Reassessing the utility of CT angiograms in penetrating injuries to the extremities

BACKGROUND

Computed tomography angiography has become routine in the management of penetrating trauma to the extremity. Our objective was to evaluate the efficacy of physical examination findings compared with computed tomography angiography for detection of clinically significant vascular injuries associated with penetrating trauma to the extremity.

METHODS

This was a retrospective chart review of patients presenting to a single level 1 trauma center from January 2013-June 2016. Patients with penetrating trauma to the extremity and no hard signs of vascular injury were included. Physical examination and computed tomography angiography findings were analyzed, with particular focus given to missed injuries.

RESULTS

We identified 393 patients with penetrating trauma to the extremity without hard signs of vascular injury. Computed tomography angiography was performed in 114 patients (29%). Four patients with distal pulses documented on their initial trauma surveys were found to have vascular injuries on computed tomography angiography, although 3 of these injuries were identified on repeat physical examination. One additional patient had a delayed presentation of a pseudoaneurysm. No mortality or limb loss resulted from these injuries. Total hospital charges for computed tomography angiography amounted to over $700,000.

CONCLUSION

Patients with penetrating trauma to the extremity and no hard signs of vascular injury do not require computed tomography angiography for identification of clinically relevant vascular injuries that require emergent operative repair. Serial physical examination appears to provide accurate detection of vascular injury requiring procedural intervention.

C. elegans SUP-46, an HNRNPM family RNA-binding protein that prevents paternally-mediated epigenetic sterility

BACKGROUND

In addition to DNA, gametes contribute epigenetic information in the form of histones and non-coding RNA. Epigenetic programs often respond to stressful environmental conditions and provide a heritable history of ancestral stress that allows for adaptation and propagation of the species. In the nematode C. elegans, defective epigenetic transmission often manifests as progressive germline mortality. We previously isolated sup-46 in a screen for suppressors of the hexosamine pathway gene mutant, gna-2(qa705). In this study, we examine the role of SUP-46 in stress resistance and progressive germline mortality.

RESULTS

We identified SUP-46 as an HNRNPM family RNA-binding protein, and uncovered a highly novel role for SUP-46 in preventing paternally-mediated progressive germline mortality following mating. Proximity biotinylation profiling of human homologs (HNRNPM, MYEF2) identified proteins of ribonucleoprotein complexes previously shown to contain non-coding RNA. Like HNRNPM and MYEF2, SUP-46 was associated with multiple RNA granules, including stress granules, and also formed granules on active chromatin. SUP-46 depletion disrupted germ RNA granules and caused ectopic sperm, increased sperm transcripts, and chronic heat stress sensitivity. SUP-46 was also required for resistance to acute heat stress, and a conserved "MYEF2" motif was identified that was needed for stress resistance.

CONCLUSIONS

In mammals, non-coding RNA from the sperm of stressed males has been shown to recapitulate paternal stress phenotypes in the offspring. Our results suggest that HNRNPM family proteins enable stress resistance and paternally-mediated epigenetic transmission that may be conserved across species.

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 (HIF) 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, although 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 tumorigenicity. 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

The galectin lattice at a glance

Galectins are a family of widely expressed β-galactoside-binding lectins in metazoans. The 15 mammalian galectins have either one or two conserved carbohydrate recognition domains (CRDs), with galectin-3 being able to pentamerize; they form complexes that crosslink glycosylated ligands to form a dynamic lattice. The galectin lattice regulates the diffusion, compartmentalization and endocytosis of plasma membrane glycoproteins and glycolipids. The galectin lattice also regulates the selection, activation and arrest of T cells, receptor kinase signaling and the functionality of membrane receptors, including the glucagon receptor, glucose and amino acid transporters, cadherins and integrins. The affinity of transmembrane glycoproteins to the galectin lattice is proportional to the number and branching of their N-glycans; with branching being mediated by Golgi N-acetylglucosaminyltransferase-branching enzymes and the supply of UDP-GlcNAc through metabolite flux through the hexosamine biosynthesis pathway. The relative affinities of glycoproteins for the galectin lattice depend on the activities of the Golgi enzymes that generate the epitopes of their ligands and, thus, provide a means to analyze biological function of lectins and of the 'glycome' more broadly.

Integrative analysis of kinase networks in TRAIL-induced apoptosis provides a source of potential targets for combination therapy

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is an endogenous secreted peptide and, in preclinical studies, preferentially induces apoptosis in tumor cells rather than in normal cells. The acquisition of resistance in cells exposed to TRAIL or its mimics limits their clinical efficacy. Because kinases are intimately involved in the regulation of apoptosis, we systematically characterized kinases involved in TRAIL signaling. Using RNA interference (RNAi) loss-of-function and cDNA overexpression screens, we identified 169 protein kinases that influenced the dynamics of TRAIL-induced apoptosis in the colon adenocarcinoma cell line DLD-1. We classified the kinases as sensitizers or resistors or modulators, depending on the effect that knockdown and overexpression had on TRAIL-induced apoptosis. Two of these kinases that were classified as resistors were PX domain-containing serine/threonine kinase (PXK) and AP2-associated kinase 1 (AAK1), which promote receptor endocytosis and may enable cells to resist TRAIL-induced apoptosis by enhancing endocytosis of the TRAIL receptors. We assembled protein interaction maps using mass spectrometry-based protein interaction analysis and quantitative phosphoproteomics. With these protein interaction maps, we modeled information flow through the networks and identified apoptosis-modifying kinases that are highly connected to regulated substrates downstream of TRAIL. The results of this analysis provide a resource of potential targets for the development of TRAIL combination therapies to selectively kill cancer cells.

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.

A novel role for Plk4 in regulating cell spreading and motility

Polo family kinase 4 (Plk4) is required for mitotic progression, and is haploinsufficient for tumor suppression and timely hepatocyte polarization in regenerating liver. At the same time, recent evidence suggests that Plk4 expression may have a role in clinical cancer progression, although the mechanisms are not clear. Here we identify a gene expression pattern predictive of reduced motility in Plk4(+/-) murine embryonic fibroblasts (MEFs) and validate this prediction with functional assays of cell spreading, migration and invasion. Increased Plk4 expression enhances cell spreading in Plk4(+/-) MEFs and migration in human embryonic kidney 293T cells, and increases invasion by DLD-1 colon cancer cells. Plk4 depletion impairs invasion of wild-type MEFs and suppresses invasion by MDA-MB231 breast cancer cells. Cytoskeletal reorganization and development of polarity are impaired in Plk4-deficient cells that have been stimulated to migrate. Endogenous Plk4 phosphorylated at the autophosphorylation site S305 localizes to the protrusions of motile cells, coincident with the RhoA GEF Ect2, GTP-bound RhoA and the RhoA effector mDia. Taken together, our findings reveal an unexpected activity of Plk4 that promotes cell migration and may underlie an association between increased Plk4 expression, cancer progression and death from metastasis in solid tumor patients.

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.

Science Signaling Podcast: 18 February 2014

The adaptor protein p66Shc decreases glucose uptake and metabolism by inhibiting mTOR signaling.

Encoding asymmetry of the N-glycosylation motif facilitates glycoprotein evolution

Protein N-glycosylation is found in all domains of life and has a conserved role in glycoprotein folding and stability. In animals, glycoproteins transit through the Golgi where the N-glycans are trimmed and rebuilt with sequences that bind lectins, an innovation that greatly increases structural diversity and redundancy of glycoprotein-lectin interaction at the cell surface. Here we ask whether the natural tension between increasing diversity (glycan-protein interactions) and site multiplicity (backup and status quo) might be revealed by a phylogenic examination of glycoproteins and NXS/T(X≠P) N-glycosylation sites. Site loss is more likely by mutation at Asn encoded by two adenosine (A)-rich codons, while site gain is more probable by generating Ser or Thr downstream of an existing Asn. Thus mutations produce sites at novel positions more frequently than the reversal of recently lost sites, and therefore more paths though sequence space are made available to natural selection. An intra-species comparison of secretory and cytosolic proteins revealed a departure from equilibrium in sequences one-mutation-away from NXS/T and in (A) content, indicating strong selective pressures and exploration of N-glycosylation positions during vertebrate evolution. Furthermore, secretory proteins have evolved at rates proportional to N-glycosylation site number, indicating adaptive interactions between the N-glycans and underlying protein. Given the topology of the genetic code, mutation of (A) is more often nonsynonomous, and Lys, another target of many PTMs, is also encoded by two (A)-rich codons. An examination of acetyl-Lys sites in proteins indicated similar evolutionary dynamics, consistent with asymmetry of the target and recognition portions of modified sites. Our results suggest that encoding asymmetry is an ancient mechanism of evolvability that increases diversity and experimentation with PTM site positions. Strong selective pressures on PTMs may have contributed to the A+T→G+C shift in genome-wide nucleotide composition during metazoan radiation.

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.

Density-dependent lectin-glycan interactions as a paradigm for conditional regulation by posttranslational modifications

Mice with null mutations in specific Golgi glycosyltransferases show evidence of glycan compensation where missing carbohydrate epitopes are found on biosynthetically related structures. Repetitive saccharide sequences within the larger glycan structures are functional epitopes recognized by animal lectins. These studies provide the first in vivo support for the existence of a feedback system that maintains and regulates glycan epitope density in cells. Receptor regulation by lectin-glycan interactions and the Golgi provides a mechanism for the adaptation of cell surface receptors and solute transporters in response to environmental cues and intracellular signaling. We suggest that other posttranslational modification systems might have similar conditional features regulated by density-dependent ligand-epitope interactions.

Galectin-3 protein regulates mobility of N-cadherin and GM1 ganglioside at cell-cell junctions of mammary carcinoma cells

Galectin-3 binding to cell surface glycoproteins, including branched N-glycans generated by N-acetylglucosaminyltransferase V (Mgat5) activity, forms a multivalent, heterogeneous, and dynamic lattice. This lattice has been shown to regulate integrin and receptor tyrosine kinase signaling promoting tumor cell migration. N-cadherin is a homotypic cell-cell adhesion receptor commonly overexpressed in tumor cells that contributes to cell motility. Here we show that galectin-3 and N-cadherin interact and colocalize with the lipid raft marker GM1 ganglioside in cell-cell junctions of mammary epithelial cancer cells. Disruption of the lattice by deletion of Mgat5, siRNA depletion of galectin-3, or competitive inhibition with lactose stabilizes cell-cell junctions. It also reduces, in a p120-catenin-dependent manner, the dynamic pool of junctional N-cadherin. Proteomic analysis of detergent-resistant membranes (DRMs) revealed that the galectin lattice opposes entry of many proteins into DRM rafts. N-cadherin and catenins are present in DRMs; however, their DRM distribution is not significantly affected by lattice disruption. Galectin lattice integrity increases the mobile fraction of the raft marker, GM1 ganglioside binding cholera toxin B subunit Ctb, at cell-cell contacts in a p120-catenin-independent manner, but does not affect the mobility of either Ctb-labeled GM1 or GFP-coupled N-cadherin in nonjunctional regions. Our results suggest that the galectin lattice independently enhances lateral molecular diffusion by direct interaction with specific glycoconjugates within the adherens junction. By promoting exchange between raft and non-raft microdomains as well as molecular dynamics within junction-specific raft microdomains, the lattice may enhance turnover of N-cadherin and other glycoconjugates that determine junctional stability and rates of cell migration.

The eggshell in the C. elegans oocyte-to-embryo transition

In egg-laying animals, embryonic development takes place within the highly specialized environment provided by the eggshell and its underlying extracellular matrix. Far from being simply a passive physical support, the eggshell is a key player in many early developmental events. Herein, we review current understanding of eggshell structure, biosynthesis, and function in zygotic development of the nematode, C. elegans. Beginning at sperm contact or entry, eggshell layers are produced sequentially. The earlier outer layers are required for secretion or organization of inner layers, and layers differ in composition and function. Developmental events that depend on the eggshell include polyspermy barrier generation, high fidelity meiotic chromosome segregation, osmotic barrier synthesis, polar body extrusion, anterior-posterior polarization, and organization of membrane and cortical proteins. The C. elegans eggshell is proving to be an excellent, tractable system to study the molecular cues of the extracellular matrix that instruct cell polarity and early development.