Modification of blood group A antigen expression in a pancreatic cancer cell line (PC-1) by inhibitors of N-glycan processing.

Pancreatic adenocarcinomas induced in Syrian hamsters by treatment with N-nitrosobis(2-oxopropyl) amine express blood group A antigen, which is absent in normal pancreatic cells. On membrane glycoproteins purified from tumors, blood group A antigen has been found to be expressed on multiantennary Asn-linked complex glycans. In this study, we investigated the effect of inhibitors of Asn-glycan processing on blood group A antigen bearing glycan structures in a cell line (PC-1) established from a primary induced pancreatic cancer. Expression of blood group A antigen on cells and in membrane preparations was blocked by treatment with 1-deoxymannojirimycin, an inhibitor of mannosidase I, but was retained after treatment with swainsonine, an inhibitor of mannosidase II. However, swainsonine treatment altered the glycan structure associated with blood group A antigen from an endoglycosidase H resistant type to a sensitive type, indicating that the blood group A structure might shift from a complex type to a hybrid type glycan by this treatment. These results demonstrate that Asn-linked glycans carry the major blood group A antigens in PC-1 cells.     

Developmental changes of blood group A-active glycosphingolipids with type 1 and type 2 chains in rat small intestine

Blood group A-active glycosphingolipids of the small intestine, A-6 and A-12, which have been characterized previously in the adult rat [Breimer ME, Hansson GC, Karlsson K-A, Leffler H (1982) J Biol Chem 257:906–12], were found to appear during postnatal development, using immunostaining on thin layer chromatograms with two monoclonal anti-A antibodies, A005 and A581. In this system, A005 was found to be specific for the A determinant based on the type 2 chain, while A581 reacted mainly with the A determinant based on the type 1 chain and only weakly with the A determinant based on the type 2 chain. A-6 Type 1 was detected first at 18 days after birth. Its concentration increased markedly during the fourth week. A-6 Type 2 was detected, at a very low level, in neonates. Its concentration increased between days 15 and 20 and then decreased almost to the neonate level by 28 days. Dodecaglycosylceramide A-12 followed the same pattern of reactivity as A-6 type 1 with A581, and remained strongly reactive with A005 after 20 days. Linear A-6 and branched A-12 appeared simultaneously. Antibodies directed against blood group H determinants based on the type 1 or type 2 chains did not detect any H structure which might have appeared as a precursor of either A-6 or A-12 at the early stages of postnatal development.Abbreviations A-6, A-12, H-5, H-10 etc the glycolipids are abbreviated by giving blood group activity, and number of sugars (see also Fig. 1) - G_M3 G_M3-ganglioside, H³NeuAc-LcCer - PBS phosphate-buffered saline     

The blood group B type-4 heptaglycosylceramide is a minor blood group B structure in human B kidneys in contrast to the corresponding A type-4 compound in A kidneys. Structural and in vitro biosynthetic studies

Blood group A glycolipid antigens have been found based upon at least four different core saccharides (types 1 to 4). The biological significance of this structural polymorphism is not known, although the successful outcome of transplantations of blood group A₂ kidneys to blood group O individuals have been partly explained by the low expression of A type-3 and -4 chain glycolipid antigens in A₂ kidneys. If graft rejection due to ABO incompatibility is, in any way, correlated to the expression of type-3 and -4 chain blood group glycolipids, it is of interest to identify possible blood group B structures based on these core saccharides. In a non-acid glycosphingolipid fraction isolated from human blood group B kidneys, mass spectrometry, high-temperature gas chromatography-mass spectrometry and probing of thin-layer chromatograms with Galα1–4Gal-specific Escherichia coli and monoclonal anti-B antibodies provided evidence for minute amounts of Gaα1–3(Fucα1–2)Galβ-HexNac-Galα1–4Galβ-Hex-Ceramide structure consistent with a B type-4 chain heptaglycosylceramide. In contrast, blood group A kidneys have the corresponding A type-4 chain heptaglycosylceramide as the predominant glood group A glycolipid. No, or very low activity of the blood group B gene enzyme on the type-4 chain blood group H hexaglycosylceramide precursor was found by biosynthetic experiments in vitro, which migh explain the low expression of type-4 chain blood group heptaglycosylceramides in human blood group B kidneys.     

N-myristoyltransferase 2 expression in human colon cancer: cross-talk between the calpain and caspase system

A number of viral and eukaryotic proteins which undergo a lipophilic modification by the enzyme N-myristoyltransferase (NMT: NMT1 and NMT2) are required for signal transduction and regulatory functions. To investigate whether NMT2 contributes to the pathogenesis of colorectal carcinoma, we observed a higher expression of NMT2 in most of the cases of cancerous tissues compared to normal tissues (84.6% of cases; P < 0.05) by Western blot analysis. Furthermore, protein-protein interaction of NMTs revealed that m-calpain interacts with NMT1 while caspase-3 interacts with NMT2. Our findings provide the first evidence of higher expression of NMT2 in human colorectal adenocarcinomas and the interaction of both forms of NMT with various signaling molecules.     

Crosstalk of tight junction components with signaling pathways

Tight junctions (TJs) regulate the passage of ions and molecules through the paracellular pathway in epithelial and endothelial cells. TJs are highly dynamic structures whose degree of sealing varies according to external stimuli, physiological and pathological conditions. In this review we analyze how the crosstalk of protein kinase C, protein kinase A, myosin light chain kinase, mitogen-activated protein kinases, phosphoinositide 3-kinase and Rho signaling pathways is involved in TJ regulation triggered by diverse stimuli. We also report how the phosphorylation of the main TJ components, claudins, occludin and ZO proteins, impacts epithelial and endothelial cell function.