Effects of heat treatment on metabolism of tobacco plants infected with Potato virus Y.

Many factors affect successful virus propagation and plant defence responses. Heat shock protein (Hsp) expression after heat shock plays an ambiguous role in viral infection. On the one hand, Hsp70 participates in plant defence response; on the other hand, Hsp70 could interact with viral proteins and facilitate virus propagation. Here, we studied metabolic adaptations of Nicotiana tabacum L. subjected to heat shock (42 °C, 2 h) before or after inoculating the plants with Potato virus Y (potyvirus). RT-qPCR and ELISA were used for potyvirus quantification. Hsp70 and Hsp90 isoforms were analysed by Western blotting. Salicylic, quinic and chlorogenic acid content was determined by LC-MS. The activity of Hatch-Slack enzymes (as markers of potyviral infection in tobacco) and glycosidases was assayed. Application of heat shock before or after inoculation showed accelerated potyviral propagation in comparison with only inoculated plants. Plants exposed to heat shock and concurrently inoculated showed higher potyviral content, higher amount of Hsp70, together with late decline of quinic acid content and low chlorogenic acid content. Spread of potyviral infection correlated with enhanced salicylic acid content and activities of enzymes of the Hatch-Slack cycle, α- and ß-galactosidase, α-mannosidase, α-glucosidase and ß-N-acetylhexosaminidase. Heat shock proteins accelerate potyviral propagation. The lower weight cytosolic and mitochondrial Hsp70 (~50-75 kDa) persist throughout the viral infection. Also, the plant defense response results in increase of salicylic and chlorogenic acids but decrease of quinic acid content.

Pharmacological inhibition of fatty-acid oxidation synergistically enhances the effect of l-asparaginase in childhood ALL cells.

l-asparaginase (ASNase), a key component in the treatment of childhood acute lymphoblastic leukemia (ALL), hydrolyzes plasma asparagine and glutamine and thereby disturbs metabolic homeostasis of leukemic cells. The efficacy of such therapeutic strategy will depend on the capacity of cancer cells to adapt to the metabolic challenge, which could relate to the activation of compensatory metabolic routes. Therefore, we studied the impact of ASNase on the main metabolic pathways in leukemic cells. Treating leukemic cells with ASNase increased fatty-acid oxidation (FAO) and cell respiration and inhibited glycolysis. FAO, together with the decrease in protein translation and pyrimidine synthesis, was positively regulated through inhibition of the RagB-mTORC1 pathway, whereas the effect on glycolysis was RagB-mTORC1 independent. As FAO has been suggested to have a pro-survival function in leukemic cells, we tested its contribution to cell survival following ASNase treatment. Pharmacological inhibition of FAO significantly increased the sensitivity of ALL cells to ASNase. Moreover, constitutive activation of the mammalian target of rapamycin pathway increased apoptosis in leukemic cells treated with ASNase, but did not increase FAO. Our study uncovers a novel therapeutic option based on the combination of ASNase and FAO inhibitors.

Lymphocyte activation receptors: new structural paradigms in group V of C-type animal lectins.

The structure-function relationship in group V of C-type animal lectins remains incompletely understood despite the new structures of NK (natural killer) cell receptors that have been solved recently. Recombinant, soluble forms of rat and human NKR-P1 and CD69 that we obtained after in vitro refolding were analysed by Fourier transform-ion cyclotron resonance MS and heteronuclear NMR ((1)H-(15)N correlation). In NKR-P1, calcium may not be removed by chelating agents because of the very high affinity of binding. In CD69, incorporation of calcium causes a structural shift in several amino acids important for the interaction with carbohydrates. Structural studies have also allowed us to understand an interesting preference of these receptors for either linear (NKR-P1) or branched (CD69) carbohydrate sequences.