Potent inhibition of cell density-dependent apoptosis and enhancement of survival by dimethyl sulfoxide in human myeloblastic HL-60 cells

Human myeloblastic cell line HL-60 cells undergo apoptosis during in vitro culture in a cell density-dependent manner, and this cell density-dependent apoptosis was observed when the concentration of cultured cells exceeded 8–10 × 10⁵ cells/ml. Dimethyl sulfoxide (DMSO), a differentiation inducer of HL-60 cells, did not amplify, but rather potently inhibited, this apoptosis. In a low density culture condition, DMSO attenuated proliferation of HL-60 cells in spite of its inhibition of apoptosis. In contrast, DMSO did support cell survival under high cell density conditions, and DMSO-treated HL-60 cells reached an extremely high concentration of 2–3 × 10⁶ cells/ml, a condition which could never be possible in a usual culture environment. Thus, DMSO exerted dual effects on cell proliferation, i.e., growth inhibition and apoptosis inhibition, and the sum of these effects resulted in an apparently distinct phenomenon according to the culture conditions including cell density. J. Cell. Physiol. 174:135–143, 1998. © 1998 Wiley-Liss, Inc.     

Bcl-2 down-regulation causes autophagy in a caspase-independent manner in human leukemic HL60 cells

To understand the roles of bcl-2 for the survival of leukemic cells, we constructed human leukemic HL60 transformant lines in which full length bcl-2 antisense message was conditionally expressed by a tetracycline-regulatable expression system. Cell growth was completely inhibited after antisense message induction and massive cell death was induced. Electron microscopic examinations show that cells died by autophagy, but not by apoptosis. The morphology and the function of mitochondria remained intact: neither the reduction in mitochondrial membrane potential nor the nuclear translocation of AIF, a mitochondrial protein that translocates to nuclei in cases of apoptosis, was observed. Caspase inhibitors did not rescue bcl-2-antisense-mediated autophagy. Thus, bcl-2 is essential for leukemic cell survival and its down-regulation results in autophagy. Cell Death and Differentiation (2000) 7, 1263 - 1269.     

Inbreeding depression of female fecundity by genetic factors retained in natural populations of a male-haploid social mite (Acari: Tetranychidae)

We previously determined that certain recessive genes decrease female fecundity in a haplo-diploid spider mite, Stigmaeopsis miscanthi (Saito). However, whether the depression was caused by the breakdown of heterosis or the expression of deleterious genes retained in a population could not be determined, because we had started our inbreeding experiment from a mixture of two isolated populations. In order to answer this basic question, inbreeding effects on survival and fecundity were measured for eight small populations occurring far from the two initial populations. There was little depression of immature survival of inbred lineages in all populations. On the other hand, in two inbred lineages, both originating from the smallest populations, female oviposition decreased significantly with the increase of Wrights f-value, showing that mildly deleterious genes are actually retained even in natural populations of haplo-diploid organisms.     

Differences in diapause attributes between two clinal forms distinguished by male-to-male aggression in a subsocial spider mite, Schizotetranychus miscanthi Saito

The nest-weaving spider mite Schizotetranychus miscanthi Saito showed a cline in male-to-male aggression intensity with minimum winter temperature. The altered kin structure in spring nests, which might be caused by winter harshness, was hypothesized to be a key factor responsible for the cline in male-to-male aggression. In Japan, we found two forms (high- and low-aggression forms) that showed different clinal trends with similar regression slopes and different intercepts. The former is characteristic of local populations from milder climates, whereas the latter occurs in harsher climates. We hypothesized that the intensity of female diapause, which may determine whether males are produced during late winter, was one of the factors separating these two clinal forms. In the four populations studied, short day length during the developmental period (egg to adult emergence) induced diapause in females. Diapause intensity varied greatly among populations, and particularly between the high-aggression and low-aggression forms. These data, together with data on winter harshness between the localities, led us to believe that female diapause is one of the factors affecting relatedness between interacting males in nests and can explain why the two forms of S.miscanthi have different clinal trends in male aggression in Japan.     

Symbiotic Nitrogen Fixation at the Late Stage of Nodule Formation in Lotus japonicus and Other Legume Plants

Lotus japonicus nodules are reviewed, and current research data on Nod-35 (uricase) gene, including that of Lotus japonicus as an example of a late nodulin gene are presented. Received 5 September 2000/ Accepted in revised form 2 October 2000     

Isolation of a New Tobacco Constituent, 5,6-Dihydro-5-hydroxy-3,6-epoxy-β-ionol,from Japanese Domestic Suifu Tobacco

Glutamine production was investigated by coupling of glutamine synthetase from Gluconobacter suboxydans with a sugar fermentation system of baker's yeast (energy generating system). Under the optimum condition, 22 mM glutamine was formed in 3 hr, and the yield was 92% based on the substrate glutamate. The first step of the process was the accumulation of fructose 1,6-diphosphate (FDP) as a reservoir of fermentation energy, in the presence of a high concentration of inorganic phosphate; and the second step was accomplished by coupling the degradation of FDP with glutamine synthetase reaction through an ADP-ATP system. The effects of enzyme concentration, additives in the reaction mixture and others on glutamine formation were investigated, and the importance of three factors was pointed out: (a) the ratio of activity of energy generating system to utilizing system, (b) contaminated enzyme(s) in the energy utilizing system and (c) the enzymatic properties of the energy utilizing system.