Undetectable apolipoprotein A-I gene expression suggests an unusual mechanism of dietary lipid mobilisation in the intestine of Cyprinus carpio
Instituto de Bioquímica, Facultad de Ciencias, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile
* Author for correspondence (e-mail: ramthaue{at}uach.cl)
Accepted 26 January 2005
![]() |
Summary |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: apoA-I, internalisation, lipid absorption, carp, Cyprinus carpio
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In mammals and birds both the liver and the intestine constitute the major
sites for apoA-I gene expression
(Lamon-Fava et al., 1992;
Oku et al., 1997
). In
contrast, the liver has always been identified as the main tissue involved in
apoA-I synthesis in teleosts, with a more variable expression in the intestine
(Kondo et al., 2001
; Llewellyn
et al., 1998; Powell et al.,
1991
). In a previous study we showed the presence of apoA-I in the
lumen and inside the epithelial cells of the proximal intestine, however, we
were unable to detect apoA-I synthesis using tissue slices from the same
intestinal region (Vera et al.,
1992
). In the same study, we demonstrated that after oral
administration of biotinylated-HDL, labelled apoA-I was found in an intact
form associated with plasma HDL, indicating the transfer of intact apoA-I from
the intestinal lumen to the blood. The luminal apoA-I detected in the carp
intestine could be of biliary and/or hepatic origin
(Vera et al., 1992
). This
apparent contradiction led us to study the localisation of apoA-I protein and
its gene expression along the entire intestine of the carp.
It remains to be established if luminal apoA-I detected in the carp intestine is of biliary or hepatic origin. The present study aims to characterise apoA-I gene expression in the intestine of carp. The localisation and potential source of apoA-I protein present in carp enterocytes is also studied.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Fish
Common carp Cyprinus carpio L. were caught in the Cayumapu River
and maintained in an outdoor tank with running river water. Fish weighing
8001200 g were acclimatised for at least 3 weeks at 20±2°C
(average summer temperature) with a photoperiod of 14 h:10 h light:dark, and
fed to satiation twice every day. Fish were anaesthetised in a bath containing
50 mg l1 of benzocaine and then sacrificed by decapitation.
The entire intestine was removed and dissected into seven segments according
to the method of Villanueva et al.
(1997), and differentially
processed for immunohistochemistry, RNA isolation or brush border membrane
(BBM) preparation.
Immunohistochemistry
Fresh slices of carp intestine were immediately fixed in Bouin's fixative
for 4 h, dehydrated and embedded in paraffin. Serial cross sections (5 µm)
were deparaffinised in xylene and rehydrated. Briefly, slides were blocked for
30 min with 1% (w/v) BSA in phosphate-buffered saline (PBS) and incubated for
1 h in a wet chamber with preimmune serum or a specific rabbit polyclonal
antiserum against carp apoA-I (dilution 1:5000). After several washings with
PBS, slides were incubated with a 1:1000 dilution of alkaline phosphatase
conjugated with goat anti-rabbit IgG antibody. Enzyme activity was detected
with Nitro Blue Tetrazolium/4-bromo-5-chloro-3-indolylphosphate solution as
dye substrates for alkaline phosphatase. The desired signal level was achieved
after 1520 min of incubation. Serial slides of intestine treated
exactly the same way but missing the primary antiserum were used as negative
controls of the reaction. Liver sections were used as positive controls.
RNA isolation, northern blot and RTPCR analyses
Slices (1 cm long) were removed from each intestinal segment, opened
longitudinally and washed in sterile saline. Epithelial cells were collected
by scraping the mucosa with a sterile glass microscope slide. Total RNA was
extracted using the Trizol Reagent (Gibco-BRL) according to the manufacturer's
instructions. RNA was quantified by absorbance at 260 nm and used immediately
or stored precipitated in ethanol at 70°C until use. Total RNA (30
µg per sample) was incubated in 1x Mops buffer, 2.2 mol
l1 formaldehyde and 50% deionised formamide for 10 min at
65°C, mixed with formaldehyde loading buffer [50% (v/v) glycerol, 1 mmol
l1 EDTA pH 8.0, 0.25% (w/v) Bromophenol Blue and 0.25% (w/v)
Xylene Cyanol] and separated by electrophoresis in 1% (w/v) agarose gel
containing 6% (v/v) formaldehyde. Samples were run in duplicate; one for
ethidium bromide staining and confirmation of the integrity of the RNA; the
other for transfer to nylon membranes (ICN Biomedicals, Inc. Costa Mesa, CA,
USA). Transfer was performed according to the manufacturer's instructions and
prehybridised for 3 h at 42°C in a solution containing 50% deionised
formamide, 6x SSC (900 mmol l1 NaCl, 90 mmol
l1 sodium citrate), 5x Denhardt's, 0.5% SDS and 100
µg ml1 of yeast tRNA. Hybridisation was carried out in
the same solution containing the 32P-labelled carp apoA-I DNA
insert (2x108 c.p.m. µg1) corresponding
to a partial cDNA clone (GenBank accession number AJ308993), for 15 h at
42°C. After hybridisation, the membranes were washed twice in 2x SSC
containing 0.1% SDS (65°C, 10 min) and then twice in 0.2x SSC/0.1%
SDS (65°C, 20 min). Total liver RNA was used as a positive control to
evaluate apoA-I expression by northern blot and RTPCR.
The RTPCR analyses were performed essentially as described by Concha
et al. (2003). Briefly, liver
and intestine total RNA (5 µg each), treated with amplification grade
deoxyribonuclease I, were incubated with antisense primer
(5'-cccttctccatctgctccctataa-3'), RNasin® (Promega), dNTP
mixture (2.5 mmol l1 of each nucleotide), enzyme buffer and
200 U of Superscript II reverse transcriptase (Gibco-BRL) at 42°C for 1 h.
Reverse transcriptase was omitted in the negative control. After enzyme
inactivation, the antisense primer and the following sense primer
(5'-ctccacggctactttcagaacg-3') were used to amplify a 428 bp
target of the carp apolipoprotein A-I gene. The reaction mixture (50
µl) contained 1 µl of the reverse transcription reaction, 0.2 µmol
l1 of each primer, 200 µmol l1 of each
dNTP, 2.5 mmol l1 MgCl2 and 2 U of Taq DNA
polymerase in a standard PCR buffer (10 mmol l1 Tris-HCl, pH
9.0, 50 mmol l1 KCl and 0.1% Triton X-100). The thermocycler
(MJ Research, Hercules, CA, USA) was programmed as follows: initial
denaturation (94°C, 3 min),followed by 30 cycles (94°C, 55°C and
72°C, for 1 min each) and a final extension step at 72°C for 5 min.
The amplification product was then separated on 1.5% (w/v) agarose gel. As no
amplification product was obtained in any of the intestinal segments, the
amplification of the ß-actin gene was used as an additional
internal control to ensure the integrity of the intestinal RNA preparations.
The primers, 5'-ggacctgtatgccaacactg-3' (sense) and
5'-gtcggcgtgaagtggtaaca-3' (antisense) that allow discrimination
of amplification product derived from cDNA and gDNA were used according to the
method of Sarmiento et al.
(2000
), essentially using the
same conditions described above expect for the annealing temperature
(50°C).
ApoA-I isolation and radiolabelling
Carp plasma HDL was isolated by affinity chromatography as described by
Amthauer et al. (1989). After
HDL delipidation with ethanolether (3:2 v/v) mixture at
10°C, the apolipoproteins were purified by filtration
chromatography on a Sephacryl S-200 column (1.5x90 cm) pre-equilibrated
with buffer 10 mmol l1 TrisHCl, pH 8.6, 1 mmol
l1 EDTA, 8 mol l1 urea
(Amthauer et al., 1989
).
ApoA-I was radiolabelled with 125I using the IODO-GEN iodination reagent (Pierce, Rockford, IL, USA) according to the manufacturer's recommendations. Briefly, 50 µg of apoA-I were incubated for 15 min at 4°C in a IODO-GEN pre-coated polypropylene tube containing 0.5 mCi of Na125I in 100 µl of 100 mmol l1 sodium phosphate buffer (pH 7.0). The reaction was stopped by addition of 200 µl of 100 mmol l1 sodium phosphate buffer (pH 7.0) and the radioactive protein was separated from free iodine on Sephadex G-50, pre-equilibrated with sodium phosphate buffer containing 0.1 mg ml1 BSA.
ApoA-I binding assays
Brush border membrane vesicles (BBMV) were isolated from carp intestinal
mucosa and characterised before their use in the binding assays as described
by Amthauer et al. (2000).
Prior to the binding assays the test tubes were blocked by incubation with 1
mg ml1 BSA for 1 h at 0°C to avoid unspecific binding of
125I-apoA-I to the test tube wall. Binding assays were carried out
at 25°C for 30 min in a final volume of 25 µl, containing 25 mmol
l1 Tris-HCl, pH 7.5, 125I-apoA-I and 0.6 mg
ml1 of membrane protein. After incubation, the reaction
mixture was cooled on ice and layered onto 400 µl of a sucrose cushion
containing 25 mmol l1 Tris-HCl, pH 7.5, and 250 mmol
l1 sucrose. Bound and unbound 125I-apoA-I were
separated by centrifugation at 14 000 g for 30 min at 4°C.
The supernatant was discarded and the pellet containing 125I-apoA-I
bound to BBMV was quantified with a gamma counter.
Peripheral and integral membrane isolation
To obtain the peripheral membrane and integral membrane protein fractions,
fresh BBMV or the pellet obtained after the binding assay were suspended in 50
µl of 50 mmol l1 Na2CO3, pH 11.5,
10 mmol l1 EDTA and incubated for 15 min on ice
(Hu et al., 1997). The
integral membrane protein fraction was recovered by centrifugation for 30 min
at 14 000 g, where the supernatant corresponds to the
peripheral membrane fraction. Aliquot portions of both fractions were diluted
in Laemmli's sample buffer and fractionated by 12% SDS-polyacrylamide gel
electrophoresis (SDS-PAGE). Radiolabelled proteins were detected by
autoradiography. For western blot analysis the proteins separated by SDS-PAGE
were transferred to Immobilon-P membranes (Millipore, Bedford, MA, USA) using
a semi-dry blotter unit (Amthauer et al.,
2000
). Membranes were blocked with 5% (w/v) non-fat dry milk in
PBS/Tween-20 (0.1% v/v). ApoA-I was detected by incubation with a rabbit
polyclonal antiserum against carp apoA-I
(Amthauer et al., 1989
) diluted
1:25 000, followed by incubation with alkaline phosphatase-conjugated antibody
(Gibco-BRL) diluted 1:3000. Finally, alkaline phosphatase activity was
developed by incubating the membrane at room temperature for 20 min in 0.1 mol
l1 Tris-HCl, pH 9.5, containing 0.1 mol l1
NaCl, 5 mmol l1 MgCl2, 0.16 mg
ml1 5-bromo-4-chloro-3-indolyl phosphate and 0.33 mg
ml1 Nitro Blue Tetrazolium.
Dimyristoylphosphatidylcholine multilamellar vesicles solubilisation assay
The solubilisation of dimyristoylphosphatidylcholine (DMPC) multilamellar
vesicles (mLV) by apoA-I was assayed according to the technique of Pownall et
al. (1978). Essentially, 0.1
mg apoA-I was added to 1 ml of the reaction mixture containing 0.01 mol
l1 Tris-HCl, pH 7.4, 8.5% KBr, 0.01% sodium azide, 0.01%
EDTA and DMPC mLV 0.5 mg ml1, preincubated at 24°C for
10 min. The cuvette content was mixed within 10 s by repeated aspiration and
release, and vesicle solubilisation (clearance) was monitored as a decrease in
absorbance at 325 nm using a Hewlett Packard Model 8453 Diode Array
Spectrophotometer. Slight differences in initial absorbance for each time
course were corrected by expressing all the values as a percentage of the
initial absorbance at 325 nm.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
ApoA-I gene expression in carp intestine
No apoA-I transcript was detected by northern blot analysis in the
intestinal segments, in clear contrast with the intense hybridisation signal
observed with total liver RNA (Fig.
3A). As shown in Fig.
3B, the integrity and the amount of RNA loaded were similar in all
cases. More sensitive RTPCR analyses confirmed that apoA-I is
not expressed in carp enterocytes (Fig.
3C). Total RNA from carp liver was used as positive control for
the RTPCR reaction as it has been demonstrated previously that
apoA-I gene is expressed in this tissue
(Concha et al., 2003). As shown
in Fig. 3C, the expected 428 bp
amplification product was found in the positive control, but no amplification
was obtained in any of the intestine RNA preparations. However, a 282 bp
product corresponding to the specific carp ß-actin cDNA was
obtained from the same intestinal RNA preparations
(Fig. 3C). These findings are
in agreement with our previous results showing no apoA-I synthesis in the carp
intestine (Vera et al., 1992
)
and suggest that apoA-I detected in the intestinal mucosa could be of biliary
and/or hepatic origin.
|
ApoA-I interaction with brush border membrane
The first step for the putative transepithelial transport of apoA-I should
be the interaction of the protein with the brush border membrane (BBM) of the
enterocytes. To test if apoA-I is transported across the epithelium by
receptor-mediated endocytosis we assayed the ability of apoA-I to bind to
isolated carp intestinal BBMV. As shown in
Fig. 4A, in the range of the
concentrations tested, a linear increase of BBMV-bound 125I-apoA-I
was observed when the same amounts of BBMV were incubated with increasing
apolipoprotein concentration. Addition of an excess of cold protein
dramatically reduced the amount of bound 125I-apoA-I showing that
the binding is specific. There was no saturation at relatively high
concentrations of 125I-apoA-I (230 nmol l1),
indicating that there are no high affinity binding sites for apoA-I in the
BBM. Given that the amphipatic nature of apoA-I favours its direct interaction
with lipid bilayers, the strength of the interaction of 125I-apoA-I
with BBM was analysed by a classical procedure designed to differentiate
between peripheral and integral membrane-associated proteins. Briefly, the
BBMV were washed with carbonate/EDTA buffer after incubation with
125I-apoA-I as described above. After centrifugation, apoA-I was
analysed by autoradiography in both supernatant and precipitate fractions. As
shown in Fig. 5B,
125I-apoA-I was found equally distributed in both fractions.
Surprisingly, endogenous apoA-I already present in the isolated BBMV exhibited
the same distribution after washing with carbonate/EDTA buffer
(Fig. 5A). These results
indicate that under these conditions approximately 50% of the bound apoA-I
behaves like an integral membrane protein by exhibiting a strong interaction
with the membrane. To confirm whether or not the apoA-I binding to BBMV is
attributable to its interaction with membrane phospholipids, the binding assay
was performed at different temperatures. The results shown in
Fig. 4B indicate that apoA-I
binding to BBMV increases almost exponentially with temperature, clearly
favouring its interaction with membrane lipids rather than with specific
binding sites (i.e. receptor). Accordingly, apoA-I effectively solubilised
DMPC mLV, clearly indicating its capacity to interact directly with
phospholipids (Fig. 6).
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The possibility that the lack of apoA-I expression could be
attributed to the presence of inhibitors of the reverse transcriptase in the
RTPCR reaction or degradation of the mRNAs in the preparations obtained
is ruled out by the successful amplification of a housekeeping transcript
(ß-actin) in the same preparations. Likewise, it is unlikely
that the probes and the primers, which were designed to be complementary to
carp liver apoA-I cDNA (Concha et
al., 2003), were inappropriate for detecting an intestinal
transcript. In the rainbow trout, two slightly different apoA-I transcripts
have been detected, only one of which corresponds to the major transcript in
normal hepatic tissue (Delcuve et al.,
1992
). The other one seems to be restricted to tumoural tissues.
Similarly, Japanese eel also expresses two different mRNA for apoA-I, but the
only transcript present in intestine corresponds to the major liver form
(Kondo et al., 2001
). The
present study therefore corroborates the findings of Vera et al.
(1992
) and strongly reinforces
the view that there is complete lack of apoA-I expression in the carp
intestine under the physiological conditions tested. Given the important role
that apoA-I plays in the mobilisation of the lipids derived from the diet,
this is a novel and intriguing finding.
Despite the evidence against apoA-I expression in the carp
intestine presented here, we demonstrate the presence of intracellular and
luminal apoA-I in all segments of this tissue. Its identity was confirmed by
western blotting. As it is very unlikely that apoA-I is synthesised in the
intestine, it must have originated from biliary or hepatic secretion. Some
evidence for this is the presence of apoA-I in the carp bile
(Vera et al., 1992) and also
vesical mucosa (data not shown). The biliary system of carp liver has an
unusual structure: the bile canaliculus is formed by deep invagination of the
cell membrane of one hepatocyte
(Kalashnikova and Kazanskaia,
1986
). This study suggests that, in periportal hepatocytes, newly
synthesised proteins could be secreted both to blood capillaries and to bile
canaliculus. Thus, it is possible that apoA-I could reach the intestinal lumen
through the bile during the lipid absorption process.
The presence of intracellular apoA-I in carp enterocytes in the absence of
local synthesis seen in the present study, and the transepithelial transport
of intact apoA-I previously reported (Vera
et al., 1992), may be explained by the existence of specific
binding sites for carp apoA-I in BBM. According to results presented here,
these sites would not correspond to high affinity receptors as no saturation
was reached at relatively high concentrations (230 nmol l1)
of the ligand apoA-I. Not withstanding, these sites could be low affinity
receptors, e.g. scavenger receptor class B type I (SR-BI), which display a
Kd in the micromolar range for free and HDL-associated
apoA-I (Schulthess et al.,
2000
). In mammals, the SR-BI receptor participates in selective
sterol and phospholipid uptake from the donor particle HDL in intestinal BBM
(Werder et al., 2001
). In the
present study, specific antiserum against the murine SR-BI, failed to detect a
protein of molecular mass in the range of monomeric mammalian SR-BI (
80
kDa), although two faint bands of >150 kDa were seen after western blotting
of carp BBM proteins (data not shown). Therefore, the presence of this protein
in carp enterocytes cannot be ruled out. It seems that apoA-I or HDL binding
to SR-BI would be involved in cholesterol and phospholipids transfer but not
in apoA-I endocytosis/transcytosis (Werder
et al., 2001
). Internalisation of a wide variety of intact
proteins across the intestinal epithelium has been demonstrated for several
teleost fish (Moriyama et al.,
1990
; Hertz et al.,
1992
; Vera et al.,
1992
). In the carp, a specific receptor protein for the
endocytosis tracer horseradish peroxidase has been identified by ligand
blotting (Amthauer et al.,
2000
; Concha et al.,
2002
) but no specific protein could be identified as a putative
receptor for apoA-I, utilising a similar approach (data not shown).
Surprisingly, the present study revealed unusually strong interaction of an
important fraction of labelled apoA-I (50% of the BBMV-bound apoA-I) that
behaves like an integral membrane protein. Human apoA-I has a central domain
capable of penetrating the bilayer of phospholipids vesicles
(Córsico et al., 2001
).
This indicates that apoA-I could interact directly and strongly with membranes
through protein insertion in the bilayer. In the present study, we
demonstrated a similar behaviour for carp apoA-I through its ability to
solubilise DMPC mLV. Also a dramatic increase of apoA-I binding to BBMV was
found at temperatures above 10°C. The amount of bound apoA-I more than
doubled with each 10°C increment between 10 and 30°C. The insertion
process of a protein into a membrane bilayer is very temperature dependent,
and occurs only above a threshold temperature
(Meijberg and Booth, 2002
).
Below 20°C membrane lipids are essentially in a highly ordered, gel-like,
phase of low fluidity, whereas at higher temperatures they are in a liquid
crystal (`fluid') phase (Mamdouh et al.,
1996
). Observations in carp favour the notion that apoA-I binding
to BBM is dependent on interaction with lipids rather than to specific
receptor proteins.
In summary, the above results demonstrate that in spite of the important
role proposed for HDL in the early mobilisation of dietary lipids (free fatty
acids and triglycerides) in the carp intestine (Iijima et al.,
1990a,b
)
and the abundant apoA-I immunodetected in carp enterocytes, no local
expression of the apoA-I gene could be detected. These apparently
contradictory results could reflect the existence of a unique recycling system
in which an important fraction of the apoA-I synthesised by the liver and/or
biliary system is subsequently released to the bile during the fat absorption
process and later on internalised by endocytosis in the enterocytes. Although
we could not detect high affinity binding sites for free apoA-I in intestinal
BBMV, the unusually strong interaction of apoA-I with BBMV suggests the
possibility of a constitutive endocytosis pathway rather than a
receptor-mediated process.
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Amthauer, R., Villanueva, J., Vera, M. I., Concha, M. I. and Krauskopf, M. (1989). Characterization of the major plasma apolipoproteins of the high density lipoprotein in the carp (Cyprinus carpio). Comp. Biochem. Physiol. 92B,787 -793.[CrossRef]
Amthauer, R., Tobar, L., Molina, H., Concha, M. I. and Villanueva, J. (2000). Horseradish peroxidase binding to intestinal brush-border membranas of Cyprinus carpio. Identification of a putative receptor. J. Cell. Biochem. 80,274 -284.[Medline]
Babin, P. J. and Vernier, J. M. (1989). Plasma lipoproteins in fish. J. Lipid Res. 30,467 -489.[Medline]
Chao, Y. S., Yamin, T. T., Thompson, G. M. and Kroon, P. A.
(1984). Tissue-specific expression of genes encoding
apolipoprotein E and apolipoprotein A-I in rabbits. J. Biol.
Chem. 259,5306
-5309.
Concha, M. I., Santander, C., Villanueva, J. and Amthauer, R. (2002). Specific binding of the endocytosis tracer horseradish peroxidase to intestinal fatty acid-binding protein (I-FABP) in apical membranes of carp enterocytes. J. Exp. Zool. 293,541 -550.[CrossRef][Medline]
Concha, M. I., Molina, S., Oyarzún, C., Villanueva, J. and Amthauer, R. (2003). Local expression of apolipoprotein A-I gene and a possible role for HDL in primary defence in the carp skin. Fish & Shellfish Immunol. 14,259 -273.[CrossRef][Medline]
Córsico, B., Toledo, J. D. and Garda, H. A.
(2001). Evidence for a central apolipoprotein A-I domain loosely
bound to lipids in discoidal lipoproteins that is capable of penetrating the
bilayer of phospholipids vesicles. J. Biol. Chem.
276,16978
-16985.
Delcuve, G. P., Sun, J. M. and Davie, J. R. (1992). Expression of rainbow trout apolipoprotein A-I genes in liver and hepatocellular carcinoma. J. Lipid Res. 33,251 -262.[Abstract]
De Smet, H., Blust, R. and Moens, L. (1998). Absence of albumin in the plasma of common carp Cyprinus carpio: binding of fatty acids to high density lipoprotein. Fish Physiol. Biochem. 19,71 -81.[CrossRef]
Hertz, Y., Shechter, Y., Madar, Z. and Gertler, A. (1992). Oral absorption of biologically active insulin in common carp (Cyprinus carpio L.). Comp. Biochem. Physiol. 101A,19 -22.
Hu, W., Mazurier, J., Montreuil, J. and Spik, G. (1997). Isolation and partial characterization of lactotransferrin receptor from mouse intestinal brush border. Biochemistry 29,535 -541.[CrossRef]
Iijima, N., Aida, S., Mankura, M. and Kayama, M. (1990a). Intestinal absorption and plasma transport of dietary triglyceride and phosphatidylcholine in the carp (Cyprinus carpio). Comp. Biochem. Physiol. 96A, 45-55.
Iijima, N., Aida, S. and Kayama, M. (1990b). Intestinal absorption and plasma transport of dietary fatty acids in carp. Nippon Suisan Gakkaishi 56,1829 -1837.
Kalashnikova, M. M. and Kazanskaia, N. I. (1986). Unusual structure of the biliary system in the liver of the grass carp and the silver carp. Bull. Exp. Biol. Med. 102,485 -488.
Kondo, H., Kawazoe, I., Nakaya, M., Kikuchi, K., Aida, K. and Watabe, S. (2001). The novel sequences of major plasma apolipoproteins in the eel Anguilla japonica. Biochim. Biophys. Acta 1531,132 -142.[Medline]
Kumar, N. S. and Mansbach, C. M. (1999). Prechylomicron transport vesicle: isolation and partial characterization. Am. J. Physiol. 276,G378 -G386.[Medline]
Lamon-Fava, S., Sastry, R., Ferrari, S., Rajavashisth, T. B., Lusis, A. J. and Karathanasis, S. K. (1992). Evolutionary distinct mechanisms regulate apolipoprotein A-I gene expression: differences between avian and mammalian apoA-I gene transcription control regions. J. Lipid Res. 33,831 -842.[Abstract]
Levy, E., Beaulieu, J., Delvin, E., Seidman, E., Yotov, W.,
Basque, J. and Menard, D. (2000). Human crypt
intestinal epithelial cells are capable of lipid production, apolipoprotein
synthesis, and lipoprotein assembly. J. Lipid Res.
41, 12-22.
Llewelyn, L., Ramsurn, V. P., Wigham, T., Sweeney, G. E. and Power, D. M. (1998). Cloning, characterization and expression of the apolipoprotein A-I gene in the sea bream (Sparus aurata). Biochim. Biophys. Acta 1442,399 -404.[Medline]
Mamdouh, Z., Giocondi, M. C., Laprade, R. and Grimellec, C. L. (1996). Temperature dependence of endocytosis in renal epithelial cells in culture. Biochim. Biophys. Acta 1282,171 -173.[Medline]
Meijberg, W. and Booth, P. J. (2002). The activation energy for insertion of transmembrane alpha-helices is dependent on membrane composition. J. Mol. Biol. 319,839 -853.[CrossRef][Medline]
Metcalf, V. J., Brennan, S. O. and George, P. M. (1999). The Antarctic toothfish (Dissostichus mawsoni) lacks plasma albumin and utilizes high density lipoprotein as its major palmitate binding protein. Comp. Biochem. Physiol. 124,147 -155.[CrossRef]
Moriyama, S., Takayashi, M., Hirano, T. and Kawauchi, H. (1990). Salmon growth hormone is transported into the circulation of rainbow trout, Onchorhynchus mykiss, after intestinal administration. J. Comp. Physiol. 160B,251 -257.
Noaillac-Depeyre, J. and Gas, N. (1974). Fat absorption by the enterocytes of the Carp. Cell Tissue Res. 155,353 -365.[Medline]
Oku, H., Toda, T., Nagata, J., Ishikawa, M., Neyazaki, K., Shinjyo, C., and Chinen, I. (1997). Apolipoprotein A-1 of Japanese quail: cDNA sequence and modulation of tissue expression by cholesterol feeding. Biosci. Biotechnol. Biochem. 61,286 -290.[Medline]
Powell, R., Higgins, D. G., Wolff, J., Byrnes, L., Stack, M., Sharp, P. M. and Gannon, F. (1991). The salmon gene encoding apolipoprotein A-I: cDNA sequence, tissue expression and evolution. Gene 104,155 -161.[CrossRef][Medline]
Pownall, H. J., Massey, J. B., Kusserow, S. K. and Gotto, A. M., Jr (1978). Kinetics of lipid-protein interactions: Interaction of apolipoprotein A-I from human high density lipoproteins with phosphatidylcholines. Biochemistry 17,1183 -1188.[CrossRef][Medline]
Sarmiento, J., Leal, S., Quezada, C., Kausel, G., Figueroa, J., Vera, M. and Krauskopf, M. (2000). Environmental acclimatization of the carp modulates the transcription of beta-actin. J. Cell. Biochem. 80,223 -228.[CrossRef][Medline]
Schulthess, G., Compassi, S., Werder, M., Han, C. H., Phillips, M. C. and Hauser, H. (2000). Intestinal sterol absorption mediated by scavenger receptors is competitively inhibited by amphipathic peptides and proteins. Biochemistry 39,12623 -12631.[CrossRef][Medline]
Vera, M. I., Romero, F., Amthauer, R., Figueroa, J., Goicoechea, O., León, G. and Krauskopf, M. (1992). Carp apolipoprotein A-I intestinal absorption and transfer into the systemic circulation during the acclimatization of the carp (Cyprinus carpio). Comp. Biochem. Physiol. 101,573 -581.[CrossRef]
Villanueva, J., Vanacore, R., Goicoechea, O. and Amthauer, R. (1997). Intestinal alkaline phosphatase of the fish Cyprinus carpio: Regional distribution and membrane association. J. Exp. Zool. 279,347 -355.[CrossRef]
Werder, M., Han, C. H., Wehrli, E., Bimmler, D., Schulthess, G. and Hauser, H. (2001). Role of scavenger receptors SR-BI and CD36 in selective sterol uptake in the small intestine. Biochemistry 40,11643 -11650.[CrossRef][Medline]
Windmueller, H. G. and Wu, A. L. (1981).
Biosynthesis of plasma apolipoproteins by rat small intestine without dietary
or biliary fat. J. Biol. Chem.
256,3012
-3016.
Wu, A. L. and Windmueller, H. G. (1979). Relative contributions by liver and intestine to individual plasma apolipoproteins in the rat. J. Biol. Chem. 254,7316 -7322.[Medline]