Immunosuppression Induced by Glutamine Deprivation Occurs via Activating PD-L1 Transcription in Bladder Cancer.

Few studies have reported whether nutrients in the tumor microenvironment can regulate the expression of PD-L1. Since tumor cells are often situated in a low-glutamine environment, we investigated PD-L1 expression under glutamine deprivation in bladder cancer cells. PD-L1 expression and the activation of the EGFR/MEK/ERK/c-Jun signaling pathway under glutamine deprivation were investigated by qPCR, Western blot, and immunofluorescence analyses. C-Jun-mediated transcriptional regulation of the PD-L1 gene was assessed by ChIP. PD-L1 expression and activation of the EGFR/MEK/ERK/c-Jun signaling pathway were assessed in T24 cells, TCCSUP cells and BALB/c mice with or without glutamine supplementation. Additionally, the impact of PD-L1 expression under glutamine deprivation on the function of T cells was investigated by ELISA. The expression of PD-L1 and EGFR/MEK/ERK/c-Jun pathway activation were elevated by glutamine deprivation, and c-Jun was enriched in the enhancer region of PD-L1. The expression of PD-L1 was considerably impaired by inhibiting the EGFR/MEK/ERK/c-Jun pathway and was elevated by activating this signaling pathway. In addition, the elevated PD-L1 expression and MEK/ERK/c-Jun signaling pathway activation were reduced by glutamine supplementation in vitro and in vivo. PD-L1 upregulation by glutamine deprivation in bladder cancer cells could reduce IFN-γ production by T cells. The expression of PD-L1 was upregulated under glutamine deprivation through the EGFR/MEK/ERK/c-Jun pathway to impair T cell function.

Glutamine affects T24 bladder cancer cell proliferation by activating STAT3 through ROS and glutaminolysis.

Changes in metabolism are common phenomena in tumors. Glutamine (Gln) has been documented to play a critical role in tumor growth. In this study, we aimed to to explore the mechanisms through which bladder cancer cells utilize Gln to fulfill their biosynthetic needs during proliferation. In addition, the roles of Gln in the tricarboxylic acid (TCA) cycle, reactive oxygen species (ROS) regulation, and signal transducer and activator of transcription 3 (STAT3) expression were examined in vitro in the T24 bladder cancer cell line. The results revealed that the T24 cell line was markedly Gln­dependent and that Gln supplementation promoted T24 proliferation through the actions of Gln as a ROS moderator and as a metabolic fuel in the TCA cycle. Importantly, extracellular Gln deprivation deregulated the production of the transcription factor, STAT3. Additionally, STAT3 expression was affected by the degree of Gln metabolism, as regulated by Gln intermediates and ROS. Thus, on the whole, the findings of this study demonstrate that Gln promotes the proliferation of the Gln­dependent bladder cancer cell line, T24, by supplementing adenosine triphosphate (ATP) production and neutralizing ROS to activate the STAT3 pathway.

N-Acetyl-Glucosamine Sensitizes Non-Small Cell Lung Cancer Cells to TRAIL-Induced Apoptosis by Activating Death Receptor 5.

BACKGROUND/AIMS: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potential anti-cancer agent due to its selective toxicity. However, many human non-small cell lung cancer (NSCLC) cells are partially resistant to TRAIL, thereby limiting its clinical application. Therefore, there is a need for the development of novel adjuvant therapeutic agents to be used in combination with TRAIL. METHODS: In this study, the effect of N-acetyl-glucosamine (GlcNAc), a type of monosaccharide derived from chitosan, combined with TRAIL was evaluated in vitro and in vivo. Thirty NSCLC clinical samples were used to detect the expression of death receptor (DR) 4 and 5. After GlcNAc and TRAIL co-treatment, DR expression was determined by real-time PCR and western blotting. Cycloheximide was used to detect the protein half-life to further understand the correlation between GlcNAc and the metabolic rate of DR. Non-reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to detect receptor clustering, and the localization of DR was visualized by immunofluorescence under a confocal microscope. Furthermore, a co-immunoprecipitation assay was performed to analyze the formation of death-inducing signaling complex (DISC). O-linked glycan expression levels were evaluated following DR5 overexpression and RNA interference mediated knockdown. RESULTS: We found that the clinical samples expressed higher levels of DR5 than DR4, and GlcNAc co-treatment improved the effect of TRAIL-induced apoptosis by activating DR5 accumulation and clustering, which in turn recruited the apoptosis-initiating protease caspase-8 to form DISC, and initiated apoptosis. Furthermore, GlcNAc promoted DR5 clustering by improving its O-glycosylation. CONCLUSION: These results uncovered the molecular mechanism by which GlcNAc sensitizes cancer cells to TRAIL-induced apoptosis, thereby highlighting a novel effective agent for TRAIL-mediated NSCLC-targeted therapy.