation of cancer-related genes by mitochondrial DNA haplogroups and the STING DNA sensing system.

Activation of the Simulator of Interferon Genes (STING) system by mitochondrial (mt) DNA can upregulate type 1 interferon genes and enhance immune responses to combat bacterial and viral infections. In cancers, the tumor-derived DNA activates STING leading to upregulation of IFN-beta and induction of antitumor T cells. The entire mtDNA from the cell lines was sequenced using next-generation sequencing (NGS) technology with independent sequencing of both strands in both directions, allowing identification of low-frequency heteroplasmy SNPs. There were 15 heteroplasmy SNPs showing a range from 3.4% to 40.5% occurrence in the K cybrid cell lines. Three H haplogroup cybrids possessed SNP heteroplasmy that ranged from 4.39% to 30.7%. The present study used qRT-PCR to determine if cybrids of H and K haplogroups differentially regulate expression levels of five cancer genes (, , , and ) and seven STING subunits genes (, , , , , , and ). Some cybrids underwent siRNA knockdown of STING followed by qRT-PCR in order to determine the impact of STING on gene expression. Rho (lacking mtDNA) ARPE-19 cells were used to determine if mtDNA is required for the expression of the cancer genes studied. Our results showed that (a) K cybrids have lower expression levels for , , , and genes but increased transcription for and compared to H cybrids; (b) STING KD decreases expression of in both H and K cybrids, and (c) expression is negligible in Rho cells. Our findings suggest that the STING DNA sensing pathway may be a previously unrecognized pathway to target modulation of cancer-related genes and the expression requires the presence of mtDNA.