33 research outputs found
Nucleon and hadron structure changes in the nuclear medium and impact on observables
We review the effect of hadron structure changes in a nuclear medium using
the quark-meson coupling (QMC) model, which is based on a mean field
description of non-overlapping nucleon (or baryon) bags bound by the
self-consistent exchange of scalar and vector mesons. This approach leads to
simple scaling relations for the changes of hadron masses in a nuclear medium.
It can also be extended to describe finite nuclei, as well as the properties of
hypernuclei and meson-nucleus deeply bound states. It is of great interest that
the model predicts a variation of the nucleon form factors in nuclear matter.
We also study the empirically observed, Bloom-Gilman (quark-hadron) duality.
Other applications of the model include subthreshold kaon production in heavy
ion collisions, D and D-bar meson production in antiproton-nucleus collisions,
and J/Psi suppression. In particular, the modification of the D and D-bar meson
properties in nuclear medium can lead to a large J/Psi absorption cross
section, which explains the observed J/Psi suppression in relativistic heavy
ion collisions.Comment: 143 pages, 77 figures, references added, a review article accepted in
Prog. Part. Nucl. Phy
Pediatric T-cell acute lymphoblastic leukemia
The most common pediatric malignancy is acute lymphoblastic leukemia (ALL), of which T-cell ALL (T-ALL) comprises 10–15% of cases. T-ALL arises in the thymus from an immature thymocyte as a consequence of a stepwise accumulation of genetic and epigenetic aberrations. Crucial biological processes, such as differentiation, self-renewal capacity, proliferation, and apoptosis, are targeted and deranged by several types of neoplasia-associated genetic alteration, for example, translocations, deletions, and mutations of genes that code for proteins involved in signaling transduction, epigenetic regulation, and transcription. Epigenetically, T-ALL is characterized by gene expression changes caused by hypermethylation of tumor suppressor genes, histone modifications, and miRNA and lncRNA abnormalities. Although some genetic and gene expression patterns have been associated with certain clinical features, such as immunophenotypic subtype and outcome, none has of yet generally been implemented in clinical routine for treatment decisions. The recent advent of massive parallel sequencing technologies has dramatically increased our knowledge of the genetic blueprint of T-ALL, revealing numerous fusion genes as well as novel gene mutations. The challenges now are to integrate all genetic and epigenetic data into a coherent understanding of the pathogenesis of T-ALL and to translate the wealth of information gained in the last few years into clinical use in the form of improved risk stratification and targeted therapies. Here, we provide an overview of pediatric T-ALL with an emphasis on the acquired genetic alterations that result in this disease
Coupling of Immunostimulants to Live Cells through Metabolic Glycoengineering and Bioorthogonal Click Chemistry
The
present study investigated the potential of metabolic glycoengineering
followed by bioorthogonal click chemistry for introducing into cell-surface
glycans different immunomodulating molecules. Mouse tumor models EG7
and MC38-OVA were treated with Ac4GalNAz and Ac4ManNAz followed by
ligation of immunostimulants to modified cell-surface glycans of the
living cells through bioorthogonal click chemistry. The presence of
covalently bound oligosaccharide and oligonucleotide immunostimulants
could be clearly established. The activation of a reporter macrophage
cell line was determined. Depending on the tumor cell line, covalently
and noncovalently bound CpG activated the macrophages by between 67
and 100% over controls. EG7 cells with covalently attached immunostimulants
and controls were injected subcutaneously into C57BL/6 mice. All tumor
cells subjected to the complete treatment with control molecules formed
tumors like nontreated cells confirming cell viability. However, when
CpG oligonucleotide was linked to cell-surface glycans, tumor growth
was slowed significantly (60% reduction, <i>n</i> = 10,
by covalently bound CpG compared to noncovalently bound CpG, <i>n</i> = 10). When mice that had not developed large tumors were
challenged with unmodified EG7 cells, no new tumors developed, suggesting
protection through the immune system
Enzymatic large-scale synthesis of MUC6-Tn glycoconjugates for antitumor vaccination.
International audienceIn cancer, mucins are aberrantly O-glycosylated, and consequently, they express tumor-associated antigens such as the Tn determinant (alpha-GalNAc-O-Ser/Thr). As compared with normal tissues, they also exhibit a different pattern of expression. In particular, MUC6, which is normally expressed only in gastric tissues, has been detected in intestinal, pulmonary, colorectal, and breast carcinomas. Recently, we have shown that the MCF7 breast cancer cell line expresses MUC6-Tn glycoproteins in vivo. Cancer-associated mucins show antigenic differences from normal mucins, and as such, they may be used as potential targets for immunotherapy. To develop anticancer vaccines based on the Tn antigen, we prepared several MUC6-Tn glycoconjugates. To this end, we performed the GalNAc enzymatic transfer to two recombinant MUC6 proteins expressed in Escherichia coli, using UDP-N-acetylgalactosamine: polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts), which catalyze in vivo the Tn antigen synthesis. We used either a mixture of ppGalNAc-Ts from MCF7 breast cancer cell extracts or a recombinant ppGalNAc-T1. In both cases, we achieved the synthesis of MUC6-Tn glycoconjugates at a semi-preparative scale (mg amounts). These glycoproteins displayed a high level of Tn antigens, although the overall density depends on both enzyme source and protein acceptor. These MUC6-Tn glycoconjugates were recognized by two anti-Tn monoclonal antibodies that are specific to human cancer cells. Moreover, the MUC6-Tn glycoconjugate glycosylated using MCF7 extracts as the ppGalNAc-T source was able to induce immunoglobulin G (IgG) antibodies that recognized a human tumor cell line. In conclusion, the large-scaled production of MUC6 with tumor-relevant glycoforms holds considerable promise for developing effective anticancer vaccines, and further studies of their immunological properties are warranted
Changes in Metabolic Chemical Reporter Structure Yield a Selective Probe of O-GlcNAc Modification
International audienceMetabolic chemical reporters (MCRs) of glycosylation are analogues of monosaccharides that contain bioorthogonal functionalities and enable the direct visualization and identification of glycoproteins from living cells. Each MCR was initially thought to report on specific types of glycosylation. We and others have demonstrated that several MCRs are metabolically transformed and enter multiple glycosylation pathways. Therefore, the development of selective MCRs remains a key unmet goal. We demonstrate here that 6-azido-6-deoxy-N-acetyl-glucosamine (6AzGlcNAc) is a specific MCR for O-GlcNAcylated proteins. Biochemical analysis and comparative proteomics with 6AzGlcNAc, N-azidoacetyl-glucosamine (GlcNAz), and N-azidoacetyl-galactosamine (GalNAz) revealed that 6AzGlcNAc exclusively labels intracellular proteins, while GlcNAz and GalNAz are incorporated into a combination of intracellular and extracellular/lumenal glycoproteins. Notably, 6AzGlcNAc cannot be biosynthetically transformed into the corresponding UDP sugar-donor by the canonical salvage-pathway that requires phosphorylation at the 6-hydroxyl. In vitro experiments showed that 6AzGlcNAc can bypass this roadblock through direct phosphorylation of its 1-hydroxyl by the enzyme phosphoacetylglucosamine mutase (AGM1). Taken together, 6AzGlcNAc enables the specific analysis of O-GlcNAcylated proteins, and these results suggest that specific MCRs for other types of glycosylation can be developed. Additionally, our data demonstrate that cells are equipped with a somewhat unappreciated metabolic flexibility with important implications for the biosynthesis of natural and unnatural carbohydrates
Synthesis and biological evaluation of a multiantigenic Tn/TF-containing glycopeptide mimic of the tumor-related MUC1 glycoprotein
Evaluation of Analogues of GalNAc as Substrates for Enzymes of the Mammalian GalNAc Salvage Pathway
Changes in glycosylation are correlated to disease and
associated
with differentiation processes. Experimental tools are needed to investigate
the physiological implications of these changes either by labeling
of the modified glycans or by blocking their biosynthesis. <i>N</i>-Acetylgalactosamine (GalNAc) is a monosaccharide widely
encountered in glycolipids, proteoglycans, and glycoproteins; once
taken up by cells it can be converted through a salvage pathway to
UDP-GalNAc, which is further used by glycosyltransferases to build
glycans. In order to find new reporter molecules able to integrate
into cellular glycans, synthetic analogues of GalNAc were prepared
and tested as substrates of both enzymes acting sequentially in the
GalNAc salvage pathway, galactokinase 2 (GK2) and uridylpyrophosphorylase
AGX1. Detailed <i>in vitro</i> assays identified the GalNAc
analogues that can be transformed into sugar nucleotides and revealed
several bottlenecks in the pathway: a modification on C6 is not tolerated
by GK2; AGX1 can use all products of GK2 although with various efficiencies;
and all analogues transformed into UDP-GalNAc analogues except those
with alterations on C4 are substrates for the polypeptide GalNAc transferase
T1. Besides, all analogues that could be incorporated <i>in vitro</i> into <i>O</i>-glycans were also integrated into cellular <i>O</i>-glycans as attested by their detection on the cell surface
of CHO-ldlD cells. Altogether our results show that GalNAc analogues
can help to better define structural requirements of the donor substrates
for the enzymes involved in GalNAc metabolism, and those that are
incorporated into cells will prove valuable for the development of
novel diagnostic and therapeutic tools