Correlation between cell enlargement and nucleic acid and protein content of HeLa cells in unbalanced growth produced by inhibitors of DNA synthesis

Selective lethal effect of thymidine on human and mouse tumor cells

Human cell lines derived from a melanoma and a colon carcinoma, and cultures of human melanocytes and intestinal epithelial cells, as well as a mouse mesenchymal non-neoplastic cell line and a malignant subline of the same have been quantitatively studied in tissue culture for their sensitivity to thymidine. All three tumor lines produced solid tumors when injected into nude thymus-deficient mice. No tumors were obtained by injecting cells of the human normal long-term cultures or the non-neoplastic mouse line. The tumor-producing lines showed a greater sensitivity to the lethal effects of high concentrations of thymidine than their non-tumor-producing counterparts. Less than 23% of the tumor cells survived 72 hours in the presence of 1 mg/ml of thymidine, in contrast to 60% or more of the non-tumor cells. Colony formation was much more inhibited by thymidine and the differential between normal and tumor cells was even more pronounced. Tumor cells which also were treated for 72 hours with 1 mg/ml of thymidine and then plated in fresh medium formed very few colonies. If the plating efficiency of the untreated controls is considered as 100%, 4.3% or less of the treated tumor cells formed colonies, in contrast to 33% or more of the non-tumor cells.

The mutagenic activity of hydroxyurea in Chlamydomonas reinhardi

Hydroxyurea, an inhibitor of ribonucleotide reductase, increases the frequency of streptomycin resistant mutants in liquid cultures of Chlamydomonas reinhardi after 45 h incubation. After more prolonged incubation in hydroxyurea medium the frequency of streptomycin resistant mutants declines. This may be due to the slower growth rate of streptomycin resistant mutants compared to wild type cells in hydroxyurea containing medium. Studies on solid medium show that both the rate of forward mutation to streptomycin resistance and reverse mutation to nicotinamide independence are increased several fold by growth on hydroxyurea.

Cell mitotic cycle synthesis of NIL hamster glycolipids including the Forssman antigen

The synthesis of phospholipids and glycolipids during the cell mitotic cycle of an established hamster line, NIL, has been studied. Cells were synchronized with excess thymidine and mitotically harvested by shaking. Cells were radioactively labeled for 4 h with palmitate, glucosamine, or galactose. Lipids were analyzed by thin-layer chromatography. As cells progressed through the mitotic cycle, incorporation into phospholipids increased but the fraction represented by each remained constant. Similarly, ceramide monohexoside, dihexoside, and hematoside were labeled equally in all phases. Ceramide trihexoside and tetrahexoside were labeled only during G(1) and S. Ceramide pentahexoside (the Forssman antigen) shows density-dependent synthesis, accumulation, and reactivity. Ceramide pentahexoside was labeled during all phases of the mitotic cycle but the rate of incorporation decreased in S and G(2). The total amount of lipid assayed immunologically in cell extracts gradually increased. Exposure of the Forssman antigen in untreated or trypsin-treated cells was studied using binding of chemically labeled antiForssman antiserum. The amount of antigen detected in trypsinized cells increased during G(1) and early S but then remained constant. Mitotic cells exposed all detectable antigen. As cells progressed through the mitotic cycle, a large fraction of the Forssman antigen became cryptic.

The cytostatic action of extracellular NAD in tumour-bearing mice

Repeated injections of NAD led to a dose-dependent inhibition of cell proliferation in tumour-bearing mice (Ehrlich ascites carcinoma and a murine mastocytoma). NAD proved clearly superior to other adenine nucleotides, including 3',5'-cyclic AMP. Experiments with differently labelled NAD and studies on HeLa cultures showed that NAD is relatively slowly degraded by extracellular enzymes to AMP and adenosine, which probably represents the true cytostatic agent.The superiority of NAD in vivo to other adenine nucleotides and to adenosine itself can be explained by the rate-limiting hydrolysis of NAD to AMP with a sustained production of cytostatic concentrations of adenosine. This may represent a new kind of "poisoning" by a potentially cytostatic compound brought about by the action of extracellular enzymes.

Cell growth in the absence of division in a root meristem

In the presence of 10(-2) M hydroxyurea cell division is prevented but cell growth continues. The rate of cell growth varies within the apex, depending on the location of the cell. The rate of growth is low in the quiescent centre and non-dividing region of the root cap but higher elsewhere.Indolyl acetic acid causes a transient increase in the rate of cell enlargement but after about 12 hours has no further effect.

Kinetics of cell volume changes of murine lymphoma cells subjected to different agents in vitro

Cell volume distributions obtained with an electronic particle analyzer were used to study the changes in volume of individual cells in the absence of cell division. Cultures of murine lymphoma (strain L5178-Y) cells in suspension were used in these studies. During a division delay following ionizing radiation, individual cells increased exponentially in volume with equal rate constants; these rate constants were indistinguishable from that describing the increase in cell number of an unirradiated population. When an originally log phase population of cells was prevented from increasing in number by inhibitors of DNA synthesis, individual cells increased exponentially in volume for about one generation time with the same rate constant as observed after exposure to ionizing radiation; thereafter, only the cells defining the upper half of the volume distribution continued to increase in volume, and they apparently did so with a first order rate constant proportional to their amount of DNA exceeding that present in one diploid complement of chromosomes in G(1). Cells arrested in mitosis with colchicine increased in volume for approximately 4 hr after which they remained constant in volume for almost one generation time; eventually these cells again increased in size. Inhibitors of protein and RNA synthesis inhibited the cell volume growth of irradiated cells.