Mitochondrial biogenesis in human fibroblasts

Inherent resistance of HeLa cell derivatives to paromomycin

The human tumor-derived cell line HeLa S3 and nuclear and mitochondrial gene mutants derived from it are resistant to the aminoglycoside antibiotic, paromomycin (PAR). Other carcinoma-derived cells, SV40-transformed cells, and four human diploid fibroblast cell lines are all sensitive to PAR. Sensitivity is dependent on cell density, and at cell numbers greater than 400/cm2 sensitive cells will proliferate in PAR. The resistance to PAR is inherited in a dominant manner in cell-to-cell fusion hybrids, but is not transferred in cytoplast-to-cell fusions. PAR resistance is therefore encoded by a nuclear gene(s). Resistance to PAR is not caused by changes in the response of mitochondrial or cytoplasmic protein synthesis to PAR in vitro. The uptake of PAR is similar in resistant and sensitive cells, and dimethyl sulfoxide does not render resistant cells more sensitive. Thus, HeLa cell PAR resistance is unlike previously reported ribosomal mutations and may derive from differences in the intracellular metabolism of PAR.

Mitochondrial biogenesis in cultured animal cells. I. Effect of chloramphenicol on morphology and mitochondrial respiratory enzymes

The effects of chloramphenicol on the morphology and respiratory enzymes of BHK-21 cells in spinner culture have been examined with time. Cells treated with chloramphenicol double twice before growth ceases; these cells have increased size as measured by several techniques. Mitochondria are enlarged and appear to degenerate with prolonged treatment. Cytochrome c oxidase and succinate cytochrome c reductase activities are reduced while there is no decrease in the activities of monoamine oxidase, glutamate dehydrogenase or NADPH-cytochrome c reductase. Cytochromes aa3 and b disappear on treatment while cytochromes c + c1 appears to be unaffected. All these effects are reversible if chloramphenicol is removed within a limited period of time.

Mitochondrial biogenesis in cultured mammalian cells. II. Mitochondrial protein and phospholipid synthesis in chloramphenicol-treated BHK-21 cells

The effect of growth of BHK-21 cells in chloramphenicol on the synthesis of cellular proteins and phospholipids has been examined. The incorporation of leucine into total cellular proteins, or into the proteins of specific subcellular fractions are not significantly reduced by cell culture in the presence of chloramphenicol. In cells treated with cycloheximide, a small amount of chloramphenicol-sensitive labelling of protein was detected within the first hour of exposure to the drug. Chloramphenicol inhibits the incorporation of delta-amino-levulinic acid into hemoproteins, only if it is present during both the 48-h culturing and 4-h labelling period. De novo synthesis of cellular lipids as measured by pulse labelling with 32Pi or [3H]glycerol, is decreased in chloramphenicol-treated cells. This decrease is observed in all sub-cellular fractions, although the mitochondrial fraction is most affected. All phospholipids are affected, with diphosphatidylglycerol labelling reduced to the greatest extent. Although fatty acid synthesis is inhibited, the labelling of diphosphatidylglycerol with fatty acids is stimulated on chloramphenicol treatment.

Poly(A) hydrolase of chick-embryo fibroblasts

1. Homogenates of cultured chick embryo fibroblasts have been quantitatively fractionated by differential centrifugation. Using cytochrome c oxidase, succinate dehydrogenase, acid phosphatase and NADPH-cytochrome c reductase as marker enzymes, poly(A) hydrolase has been shown to be a mitochondrial enzyme. 2. To test the biosynthetic origin of mitochondrial poly(A) hydrolase and to demonstrate its cytoplasmic site of synthesis, we have treated the cells with ethidium bromide, inhibitor of mitochondrial transcription, and chloramphenicol and cycloheximide, inhibitors of mitochondrial and cytoplasmic translations respectively. The activity of poly(A) hydrolase has been compared to that of succinate dehydrogenase, an enzyme coded for by the nuclear genome and that of cytochrome c oxidase, an enzyme coded for partly by the nuclear genome and partly by the mitochondrial genome. The results obtained indicate that in chick embryo fibroblasts poly(A) hydrolase is an enzyme coded for by the nuclear genome. Further, the hydrolase is synthesized on cytoplasmic ribosomes and has a half-life much shorter than succinate dehydrogenase and cytochrome c oxidase.