Nitric oxide protects murine embryonic liver cells (BNL CL.2) from cytotoxicity induced by glucose deprivation

Targeting purine synthesis in ASS1-expressing tumors enhances the response to immune checkpoint inhibitors

Argininosuccinate synthase (ASS1) downregulation in different tumors has been shown to support cell proliferation and yet, in several common cancer subsets ASS1 expression associates with poor patient prognosis. Here we demonstrate that ASS1 expression under glucose deprivation is induced by c-MYC, providing survival benefit by increasing nitric oxide synthesis and activating the gluconeogenic enzymes pyruvate carboxylase and phosphoenolpyruvate carboxykinase by S-nitrosylation. The resulting increased flux through gluconeogenesis enhances serine, glycine and subsequently purine synthesis. Notably, high ASS1-expressing breast cancer mice do not respond to immune checkpoint inhibitors and patients with breast cancer with high ASS1 have more metastases. We further find that inhibiting purine synthesis increases pyrimidine to purine ratio, elevates expression of the immunoproteasome and significantly enhances the response of autologous primary CD8⁺ T cells to anti-PD-1. These results suggest that treating patients with high-ASS1 cancers with purine synthesis inhibition is beneficial and may also sensitize them to immune checkpoint inhibition therapy.

116 kDa glycoprotein isolated from Ulmus davidiana Nakai (UDN) inhibits glucose/glucose oxidase (G/GO)-induced apoptosis in BNL CL.2 cells

Ulmus davidiana Nakai (UDN) has been used in folk medicine for its anti-inflammatory activity. In the present study, we investigated the antiapoptotic effect of UDN glycoprotein in glucose/glucose oxidase (G/GO)-induced BNL CL.2 cells. To evaluate the antiapoptotic effect of UDN glycoprotein, experiments were carried out using Western blot analysis for nuclear factor-kappa B (NF-kappaB), caspase-3, and poly(ADP-ribose) polymerase (PARP). We also examined nitric oxide (NO) production and nuclear staining. When BNL CL.2 cells were treated with G/GO (50 mU/ml), viability of the cells was 54.1%. However, the number of living cells after the addition of UDN glycoprotein in the presence of G/GO increased. UDN glycoprotein protected from cell damage caused by G/GO. Interestingly, UDN glycoprotein decreased NF-kappaB activation and stimulated NO production in G/GO-induced BNL CL.2 cells. In apoptotic parameters, UDN glycoprotein inhibited activations of caspase-3 and PARP cleavage in G/GO-induced BNL CL.2 cells. The results of nuclear staining indicated that UDN glycoprotein (50 microg/ml) has a protective ability from apoptotic cell death caused G/GO (50 mU/ml). In conclusion, UDN glycoprotein has a protective effect on apoptosis induced by G/GO through the inhibition of NF-kappaB, caspase-3, and PARP activity, and the stimulation of NO production in BNL CL.2 cells.

Roles of Heme Oxygenase-1 in the Antiproliferative and Antiapoptotic Effects of Nitric Oxide on Jurkat T Cells

Nitric oxide (NO) has been shown to exert antiproliferative and antiapoptotic effects on human T cells. Heme oxygenase-1 (HO-1), which degrades heme into biliverdin, free iron (Fe(2+)), and carbon monoxide (CO), has also been known to have antiproliferative and antiapoptotic effects. Recent evidence suggests that HO-1 is an important cellular target of NO; whether HO-1 expression contributes to the antiproliferative and/or antiapoptotic effects mediated by NO remains to be investigated. In the present study, we examined the effects of NO on HO-1 expression and possible roles of HO-1 in T cell proliferation and apoptosis. Using human Jurkat T cells, we found that the NO donor sodium nitroprusside (SNP) induced HO-1 expression and that preincubation with SNP suppressed T cell proliferation induced by concanavalin A and apoptosis triggered by anti-Fas antibody. Suppressions of T cell proliferation and apoptosis comparable with SNP were also observed when the T cells were preincubated with the HO-1 inducer cobalt protoporphyrin. A phosphorothioate-linked HO-1 antisense oligonucleotide blocked HO-1 expression, and subsequently abrogated the antiproliferative and antiapoptotic effects of SNP. Overexpression of the HO-1 gene after transfection into Jurkat T cells resulted in significant decreases in T cell proliferation and apoptosis. The CO donor tricarbonyldichlororuthenium (II) dimer mimicked the antiproliferative effect of SNP, and the Fe(2+) donor FeSO(4) blocked anti-Fas-induced apoptosis. Taken together, our results suggest that NO induces HO-1 expression in T cells and that suppressions of T cell proliferation and apoptosis afforded by NO are associated with an increased expression of HO-1 by NO.

Nitric oxide-mediated cytoprotection of hepatocytes from glucose deprivation-induced cytotoxicity: involvement of heme oxygenase-1

Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in heme catabolism, which leads to the generation of carbon monoxide (CO), biliverdin, and free iron. One of 3 mammalian HO isoforms, HO-1, is a stress-responsive protein and known to modulate such cellular functions as cytokine production, cell proliferation, and apoptosis to protect organs and tissues from acute injury. Although nitric oxide (NO)-mediated cytoprotective effects against cytotoxicity induced by glucose deprivation have been well recognized, the underlying mechanisms remain to be elucidated. Thus, we investigate the involvement of HO-1 in the cytoprotective effects of NO. Deprivation of glucose markedly reduced the viability of BNL CL.2 cells and primary rat hepatocytes. Pretreatment with NO donor, sodium nitroprusside (SNP), protected hepatocytes from glucose deprivation-induced cytotoxicity; zinc protoporphyrin (ZnPP) IX, an inhibitor of HO, was found to block the SNP-induced cytoprotection. SNP increased the induction of HO-1 protein as well as its activity in hepatocytes. A cytoprotective effect comparable to SNP was observed when the cells were transfected with HO-1 gene or preincubated with another HO-1 inducer, hemin. Additional experiments revealed the involvement of CO in the cytoprotective effect of SNP/HO-1 in BNL CL.2 cells. CO mediated cytoprotective effect through suppression of ERK MAPK activation. In conclusion, our results show that SNP protects hepatocytes from glucose deprivation-induced cytotoxicity through up-regulation of HO-1. Thus, HO-1 might be an important cellular target of NO donor with clinical implications for the prevention of acute liver injury in several pathological conditions.