Asialoglycoprotein Receptor Deficiency in Mice Lacking the Major
Receptor Subunit
ITS OBLIGATE REQUIREMENT FOR THE STABLE EXPRESSION OF OLIGOMERIC
RECEPTOR*
Ryu-ichi
Tozawa
,
Shun
Ishibashi
§,
Jun-ichi
Osuga
,
Kazuo
Yamamoto¶,
Hiroaki
Yagyu
,
Ken
Ohashi
,
Yoshiaki
Tamura
,
Naoya
Yahagi
,
Yoko
Iizuka
,
Hiroaki
Okazaki
,
Kenji
Harada
,
Takanari
Gotoda
,
Hitoshi
Shimano
,
Satoshi
Kimura**,
Ryozo
Nagai
, and
Nobuhiro
Yamada
From the Departments of
Metabolic Diseases,

Cardiovascular Medicine, and ** Infectious
Diseases, Faculty of Medicine and ¶ Department of Integrated
Biosciences, Graduate School of Frontier Sciences, University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655 and
Metabolism,
Endocrinology, and Atherosclerosis, Institute of Clinical Medicine,
University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan
Received for publication, December 8, 2000, and in revised form, January 11, 2001
 |
ABSTRACT |
The asialoglycoprotein receptor is an
abundant hetero-oligomeric endocytic receptor that is predominantly
expressed on the sinusoidal surface of the hepatocytes. A number of
physiological and pathophysiological functions have been ascribed to
this hepatic lectin (HL), the removal of desialylated serum
glycoproteins and apoptotic cells, clearance of lipoproteins, and the
sites of entry for hepatotropic viruses. The assembly of two homologous
subunits, HL-1 and HL-2, is required to form functional, high affinity
receptors on the cell surface. However, the importance of the
individual subunits for receptor transport to the cell surface is
controversial. We have previously generated HL-2-deficient mice and
showed that the expression of HL-1 was significantly reduced, and the
functional activity as the asialoglycoprotein receptor was virtually
eliminated. However, we failed to detect phenotypic abnormalities. To
explore the significance of the major HL-1 subunit for receptor
expression and function in vivo, we have disrupted the
HL-1 gene in mice. Homozygous HL-1-deficient animals
are superficially normal. HL-2 expression in the liver is virtually
abrogated, indicating that HL-1 is strictly required for the stable
expression of HL-2. Although these mice are almost unable to clear
asialo-orosomucoid, a high affinity ligand for asialoglycoprotein
receptor, they do not accumulate desialylated glycoproteins or
lipoproteins in the plasma.
 |
INTRODUCTION |
The asialoglycoprotein receptor
(ASGPR)1 was originally
identified by Ashwell and Morell as a hepatic receptor that
mediates the rapid clearance of serum glycoproteins containing terminal galactose residues from the circulation (see Refs. 1-3 for review). ASGPR is abundantly expressed on the sinusoidal surface of the parenchymal cells of the liver. Its primary physiological function has
been considered to be the removal and degradation of desialylated circulating proteins.
Nonreducing terminal of oligosaccharide moieties of
glycoproteins are usually capped by sialic acid residues. When the
terminal sialic acid residues are removed by neuraminidases,
penultimate galactose residues are exposed and recognized by ASGPR.
High affinity binding requires the receptor to be assembled as a
hetero-oligomer consisting of two highly homologous subunits termed
hepatic lectin (HL) 1 and 2 (4). Both subunits contain an N-terminal
cytoplasmic domain, a single transmembrane segment, a stalk domain, and
a C-terminal carbohydrate recognition domain (5). ASGPR belongs to C-type animal lectins because of the requirement of Ca2+
for ligand binding and disulfide bonds in carbohydrate recognition domains (6).
A number of diverse physiological roles have been proposed for ASGPR
over the years. Among them, hepatic clearance of the desialylated and
senascent serum proteins was most originally proposed (1). ASGPR was
also postulated to account for the low density lipoprotein (LDL)
receptor-independent clearance of lipoproteins including chylomicron
remnants (7, 8). Recently, immunoglobulin A (9) and fibronectin (10)
have emerged as likely candidates of natural ligands for ASGPR. The
clearance of apoptotic cells or a subpopulation of lymphocytes in the
liver has also attributed to ASGPR (See Ref. 3 for review). It is particularly noteworthy that ASGPR has also been proposed to be utilized as entry sites into hepatocytes by several hepatotropic viruses including hepatitis B virus (11), Marburg virus (12), and
hepatitis A virus (13).
As an attempt to elucidate the bona fide functions of ASGPR,
we have previously generated mice lacking a minor subunit of mouse
ASGPR (MHL-2) (14). As a result of disruption of MHL-2, the expression
of MHL-1 was severely reduced, and the plasma clearance of
asialo-orosomucoid was almost completely abrogated in the
MHL-2
/
mice. However, the MHL-2
/
mice
were apparently normal and showed no detectable abnormalities even in
the metabolism of remnant lipoproteins. Because MHL-2
/
liver expresses small but significant amounts of MHL-1 (14, 15), it is
still possible that the residual MHL-1 is sufficient to execute the
primary task of ASGPR as suggested by in vitro transfection
experiments (16, 17). In the current study we have generated
mice lacking the major subunit (MHL-1) of ASGPR in mice and analyzed
the resulting phenotypes.
 |
EXPERIMENTAL PROCEDURES |
Generation of MHL-1 Knockout Mice--
The MHL-1 gene
was cloned from the 129/Sv mouse genomic library. The genomic
organization of the MHL-1 gene was essentially the same as
recently reported by Soukharev et al. (18). A
replacement-type targeting vector was constructed so that the genomic
fragment containing exons 2-3, which encoded the ATG initiation codon
and transmembrane domain, was replaced by the pol2neo cassette (19). The short arm containing a 0.8-kb StuI/BamHI
fragment containing exon 2 and the long arm containing a 9-kb
XhoI/SalI fragment spanning exons 3-9 were
inserted into the XhoI and NotI sites,
respectively, of the vector pPol2short-neobpA-HSVTK as described
previously (14, 20).
After linearization by digestion with SalI, the vector was
electroporated into JH-1 embryonic stem (ES) cells (a gift from Dr. Herz at the University of Texas Southwestern Medical Center). Targeted clones, which had been selected in the presence of G418 and
1-(2-deoxy,2-fluoro-
-D-arabinofuranosyl)-5 iodouracil,
were identified by polymerase chain reaction using the following
primers: 5'-CTGGTCAGGGATATTTGGAGATACGG-3' and
5'-GATTGGGAAGACAATAGCAGGCATGC-3' (see Fig. 1). Homologous
recombination was verified by Southern blot analysis after digesting
the genomic DNA with EcoRI using a 0.7-kbp StuI
fragment as a probe (see Fig. 1). Targeted ES clones were injected into
the C57BL/6 blastocysts, yielding 14 lines of chimeric mice that
transmitted the disrupted allele through the germline from four
independent ES cell clones. All experiments reported here were
performed with 129/Sv-C57BL6 hybrid descendants (F1 and subsequent
generations) of these animals.
Northern Blot Analysis--
Total RNA was isolated from the
liver by TRIZOLTM reagent (Life Technologies,
Inc.). 20 µg of total RNA was subjected to electrophoresis in an
agarose gel and transferred to a nylon membrane (Hybond-N; Amersham Pharmacia Biotech). MHL-1 and MHL-2
cDNA fragments were labeled with [
-32P]dCTP
using a kit (Megaprime labeling kit; Amersham Pharmacia Biotech) and
were used as probes for hybridization (14). Image capture and analysis
were performed with BAS 2000 (Fuji Film).
Immunoblot Analysis--
Liver membrane proteins were prepared
as described (14). 50 µg of the proteins was separated by 5-20% SDS
polyacrylamide gel electrophoresis under a nonreducing condition.
Proteins were transferred to nitrocellulose membrane, and immunoblot
analyses were performed using specific rabbit polyclonal anti-peptide
antibodies for MHL-1 and MHL-2 (14). The antibodies were visualized by peroxidase-conjugated anti-rabbit IgG and with an ECL chemiluminescence detection kit (Amersham Pharmacia Biotech).
Plasma Turnover Experiments--
Asialo-orosomucoid (ASOR) was
prepared by incubating 100 mg of orosomucoid (Sigma) at 37 °C in 10 ml of sodium acetate buffer containing 2 mM
CaCl2, pH 5, together with 1 unit of
neuraminidase-type XA (Clostridium perfringens) attached to
agarose beads (Sigma). After 4 h another unit of enzyme was added,
and the incubation was continued overnight. Asialofetuin (Sigma) and
ASOR were labeled with 125I using the IODO-GEN procedure
(Pierce). Specific activities of 125I-asialofetuin and
125I-ASOR were 257 and 502 cpm/ng, respectively. 10 µg of
iodinated protein in 200 µl of saline containing 2 mg/ml bovine serum
albumin were injected intravenously into the jugular vein of
anesthetized male mice (n = 3) that were wild-type and
homozygous for MHL-1 gene disruption. Blood was collected at
the indicated intervals from the retroorbital venous plexus. After the
labeled proteins in 20 µl of plasma were precipitated with
trichloroacetic acid, their radioactivities were determined.
Analyses of Mouse Plasma Lipoprotein Profile--
Plasma
lipoprotein analyses were performed as previously described (21).
Briefly, after mice were bled from the retroorbital venous plexus, the
blood was collected into tubes containing EDTA. Total cholesterol and
triglyceride levels in the plasma were determined enzymatically using
kits (Determiner TC555 and Determiner TG555; Kyowa Medex). 5 µl of
plasma was diluted to 100 µl with saline and subjected to high
performance liquid chromatography (HPLC) analyses using four columns of
TSK gel Lipopropak XL (TOSOH, Tokyo, Japan) connected in tandem.
Lectin Blot Analyses of Plasma Protein--
1 µl of plasma was
separated by 3-15% SDS polyacrylamide gel electrophoresis under a
reducing condition and transferred to polyvinylidene difluoride
membranes. Lectin blotting was done using Maackia amurensis
agglutinin (MAA; Roche Molecular Biochemicals) and Sambucus
nigra agglutinin (SNA; Roche Molecular Biochemicals), which were
conjugated with digoxigenin, and Ricinus communis agglutinin (RCA120; Sigma), which was conjugated with biotin. Digoxigenin and
biotin were detected by alkaline phosphatase-labeled anti-digoxigenin antibody (Digoxigenin detection kit; Roche Molecular Biochemicals) and alkaline phosphatase-labeled anti-biotin antibody (Roche
Molecular Biochemicals), respectively.
 |
RESULTS |
The MHL-1 gene was cloned by hybridization screening of
a mouse genomic library using a mouse cDNA probe. A gene
replacement vector was constructed so that the initiation codon and
transmembrane domain were interrupted by the pol2neo cassette (Fig.
1A). Following electroporation
of the linearized targeting vector into JH-1 ES cells, targeted clones
were obtained. Chimeric mice were generated from six independently
targeted clones using a standard procedure. Four independent ES cell
cloned yielded total of 14 germ line chimeric males. They were bred to
wild-type female C57BL/6 mice. Heterozygous offspring (F1 generation)
were crossed with each other and gave rise to mice wild-type (+/+),
heterozygous (±), or homozygous (
/
) for the disrupted
MHL-1 allele in accordance with Mendelian law (+/+:±:
/
= 29:65:43;
2 = 1.51; p = 0.47) (Fig.
1B). Homozygous MHL-1-deficient mice were viable
and displayed no obvious phenotype under laboratory housing conditions.
The animals appeared to have a normal life span.

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Fig. 1.
Targeted disruption of the MHL-1 gene.
A, a targeting vector of the replacement type was
constructed by replacing the exons encoding the ATG initiation codon
and transmembrane domain by the pol2neo cassette
(Neor). Two copies of herpes simplex virus
thymidine kinase (HSV-TK) were attached to the 5' side of
the vector. E, EcoRI; B,
BamHI. The probe for Southern blot analysis is indicated by
the shaded box. B, genotypes of offspring from
matings of MHL-1+/ mice. Tail DNA was digested with EcoRI.
After the transfer, the membranes were hybridized with
32P-labeled probe (a 0.7-kbp StuI fragment). The
positions of migration of disrupted (5.4 kb) and of wild-type alleles
(16 kb) are indicated.
|
|
Northern blot analysis showed that MHL-1
/
mice lacked
1.3-kb wild-type MHL-1 transcript completely (Fig.
2A). MHL-1+/
mice expressed an intermediate amount of the MHL-1 transcript. A
reduced amount of truncated MHL-1 transcript was expressed
in mice having the disrupted MHL-1 allele
(MHL-1+/
or MHL-1
/
). On the other hand,
there were no differences in the size and amounts of MHL-2 mRNA. The disruption of the MHL-1 gene resulted in
complete absence of the 40-kDa-encoded protein in MHL-1
/
animals (Fig. 2B). MHL-1+/
mice showed reduced
expression of MHL-1 protein as compared with the wild-type mice,
indicating the gene dosage effect on the expressed protein levels of
MHL-1. In wild-type and MHL-1+/
mice, four distinct bands
that were immunoreactive with the anti-MHL-2 antibody were observed
(36, 47, 80, and 192 kDa). Because the bands with higher molecular
mass were not observed under a reducing condition (data not
shown), three of these multiple bands may represent oligomers of MHL-2
protein in different degrees (monomer for 36 kDa, dimer for 80 kDa, and
tetramer for 192 kDa). No bands immunoreactive with the anti-MHL-2
antibody were visible in MHL-1
/
mice.

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Fig. 2.
Northern and Western blot analysis of ASGPR
subunits in mouse liver. A, Northern blot analysis of
MHL-1 (lanes 1-6) and MHL-2 (lanes 7-12) in the
liver of 6-week-old mice wild-type (+/+; lanes 1,
2, 7, and 8), heterozygous (+/ ;
lanes 3, 4, 9, and 10), and
homozygous ( / ; lanes 5, 6, 11, and
12) for MHL-1 gene disruption. 15 µg of total
RNA was used for Northern blot analysis. 1.3-kb MHL-1 and
1.4-kb MHL-2 wild-type transcripts are indicated.
B, Western blot analysis of MHL-1 (lanes 1-6)
and MHL-2 (lanes 7-12) in the liver of 6-week-old mice
wild-type (+/+; lanes 1, 2, 7, and
8), heterozygous (+/ ; lanes 3, 4,
9, and 10), and homozygous ( / ; lanes
5, 6, 11, and 12) for the
MHL-1 gene disruption. The size of the molecular mass
markers are indicated.
|
|
To examine whether the disruption of the MHL-1 gene resulted
in the impairment of the hepatic clearance of asialoglycoproteins, we
injected the iodinated asialofetuin or ASOR into +/+, +/
, and
/
mice and compared the radioactivities remaining in the plasma (Fig.
3). The plasma clearance of
125I-asialofetuin was severely, albeit not completely,
impaired in MHL-1
/
mice (Fig. 3A). At 30 min
after the injection, plasma 125I-asialofetuin was decreased
to 4, 8, and 40% of the initial dose in +/+, +/
, and
/
mice,
respectively. Heterozygous mice cleared 125I-asialofertuin
with only partially reduced efficiency. The plasma clearance of
125I-ASOR was more severely impaired in
MHL-1
/
mice (Fig. 3B). At 30 min after the
injection, plasma 125I-ASOR was decreased to 3, 24, and
65% of the initial dose in +/+, +/
, and
/
mice, respectively.
Heterozygous mice cleared 125I-ASOR with intermediate
efficiency.

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Fig. 3.
Disappearance of 125I-labeled
glycoproteins from the plasma. 125I-labeled
asialofetuin (Panel A) or asialo-orosomucoid (Panel
B) was injected into 12-week-old female mice wild-type ( ),
heterozygous ( ), and homozygous (X) for the
MHL-1 gene disruption. Values shown are means of triplicates
of trichloroacetic acid-insoluble radioactivity remaining in plasma at
the indicated time points and are calculated as a percentage of
radioactivity present 1 min after injection of the label.
|
|
To examine the expression of the sialic acid- and galactose-terminated
serum glycoproteins, plasma from the wild-type and MHL-1
/
mice were subjected to lectin blot analysis (Fig.
4). The following lectins were used to
detect terminal sugars: MAA, a lectin specific for NeuNAc(
2-3)Gal
on N-linked carbohydrate; SNA, a lectin specific for
NeuNAc(
2-6)Gal on N-linked carbohydrate; and RCA120, a
lectin specific for
-galactose. There were no consistent differences
either in the pattern of the bands or in their intensities between
MHL-1+/+ and MHL-1
/
mice.

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Fig. 4.
Lectin blot of plasma proteins. Blood
was collected from 32-week-old male mice wild-type (lanes
1-5) or homozygous (lanes 6-10) for the
MHL-1 disruption. Lectin blotting was done using MAA,
SNA that were conjugated with digoxygenin, and RCA120 that was
conjugated with biotin. Digoxigenin and biotin were detected by
alkaline phosphatase-labeled anti-digoxigenin antibody and alkaline
phosphatase-labeled anti-biotin antibody, respectively.
|
|
To test whether ASGPR is involved in chylomicron remnant clearance by
the liver, we analyzed the plasma lipid levels of MHL-1
/
mice and MHL-1
/
mice that also lacked the LDL
receptor (Table I). The plasma lipid
levels of the MHL-1
/
mice were indistinguishable from
those of control animals expressing wild-type MHL-1, in the absence or
presence of functional LDL receptors. The lipoprotein profiles
evaluated by HPLC analyses failed to reveal any differences in
lipoprotein fractions between wild-type and MHL-1
/
mice (Table II).
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Table I
Plasma lipid levels in mice deficient in MHL-1
Blood was collected from mice aged 8-12 weeks after an overnight fast.
Total cholesterol (TC) and triglyceride (TC) concentrations in the
plasma were determined and expressed as means ± S.D. Analysis of
variance was employed to compare the means between the genotypes.
LDLR and MHL-1 denote low density lipoprotein
receptor and mouse hepatic lectin-1, respectively.
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Table II
Plasma lipoproteins in mice deficient in MHL-1
Blood was collected from 4-5 mice aged 12 weeks after an overnight
fast. Plasma lipoproteins were analyzed by high performance liquid
chromatography. The results were expressed as means ± S.D.
Analysis of variance was employed to compare the means between the
genotypes. CM, VLDL, LDL, and HDL denote chylomicron; very low density
lipoproteins, low density lipoproteins, and high density lipoproteins,
respectively.
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|
 |
DISCUSSION |
We have generated mice lacking functional asialoglycoprotein
receptors by disrupting the gene for the major MHL-1 receptor subunit
by homologous recombination in embryonic stem cells. Homozygous MHL-1-deficient mice displayed no obvious phenotype as long
as they were maintained under the standard laboratory housing condition.
Although MHL-1
/
liver expressed a reduced amount of a
truncated transcript, no band immunoreactive with the anti-MHL-1
antibody was detected, indicating that MHL-1
/
mice were
virtually null for the MHL-1 gene. In MHL-1+/
mice, the amounts of both mRNA and protein of MHL-1 were reduced
2-fold, indicating the gene-dosage effects of the inactivation. This
reduction was accompanied by the reduction in the amounts of MHL-2
protein, even if the mRNA levels were not affected. In
MHL-1
/
mice, MHL-2 protein was undetectable. These
results strongly indicate that MHL-1 is obligatorily required for the
stable expression of MHL-2. This is consistent with the in
vitro results in transfected cells that the minor subunit is
unstable in the absence of coexpression of the major subunit (22-24).
Without HL-1, HL-2 may succumb to degradation within endoplasmic
reticulum. It is interesting to compare this to MHL-2
/
mice in which substantially reduced but still significant amounts of
MHL-1 were expressed. Together these results indicate that both
subunits are required for the stable expression of oligomeric receptor
and that HL-1 is more strictly required than HL-2.
As was observed in MHL-2
/
mice, the plasma clearance of
asialoglycoproteins was severely impaired in MHL-1
/
mice
(Fig. 3). It is interesting to note that the impairment of the
clearance of ASOR appeared milder than that of asialofetuin in the
heterozygotes. This is probably because some other pathway also
contributes to the plasma clearance of asialofetuin but not to that of
ASOR. For example, a macrophage lectin that is conceivably expressed in
hepatic Kupffer cells may mediate this uptake, because it recognizes both galactose and N-acetylgalactosamine (25, 26). The
plasma clearance curve of ASOR was indistinguishable from that of
orosomucoid (data not shown), suggesting that MHL-1
/
mice clear ASOR via a pathway(s) that is irrelevant to the
galactose-recognition system. Although ASGPR function was severely
impaired in MHL-1
/
mice, the plasma glycoproteins levels
were not significantly increased (Fig. 4). Together with our previous
observations in MHL-2 knockout mice, ASGPR is unlikely to be
essential for the homeostasis of the major plasma glycoproteins as has
been frequently discussed. In support of this, Kido et al.
(27) have recently reported that serum glycoprotein levels were
maintained in mice lacking
-1,4-galactosyltransferase I. Although
nearly 90% of the serum glycoproteins lacked
-1,4-galactose in the
knockout mice, their serum protein concentrations were similar to those
in wild-type mice. This does not necessarily rule out the possible role
of ASGPR in the regulation of minor serum glycoproteins (28). In this
context, Rotundo et al. (10) have proposed that ASGPR is responsible for the disposal of cellular fibronectin from the plasma
and/or in the liver. Cellular fibronectin contains large amounts of
terminal galactose residues, and intravenous infusion of excess
asialofetuin caused retention of labeled cellular fibronectin in the
liver (29). However, in multiple experiments not shown here, by Western
blot analyses in the liver membrane we failed to find the abnormal
accumulation of fibronectin in the liver of MHL-1
/
mice.
Furthermore, we failed to find significant morphological changes in the
liver of MHL-1
/
mice. With regard to IgA metabolism, Rifai et al. (9) have recently reported the impaired
clearance of the IgA2 isoform in MHL-2
/
mice. However,
its physiological relevance is currently unknown.
Windler et al. (7) proposed a possible function of ASGPR in
the hepatic lipoproteins metabolism. ApoB-100 and apo(a) are heavily
glycosylated giant proteins. Therefore it is reasonable to consider
that the lipoproteins containing these apolipoproteins is cleared by
ASGPR when the LDL receptor system is dysfunctional. To test this
hypothesis, we crossed MHL-1
/
mice to the LDL
receptor-deficient mice to generate mice lacking both ASGPR and the LDL
receptor. As was the case in the mice lacking both MHL-2 and the LDL
receptor, we failed to detect the elevation of plasma lipoproteins as
compared with the LDL receptor knockout mice (Tables I and II).
Accumulating evidence indicates that LDL receptor-related protein is
involved in the plasma clearance of apoE-rich remnant lipoproteins
(30). Therefore, the role of ASGPR in the plasma clearance of
lipoproteins is minimal if present.
ASGPR is a member of animal C-type lectins (6). Because most of C-type
lectins appear to be involved in host defense, ASGPR may have been
evolved as a molecule to protect mammals from viral or bacterial
insults (31), probably because exposed galactose residues may be
harmful to the vascular system (32). Avian and reptiles have a similar
hepatic lectin that binds to N-acetylglucosamine. The ASGPR
system may protect vertebrates from pathogenic organisms that take
advantage of neuraminidase to invade the hosts. A significant decrease
in the expression of ASGPR accompanied by accumulation of serum
asialoglycoproteins is observed in the patients with advanced liver
diseases such as liver cirrhosis (33, 34). They frequently develop
serious infectious diseases such as spontaneous bacterial peritonitis
and sepsis. It is tempting to speculate that ASGPR is relevant to these
complications associated with liver diseases. Besides hepatocytes,
macrophages express a lectin specific for both galactose and
N-acetylgalactosamine as mentioned above (25, 26). Its
presence may have masked the phenotype in ASGPR-deficient animals.
Further studies are absolutely needed to prove these possibilities. In
this context, it is intriguing that some hepatotropic virus infects the
hepatocytes through ASGPR (11-13).
In summary, ASGPR functions were more completely abrogated in
MHL-1-deficient mice as compared with in
MHL-2-deficient mice. Probably, requirement of HL-1 for
stable expression of functional ASGPR is stricter than that of HL-2.
Despite such absolute deficiency of ASGPR function, we failed to detect
physiological evidence for several postulated functions that have been
ascribed to ASGPR. These MHL-1-deficient mice should provide
the basis for understanding the physiology of this receptor.
 |
FOOTNOTES |
*
This work was supported by a grant-in-aid for Scientific
Research from the Ministry of Education, Science and Culture, by the
Promotion of Fundamental Studies in Health Science of The Organization
for Pharmaceutical Safety and Research, by Health Sciences Research
grants from the Ministry of Health and Welfare, and by Takeda Medical
Research Foundation, Ymanouchi Foundation for Research on Metabolic
Disorders, and Asahi Life Foundation.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
§
To whom correspondence should be addressed. Tel.: 81-3-3815-5411 (ext. 33113); Fax: 81-3-5802-2955; E-mail:
ishibash-tky@umin.ac.jp.
Published, JBC Papers in Press, January 16, 2001, DOI 10.1074/jbc.M011063200
 |
ABBREVIATIONS |
The abbreviations used are:
ASGPR, asialoglycoprotein receptor;
HL, hepatic lectin;
MHL, mouse hepatic
lectin;
ES, embryonic stem;
ASOR, asialo-orosomucoid;
HPLC, high
performance liquid chromatography;
LDL, low density lipoprotein;
HDL, high density lipoprotein;
apo, apolipoprotein;
MAA, Maackia
amurensis agglutinin;
SNA, Sambucus nigra agglutinin;
RCA, Ricinus communis agglutinin;
kb, kilobase;
kbp, kilobase pair.
 |
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