Fucosylation of N-Glycans Regulates the Secretion of Hepatic Glycoproteins into Bile Ducts

Abstract

Fucosylated ␣-fetoprotein (AFP) is a highly specific tumor marker for hepatocellular carcinoma (HCC). However, the molecular mechanism by which serum level of fucosylated AFP increases in patients with HCC remains largely unknown. Here, we report that the fucosylation of glycoproteins could be a possible signal for secretion into bile ducts in the liver. We compared oligosaccharide structures on glycoproteins in human bile with those in serum by several types of lectin blot analyses. Enhanced binding of biliary glycoproteins to lectins that recognize a fucose residue was observed over a wide range of molecular weights compared with serum glycoproteins. A structural analysis of oligosaccharides by two-dimensional mapping high performance liquid chromatography and matrix-assisted laser desorption ionization time-of flight mass spectrometry confirmed the increases in the fucosylation of biliary glycoproteins. Purification followed by structural analysis on ␣1-antitrypsin, ␣1-acid glycoprotein and haptoglobin, which are synthesized in the liver, showed higher fucosylation in bile than in serum. To find direct evidence for fucosylation and sorting signal into bile ducts, we used ␣1-6 fucosyltransferase (Fut8)-deficient mice because fucosylation of glycoproteins produced in mouse liver was mainly an ␣1-6 linkage. Interestingly, the levels of ␣1-antitrypsin and ␣1-acid glycoprotein were quite low in bile of Fut8-deficient mice as compared with wild-type mice. An immunohistochemical study showed dramatic changes in the localization of these glycoproteins in the liver of Fut8-deficient mice. Taken together, these results suggest that fucosylation is a possible signal for the secretion of glycoproteins into bile ducts in the liver. A disruption in this system might involve an increase in fucosylated AFP in the serum of patients with HCC.

Haptoglobin Levels in Turkish Patients with Bladder Cancer and its Association with Clinicopathological Features

“…Some haptoglobin proteins are released from normal hepatocytes from the apical region of the liver into the bile duct (Nakagawa et al, 2006). Although cancer cells in the bladder produce prostate specific antigen (PSA) (Glybchenko et al, 2011), this polypeptide is secreted into bile but not blood.…”

Wisteria floribunda agglutinin-positive mucin 1 is a sensitive biliary marker for human cholangiocarcinoma

“…The protein concentration was measured with Micro BCA (Pierce, Rockford, IL) using BSA as a standard. 27,28 For WFA-affinity purification, 20 lg of total protein from the bile samples described above and 2 lg of preconjugated biotinylated WFA, streptavidin-immobilized magnetic beads (Streptavidincoupled Dynabeads; Invitrogen) were used. 29 The beads were incubated with bile for 9 hours at 4 C, the supernatants were then excluded, and the beads were washed twice with 200 lL of PBS containing 1% Triton X-100 (PBSTx).…”

Association of fucosyltransferase 8 (FUT8) polymorphism Thr267Lys with pulmonary emphysema

“…5,17 The FUT8 product is the sole enzyme that catalyzes this transfer in mammals. Core glycoprotein fucosylation is widely distributed in mammalian tissues and is seen in various proteins including TGFb receptor, 4 epidermal growth factor receptor, 18 alpha-1-antitrypsin 19 and integrins. 20 Recently, mice with a disrupted fut8 gene were developed.…”