Thermal sensitivity and resistance of insulin-receptor binding in thermotolerant cells

NOP receptor mediates anti-analgesia induced by agonist-antagonist opioids

Clinical studies have shown that agonist-antagonist opioid analgesics that produce their analgesic effect via action on the kappa-opioid receptor, produce a delayed-onset anti-analgesia in men but not women, an effect blocked by co-administration of a low dose of naloxone. We now report the same time-dependent anti-analgesia and its underlying mechanism in an animal model. Using the Randall-Selitto paw-withdrawal assay in male rats, we found that nalbuphine, pentazocine, and butorphanol each produced analgesia during the first hour followed by anti-analgesia starting at ∼90min after administration in males but not females, closely mimicking its clinical effects. As observed in humans, co-administration of nalbuphine with naloxone in a dose ratio of 12.5:1 blocked anti-analgesia but not analgesia. Administration of the highly selective kappa-opioid receptor agonist U69593 produced analgesia without subsequent anti-analgesia, and confirmed by the failure of the selective kappa antagonist nor-binaltorphimine to block nalbuphine-induced anti-analgesia, indicating that anti-analgesia is not mediated by kappa-opioid receptors. We therefore tested the role of other receptors in nalbuphine anti-analgesia. Nociceptin/orphanin FQ (NOP) and sigma-1 and sigma-2 receptors were chosen on the basis of their known anti-analgesic effects and receptor binding studies. The selective NOP receptor antagonists, JTC801, and J-113397, but not the sigma receptor antagonist, BD 1047, antagonized nalbuphine anti-analgesia. Furthermore, the NOP receptor agonist NNC 63-0532 produced anti-analgesia with the same delay in onset observed with the three agonist-antagonists, but without producing preceding analgesia and this anti-analgesia was also blocked by naloxone. These results strongly support the suggestion that clinically used agonist-antagonists act at the NOP receptor to produce anti-analgesia.

Hsp70 and Hsp40 chaperone activities in the cytoplasm and the nucleus of mammalian cells

The existence and function of a Hsp40-Hsp70 chaperone machinery in mammalian cells in vivo was investigated. The rate of heat inactivation of firefly luciferase transiently expressed in hamster O23 fibroblasts was analyzed in cells co-transfected with the gene encoding the human Hsp40 (Ohtsuka, K. (1993) Biochem. Biophys. Res. Commun. 197, 235-240), the human inducible Hsp70 (Hunt, C., and Morimoto, R. I. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 6455-6459), or a combination of both. Whereas the expression of human Hsp70 alone in hamster cells was sufficient for the protection of firefly luciferase during heat shock, expression of the human Hsp40 alone was not. Rather, this led to a small but significant increase in the heat sensitivity of luciferase. The expression of the human Hsp40 only led to heat protection when the human Hsp70 was expressed as well. Under such conditions the rate of luciferase reactivation from the heat-inactivated state was increased, but the rate of inactivation during heat shock was not affected. Using constructs that direct firefly luciferase either to the cytoplasm or to the nucleus (Michels, A. A., Nguyen, V.-T., Konings, A. W. T., Kampinga, H. H., and Bensaude, O. (1995) Eur. J. Biochem. 234, 382-389), it was demonstrated that these chaperone functions are found in both compartments. Our data provide the first evidence on how the Hsp40/Hsp70 chaperone complex acts as heat protector in mammalian cells in vivo.

Expression of melanoma-associated antigen of thermotolerant human cells

The expression of the melanoma-associated antigen p250 on thermotolerant cells and the effect of a second heat dose on the antigen expression have been measured by flow cytometry. The human melanoma cell line FME was heated at 43.5 degrees C for 120 min after a priming heat dose at 43.5 degrees C for 20, 40 or 60 min. Cells preheated at 43.5 degrees C for 40 and 60 min followed the same kinetics of development and decay of thermotolerance, with maximum thermotolerance 16 h after the priming heating, and the thermotolerance had decayed by 48 h. Cells preheated at 43.5 degrees C for 20 min showed maximum thermotolerance after 7 h and decay by 24 h. Heat reduced the expression of the melanoma-associated antigen in a dose-dependent manner. Thermotolerant cells were given a second heat dose (43.5 degrees C for 120 min) and the antigen expression measured immediately after heating. Fractionated hyperthermia using the lower predose (43.5 degrees C for 20 min) might have an additive effect on the reduction of antigen expression, while the highest predose (43.5 degrees C for 60 min) protected against reduction in antigen expression. The development and decay of resistance against heat-induced reduction in expression of melanoma-associated antigen followed a similar time course as thermotolerance in terms of cell survival. Maximum resistance was observed 12 h after the priming heat treatment, and the resistance had decayed by 48 h.

Plasma membrane activities retained after lethal heat shock

Cultures of Chinese hamster ovary (CHO) cells were examined to determine if heat killing could be attributed to severe damage in the plasma membrane. Three independent transport activities of the plasma membrane were measured. Glucose transport into the cells (measured with the non-metabolizable analogue 3-O-methyl-D-glucose) was stimulated rather than inhibited by heat. Most of the stimulation was found after non-toxic heat doses. Although amino acid transport (measured with the non-metabolizable analogue 2-aminoisobutyric acid) was slightly inhibited by heat, heat-sterilized cells were able to accumulate high intracellular concentrations. Cellular uptake of the nucleoside uridine was unaffected for at least 4 h after heating. In contrast, its incorporation into RNA was immediately inhibited. To further study plasma membrane damage, cells were either heated or treated with drugs which localize to the plasma membrane, ionophore A23187 or amphotericin B. The mode of cell killing by heat was radically different from that of the two drugs: heat-sterilized cells retained a phase-bright morphology and excluded the viability dye trypan blue while drug-killed cells rapidly became phase-dark and absorbed the dye. These results add to a growing list of plasma membrane activities which are retained in heat-sterilized cells, and suggest that the initial thermal damage responsible for cell killing is at an alternate site(s).

Changes in the expression of idiotype antigen on murine B-cell lymphoma after hyperthermia alone and in combination with interferon and tumour necrosis factor

The effect of interferon (IFN) and tumour necrosis factor (TNF), either alone or combined with hyperthermia, on cell proliferation and expression of idiotype antigen on a murine B-cell lymphoma has been studied. Incubation with same doses of IFN-alpha and IFN-gamma reduced cell proliferation to the same extent. Hyperthermia potentiated the antiproliferative activity of IFN-alpha and IFN-gamma. Pretreatment with IFN-gamma induced a synergistic response with heat, while IFN-alpha and heat had an additive effect. Tumour necrosis factor (TNF) alone did not affect cell proliferation, nor did TNF modify the heat-induced delay in cell growth. The quantitative expression of surface idiotype antigen was studied by flow cytometry using an anti-idiotype monoclonal antibody (MAb). Heat reduced the expression of idiotype antigen approximately 50%. The duration of the reduction depended on the heat-dose. Recovery of antigen expression correlated with recovery of cell growth, and 2-5 days after the treatment antigen expression returned to the normal level for untreated cells. IFN-gamma and TNF increased antigen expression (30-50%) which lasted for 4-6 days after treatment. When cells were incubated with IFN-gamma or TNF for 2 days prior to hyperthermia, the increase in antigen expression was observed immediately after heating, but by the following day, antigen expression was similar to that after heat treatment alone. Expression of idiotype antigen recovered within 2-5 days to the same values as after heat treatment alone. IFN-alpha alone or combined with hyperthermia did not have any significant effect on antigen expression.

Studies on the mechanism by which glutamine and heat shock increase lactate synthesis by L929 cells in the presence of insulin

Both glutamine and heat shock increase lactate production in the L929 cell system. Glutamine is now shown to increase hexose uptake in the presence of insulin, to inhibit pyruvate oxidation, and to provide reducing equivalents to the cytosolic compartment. The relative contribution of these processes to lactate production depends on the availability of pyruvate. When ample pyruvate is available from the culture medium, stimulation of lactate synthesis by glutamine and heat shock is transaminase dependent, suggesting that shuttling of reducing equivalents from mitochondria to cytoplasm is involved. In the absence of medium pyruvate, stimulation of glycolysis by both glutamine and heat shock is largely responsible for increased lactate synthesis. None of the observed effects of glutamine appears to be sufficient to explain the observed stimulation of glycolysis.

Investigation of adenylate energy charge, phosphorylation potential, and ATP concentration in cells stressed with starvation and heat

We have attempted to determine the appropriate parameter of energy status associated with the survival of CHO fibroblasts under starvation conditions. Survival correlated well with adenylate energy charge (EC) but not so well with the phosphorylation potential or ATP concentration. Starved cells exhibited the capacity to resist (transiently) decreases in both EC and survival. A fall in EC was associated with decreased survival. Using this correlation, we subsequently investigated whether killing after thermal stress occurred by a mechanism analogous to starvation, perhaps due to inhibition of energy yielding pathways. This hypothesis proved to be false; over 99% of cells were killed before a decrease was observed in any of the parameters of energy status. Cells were, however, sensitized to heat under nutritionally deprived conditions, a finding which may be significant for tumor treatment by heat in vivo.