Gene purging and the evolution of Neoave metabolism and longevity

Maintenance of the proteasome requires oxidative phosphorylation (ATP) and mitigation of oxidative damage, in an increasingly dysfunctional relationship with aging. SLC3A2 plays a role on both sides of this dichotomy as an adaptor to SLC7A5, a transporter of branched-chain amino acids (BCAA: Leu, Ile, Val), and to SLC7A11, a cystine importer supplying cysteine to the synthesis of the antioxidant glutathione. Endurance in mammalian muscle depends in part on oxidation of BCAA; however, elevated serum levels are associated with insulin resistance and shortened lifespans. Intriguingly, the evolution of modern birds (Neoaves) has entailed the purging of genes including SLC3A2, SLC7A5, -7, -8, -10, and SLC1A4, -5, largely removing BCAA exchangers and their interacting Na+/Gln symporters in pursuit of improved energetics. Additional gene purging included mitochondrial BCAA aminotransferase (BCAT2), pointing to reduced oxidation of BCAA and increased hepatic conversion to triglycerides and glucose. Fat deposits are anhydrous and highly reduced, maximizing the fuel/weight ratio for prolonged flight, but fat accumulation in muscle cells of aging humans contributes to inflammation and senescence. Duplications of the bidirectional α-ketoacid transporters SLC16A3, SLC16A7, the cystine transporters SLC7A9, SLC7A11, and N-glycan branching enzymes MGAT4B, MGAT4C in Neoaves suggests a shift to the transport of deaminated essential amino acid, and stronger mitigation of oxidative stress supported by the galectin lattice. We suggest that Alfred Lotka's theory of natural selection as a maximum power organizer (PNAS 8:151,1922) made an unusually large contribution to Neoave evolution. Further molecular analysis of Neoaves may reveal novel rewiring with applications for human health and longevity.

SLC3A2 N-glycosylation and Golgi remodeling regulate SLC7A amino acid exchangers and stress mitigation

Proteostasis requires oxidative metabolism (ATP) and mitigation of the associated damage by glutathione, in an increasingly dysfunctional relationship with aging. SLC3A2 (4F2hc, CD98) plays a role as a disulfide-linked adaptor to the SLC7A5 and SLC7A11 exchangers which import essential amino acids and cystine while exporting Gln and Glu, respectively. The positions of N-glycosylation sites on SLC3A2 have evolved with the emergence of primates, presumably in synchrony with metabolism. Herein, we report that each of the four sites in SLC3A2 has distinct profiles of Golgi-modified N-glycans. N-glycans at the primate-derived site N381 stabilized SLC3A2 in the galectin-3 lattice against coated-pit endocytosis, while N365, the site nearest the membrane promoted glycolipid-galectin-3 (GL-Lect)-driven endocytosis. Our results indicate that surface retention and endocytosis are precisely balanced by the number, position, and remodeling of N-glycans on SLC3A2. Furthermore, proteomics and functional assays revealed an N-glycan-dependent clustering of the SLC3A2∗SLC7A5 heterodimer with amino-acid/Na+ symporters (SLC1A4, SLC1A5) that balances branched-chain amino acids and Gln levels, at the expense of ATP to maintain the Na+/K+ gradient. In replete conditions, SLC3A2 interactions require Golgi-modified N-glycans at N365D and N381D, whereas reducing N-glycosylation in the endoplasmic reticulum by fluvastatin treatment promoted the recruitment of CD44 and transporters needed to mitigate stress. Thus, SLC3A2 N-glycosylation and Golgi remodeling of the N-glycans have distinct roles in amino acids import for growth, maintenance, and metabolic stresses.

N-acetylglucosamine inhibits inflammation and neurodegeneration markers in multiple sclerosis: a mechanistic trial

BACKGROUND

In the demyelinating disease multiple sclerosis (MS), chronic-active brain inflammation, remyelination failure and neurodegeneration remain major issues despite immunotherapy. While B cell depletion and blockade/sequestration of T and B cells potently reduces episodic relapses, they act peripherally to allow persistence of chronic-active brain inflammation and progressive neurological dysfunction. N-acetyglucosamine (GlcNAc) is a triple modulator of inflammation, myelination and neurodegeneration. GlcNAc promotes biosynthesis of Asn (N)-linked-glycans, which interact with galectins to co-regulate the clustering/signaling/endocytosis of multiple glycoproteins simultaneously. In mice, GlcNAc crosses the blood brain barrier to raise N-glycan branching, suppress inflammatory demyelination by T and B cells and trigger stem/progenitor cell mediated myelin repair. MS clinical severity, demyelination lesion size and neurodegeneration inversely associate with a marker of endogenous GlcNAc, while in healthy humans, age-associated increases in endogenous GlcNAc promote T cell senescence.

OBJECTIVES AND METHODS

An open label dose-escalation mechanistic trial of oral GlcNAc at 6 g (n = 18) and 12 g (n = 16) for 4 weeks was performed in MS patients on glatiramer acetate and not in relapse from March 2016 to December 2019 to assess changes in serum GlcNAc, lymphocyte N-glycosylation and inflammatory markers. Post-hoc analysis examined changes in serum neurofilament light chain (sNfL) as well as neurological disability via the Expanded Disability Status Scale (EDSS).

RESULTS

Prior to GlcNAc therapy, high serum levels of the inflammatory cytokines IFNγ, IL-17 and IL-6 associated with reduced baseline levels of a marker of endogenous serum GlcNAc. Oral GlcNAc therapy was safe, raised serum levels and modulated N-glycan branching in lymphocytes. Glatiramer acetate reduces TH1, TH17 and B cell activity as well as sNfL, yet the addition of oral GlcNAc dose-dependently lowered serum IFNγ, IL-17, IL-6 and NfL. Oral GlcANc also dose-dependently reduced serum levels of the anti-inflammatory cytokine IL-10, which is increased in the brain of MS patients. 30% of treated patients displayed confirmed improvement in neurological disability, with an average EDSS score decrease of 0.52 points.

CONCLUSIONS

Oral GlcNAc inhibits inflammation and neurodegeneration markers in MS patients despite concurrent immunomodulation by glatiramer acetate. Blinded studies are required to investigate GlcNAc's potential to control residual brain inflammation, myelin repair and neurodegeneration in MS.

A noncoding single-nucleotide polymorphism at 8q24 drives IDH1-mutant glioma formation

Establishing causal links between inherited polymorphisms and cancer risk is challenging. Here, we focus on the single-nucleotide polymorphism rs55705857, which confers a sixfold greater risk of isocitrate dehydrogenase (IDH)-mutant low-grade glioma (LGG). We reveal that rs55705857 itself is the causal variant and is associated with molecular pathways that drive LGG. Mechanistically, we show that rs55705857 resides within a brain-specific enhancer, where the risk allele disrupts OCT2/4 binding, allowing increased interaction with the Myc promoter and increased Myc expression. Mutating the orthologous mouse rs55705857 locus accelerated tumor development in an Idh1R132H-driven LGG mouse model from 472 to 172 days and increased penetrance from 30% to 75%. Our work reveals mechanisms of the heritable predisposition to lethal glioma in ~40% of LGG patients.

Age-associated impairment of T cell immunity is linked to sex-dimorphic elevation of N-glycan branching

Impaired T cell immunity with aging increases mortality from infectious disease. The branching of Asparagine-linked glycans is a critical negative regulator of T cell immunity. Here we show that branching increases with age in females more than males, in naïve more than memory T cells, and in CD4+ more than CD8+ T cells. Female sex hormones and thymic output of naïve T cells (TN) decrease with age, however neither thymectomy nor ovariectomy altered branching. Interleukin-7 (IL-7) signaling was increased in old female more than male mouse TN cells, and triggered increased branching. N-acetylglucosamine, a rate-limiting metabolite for branching, increased with age in humans and synergized with IL-7 to raise branching. Reversing elevated branching rejuvenated T cell function and reduced severity of Salmonella infection in old female mice. These data suggest sex-dimorphic antagonistic pleiotropy, where IL-7 initially benefits immunity through TN maintenance but inhibits TN function by raising branching synergistically with age-dependent increases in N-acetylglucosamine.

TMOD-18. DIRECT IN VIVO CRISPR SCREEN IDENTIFIES COOPERATING TUMOR SUPPRESSORS THAT DRIVE PROGRESSION OF IDH1-MUTANT LOW-GRADE GLIOMA TO AGGRESSIVE GLIOBLASTOMA

Low-grade glioma (LGG) are generally slowly growing brain cancers, that frequently undergo malignant progression to aggressive, secondary glioblastoma with a dismal prognosis. By combining genetically engineered Idh1-mutant mice with in vivo CRISPR gene editing we generated a mouse model faithfully recapitulating the founder mutations of LGG. Clonal activation of the neomorphic Idh1 R132H mutation cooperates with Trp53 and Atrx mutations to trigger development of brain tumors but only with ~30% penetrance and very long latency. To elucidate the molecular mechanisms underlying the malignant progression of IDH1-mutant LGG, we devised and deployed a direct in vivo CRISPR screen targeting genes commonly mutated in human IDH-mutant secondary glioblastoma. Stereotaxic delivery of a lentiviral sgRNA library targeting the mouse orthologs of these genes into the brain of Idh1 R132H ;Trp53;Atrx;Cas9 and control Idh1 wt ;Trp53;Atrx;Cas9 compound mutant mice resulted in rapid formation of tumors that recapitulate human Idh1-mutant glioblastoma. Deconvoluting the screen showed that PI3K pathway members Pten and Pik3ca as well as Notch1, Smarca4 and Fat1 are preferentially enriched in Idh1 R132H-tumors, while Rb1 and NF2 were enriched in Idh1 wt tumors. Co-mutation analysis further identified additional co-occurring driver combinations such as Bcor-Met, Olig2-Met, Olig2-Med12 or Bcor-Olig2. We validated the tumor suppressive function of Notch1 and Pten using conventional floxed knock-out alleles and found that Notch1 functions in a haploinsufficient manner. Interestingly, Idh1 R132H did not alter tumor latency or pathology in a high grade p53;Pten;Rb1 mutant background, indicating that the neomorphic IDH-mutations can drive low but not high grade glioma development. Our study provides a functional landscape of gliomagenesis suppressors in vivo.

Molecular and Metabolomic Investigation of Celecoxib Antiproliferative Activity in Mono-and Combination Therapy Against Breast Cancer Cell Models

BACKGROUND

Chronic inflammation plays a crucial role in the initiation, promotion, and invasion of tumors, and thus the antiproliferative effects of numerous anti-inflammatory drugs have been frequently reported in the literature. Upregulation of the pro-inflammatory enzyme cyclooxygenase-2 (COX-2) has been linked to various human cancers, including breast cancer.

OBJECTIVES

This research aims to investigate the antiproliferative activity of different Non-steroidal anti-inflammatory drugs (NSAIDs), including COX-2 selective and non-selective agents, against various breast cancer cell lines and to elucidate possible molecular pathways involved in their activity.

METHODS

The antiproliferative and combined effects of NSAIDs with raloxifene were evaluated by MTT assay. Cell migration was assessed using a wound-healing assay. The mechanism of cell death was determined using the Annexin V-FITC/ propidium iodide staining flow cytometry method. A mass spectrometry-based targeted metabolomics approach was used to profile the metabolomic changes induced in the T47d cells upon drug treatment.

RESULTS

Our results have demonstrated that celecoxib, a potent and selective COX-2 inhibitor, resulted in significant antiproliferative activity against all examined breast cancer cell lines with IC50 values of 95.44, 49.50. and 97.70 μM against MDA-MB-231, T47d, and MCF-7, respectively. Additionally, celecoxib exhibited a synergistic effect against T47d cells combined with raloxifene, a selective estrogen receptor modulator. Interestingly, celecoxib treatment increased cell apoptosis and resulted in substantial inhibition of cancer cell migration. In addition, the metabolomic analysis suggests that celecoxib may have affected metabolites (n = 43) that are involved in several pathways, including the tricarboxylic acid cycle, amino acids metabolism pathways, and energy production pathways in cancer cells.

CONCLUSION

Celecoxib may possess potential therapeutic utility for breast cancer treatment as monotherapy or in combination therapy. The reported metabolic changes taking place upon celecoxib treatment may shed light on possible molecular targets mediating the antiproliferative activity of celecoxib in an independent manner of its COX-2 inhibition.

Association of a Marker of N-Acetylglucosamine With Progressive Multiple Sclerosis and Neurodegeneration

Question

Is the serum concentration of N-acetylglucosamine (GlcNAc) altered in patients with multiple sclerosis?

Findings

This cross-sectional study found that patients with a progressive multiple sclerosis subtype and more severe disease have reduced serum levels of a marker of GlcNAc. In addition, GlcNAc is a rate-limiting substrate for N-glycan branching, which has been shown to regulate immunoactivity and myelination.

Meaning

This study suggests that GlcNAc and N-glycan branching are associated with multiple sclerosis in general and progressive multiple sclerosis in particular.

Importance

N-glycan branching modulates cell surface receptor availability, and its deficiency in mice promotes inflammatory demyelination, reduced myelination, and neurodegeneration. N-acetylglucosamine (GlcNAc) is a rate-limiting substrate for N-glycan branching, but, to our knowledge, endogenous serum levels in patients with multiple sclerosis (MS) are unknown.

Objective

To investigate a marker of endogenous serum GlcNAc levels in patients with MS.

Design, Setting, and Participants

A cross-sectional discovery study and cross-sectional confirmatory study were conducted at 2 academic MS centers in the US and Germany. The discovery study recruited 54 patients with MS from an outpatient clinic as well as 66 healthy controls between April 20, 2010, and June 21, 2013. The confirmatory study recruited 180 patients with MS from screening visits at an academic MS study center between April 9, 2007, and February 29, 2016. Serum samples were analyzed from December 2, 2013, to March 2, 2015. Statistical analysis was performed from February 23, 2020, to March 18, 2021.

Main Outcomes and Measures

Serum levels of GlcNAc plus its stereoisomers, termed N-acetylhexosamine (HexNAc), were assessed using targeted tandem mass spectroscopy. Secondary outcomes (confirmatory study) comprised imaging and clinical disease markers.

Results

The discovery cohort included 66 healthy controls (38 women; mean [SD] age, 42 [20] years), 33 patients with relapsing-remitting MS (RRMS; 25 women; mean [SD] age, 50 [11] years), and 21 patients with progressive MS (PMS; 14 women; mean [SD] age, 55 [7] years). The confirmatory cohort included 125 patients with RRMS (83 women; mean [SD] age, 40 [9] years) and 55 patients with PMS (22 women; mean [SD] age, 49 [80] years). In the discovery cohort, the mean (SD) serum level of GlcNAc plus its stereoisomers (HexNAc) was 710 (174) nM in healthy controls and marginally reduced in patients with RRMS (mean [SD] level, 682 [173] nM; P = .04), whereas patients with PMS displayed markedly reduced levels compared with healthy controls (mean [SD] level, 548 [101] nM; P = 9.55 × 10⁻⁹) and patients with RRMS (P = 1.83 × 10⁻⁴). The difference between patients with RRMS (mean [SD] level, 709 [193] nM) and those with PMS (mean [SD] level, 405 [161] nM; P = 7.6 × 10⁻¹⁸) was confirmed in the independent confirmatory cohort. Lower HexNAc serum levels correlated with worse expanded disability status scale scores (ρ = –0.485; P = 4.73 × 10⁻¹²), lower thalamic volume (t = 1.7; P = .04), and thinner retinal nerve fiber layer (B = 0.012 [SE = 7.5 × 10⁻¹¹]; P = .008). Low baseline serum HexNAc levels correlated with a greater percentage of brain volume loss at 18 months (t = 1.8; P = .04).

Conclusions and Relevance

This study suggests that deficiency of GlcNAc plus its stereoisomers (HexNAc) may be a biomarker for PMS. Previous preclinical, human genetic, and ex vivo human mechanistic studies revealed that N-glycan branching and/or GlcNAc may reduce proinflammatory responses, promote myelin repair, and decrease neurodegeneration. Combined, the data suggest that GlcNAc deficiency may be associated with progressive disease and neurodegeneration in patients with MS.

N-acetylglucosamine drives myelination by triggering oligodendrocyte precursor cell differentiation

Myelination plays an important role in cognitive development and in demyelinating diseases like multiple sclerosis (MS), where failure of remyelination promotes permanent neuro-axonal damage. Modification of cell surface receptors with branched N-glycans coordinates cell growth and differentiation by controlling glycoprotein clustering, signaling, and endocytosis. GlcNAc is a rate-limiting metabolite for N-glycan branching. Here we report that GlcNAc and N-glycan branching trigger oligodendrogenesis from precursor cells by inhibiting platelet-derived growth factor receptor-α cell endocytosis. Supplying oral GlcNAc to lactating mice drives primary myelination in newborn pups via secretion in breast milk, whereas genetically blocking N-glycan branching markedly inhibits primary myelination. In adult mice with toxin (cuprizone)-induced demyelination, oral GlcNAc prevents neuro-axonal damage by driving myelin repair. In MS patients, endogenous serum GlcNAc levels inversely correlated with imaging measures of demyelination and microstructural damage. Our data identify N-glycan branching and GlcNAc as critical regulators of primary myelination and myelin repair and suggest that oral GlcNAc may be neuroprotective in demyelinating diseases like MS.

The GATOR–Rag GTPase pathway inhibits mTORC1 activation by lysosome-derived amino acids

The mechanistic target of rapamycin complex 1 (mTORC1) couples nutrient sufficiency to cell growth. mTORC1 is activated by exogenously acquired amino acids sensed through the GATOR–Rag guanosine triphosphatase (GTPase) pathway, or by amino acids derived through lysosomal degradation of protein by a poorly defined mechanism. Here, we revealed that amino acids derived from the degradation of protein (acquired through oncogenic Ras-driven macropinocytosis) activate mTORC1 by a Rag GTPase–independent mechanism. mTORC1 stimulation through this pathway required the HOPS complex and was negatively regulated by activation of the GATOR-Rag GTPase pathway. Therefore, distinct but functionally coordinated pathways control mTORC1 activity on late endocytic organelles in response to distinct sources of amino acids.

A Genetic Map of the Response to DNA Damage in Human Cells

The response to DNA damage is critical for cellular homeostasis, tumor suppression, immunity, and gametogenesis. In order to provide an unbiased and global view of the DNA damage response in human cells, we undertook 31 CRISPR-Cas9 screens against 27 genotoxic agents in the retinal pigment epithelium-1 (RPE1) cell line. These screens identified 890 genes whose loss causes either sensitivity or resistance to DNA-damaging agents. Mining this dataset, we discovered that ERCC6L2 (which is mutated in a bone-marrow failure syndrome) codes for a canonical non-homologous end-joining pathway factor, that the RNA polymerase II component ELOF1 modulates the response to transcription-blocking agents, and that the cytotoxicity of the G-quadruplex ligand pyridostatin involves trapping topoisomerase II on DNA. This map of the DNA damage response provides a rich resource to study this fundamental cellular system and has implications for the development and use of genotoxic agents in cancer therapy.

Systematic mapping of genetic interactions for de novo fatty acid synthesis identifies C12orf49 as a regulator of lipid metabolism

The de novo synthesis of fatty acids has emerged as a therapeutic target for various diseases, including cancer. Because cancer cells are intrinsically buffered to combat metabolic stress, it is important to understand how cells may adapt to the loss of de novo fatty acid biosynthesis. Here, we use pooled genome-wide CRISPR screens to systematically map genetic interactions (GIs) in human HAP1 cells carrying a loss-of-function mutation in fatty acid synthase (FASN), whose product catalyses the formation of long-chain fatty acids. FASN-mutant cells show a strong dependence on lipid uptake that is reflected in negative GIs with genes involved in the LDL receptor pathway, vesicle trafficking and protein glycosylation. Further support for these functional relationships is derived from additional GI screens in query cell lines deficient in other genes involved in lipid metabolism, including LDLR, SREBF1, SREBF2 and ACACA. Our GI profiles also identify a potential role for the previously uncharacterized gene C12orf49 (which we call LUR1) in regulation of exogenous lipid uptake through modulation of SREBF2 signalling in response to lipid starvation. Overall, our data highlight the genetic determinants underlying the cellular adaptation associated with loss of de novo fatty acid synthesis and demonstrate the power of systematic GI mapping for uncovering metabolic buffering mechanisms in human cells.

Caveolin-1 Y14 phosphorylation suppresses tumor growth while promoting invasion

Caveolin-1 is a transmembrane protein with both tumor promoter and suppressor functions that remain poorly understood. Cav1 phosphorylation by Src kinase on tyrosine 14 is closely associated with focal adhesion dynamics and tumor cell migration, however the role of pCav1 in vivo in tumor progression remains poorly characterized. Herein, we expressed phosphomimetic Y14D, wild type, and non-phosphorylatable Y14F forms of Cav1 in MDA-MB-435 cancer cells. Expression of Cav1Y14D reduced cell proliferation and induced the TP53 tumor suppressor. Ectopic expression in MDA-MB-435 cells of Y14 phosphorylatable Cav1 was required for induction of TP53 in response to oxidative stress. Cav1Y14D promotes an apparent reversal of the Warburg effect and markedly inhibited tumor growth in vivo. However, Cav1 induced pseudopodial recruitment of glycolytic enzymes, and time-lapse intravital imaging showed increased invadopodia protrusion and extravasation into blood vessels for Cav1WT and Y14D but not for Y14F. Our results suggest that Cav1 Y14 phosphorylation levels play a role in the conflicting demands on metabolic resources associated with cancer cell proliferation versus motility.

Increasing cell permeability of N-acetylglucosamine via 6-acetylation enhances capacity to suppress T-helper 1 (TH1)/TH17 responses and autoimmunity

N-acetylglucosamine (GlcNAc) branching of Asn (N)-linked glycans inhibits pro-inflammatory T cell responses and models of autoimmune diseases such as Multiple Sclerosis (MS). Metabolism controls N-glycan branching in T cells by regulating de novo hexosamine pathway biosynthesis of UDP-GlcNAc, the donor substrate for the Golgi branching enzymes. Activated T cells switch metabolism from oxidative phosphorylation to aerobic glycolysis and glutaminolysis. This reduces flux of glucose and glutamine into the hexosamine pathway, thereby inhibiting de novo UDP-GlcNAc synthesis and N-glycan branching. Salvage of GlcNAc into the hexosamine pathway overcomes this metabolic suppression to restore UDP-GlcNAc synthesis and N-glycan branching, thereby promoting anti-inflammatory T regulatory (Treg) over pro-inflammatory T helper (TH) 17 and TH1 differentiation to suppress autoimmunity. However, GlcNAc activity is limited by the lack of a cell surface transporter and requires high doses to enter cells via macropinocytosis. Here we report that GlcNAc-6-acetate is a superior pro-drug form of GlcNAc. Acetylation of amino-sugars improves cell membrane permeability, with subsequent de-acetylation by cytoplasmic esterases allowing salvage into the hexosamine pathway. Per- and bi-acetylation of GlcNAc led to toxicity in T cells, whereas mono-acetylation at only the 6 > 3 position raised N-glycan branching greater than GlcNAc without inducing significant toxicity. GlcNAc-6-acetate inhibited T cell activation/proliferation, TH1/TH17 responses and disease progression in Experimental Autoimmune Encephalomyelitis (EAE), a mouse model of MS. Thus, GlcNAc-6-Acetate may provide an improved therapeutic approach to raise N-glycan branching, inhibit pro-inflammatory T cell responses and treat autoimmune diseases such as MS.

Abstract 1031: Fumarate hydratase deficiency redirects glucose metabolism of hypoxic cancer cells into the pentose phosphate pathway

Hypoxia is a common feature of all solid cancers and strongly correlated with poor prognosis. As an adaptive response to hypoxia, cancer cells reprogram their metabolism by increasing glycolysis and reductive carboxylation at the expense of mitochondrial respiration, a phenomenon orchestrated by the transcription factor hypoxia inducible factor (HIF) -1. Mutations in the gene encoding for the mitochondrial enzyme fumarate hydratase (FH), found in the hereditary leiomyomatosis and renal cell carcinoma (HLRCC) syndrome, lead to a similar phenotype despite the presence of O2, a phenomenon due to normoxic stabilization of HIF-1 (pseudohypoxia). Here, we report for the first time that FH loss-of-function (LOF) redirects glucose metabolism into the pentose phosphate pathway (PPP) in non-RCC cells subjected to severe hypoxia (O2< .02%). We show that this metabolic shift favors the buildup of biosynthetic precursors supporting hypoxic cell growth and proliferation.

HCT-116 (colon), HeLa (cervix) and H460 (lung) adenocarcinoma cells were transfected with lentiviral vectors encoding for shRNAs targeting FH. Immunoblot analysis showed that FH LOF did not induce pseudohypoxia in these cells. In contrast, HLRCC-derived UOK262 cells showed accumulation of HIF-1 under normoxia which was reversed upon FH re-introduction. A comprehensive analysis utilizing a RT-qPCR array to profile the mRNA expression of 84 HIF-1 target genes, further confirmed that FH LOF did not result in a pseudohypoxic phenotype in HCT-116 cells. An unbiased analysis of 250 metabolites detected by liquid chromatography-tandem mass spectrometry followed by quantitative enrichment analysis, identified glycolysis and the PPP among the most enriched metabolic pathways in hypoxic FH knockdown cells (P< 5×10-8). Since the PPP provides precursors for synthesis of nucleic acids, we analyzed the effect of FH LOF on cell cycle progression and found an inhibition of hypoxia-induced cell cycle arrest in HCT-116 and HeLa cells.

Our study reveals novel insights into the effect of FH loss-of-function in cancer cells and indicates a stark contrast between the pseudohypoxic phenotype described in kidney cancer cell lines obtained from HLRCC patients (i.e, UOK-262) and a HIF- independent mechanism of metabolic rerouting in colon, lung and cervix cancer cell lines. Our data show that FH LOF promotes an anabolic phenotype in hypoxic cancer cells that could be exploited to enhance the therapeutic response targeting this resistant subset of cancer cells.

Citation Format: Luana Schito, Sergio Rey, Judy Pawling, James W. Dennis, Bradly G. Wouters, Marianne Koritzinsky. Fumarate hydratase deficiency redirects glucose metabolism of hypoxic cancer cells into the pentose phosphate pathway. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1031.

PTP1B controls non-mitochondrial oxygen consumption by regulating RNF213 to promote tumour survival during hypoxia

Tumours exist in a hypoxic microenvironment and must limit excessive oxygen consumption. Hypoxia-inducible factor controls mitochondrial oxygen consumption, but how/if tumours regulate non-mitochondrial oxygen consumption (NMOC) is unknown. Protein-Tyrosine Phosphatase-1B (PTP1B) is required for Her2/Neu-driven breast cancer (BC) in mice, though the underlying mechanism and human relevance remain unclear. We found that PTP1B-deficient HER2⁺ xenografts have increased hypoxia, necrosis and impaired growth. In vitro, PTP1B deficiency sensitizes HER2⁺ BC lines to hypoxia by increasing NMOC by α-KG-dependent dioxygenases (α-KGDDs). The Moyamoya disease gene product RNF213 , an E3 ligase, is negatively regulated by PTP1B in HER2⁺ BC cells. RNF213 knockdown reverses the effects of PTP1B-deficiency on α-KGDDs, NMOC and hypoxia-induced death of HER2⁺ BC cells, and partially restores tumourigenicity. We conclude that PTP1B acts via RNF213 to suppress α-KGDD activity and NMOC. This PTP1B/RNF213/α-KGDD pathway is critical for survival of HER2⁺ BC, and possibly other malignancies, in the hypoxic tumour microenvironment.

Mgat5 modulates the effect of early life stress on adult behavior and physical health in mice

Psychosocial adversity in early life increases the likelihood of mental and physical illness, but the underlying mechanisms are poorly understood. Mgat5 is an N-acetylglucosaminyltransferase in the Golgi pathway that remodels the N-glycans of glycoproteins at the cell surface. Mice lacking Mgat5 display conditional phenotypes in behaviour, immunity, metabolism, aging and cancer susceptibility. Here we investigated potential gene-environment interactions between Mgat5 and early life adversity on behaviour and physiological measures of physical health. Mgat5(-/-) mutant and Mgat5(+/+) wild-type C57Bl/6 littermates were subject to maternal separation or foster rearing as an early life stressor, in comparison to control mice reared normally. We found an interaction between Mgat5 genotype and maternal rearing condition in which Mgat5(-/-) mice subjected to early life stress had lower glucose levels and higher bone density. Mgat5(-/-) genotype was also associated with less immobility in the forced swim test and greater sucrose consumption, consistent with a less depression-like phenotype. Cortical neuron dendrite spine density and branching was altered by Mgat5 deletion as well. In general, Mgat5 genotype affects both behaviour and physical outcomes in response to early life stress, suggesting some shared pathways for both in this model. These results provide a starting point for studying the mechanisms by which protein N-glycosylation mediates the effects of early life adversity.

Abstract LB-302: PTP1B regulates the Moyamoya disease-associated E3 ligase, RNF213 and cellular dioxygenase activity to allow breast tumor survival in hypoxia

Deletion of Ptpn1, which encodes Protein-Tyrosine Phosphatase-1B (PTP1B), delays the onset of Her2/Neu-driven breast cancers in mice, but the underlying mechanism(s) remains controversial. Moreover, the role of PTP1B in HER2+ human breast cancer is unresolved. We found that, unexpectedly, PTP1B protects HER2+ breast cancer (BC) cell lines and tumors from hypoxia-induced death. Although there was no consistent effect of PTPN1 depletion or PTP1B inhibition on growth factor signaling or proliferation of HER2+ BC cells in vitro, PTP1B-deficient HER2+ xenografts showed increased hypoxia, necrosis and impaired growth. PTPN1-knockdown (1B-KD) also sensitized HER2+ BC lines to hypoxia-induced death in vitro. Studies using catalytically inactive mutants or an allosteric PTP1B inhibitor demonstrated that the ability of PTP1B to promote survival in hypoxia requires catalytic activity. Metabolic analysis revealed increased non-mitochondrial oxygen consumption, accompanied by decreased α-ketoglutarate (α-KG) levels, in 1B-KD cells, suggestive of enhanced activity of one or more α-KG-dependent dioxygenases. Consistent with this notion, addition of the pan-oxygenase inhibitors IOXI or DMOG protected 1B-KD HER2+ BC cells from hypoxia-induced death. Studies with “substrate-trapping” mutants identified the product of the Moyamoya disease-associated gene RNF213, as a PTP1B substrate in HER2+ BC cells. Remarkably, RNF213-knockdown (RNF213-KD) rescued the effects of PTP1B-deficiency on non-mitochondrial oxygen consumption and hypoxia-induced death of HER2+ BC cells. RNF213-KD also partially restored growth of tumors evoked by 1B-KD HCC1954 cells. RNF213 is a 591kDa E3-ligase with RING finger and AAA+ ATPase domains, not previously implicated in PTP1B action. Preliminary proteomic characterization revealed that BT474 1B-KD cells have RNF213-dependent alterations in the ubiquitylome. Future work will determine how these changes affect α-KG-dependent dioxygenase(s) activity. Our results reveal a new function for PTP1B, acting via RNF213, to control one or more α-KG-dependent dioxygenases in HER2+ BC cells. This novel PTP1B/RNF213 hypoxia-regulatory pathway is critical for the survival of breast cancer and possibly other malignant cells in the tumor microenvironment.

Note: This abstract was not presented at the meeting.

Citation Format: Robert S. Banh, Caterina Iorio, Richard Marcotte, Yang Xu, Dan Cojocari, Anas Abdel Rahman, Judy Pawling, Ankit Sinha, Toshiaki Hitomi, Toshiyuki Habu, Akio Koizumi, Sarah Wilkins, Thomas Kislinger, Christopher J. Schofield, James W. Dennis, Bradly G. Wouters, Benjamin G. Neel. PTP1B regulates the Moyamoya disease-associated E3 ligase, RNF213 and cellular dioxygenase activity to allow breast tumor survival in hypoxia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-302. doi:10.1158/1538-7445.AM2015-LB-302

Golgi N-glycan branching N-acetylglucosaminyltransferases I, V and VI promote nutrient uptake and metabolism

Nutrient transporters are critical gate-keepers of extracellular metabolite entry into the cell. As integral membrane proteins, most transporters are N-glycosylated, and the N-glycans are remodeled in the Golgi apparatus. The Golgi branching enzymes N-acetylglucosaminyltransferases I, II, IV, V and avian VI (encoded by Mgat1, Mgat2, Mgat4a/b/c Mgat5 and Mgat6), each catalyze the addition of N-acetylglucosamine (GlcNAc) in N-glycans. Here, we asked whether N-glycan branching promotes nutrient transport and metabolism in immortal human HeLa carcinoma and non-malignant HEK293 embryonic kidney cells. Mgat6 is absent in mammals, but ectopic expression can be expected to add an additional β1,4-linked branch to N-glycans, and may provide evidence for functional redundancy of the N-glycan branches. Tetracycline (tet)-induced overexpression of Mgat1, Mgat5 and Mgat6 resulted in increased enzyme activity and increased N-glycan branching concordant with the known specificities of these enzymes. Tet-induced Mgat1, Mgat5 and Mgat6 combined with stimulation of hexosamine biosynthesis pathway (HBP) to UDP-GlcNAc, increased cellular metabolite levels, lactate and oxidative metabolism in an additive manner. We then tested the hypothesis that N-glycan branching alone might promote nutrient uptake when glucose (Glc) and glutamine are limiting. In low glutamine and Glc medium, tet-induced Mgat5 alone increased amino acids uptake, intracellular levels of glycolytic and TCA intermediates, as well as HEK293 cell growth. More specifically, tet-induced Mgat5 and HBP elevated the import rate of glutamine, although transport of other metabolites may be regulated in parallel. Our results suggest that N-glycan branching cooperates with HBP to regulate metabolite import in a cell autonomous manner, and can enhance cell growth in low-nutrient environments.

Targeted metabolomics in cultured cells and tissues by mass spectrometry: method development and validation

Metabolomics is the identification and quantitation of small bio-molecules (metabolites) in biological samples under various environmental and genetic conditions. Mass spectrometry provides the unique opportunity for targeted identification and quantification of known metabolites by selective reaction monitoring (SRM). However, reproducibility of this approach depends on careful consideration of sample preparation, chemical classes, and stability of metabolites to be evaluated. Herein, we introduce and validate a targeted metabolite profiling workflow for cultured cells and tissues by liquid chromatography-triple quadrupole tandem mass spectrometry. The method requires a one-step extraction of water-soluble metabolites and targeted analysis of central metabolites that include glycolysis, amino acids, nucleotides, citric acid cycle, and the hexosamine biosynthetic pathway. The sensitivity, reproducibility and molecular stability of each targeted metabolite were assessed under experimental conditions. Quantitation of metabolites by peak area ratio was linear with a dilution over a 4 fold dynamic range with minimal deviation R(2)=0.98. Inter- and intra-day precision with cells and tissues had an average coefficient of variation <15% for cultured cell lines, and somewhat higher for mouse liver tissues. The method applied in triplicate measurements readily distinguished immortalized cells from malignant cells, as well as mouse littermates based on their hepatic metabolic profiles.

N-glycan remodeling on glucagon receptor is an effector of nutrient sensing by the hexosamine biosynthesis pathway

Glucose homeostasis in mammals is dependent on the opposing actions of insulin and glucagon. The Golgi N-acetylglucosaminyltransferases encoded by Mgat1, Mgat2, Mgat4a/b/c, and Mgat5 modify the N-glycans on receptors and solute transporter, possibly adapting activities in response to the metabolic environment. Herein we report that Mgat5(-/-) mice display diminished glycemic response to exogenous glucagon, together with increased insulin sensitivity. Glucagon receptor signaling and gluconeogenesis in Mgat5(-/-) cultured hepatocytes was impaired. In HEK293 cells, signaling by ectopically expressed glucagon receptor was increased by Mgat5 expression and GlcNAc supplementation to UDP-GlcNAc, the donor substrate shared by Mgat branching enzymes. The mobility of glucagon receptor in primary hepatocytes was reduced by galectin-9 binding, and the strength of the interaction was dependent on Mgat5 and UDP-GlcNAc levels. Finally, oral GlcNAc supplementation rescued the glucagon response in Mgat5(-/-) hepatocytes and mice, as well as glycolytic metabolites and UDP-GlcNAc levels in liver. Our results reveal that the hexosamine biosynthesis pathway and GlcNAc salvage contribute to glucose homeostasis through N-glycan branching on glucagon receptor.

The adaptor protein p66Shc inhibits mTOR-dependent anabolic metabolism

Adaptor proteins link surface receptors to intracellular signaling pathways and potentially control the way cells respond to nutrient availability. Mice deficient in p66Shc, the most recently evolved isoform of the Shc1 adaptor proteins and a mediator of receptor tyrosine kinase signaling, display resistance to diabetes and obesity. Using quantitative mass spectrometry, we found that p66Shc inhibited glucose metabolism. Depletion of p66Shc enhanced glycolysis and increased the allocation of glucose-derived carbon into anabolic metabolism, characteristics of a metabolic shift called the Warburg effect. This change in metabolism was mediated by the mammalian target of rapamycin (mTOR) because inhibition of mTOR with rapamycin reversed the glycolytic phenotype caused by p66Shc deficiency. Thus, unlike the other isoforms of Shc1, p66Shc appears to antagonize insulin and mTOR signaling, which limits glucose uptake and metabolism. Our results identify a critical inhibitory role for p66Shc in anabolic metabolism.

Probing the hexosamine biosynthetic pathway in human tumor cells by multitargeted tandem mass spectrometry

Cancer progression is accompanied by increases in glucose and glutamine metabolism, providing the carbon and nitrogen required in downstream anabolic pathways. Fructose-6P, glutamine, and acetyl-CoA are central metabolites and substrates of the hexosamine biosynthesis pathway (HBP) to UDP-N-acetylglucosamine (UDP-GlcNAc), an essential high-energy donor for protein glycosylation. Golgi and cytosolic glycosylation pathways are sensitive to UDP-GlcNAc levels, which in turn regulates metabolic homeostasis in a poorly understood manner. To study the hexosamine biosynthesis pathway in cancer cells, we developed a targeted approach for cellular metabolomics profiling by liquid chromatography-tandem mass spectrometry. Human cervical (HeLa) and prostate cancer (PC-3) cell lines were cultured in medium with increasing concentrations of glucose, glutamine, or GlcNAc to perturb the metabolic network. Principal component analysis indicated trends that were further analyzed as individual metabolites and pathways. HeLa cell metabolism was predominantly glycolytic, while PC-3 cells showed a greater dependency on extracellular glutamine. In both cell lines, UDP-GlcNAc levels declined with glucose but not glutamine starvation, whereas glutamine abundance increased UDP-GlcNAc levels 2-3-fold. GlcNAc supplementation increased UDP-GlcNAc 4-8-fold in both HeLa and PC-3 cells. GlcNAc supplementation in HeLa cells induced nonmonotonic changes in NADH/NAD+, NADPH/NADP+, reactive oxygen species, and reduced/oxidized glutathione. In PC-3 cells, GlcNAc supplementation also increased glucose and glutamine uptake and catabolism. Our results suggest that stimulation of the HBP in cancer cells regulates metabolism and redox potential, which might be exploited to target cancer cells.

Complex N-glycan and metabolic control in tumor cells

Golgi beta1,6N-acetylglucosaminyltransferase V (Mgat5) produces beta1,6GlcNAc-branched complex N-glycans on cell surface glycoproteins that bind to galectins and promote surface residency of glycoproteins, including cytokine receptors. Carcinoma cells from polyomavirus middle T (PyMT) transgenic mice on a Mgat5-/- background have reduced surface levels of epidermal growth factor (EGF) and transforming growth factor-beta (TGF-beta) receptors and are less sensitive to acute stimulation by cytokines in vitro compared with PyMT Mgat5+/+ tumor cells but are nonetheless tumorigenic when injected into mice. Here, we report that PyMT Mgat5-/- cells are reduced in size, checkpoint impaired, and following serum withdrawal, fail to down-regulate glucose transport, protein synthesis, reactive oxygen species (ROS), and activation of Akt and extracellular signal-regulated kinase. To further characterize Mgat5+/+ and Mgat5-/- tumor cells, a screen of pharmacologically active compounds was done. Mgat5-/- tumor cells were comparatively hypersensitive to the ROS inducer 2,3-dimethoxy-1,4-naphthoquinone, hyposensitive to tyrosine kinase inhibitors, to Golgi disruption by brefeldin A, and to mitotic arrest by colcemid, hydroxyurea, and camptothecin. Finally, regulation of ROS, glucose uptake, and sensitivities to EGF and TGF-beta were rescued by Mgat5 expression or by hexosamine supplementation to complex N-glycan biosynthesis in Mgat5-/- cells. Our results suggest that complex N-glycans sensitize tumor cells to growth factors, and Mgat5 is required to balance responsiveness to growth and arrest cues downstream of metabolic flux.

Plasma membrane domain organization regulates EGFR signaling in tumor cells

Macromolecular complexes exhibit reduced diffusion in biological membranes; however, the physiological consequences of this characteristic of plasma membrane domain organization remain elusive. We report that competition between the galectin lattice and oligomerized caveolin-1 microdomains for epidermal growth factor (EGF) receptor (EGFR) recruitment regulates EGFR signaling in tumor cells. In mammary tumor cells deficient for Golgi β1,6N-acetylglucosaminyltransferase V (Mgat5), a reduction in EGFR binding to the galectin lattice allows an increased association with stable caveolin-1 cell surface microdomains that suppresses EGFR signaling. Depletion of caveolin-1 enhances EGFR diffusion, responsiveness to EGF, and relieves Mgat5 deficiency–imposed restrictions on tumor cell growth. In Mgat5^+/+ tumor cells, EGFR association with the galectin lattice reduces first-order EGFR diffusion rates and promotes receptor interaction with the actin cytoskeleton. Importantly, EGFR association with the lattice opposes sequestration by caveolin-1, overriding its negative regulation of EGFR diffusion and signaling. Therefore, caveolin-1 is a conditional tumor suppressor whose loss is advantageous when β1,6GlcNAc-branched N-glycans are below a threshold for optimal galectin lattice formation.

N-glycan processing deficiency promotes spontaneous inflammatory demyelination and neurodegeneration

Multiple sclerosis (MS) is characterized by inflammatory demyelination of axons and neurodegeneration, the latter inadequately modeled in experimental autoimmune encephalomyelitis (EAE). Susceptibility of inbred mouse strains to EAE is in part determined by major histocompatibility complex haplotype; however, other molecular mechanisms remain elusive. Galectins bind GlcNAc-branched N-glycans attached to surface glycoproteins, forming a molecular lattice that restricts lateral movement and endocytosis of glycoproteins. GlcNAc branching negatively regulates T cell activity and autoimmunity, and when absent in neurons, induces apoptosis in vivo in young adult mice. We find that EAE susceptible mouse strains PL/J, SJL, and NOD have reduced GlcNAc branching. PL/J mice display the lowest levels, partial deficiencies in N-acetylglucosaminyltransferase I, II, and V (i.e. Mgat1, -2, and -5), T cell hyperactivity and spontaneous late onset inflammatory demyelination and neurodegeneration; phenotypes markedly enhanced by Mgat5(+/-) and Mgat5(-/-) backgrounds in a gene dose-dependent manner. Spontaneous disease is transferable and characterized by progressive paralysis, tremor, dystonia, neuronophagia, and axonal damage in both demyelinated lesions and normal white matter, phenocopying progressive MS. Our data identify hypomorphic Golgi processing as an inherited trait that determines susceptibility to EAE, provides a unique spontaneous model of MS, and suggests GlcNAc-branching deficiency may promote T cell-mediated demyelination and neurodegeneration in MS.

Metabolic homeostasis and tissue renewal are dependent on beta1,6GlcNAc-branched N-glycans

Golgi beta1,6-N-acetylglucosaminyltransferase V (Mgat5) produces beta1,6GlcNAc-branched N-glycans on glycoproteins, which increases their affinity for galectins and opposes loss from the cell surface to constitutive endocytosis. Oncogenic transformation increases Mgat5 expression, increases beta1,6GlcNAc-branched N-glycans on epidermal growth factor and transforming growth factor-beta receptors, and enhances sensitivities to ligands, cell motility, and tumor metastasis. Here, we demonstrate that Mgat5(-/-) mouse embryonic fibroblasts (MEFs) display reduced sensitivity to anabolic cytokines and reduced glucose uptake and proliferation. Mgat5(-/-) mice are also hypoglycemic, resistant to weight gain on a calorie-enriched diet, hypersensitive to fasting, and display increased oxidative respiration and reduced fecundity. Serum-dependent activation of the extracellular response kinase (growth) and Smad2/3 (arrest) pathways in Mgat5(-/-) MEFs and bone marrow cells reveals an imbalance favoring arrest. Mgat5(-/-) mice have fewer muscle satellite cells, less osteogenic activity in bone marrow, and accelerated loss of muscle and bone mass with aging. Our results suggest that beta1,6GlcNAc-branched N-glycans promote sensitivity to anabolic cytokines, and increase fat stores, tissue renewal, and longevity.

Chemical enhancers of cytokine signaling that suppress microfilament turnover and tumor cell growth

The transforming growth factor-beta (TGF-beta) family of cytokines regulates cell proliferation, morphogenesis, and specialized cell functions in metazoans. Herein, we screened a compound library for modifiers of TGF-beta signaling in NMuMG epithelial cells using a cell-based assay to measure Smad2/3 nuclear translocation. We identified five enhancers of TGF-beta signaling that share a core structure of diethyl 2-(anilinomethylene)malonate (DAM), and D(50) values of 1 to 4 micromol/L. Taking advantage of the Mgat5 mutant phenotype of accelerated receptor loss to endocytosis, we determined that DAM-1976 restored the sensitivity of Mgat5(-/-) carcinoma cells to both TGF-beta and epidermal growth factor (EGF). In Mgat5 mutant and wild-type carcinoma cells, DAM-1976 enhanced and prolonged TGF-beta- and EGF-dependent Smad2/3 and Erk activation, respectively. DAM-1976 reduced ligand-dependent EGF receptor endocytosis, actin microfilament turnover, and cell spreading, suggesting that the compound attenuates vesicular trafficking. Hyperactivation of intracellular signaling has the potential to suppress tumor cell growth and, in this regard, DAM-1976 represents a new pharmacophore that increases basal activation of Smad2/3 and Erk, inhibits microfilament remodeling, and suppresses carcinoma cell growth.

N-acetylglucosaminyltransferase V (Mgat5)-mediated N-glycosylation negatively regulates Th1 cytokine production by T cells

The differentiation of naive CD4(+) T cells into either proinflammatory Th1 or proallergic Th2 cells strongly influences autoimmunity, allergy, and tumor immune surveillance. We previously demonstrated that beta1,6GlcNAc-branched complex-type (N-acetylglucosaminyltransferase V (Mgat5)) N-glycans on TCR are bound to galectins, an interaction that reduces TCR signaling by opposing agonist-induced TCR clustering at the immune synapse. Mgat5(-/-) mice display late-onset spontaneous autoimmune disease and enhanced resistance to tumor progression and metastasis. In this study we examined the role of beta1,6GlcNAc N-glycan expression in Th1/Th2 cytokine production and differentiation. beta1,6GlcNAc N-glycan expression is enhanced by TCR stimulation independent of cell division and declines at the end of the stimulation cycle. Anti-CD3-activated splenocytes and naive T cells from Mgat5(-/-) mice produce more IFN-gamma and less IL-4 compared with wild-type cells, the latter resulting in the loss of IL-4-dependent down-regulation of IL-4Ralpha. Swainsonine, an inhibitor of Golgi alpha-mannosidase II, blocked beta1,6GlcNAc N-glycan expression and caused a similar increase in IFN-gamma production by T cells from humans and mice, but no additional enhancement in Mgat5(-/-) T cells. Mgat5 deficiency did not alter IFN-gamma/IL-4 production by polarized Th1 cells, but caused an approximately 10-fold increase in IFN-gamma production by polarized Th2 cells. These data indicate that negative regulation of TCR signaling by beta1,6GlcNAc N-glycans promotes development of Th2 over Th1 responses, enhances polarization of Th2 cells, and suggests a mechanism for the increased autoimmune disease susceptibility observed in Mgat5(-/-) mice.

Regulation of cytokine receptors by Golgi N-glycan processing and endocytosis

The Golgi enzyme beta1,6 N-acetylglucosaminyltransferase V (Mgat5) is up-regulated in carcinomas and promotes the substitution of N-glycan with poly N-acetyllactosamine, the preferred ligand for galectin-3 (Gal-3). Here, we report that expression of Mgat5 sensitized mouse cells to multiple cytokines. Gal-3 cross-linked Mgat5-modified N-glycans on epidermal growth factor and transforming growth factor-beta receptors at the cell surface and delayed their removal by constitutive endocytosis. Mgat5 expression in mammary carcinoma was rate limiting for cytokine signaling and consequently for epithelial-mesenchymal transition, cell motility, and tumor metastasis. Mgat5 also promoted cytokine-mediated leukocyte signaling, phagocytosis, and extravasation in vivo. Thus, conditional regulation of N-glycan processing drives synchronous modification of cytokine receptors, which balances their surface retention against loss via endocytosis.

UDP-N-acetylglucosamine:alpha-6-D-mannoside beta1,6 N-acetylglucosaminyltransferase V (Mgat5) deficient mice

Targeted gene mutations in mice that cause deficiencies in protein glycosylation have revealed functions for specific glycans structures in embryogenesis, immune cell regulation, fertility and cancer progression. UDP-N-acetylglucosamine:alpha-6-D-mannoside beta1,6 N-acetylglucosaminyltransferase V (GlcNAc-TV or Mgat5) produces N-glycan intermediates that are elongated with poly N-acetyllactosamine to create ligands for the galectin family of mammalian lectins. We generated Mgat5-deficient mice by gene targeting methods in embryonic stem cells, and observed a complex phenotype in adult mice including susceptibility to autoimmune disease, reduced cancer progression and a behavioral defect. We found that Mgat5-modified N-glycans on the T cell receptor (TCR) complex bind to galectin-3, sequestering TCR within a multivalent galectin-glycoprotein lattice that impedes antigen-dependent receptor clustering and signal transduction. Integrin receptor clustering and cell motility are also sensitive to changes in Mgat5-dependent N-glycosylation. These studies demonstrate that low affinity but high avidity interactions between N-glycans and galectins can regulate the distribution of cell surface receptors and their responsiveness to agonists.

alpha 2-HS glycoprotein/fetuin, a transforming growth factor-beta/bone morphogenetic protein antagonist, regulates postnatal bone growth and remodeling

Soluble transforming growth factor-beta (TGF-beta)/bone morphogenetic protein (BMP)-binding proteins are widely distributed in mammalian tissues and control cytokine access to membrane signaling receptors. The serum and bone-resident glycoprotein alpha2-HS-glycoprotein/fetuin (ASHG) binds to TGF-beta/BMP cytokines and blocks TGF-beta1 binding to cell surface receptors. Therefore, we examined bone growth and remodeling phenotypes in ASHG-deficient mice. The skeletal structure of Ahsg(-/-) mice appeared normal at birth, but abnormalities were observed in adult Ahsg(-/-) mice. Maturation of growth plate chondrocytes was impaired, and femurs lengthened more slowly between 3 and 18 months of age in Ahsg(-/-) mice. However, bone formation was increased in Ahsg(-/-) mice as indicated by greater cortical thickness, accelerated trabecular bone remodeling, and increased osteoblast numbers on bone surfaces. The normal age-related increase in cortical thickness and bone mineral density was accelerated in Ahsg(-/-) mice and was associated with increased energy required to fracture. Bone formation in response to implanted BMP cytokine extended further from the implant in Ahsg(-/-) compared with Ahsg(+/+) mice, confirming the interaction between ASHG and TGF-beta/BMP cytokines in vivo. Our results demonstrate that ASHG blocks TGF-beta-dependent signaling in osteoblastic cells, and mice lacking ASHG display growth plate defects, increased bone formation with age, and enhanced cytokine-dependent osteogenesis.

Suppression of tumor growth and metastasis in Mgat5-deficient mice

Golgi beta1,6N-acetylglucosaminyltransferase V (MGAT5) is required in the biosynthesis of beta1,6GlcNAc-branched N-linked glycans attached to cell surface and secreted glycoproteins. Amounts of MGAT5 glycan products are commonly increased in malignancies, and correlate with disease progression. To study the functions of these N-glycans in development and disease, we generated mice deficient in Mgat5 by targeted gene mutation. These Mgat5-/- mice lacked Mgat5 products and appeared normal, but differed in their responses to certain extrinsic conditions. Mammary tumor growth and metastases induced by the polyomavirus middle T oncogene was considerably less in Mgat5-/- mice than in transgenic littermates expressing Mgat5. Furthermore, Mgat5 glycan products stimulated membrane ruffling and phosphatidylinositol 3 kinase-protein kinase B activation, fueling a positive feedback loop that amplified oncogene signaling and tumor growth in vivo. Our results indicate that inhibitors of MGAT5 might be useful in the treatment of malignancies by targeting their dependency on focal adhesion signaling for growth and metastasis.

Dissecting the role of N-myc in development using a single targeting vector to generate a series of alleles

The N-myc proto-oncogene is expressed in many organs of the mouse embryo, suggesting that it has multiple functions. A null mutation leads to mid-gestation lethality [1-4], obscuring the later roles of the gene in organogenesis. We have generated a multi-purpose gene alteration by combining the potential for homologous and site-specific recombination in a single targeting vector, and using the selectable marker for neomycin-resistance, neo, to downregulate gene activity. This allowed us to create a series of alleles that led to different levels of N-myc expression. The phenotypes revealed a spectrum of developmental problems. The hypomorphic allele produced can be repaired in situ by Cre-recombinase-mediated DNA excision. We show here for the first time the use of a single targeting vector to generate an allelic series. This, and the possibility of subsequent lineage-specific or conditional allele repair in situ, represent new genome modification strategies that can be used to investigate multiple functions of a single gene.

Abnormal blood vessel development and lethality in embryos lacking a single VEGF allele

The endothelial cell-specific vascular endothelial growth factor (VEGF) and its cellular receptors Flt-1 and Flk-1 have been implicated in the formation of the embryonic vasculature. This is suggested by their colocalized expression during embryogenesis and the impaired vessel formation in Flk-1 and Flt-1 deficient embryos. However, because Flt-1 also binds placental growth factor, a VEGF homologue, the precise role of VEGF was unknown. Here we report that formation of blood vessels was abnormal, but not abolished, in heterozygous VEGF-deficient (VEGF+/-) embryos, generated by aggregation of embryonic stem (ES) cells with tetraploid embryos (T-ES) and even more impaired in homozygous VEGF-deficient (VEGF-/-) T-ES embryos, resulting in death at mid-gestation. Similar phenotypes were observed in F1-VEGF+/- embryos, generated by germline transmission. We believe that this heterozygous lethal phenotype, which differs from the homozygous lethality in VEGF-receptor-deficient embryos, is unprecedented for a targeted autosomal gene inactivation, and is indicative of a tight dose-dependent regulation of embryonic vessel development by VEGF.

Tolerance is overcome in beef insulin-transgenic mice by activation of low-affinity autoreactive T cells

To gain insight into the factors controlling the maintenance or loss of T cell self tolerance we produced beef insulin (BI)-transgenic BALB/c mice. Transgenic mice express BI under control of the human insulin promoter and secrete physiological amounts of beef insulin. Although these mice are tolerant to BI, as evidenced by the lack of insulin-specific IgG antibody production following intraperitoneal immunization, tolerance is not complete. Footpad immunization results in a weak antigen-specific T cell proliferative response, indicating the presence of self-reactive BI-specific T cell in the periphery. These T cells are functional in vivo, providing support for IgG1, IgG2a, and IgG2b BI-specific antibody production, but require higher higher concentrations of antigen than nontransgenic T cells (both in vivo and following recall responses in vitro) to become activated. In vitro, BI-specific T cell proliferation in BI-transgenic mice can be largely restored by addition of interleukin-2, indicating that a significant component of T cell tolerance is mediated by anergy. To characterize the autoreactive T cells that become activated when tolerance is broken, BI-specific T cell hybridomas were generated from transgenic mice and compared to a panel of hybridomas previously derived from nontransgenic BALB/c mice. The majority of BI-transgenic hybridomas recognized the immunodominant A1-14 beef insulin peptide but with lower avidity than BALB/c hybridomas. Consistent with this, none of the dominant T cell receptor rearrangements found in the BALB/c BI-specific T cell receptor repertoire were found in the transgenic hybridomas. These results indicate that, despite evidence for clonal inactivation of many BI-specific T cells in BI-transgenic mice, loss of tolerance results from activation of low-affinity antigen-specific T cells that appear to have escaped this process.

Both MHC and background gene heterozygosity alter T cell receptor repertoire selection in an antigen-specific response

Many autoimmune diseases are associated with specific class II MHC alleles; however, this association is not complete. One explanation for the variable expression of disease in susceptible individuals is that variability in the TCR repertoire may alter the potential to generate pathogenic autoreactive T cells. The current study was undertaken to examine the possibility that MHC and background heterozygosity, which is the norm in the outbred human population, alters the expressed TCR repertoire and, if so, whether this has an impact on peptide recognition and antigenic specificity. We, therefore, systematically analysed the beef insulin-specific TCR repertoire in inbred BALB/c mice before and after introduction of MHC heterozygosity (BALB/c x BALB.K)F1 mice, or MHC and background gene heterozygosity (BALB/c x A/J)F1 mice. We show that T cells from all three repertoires are predominantly Ad-restricted and recognize the same immunodominant peptide. Despite this, the beef insulin-specific TCR repertoires in F1 mice differ from those seen in BALB/c mice with the most dramatic changes seen in (BALB/c x A/J)F1 mice. These changes are accompanied by subtle differences in the antigenic specificity of the T cells. The results demonstrate that both MHC and background gene heterozygosity affect TCR repertoire selection, suggesting that the variable expression of autoimmune disease in individuals with a susceptible MHC allele may result, in part, from variability in the TCR repertoire introduced by this heterozygosity.

Conserved amino acid residues in the complementarity-determining region 1 of the TCR beta-chain are involved in the recognition of conventional Ag and Mls-1 superantigen

Superantigens activate T cells by interacting primarily with the V beta region of the TCR. This report describes a series of studies performed to elucidate the role of the conserved amino acid motif (Asp-His-Asn) in the complementarity-determining region 1 (CDR1) of the TCR V beta chains that recognize murine endogenous superantigen Mls-1. By using site-directed mutagenesis of the Mls-1-reactive TCR V beta 6 gene, it is shown that the alterations of the conserved CDR1 motif disrupt Mls-1 superantigen and conventional Ag recognition in vitro. The loss of V beta 6 (mutant)+ TCR reactivity to Mls-1 superantigen is apparently dependent on the partner alpha-chain in the V beta 6/V alpha 3 TCR pairing shows some reactivity to Mls-1, whereas other TCR pairings do not. The examination of the developmental fate of the mutated form of the V beta 6 chain in Mls-1+ mice by using retroviral vector-mediated gene transfer confirms the critical role played by the CDR1 residues in Mls-1 recognition in vivo. Collectively, the results indicate that the CDR1 of the TCR V beta 6 chain is involved in interacting with peptide/MHC as well as in Mls-1 recognition. The observation that the conserved residues in selective TCR V beta chains are imparting a significant contribution to Ag recognition suggests a molecular basis for the intrinsic bias of some V beta chains for MHC molecules.

Conserved amino acid residues in the complementarity-determining region 1 of the TCR beta-chain are involved in the recognition of conventional Ag and Mls-1 superantigen

Superantigens activate T cells by interacting primarily with the V beta region of the TCR. This report describes a series of studies performed to elucidate the role of the conserved amino acid motif (Asp-His-Asn) in the complementarity-determining region 1 (CDR1) of the TCR V beta chains that recognize murine endogenous superantigen Mls-1. By using site-directed mutagenesis of the Mls-1-reactive TCR V beta 6 gene, it is shown that the alterations of the conserved CDR1 motif disrupt Mls-1 superantigen and conventional Ag recognition in vitro. The loss of V beta 6 (mutant)+ TCR reactivity to Mls-1 superantigen is apparently dependent on the partner alpha-chain in the V beta 6/V alpha 3 TCR pairing shows some reactivity to Mls-1, whereas other TCR pairings do not. The examination of the developmental fate of the mutated form of the V beta 6 chain in Mls-1+ mice by using retroviral vector-mediated gene transfer confirms the critical role played by the CDR1 residues in Mls-1 recognition in vivo. Collectively, the results indicate that the CDR1 of the TCR V beta 6 chain is involved in interacting with peptide/MHC as well as in Mls-1 recognition. The observation that the conserved residues in selective TCR V beta chains are imparting a significant contribution to Ag recognition suggests a molecular basis for the intrinsic bias of some V beta chains for MHC molecules.

Expression of Mtv-7 sag gene in vivo using a retroviral vector results in selective inactivation of superantigen reactive T cells

T cells expressing specific TCR V beta chains are intrathymically eliminated in mice expressing the murine Mls (minor lymphocyte stimulating) superantigens. Recently, in vitro studies have shown that the endogenous mouse mammary tumor virus (MMTV)-7 sag gene encodes Mls-1 Ag. The demonstrated ability of MMTV superantigen proteins to react with TCRs has led to the postulate that other infectious retroviruses may use superantigen-like molecules to modify the host's immune system. In this report, successful retrovirus-mediated Mtv-7 sag gene transfer into pluripotent hematopoietic stem cells is described. In two different strains of Mls-1- host mice (CBA/Ca and BALB/c) reconstituted with Mtv-7 sag gene expressing bone marrow cells, low levels of ectopic Mtv-7 sag gene expression on syngeneic donor hematopoietic stem cell-derived population alone can induce partial clonal deletion of Mls-1 reactive V beta 6+ and V beta 8.1+ T cells, and complete clonal inactivation of V beta 8.1+ T cells.

Exogenous Mtv-7 superantigen transgene expression in major histocompatibility complex class II I-E- mice reconstituted with embryonic stem cell-derived hematopoietic stem cells

Direct genetic manipulation of hematopoietic cells is limited by the lack of an established hematopoietic stem cell line. It has been demonstrated that embryonic stem (ES) cell<-->tetraploid embryos are completely ES cell-derived and that fetal liver (FL) cells from these embryos support hematopoiesis in lethally irradiated recipients. In this report, we demonstrate that FL cells from ES cell<-->tetraploid embryos support normal lymphopoiesis and T-cell repertoire development. Moreover, the introduction of the Mtv-7 superantigen transgene coding for minor lymphocyte stimulatory antigen 1 into murine hematopoietic cells via reconstitution with ES cell<-->tetraploid FL cells demonstrates that this method can effectively confer stable genetic changes into the hematopoietic tissues without going through the germ line. Long-term and secondary reconstitution with ES cell<-->tetraploid FL cells expressing the Mtv-7 superantigen transgene clonally deleted minor lymphocyte stimulatory antigen 1-reactive T-cell receptor V beta 6+, -8.1+, and -9+ T cells, but not V beta 7+ T cells, in H-2b (I-E-) mice. This model system will be extremely important for analyzing structure-function relationships of molecules involved in proliferation, differentiation, and selection of hematopoietic cells in vivo and for examining hematopoiesis-specific effects of mutations that are lethal during embryogenesis.

Expression of Mtv-7 sag gene in vivo using a retroviral vector results in selective inactivation of superantigen reactive T cells

T cells expressing specific TCR V beta chains are intrathymically eliminated in mice expressing the murine Mls (minor lymphocyte stimulating) superantigens. Recently, in vitro studies have shown that the endogenous mouse mammary tumor virus (MMTV)-7 sag gene encodes Mls-1 Ag. The demonstrated ability of MMTV superantigen proteins to react with TCRs has led to the postulate that other infectious retroviruses may use superantigen-like molecules to modify the host's immune system. In this report, successful retrovirus-mediated Mtv-7 sag gene transfer into pluripotent hematopoietic stem cells is described. In two different strains of Mls-1- host mice (CBA/Ca and BALB/c) reconstituted with Mtv-7 sag gene expressing bone marrow cells, low levels of ectopic Mtv-7 sag gene expression on syngeneic donor hematopoietic stem cell-derived population alone can induce partial clonal deletion of Mls-1 reactive V beta 6+ and V beta 8.1+ T cells, and complete clonal inactivation of V beta 8.1+ T cells.

Amino acid residues in the T cell receptor CDR3 determine the antigenic reactivity patterns of insulin-reactive hybridomas

We examined TCR gene usage in a panel of beef insulin/I-Ad-restricted T cell hybrids obtained from BALB/c mice. These hybrids demonstrated several distinct patterns of reactivity defined by their ability to respond to species variants of insulin. Correlation of TCR-alpha and -beta-gene usage with these patterns of reactivity demonstrated that TCR gene usage was restricted within Ag reactivity groups. In particular, V-J junctional regions (CDR3 equivalent) were restricted with conserved junctional amino acid motifs present in both TCR-alpha- and -beta-chains. Comparison of TCR gene usage in hybrids expressing identical V alpha and V beta gene segments but demonstrating different patterns of reactivity revealed that changes in either J alpha and/or J beta gene segment usage could alter antigenic reactivity. Indeed, single or limited amino acid differences within the CDR3 region were sufficient to markedly alter fine specificity. These data demonstrate the critical role for CDR3 in determining antigenic reactivity in beef insulin-reactive hybrids and are compatible with the current model of TCR/peptide/MHC interaction.

Amino acid residues in the T cell receptor CDR3 determine the antigenic reactivity patterns of insulin-reactive hybridomas

We examined TCR gene usage in a panel of beef insulin/I-Ad-restricted T cell hybrids obtained from BALB/c mice. These hybrids demonstrated several distinct patterns of reactivity defined by their ability to respond to species variants of insulin. Correlation of TCR-alpha and -beta-gene usage with these patterns of reactivity demonstrated that TCR gene usage was restricted within Ag reactivity groups. In particular, V-J junctional regions (CDR3 equivalent) were restricted with conserved junctional amino acid motifs present in both TCR-alpha- and -beta-chains. Comparison of TCR gene usage in hybrids expressing identical V alpha and V beta gene segments but demonstrating different patterns of reactivity revealed that changes in either J alpha and/or J beta gene segment usage could alter antigenic reactivity. Indeed, single or limited amino acid differences within the CDR3 region were sufficient to markedly alter fine specificity. These data demonstrate the critical role for CDR3 in determining antigenic reactivity in beef insulin-reactive hybrids and are compatible with the current model of TCR/peptide/MHC interaction.