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Citrate is one of the most important metabolites determining the flavour of citrus fruit. It has been reported that nitrogen supply may have an impact on acid level of fruit. Here, the relationship between nitrogen metabolism and citrate catabolism was studied in pumelo juice sacs. Differences in metabolites, gene expression and flux distributions were analyzed in juice sacs incubated in medium with and without NH 4 +. Compared with those incubated with NH 4 +, juice sacs under nitrogen deficiency exhibited enhanced flux through phosphoenolpyruvate carboxykinase (PEPCK) and accelerated consumption of citrate, while the other two TCA cycle efflux points, through malic enzyme (ME) and glutamate dehydrogenase (GDH), were both repressed. Consistent with the estimated fluxes, the expression of PEPCK1 was upregulated under nitrogen deficiency, while that of GDH1 , GDH2 , NAD-ME1 and NADP-ME2 were all repressed. Thus, we propose that PEPCK1 contributes to citrate degradation under nitrogen limitation. • Metabolism in pomelo juice sacs was analyzed systematically and quantitatively with stoichiometric metabolic flux analysis. • Nitrogen deficiency accelerated decrease in citrate content of juice sacs. • Nitrogen deficiency enhanced reaction of PEPCK and suppressed other TCA cycle exporting reactions. • CitPEPCK1 gene expression was activated under different conditions where inorganic nitrogen is absent. [ABSTRACT FROM AUTHOR]

Oncolytic virus is an effective therapeutic strategy for cancer treatment, which exploits natural or manipulated viruses to selectively target and kill cancer cells. However, the innate antiviral system of cancer cells may resistant to the treatment of oncolytic virus. M1 virus is a newly identified oncolytic virus belonging to alphavirus species, but the molecular mechanisms underlying its anticancer activity are largely unknown. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays. RNA seq analysis was used to analyze the gene alternation after M1 virus infection. Small interfering RNAs transfection for gene knockdown was used for gene functional tests. Caspase-3/7 activity was detected by Caspase-Glo Assay Systems. A mice model of orthotopic bladder tumor was established to determine the oncolytic effectiveness of the M1 virus. The expression of cleaved-Caspase 3 as well as Ki-67 in tumor cells were detected by immunohistochemical analysis. To further define the molecular factors involved in M1 virus-mediated biological function, we knocked down genes related to alphavirus' activity and found that CCDC6 plays an important role in the oncolytic activity of M1 virus. Moreover, knocked down of CCDC6 augments the reproduction of M1 virus and resulted in endoplasmic reticulum (ER) stress-induced cell apoptosis in vitro as well as in vivo orthotopic bladder cancer model. Our research provides a rational new target for developing new compounds to promote the efficacy of oncolytic virus therapy. [ABSTRACT FROM AUTHOR]