The core fucosylation (α1,6-fucosylation) of glycoproteins is widely distributed in mammalian tissues, and is altered under pathological conditions. To investigate physiological functions of the core fucose, we generated α1,6-fucosyltransferase ( Fut8 )-null mice and found that disruption of Fut8 induces severe growth retardation and death during postnatal development. Histopathological analysis revealed that Fut8 ^-/- mice showed emphysema-like changes in the lung, verified by a physiological compliance analysis. Biochemical studies indicated that lungs from Fut8 ^-/- mice exhibit a marked overexpression of matrix metalloproteinases (MMPs), such as MMP-12 and MMP-13, highly associated with lung-destructive phenotypes, and a down-regulation of extracellular matrix (ECM) proteins such as elastin, as well as retarded alveolar epithelia cell differentiation. These changes should be consistent with a deficiency in TGF-β1 signaling, a pleiotropic factor that controls ECM homeostasis by down-regulating MMP expression and inducing ECM protein components. In fact, Fut8 ^-/- mice have a marked dysregulation of TGF-β1 receptor activation and signaling, as assessed by TGF-β1 binding assays and Smad2 phosphorylation analysis. We also show that these TGF-β1 receptor defects found in Fut8 ^-/- cells can be rescued by reintroducing Fut8 into Fut8 ^-/- cells. Furthermore, exogenous TGF-β1 potentially rescued emphysema-like phenotype and concomitantly reduced MMP expression in Fut8 ^-/- lung. We propose that the lack of core fucosylation of TGF-β1 receptors is crucial for a developmental and progressive/destructive emphysema, suggesting that perturbation of this function could underlie certain cases of human emphysema.

The β‐site amyloid precursor protein cleaving enzyme‐1 (BACE1), an essential protease for the generation of amyloid‐β (Aβ) peptide, is a major drug target for Alzheimer's disease (AD). However, there is a concern that inhibiting BACE1 could also affect several physiological functions. Here, we show that BACE1 is modified with bisecting N‐acetylglucosamine (GlcNAc), a sugar modification highly expressed in brain, and demonstrate that AD patients have higher levels of bisecting GlcNAc on BACE1. Analysis of knockout mice lacking the biosynthetic enzyme for bisecting GlcNAc, GnT‐III ( Mgat3 ), revealed that cleavage of Aβ‐precursor protein (APP) by BACE1 is reduced in these mice, resulting in a decrease in Aβ plaques and improved cognitive function. The lack of this modification directs BACE1 to late endosomes/lysosomes where it is less colocalized with APP, leading to accelerated lysosomal degradation. Notably, other BACE1 substrates, CHL1 and contactin‐2, are normally cleaved in GnT‐III‐deficient mice, suggesting that the effect of bisecting GlcNAc on BACE1 is selective to APP. Considering that GnT‐III‐deficient mice remain healthy, GnT‐III may be a novel and promising drug target for AD therapeutics.

Oligosaccharide moieties of glycoproteins are structurally altered during development, carcinogenesis, and malignant transformations. It is well known that β1–6 GlcNAc branching, a product of UDP-GlcNAc α-mannoside β1–6-N-acetylglucosaminyltransferase (GnT-V), is associated with malignant transformation as the results of such alterations. However, the mechanism by which β1–6 GlcNAc branching is linked to metastasis remains unclear, because the identification of specific glycoprotein(s) that are glycosylated by GnT-V and its biological function have not been examined. We herein report that matriptase, which activates both urokinase-type plasminogen activator and hepatocyte growth factor, is a target protein for GnT-V. The overexpression of GnT-V in gastric cancer cells leads to severe peritoneal dissemination in athymic mice, which can be attributed to the increased expression of matriptase. This increase was due to the acquired resistance of matriptase to degradation, since it is glycosylated by GnT-V and a corresponding increase in the active form. These results indicate that this process is a key element in malignant transformation, as the direct result of oligosaccharide modification.

Peroxiredoxins (PRxs) play a role in protecting protein free thiol groups against oxida-tive damage and thioredoxin-dependent peroxidase activity. This report describes the characteristics of the fourth member of the mammalian PRxs, PRx TV. Rat PRx TV produced in Sf21 cells by a baculovirus expression system has two bands with different electrophoretic mobilities, 31 and 27 kDa [Matsumoto et al. (1999) FEBS Lett. 443, 246-250]. The 27-kDa PRx TV lacks the NHj-terminal 36 amino acids which correspond to a predicted leader peptide, which is required for secretion from cells. Thus, the 31-kDa form is probably a precursor form, and the 27-kDa form, a secretable form which is enzymatically active. Pulse-chase experiments of PRx IV-transfected COS-1 cells showed that PRx IV is processed within 10 min and released from cells. The secretable form contains both reduced and oxidized forms. The reduced form binds to both a heparin affinity column and human umbilical vein endothelial cells, while the oxidized form does not. The equilibrium dissociation constants, K_D, for heparin and heparan sulfate as judged by surface plasmon resonance experiments were 19 and 870 nM, respectively. The secretable form corresponds to the major bands found in most tissues, as evidenced by immunoblot analysis. Within cells, secretable form was largely localized on the endo-plasmic reticulum, as judged by colocalization with calreticulin. Moreover, PRx TV has glutathione-dependent peroxidase activity in addition to thioredoxin-dependent activity. These data indicate that PRx TV is a secretable protein and may exert its protective function against oxidative damage by scavenging reactive oxygen species in the extracellular space.