Enhanced transcription of mitochondrial genes after growth stimulation and glucocorticoid treatment of Reuber hepatoma H-35

When a serum-deprived culture of Reuber hepatoma H-35 cells was stimulated by serum, cells proliferated synchronously showing a peak of [³H]thymidine incorporation within 16 h and doubling of cell number within 24 h. A 5-10-fold increase of mRNAs of mitochondrial genes was observed prior to S-phase by Northern hybridization of total cellular RNA with cloned fragments of rat mitochondrial DNA as probes. In organelle transcription by mitochondria isolated from growth-arrested or growth-stimulated cells suggested that the increase of mitochondrial mRNAs was mainly due to enhanced transcription. Less enhanced transcription was observed by treating the cells with dexamethasone, which causes translocation of large amount of protein into mitochondria. The latter effect was counteracted by insulin.