Nonlethal G0-ts mutant tsJT60 becomes lethal at the nonpermissive temperature after transformation: a hint for new cancer chemotherapeutics

tsJT60 is a nonlethal temperature-sensitive (ts) mutant of a Fischer rat cell line (3Y1) classified as a G0 mutant; i.e., the ts defect is not expressed within the cell growth cycle but is expressed only between the G0 and S phase. tsJT60 clones transformed with oncogenes such as adenovirus E1A, polyoma large T, polyoma middle T, v-Ki-ras, and LTR activated c-myc, or with a chemical carcinogen N-methyl-N'-nitro-N-nitrosoguanidine, grew well at 34 degrees C. However, most of these clones grew slowly at 40 degrees C, producing many floating dead cells, and some clones were killed at 40 degrees C. When they were cultured under conditions inadequate for growth of untransformed cells, such as high cell density or serum restriction, they were killed at 40 degrees C. These and previous results from SV40- and adenovirus-transformed tsJT60 clones favour the idea that transformed tsJT60 cells occasionally enter the G0 phase and are metabolically imbalanced at 40 degrees C during self-stimulation from the G0 to S phase. We propose that a drug which exclusively block, G0-G1 transition would be cytocidal to transformed cells but cytostatic to normal cells.     

Immune response to Toxoplasma gondii--analysis of suppressor T cells in a patient with symptomatic acute toxoplasmosis

Unresponsiveness of antigen-dependent (Toxoplasma-specific and purified protein derivative of tuberculin [PPD]-specific) T-cell proliferative responses of peripheral blood leukocytes (PBL) was observed in a patient with symptomatic acute toxoplasmosis. The immunosuppression of T-cell responses was mediated by Leu 1+, Leu 2a+, and Leu 3a- suppressor T cells that were induced by Toxoplasma gondii antigen and suppressed both Toxoplasma-specific and PPD-specific PBL T-cell responses from a patient with chronic toxoplasmosis when PBL of these patients were mixed and cocultured in vitro. Participation of class II molecules of HLA in Toxoplasma-specific proliferative T-cell responses and activation of suppressor T cells was examined by using monoclonal antibodies specific for HLA-DR and HLA-DQ molecules. Anti-HLA-DQ monoclonal antibody released the suppressive activity, while anti-HLA-DR monoclonal antibody inhibited Toxoplasma-specific T-cell responses. Thus, the suppressive effect of PBL from a patient with acute toxoplasmosis on antigen-dependent PBL T-cell responses from a patient with chronic toxoplasmosis was mediated by HLA-DQ molecules. By contrast, Toxoplasma-specific T-cell responses were activated by HLA-DR molecules (presumably present on antigen-presenting cells).     

Holocene sedimentary history of some coastal plains in Hokkaido,Japan IV. Diatom assemblages in the sediments from Kushiro moor (2)

Diatom assemblages of sediments obtained from three sites on Kushiro Moor were analyzed to investigate the Holocene sedimentary history. The results showed that: 1) The Takkobu site was originally at the bottom of the paleo-Kushiro Bay, and after-wards the paleo-Takkobu Lagoon developed, became sealed off, and changed to a freshwater lake. The succession to peat moor probably began about 2000 yr B.P. at the Takkobu site. 2) The Tsurui site was originally at the bottom of the paleo-Kushiro Bay, then changed to the paleo-Kushiro Lagoon and became peat moor as a result of the first Holocene regression, which finished about 3600 yr B.P. The site then returned to a brackish lake again, probably due to the second Holocene transgression between 3600 and 3000 yr B.P., thereafter passing through brackish lake and freshwater lake stages, and eventually becaming peat moor at about 2000 yr B.P., 3) At the Chuo site, the second paleo-Kushiro Bay developed again as a result of the second Holocene transgression, which finished about 3000 yr B.P. Thereafter, brackish or freshwater lakes, rivers, and then peat moor developed in the central area of Kushiro Moor. 4) The second marine diatom zone (MD₂ Zone), which indicates the second Holocene transgression, complete by about 3000 yr B.P., is detected only at the Chuo site in the central area of Kushiro Moor.     

Transformation by viral and cellular oncogenes of a mouse BALB/3T3 cell mutant resistant to transformation by chemical carcinogens.

The mouse cell line MO-5 is resistant to transformation by various chemical carcinogens and also by UV irradiation (C. Yasutake, Y. Kuratomi, M. Ono, S. Masumi, and M. Kuwano, Cancer Res. 47:4894-4899, 1987). Northern (RNA) blot analysis showed active expression of ras and myc genes in MO-5 and BALB/3T3 cells. The effect of transfection of various oncogenes on transformation was compared in MO-5 cells and parental BALB/3T3 cells. Activated c-H-ras, c-N-ras, and v-mos gene induced transformation foci of MO-5 and BALB/3T3. Introduction of the polyomavirus middle T-antigen (mTag) or the Rous sarcoma virus-related oncogene v-src, however, efficiently transformed BALB/3T3 but not MO-5 cells. Expression and phosphorylation of mTag and the associated c-src proteins were observed in mTag-transfected clones of MO-5 as in BALB/3T3 and phosphorylation of the src protein was observed in v-src-transfected BALB/3T3 and MO-5 clones. Hybrids between mTag- or v-src-induced transformants of BALB/3T3 and untransformed MO-5 maintained the transformation phenotype, suggesting that no dominant suppressor of transformation exists in MO-5. A hybrid clone between BALB/3T3 and MO-5 induced efficient transformation foci after transfection with the mTag gene, suggesting that the deficient transformation phenotype of MO-5 was recessive. Instead, some other alteration of MO-5, plausibly membrane function, might lead to abortive transformation by chemical carcinogens and also by mTag and the v-src gene product.     

Electron-microscopic studies on the threshold value of calcium concentration for the release of storage granules and the acceleration of their degradation in the rat parathyroid gland

Summary To determine both a threshold value of calcium concentration (CC) for the release of storage granules and that for the acceleration of degradation of these granules, the rat parathyroid glands were perfused in situ with HEPES-Ringer solutions containing different concentration of Ca²⁺ for 10 min. With perfusates containing 0.83–1.21 mM Ca²⁺ (equivalent to 8–11 mg/dl serum calcium), the number of type-I storage granules (large core) [NSG-I] and that of type-II storage granules (small core) [NSG-II] remained unchanged. With perfusates containing 0.83 mM Ca²⁺ (7.5 mg/dl) or less, however, both NSG-I and NSG-II decreased remarkably and the former was larger than the latter. On the contrary, with perfusates containing 1.27 mM Ca²⁺ (11.5 mg/dl) or more, NSG-II increased and the ratio of NSG-I to NSG-II was changed reversely. We concluded that a thereshold value of CC required for the release of storage granules may be present between 0.88 and 0.83 mM Ca²⁺ (8 and 7.5 mg/dl) and that a threshold value of CC for accelerating the transformation of type-I granules into type-II, the degradation of storage granules, may be situated at about 1.27 mM Ca²⁺ (11.5 mg/dl). Additionally, it was suggested that both prosecretory and storage granules are not only formed at the innermost Golgi cisterna but also at the trans-Golgi network.     

A monoclonal antibody to the carbohydrate chain on human hepatocellular carcinoma-associated antigen which suppressed tumor growth in nude mice

Summary There have been few reports stating that monoclonal antibody alone inhibits human solid tumor growth in vivo. The present study demonstrated that monoclonal antibody S1 (IgG2a), which recognized the antigenic determinant of the carbohydrate moiety, showed antibody-dependent cell (or macrophage)-mediated cytotoxicity (ADCC or ADMC) in conjunction with murine splenocytes of both BALB/c and athymic mice. In vivo experiments demonstrated that the antibody S1 clearly prolonged the survival of athymic mice which had been inoculated with a human liver carcinoma cell line. In addition, the antibody S1 significantly suppressed the human hepatoma line transplanted s.c. into nude mice. ¹²⁵I-Labeled monoclonal antibody S1 revealed that the antibody accumulated significantly in the tumor mass. Many mononuclear cells were observed surrounding tumor cells when the antibody was given. This model system might be useful for analyzing the ADCC (or ADMC) mechanism in vivo.     

Ca2+-dependent Cl− efflux in tonoplast-free cells ofNitellopsis obtusa

Summary In order to demonstrate the presence of a Ca²⁺-activated Cl^–-channel in theNitellopsis plasmalemma, tonoplast-free cells were prepared and their intracellular Ca²⁺ concentration was modified by internal perfusion. An increase in the Ca²⁺ concentration caused a large Cl^– efflux with a concomitant depolarization of the membrane potential. These changes were for the most part reversible. The critical Ca²⁺ concentration was about 4.0 m. Neither the Cl^– efflux nor the membrane depolarization showed a time-dependent inactivation. A Cl^–-channel blocker, A-9-C (9-anthracenecarboxylic acid) reduced both the Cl^– efflux and the magnitude of the membrane potential depolarization. A small increase in the intracellular Ca²⁺ concentration, which is caused by membrane excitation of tonoplast-free cells is not sufficient to activate this Ca²⁺-dependent Cl^–-channel.     

Induction of Cytoplasmic Streaming and Movement of Chloroplast Induced by L-Histidine and its Derivatives in Leaves of Egeria densa

Rotational cytoplasmic streaming in leaves of Egeria densa wasinduced by light as well as by L-histidine (L-His). During bothtreatement with light and with L-His chloroplasts on the periclinalface were dislodged and moved to the anticlinal face where rotationalcytoplasmic streaming occurred. The effective concentrationof L-His was about 0.01 mM and the effect was almost saturatedat 0.1 mM. A derivative of L-His, 3-methyl-L-histidine, wasslightly less effective than L-His. By contrast, 1-methyl-L-histidinewas almost ineffective for induction of streaming, not onlyin Egeria but also in Vallisneria. Our resutlts are in markedcontrast to Fitting's result (1936) that 1-M-L-His is more effectivethan L-His. In Egeria, 1-methyl-L-His counteracted the stimulativeeffect of L-His. 1-Methyl-L-His penetrated into leaf cells ofEgeria to the same extent as 3-methyl-L-His and to a greaterextent than L-His. This observation excludes the possibilitythat the impermeability of leaves to 1-M-L-His might be responsiblefor its ineffectiveness. 1-M-L-His did not interfere with photodinesis.Differences in the mechanism of induction of rotational streamingby L-His and by light are discussed. ⁴ Present address: Fukui Institute of Technology, Gakuen, Fukui,910 Japan (Received July 16, 1990; Accepted December 20, 1990)