Mitochondrial Genome-Encoded ATPase Subunit 6+8 mRNA Increases in Human Hepatoblastoma Cells in Response to Nonfatal Cold Stress

• Published in: Cryobiology 2000-03, Vol.40 (2), p.92-101
• Main Authors: Ohsaka, Yasuhito, Ohgiya, Satoru, Hoshino, Tamotsu, Ishizaki, Kozo
• Format: Article
• Language: English
• Subjects: actinomycin D; Apoptosis; ATPase subunit 6+8; Biological and medical sciences; cell growth; chloramphenicol; cold; Cold Temperature; DNA Replication; DNA, Complementary - genetics; DNA, Mitochondrial - genetics; Enzyme Induction; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Neoplastic; Hepatoblastoma - enzymology; Hepatoblastoma - pathology; HepG2; Humans; Liver Neoplasms - enzymology; Liver Neoplasms - pathology; Liver. Bile. Biliary tracts; mitochondrial genome; protein synthesis; Proton-Translocating ATPases - genetics; RNA synthesis; RNA, Messenger - biosynthesis; RNA, Neoplasm - biosynthesis; Stress, Physiological - genetics; Stress, Physiological - metabolism; subtraction; Subtraction Technique; Tumor Cells, Cultured - enzymology; Vertebrates: digestive system
• ISSN: 0011-2240; 1090-2392
• DOI: 10.1006/cryo.2000.2237

Cellular responses to cold stress have not been well clarified, compared with heat shock responses, especially in mammalian cells. We investigated cold-stress responses in human hepatoblastoma cells (HepG2) exposed to a nonfatal temperature of 17°C. Under the condition, RNA and protein syntheses in the cells were highly, but incompletely, depressed and cell growth was impaired. A cDNA subtraction method was used to isolate mRNAs for which the levels were increased in cold-stressed cells compared with cells cultured at 37°C. A transcript isolated by the screening was identified as ATPase subunit 6+8 mRNA that encodes components of a mitochondrial ATPase complex and that is transcribed from a mitochondrial genome. The copy number of the mitochondrial genome in cells was not changed by cold stress. Thus, HepG2 cells were treated with various concentrations of actinomycin D and chloramphenicol to assess the effects of transcriptional and translational reduction on the increased level of the ATPase subunit 6+8 mRNA. The mRNA level was increased in cells treated with low concentrations of the RNA or protein synthesis inhibitors. These results indicate that the increase in ATPase subunit 6+8 mRNA stimulated by cold stress could be mediated by a partial decline of transcription and/or translation in the cells. In addition, the degradation of ATPase subunit 6+8 mRNA was suppressed in cold-stressed cells compared with that in 37°C-cultured cells. This result implies that posttranscriptional regulation is also involved in the cold-stimulated increase in ATPase subunit 6+8 mRNA in HepG2 cells.