Repression of the Lewis fucosyl transferase by retinoic acid increases apical sialosyl Lewis(a) secretion in colorectal carcinoma cultures

Analysis of glycosyltransferase expression in metastatic prostate cancer cells capable of rolling activity on microvascular endothelial (E)-selectin

Prostate cancer (PCa) cell tethering and rolling on microvascular endothelium has been proposed to promote the extravasation of PCa cells. We have shown that these adhesive events are mediated through binding interactions between endothelial (E)-selectin and Lewis carbohydrates on PCa cells. Prior data indicate that E-selectin-mediated rolling of bone-metastatic PCa MDA PCa 2b (MDA) cells is dependent on sialyl Lewis X (sLe(X))-bearing glycoproteins. To explore the molecular basis of sLe(X) synthesis and E-selectin ligand (ESL) activity on PCa cells, we compared and contrasted the expression level of glycosyltransferases, characteristically involved in sLe(X) and ESL synthesis, in ESL(+) MDA cells among other ESL(-) metastatic PCa cell lines. We also created and examined ESL(hi) and ESL(lo) variants of MDA cells to provide a direct comparison of the glycosyltransferase expression level. We found that normal prostate tissue and all metastatic PCa cell lines expressed glycosyltransferases required for sialo-lactosamine synthesis, including N-acetylglucosaminyl-, galactosyl-, and sialyltransferases. However, compared with expression in normal prostate tissue, ESL(+) MDA cells expressed a 31- and 10-fold higher level of alpha1,3 fucosyltransferases (FT) 3 and 6, respectively. Moreover, FT3 and FT6 were expressed at 2- to 354-fold lower levels in ESL(-) PCa cell lines. Consistent with these findings, ESL(hi) MDA cells expressed a 131- and 51-fold higher level of FT3 and FT6, respectively, compared with expression in ESL(lo) MDA cells. We also noted that alpha1,3 FT7 was expressed at a 5-fold greater level in ESL(hi) MDA cells. Furthermore, ESL(lo) MDA cells did not display sLe(X) on glycoproteins capable of bearing sLe(X), notably P-selectin glycoprotein ligand-1. These results implicate the importance of alpha1,3 FT3, FT6, and/or FT7 in sLe(X) and ESL synthesis on metastatic PCa cells.

Cell surface fucose ablation as a therapeutic strategy for malignant neoplasms

The sugar alpha-L-fucose is overexpressed in many human malignancies, especially on specific glycoproteins, glycolipids, certain mucins, and putative cell adhesion ligands found on cancer cell surfaces. Many of these molecules are known or suspected mediators of cell-cell adhesion, cell signaling, motility, or invasion. As knowledge of fucose metabolism evolves and specific mechanisms of its distribution and incorporation are more exactly documented, modulation of fucose expression in cancer is becoming increasingly more feasible. The authors propose that cancer cell surface alpha-L-fucose is a logical target for selective therapeutic ablation. Reduction of fucose content on the surfaces of malignant cells should effectively cripple the cells' physiologic functions by altering or dysregulating cell-cell or cell-matrix interactions, critical for maintaining the malignant phenotype. Significant therapeutic benefits might include modulation of adhesion abnormalities in the cancer cells, reduction of cancer cell motility or invasiveness, reexposure to immune surveillance, or a combination of these events.

Attenuation of 19-9 antigen secretion in human colorectal carcinoma cell cultures by transfection with cDNA encoding novel ADP-ribosylation factor-like proteins

We have used cDNAs coding for novel ADP-ribosylation factor-like molecules (ARL184 and ARL184Delta) to alter 19-9 antigen glycoprotein secretion in cultured human colorectal carcinoma cells SW1116 by transfection and cloning. This ARL contains a lipophilic N-terminal with an isoleucyl and 3 leucyl residues, 4 functioning consensus sequence GTP binding sites, and 184 total aminoacyl residues. An ARL cDNA was also constructed deleting the codon for the N-terminal glycyl moiety. The resulting cell clones were shown by Northern blots to overexpress ARL mRNA. Electron microscopy-immunocytochemistry also indicated the overexpression of ARL granules subcellularly. Secretion of the tumor-associated 19-9 antigen into apical medium was decreased 3- to 5-fold and the secretion of TCA/PTA precipitable 3H-labeled glycoprotein was decreased by 34% in clone SW1116(ARL184)Delta. Western blot analyses of cell homogenates and media were in agreement with the secretion assays and showed a diminution of 170-200 kDa, 19-9, antigenicity in transfected cells and their media. Apical secretion of 19-9 antigen was diminished 14-fold in cells, SW1116 (ARL184)alpha, transfected with the complete ARL cDNA sequence, suggesting that the glycyl moiety may be required for maximal abatement. However, incorporation of label from [3H]myristate into 22-kDa bands of NP-40 extracts and ARL-antigenic molecules of parent cells was 3-fold greater than that in samples from the two transfectants; thus the transfected cells may not myristylate the overexpressed ARL efficiently. Notwithstanding the N-terminal glycyl moiety undergoing some other modification, we conclude that overexpression of this ARL is sufficient to generate a 19-9-deficient phenotype. These ARLs may eventually disrupt terminal oligosaccharide glycosylation, resulting in an apparent diminished exocytosis of 19-9 glycoprotein carriers by transfected and cloned cells.

Apical release of base-labile fatty acyl groups commensurate with stimulation of glycoprotein sialosyl Lewis(a) secretion in colorectal carcinoma cells

The rate of polarized secretion of a putative adhesion ligand, sialosyl Lewis(a) (19-9), by SW1116 colorectal carcinoma cells is stimulated at least 20-fold after pre-incubation with, and the incorporation of, retinoic acid (RA). In order to investigate the possible involvement of fatty acylation in the export of the epitope, purified ligands from carcinoma-cell membranes, membrane subfractions and media were analyzed during RA-induced secretion. Incorporation of radioactivity from (3H)palmitate into membrane subfractions and purified sialosyl Lewis(a) antigenic molecular species of M(r) > 150,000 (SiaLeams) was stimulated by RA treatment. Most of the intracellular lipid radioactivity which bound to solid-phase 19-9 antibody behaved chromatographically, either like ganglioside or like NH2 OH-labile acyl groups, but most of the (3H) bound to SiaLeams of post-incubation media behaved like base-labile fatty acyl groups, or free fatty acid. Release of base-labile lipid radioactivity after 3 hr (associated with antigen) was almost exclusively into the apical media of membrane inserts. Gas-liquid chromatography/mass spec. analyses of purified Sialeams revealed the presence of palmitate (16:0), as well as stearate (18:0) and oleate (18:1) fatty acyl groups. Our results suggest that fatty acylation of SiaLeams may be co-ordinated with alterations in glycosylation and participate in directing these molecules to the apical surface. Lipid analyses were consistent with ganglioside chaperonage of SiaLeams to the apical surface, where N-fatty-acylated gangliosides remain for the most part integrated into the bilayer, but some oxyester or thioester bonds may be cleaved to permit release of SiaLeams to the apical medium.