The Caenorhabditis elegans ARIP-4 DNA helicase couples mitochondrial surveillance to immune, detoxification, and antiviral pathways

Surveillance of Caenorhabditis elegans mitochondrial status is coupled to defense responses such as drug detoxification, immunity, antiviral RNA interference (RNAi), and regulation of life span. A cytochrome p540 detoxification gene, cyp-14A4, is specifically activated by mitochondrial dysfunction. The nuclear hormone receptor NHR-45 and the transcriptional Mediator component MDT-15/MED15 are required for the transcriptional activation of cyp-14A4 by mitochondrial mutations, gene inactivations, or toxins. A genetic screen for mutations that fail to activate this cytochrome p450 gene upon drug or mutation-induced mitochondrial dysfunction identified a DNA helicase ARIP-4 that functions in concert with the NHR-45 transcriptional regulatory cascade. In response to mitochondrial dysfunction, ARIP-4 and NHR-45 protein interaction is enhanced, and they relocalize from the nuclear periphery to the interior of intestinal nuclei. NHR-45/ARIP-4 also regulates the transcriptional activation of the eol-1 gene that encodes a decapping enzyme required for enhanced RNAi and transgene silencing of mitochondrial mutants. In the absence of arip-4, animals were more susceptible to the mitochondrial inhibitor antimycin. Thus, ARIP-4 serves as a transcriptional coactivator of NHR-45 to promote this defense response. A null mutation in arip-4 extends the life span and health span of both wild type and a mitochondrial mutant, suggesting that the activation of detoxification pathways is deleterious to health when the mitochondrial dysfunction is caused by mutation that cannot be cytochrome p450-detoxified. Thus, arip-4 acts in a pathway that couples mitochondrial surveillance to the activation of downstream immunity, detoxification, and RNAi responses.