Sialylation of  1 Integrins Blocks Cell Adhesion to Galectin-3 and Protects Cells against Galectin-3-induced Apoptosis

In previous studies, we determined that β1 integrins from human colon tumors have elevated levels of α2-6 sialylation, a modification added by β-galactosamide α-2,6-sialyltranferase I (ST6Gal-I). Intriguingly, the β1 integrin is thought to be a ligand for galectin-3 (gal-3), a tumor-associated lectin. The effects of gal-3 are complex; intracellular forms typically protect cells against apoptosis through carbohydrate-independent mechanisms, whereas secreted forms bind to cell surface oligosaccharides and induce apoptosis. In the current study, we tested whether α2-6 sialylation of the β1 integrin modulates binding to extracellular gal-3. Herein we report that SW48 colonocytes lacking α2-6 sialylation exhibit β1 integrin-dependent binding to gal-3-coated tissue culture plates; however, binding is attenuated upon forced expression of ST6Gal-I. Removal of α2-6 sialic acids from ST6Gal-I expressors by neuraminidase treatment restores gal-3 binding. Additionally, using a blot overlay approach, we determined that gal-3 binds directly and preferentially to unsialylated, as compared with α2-6-sialylated, β1 integrins. To understand the physiologic consequences of gal-3 binding, cells were treated with gal-3 and monitored for apoptosis. Galectin-3 was found to induce apoptosis in parental SW48 colonocytes (unsialylated), whereas ST6Gal-I expressors were protected. Importantly, gal-3-induced apoptosis was inhibited by function blocking antibodies against the β1 subunit, suggesting that β1 integrins are critical transducers of gal-3-mediated effects on cell survival. Collectively, our results suggest that the coordinate up-regulation of gal-3 and ST6Gal-I, a feature that is characteristic of colon carcinoma, may confer tumor cells with a selective advantage by providing a mechanism for blockade of the pro-apoptotic effects of secreted gal-3. In previous studies, we determined that β1 integrins from human colon tumors have elevated levels of α2-6 sialylation, a modification added by β-galactosamide α-2,6-sialyltranferase I (ST6Gal-I). Intriguingly, the β1 integrin is thought to be a ligand for galectin-3 (gal-3), a tumor-associated lectin. The effects of gal-3 are complex; intracellular forms typically protect cells against apoptosis through carbohydrate-independent mechanisms, whereas secreted forms bind to cell surface oligosaccharides and induce apoptosis. In the current study, we tested whether α2-6 sialylation of the β1 integrin modulates binding to extracellular gal-3. Herein we report that SW48 colonocytes lacking α2-6 sialylation exhibit β1 integrin-dependent binding to gal-3-coated tissue culture plates; however, binding is attenuated upon forced expression of ST6Gal-I. Removal of α2-6 sialic acids from ST6Gal-I expressors by neuraminidase treatment restores gal-3 binding. Additionally, using a blot overlay approach, we determined that gal-3 binds directly and preferentially to unsialylated, as compared with α2-6-sialylated, β1 integrins. To understand the physiologic consequences of gal-3 binding, cells were treated with gal-3 and monitored for apoptosis. Galectin-3 was found to induce apoptosis in parental SW48 colonocytes (unsialylated), whereas ST6Gal-I expressors were protected. Importantly, gal-3-induced apoptosis was inhibited by function blocking antibodies against the β1 subunit, suggesting that β1 integrins are critical transducers of gal-3-mediated effects on cell survival. Collectively, our results suggest that the coordinate up-regulation of gal-3 and ST6Gal-I, a feature that is characteristic of colon carcinoma, may confer tumor cells with a selective advantage by providing a mechanism for blockade of the pro-apoptotic effects of secreted gal-3. Aberrant cell surface carbohydrates are highly associated with tumor invasion and metastasis. In particular, N-linked glycans on tumor cells tend to be more highly branched, with greater levels of terminal sialylation (1Hakomori S. Cancer Res. 1996; 56: 5309-5318PubMed Google Scholar, 2Gorelik E. Galili U. Raz A. Cancer Metastasis Rev. 2001; 20: 245-277Crossref PubMed Scopus (247) Google Scholar, 3Dennis J.W. Semin. Cancer Biol. 1991; 2: 411-420PubMed Google Scholar, 4Dall'Olio F. Glycoconj. J. 2000; 17: 669-676Crossref PubMed Scopus (94) Google Scholar, 5Bellis S.L. Biochim. Biophys. Acta. 2004; 1663: 52-60Crossref PubMed Scopus (132) Google Scholar). The ST6Gal-I 2The abbreviations used are: ST6Gal-Iβ-galactosamide α-2,6-sialyltranferase IAPalkaline phosphatasegalgalectinParparentalEVempty vectorBSAbovine serum albuminPBSphosphate-buffered salineFITCfluorescein isothiocyanatePVDFpolyvinylidene difluoride. 2The abbreviations used are: ST6Gal-Iβ-galactosamide α-2,6-sialyltranferase IAPalkaline phosphatasegalgalectinParparentalEVempty vectorBSAbovine serum albuminPBSphosphate-buffered salineFITCfluorescein isothiocyanatePVDFpolyvinylidene difluoride. sialyltransferase, which adds α2-6-linked sialic acids to glycoproteins (4Dall'Olio F. Glycoconj. J. 2000; 17: 669-676Crossref PubMed Scopus (94) Google Scholar, 6Chammas R. McCaffery J.M. Klein A. Ito Y. Saucan L. Palade G. Farquhar M.G. Varki A. Mol. Biol. Cell. 1996; 7: 1691-1707Crossref PubMed Scopus (21) Google Scholar), is up-regulated in a number of tumors including colon adenocarcinoma, and its expression positively correlates with tumor metastasis and poor patient survival (4Dall'Olio F. Glycoconj. J. 2000; 17: 669-676Crossref PubMed Scopus (94) Google Scholar, 5Bellis S.L. Biochim. Biophys. Acta. 2004; 1663: 52-60Crossref PubMed Scopus (132) Google Scholar, 7Bresalier R.S. Rockwell R.W. Dahiya R. Duh Q.Y. Kim Y.S. Cancer Res. 1990; 50: 1299-1307PubMed Google Scholar). Moreover, both in vitro and animal studies have implicated ST6Gal-I in regulating tumor cell invasiveness and metastasis (7Bresalier R.S. Rockwell R.W. Dahiya R. Duh Q.Y. Kim Y.S. Cancer Res. 1990; 50: 1299-1307PubMed Google Scholar, 8Le Marer N. Stehelin D. Glycobiology. 1995; 5: 219-226Crossref PubMed Scopus (50) Google Scholar, 9Lin S. Kemmner W. Grigull S. Schlag P.M. Exp. Cell Res. 2002; 276: 101-110Crossref PubMed Scopus (161) Google Scholar, 10Zhu Y. Srivatana U. Ullah A. Gagneja H. Berenson C.S. Lance P. Biochim. Biophys. Acta. 2001; 1536: 148-160Crossref PubMed Scopus (87) Google Scholar). However, the mechanisms linking elevated α2-6 sialylation to tumor progression are still poorly understood. Previously, our group identified the β1 integrin subunit as a target for oncogenic Ras-induced ST6Gal-I activity (11Seales E.C. Jurado G.A. Singhal A. Bellis S.L. Oncogene. 2003; 22: 7137-7145Crossref PubMed Scopus (107) Google Scholar) and further determined that α2-6 sialylation of β1 integrins stimulated cell attachment and migration on collagen I (12Seales E.C. Jurado G.A. Brunson B.A. Wakefield J.K. Frost A.R. Bellis S.L. Cancer Res. 2005; 65: 4645-4652Crossref PubMed Scopus (261) Google Scholar). We also reported that β1 integrins in colon tumor tissues carry elevated levels of α2-6-linked sialic acid (12Seales E.C. Jurado G.A. Brunson B.A. Wakefield J.K. Frost A.R. Bellis S.L. Cancer Res. 2005; 65: 4645-4652Crossref PubMed Scopus (261) Google Scholar). Collectively, these results suggest that hypersialylation of the β1 integrin may contribute to the invasive tumor cell phenotype by modulating cell-matrix interactions. β-galactosamide α-2,6-sialyltranferase I alkaline phosphatase galectin parental empty vector bovine serum albumin phosphate-buffered saline fluorescein isothiocyanate polyvinylidene difluoride. β-galactosamide α-2,6-sialyltranferase I alkaline phosphatase galectin parental empty vector bovine serum albumin phosphate-buffered saline fluorescein isothiocyanate polyvinylidene difluoride. There is a vast literature directed at understanding integrin association with traditional extracellular matrix ligands such as collagen, fibronectin, etc. However, accumulating data suggest that integrins also bind to galectins, a family of lectins that can associate with the matrix through interactions with laminin and fibronectin (13Elola M.T. Wolfenstein-Todel C. Troncoso M.F. Vasta G.R. Rabinovich G.A. CMLS Cell Mol. Life Sci. 2007; 64: 1679-1700Crossref PubMed Scopus (279) Google Scholar, 14Ochieng J. Furtak V. Lukyanov P. Glycoconj. J. 2004; 19: 527-535Crossref PubMed Scopus (281) Google Scholar). Galectins are β-galactoside-binding proteins that bind to target molecules through conserved carbohydrate recognition domains. So far, at least 15 mammalian galectins have been identified, and these are known to regulate numerous biological processes including cell adhesion/migration, apoptosis, angiogenesis, and immune responses (13Elola M.T. Wolfenstein-Todel C. Troncoso M.F. Vasta G.R. Rabinovich G.A. CMLS Cell Mol. Life Sci. 2007; 64: 1679-1700Crossref PubMed Scopus (279) Google Scholar, 15Liu F.T. Rabinovich G.A. Nat. Rev. Cancer. 2005; 5: 29-41Crossref PubMed Scopus (1160) Google Scholar). One unique member of the galectin family is galectin-3 (gal-3), which has only one carbohydrate recognition domain, in combination with an extended N-terminal domain that is thought to promote oligomerization (16Dumic J. Dabelic S. Flogel M. Biochim. Biophys. Acta. 2006; 1760: 616-635Crossref PubMed Scopus (829) Google Scholar). Galectin-3 is expressed intracellularly but can also be secreted through a nonclassical pathway (17Hughes R.C. Biochim. Biophys. Acta. 1999; 1473: 172-185Crossref PubMed Scopus (537) Google Scholar). Intracellular gal-3 effects through carbohydrate-independent whereas extracellular gal-3 binds to cell surface oligosaccharides and apoptosis and also modulates cell-matrix interactions F.T. Rabinovich G.A. Nat. Rev. Cancer. 2005; 5: 29-41Crossref PubMed Scopus (1160) Google Scholar, J. Dabelic S. Flogel M. Biochim. Biophys. Acta. 2006; 1760: 616-635Crossref PubMed Scopus (829) Google Scholar, S. N. Raz A. 2005; PubMed Scopus Google Scholar). the and of the of on tumor cell and upon the of from intracellular extracellular gal-3. ST6Gal-I, gal-3 to in cell metastasis. of gal-3 colon cells the cells to more of In of gal-3 a highly colon cell R.S. N. P. Raz A. PubMed Scopus Google Scholar). Galectin-3 is reported to be highly expressed in tumor including colon carcinoma, and up-regulated gal-3 expression is associated with tumor F.T. Rabinovich G.A. Nat. Rev. Cancer. 2005; 5: 29-41Crossref PubMed Scopus (1160) Google Scholar, J. Dabelic S. Flogel M. Biochim. Biophys. Acta. 2006; 1760: 616-635Crossref PubMed Scopus (829) Google Scholar). studies have that galectin binding to may be to terminal group J. Y. N. M. M. F. Biochim. Biophys. Acta. 2002; PubMed Scopus Google Scholar) used to that the binding of gal-3 to oligosaccharides to in the of but sialylation of of immune cells cell surface α2-6 sialylation was reported to apoptosis by M. M. J. J. Biol. 2003; PubMed Scopus Google Scholar, Y. M. J. 2006; Google Scholar). However, the of gal-3 and ST6Gal-I in regulating cell survival have the that both gal-3 and ST6Gal-I are implicated in tumor we compared the effects of gal-3 on SW48 cells that ST6Gal-I have forced expression of ST6Gal-I. studies that gal-3 preferentially binds to cells with β1 integrins. Moreover, α2-6 sialylation of the β1 integrin was found to protect cells against gal-3-mediated cell apoptosis, a for ST6Gal-I in regulating tumor cell survival. Cell human SW48 colon cell was from the cells are from a colon adenocarcinoma, and of SW48 cells results in tumor of the R. J. M. P. Y. Cell and Scholar). SW48 cells have α2-6 activity F. M. P. Biophys. Res. 1995; PubMed Scopus Google Scholar). SW48 cells empty vector ST6Gal-I were as using a vector (12Seales E.C. Jurado G.A. Brunson B.A. Wakefield J.K. Frost A.R. Bellis S.L. Cancer Res. 2005; 65: 4645-4652Crossref PubMed Scopus (261) Google Scholar), and of were for The cells were in with with bovine serum and cells were with in culture was from the at least in of cells were at in a Cell were from to the the were with of gal-3 in by blocking with in and were used as and The were to were by cell and in the cells were in and for at The attachment was cells typically bind to cells to for the that cells matrix molecules such as fibronectin collagen, which the of a cells were with and with for at The number of cells was by at cells were in the of the β1 integrin blocking study, function blocking antibodies against the β1 integrin number a were with SW48 cells for at to cells the data were by a were by cell and were to with of in of integrin only were added to and on for The cells were with in and in of in for on were in with and Cell were by and to The were with in saline The were with a against gal-3 β1 integrins The were with antibodies and with of Cell of cell were treated in in the of of from for at The cell were in by and for the β1 integrin of cells were treated in the of of neuraminidase from C. in for at the cells were with and in culture for gal-3 cell were with collagen I The cells were on the for at and with at for 15 The cells were treated with in for and with The cells were with for at by for at The were with and cells were of a were by a Galectin-3 of were at with a integrin were and were for at with The were with and in proteins were by on and to were to alkaline phosphatase gal-3 and with D. R.S. S. R. J. 2007; PubMed Scopus Google Scholar). were in in for The cells were with and in in the of gal-3 gal-3 for of the cells the gal-3 in the number of suggesting that the of gal-3 on cell to tissue culture gal-3 the cells were for in for The for responses to gal-3 was is a for apoptosis of cells and has been used to and gal-3-induced apoptosis of We that gal-3 was used in the of gal-3 used for binding We apoptosis in to gal-3 but that such be to cells on gal-3 in and extended in be to apoptosis gal-3-induced apoptosis. To integrin in gal-3-induced apoptosis, cells were to to tissue culture for as and integrin antibodies were added to the cells for by the of the antibodies were tested antibodies and and number and number the the antibodies on cell attachment were with in and treated with in for The cells were with and with for at The were with and the of cells was from at were by and data were by a were in in for The cells were with and in for The cells were in for α2-6 the of SW48 to SW48 cells were for cell to gal-3. cells were to for to tissue culture with gal-3. and were used as and in of the cell binding to was In and cells binding to whereas the binding of cells was Cell attachment to gal-3 was inhibited by but by an of that gal-3 binds to carbohydrate these data suggest that α2-6 sialic added by the ST6Gal-I sialyltransferase, the binding of gal-3 to cell surface Cell to Galectin-3 upon β1 that β1 integrins can be S.L. Biochim. Biophys. Acta. 2004; 1663: 52-60Crossref PubMed Scopus (132) Google Scholar, E.C. Jurado G.A. Singhal A. Bellis S.L. Oncogene. 2003; 22: 7137-7145Crossref PubMed Scopus (107) Google Scholar, E.C. Jurado G.A. Brunson B.A. Wakefield J.K. Frost A.R. Bellis S.L. Cancer Res. 2005; 65: 4645-4652Crossref PubMed Scopus (261) Google Scholar) and are binding for galectins Y. Kim V. H. S. Raz A. Cancer Res. 2003; Google Scholar) to whether gal-3 binding was by the β1 and cells of cell surface β1 integrins attachment of cells is to a in integrin To the of the β1 integrin in gal-3 binding, cell attachment was in the of integrin function blocking in blocking antibodies inhibited the binding of parental cells to and also attenuated the binding of I results suggest that β1 integrins a in regulating cell to lectin. of Cell to that α2-6 sialylation gal-3 binding, cells were treated with neuraminidase to sialic acids and for binding to gal-3-coated We tested neuraminidase by the of the β1 integrin neuraminidase in the of the β1 integrin from cells has a as compared with integrins from was to from α2-6 sialylation (12Seales E.C. Jurado G.A. Brunson B.A. Wakefield J.K. Frost A.R. Bellis S.L. Cancer Res. 2005; 65: 4645-4652Crossref PubMed Scopus (261) Google Scholar). treatment of integrins from cells a in the of the β1 with the of sialic In the of β1 integrins from cells was by neuraminidase with the that parental SW48 cells α2-6 F. M. P. Biophys. Res. 1995; PubMed Scopus Google Scholar). treatment also on the of the β1 from which was that the is thought to be to the is a for in cells treated with neuraminidase a in gal-3 binding as compared with In neuraminidase treatment on the binding of parental cells to gal-3. Collectively, these results suggest that α2-6 sialylation the binding of SW48 cells to gal-3. α2-6 of β1 Galectin-3 whether gal-3 binds directly to β1 we used a gal-3 overlay β1 integrins were from parental by and to The was with an gal-3. in gal-3 can directly bind to the of β1 integrins from but data suggest that α2-6 sialylation of β1 integrins gal-3 binding. a was also in the gal-3 overlay of β1 suggesting that gal-3 ligand and is The of is To that of β1 were were for β1 gal-3 to bind to the β1 which is with the that β1 is with glycans that are for α2-6 of Cell the of number of studies have reported that gal-3 is highly expressed in tumor including colon cells H. S. A. H. E. Glycoconj. J. 2004; 20: PubMed Scopus Google we tested whether SW48 cells gal-3. To the levels of from and SW48 cells were from these that and cells levels of gal-3 but cells were as a for In to gal-3 gal-3 was monitored by in and the of gal-3 was in SW48 which is in of studies suggesting that a of gal-3 is F.T. Rabinovich G.A. Nat. Rev. Cancer. 2005; 5: 29-41Crossref PubMed Scopus (1160) Google Scholar, J. Dabelic S. Flogel M. Biochim. Biophys. Acta. 2006; 1760: 616-635Crossref PubMed Scopus (829) Google Scholar). our data suggest that and cells of and forced expression of ST6Gal-I gal-3 levels ST6Gal-I from our results suggesting that α2-6 sialylation gal-3 binding, we that ST6Gal-I expression gal-3-induced apoptosis in SW48 To and cells were treated with of human gal-3 for and for was used to and in the of gal-3 apoptosis in parental cells in a whereas the cells were against apoptosis. To that the effects of added gal-3 were to the binding of gal-3 to cell surface gal-3-induced apoptosis was in the and of studies that inhibited gal-3-induced apoptosis To further that α2-6 sialylation gal-3-mediated apoptosis, we levels of in the and in added gal-3 stimulated by for the of in and cells but in gal-3-induced was by that the effects of gal-3 are through gal-3 binding to upon β1 in and cell to gal-3 is upon β1 and gal-3 binds directly to the β1 we whether gal-3-induced apoptosis was by β1 integrins. To gal-3 was added to parental cells in the of integrin function blocking The cells were and monitored for in integrin blocking antibodies a on gal-3-induced whereas antibodies a To further whether integrin sialylation a in regulating gal-3-induced apoptosis, we apoptosis in to the and the of be by in cell surface in levels of in parental and ST6Gal-I with the that cell surface α2-6 sialylation as a for gal-3 binding and suggest that α2-6 sialic acid and ST6Gal-I are elevated in of human in highly invasive (4Dall'Olio F. Glycoconj. J. 2000; 17: 669-676Crossref PubMed Scopus (94) Google Scholar, 5Bellis S.L. Biochim. Biophys. Acta. 2004; 1663: 52-60Crossref PubMed Scopus (132) Google Scholar). However, the mechanisms the of ST6Gal-I in tumor cell and metastasis to be we ST6Gal-I promote tumor we that α2-6 sialylation of the β1 integrin tumor cells from gal-3-induced apoptosis. literature the that extracellular galectins, including gal-3 and promote cell apoptosis. However, the vast of studies have on cells of the immune is thought to cell in cells M. J. J. J. M. 2006; PubMed Scopus Google Scholar) and human cells M. V. N. P. M. Glycobiology. 2003; PubMed Scopus Google Scholar) through binding to glycans on the cell In the study, binding to cells was upon of sialic extracellular gal-3 apoptosis in human cell Y. Kim V. H. S. Raz A. Cancer Res. 2003; Google Scholar), human cells Y. Kim V. H. S. Raz A. Cancer Res. 2003; Google Scholar), cells Y. Kim V. H. S. Raz A. Cancer Res. 2003; Google Scholar), human cell M. 19: Google Scholar), E. L. M. Rabinovich G.A. F.T. W. R. J. 2007; PubMed Scopus Google Scholar), cells Y. C. Biochim. Biophys. Acta. PubMed Scopus (50) Google Scholar), and J.M. M. Rabinovich G.A. Glycobiology. 2005; PubMed Scopus Google Scholar). studies as with immune gal-3 a in regulating cell survival. is also an a tumor cell both gal-3 and ST6Gal-I ST6Gal-I the binding of gal-3 to the cell We that levels of intracellular forms of gal-3 function through carbohydrate-independent promote tumor cell whereas extracellular gal-3 is is by a intracellular gal-3 cells against including and F.T. Sci. U. S. A. 1996; PubMed Scopus Google Scholar). the activity of intracellular gal-3 is thought to be through binding to molecules such as family S. P. H. Kim Raz A. Cancer Res. Google Scholar), F. Raz A. Kim J. Biol. 2002; PubMed Scopus Google Scholar), Y. N. V. H. Kim Raz A. Cancer Res. 2004; 64: PubMed Scopus Google Scholar), and G. R. E. Y. J. Biol. 2004; PubMed Scopus Google Scholar). The binding of gal-3 to Ras-induced U. G. R. Y. Cell. Mol. 2006; PubMed Scopus Google Scholar), which is in of studies that ST6Gal-I expression (11Seales E.C. Jurado G.A. Singhal A. Bellis S.L. Oncogene. 2003; 22: 7137-7145Crossref PubMed Scopus (107) Google Scholar, M. F. A. V. F. J. 2004; PubMed Scopus Google Scholar). The of intracellular gal-3 is also thought to be was reported that of gal-3 in the its whereas of gal-3 in the its activity in cells S. V. M. F. Oncogene. 2004; PubMed Scopus Google Scholar). In our study, both parental and SW48 cells expressed levels of intracellular gal-3 that to the suggesting that expressed gal-3 have In to the effects of intracellular studies of immune with our current results from suggest that extracellular gal-3 as an apoptosis these results suggest that ST6Gal-I, in with gal-3 the pro-apoptotic effects of secreted the effects of intracellular providing a selective advantage for the tumor The up-regulated of gal-3 in tumor cells results in in both intracellular and secreted forms of as by the that with have levels of gal-3 in N. C. D. E. S. Cancer Res. 2000; Google Scholar). the tumor secreted gal-3 is thought to promote and also immune responses by cell apoptosis F.T. Rabinovich G.A. Nat. Rev. Cancer. 2005; 5: 29-41Crossref PubMed Scopus (1160) Google Scholar). with the of by cells the of cells R. H. P. Cancer Res. 2007; PubMed Scopus Google Scholar). we that the pro-apoptotic of galectins secreted from tumor cells contribute to tumor from the immune by on cells but have on tumor cells that have cell surface α2-6 The that α2-6 sialylation as an for galectin binding and function is by studies of both oligosaccharides J. Y. N. M. M. F. Biochim. Biophys. Acta. 2002; PubMed Scopus Google Scholar, A. S. J. Biol. 2005; PubMed Scopus Google Scholar) and cell surface glycans M. M. J. J. Biol. 2003; PubMed Scopus Google Scholar, Y. M. J. 2006; Google Scholar, M. 19: Google Scholar, E. J. J. M. S. H. J. J. R. 2002; PubMed Scopus Google Scholar, G.A. J.M. J. F. Rabinovich G.A. Nat. 2007; PubMed Scopus Google Scholar, S. H. H. M. J. P. Kemmner W. C. M. S. S. J. 2007; PubMed Scopus Google Scholar). ST6Gal-I on to regulate cell M. M. J. J. Biol. 2003; PubMed Scopus Google Scholar). which are to apoptosis, levels of α2-6 sialylation cells are and can be by the of but sialic acids G.A. J.M. J. F. Rabinovich G.A. Nat. 2007; PubMed Scopus Google Scholar) In with studies of cell surface that sialylation of was by galectins, but of the galectins bind to α2-6 J. Y. N. M. M. F. Biochim. Biophys. Acta. 2002; PubMed Scopus Google Scholar). was reported by D. R.S. S. R. J. 2007; PubMed Scopus Google Scholar). group binding of gal-3 to oligosaccharides with α2-6 however, the of binding was that with group P. H. J. Biol. PubMed Scopus Google Scholar) also reported that α2-6 sialylation inhibited the of gal-3 with the α2-6 sialylation of at blocking gal-3 binding. that gal-3 can bind to the a the of the terminal sialic In the current study, we found that expression of ST6Gal-I in colon cells inhibited cell attachment to gal-3-coated and attachment be by cells with In we used a blot overlay to that gal-3 binds directly and preferentially to β1 as compared with integrins. cells binding to gal-3-coated and of binding was β1 The mechanisms attachment of cells to gal-3 are understood. is that cells with α2-6 sialylation of for through the binding of gal-3 to as by group P. H. J. Biol. PubMed Scopus Google Scholar). studies be to the for cell attachment to our results a of α2-6-linked sialic acids on cell binding to as as apoptosis. which cell surface are for is still however, the literature that is in Y. C. Biochim. Biophys. Acta. PubMed Scopus (50) Google Scholar) that gal-3 binding to for on cells to cell group M. P. F.T. J. 2006; PubMed Scopus Google Scholar) that bind to β1 and in however, in to be the regulating apoptosis. In to study, Y. Kim V. H. S. Raz A. Cancer Res. 2003; Google Scholar) that the β1 integrin was the for gal-3-mediated cell apoptosis. The β1 family of integrins to be a ligand for galectins, as by the that have been for binding to gal-3 binding to and binding to F.T. Rabinovich G.A. Nat. Rev. Cancer. 2005; 5: 29-41Crossref PubMed Scopus (1160) Google Scholar). results suggest that the β1 integrin is one of the colon cell association and responses extracellular gal-3. Importantly, we that sialylation of β1 by ST6Gal-I the pro-apoptotic effects of extracellular gal-3. sialylation of β1 integrins only modulates cell responses to traditional extracellular matrix proteins collagen and fibronectin, as we have reported (11Seales E.C. Jurado G.A. Singhal A. Bellis S.L. Oncogene. 2003; 22: 7137-7145Crossref PubMed Scopus (107) Google Scholar, E.C. Jurado G.A. Brunson B.A. Wakefield J.K. Frost A.R. Bellis S.L. Cancer Res. 2005; 65: 4645-4652Crossref PubMed Scopus (261) Google Scholar, E.C. Singhal A. Bellis S.L. J. Biol. 2002; PubMed Scopus Google Scholar, E.C. P. Bellis S.L. J. Biol. 2005; PubMed Scopus Google Scholar), but also as a mechanism for regulating cell interactions with In the these studies suggest that integrin a in regulating tumor cell with Importantly, the expression of integrin in to such as oncogenic Ras-induced cell (11Seales E.C. Jurado G.A. Singhal A. Bellis S.L. Oncogene. 2003; 22: 7137-7145Crossref PubMed Scopus (107) Google Scholar). α2-6 sialylation of β1 integrins is elevated in human colon as compared with (12Seales E.C. Jurado G.A. Brunson B.A. Wakefield J.K. Frost A.R. Bellis S.L. Cancer Res. 2005; 65: 4645-4652Crossref PubMed Scopus (261) Google Scholar). integrin function blocking antibodies of the cell to suggesting that interactions may be In with these the gal-3 overlay that was in β1 integrin the of is ligands for gal-3 have been including the C. J. P. M. J.W. 2004; PubMed Scopus Google Scholar), C. J. P. M. J.W. 2004; PubMed Scopus Google Scholar, M. M. S. J.W. 2001; PubMed Scopus Google Scholar), cell M. M. S. J.W. 2001; PubMed Scopus Google Scholar), S. J. Biol. 1991; PubMed Google Scholar), Y. C. Biochim. Biophys. Acta. PubMed Scopus (50) Google Scholar), and D. P. J.M. M. R. Cancer Res. 1995; Google Scholar). is highly expressed in colon and the β1 is known to be with α2-6 sialic acid C. L. R. W. M. Glycobiology. 1999; PubMed Scopus Google Scholar). be to proteins and also to the of these In the of is that α2-6 sialylation of the β1 integrin gal-3-induced cell apoptosis, which in a for the up-regulation of ST6Gal-I and gal-3 in tumor cells a selective our results have in that galectins are for in treatment E. G. L. W. Mol. 2006; PubMed Scopus Google Scholar). is highly that such a be with colon which typically levels of α2-6 We H. M. from for