Polynucleotide degradation during early stage response to oxidative stress is specific to mitochondria

Oxidative stress is known to modulate RNA expression in both prokaryotic and eukaryotic cells. We have previously determined that a preferential and calcium-dependent downregulation of mitochondrial RNA occurs in HA-1 hamster fibroblasts in response to hydrogen peroxide, and that this is accompanied by the degradation of mitochondrial genomic DNA. Here we extended these studies to determine whether downregulation is specific to transcripts derived from mitochondrial-encoded genes; to determine whether genomic DNA degradation occurs in the nucleus; and to compare overall polynucleotide stress response with cellular growth arrest and apoptosis. We observed that nuclear genome-encoded mRNAs whose protein products are targeted for the electron transport chain of mitochondria were not degraded. Furthermore, early stage degradation of genomic DNA, assessed within the first 5 h of peroxide exposure, was specific to mitochondria, as nuclear genomic DNA was not degraded under the same treatment conditions. These differential degradations occurred under conditions where extensive growth-arrest and moderate apoptosis were observed, and were accompanied by significant induction of the growth arrest mRNAs gadd45, gadd153, and adapt15/gadd7. Combined, these results indicate that there is a general degradation of mitochondrial- but not nuclear-polynucleotides during early stage response of HA-1 fibroblasts to oxidative stress.