DOWN-REGULATION OF MAMMALIAN MITOCHONDRIAL RNAS DURING OXIDATIVE STRESS

We have identified an RNA species that appears to be induced by oxidat ive stress in hamster HA-1 fibroblasts using the differential display technique, but instead is found to be degraded when evaluated by North ern blot hybridization. Cloning and subsequent sequencing identified t he partially degraded RNA as 16S ribosomal RNA (rRNA), a major compone nt of mitochondrial ribosomes. Degradation, and associated decreases i n the levels of the mature- and precursor-species of 16S rRNA, appear to be dependent upon calcium, but not cytoplasmic protein synthesis no r nuclear transcription. Other decreased mitochondrial RNAs were also identified, including 12S rRNA, NADH dehydrogenase subunit 6, ATPase s ubunit 6, and cytochrome oxidase subunits I and m. A significant part of many, if not all, of these RNA decreases was due to degradation. As compared with 16S rRNA, significantly less degradation was observed f or cytoplasmic 28S/18S rRNAs, even at very high peroxide concentration . Analysis of 21 cytoplasmic mRNAs revealed little or no decrease in m ature band signal in response to peroxide, and several cytoplasmic mRN As were actually up-regulated. Thus, a preferential down-regulation of mitochondrial RNAs occurs in HA-1 fibroblasts in response to hydrogen peroxide. Subcellular fractionation analysis, using 16S rRNA degradat ion as a gauge, indicates that this down-regulation is specific to mit ochondria. The down-regulation of mitochondrial RNAs may represent a g eneral mechanism by which cells protect themselves against oxidative s tress. Copyright (C) 1996 Elsevier Science Inc.