Induction of thermotolerance and heat shock protein synthesis in normal and respiration-deficient chick embryo fibroblasts

Normal and transformed chick embryo cells and their respective ethidium bromide-treated derivatives that are devoid of a functional respiratory chain were comparatively evaluated for their responses to hyperthermia treatment. No significant difference was found between the control and the respiration-deficient cells. The cells have a similar intrinsic thermosensitivity as judged by their capacity to form colonies after treatment at supraoptimal temperatures, and heat triggers in both cases an equal production of heat shock proteins and a strong induction of thermotolerance. In addition, sodium arsenite, carbonyl cyanide m-chlorophenylhydrazone, oligomycin, and antimycin A induce a similar heat shock protein response in the control and the treated cells. Based on these results, it is concluded that the inhibition by heat of the mitochondrial energy production does not constitute an obligatory rate-limiting event in hyperthermic cell killing and that the intracellular signal triggering development of thermotolerance or heat shock protein production does not obligatorily originate from damages to the respiratory chain. Moreover, the results indicate that the modifications responsible for the increased heat resistance of thermotolerant cells may not, or do not necessarily, involve a stabilization of the mitochondrial energy production.

Uroporphyria development in cultured chick embryo fibroblasts long-term treated with chloramphenicol and ethidium bromide

Long-term chloramphenicol- and ethidium bromide-treated chick embryo fibroblasts synthesize large amounts of porphyrins from exogenously added delta-aminolevulinic acid. The porphyrins consist mainly of uro- and heptacarboxyporphyrins and are retained within cells. Uroporphyria development is a time-dependent process which accompanies a step-wise decrease in the capacity of the mitochondrial respiratory chain. Upon removal of chloramphenicol from the medium, the pattern of porphyrin production readily returns to normal (mainly proto- and coproporphyrins found in the medium) while ethidium bromide-treated cells remain uroporphyric. The results suggest that impairment of mitochondrial functions in chicken by xenobiotics leads to uroporphyria development.

On auxotrophy for pyrimidines of respiration-deficient chick embryo cells

Chick embryo cells treated with chloramphenicol are inherently resistant to the growth-inhibitory effect of the drug when cultured in the presence of tryptose phosphate broth. The cells were found to be auxotrophic for pyrimidines and the presence in the broth of compounds of pyrimidine origin is demonstrated by chromatographic procedures and mass spectral analyses. They are in the form of ribonucleosides, ribonucleotides and pyrimidine-containing oligoribonucleotides. To understand the mechanism responsible for pyrimidine auxotrophy, the activity of enzymes involved in the pyrimidine biosynthetic pathway was determined. Measurement of the conversion of dihydroorotic acid to orotic acid in cell-free extracts revealed that chloramphenicol-treated chick embryo cells are deficient in dihydroorotate dehydrogenase activity. The data in vitro are supported by studies on the nutritional requirements of the respiration-deficient cells and by the incorporation in vivo of labelled dihydroorotic acid into the acid-insoluble fraction of the cells. Although the activity of the dehydrogenase in vitro is decreased by 95%, the enzyme is present in chloramphenicol-treated cells and its activity is unmasked by the artificial electron acceptor menadione. A study of the activity of other enzymes of the pyrimidine biosynthetic pathway demonstrated that their activity is comparable to that in control cells. The present results indicate that auxotrophy for pyrimidines results from the inhibition of the flow of electrons along the mitochondrial electron transport chain.

On the contribution of the mitochondrial genome to the growth of Chinese hamster embryo cells in culture

The present results demonstrate that Chinese hamster embryo cell populations in culture can be adapted to grow in the presence of chloramphenicol. It is shown that tryptose phosphate broth and uridine, one of its components, prevent the growth inhibitory effect of the drug. Study of some respiratory parameters (cytochrome c oxidase, cytochrome spectra, oxygen consumption) indicated that neither the broth nor uridine prevented the inhibitory effect of chloramphenicol on mitoribosomal protein synthesis. The cells grew with mitochondria devoid of a functional respiratory chain. Auxotrophy for pyrimidines appeared to result from the absence of dihydroorotate dehydrogenase, a respiratory chain-linked enzyme that catalyzes the fourth step of de novo pyrimidine biosynthesis. These and other results suggest that the synthesis of orotic acid may be considered as one of the main contributions of mitochondria to the growth of animal cells in culture.

On suppression of tumorigenicity in hybrid and cybrid mouse cells

The contribution of cytoplasm in the suppression of tumorigenicity was examined in cybrids constructed by fusing whole tumorigenic mouse mammary cells (Balb/c, cell line C2B2 from line MT29240) with enucleated nontumorigenic cells (BALB/c, cell line THOC from clone A31). Chloramphenicol resistance was used as a cytoplasmic marker in selecting the cybrids. Hybrids from parental nonenucleated cells were also isolated and analyzed for the expression of tumorigenicity. A reduction of the tumorigenic capacity in terms of tumor incidence and latency was clearly expressed in most of the cybrid clones studied. In the cybrids, saturation density and colony formation in agarose was also reduced. In most of the hybrid clones studied, a reduction was also observed in the tumorigenic capacity but not in saturation density or anchorage independence.

On the effect of inhibitors of mitochondrial macromolecular-synthesizing systems and respiration on the growth of cultured chick embryo cells

We have found that chick embryo fibroblasts (DEF) cultivated in the presence of tryptose phosphate broth (TPB) are inherently resistant to the growth inhibitory effect of ethidium bromide (EB). As demonstrated by cytochrome oxidase activity and oxygen consumption measurements, analyses of reduced-minus-oxidized cytochrome spectra and electron microscopic observations, TPB did not seem to prevent the inhibitory effect of EB on mitochondrial DNA transcription. EB-treated chick cell populations cultivated in the presence of TPB behave essentially the same as populations treated with chloramphenicol (CAM) and grow with mitochondria devoid of a functional respiratory chain. In contrast to CAM-treated CEF populations, however, the respiratory activity of EB-treated cell populations did not reappear when the cells were shifted back to EB-free medium. Attempts to demonstrate that TPB confers resistance to the growth inhibitory effect of carbomycin and mikamycin, inhibitors of the mitochondrial protein-synthesizing system, have failed, the drugs being cytotoxic at doses where protein synthesis on mitoribosomes is not suppressed. On the other hand, the present results demonstrated that chick cell populations proliferate in the presence of the respiratory inhibitors rotenone, antimycin A, amytal and oligomycin whether or not TPB is present in the growth medium.

On the adaptation of cultured chick embryo cells to growth in the presence of chloramphenicol

We have found that tryptose phosphate broth (TPB) prevents the inhibitory effect of chloramphenicol (CAM) on the cell proliferation of chick embryo fibroblasts. Study of growth parameters indicated that no lag or adaptation period appeared necessary for TPB-exposed chick cell populations to grow in the presence of CAM suggesting that a particular cell type was not selected. TPB did not prevent the inhibitory effect of CAM on the mitochondrial protein-synthesizing system. This was supported by cytochrome oxidase activity measurements, studies on the incorporation of 35S-metionine into mitochondrial proteins, electron microscopic observation of alterations in mitochondrial structure. Oxygen consumption was reduced by 95% and cyanide, 2-4-dinitrophenol, and salicylhydroxamic acid do not significantly affect the residual respiration. Analyses of reduced-minus-oxidized-cytochrome spectra of CAM-treated chick cells demonstrate the disappearance of the absorption bands of cytochromes aa3, b559, c1, and c. The presence of a type b cytochrome with maxima at 552 and 557 nm was observed. The results obtained indicate that long-term cultures of CAM-treated chick embryo cells cultivated in the presence of TPB grow with mitochondria devoid of a functional respiratory chain.

Studies of the effect of chloramphenicol, ethidium bromide and camptothecin on the reproduction of Rous sarcoma virus in infected chick embryo cells

A function for mitochondria in the reproduction of Rous sarcoma virus (RSV) in chronically and newly infected chick embryo cells was studied by using chloramphenicol and ethidium bromide. Chloramphenicol (CAM) and ethidium bromide (EB) were both shown to decrease the rate of growth of infected chick embryo cells and to inhibit the synthesis of mitochondrial macromolecules. Both drugs however had little or no effect on the incorporation of labelled leucine, thymidine and uridine into total cellular macromolecules. Neither CAM (80 microgram/ml) nor EB (0.4 microgram/ml) inhibited the production of infectious virus. In contrast, camptothecin, an inhibitor of cellular but not mitochondrial macromolecular synthesis, was shown to depress the production of infectious virus. The results indicate that the mitochondrial macromolecular synthesis machinery of RSV-infected chick embryo cells does not contribute to virus production.

Protein content and enzyme levels of cultured chick embryo cells treated with camptothecin and actinomycin D

The alkaloid camptothecin uncouples the growth and adivision of chick embryo cells. At a moderate dose (0.5 microgram/ml) it inhibits the incorporation of thymidine but not of uridine and leucine and the cell protein content increases and reaches twice that of control after 4 days of treatment. Twelve hours after addition of the drug, the activities per cell of the mitochondrial enzymes poly A hydrolase (EC 3.1. 4.21), cytochrome c oxidase (EC 1.9.3.1), and succinate dehydrogenase (EC 1.3.99.1) are greater than that of the control and keep increasing for at least 96 H. The increase in the activities of the mitochondrial enzymes precede that of NADPH-cytochrome c reductase (EC 1.6.2.4) and cytidine triphosphatase (EC 3.6.1.15), which are microsomal and plasma membranes enzymes respectively. Actinomycin D (0.01 microgram/ml) also inhibits the multiplication of the chick cells and the synthesis of DNA. The protein content of the actinomycin D treated cells decreases to 70% of the control by day 2. Nevertheless, the activities of the mitochondrial enzymes increase over that of the control but to a smaller extent that with camptothecin. The activities of the enzymes of the other organelles are not stimulated. Camptothecin at a higher dose (5.0 microgram/ml) induces effects similar to those of actinomycin D.

Long-term cultures of chick embryo fibroblasts transformed by the Schmidt-Ruppin strain (D) of Rous sarcoma virus

Attempts have been made to keep in vitro, for extended periods of time, cultures of chick embryo fibroblasts transformed by the Schmidt-Ruppin strain of Rous sarcoma virus, subgroup D. Roller cultures of transformed chick cells kept in serum-deficient medium can be maintained without subcultivation for up to 6 months. The confluent cultures continuously release viruses and viable tumor cells into the medium. The released cells can be plated and have characteristics of growth and morphology which are relatively stable with time until the culture degenerates. Cells released at later stages of the culture produced substantially more viruses than those released earlier, suggesting that cell selection or differentiation occurs during long-term cultivation in low serum concentration. Long-term cultures of untransformed chick embryo fibroblasts can also be maintained in the same way. The release of viable cells by these confluent cultures, however, is negligible.

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.

Pancreatic-like ribonuclease activity in the ascites fluid of the Novikoff and Ehrlich tumors

The ascitic fluid of Novikoff and Ehrlich tumors contains a pancreatic-like ribonuclease. The enzyme catalyzes the hydrolysis of natural RNA and that of the synthetic pyrimidine (poly U, poly C) but not (poly A, poly G) or slightly (poly I) purine polymers. The synthetic duplex molecules poly I: poly C and poly A: poly U are rather resistant to hydrolysis.

The histochemical demonstration of nuclease activity with films of soluble ribonucleic acid and polyadenylic acid

Films of soluble ribonucleic acid (sRNA) and polyadenylic acid (poly-A) were used to investigate the distribution of nuclease activity in normal rat tissues. The reactions obtained with films of sRNA were similar to those previously observed with standard RNA and both substrates apparently reveal the same group of nucleases. On the other hand, the distribution of enzyme activity shown by films of poly-A differed markedly from that observed with RNA films, and it appears that films of poly-A demonstrate a different group of nucleases.