[Immunological function of mannan-binding protein].
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Animals↗
Biomedical subjects
Toshisuke Kawasaki
Publications and source records attributed to Toshisuke Kawasaki.
L-MBP is expressed in epithelial cells of mouse small intestine.
The mannan-binding proteins (L-MBP and S-MBP, also denoted MBL-C and MBL-A), mainly produced in liver and existing in liver and serum, play important roles in the innate immunity against a variety of pathogens. Total RNA from mouse tissues were screened for MBP mRNA by RT-PCR. In addition to liver, S-MBP mRNA was detected in lung, kidney, and testis, and L-MBP mRNA was detected in kidney, thymus, and small intestine. Quantitative RT-PCR revealed that the small intestine is a predominant site of extrahepatic expression of L-MBP. Western blotting with polyclonal Abs against rat L-MBP demonstrated this protein in Triton X-100 extracts of the small intestine obtained from mice that had undergone systemic perfusion. Immunohistochemical staining with an mAb against mouse L-MBP and in situ hybridization revealed that L-MBP is selectively expressed in some villous epithelial cells of the small intestine. These findings suggest that L-MBP plays a role in mucosal innate immunity.
Animals↗
High mannose glycans and sialic acid on gp120 regulate binding of mannose-binding lectin (MBL) to HIV type 1.
Mannose-binding lectin (MBL) is a C-type lectin of the innate immune system that binds to carbohydrates on the surface of certain microorganisms. Previous studies showed that MBL binds to gp120, the envelope glycoprotein of HIV-1. gp120 is extensively glycosylated, with N-linked complex and high mannose carbohydrates accounting for about half of the molecular weight. The objectives of this study were to determine the types of glycans on gp120 important for MBL binding and to determine if alteration of complex glycans with neuraminidase (NA) could enhance the interaction of MBL with virus. Lectin blot analyses revealed that MBL interacted with recombinant gp120 (rgp120) from both T cell-tropic and M-tropic virus strains. Treatment of rgp120 with endoglycosidase H (eH) or endoglycosidase F1 (eF1) abrogated binding of MBL, but did not decrease binding of wheat germ agglutinin indicating that high mannose and/or hybrid N-linked glycans were required for MBL binding. Removal of sialic acids from rgp120 with NA enhanced MBL binding. Treatment of intact virus from T cell lines or primary isolates with eF1 also significantly decreased HIV binding to MBL, while treatment with NA substantially increased binding. Treatment of virus with both eF1 and NA did not decrease binding compared to NA alone suggesting that NA treatment exposed binding sites on gp120 that are not high mannose glycans. These studies provide evidence that MBL binds to HIV via high mannose carbohydrates on gp120 and shows that the interaction of MBL with virus is regulated by sialylation.
HIV Envelope Protein gp120↗
cDNA cloning, genomic structure and chromosomal mapping of the mouse glucuronyltransferase-S involved in the biosynthesis of the HNK-1 carbohydrate epitope.
The HNK-1 carbohydrate epitope is expressed on a series of cell adhesion molecules and some glycolipids in the nervous system. Two glucuronyltransferases (GlcAT-P and GlcAT-S) are involved in the biosynthesis of the HNK-1 carbohydrate epitope. In this study, we isolated cDNA and genomic clones encoding the mouse glucuronyltransferase-S involved in the biosynthesis of the HNK-1 carbohydrate epitope and determined the structural organization of the gene. The deduced amino acid sequence of mouse GlcAT-S consists of 324 amino acids and has a type II membrane topology. The predicted amino acid sequence of mouse GlcAT-S is 98.1% identical to that of rat GlcAT-S. Northern blot analysis revealed that the mouse GlcAT-S transcript is specifically expressed in the nervous system. Moreover, the mouse GlcAT-S gene is composed of four exons spanning over more than 25 kilobase pairs. Southern blot analysis and chromosomal mapping indicated that the mouse GlcAT-S gene is a single copy gene and it was mapped to the A4-B region of mouse chromosome 1.
5' Flanking Region↗
Mice deficient in nervous system-specific carbohydrate epitope HNK-1 exhibit impaired synaptic plasticity and spatial learning.
The HNK-1 carbohydrate epitope, a sulfated glucuronic acid at the non-reducing terminus of glycans, is expressed characteristically on a series of cell adhesion molecules and is synthesized through a key enzyme, glucuronyltransferase (GlcAT-P). We generated mice with a targeted deletion of the GlcAT-P gene. The GlcAT-P -/- mice exhibited normal development of gross anatomical features, but the adult mutant mice exhibited reduced long term potentiation at the Schaffer collateral-CA1 synapses and a defect in spatial memory formation. This is the first evidence that the loss of a single non-reducing terminal carbohydrate residue attenuates brain higher functions.
Animals↗
Genomic organization and fine-mapping of the human leucine zipper-bearing kinase (LZK) gene.
Leucine zipper-bearing kinase (LZK) is a new member of the mixed lineage protein kinase family. We previously cloned a cDNA encoding LZK from a human cerebellum cDNA library. The following studies indicated that LZK serves as a MAPKKK in the JNK/SAPK pathway in cells, and a scaffold protein, JIP-1, enhances LZK-induced JNK/SAPK pathway activation via physical association. Here we report characterization of the gene structure and fine chromosomal mapping of the human LZK gene. Polymerase chain-reaction (PCR) studies indicated that the human LZK coding sequence is composed of 13 exons, and that all the splice acceptor and donor sequences obey the GT-AG rule. Chromosomal localization studies involving FISH mapping demonstrated that the human LZK gene is located at 3q27.
Amino Acid Sequence↗
Molecular cloning and genomic analysis of mouse glucuronyltransferase involved in biosynthesis of the HNK-1 epitope.
cDNA and genomic clones encoding the mouse glucuronyltransferase (GlcAT-P) involved in biosynthesis of the HNK-1 carbohydrate epitope were isolated and the structural organization of the gene was determined. The predicted amino acid sequence of mouse GlcAT-P is 96.2 and 98.2% identical to those of the rat and human enzymes, respectively. Alternatively spliced isoforms of mouse GlcAT-P are present in the brain and encode two proteins that are identical throughout their length except for an additional 13 amino acids in the N-terminal cytoplasmic domain of the major form. The coding region of GlcAT-P is composed of 5 exons spanning approximately 6 kb, and the GlcAT-P gene was mapped to the A4 region of mouse chromosome 9. Upstream of the transcriptional start site, no typical TATA or CCAAT box was found, but binding sites for several known transcription factors including Sp1 and Krox-20 were identified. Transient transfection of luciferase reporter constructs demonstrated that a 207 bp fragment of the 5'-upstream region acts as a strong promoter in PC-12 cells, which express the HNK-1 epitope, but not in COS-1 cells. Thus, this minimal promoter region of GlcAT-P is suggested to be associated with the regulation of HNK-1 expression.
5' Flanking Region↗
Role of mannan-binding protein, MBP, in innate immunity.
Mannan-binding protein (MBP) is a C-type lectin, which binds to carbohydrates on the surface of some microorganisms and kills them through the activation of complement. This complement activation pathway is called the lectin pathway. MBP also kills mammalian cells that express MBP ligands on their surfaces via the lectin pathway. Recently, we found anti-tumor activity of MBP in vivo using tumor cells transplanted into nude mice. We propose to call this anti-tumor effect mannan-binding protein-dependent cell-mediated cytotoxicity (MDCC), because it does not require complement activation, and the involvement of some immune cells was assumed. Very recently, MBP was demonstrated to be selectively expressed in epithelial cells of the small intestine. This finding may suggest that MBP plays an important role in the small intestine as a host defense factor.
Animals↗