Surfactant protein D suppresses lung cancer progression by downregulation of epidermal growth factor signaling.

Surfactant protein D (SP-D) is a member of the collectin family that has an important role in maintaining pulmonary homeostasis. In this study, we demonstrated that SP-D inhibited the proliferation, migration and invasion of A549 human lung adenocarcinoma cells. We found that SP-D suppressed epidermal growth factor (EGF) signaling in A549 cells, H441 human lung adenocarcinoma cells and human EGF receptor (EGFR) stable expression CHO-K1 cells. A binding study using (125)I-EGF demonstrated that SP-D downregulated the binding of EGF to EGFR. A ligand blot indicated that SP-D bound to EGFR, and a lectin blot suggested that EGFR in A549 cells had both high-mannose type and complex type N-glycans. We purified the recombinant extracellular domain of EGFR (soluble EGFR=soluble EGFR (sEGFR)), and demonstrated that SP-D directly bound to sEGFR in a Ca(2+)-dependent manner. The binding of SP-D to sEGFR was suppressed by EDTA, mannose or N-glycopeptidase F treatment. Mass spectrometric analysis indicated that N-glycans in domain III of EGFR were of a high-mannose type. These data suggest that SP-D reduces EGF binding to EGFR through the interaction between the carbohydrate recognition domain of SP-D and N-glycans of EGFR, and downregulates EGF signaling. Our finding suggests the novel type of regulation system of EGF signaling involving lectin-to-carbohydrate interaction and downregulation of ligand binding.

A novel fungal endo-beta-N-acetylglucosaminidase that specifically acts on plant glycoproteins.

An endo-beta-N-acetylglucosaminidase specific for plant glycoprotein oligosaccharides was purified from the culture fluid of a fungus. The Mr of the purified enzyme was 89,000. This enzyme was stable at pH 5.5-7.0, up to 30 degrees C, and showed the highest activity at pH 6.0. Among sugar chains tested, xylose-containing sugar chains (M3X, M3FX, and M2FX) were the most favored substrates. Oligomannose type (M3, M5, and M9) and hybrid type (GNM3) sugar chains were hydrolyzed much more slowly than xylose-containing sugar chains, and a complex type sugar chain (GN2M3) was not hydrolyzed at all by the enzyme. Moreover, the enzyme released sugar chains from native horseradish peroxidase and stem bromelain, which were not hydrolyzed by other endo-beta-N-acetylglucosaminidases (Endo H, D, and F). The enzyme could transfer the xylose-containing sugar chain from bromelain to DNS-Asn-GlcNAc-Fuc.

Efficient production and purification of extracellular 1,2-alpha-L-fucosidase of Bacillus sp. K40T.

When Bacillus sp. K40T was cultured in the presence of L-fucose, 1,2-alpha-L-fucosidase was found to be produced specifically in the culture fluid. The enzyme was purified to homogeneity from a culture containing only L-fucose by chromatography on hydroxylapatite and chromatofocusing. The molecular weight of the enzyme was estimated to be 200,000 by gel filtration on Sephadex G-200. The enzyme was optimal at pH 5.5-7.0 and was stable at pH 6.0-9.0. The enzyme hydrolyzed the alpha-(1-->2)- L-fucosidic linkages in various oligosaccharides and glycoproteins such as lacto-N-fucopentaose (LNF)-I 2)-O-beta-D-galactose-(1-->3)-N-acetyl-O-beta-D- glucosamine-(1-->3)-O-beta-D-galactose-(1-->4)-D-glucose>, porcine gastric mucin, and porcine submaxillary mucin. The enzyme also acted on human erythrocytes, which was confirmed by the hemagglutination test using Ulex anti-H lectin. The enzyme did not hydrolyze alpha-(1-->3)-, alpha-(1-->4)- and alpha-(1-->6)-L-fucosidic linkages in LNF-III 4)[O- alpha-L-fucose-(1-->3)-]-N-acetyl-O-beta-D-glucosamine-(1-->3)-O-beta-D- galactose-(1-->4)-D-glucose>, LNF-II 3)[O-alpha-L- fucose-(1-->4)-]-N-acetyl-O-beta-D-glucosamine-(1-->3)-O-beta-D- galactose-(1-->4)-D-glucose> or 6-O-alpha-L-fucopyranosyl-N-acetylglucosamine.