Shinji Asano

Glycosylation-Dependent Interactions of C-Type Lectin DC-SIGN with Colorectal Tumor-Associated Lewis Glycans Impair the Function and Differentiation of Monocyte-Derived Dendritic Cells

Dendritic cells (DCs) are APCs that play an essential role by bridging innate and adaptive immunity. DC-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) is one of the major C-type lectins expressed on DCs and exhibits high affinity for nonsialylated Lewis (Le) glycans. Recently, we reported the characterization of oligosaccharide ligands expressed on SW1116, a typical human colorectal carcinoma recognized by mannan-binding protein, which is a serum C-type lectin and has similar carbohydrate-recognition specificities as DC-SIGN. These tumor-specific oligosaccharide ligands were shown to comprise clusters of tandem repeats of Lea/Leb epitopes. In this study, we show that DC-SIGN is involved in the interaction of DCs with SW1116 cells through the recognition of aberrantly glycosylated forms of Lea/Leb glycans on carcinoembryonic Ag (CEA) and CEA-related cell adhesion molecule 1 (CEACAM1). DC-SIGN ligands containing Lea/Leb glycans are also highly expressed on primary cancer colon epithelia but not on normal colon epithelia, and DC-SIGN is suggested to be involved in the association between DCs and colorectal cancer cells in situ by DC-SIGN recognizing these cancer-related Le glycan ligands. Furthermore, when monocyte-derived DCs (MoDCs) were cocultured with SW1116 cells, LPS-induced immunosuppressive cytokines such as IL-6 and IL-10 were increased. The effects were significantly suppressed by blocking Abs against DC-SIGN. Strikingly, LPS-induced MoDC maturation was inhibited by supernatants of cocultures with SW1116 cells. Our findings imply that colorectal carcinomas affecting DC function and differentiation through interactions between DC-SIGN and colorectal tumor-associated Le glycans may induce generalized failure of a host to mount an effective antitumor response.

A novel transporter of SLC22 family specifically transports prostaglandins and co-localizes with 15-hydroxyprostaglandin dehydrogenase in renal proximal tubules

We identified a novel prostaglandin (PG)-specific organic anion transporter (OAT) in the OAT group of the SLC22 family. The transporter designated OAT-PG from mouse kidney exhibited Na+-independent and saturable transport of PGE2 when expressed in a proximal tubule cell line (S2). Unusual for OAT members, OAT-PG showed narrow substrate selectivity and high affinity for a specific subset of PGs, including PGE2, PGF2α, and PGD2. Similar to PGE2 receptor and PGT, a structurally distinct PG transporter, OAT-PG requires for its substrates an α-carboxyl group, with a double bond between C13 and C14 as well as a (S)-hydroxyl group at C15. Unlike the PGE2 receptor, however, the hydroxyl group at C11 in a cyclopentane ring is not essential for OAT-PG substrates. Addition of a hydroxyl group at C19 or C20 impairs the interaction with OAT-PG, whereas an ethyl group at C20 enhances the interaction, suggesting the importance of hydrophobicity around the ω-tail tip forming a “hydrophobic core” accompanied by a negative charge, which is essential for substrates of OAT members. OAT-PG-mediated transport is concentrative in nature, although OAT-PG mediates both facilitative and exchange transport. OAT-PG is kidney-specific and localized on the basolateral membrane of proximal tubules where a PG-inactivating enzyme, 15-hydroxyprostaglandin dehydrogenase, is expressed. Because of the fact that 15-keto-PGE2, the metabolite of PGE2 produced by 15-hydroxyprostaglandin dehydrogenase, is not a substrate of OAT-PG, the transport-metabolism coupling would make unidirectional PGE2 transport more efficient. By removing extracellular PGE2, OAT-PG is proposed to be involved in the local PGE2 clearance and metabolism for the inactivation of PG signals in the kidney cortex.

Sex hormones induce a gender-related difference in renal expression of a novel prostaglandin transporter, OAT-PG, influencing basal PGE2 concentration

Based on the nucleotide sequence of a mouse prostaglandin-specific transporter (mOAT-PG), we identified a rat homolog (rOAT-PG) which shares 80% identity with mOAT-PG in a deduced amino acid sequence. rOAT-PG transports PGE(2) and colocalizes with 15-hydroxyprostaglandin dehydrogenase (15-PGDH), a metabolic enzyme for PGs, in proximal tubules, suggesting that rOAT-PG is involved in PGE(2) clearance to regulate its physiological function in the renal cortex. We found that the expression level of rOAT-PG in the renal cortex was much higher in male rats than in female rats whereas there was no gender difference in the expression level of cyclooxygenase-2, a key enzyme producing PGE(2), and 15-PGDH in the renal cortex. Tissue PGE(2) concentration in the renal cortex was lower in male rats than in female rats, suggesting that renocortical PGE(2) concentration is primarily determined by the expression level of OAT-PG, which is regulated differently between male and female rats. Castration of male rat led to a remarkable reduction in OAT-PG expression and a significant increase in renocortical PGE(2) concentration. These alterations were recovered by testosterone supplementation. These results suggest that OAT-PG is involved in local PGE(2) clearance in the renal cortex. Although the physiological importance of the gender difference in local PGE(2) clearance is still unclear, these findings might be a key to clarifying the physiological roles of PGE(2) in the kidney.

Ezrin, a membrane cytoskeletal cross-linker, is essential for the regulation of phosphate and calcium homeostasis

Ezrin cross-links plasma membrane proteins with the actin cytoskeleton. In the kidney, ezrin mainly localizes at the brush border membrane of proximal tubules with the scaffolding protein, Na(+)/H(+) exchanger regulatory factor (NHERF) 1. NHERF1 interacts with the sodium/phosphate cotransporter, Npt2a. Defects in NHERF1 or Npt2a in mice cause hypophosphatemia. Here we studied the physiological role of ezrin in renal phosphate reabsorption using ezrin knockdown mice (Vil2). These mice exhibit hypophosphatemia, hypocalcemia, and osteomalacia. The reduced plasma phosphate concentrations were ascribed to defects in urinary phosphate reabsorption. Immunofluorescence and immunoblotting indicated a marked reduction in renal Npt2a and NHERF1 expression at the apical membrane of proximal tubules in the knockdown mice. On the other hand, urinary loss of calcium was not found in Vil2 mice. Plasma concentrations of 1,25-dihydroxyvitamin D were elevated following reduced plasma phosphate levels, and mRNA of the vitamin D-dependent TRPV6 calcium channel were significantly increased in the duodenum of knockdown mice. Expression of TRPV6 at the apical membrane, however, was significantly decreased. Furthermore, tibial bone mineral density was significantly lower in both the adult and young Vil2 mice. These results suggest that ezrin is required for the regulation of systemic phosphate and calcium homeostasis in vivo.

Characterization of the interaction between serum mannan-binding protein and nucleic acid ligands

Serum MBP, also known as MBL, is a C‐type lectin that is known to be a soluble host defense factor involved in innate immunity. It has been well established that dying microbes and apoptotic cells release highly viscous DNA that induces inflammation and septic shock, and apoptotic cells display fragmented DNA on their surfaces. However, PRRs that mediate the recognition and clearance of free DNA and fragmented DNA in apoptotic cells have not been characterized clearly. Although MBP was reported recently to bind DNA as a novel ligand, binding characterization and the recognition implications have not been addressed yet. In this study, we show that MBP can bind DNA and RNA in a calcium‐dependent manner from a variety of origins, including bacteria, plasmids, synthetic oligonucleotides, and fragmented DNA of apoptotic cells. Direct binding and competition studies indicate that MBP binds nucleic acids via its CRD to varying degrees and that MBP binds dsDNA more effectively than ssDNA and ssRNA. Furthermore, we reveal that the MBP‐DNA complex does not trigger complement activation via the MBP lectin pathway, and the lectin pathway of complement activation is required for MBP‐mediated enhancement of phagocytosis of targets bearing MBP ligands and that MBP can recognize the fragmented DNA presented on apoptotic cells. Therefore, we propose that the MBP lectin pathway may support effective recognition and clearance of cellular debris by facilitating phagocytosis, possibly through immunomodulatory mechanisms, thus preventing autoimmunity.

Knockdown of ezrin causes intrahepatic cholestasis by the dysregulation of bile fluidity in the bile duct epithelium in mice

Cholangiopathies share common features, including bile duct proliferation, periportal fibrosis, and intrahepatic cholestasis. Damage of biliary epithelium by autoimunne disorder, virus infection, toxic compounds, and developmental abnormalities causes severe progressive hepatic disorders responsible for high mortality. However, the etiologies of these cholestatic diseases remain unclear because useful models to study the pathogenic mechanisms are not available. In the present study, we have found that ezrin knockdown (Vil2kd/kd) mice develop severe intrahepatic cholestasis characterized by extensive bile duct proliferation, periductular fibrosis, and intrahepatic bile acid accumulation without developmental defects of bile duct morphology and infiltration of inflammatory cells. Ezrin is a membrane cytoskeletal cross‐linker protein, which is known to interact with transporters, scaffold proteins, and actin cytoskeleton at the plasma membrane. We found that the normal apical membrane localizations of several transport proteins including cystic fibrosis transmembrane conductance regulator (CFTR), anion exchanger 2 (AE‐2), aquaporin 1 (AQP1), and Na+/H+ exchanger regulatory factor were disturbed in bile ducts of Vil2kd/kd mice. Stable expression of a dominant negative form of ezrin in immortalized mouse cholangiocytes also led to the reduction of the surface expression of CFTR, AE‐2, and AQP1. Reduced surface expression of these transport proteins was accompanied by reduced functional expression, as evidenced by the fact these cells exhibited decreased CFTR‐mediated Cl− efflux activity. Furthermore, bile flow and biliary HCO3− concentration were also significantly reduced in Vil2kd/kd mice. Conclusion: Dysfunction of ezrin mimics important aspects of the pathological mechanisms responsible for cholangiopathies. The Vil2kd/kd mouse may be a useful model to exploit in the development and testing of potential therapies for cholangiopathies. (Hepatology 2015;61:1660‐1671)

Ezrin mediates neuritogenesis via down-regulation of RhoA activity in cultured cortical neurons.

Neuronal morphogenesis is implicated in neuronal function and development with rearrangement of cytoskeletal organization. Ezrin, a member of Ezrin/Radixin/Moesin (ERM) proteins links between membrane proteins and actin cytoskeleton, and contributes to maintenance of cellular function and morphology. In cultured hippocampal neurons, suppression of both radixin and moesin showed deficits in growth cone morphology and neurite extensions. Down-regulation of ezrin using siRNA caused impairment of netrin-1-induced axon outgrowth in cultured cortical neurons. However, roles of ezrin in the neuronal morphogenesis of the cultured neurons have been poorly understood. In this report, we performed detailed studies on the roles of ezrin in the cultured cortical neurons prepared from the ezrin knockdown (Vil2kd/kd) mice embryo that showed a very small amount of ezrin expression compared with the wild-type (Vil2+/+) neurons. Ezrin was mainly expressed in cell body in the cultured cortical neurons. We demonstrated that the cultured cortical neurons prepared from the Vil2kd/kd mice embryo exhibited impairment of neuritogenesis. Moreover, we observed increased RhoA activity and phosphorylation of myosin light chain 2 (MLC2), as a downstream effector of RhoA in the Vil2kd/kd neurons. In addition, inhibition of Rho kinase and myosin II rescued the impairment of neuritogenesis in the Vil2kd/kd neurons. These data altogether suggest a novel role of ezrin in the neuritogenesis of the cultured cortical neurons through down-regulation of RhoA activity.

Initiation of malignancy by duodenal contents reflux and the role of ezrin in developing esophageal squamous cell carcinoma

(Cancer Sci 2010; 101: 624–630)

Effects of ezrin knockdown on the structure of gastric glandular epithelia.

Ezrin, an adaptor protein that cross-links plasma membrane-associated proteins with the actin cytoskeleton, is concentrated on apical surfaces of epithelial cells, especially in microvilli of the small intestine and stomach. In the stomach, ezrin is predominantly expressed on the apical canalicular membrane of parietal cells. Transgenic ezrin knockdown mice in which the expression level of ezrin was reduced to <7xa0% compared with the wild-type suffered from achlorhydria because of impairment of membrane fusion between tubulovesicles and apical membranes. We observed, for the first time, hypergastrinemia and foveolar hyperplasia in the gastric fundic region of the knockdown mice. Dilation of fundic glands was observed, the percentage of parietal and chief cells was reduced, and that of mucous-secreting cells was increased. The parietal cells of knockdown mice contained dilated tubulovesicles and abnormal mitochondria, and subsets of these cells contained abnormal vacuoles and multilamellar structures. Therefore, lack of ezrin not only causes achlorhydria and hypergastrinemia but also changes the structure of gastric glands, with severe perturbation of the secretory membranes of parietal cells.

The lectin Jacalin induces human B‐lymphocyte apoptosis through glycosylation‐dependent interaction with CD45

It has been well established that CD45 is a key receptor‐type protein tyrosine phosphatase (PTPase) regulating Src‐family protein tyrosine kinase (Src‐PTK) in T and B lymphocytes. However, precisely how CD45 exerts its effect in these lymphocytes remains controversial. We recently reported that Jacalin, an α‐O‐glycoside of the disaccharide Thomsen–Friedenreich antigen‐specific lectin from jackfruit seeds, caused marked T‐cell activation in response to T‐cell receptor ligation and CD28 costimulation by binding to CD45. On extending the reported research, we found that CD45 and isoforms are major Jacalin receptors on B lymphocytes, and that the glycosylation of CD45 is involved in the interaction of Jacalin with the PTPase. In contrast to Jacalin‐stimulated T‐cell activation, we found that Jacalin induced human B‐lymphocyte apoptosis, resulting in calcium mobilization and calpain activation, suggesting that the calcium–calpain pathway may mediate the Jacalin‐induced apoptosis. Importantly, the apoptosis was effectively blocked by a specific CD45 PTPase inhibitor, indicating that Jacalin induces human B‐lymphocyte apoptosis through CD45 triggering. Furthermore, we found that Jacalin significantly increased the C‐terminal inhibitory tyrosine (Tyr507) phosphorylation of Src‐PTK Lyn, one of the major substrates of CD45 PTPase, and this effect was also observed on incubation of B lymphocytes with the specific CD45 PTPase inhibitor, suggesting that Jacalin stimulation results in increasing C‐terminal tyrosine phosphorylation of the kinase through inhibition of CD45 tyrosine phosphatase activity in human B lymphocytes. Therefore, the down‐modulation of Lyn kinase may play a role in the regulation of B‐lymphocyte viability.