Rapidly proliferating cells switch from oxidative phosphorylation to aerobic glycolysis plus glutaminolysis, markedly increasing glucose and glutamine catabolism. Although Otto Warburg first described aerobic glycolysis in cancer cells >90 years ago, the primary purpose of this metabolic switch remains controversial. The hexosamine biosynthetic pathway requires glucose and glutamine for de novo synthesis of UDP-GlcNAc, a sugar-nucleotide that inhibits receptor endocytosis and signaling by promoting N-acetylglucosamine branching of Asn (N)-linked glycans. Here, we report that aerobic glycolysis and glutaminolysis co-operatively reduce UDP-GlcNAc biosynthesis and N-glycan branching in mouse T cell blasts by starving the hexosamine pathway of glucose and glutamine. This drives growth and pro-inflammatory TH17 over anti-inflammatory-induced T regulatory (iTreg) differentiation, the latter by promoting endocytic loss of IL-2 receptor-α (CD25). Thus, a primary function of aerobic glycolysis and glutaminolysis is to co-operatively limit metabolite supply to N-glycan biosynthesis, an activity with widespread implications for autoimmunity and cancer.DOI: http://dx.doi.org/10.7554/eLife.21330.001
Essential biological systems employ self-correcting mechanisms to maintain cellular homeostasis. Mammalian cell function is dynamically regulated by the interaction of cell surface galectins with branched N-glycans. Here we report that N-glycan branching deficiency triggers the Golgi to generate bioequivalent N-glycans that preserve galectin-glycoprotein interactions and cellular homeostasis. Galectins bind N-acetyllactosamine (LacNAc) units within N-glycans initiated from UDP-GlcNAc by the medial-Golgi branching enzymes as well as the trans-Golgi poly-LacNAc extension enzyme β1,3-N-acetylglucosaminyltransferase (B3GNT). Marginally reducing LacNAc content by limiting N-glycans to three branches results in T-cell hyperactivity and autoimmunity; yet further restricting branching does not produce a more hyperactive state. Rather, new poly-LacNAc extension by B3GNT maintains galectin binding and immune homeostasis. Poly-LacNAc extension is triggered by redistribution of unused UDP-GlcNAc from the medial to trans-Golgi via inter-cisternal tubules. These data demonstrate the functional equivalency of structurally dissimilar N-glycans and suggest a self-correcting feature of the Golgi that sustains cellular homeostasis.DOI: http://dx.doi.org/10.7554/eLife.14814.001
Xenografts of human colorectal cancer (CRC) in immune-deficient mice have great potential for accelerating the study of tumor biology and therapy. We evaluated xenografts established in NOD/scid/IL2Rγ-null mice from the primary or metastatic tumors of 27 patients with CRC to estimate their capacity for expanding tumor cells for in vitro studies and to assess how faithfully they recapitulated the transcriptional profile of their parental tumors. RNA-seq analysis of parental human CRC tumors and their derivative xenografts demonstrated that reproducible transcriptional changes characterize the human tumor to murine xenograft transition. In most but not all cases, the human stroma, vasculature, and hematopoietic elements were systematically replaced by murine analogues while the carcinoma component persisted. Once established as xenografts, human CRC cells that could be propagated by serial transplantation remained transcriptionally stable. Three histologically atypical xenografts, established from patients with peritoneal metastases, contained abundant human stromal elements and blood vessels in addition to human tumor cells. The transcriptomes of these mixed tumor/stromal xenografts did not closely resemble those of their parental tumors, and attempts to propagate such xenografts by serial transplantation were unsuccessful. Stable expression of numerous genes previously identified as high priority targets for immunotherapy was observed in most xenograft lineages. Aberrant expression in CRC cells of human genes that are normally only expressed in hematopoietic cells was also observed. Our results suggest that human CRC cells expanded in murine xenografts have great utility for studies of tumor immunobiology and targeted therapies such as immunotherapy but also identify potential limitations.
Summary B cell depletion potently reduces episodes of inflammatory demyelination in multiple sclerosis (MS), predominantly through loss of innate rather than adaptive immunity. However, molecular mechanisms controlling innate versus adaptive B cell function are poorly understood. N -glycan branching, via interactions with galectins, controls endocytosis and signaling of cell surface receptors to control cell function. Here we report that N -glycan branching in B cells dose dependently reduces pro-inflammatory innate responses by titrating decreases in Toll-like receptor-4 (TLR4) and TLR2 surface expression via endocytosis. In contrast, a minimal level of N -glycan branching maximizes surface retention of the B cell receptor (BCR) and the CD19 co-receptor to promote adaptive immunity. Branched N -glycans inhibit antigen presentation by B cells to reduce T helper cell-17 (T H 17)/T H 1 differentiation and inflammatory demyelination in mice. Thus, N -glycan branching negatively regulates B cell innate function while promoting/maintaining adaptive immunity via BCR, providing an attractive therapeutic target for MS.
Development of specific immunotherapy for colorectal cancer (CRC) will require identification of antigens selectively or exclusively expressed on CRC cells and strategies to induce and enhance immune responses against these antigenic targets. Cancer-testis (C-T) antigens are proving to be excellent targets for immunotherapy of solid tumors such as melanoma, but their clinical utility for treatment of CRC has to date been limited by their infrequent expression in CRC cells. Here we report that the hypomethylating agent 5-aza-2′-deoxycytidine (DAC) induces expression of NY-ESO-1 and other C-T genes in CRC cells both in vitro and in vivo in a dose-dependent manner but has negligible effects on the expression of C-T genes in normal non-transformed cells such as fibroblasts. The induction by DAC of NY-ESO-1 expression in CRC cells persists over 100 days after DAC exposure and is associated with increased levels of NY-ESO-1 protein. CRC cells exposed to DAC at concentrations that can be readily achieved in vivo are rendered susceptible to MHC-restricted recognition by CD8+ NY-ESO-1-specific T cells. We also demonstrate that retroviral transduction of polyclonal peripheral blood T cells from a metastatic CRC patient with the T cell receptor (TCR) α and β chain genes encoding an HLA-A2-restricted, NY-ESO-1157-165-specific TCR can be used to generate both CD8+ and CD4+ NY-ESO-1157-165-specific T cells that selectively recognize DAC-treated CRC but not non-transformed cells. Collectively, these results suggest that the combination of epigenetic modulation and adoptive transfer of genetically engineered T lymphocytes may enable specific immunotherapy of CRC.
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