Mariella Chiricolo

Sialyltransferases in cancer

It has long been known that cancer cells often express more heavily sialylated glycans on their surface and that this feature sometimes correlates with invasion. It is now well established that specific sialylated structures, such as the Thomsen-Friedenreich-related antigens, the sialyl Lewis antigens, the sialyl α2-6 lactosaminyl structure, the polysialic acid or some gangliosides, can mediate cellular interactions and are altered in cancer cells. This review summarizes the current knowledge on the cancer-associated alterations in sialyltransferase expression which are often at the basis of the deranged expression of sialylated structures.

Mechanisms of cancer-associated glycosylation changes.

Cell membrane glycoconjugates undergo characteristic changes as a consequence of neoplastic transformation. The cancer-associated carbohydrate structures play key roles in cancer progression by altering the cell-cell and cell-environment interactions. In this review, we will discuss some of the most relevant cancer-associated carbohydrate structures, including the β1,6-branching of N-linked chains, the sialyl Lewis antigens, the α2,6-sialylated lactosamine, the Thomsen-Friedenreich-related antigens and gangliosides. We will describe the mechanisms leading to the expression of these structures and their interactions with sugar binding molecules, such as selectins and galectins. Finally, we will discuss how the glycosylation machinery of the cell is controlled by signal transduction pathways, epigenetic mechanisms and responds to hypoxia.

Sialosignaling: sialyltransferases as engines of self-fueling loops in cancer progression.

BACKGROUND Glycosylation is increasingly recognized as one of the most relevant postranslational modifications. Sialic acids are negatively charged sugars which frequently terminate the carbohydrate chains of glycoproteins and glycolipids. The addition of sialic acids is mediated by sialyltransferases, a family of glycosyltransferases with a crucial role in cancer progression. SCOPE OF THE REVIEW To describe the phenotypic and clinical implications of altered expression of sialyltransferases and of their cognate sialylated structures in cancer. To propose a unifying model of the role of sialyltransferases and sialylated structures on cancer progression. MAJOR CONCLUSIONS We first discuss the biosynthesis and the role played by the major cancer-associated sialylated structures, including Thomsen-Friedenreich-associated antigens, sialyl Lewis antigens, α2,6-sialylated lactosamine, polysialic acid and gangliosides. Then, we show that altered sialyltransferase expression in cancer, consequence of genetic and epigenetic alterations, generates a flow of information toward the membrane through the biosynthesis of aberrantly sialylated molecules (inside-out signaling). In turn, the presence of aberrantly sialylated structures on cell membrane receptors generates a flow of information toward the nucleus, which can exacerbate the neoplastic phenotype (outside-in signaling). We provide examples of self-fueling loops generated by these flows of information. GENERAL SIGNIFICANCE Sialyltransferases have a wide impact on the biology of cancer and can be the target of innovative therapies. Our unified view provides a conceptual framework to understand the impact of altered glycosylation in cancer.

β-Galactoside α2,6 sialyltransferase in human colon cancer : Contribution of multiple transcripts to regulation of enzyme activity and reactivity with Sambucus nigra agglutinin

Colon cancer tissues display an increased activity of β‐galactoside α2,6 sialyltransferase (ST6Gal.I) and an increased reactivity with the lectin from Sambucus nigra (SNA), specific for α2,6‐sialyl‐linkages. Experimental and clinical studies indicate a contribution of these alterations to tumor progression, but their molecular bases are largely unknown. In many tissues, ST6Gal.I is transcriptionally regulated through the usage of different promoters that originate mRNAs diverging in the 5`‐untranslated regions. RT‐PCR analysis of 14 carcinoma samples, all expressing an increased ST6Gal.I enzyme activity, and of the corresponding normal mucosa revealed the presence of at least 2 transcripts. One, containing the 5`‐untranslated exons, Y+Z, is thought to represent the “housekeeping” expression, and another previously described in hepatic tissues. Both the Y+Z and the hepatic transcripts were detectable in normal and cancer tissues but that latter form had a marked tendency to accumulate in cancer. The extent of α2,6‐sialylation of glycoconjugates, as determined by SNA‐dot blot analysis, was markedly enhanced in all cancer specimens, but the level of reactivity only partially correlated with the level of enzyme expression. Western blot analysis revealed a strikingly heterogeneous pattern of SNA reactivity among cancer tissues. These data indicate that: i) during neoplastic transformation of colonic cells, ST6Gal.I expression may be modulated through a differential promoter usage; ii) the extent of α2,6‐sialylation of cancer cell membranes is not a direct function of the ST6Gal.I activity, strongly suggesting the existence of other, more complex mechanisms of regulation. Int. J. Cancer 88:58–65, 2000.

Enhanced DNA repair in lymphocytes of Down syndrome patients: the influence of zinc nutritional supplementation

Oral zinc supplementation is able to correct zinc deficiency and some immune defects present in Downs syndrome (DS), while other beneficial effects can be predicted because of the broad spectrum of biochemical pathways and the great variety of enzymes which depend on zinc bio-availability. To test if the maintenance of DNA integrity is also affected by zinc supplementation, DNA damage and repair after gamma-radiation was studied by alkaline elution assay in phytohemagglutinin-stimulated lymphocytes from Downs syndrome children before and after an oral zinc supplementation given for 4 months to correct their immune defects. In comparison with lymphocytes from normal children the DNA damage induction after ionizing radiation in DS lymphocytes both before and after zinc supplementation was normal. On the other hand, the rate of DNA repair in DS was highly and significantly accelerated before zinc treatment. After supplementation with zinc sulfate, the DNA repair rate was consistently slowed down becoming similar to that of control subjects. This is the first demonstration that a nutritional intervention in humans is apparently able to modify the biochemical steps which control the rate of DNA repair.

The biosynthesis of the selectin-ligand sialyl Lewis x in colorectal cancer tissues is regulated by fucosyltransferase VI and can be inhibited by an RNA interference-based approach

Sialyl Lewis x (sLex) is a selectin ligand whose overexpression in epithelial cancers mediates metastasis formation. The molecular basis of sLex biosynthesis in colon cancer tissues is still unclear. The prerequisite for therapeutic approaches aimed at sLex down-regulation in cancer, is the identification of rate-limiting steps in its biosynthesis. We have studied the role of α1,3-fucosyltransferases (Fuc-Ts) potentially involved in sLex biosynthesis in specimens of normal and cancer colon as well as in experimental systems. We found that: (i) in colon cancer, but not in normal mucosa where the antigen was poorly expressed, sLex correlated with a Fuc-T which, like Fuc-TVI, was active on 3sialyllactosamine at a low concentration (Fuc-T(SLN)); (ii) competitive RT-PCR analysis revealed that the level of Fuc-T mRNA expression in both normal and cancer colon was Fuc-TVI>Fuc-TIII>Fuc-TIV; Fuc-TV and Fuc-TVII expression was negligible; (iii) sLex was expressed only by the gastrointestinal cell lines displaying both Fuc-TVI mRNA and Fuc-T(SLN) activity, but not by those expressing only Fuc-TIII mRNA; (iv) transfection with Fuc-TVI cDNA, but not with Fuc-TIII cDNA, induced sLex expression in gastrointestinal cell lines; (v) Fuc-TVI knock-down with specific siRNA induced down-regulation of Fuc-TVI mRNA and Fuc-T(SLN) activity and a dramatic inhibition of sLex expression. These data indicate that in colon cancer tissues Fuc-TVI is a key regulator of sLex biosynthesis which can be the target of RNA-interference-based gene knock-down approaches.

Enhancing effect of lithium and potassium ions on lectin-induced lymphocyte proliferation in aging and down's syndrome subjects

The effect of different concentrations of LiCl or KCl (0.6-20 meq/liter) on PHA-stimulated lymphocytes from young, old, and Downs syndrome subjects was studied. LiCl showed a dramatic enhancing effect on [3H]thymidine incorporation induced by a suboptimal dose of PHA in old subjects and Downs syndrome patients. An increase of [3H]thymidine incorporation in human lymphocytes stimulated by a suboptimal dose of PHA was also observed with KCl. This effect was higher in old subjects than that observed in young and Downs subjects. LiCl and KCl can modulate and partially restore the derangement in early events of mitogen stimulation which seems to be present in lymphocytes from both old and Downs syndrome subjects.

Alterations of the Capping Phenomenon on Lymphocytes from Aged and Down’s Syndrome Subjects

The redistribution with the time of concanavalin A (Con A) receptors at one pole of the cell after addition of FITC-Con A - so-called capping - in the peripheral blood lymphocytes from 13 aged subjects (mean: 84 +/- 1 years old), and of 16 noninstitutionalized patients affected by a syndrome of precocious aging, such as Downs syndrome (mean: 17 +/- 2 years old), was studied and compared with a group of 15 normal young people (mean: 23 +/- 2 years old). An opposite alteration in the percentage of capped cells, i.e. a decrease in aged subjects and an increase in Downs syndrome patients, was observed. A derangement of lymphocyte membrane fluidity appears to be present in both groups even if the underlying biochemical defect may be different. However, a similar alteration of the kinetics of the phenomenon was present either in aged or in Downs syndrome subjects. Both groups did not show any significant increase with time of the percentage of capped cells, suggesting that they were lacking a lymphocyte subpopulation(s) which start capping later.

The expanding roles of the Sda/Cad carbohydrate antigen and its cognate glycosyltransferase B4GALNT2

BACKGROUND The histo-blood group antigens are carbohydrate structures present in tissues and body fluids, which contribute to the definition of the individual immunophenotype. One of these, the Sd(a) antigen, is expressed on the surface of erythrocytes and in secretions of the vast majority of the Caucasians and other ethnic groups. SCOPE OF REVIEW We describe the multiple and unsuspected aspects of the biology of the Sd(a) antigen and its biosynthetic enzyme β1,4-N-acetylgalactosaminyltransferase 2 (B4GALNT2) in various physiological and pathological settings. MAJOR CONCLUSIONS The immunodominant sugar of the Sd(a) antigen is a β1,4-linked N-acetylgalactosamine (GalNAc). Its cognate glycosyltransferase B4GALNT2 displays a restricted pattern of tissue expression, is regulated by unknown mechanisms - including promoter methylation, and encodes at least two different proteins, one of which with an unconventionally long cytoplasmic portion. In different settings, the Sd(a) antigen plays multiple and unsuspected roles. 1) In colon cancer, its dramatic down-regulation plays a potential role in the overexpression of sialyl Lewis antigens, increasing metastasis formation. 2) It is involved in the lytic function of murine cytotoxic T lymphocytes. 3) It prevents the development of muscular dystrophy in various dystrophic murine models, when overexpressed in muscular fibers. 4) It regulates the circulating half-life of the von Willebrand factor (vWf), determining the onset of a bleeding disorder in a murine model. GENERAL SIGNIFICANCE The expression of the Sd(a) antigen has a wide impact on the physiology and the pathology of different biological systems.

Exposure of α2,6-sialylated lactosaminic chains marks apoptotic and necrotic death in different cell types

Many observations have reported glycosylation changes associated with apoptosis in different biological systems, although none of these has shown any general significance. In this work, we show that in cell lines from different histological origin, (colon, breast, pancreas, and bladder cancer) as well as in normal human and mice neutrophils, apoptosis is accompanied by the exposure of sugar chains recognized by the lectin from Sambucus nigra (SNA), specific for Sia alpha 2,6Gal/GalNAc structures. Also, cells undergoing primary necrosis induced by heat treatment (56 degrees C, 30 min) expose specifically binding sites for SNA. While this modification is recognized also by the lectin from the mushroom Polyporus squamosus, which is highly specific for alpha2,6-sialylated lactosamine, no significant changes were detected in the binding of lectins specific for other carbohydrate structures, such as those from Phaseolus vulgaris, Arachis hypogea, and Maackia amurensis. The binding of SNA to apoptotic/necrotic cells is inhibited by neuraminidase treatment and by alpha2,6-sialylated compounds. In apoptotic, but not in necrotic SW948 cells, SNA reactivity is specifically associated with 65, 69, and 87 kDa glycoproteins. The exposure of SNA-reactive chains by apoptotic/necrotic cells occurs also in cells not expressing sialyltransferases ST6Gal.1 or ST6Gal.2 and is largely independent of the presence of alpha2,6-sialylated lactosaminic chains on the surface of preapoptotic cells. In neutrophils from ST6Gal.1 knock-out mice, the apoptosis-related increase in SNA reactivity is reduced but not abolished. These data demonstrate that apoptosis and primary necrosis induce a specific glycosylation change independent of the cell type and nature of the stimulus.