Cell surface glycan-lectin interactions in tumor metastasis

Molecular recognition with boronic acids-applications in chemical biology

Small molecules have long been used for the selective recognition of a wide range of analytes. The ability of these chemical receptors to recognise and bind to specific targets mimics certain biological processes (such as protein-substrate interactions) and has therefore attracted recent interest. Due to the abundance of biological molecules possessing polyhydroxy motifs, boronic acids-which form five-membered boronate esters with diols-have become increasingly popular in the synthesis of small chemical receptors. Their targets include biological materials and natural products including phosphatidylinositol bisphosphate, saccharides and polysaccharides, nucleic acids, metal ions and the neurotransmitter dopamine. This review will focus on the many ways in which small chemical receptors based on boronic acids have been used as biochemical tools for various purposes, including sensing and detection of analytes, interference in signalling pathways, enzyme inhibition and cell delivery systems. The most recent developments in each area will be highlighted.

Protein O-mannosylation: what we have learned from baker's yeast

BACKGROUND

Protein O-mannosylation is a vital type of glycosylation that is conserved among fungi, animals, and humans. It is initiated in the endoplasmic reticulum (ER) where the synthesis of the mannosyl donor substrate and the mannosyltransfer to proteins take place. O-mannosylation defects interfere with cell wall integrity and ER homeostasis in yeast, and define a pathomechanism of severe neuromuscular diseases in humans.

SCOPE OF REVIEW

On the molecular level, the O-mannosylation pathway and the function of O-mannosyl glycans have been characterized best in the eukaryotic model yeast Saccharomyces cerevisiae. In this review we summarize general features of protein O-mannosylation, including biosynthesis of the mannosyl donor, characteristics of acceptor substrates, and the protein O-mannosyltransferase machinery in the yeast ER. Further, we discuss the role of O-mannosyl glycans and address the question why protein O-mannosylation is essential for viability of yeast cells.

GENERAL SIGNIFICANCE

Understanding of the molecular mechanisms of protein O-mannosylation in yeast could lead to the development of novel antifungal drugs. In addition, transfer of the knowledge from yeast to mammals could help to develop diagnostic and therapeutic approaches in the frame of neuromuscular diseases. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum.

Alteration of plasma galactose/N-acetylgalactosamine level after irradiation

Although glycoproteins possess a variety of functional and structural roles in intracellular and intercellular activities, the effect of ionizing radiation (IR) on glycosylation is largely unknown. To explore this effect, we established a sandwich assay in which PHA-L, a phytohaemagglutinin that agglutinates leukocytes, was used as a coating layer to capture glycoproteins containing complex oligosaccharides; the bound glycoproteins were then measured. C57BL/6 mice were exposed to 0, 3, 6, or 10 Gy, and the plasma was collected at 6, 12, 18, 24, 48, 72, or 168 h and then analyzed for galactose/N-acetylgalactosamine (Gal/GalNAc) containing proteins. We found that (1) the sandwich assay accurately measured the level of glycoproteins, (2) 6-12 h after IR, the amount of glycoproteins containing GalNAc increased, and (3) at 72 and 168 h, 10 Gy was associated with a decrease in Gal/GalNAc. These IR-induced alterations might relate to the release of glycoproteins into the blood and the damage of the proteins and genes that are related to the glycosylation process.

Poly(2-hydroxyethyl methacrylate) brush surface for specific and oriented adsorption of glycosidases

We present a detailed picture to screen general ligands from simple chemicals for fabricating affinity surface to glycosidase enzymes. The surface was constructed by grafting poly(2-hydroxyethyl methacrylate) (PHEMA) brush on SPR gold chip via surface-initiated atom-transfer radical polymerization, after which poly(methoxyethyl methacrylate) (PMEMA) and poly(oligo(ethylene glycol) methacrylate) (POEGMA) brushes were also prepared for comparison. SPR measurements were adopted to monitor the early-stage adsorption of two glycosidases and three other typical proteins. PHEMA resists the adsorption of lysozyme, bovine serum albumin, and fibrinogen, while it is capable of specifically adsorbing β-glucosidase (GLU) and β-galactosidase (GAL). These are quite different from the nonspecific adsorption of PMEMA and the anti-nonspecific adsorption of POEGMA to the studied proteins, because PHEMA is the acceptor substrate of the glycosidases. About 69.6 and 93.7 ng/cm(2) of GAL and GLU are adsorbed on the PHEMA brush surface, of which more than 49.6 ng/cm(2) is remained after washing with PBS. The specific adsorption process is appropriately described by Freundlich isothermal model rather than Langmuir one, and is also indicated to be spontaneous, endothermic, and entropy driven through thermodynamic studies. Taking into account all stated results above, we propose that molecular recognition takes place between the hydroxyl groups of PHEMA and the active sites of glycosidases, which subsequently enables the oriented adsorption of glycosidases on the brush surface. The adsorbed enzyme can be effectively eluted with 1.0 M aqueous solution of ethanol. Our findings open the door to the further development in the design of novel acceptor substrate-ligand affinity chromatography for enzyme purification.

Anti-metastatic and anti-angiogenic activities of sulfated polysaccharide of Sepiella maindroni ink

A previous study demonstrated that SIP-SII, a sulfated Sepiella maindroni ink polysaccharide, suppressed the invasion and migration of cancer cells via the inhibition of the proteolytic activity of matrix metalloproteinase-2 (MMP-2). Therefore, this study investigated the anti-metastatic effect of SIP-SII in vivo. SIP-SII (15 and 30 mg/kg d) markedly decreased B16F10 pulmonary metastasis in mice models by 85.9% and 88.0%, respectively. Immunohistochemistry showed that SIP-SII decreased the expression of the intercellular adhesion molecule 1 (ICAM-1) and basic fibroblast growth factor (bFGF) in lung metastasis nodules. In addition, SIP-SII inhibited neovascularization in chick chorioallantoic membrane assay at 0.08-2 mg/mL. In the in vitro experiments, SIP-SII (0.8-500 μg/mL) significantly decreased the protein and mRNA expression of ICAM-1 and bFGF in SKOV3 and EA.hy926 cells, respectively. These results suggested that SIP-SII might suppress melanoma metastasis via the inhibition of the tumor adhesion mediated by ICAM-1 and the angiogenesis mediated by bFGF, as well as resulting in depression of the invasion and migration of carcinoma cells.

The sweet side of tumor immunotherapy

Carbohydrate signatures on tumor cells have functional implications in tumor growth and metastasis and constitute valuable tools in cancer diagnosis and immunotherapy. Increasing data regarding the mechanisms by which they are recognized by the immune system are facilitating the design of more efficient immunotherapeutic protocols based on cancer-associated glycan structures. Recent molecular and proteomic studies revealed that carbohydrates are recognized, not only by B cells and antibodies, but also by cells from the innate arm of immunity, as well as by T cells, and are able to induce specific T-cell immunity and cytotoxicity. In this review, we discuss and update the different strategies targeting tumor-associated carbohydrate antigens that are being evaluated for antitumor immunotherapy, an approach that will be highly relevant, especially when combined with other strategies, in the future fight against cancer.

MicroRNA and cutaneous melanoma: from discovery to prognosis and therapy

Melanoma incidence and associated mortality continue to increase worldwide. The lack of treatments with durable responses for stage IV melanoma may be due, at least in part, to an incomplete understanding of the molecular mechanisms that regulate tumor initiation and/or progression to metastasis. Recent evidence supports miRNA dysregulation in melanoma impacting several well-known pathways such as the PI3K/AKT or RAS/MAPK pathways, but also underexplored cellular processes like protein glycosylation and immune modulation. There is also increasing evidence that miRNA can improve patient prognostic classification over the classical staging system and provide new therapeutic opportunities. The integration of this recently acquired knowledge with known molecular alterations in protein coding genes characteristic of these tumors (i.e., BRAF and NRAS mutations, CDKN2A inactivation) is critical for a complete understanding of melanoma pathogenesis. Here, we compile the evidence of the functional roles of miRNAs in melanomagenesis and progression, and of their clinical utility as biomarkers, prognostic tools and potential therapeutic targets. Characterization of miRNA alterations in melanoma may provide new angles for therapeutic intervention, help to decipher mechanisms of drug resistance, and improve patient classification for disease surveillance and clinical benefit.

Beyond the genome and proteome: targeting protein modifications in cancer

Nearly all proteins are modified in post translational events, indeed, understanding the control and function of post translational modifications (PTMs) is arguably the 'next frontier' for cancer cell biologists. The most well understood PTMs include glycosylation, phosphorylation, ubiquitination, methylation and palmitylation. Each of these modifications has been observed to be altered in cancer, affecting key cellular pathways including signal transduction, cell membrane receptor function, and protein-protein interactions. A number of strategies have been proposed that aim to target the modified proteins themselves, the enzymes that construct them, or that boost host-cellular immunity against modified residues aberrantly expressed in cancer.

L1CAM from human melanoma carries a novel type of N-glycan with Galβ1-4Galβ1- motif. Involvement of N-linked glycans in migratory and invasive behaviour of melanoma cells

Dramatic changes in glycan biosynthesis during oncogenic transformation result in the emergence of marker glycans on the cell surface. We analysed the N-linked glycans of L1CAM from different stages of melanoma progression, using high-performance liquid chromatography combined with exoglycosidase sequencing, matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, and lectin probes. L1CAM oligosaccharides are heavily sialylated, mainly digalactosylated, biantennary complex-type structures with galactose β1-4/3-linked to GlcNAc and with or without fucose α1-3/6-linked to GlcNAc. Hybrid, bisected hybrid, bisected triantennary and tetraantennary complex oligosaccharides, and β1-6-branched complex-type glycans with or without lactosamine extensions are expresses at lower abundance. We found that metastatic L1CAM possesses only α2-6-linked sialic acid and the loss of α2-3-linked sialic acid in L1CAM is a phenomenon observed during the transition of melanoma cells from VGP to a metastatic stage. Unexpectedly, we found a novel monoantennary complex-type oligosaccharide with a Galβ1-4Galβ1- epitope capped with sialic acid residues A1[3]G(4)2S2-3. To our knowledge this is the first report documenting the presence of this oligosaccharide in human cancer. The novel and unique N-glycan should be recognised as a new class of human melanoma marker. In functional tests we demonstrated that the presence of cell surface α2-3-linked sialic acid facilitates the migratory behaviour and increases the invasiveness of primary melanoma cells, and it enhances the motility of metastatic cells. The presence of cell surface α2-6-linked sialic acid enhances the invasive potential of both primary and metastatic melanoma cells. Complex-type oligosaccharides in L1CAM enhance the invasiveness of metastatic melanoma cells.

Inhibition of fatty acid synthase attenuates CD44-associated signaling and reduces metastasis in colorectal cancer

Fatty acid synthase (FASN) and ATP-citrate lyase, key enzymes of de novo lipogenesis, are significantly upregulated and activated in many cancers and portend poor prognosis. Even though the role of lipogenesis in providing proliferative and survival advantages to cancer cells has been described, the impact of aberrant activation of lipogenic enzymes on cancer progression remains unknown. In this study, we found that elevated expression of FASN is associated with advanced stages of colorectal cancer (CRC) and liver metastasis, suggesting that it may play a role in progression of CRC to metastatic disease. Targeted inhibition of lipogenic enzymes abolished expression of CD44, a transmembrane protein associated with metastases in several cancers including CRC. In addition, inhibition of lipogenic enzymes and reduced expression of CD44 attenuated the activation of MET, Akt, FAK, and paxillin, which are known to regulate adhesion, migration, and invasion. These changes were consistent with an observed decrease in migration and adhesion of CRC cells in functional assays and with reorganization of actin cytoskeleton upon FASN inhibition. Despite the modest effect of FASN inhibition on tumor growth in xenografts, attenuation of lipogenesis completely abolished establishment of hepatic metastasis and formation of secondary metastasis. Together, our findings suggest that targeting de novo lipogenesis may be a potential treatment strategy for advanced CRC.