Up-regulation of nuclear genes in response to inhibition of mitochondrial DNA expression in chicken cells

Vertebrate cells depleted of (rho⁰) mitochondrial DNA (mtDNA) exhibited phenotypic traits that differed from the parental (rho⁺) cells. To isolate genes whose expression is associated with mtDNA depletion, we constructed cDNA libraries from mRNAs isolated from chicken rho⁺ cells transformed by the MC29 (v-myc-containing) retrovirus and from rho⁰ cells developed by long-term exposure of the rho⁺ cells to ethidium bromide (EtdBr). Through subtractive hybridization procedures, three genes, elongation factor 1α (EF- 1 α), β-actin and v-myc were identified and found to be up-regulated in rho⁰ cells. In addition. Northern analysis demonstrated that the mRNA content for GAPDH was also elevated in rho⁰ cells. Run-on transcription assays and mRNA stability studies in the presence of actinomycin D indicated that elevated expression of these four genes depends, at least in part, upon increased rate of transcription. Other regulatory mechanisms contribute to the elevated expression of the transcripts in rho⁰ cells, as suggested by cycloheximide enhancement of the accumulation of the mRNAs for EF-1α and β- actin in rho⁰ cells, but not in parental rho⁺ cells. Moreover, inhibition of mtDNA replication and transcription by EtdBr and inhibition of translation on mitoribosomes by chloramphenicol also increased the expression of the four genes in parental rho⁺ cells, thus mimicking the situation in rho⁰ cells. These data suggest that information encoded within mtDNA participates in the regulation of nuclear genes in chicken cells.