Adhesive interactions between the molecules on cancer cells and the target organ are one of the key determinants of the organ specific metastasis. In this communication we show that b1,6 branched N-oligosaccharides which are expressed in a metastasis-dependent manner on B16-melanoma metastatic cell lines, participate in the adhesion process. We demonstrate that high metastatic cells show significantly increased translocation of one of the major carriers of these oligosaccharides, lysosome associated membrane protein (LAMP1), to the cell surface. LAMP1 on high metastatic cells, carry very high levels of these oligosaccharides, which are further substituted with poly N-acetyl lactosamine (polylacNAc), resulting in the expression of high density of very high affinity ligands for galectin-3 on the cell surface. We show that galectin-3 is expressed in highest amount in the lungs as compared to other representative organs. Blocking galectin-3 by pre-incubating the frozen sections of the lungs with 100 mM lactose, substantially inhibited the adhesion of high metastatic cells, while pre-incubation with sucrose had no effect. Finally, by in situ labeling and immunoprecipitation experiment, we demonstrated that the lung vascular endothelial cells express galectin-3 constitutively on their surface. Galectin-3 on the organ endothelium could thus serve as the first anchor for the circulating cancer cells, expressing high density of very high affinity ligands on their surface, and facilitate organ specific metastasis.

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Keratins 8 and 18 (K8/18) are intermediate filament proteins expressed specifically in simple epithelial tissues. Dynamic equilibrium of these phosphoglycoproteins in the soluble and filament pool is an important determinant of their cellular functions, and it is known to be regulated by site-specific phosphorylation. However, little is known about the role of dynamic O-GlcNAcylation on this keratin pair. Here, by comparing immortalized (Chang) and transformed hepatocyte (HepG2) cell lines, we have demonstrated that O-GlcNAcylation of K8/18 exhibits a positive correlation with their solubility (Nonidet P-40 extractability). Heat stress, which increases K8/18 solubility, resulted in a simultaneous increase in O-GlcNAc on these proteins. Conversely, increasing O-GlcNAc levels were associated with a concurrent increase in their solubility. This was also associated with a notable decrease in total cellular levels of K8/18. Unaltered levels of transcripts and the reduced half-life of K8 and K18 indicated their decreased stability on increasing O-GlcNAcylation. On the contrary, the K18 glycosylation mutant (K18 S29A/S30A/S48A) was notably more stable than the wild type K18 in Chang cells. The K18-O-GlcNAc mutant accumulated as aggregates upon stable expression, which possibly altered endogenous filament architecture. These results strongly indicate the involvement of O-GlcNAc on K8/18 in regulating their solubility and stability, which may have a bearing on the functions of these keratins.