Cell susceptibility to apoptosis by glutamine deprivation and rescue: Survival and apoptotic death in cultured lymphoma-leukemia cell lines

Human leukemia/lymphoma cells maintained in culture medium without provision of fresh nutrients lose viability and die by a process resembling apoptosis within a few days. Upon incubation in an FCS-supplemented RPMI 1640 medium containing 2 mM L-glutamine CEM, Namalwa, HL-60 and U937 cells, seeded at initial densities of 0.2 to 1 × 10⁶ cells/ml, ceased growing within 3–5 days and progressively entered an apoptotic pathway, as assessed by nucleosomal DNA fragmentation and morphology. Both the major energy-source nutrients in the medium, glucose and glutamine, became rapidly exhausted during the incubation. Further studies were performed using CEM cells. Incubation in glutamine-free or glucose-free medium renewed every 24 h showed that glutamine deprivation is associated with cell death by apoptosis independent of energetic failure, whereas glucose deprivation is followed by rapid loss of mitochondrial function with sharp drop of intracellular ATP and cell death by necrosis. A 12–24 h incubation in glutamine-depleted medium was required to direct the cells toward the apoptotic pathway. Growth arrest followed by apoptotic death was detected in CEM cells when medium glutamine concentration remained below 0.3–0.4 mM for at least 24 h, but a reinstatement of medium glutamine to 2 mM within this period rescued the cells from growth arrest and death. © 1996 Wiley-Liss, Inc.     

Monoclonal antibodies against pertussis toxin subunits

Abstract Twenty monoclonal antibodies (mAbs) reacting with cholera toxin (CT) of Vibrio cholerae strain 569B were characterized in cross-section and G_M1 ganglioside inhibition assays. MAbs were characterized by reaction with CT and Escherichia coli heat-labile porcine strain (LT_p) and human strain (LTh) enterotoxins, and by G_M1 ganglioside inhibition of mAb binding. Eight of 10 CT-A specific and 3 of 10 CT-B-specific mAbs cross-reacted with LTh and LTp. G_M1 ganglioside inhibited reactions of the CT-B cross-reacting antibodies. Results showed that these epitodes common to the B subunit of CT and LT are located in or near the G_M1 ganglioside binding region, and that the G_M1 ganglioside-binding region of LT differs from that of CT.     

Altered adhesion features and signal transduction in NRK-49F cells transformed by down-regulation of lysyl oxidase

Lysyl oxidase (LOX) down-regulation induced an oncogenic phenotype in NRK-49F. This event was accompanied by a constitutive activation of ras oncogene and down-regulation of PDGF beta receptor, among other important phenotypic and molecular modifications. In the present paper we show that ras activation is not accompanied by a constitutive activation of the MAP kinases as expected. Surprisingly, even if MAPK-independent, ras activation was accompanied by a constitutive Ser(63) and Ser(73) phosphorylation of c-jun, a further downstream target of ras. Although rare, this ras alternative pathway has been described. Since ras alone is seldom able to trigger cell transformation and the transformed phenotype showed clearly an abnormal adhesion pattern, we investigated the main molecules involved in cell-cell adhesion. In fact, we found that beta-catenin was up-regulated, escaping the glycogen synthase kinase-3 beta (GSK-3 beta) control, through unclear mechanisms. Its nuclear accumulation was accompanied by an up-regulation of cyclin D1, as classically described in the activation of the Wnt/beta-catenin signal pathway. We believe that the resulting up-regulation of cyclin D1 acted in synergy with ras to induce the cell transformation.     

Palmitate acutely raises glycogen synthesis in rat soleus muscle by a mechanism that requires its metabolization (Randle cycle)

The acute effect of palmitate on glucose metabolism in rat skeletal muscle was examined. Soleus muscles from Wistar male rats were incubated in Krebs-Ringer bicarbonate buffer, for 1 h, in the absence or presence of 10 mU/ml insulin and 0, 50 or 100 microM palmitate. Palmitate increased the insulin-stimulated [(14)C]glycogen synthesis, decreased lactate production, and did not alter D-[U-(14)C]glucose decarboxylation and 2-deoxy-D-[2,6-(3)H]glucose uptake. This fatty acid decreased the conversion of pyruvate to lactate and [1-(14)C]pyruvate decarboxylation and increased (14)CO(2) produced from [2-(14)C]pyruvate. Palmitate reduced insulin-stimulated phosphorylation of insulin receptor substrate-1/2, Akt, and p44/42 mitogen-activated protein kinases. Bromopalmitate, a non-metabolizable analogue of palmitate, reduced [(14)C]glycogen synthesis. A strong correlation was found between [U-(14)C]palmitate decarboxylation and [(14)C]glycogen synthesis (r=0.99). Also, palmitate increased intracellular content of glucose 6-phosphate in the presence of insulin. These results led us to postulate that palmitate acutely potentiates insulin-stimulated glycogen synthesis by a mechanism that requires its metabolization (Randle cycle). The inhibitory effect of palmitate on insulin-stimulated protein phosphorylation might play an important role for the development of insulin resistance in conditions of chronic exposure to high levels of fatty acids.     

Comparative importance in vivo of conserved glutamate residues in the EX7E motif retaining glycosyltransferase Gpi3p, the UDP-GlcNAc-binding subunit of the first enzyme in glycosylphosphatidylinositol assembly.

Saccharomyces cerevisiae Gpi3p is the UDP-GlcNAc-binding and presumed catalytic subunit of the enzyme that forms GlcNAc-phosphatidylinositol in glycosylphosphatidylinositol biosynthesis. It is an essential protein with an EX7E motif that is conserved in four families of retaining glycosyltransferases. All Gpi3ps contain a cysteine residue four residues C-terminal to EX7E. To test their importance for Gpi3p function in vivo, Glu289 and 297 in the EX7E motif of S. cerevisiae Gpi3p, as well as Cys301, were altered by site-specific mutagenesis, and the mutant proteins tested for their ability to complement nonviable GPI3-deleted haploids. Gpi3p-C301A supported growth but membranes from C301A-expressing cells had low in vitro N-acetylglucosaminylphosphatidylinositol (GlcNAc-PI) synthetic activity. Haploids harboring Gpi3p-E289A proved viable, although slow growing but Gpi3-E297A did not support growth. The E289D and E297D mutants both supported growth at 25 degrees C, but, whereas the E289D strain grew at 37 degrees C, the E297D mutant did not. Membranes from E289D mutants had severely reduced in vitro GlcNAc-PI synthetic activity and E297D membranes had none. The mutation of the first Glu in the EX7E motif of Schizosaccharomyces pombe Gpi3p (Glu277) to Asp complemented the lethal null mutation in gpi3+ and supported growth at 37 degrees C, but the E285D mutant was nonviable. Our results suggest that the second Glu residue of the EX7E motif in Gpi3p is of greater importance than the first for function in vivo. Further, our findings do not support previous suggestions that the first Glu of an EX7E protein is the nucleophile and that Cys301 has an important role in UDP-GlcNAc binding by Gpi3ps.     

Development of a nuclear polyhedrosis virus in midgut cells and penetration of the virus into the hemocoel of the armyworm,Pseudaletia unipuncta

The development of a nuclear polyhedrosis virus (NPV) in larval midgut cells of the armyworm, Pseudaletia unipuncta, is similar to that of other NPV. In the nucleus, the envelopes around the nucleocapsids seem to be derived de novo or from the inner layer of the nuclear envelope wich forms cisternae, blebs, or infoldings. The nucleocapsids are also enveloped by synhymenosis during passage through the nuclear membrane, the cell membrane, or the endoplasmic reticulum membrane. Both enveloped and unenveloped nucleocapsids may enter the cytoplasm through the nuclear pore or budding through the nuclear membrane. From the cytoplasm the virions may enter the hemocoel through the basal cell and basement membranes or through the endoplasmic reticulum, intercellular space, and the basement membrane.     

Reduction of 1,4-quinone and ubiquinones by hydrogen atom transfer under UVA irradiation

1,4-Benzoquinone, coenzyme Q 0 and Q 10 were reacted with a series of hydrogen donors in the ESR cavity in the presence or absence of UVA irradiation. The signals of the radicals generated from the hydrogen donors or of those of the semiquinones were detected. The reaction mechanism was interpreted by a hydrogen atom transfer instead of the usual electron transfer mechanism on the basis of the redox potentials of the reactants and the Marcus theory. The hydrogen atom transfer is explained by the excited triplet state of quinones, which, on the basis of quantum mechanic calculations, may be reached even under visible light. In some cases, hydrogen atom transfer was also observed without irradiation, although to a lesser extent.     

Beta-alanine protection against hypoxic liver injury in the rat

Liver hypoxia still represents an important cause of liver injury during shock and liver transplantation. We have investigated the protective effects of beta-alanine against hypoxic injury using isolated perfused rat livers and isolated rat hepatocyte suspensions. Perfusion with hypoxic Krebs-Henseleit buffer increased liver weight and caused a progressive release of lactate dehydrogenase (LDH) in the effluent perfusate. The addition of 5 mmol/l beta-alanine to the perfusion buffer completely prevented both weight increase and LDH leakage. These findings were confirmed by histological examinations showing that beta-alanine blocked the staining by trypan blue of either liver parenchymal and sinusoidal cells. Studies performed in isolated hepatocytes revealed that beta-alanine exerted its protective effects by interfering with Na+ accumulation induced by hypoxia. The addition of gamma-amino-butyric acid, which interfered with beta-alanine uptake by the hepatocytes or of Na+/H+ ionophore monensin, reverted beta-alanine protection in either hepatocyte suspensions or isolated perfused livers. We also observed that liver receiving beta-alanine were also protected against LDH leakage and weight increase caused by the perfusion with an hyposmotic (205 mosm) hypoxic buffer obtained by decreasing NaCl content from 118 to 60 mmol/l. This latter effect was not reverted by blocking K+ efflux from hepatocyte with BaCl(2) (1mmol/l). Altogether these results indicated that beta-alanine protected against hypoxic liver injury by preventing Na+ overload and by increasing liver resistance to osmotic stress consequent to the impairment of ion homeostasis during hypoxia.