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1 From the Department of Ophthalmology and Visual Science, College of Medicine, The Catholic University of Korea; and the 2 Department of Biochemistry, School of Medicine, Kyungpook National University, Korea.
| Abstract |
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METHODS. Lens epithelial cells attached to the anterior capsules of human cataractous lenses and noncataractous lenses were examined for the expression of ßig-h3 mRNA and protein using reverse transcriptionpolymerase chain reaction and immunohistochemical analyses. The effect of TGF-ß on ßig-h3 gene expression was also tested in human lens epithelial B-3 cells using Northern and Western blot analyses.
RESULTS. ßig-h3 mRNA was not detected in lens epithelial cells from patients with clear lenses or patients with nuclear cataracts. Significant expression of mRNA for ßig-h3 was observed in lens epithelial cells from patients with anterior polar cataracts. Immunohistochemical analysis using antißig-h3 antiserum indicated that ßig-h3 protein was present within the subcapsular plaques of anterior polar cataracts. Treatment of human lens epithelial B-3 cells with TGF-ß1 led to an increase in ßig-h3 mRNA and the secretion of ßig-h3 protein into the culture medium.
CONCLUSIONS. ßig-h3 may serve as a marker for anterior polar cataracts in addition
to previously known proteins, fibronectin, type I collagen, and
-smooth muscle actin. The functions of this protein in lens
pathology need to be further investigated.
| Introduction |
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TGF-ßinducible gene h3 (ßig-h3) was initially identified as a novel gene that was induced by TGF-ß in a human lung adenocarcinoma cell line.6 It was later shown that TGF-ß induces the expression of ßig-h3 mRNA and secretion of a 68-kDa ßig-h3 protein in several other cell types.6 7 8 ßig-h3 transcripts were detected in several human tissues, suggesting that this protein may have an important function throughout the body. In the normal human eye, ßig-h3 is expressed almost exclusively in the cornea.9 Recently, mutations in this gene were found in 5q31-linked autosomal dominant corneal dystrophies.10 ßig-h3 protein is thought to be a major constituent of the abnormal extracellular deposits found in these hereditary corneal diseases.11 12 Although the biological function of ßig-h3 remains to be clarified, this protein has been shown to be associated with matrix molecules.7 8 9 13
We have previously shown that treatment of lens epithelial cells with TGF-ß increases the synthesis of pathologic extracellular matrix proteins characteristic of fibroblasts.14 Because ßig-h3 is a TGF-ßinducible protein that plays a role in the development of pathologic extracellular deposits, we hypothesized that this protein might be implicated in the aberrant accumulation of extracellular matrix seen in anterior polar and secondary cataracts. To test this, we examined whether this protein and its mRNA were expressed in lens epithelial cells from patients with anterior polar cataracts. We also provide evidence that the expression of ßig-h3 is increased by TGF-ß in cultured lens epithelial cells.
| Methods |
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Cell Culture and Treatment
Human lens epithelial cell line HLE B-3 was kindly provided by
Usha Andley, PhD, and maintained as described
previously.15
The cultures were treated with various
cytokines at 10 ng/ml in serum-free medium. At the indicated time
points, total cellular RNA and culture supernatants were collected for
Northern and Western blot analyses, respectively. Human recombinant
interleukin (IL)-1
was purchased from Pepro Tech (Rocky Hill, NJ);
human recombinant interferon (IFN)-
and tumor necrosis factor
(TNF)-
were obtained from Upstate Biotechnology (Lake Placid, NY);
and human recombinant TGF-ß1 and fibroblast growth factor (FGF)-2
were from Sigma (St. Louis, MO). For the inhibition of new protein
synthesis, cycloheximide (10 µg/ml; Sigma) was added to the cultures
1 hour before treatment with TGF-ß1.
Reverse TranscriptionPolymerase Chain Reaction
Total cellular RNA was isolated and 1 µg was
reversetranscribed using the First Strand cDNA Synthesis Kit
(Boehringer Mannheim, Indianapolis, IN). The resultant cDNA (0.21
µl) was amplified using gene-specific primers. DNA size markers were
run in parallel to validate the predicted sizes of the amplified bands
(D-15 DNA marker; Novex, San Diego, CA). The primer sequences specific
for the genes examined and predicted product sizes are as follows:
5'-AGGCCAACCGCGAAGATTGACC-3' (sense), 5'-GAAGTCCAGGGCGACGTAGCAC-3'
(antisense), 350 bp for ß-actin,16
and
5'-CCATCACCAACAACATCCAG-3' (sense), 5'-GAGTTTCCAGGGTCTGTCCA-3'
(antisense), 660 bp for ßig-h3.
Immunohistochemical Analysis
Anterior lens capsules with attached lens epithelial cells were
fixed in 10% neutral-buffered formalin and embedded in paraffin. The
paraffin-embedded samples were sectioned on a microtome at a
thickness of 5 µm, deparaffinized in xylene, and rehydrated in
alcohol. The sections were incubated in 2%
H2O2 for 5 minutes, 20%
nonimmune horse serum (Biomeda, Foster City, CA) for 10 minutes, and
1:200 dilution of rabbit antißig-h3 antiserum or normal rabbit
serum for 2 hours at room temperature. The sections were then incubated
in biotinylated anti-rabbit IgG (Amersham, Cleveland, OH) for
10 minutes, and then visualized according to the manufacturers
protocol using a detection kit (UltraTek HRP; ScyTek Laboratories,
Logan, UT). The immunolabeled sections were counter-stained with 10%
Mayers hematoxylin and examined under light microscope.
Northern Blot Analysis
Samples of RNA (10 µg of total RNA per lane) were separated on
1% agarose formaldehyde gels17
and transferred by
downward alkaline transfer (Turboblotter; Schleicher & Schuell, Keene,
NH) to nitrocellulose membranes (Optitran BA-S; Schleicher & Schuell).
A ßig-h3 cDNA probe and a probe for the housekeeping gene ß-actin
were labeled with random priming (Random primed DNA labeling kit;
Boehringer Mannheim) and [32P]-dCTP (3000
Ci/mmol; Amersham). Blots were prehybridized and hybridized in 50%
formamide, 5x SSPE, 10x Denhardts solution, and 0.5% sodium
dodecyl sulfate (SDS) at 42°C. Blots were then washed and exposed to
autoradiographic film. Equal loading was assessed by hybridization with
a ß-actin probe.
Western Blot Analysis
Culture supernatants of B-3 cells were centrifuged to remove cell
debris and were concentrated using a concentrator (Centricon-10;
Amicon, Beverly, MA). Aliquots of 20 µl were subjected to
SDSpolyacrylamide gel electrophoresis (PAGE) and electroblotting to
nitrocellulose membrane. The membranes were blocked, incubated with
rabbit antißig-h3 antiserum (1:1000 dilution), and then reacted
with horseradish peroxidaseconjugated anti-rabbit antibody (Amersham;
1:1000 dilution). The blots were developed using chromogenic substrate
solution (DAB substrate; Boehringer Mannheim). Prestained molecular
weight standards (SeeBlue) were purchased from Novex.
Preparation of Polyclonal ßig-h3 Antiserum
A NdeI/BglII fragment corresponding to amino
acids 175 to 653 of ßig-h3 was inserted into pET-29b vector (Novagen;
Madison, WI) and expressed in Escherichia coli. The
His-tagged recombinant ßig-h3 protein was purified using Ni-NTA resin
(Qiagen; Valencia, CA) according to the manufacturers manual. All
animal experiments were carried out in accordance with the ARVO
Statement for the Use of Animals in Ophthalmic and Vision Research.
Antibodies were then raised in rabbits by subcutaneous injection of the
protein (200 µg) in Complete Freunds adjuvant. Immunizations were
repeated four times in Incomplete Freunds adjuvant, every 3 weeks.
Titer of the antibody was monitored by immunoblot analysis using
recombinant ßig-h3 protein and culture supernatant of COS cells
overexpressing ßig-h3.
Overexpression of ßig-h3 in COS Cells
The cDNA encoding amino acids 1 to 653 of ßig-h3 was subcloned
into pcDNA 3.1/Myc-His A (Invitrogen; Carlsbad, CA). For transient
expression, the plasmid was transfected into COS cells using
Lipofectamine (GIBCO) according to the manufacturers protocol. After
cells were incubated overnight in Dulbeccos modified Eagles medium
(DMEM) supplemented with 10% fetal bovine serum, the medium was
replaced with serum-free DMEM. The cells were then incubated for 48
hours before supernatant collection. The supernatants were collected
and analyzed by immunoblot analysis using ßig-h3 antiserum and
anti-Myc antibody.
| Results |
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Increased mRNA Expression for ßig-h3 after TGF-ß Treatment in
Human Lens Epithelial Cells
We then determined whether the expression of mRNA for ßig-h3
could be stimulated in cultured human lens epithelial cells by
treatment with TGF-ß. Northern blot analysis results showed that HLE
B-3 cells produced ßig-h3 under normal culture conditions and that
treatment with TGF-ß1 resulted in a time-dependent increase in a
single ßig-h3 transcript of approximately 3.4 kb (Fig. 2A
). Pretreatment of HLE B-3 cells with cycloheximide did not influence
the stimulation of ßig-h3 mRNA expression by TGF-ß1 (Fig. 2B)
,
suggesting that the upregulation of ßig-h3 mRNA expression by
TGF-ß1 does not require the de novo synthesis of transcription
factors.
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, TNF-
, FGF-2, or IFN-
did not
increase the secretion of ßig-h3 protein, suggesting that the
stimulation of ßig-h3 expression is specific for TGF-ß (Fig. 3C)
.
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| Discussion |
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We have previously shown that proteins that are not normally produced
by lens epithelial cells (including fibronectin, type I collagen, and
-smooth muscle actin) are prominently expressed in lens epithelial
cells from patients with anterior polar cataracts. TGF-ß mRNA was
also overexpressed in lens epithelial cells of anterior polar
cataracts.14
We demonstrated in this study that
significant expression of ßig-h3 was detected within the fibrotic
plaques formed in anterior polar cataracts. This result suggests that
ßig-h3 protein provides an additional pathologic marker for anterior
polar cataracts. We also observed that the expression for ßig-h3 was
augmented by TGF-ß in lens epithelial cells in vitro. Based on
previous results obtained by Skonier et al.,6
ßig-h3 is
not induced in all cell types tested. Our results add lens cells to the
group of cells showing an increase in ßig-h3 in response to TGF-ß
and suggest that ßig-h3 plays a role in the cellular responses evoked
by TGF-ß in lens epithelial cells.
According to Escribano et al.,9 ßig-h3 transcripts are found in various tissues but not in normal human lens. In agreement with the report, ßig-h3 message was not detected in cells of noncataractous lens specimens by RTPCR analysis (Fig. 1A) . However, we observed constitutive ßig-h3 expression in untreated HLE B-3 cells (Figs. 2 and 3) . LeBaron et al. found that ßig-h3 was normally expressed at low levels in all cell lines they examined.8 Similarly, ciliary epithelial cell lines but not normal ciliary epithelium showed prominent expression of ßig-h3 mRNA.9 Thus, the background level of ßig-h3 transcripts in HLE B-3 cells could be attributed to the fact that B-3 cells are immortalized, or as a consequence of in vitro culture. This raises a general point that caution should be exercised when drawing conclusions about normal lens biology from work on cell lines.
The biochemical functions of the ßig-h3 gene product have not been precisely identified yet. ßig-h3 protein is prominently expressed in the cornea, skin, and extracellular matrix of many connective tissues.6 8 20 21 This protein contains a RGD (Arg-Gly-Asp) motif near the carboxyl-terminus, as found in various extracellular matrix molecules that interact with cell-surface integrins.6 ßig-h3 has also been proposed to have adhesive functions.7 8 In the lens, ßig-h3 protein may be important in mediating interaction between abnormal lens epithelial cells and the altered extracellular matrix. Further studies are required to elucidate the significance of the presence of ßig-h3 protein in fibrotic plaques of anterior polar cataracts.
The observation that mRNA level for ßig-h3 increases in healing corneal tissues11 22 suggests that ßig-h3 protein might play a role in the formation of extracellular matrix during the healing process. Tissue fibrosis is caused by excessive extracellular matrix deposition due to unregulated wound healing.1 Pathologic mechanisms underlying anterior polar cataracts and fibrosis type of after-cataract have been recognized to share many common points with those proposed for other fibrotic diseases in which TGF-ß is implicated as a key cytokine.23 In this regard, our data may give valuable insights into studies for the potential role of ßig-h3 protein in the fibrosis that often develops in other major organs, such as the liver, kidney, and lung.
Further characterization of the role of ßig-h3 in the lens may provide a better understanding of the mechanisms of TGF-ß action with respect to cataract formation. Furthermore, it is expected that studies aimed at finding antagonists to the pathologic effects of TGF-ß24 could be used to prevent after-cataract.
| Acknowledgements |
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| Footnotes |
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Supported by Grants 98-0403-17-01-3 (CKJ) and 981-0703-024-2 (JHK) from Korean Science & Engineering Foundation (KOSEF) and a grant to the Biomolecular Engineering Center at Kyungpook National University (ISK) from KOSEF.
Submitted for publication August 3, 1999; revised November 30, 1999; accepted December 2, 1999.
Commercial relationships policy: N.
Corresponding author: ChounKi Joo, Department of Ophthalmology and Visual Science, College of Medicine, The Catholic University of Korea, 505 Banpo-dong, Seocho-ku, Seoul 137-701, Korea. ckjoo{at}cmc.cuk.ac.kr
| References |
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1(VI) collagen,
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