EFFECTS OF PUROMYCIN ON THE NUCLEOPROTEINS OF THE HELA CELL

The nature of unbalanced cell growth caused by cytotoxic agents

The volume of cells grown in tissue culture following exposure to a wide variety of cytotoxic drugs or x-rays increases at a rate of 1 to 10% of cell mass per hour. The same phenomenon is seen in animal neoplasias and human leukemias. This increase in cell volume is the result of unbalanced cell growth with a resulting disproportionate synthesis of proteins and possibly other macromolecules in the cytoplasm and nucleus. The dose response curve for a decrease in cell survival as measured by cloning efficiency in tissue culture is quantitatively correlated with the dose response curve for inducing an increase in cell volume. This quantitative relationship makes feasible the use of the phenomenon of unbalanced cell growth as a measure of cell death in screening for cytotoxic drugs or in monitoring response to therapy. An hypothesis to explain this increase in cell volume following chemotherapy is that cells are by the action of these drugs induced into an abortive or unbalanced pseudo-cycle which is characterized by synthesis of substantial amounts of protein without other preparative steps for cell division.

Inhibitor induced alterations of chromatoid bodies in male germ line cells of Xenopus laevis

The action of inhibitors of protein synthesis on the structure of cytoplasmic inclusions found in the male germ cell line of the anuran, Xenopus laevis, has been studied by light and electron microscopy. Results indicate that one such inclusion, the chromatoid body, is sensitive to treatment with either chloramphenicol or puromycin. These drugs administered in vivo or in vitro cause up to a thirty-fold increase in the volume of the chromatoid body in all stages where it is normally present. Maximum size increase obtainable is the same for either drug, but is different and characteristic for each germ cell stage. Drug action is dose dependent, with "chromatoid body syndrome" occurring over a relatively narrow concentration range. Cyclohexamide, in contrast to chloramphenicol or puromycin, does not produce a clear increase in the size of chromatoid bodies, and is capable of blocking the action of the other drugs at normally effective concentrations. Results obtained in this investigation suggest that primary spermatogonia contain enough chromatoid body material to account for the total amount present in all subsequent germ cell stages. This fact, coupled with other studies where chromatoid-like bodies have been observed, suggests the hypothesis that the chromatoid body represents at least in part an aggregation stage of materials associated with the microtubule population of the germ cell line. Alternately, or in addition, ribonucleoprotein may contribute to the structure of the chromatoid body.

Effect of temperature of aldehyde fixation on the radioautographic localization of ribonucleoprotein in nucleoli of HeLa cells. Inhibition by puromycin and actinomycin D

In efforts to clarify the role of the nucleolus and substructures thereof in the assembly or synthesis of protein associated with formation of the complete ribosome, the effect of variation of some conditions of aldehyde fixation on the intranuclear distribution of lysine-(3)H, arginine-(3)H, and uridine-(3)H was studied by differential grain count in radioautographs of PPLO-free HeLa cells. It was found that the nucleolus is a site of rapid assembly or synthesis of a protein, the synthesis of which is inhibited equally by puromycin (200 microg/ml) and by actinomycin D under conditions inhibitory for ribosomal precursor RNA synthesis (P < 0.01). This protein is fixed by phosphate-buffered formalin or glutaraldehyde at pH 7.3, but the label is diminished by fixation in customarily employed acetic ethanol or in formalin at acid pH. Elevation of temperature of formalin or glutaraldehyde fixatives to 37 degrees C consistently reduces the nucleolar protein label, but not the RNA label, by a proportion identical with that incurred by puromycin or actinomycin inhibition. This proportional reduction of nucleolar protein label occurs without evident loss of total grain count and is independent of length of fixation between 30 min and 4 hr, but it is not observed at 23 degrees C. The data support the interpretation that the proportion of nucleolar protein not fixed at 37 degrees C is associated with nucleolar ribosomal RNA but that it is dissociated at 37 degrees C in formalin or glutaraldehyde fixatives, probably on the basis of ionic dissociation of a conjugated ribonucleoprotein.

Persistence of nucleoli in short term and long term cell cultures and in direct bone marrow preparations in mammalian materials

Persistent nucleoli were studied in Chinese hamster and human long term cultures, human peripheral blood short term cultures, as well as direct bone marrow preparations. No colchicine or hypotonic treatments were applied and the cells were differentially stained with the Feulgen method and light green. Nucleoli were found to persist in the three systems studied, although to a much greater extent in the long term culture. The persistent nucleolar materials were usually in the form of individualized nucleoli mainly at chromosome ends. They also sometimes existed in a fluidlike or dropletlike condition around the chromosomes. Association of acrocentrics in humans and end-to-end associations in hamsters are likely to result from persistence of nucleoli and the possible effects of colchicine and hypotonic treatments that are usually applied. Other phenomena, such as stickiness at metaphase and separation difficulties and fragmentation at anaphase, may result from persistence of nucleoli. Nucleoli were often associated with large chromosomes and sometimes at sites exhibiting faint or clear constrictions. The possibilities of a partial correspondence between sites of persistence and sites of organization, as well as of the organization of nucleolar materials at sites other than the main organizers, are discussed. The persistent nucleoli were not included in daughter nuclei. They either degenerated in the cytoplasm or were eliminated from the cell. The three systems used may represent different intensities of metabolism reflected in the amounts of nucleolar materials built up and the amount that persists.

Puromycin-induced necrosis of crypt cells of the small intestine of mouse

Chemical and radioautographic analysis of the small intestine of mice injected intraperitoneally with puromycin revealed an immediate decrease of precursor incorporation into DNA and protein and a delayed decrease of precursor incorporation into RNA. In addition to this decrease of precursor incorporation, damage to the crypt cells, but not to the cells of the villus of the small intestine, was observed. Further examination of other dividing cells (spleen) and nondividing cells (liver and heart) of these mice showed again that only cells of actively dividing tissues were damaged. The metabolic inhibitors actinomycin D, cytosine arabinoside, actidione, and puromycin aminonucleoside were used in an attempt to clarify the mechanism of cell damage by puromycin. The results showed that there was no clear correlation between cell necrosis and the pattern of inhibition of synthesis of DNA, RNA, or protein.

Relationship between RNA synthesis, cell division, and morphology of mammalian cells. I. Puromycin aminonucleoside as an inhibitor of RNA synthesis and division in HeLa cells

Logarithmically growing HeLa cell monolayers were treated with a range of concentrations of puromycin aminonucleoside (AMS). The effects of AMS were studied by the following means: microscope examination of treated cells; enumeration of the cell number using an electronic particle counter; analyses for DNA, RNA, and protein content; incorporation of P(32) and H(3)-thymidine into nucleic acids; and fractionation of nucleic acids by column chromatography. Taking the rate of incorporation of the isotopic precursor as a measure of nucleic acid synthesis, it was found that concentrations of the inhibitor which had a rapid effect on the rate of cell division inhibited the synthesis of all types of nucleic acids and of protein, but depressed ribosomal RNA synthesis most markedly. Lower concentrations of AMS selectively inhibited ribosomal RNA and, to a lesser extent, transfer RNA synthesis. Partial inhibition of ribosomal RNA synthesis with low doses had no effect on the rate of cell division within the period studied (3 generation times). The cell content of RNA returned to normal when the inhibitor was removed.

Studies of infectious bovine rhinotracheitis virus. II. Effect of metabolic inhibitors on virus multiplication

The suppression of infectious bovine rhinotracheitis (IBR) virus multiplication by certain metabolic inhibitors was studied. Viral inhibition with analogues of deoxyuridine and the reversal of this inhibitory effect by thymidine indicates a deoxyribose type of nucleic acid in IBR. Experimental evidence showed no difference in antigenic constitution between IBR and analogue-resistant IBR viruses.