BIOSYNTHESIS OF CANCER-RELATED CARBOHYDRATE ANTIGENS Fabio Dall Olio Department of Experimental Pathology University of Bologna, Italy
TOPICS OF THE LECTURE 1. Structure and function of some representative cancer-associated carbohydrate antigens β1,6-branching Sialyl-Lewis antigens Sia6LacNAc 2. Mechanisms leading to the expression of cancer-associated carbohydrate antigens Overexpression of glycosyltransferases Altered glycosidase expression Masking of sugar structures by substituent groups Competition between normal and cancer-associated carbohydrate structures 3. Glycosylation and cell signalling: a bi-directional talk
1. SOME CANCER-ASSOCIATED CARBOHYDRATE ANTIGENS β1,6-branching Sialyl-Lewis antigens Sia6LacNAc
β1,6 BRANCHING AND BISECTING GlcNAc ARE ALTERNATIVE STRUCTURES β1,6-branching Fucα1,3 Siaα2,3Galβ1,4GlcNAcβ1,3(Galβ1,4GlcNAc n β1,3galβ1,4glcnacβ1,6 Siaα2,3(6Galβ1,4GlcNAcβ1,2Man Siaα2,3(6Galβ1,4GlcNAcβ1,2Man Manβ1,4GlcNAcβ1,4GlcNAc-Asn GnT5 Bisecting GlcNAc Siaα2,3(6Galβ1,4GlcNAcβ1,2Man Siaα2,3(6Galβ1,4GlcNAcβ1,2Man Siaα2,3(6Galβ1,4GlcNAcβ1,2Man Manβ1,4GlcNAcβ1,4GlcNAc-Asn GnT3 Siaα2,3(6Galβ1,4GlcNAcβ1,2Man GlcNAcβ1,4Manβ1,4GlcNAcβ1,4GlcNAc-Asn An N-linked chain can be transformed in a β1,6-branched structure (upper by the action of GnT5. The β1,6-linked branch is frequently elongated by polylactosaminic chains, which are often terminated by complex structures, such as the sialyl Lex antigen. The action of GnT3 leads to the addition of a bisecting GlcNAc, which inhibits the formation of the β1,6-branched structure. From: Dall Olio et al. Carbohydr. Chem. 2012 37 21-56
β1,6-branching AND METASTASIS 1. The β1,6-branching, as detected with leukoagglutinin (L-PHA, is associated with metastasis (Dennis et al. 1987 2. GnT5 is controlled by ras and other oncogenes (Lu et al. 1993. 3. GnT5 null mice in a PyMT background display strong inhibition of tumor growth and metastasis (Granowsky et al. 2000 4. β1,6-branched glycans on growth factor receptors enhance their signalling, through interaction with galectin-3 (Lau et al. 2007. 5. β1,6-branched glycans stabilize matriptase, an activator of hepatocyte growth factor (Ihara et al. 2004
SIALYL LEWIS ANTIGENS The basic units of type 1 or type 2 chains are obtained by the addition on GlcNAc of a β1,3- linked or a β1,4-linked galactose, respectively. The α2,3-sialylation of type 1 or 2 chains, followed by the addition of α1,4- or α1,3-linked fucose, respectively, leads to the biosynthesis of the sialyl Lea (slea and sialyl Lex (slex antigens.
ROLE OF SELECTIN INTERACTIONS DURING CELL EXTRAVASATION Selectin ligands slea/slex on circulating cells interact with E and P- selectins expressed by activated endothelia. These interactions mediate the tethering and rolling of leukocytes or cancer cells. The firm adhesion, which precedes extravasation is mediated by integrins.
SIALYL LEWIS ANTIGENS AND CANCER 1.The up-regulation of sialyl Lewis antigens (sle is frequently observed in cancer (Izawa et al. 2000 2.sLea (CA19.9 is a widely used tumor marker 3.In many systems sle antigens are associated with metastasis 4.sLe antigens are selectin-ligands
SIALYL LEWIS-X ANTIGEN IS OVEREXPRESSED IN COLON CANCER From: Izawa et al. 2000 slex (arbitrary units 5 2.5 0 Patient normal tumor 1 2 3 4 5 6 7 8 9 1011121314151617 Staining with the anti slex antibody CSLEX reveals that slex is expressed only by cancer tissues. From: Trinchera et al. 2011 By immunoblot analysis, only a few colon cancer tissues express high levels of slex
α2,6-sialylated LACTOSAMINE (Sia6LacNAc Siaα2,6 Galβ1,4GlcNAcβ1, 6 Manα1 Siaα2,6Galβ1,4GlcNAcβ1, 3 Siaα2,6Galβ1,4GlcNAcβ1,2 Manα1 6 3 Manβ1,4GlcNAcβ1,4GlcNAc---Asn Sialic acid can be linked to lactosaminic chains either through a α2,3- or a α2,6-linkage. ST6Gal.1 mediates this reaction on glycoproteins Sambucus nigra agglutinin (SNA recognizes Sia6LacNAc
Sia6LacNAc AND CANCER 1.The up-regulation of ST6Gal.1 and/or Sia6LacNAc is frequently observed in cancers (Dall Olio 2000a, Dall Olio et al. 2001 2.The β1 subunit of integrins is a substrate of ST6Gal.1 (Seales et al. 2005 3.High ST6Gal.1 induces radiation resistance (Lee et al. 2008 4.Breast cancers developed by ST6Gal.1 null mice in a PyMT background are more differentiated (Hedlund et al. 2008
ST6Gal.1 AND α2,6 SIALYLATED SUGAR CHAINS INCREASE IN COLORECTAL CANCER 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 Normale Tumorale 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ST6Gal.I activity increases in nearly 100% of the colorectal cancer cases although at a variable level among patients (Dall Olio et al. 1989, 2000b The increase of Sia6LacNAc expression, detected with SNA, marks the transition between normal and cancer tissue (Dall Olio and Trerè 1993
ST6Gal.I IS UNDER THE CONTROL OF THE RAS ONCOGENE Northern blot analysis of mock-transfected and K-ras transfected NIH3T3 cells with probes for different sialyltransferases. Only ST6Gal.I shows ras-dependent modulation SNA FACS analysis of mocktransfected and K- ras transfected NIH3T3 cells. Ras expression induces α2,6- sialylation of cell membrane. From: Dalziel et al. 2004
PHENOTYPIC CHANGES INDUCED BY ST6Gal.1 EXPRESSION IN SW948 COLON CANCER CELLS A 1,5 Fibronectin * B C 1 * A 6 5 0 A 6 5 0 0,5 0 3,5 7 14 Fibronectin (µg/well 2,5 2 1,5 1 0,5 * Collagen IV * * Mock ST6Gal.1+ Day 0 Day 6 0 14 21 42 Collagen IV (µg/well A: adhesion to ECM components (grey=mock; black=st6gal.1+ B: scratch wound assay C: SNA reactivity (left and morphology (right of ST6Gal.1+ cells. From: Chiricolo et al. 2006
2. MECHANISMS DRIVING THE EXPRESSION OF CANCER-RELATED CARBOHYDRATE ANTIGENS Overexpression of glycosyltransferases Altered glycosidase expression Masking by substituent groups Competition between glycosyltransferases
THE OVEREXPRESSION OF CARBOHYDRATE STRUCTURES IS USUALLY MULTIFACTORIAL Cognate glycosyltransferase e.g.: ST6Gal.1 GnT5 Masking by substituents e.g.: O-acetylation of sialic acids Structure overexpression Glycosidases e.g.: Neu sialidases Competing glycosyltransferases e.g.: β4galnact2/slex GnT3/β1,6-branching
INCREASE OF COGNATE GLYCOSYLTRANSFERASE: ST6Gal.1 AND SNA REACTIVITY The SNA reactivity and the ST6Gal.1 activity of 21 pairs of cancer and non-cancer liver tissues were determined and plotted. The relationship between SNA and ST6Gal.1 is non linear, indicating that factors other than ST6Gal.1 activity affect the biosynthesis of Sia6LacNAc From: Dall Olio et al. Glycobiology 2004
MASKING BY SUBSTITUENTS: O- ACETYLATION OF SIALIC ACIDS anti slex 2.5 µg 1.2 µg 0.6 µg 2.5 µg 1.2 µg 0.6 µg Patient number 1 2 3 4 5 6 7 8 9 10 N T N T N T N T N T N T N T N T N T N T Untreated Alkali-treated O-acetyl groups on sialic acids can hinder the recognition of sialylated sugar antigens by antibodies (Ogata et al. 1995. Removal of O- acetyl groups by alkali enhances the detection of slex in normal colon From: Malagolini et al. Glycobiology 2007
DECREASED GLYCOSIDASE EXPRESSION: SIALIDASES 1.Neu sialidases are a group of 4 enzymes with different intracellular localization 2.Downregulation of lysosomal Neu1 in cancer promotes anchorage-independent growth and metastatic ability 3.Over-expression of cytosolic Neu2 leads to reduced invasion of cancer cells (Miyagi et al. 2008
COMPETITION BETWEEN THE slex AND Sd a ANTIGENS IN COLON CANCER slex FucT-VI activity 5 2.5 12 6 0 A B normal tumor 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Patient Attività FucT-VI 10 5 0 Attività FucT-VI 8 4 0 tumor P<0.0001 NS 3 6 slex normal C D 0.3 0.6 slex A: slex is highly expressed by some cancer tissues and very little by normal tissue. B: Its biosynthetic enzyme (FucT-VI is high in both normal and cancer. slex correlates with FucT-VI in cancer (C but not in normal tissue (D. From: Trinchera et al. 2011
ENZIMATIC BASIS OF REDUCED slex BIOSYNTHESIS IN NORMAL COLON Attivitàβ4GalNAcT-II 2 1 0 normal 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Patient tumor β4galnact-ii is downregulated in colon cancer tissues FucT-VI/β4GalNAcT-II P<0.0001 slex In normal colon slex correlates with the FucT- VI/ β4galnact-ii ratio
Sd a AND slex ANTIGENS Neu5Acα2,3Galβ1,4GlcNAc-R GalNAcβ1,4 Good Sd a Neu5Acα2,3Galβ1,4GlcNAc-R Neu5Acα2,3Galβ1,4GlcNAc-R Fucα1,3 Bad sle x
β4galnact-ii INHIBITS slex BIOSYNTHESIS IN LS174T COLON CANCER CELLS A Mock β4galnact-ii+ B µg homogenate 25 12.5 6 3 1.5 0.7 Anti slex mock C Mock β4galnact-ii+ Anti Sd a Anti slex β4galnact-ii+ Expression of β4galnact-ii results in slex inhibition in dot blot analysis (A, FACS (B and fluorescence microscopy (C. Malagolini et al. 2007
BALANCE BETWEEN Sd a AND slex ANTIGENS IN COLON Sd a β4galnact-ii β4galnact-ii FucT-VI FucT-VI Normal slex Tumor Reduced β4galnact-ii expression in cancer tissue results in slex overexpression even in the presence of constant FucT-VI activity
3. GLYCOSYLATION AND CELL SIGNALLING: A BI-DIRECTIONAL TALK The cancer-related carbohydrate changes can be at the same time ʐ the cause and the effect of the malignant phenotype
DYNAMIC OF CANCER-ASSOCIATED GLYCOSYLATION CHANGES Cancer markers Cell transformation Inside out Outside in Glycosylation changes Altered phenotype
EXAMPLE OF BI-DIRECTIONAL SIGNALLING Sia6LacNAc β1,6-branching Integrins Growth Factor Receptors Oncogene signalling Outside-in signalling. Sugar structures, such as Sia6 LacNAc and β1,6-branching, decorate cell surface molecules, including integrins and growth factor receptors. This results in a potentiation of their signalling, eventually leading to oncogene activation. Inside-out signalling. Oncogenes like ras, directly upregulate the expression of the enzymes (ST6Gal.1 and GnT5 which synthesize Sia6LacNAc and β1,6-branching. This bidirectional signalling might create a self-fuelling loop.
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