| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
ARTICLES |
Department of Biochemistry, Chang-Gung University, Taoyuan, Taiwan 333, Republic of China
Address all correspondence and requests for reprints to: Dr. Kwang-huei Lin, Department of Biochemistry, Chang-Gung University, 259 Wen-hwa 1 Road, Taoyuan, Taiwan, Republic of China. E-mail: khlin{at}mail.cgu.edu.tw
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
1 (TR1) is expressed at a low level, were stably
transfected, either with expression plasmids encoding wild-type TR1
or a dominant negative mutant of TR1, or with the empty vector
(yielding HepG2-Wt, HepG2-Mt, and HepG2-Neo cells, respectively).
Immunoblot analysis revealed that exposure of HepG2-Wt and HepG2-Neo
cells, but not HepG2-Mt cells, to T3-induced time-dependent
decreases in the abundance of Nm23-H1 messenger RNA and protein,
with the extent of these effects correlating with the level of
expression of TR1. An in vitro assay also revealed
that T3 induced a marked increase in the invasive activity
of HepG2-Wt cells; it induced a smaller increase in that of HepG2-Neo
cells but had no effect on that of HepG2-Mt cells. Finally, the
promoter region of Nm23-H1 spanning nucleotides -471 to
-437 (relative to the transcriptional initiation site) inhibited the
expression of a downstream reporter gene, in a T3-dependent
manner, in COS-1 cells also transfected with an expression plasmid
encoding TR1 or TRß1. The DNA binding domain of TRß1 was
required for this inhibitory effect. These results indicate that
T3, acting through TRs, inhibits transcription of
Nm23-H1, and that this effect is mediated by a negative
regulatory element in the promoter region of the gene. Thus, it is
possible that T3 promotes tumor metastasis by inducing
down-regulation of Nm23-H1 expression. |
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
The metastasis-associated gene Nm23-H1, which encodes an 18-kDa nucleoside diphosphate kinase, was identified by a differential hybridization approach with K-1735 murine melanoma cells of high and low metastatic potential (4). However, many studies suggest that in vitro nucleoside diphosphate kinase activity of Nm23-H1 might be unrelated to its metastasis suppressor function. The related Nm23-H2 gene was subsequently cloned (5, 6) and was shown to encode the c-MYC transcription factor PuF and not to be associated with metastasis (7). Both Nm23-H1 and Nm23-H2 have been mapped to human chromosome 17q11–21 (8). The abundance of Nm23-H1 messenger RNA (mRNA) is markedly reduced in highly metastatic tumor cell lines such as K-1735 melanoma cells (4) and Ras- and adenoviral E1A-transfected REF cells (9), as well as in human primary breast, hepatocellular, gastric, ovarian, and cervical carcinomas (10). Moreover, the expression of Nm23-H1 in malignant melanoma has been shown to be a predictive prognostic parameter for survival (11). The Nm23-H1 protein functions as a suppressor of metastasis in a wide variety of cell lines (12, 13, 14, 15, 16, 17). However, it is also thought to function in the formation of basement membrane and in growth arrest in mammary epithelial cells (18) and to influence proliferation and differentiation of PC12 cells in response to nerve growth factor (19).
Thyroid hormones (THs) regulate growth, development, differentiation,
and metabolic processes by interacting with TH receptors (TRs) that
bind to specific DNA sequences in the regulatory regions of target
genes (20). TRs are members of the steroid hormone and retinoic acid
superfamily of ligand-dependent transcription factors. Two TR genes,
TR and TRß, have been identified and are
located on human chromosomes 17 and 3, respectively. Each gene encodes
two TR isoforms (TR1 and TR2, and TRß1 and TRß2) that are
generated as a result of alternative RNA splicing. Although much
progress has been made in our understanding of the transcriptional
regulation of TR target genes, little is known of the role of TRs in
cancer development and metastasis (21, 22, 23).
To investigate the role of TRs in tumorigenesis and metastasis, we
previously examined the expression of Nm23-H1 and TRß1 in nine
hepatoma cell lines. We showed that endogenous TRß1 is abundant in
Mahlavu, SK-Hep-1, and HA22T cells; present in moderate amounts in J5,
J7, and J3–28 cells; and expressed at low concentrations in HepG2,
Hep3B, and PLC/PRF/5 cells (24). We further showed that the abundance
of the Nm23-H1 protein in these cells is inversely correlated with that
of TRß1 (25). However, the relation between TR1 and Nm23-H1
expression has remained unknown because of the lack of cell lines in
which TR1 is expressed at a high level. In the present study, we
therefore prepared isogenic cell lines derived from HepG2 that stably
express high levels of either wild-type TR1 (HepG2-Wt cells) or the
potent dominant negative mutant TR1-M259I (HepG2-Mt cells) (26). We
show that the expression of Nm23-H1 is inhibited by
T3 and that the extent of this effect is
correlated with that of TR1 expression. The regulation of Nm23-H1
expression by T3 was shown to be mediated, at
least in part, at the transcriptional level. Furthermore, we detected a
functional negative TH response element (TRE) in the promoter region of
the Nm23-H1 gene, suggesting that TRs might play an
important role in tumor metastasis.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Stable transfection of HepG2 cells with TR complementary DNA
(cDNA)
HepG2 cells were seeded at a density of
106 cells per 100-mm-diameter dish and, after
24 h, were transfected with either wild-type or mutant (M259I)
TR1 cDNA in the pcDNA3 vector (Invitrogen, Carlsbad,
CA), with the use of Lipofectamine (Life Technologies, Inc., Rockville, MD). Cells were also transfected with the empty
vector as a control. Forty-eight hours after transfection, cells were
cultured in the presence of G418 (800 µg/ml) (Life Technologies, Inc.) for selection. After approximately 10–14
days, G418-resistant clones were selected and transferred to a 24-well
plate for further propagation. The resistant clones were screened by
immunoblot analysis, for expression of TR protein. HepG2 cells stably
expressing either wild-type TR1 (HepG2-Wt cells), mutant TR1
(HepG2-Mt cells), or the Neo protein alone (HepG2-Neo cells) were used
in this study.
Immunoblot analysis
Cell lysates were fractionated by SDS-PAGE on a 10% gel, and
the separated proteins were transferred to a nitrocellulose membrane
(PH 7.9 membrane, Schleicher & Schuell, Inc., Keene, NH).
The membrane was gently shaken for 2 h at room temperature in 5%
(wt/vol) nonfat dried milk in Tris-buffered saline (TBS), washed three
times with TBS, and then incubated for 1 h with rabbit polyclonal
antibodies to Nm23-H1 (1:1000 dilution in TBS) (Santa Cruz Biotechnology, Inc., Santa Cruz, CA) or with mouse monoclonal
antibody C4 to TR1 (1:1000 dilution in TBS) (kindly provided by
S.-Y. Cheng). After further washing, the membrane was incubated for
1 h with horseradish peroxidase-conjugated, affinity-purified
antibodies to either rabbit (1:2000 dilution in TBS) or mouse (1:2000
dilution in TBS) Ig (Santa Cruz Biotechnology, Inc.).
Immune complexes were then visualized by chemiluminescence with an
ECL detection kit (Amersham Pharmacia Biotech,
Buckinghamshire, UK). The intensities of immunoreactive bands were
quantitated by analysis with Image Gauge software (Fuji Photo Film Co., Ltd. Film, Tokyo, Japan).
Determination of the transactivation activity of TRs
T3-dependent transactivation activity of
TRs was assayed in the various HepG2 cell lines, as described (26).
Briefly, cells were transfected with a luciferase reporter plasmid (2
µg) containing the Lys-TRE, which is the chicken lysozyme gene TRE
(an inverted palindrome), as well as with a ß-galatosidase plasmid (1
µg) to control for transfection efficiency. They were subsequently
incubated for 24 h in T3-depleted (Td)
medium (27) containing various concentrations of
T3 (Sigma, St. Louis, MO), after
which the activities of luciferase and ß-galatosidase in cell lysates
were measured (28). The activity of luciferase was normalized on the
basis of the activity of ß-galactosidase.
Northern blot analysis
Total RNA was extracted from cells with the use of guanidinium
thiocyanate and then isolated by centrifugation on a cushion of 5.7
M CsCl (29). Equal amounts of total RNA (20 µg) were
analyzed on a 1.2% agarose-formaldehyde gel, as described (29). The
separated RNA molecules were then transferred to a nitrocellulose
membrane and subjected to Northern blot analysis, as described (25),
with a full-length Nm23-H1 cDNA fragment (746 bp) that was amplified
and labeled with [-32P]deoxycycidine
triphosphate (3000 Ci/mmol; Amersham Pharmacia Biotech) by
the PCR. The membrane was subsequently reprobed with a
32P-labeled glyceraldehyde-3-phosphate
dehydrogenase (GAPDH) cDNA fragment to verify equal application of RNA
to each lane.
In vitro assay of invasive activity
The effect of T3 on the invasive activity
of the various HepG2 cell lines was examined with a rapid in
vitro assay for quantifying the potential of tumor cells for
metastatic invasion (Transwell method) (30). The assay was performed in
Transwell chambers (Costar, Greenwich, CT) fitted with
6.5-mm-diameter polyvinylpyrrolidone-free polycarbonate filters (pore
size, 8 µm). The filters were coated with 100 µl of Matrigel (1:20
dilution in ice-cold DMEM) to form a thin, continuous film on the top
side. Cell density was adjusted to 5 x
105/ml, and 200 µl of the suspension were added
to each of triplicate wells. The medium in the upper chamber was
serum-free DMEM supplemented or not with 10 or 100
nM T3, and that in the
lower chamber was Td supplemented with 10% FBS and with or without 10
or 100 nM T3. After
incubation for 48 h at 37 C, the number of cells that had
traversed the filter to the lower chamber was counted and was then
expressed as a percentage of the total number of cells, to provide an
index of invasive activity.
Cloning of the Nm23-H1 promoter and assay of promoter
activity
Fragments of the Nm23-H1 promoter were amplified by
the PCR ,on the basis of the published nucleotide sequence (31), and
were then inserted into the pCAT3-enhancer vector (Promega Corp., Madison, WI). Various deletion mutants of the
Nm23-H1 promoter were constructed on the basis of convenient
restriction enzyme sites. The sequences of all promoter constructs were
confirmed by automated DNA sequencing. To determine the transcriptional
activity of putative negative TREs in the Nm23-H1 promoter,
we transfected COS-1 cells (1 x 105 per
35-mm dish) with 1.6 µg of the pCAT3 vector containing
Nm23-H1 promoter sequences, with the use of Lipofectamine.
Cells were also transfected with 1.6 µg of pcDNA3 expression vectors
for TR1 or TRß1 and with 1.2 µg of the pSVß plasmid
(CLONTECH Laboratories, Inc., Palo Alto, CA), which
contains the bacterial ß-galactosidase gene under the control of the
simian virus 40 promoter. Twenty-four hours after transfection, the
cells were incubated in the absence or presence of 100
nM T3 for 24 h and
then lysed for measurement of chloramphenicol acetyltransferase (CAT)
and ß-galactosidase activities (32). In addition, Avr
II-RsaI and Hph l-AflIII promoter fragments were
subcloned into the pA3TK-Luc reporter plasmid (kindly provided by
A. N. Hollenberg) for further study; luciferase activity was
assayed as described previously (28).
Construction of TR deletion mutants
The construction of a series of TRß1 deletion mutants (JL05,
JL06, JL08) was described previously (33). TR cDNA inserts were
released and subcloned into the pcDNA3 vector for expression.
Electrophoretic mobility-shift assay (EMSA)
A 32P-labeled Lys-TRE oligonucleotide was
prepared as described previously (28). TR proteins were synthesized and
labeled with 35S by in vitro
transcription and translation with a reticulocyte kit (Promega Corp.); they were quantified on the basis of the intensity of
the 35S-labeled protein bands after SDS-PAGE and
autoradiography. For EMSA, identical amounts of TRs were incubated with
32P-labeled TRE oligonucleotide in the absence or
presence of the retinoid X receptor (RXR). Supershift analysis
was performed with the C4 monoclonal antibody to TR1 and TRß1.
Protein-probe complexes were detected by PAGE and autoradiography.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
1 in HepG2 cell
lines1 in regulation of the
Nm23-H1 gene, we prepared isogenic cell lines from HepG2
that stably express either wild-type TR1 (HepG2-Wt cells) or a
dominant negative mutant of TR1 (HepG2-Mt cells). As a control, we
also transfected HepG2 cells with the empty vector, yielding a cell
line that expresses the Neo protein (HepG2-Neo cells). The mutant
TR1 expressed by the HepG2-Mt cells contains a
Met259 
Ile mutation that was originally
detected in the human hepatocarcinoma cell line J7 (26). The mutant
protein does not bind T3 and inhibits the
transactivation activity of TR1 in a dominant negative manner (26).
The expression of TR1 in parental HepG2 cells or in HepG2-Neo cells
was not detectable in the immunoblot shown in Fig. 1A
; a faint immunoreactive band was
apparent in these cells, however, after longer exposure times (data not
shown). A prominent immunoreactive band corresponding to TR1 was
detected in both HepG2-Wt and HepG2-Mt cells with the monoclonal
antibody C4 (Fig. 1A), which recognizes an epitope at the COOH-terminus
of TR1 and TRb1 (34). Quantitation of the intensities of the
immunoreactive bands revealed that the abundance of TR1 protein in
HepG2-Wt and HepG2-Mt cells was increased about 7-fold, relative to
that in HepG2-Neo cells.
|
1 in HepG2-Wt, HepG2-Mt, HepG2, and
HepG2-Neo cells (Fig. 1B
). HepG2-Wt cells exhibited the highest
transactivation activity, which was increased by
T3 in a concentration-dependent manner. Both
HepG2 and HepG2-Neo cells exhibited a low level of transactivation
activity, whereas virtually no such activity was detected in HepG2-Mt
cells, presumably because of the dominant negative action of the
expressed mutant TR1 [consistent with previous observations (26)].
These results indicate that the level of expression of TR1 protein
correlates with the extent of transactivation activity.
Effects of T3 on the abundance of Nm23-H1 mRNA and
protein in HepG2 cell lines
The expression of the Nm23-H1 protein (18 kDa) was compared among
the various HepG2 cell lines after incubation in the absence or
presence of T3 for various times (Fig. 2). Immunoblot analysis revealed that the
exposure of HepG2-Neo cells to 100 nM
T3 resulted in a time-dependent decrease in the
amount of Nm23-H1 protein. T3 also reduced the
abundance of Nm23-H1 in HepG2-Wt cells but to a greater extent than
that apparent in HepG2-Neo cells; the amount of Nm23-H1 was reduced by
20, 75, and 86% after incubation of HepG2-Wt cells with 100
nM T3 for 2, 4, and 6 days,
respectively. Incubation of HepG2-Wt cells with
T3 at 10 nM also reduced the amount
of Nm23-H1, but to a lesser extent than did incubation with 100
nM T3, indicating that the effect of
T3 was also dose dependent (data not shown). In
contrast, the expression of Nm23-H1 protein in HepG2-Mt cells was
largely unaffected by T3. Thus, the extent of
inhibition of the expression of Nm23-H1 protein by
T3 correlated with the level of expression of
TR1. The abundance of Nm23-H1 protein did not differ among the three
cell lines in the absence of T3.
|
). Exposure of HepG2-Neo
and HepG2-Wt cells to 100 nM
T3 resulted in a time-dependent decrease in the
amount of Nm23-H1 mRNA, with decreases of 9.4 and 32.7%, respectively,
apparent after incubation with T3 for 4 days;
T3 had little effect on the abundance of Nm23-H1
mRNA in HepG2-Mt cells (Fig. 3B). Incubation of HepG2-Wt cells with
T3 at 10 nM also reduced
the amount of Nm23-H1 transcript, but to a lesser extent
than did incubation with 100 nM
T3, indicating that the effect of
T3 was also dose dependent (data not shown). The
abundance of Nm23-H1 mRNA did not differ among the three cell lines in
the absence of T3. Thus, at least part of the
effect of T3 on the expression of Nm23-H1 protein
seems to be mediated at the transcriptional or mRNA level.
|
). Incubation with
T3 induced an increase of approximately 15-fold
in the invasive activity of HepG2-Wt cells. T3
induced an increase of approximately 2-fold in the invasive activity of
HepG2-Neo cells, but it had no effect on that of HepG2-Mt cells.
Incubation of HepG2-Wt cells with 10 nM
T3 also increased invasive activity but to a
lesser extent, compared with the effect of 100 nM
T3 (data not shown). The marked
T3-induced increase in the invasive activity of
HepG2-Wt cells was thus consistent with the high level of TR1
expression and the large inhibitory effect of T3
on the expression of Nm23-H1 protein in these cells.
|
1 on Nm23-H1 transcription, we cloned
the MboII-TaqI fragment of the Nm23-H1
promoter encompassing nucleotides -597 to -1 (relative to the
transcriptional initiation site) and then inserted it upstream of the
CAT reporter gene in pCAT3. Vectors containing a series of truncated
Nm23-H1 promoter sequences were also constructed. Each of
these reporter constructs was introduced separately into COS-1 cells,
together with expression plasmids encoding TR1 and
ß-galactosidase. The transfected cells were incubated in the absence
or presence of 100 nM T3
for 24 h; after which, cell lysates were assayed for CAT and
ß-galactosidase activities. CAT activity was normalized on the basis
of ß-galactosidase activity, and the T3-induced
change in normalized CAT activity was used as a measure of
Nm23-H1 promoter activity (Fig. 5). The transcriptional activities of the
various constructs were similar when cells were incubated in the
absence of T3, and that of the control vector
(pCAT3) was not significantly affected by
T3. The transcriptional activity of
the -597/-1 (MboII-TaqI) construct was reduced
by 23% in the presence of T3. Whereas the
T3-induced change in CAT activity was not
substantially affected by 3' deletion of the Nm23-H1
sequence to yield the -597/-302 (MboII-Nru I) construct,
the transcriptional activity of the -597/-337
(MboII-AflIII) construct was reduced by 77% in
the presence of T3. To delineate further the
promoter sequence responsible for this marked inhibition of
transcriptional activity by T3, we first divided
the promoter into two fragments: -597/-472 (MboII-Avr II)
and -471/-337 (Avr II-AflIII). The negative TRE was shown
to be located in the latter of these two fragments, which was therefore
further divided into -392/-337 (Hph I-AflIII), -471/-437
(Avr II-RsaI), and -436/-393 (RsaI-Hph I). The
negative TRE was thus localized to the -471/-437 fragment. The
presence of this negative TRE in the Nm23-H1 promoter
suggested that the inhibition of Nm23-H1 expression by
TR1 in HepG2 cells was a direct effect mediated at the
transcriptional level.
|
1. However, this minor difference was not statistically
significant (data not shown).
Given that only a relatively small number of negative response elements
for nuclear receptors have been characterized (35, 36, 37, 38, 39, 40), consensus
sequences for such elements have not been determined. However, the
35-bp fragment of the Nm23-H1 promoter containing the
negative TRE includes two hexameric sequences that show similarity to
the half-sites of a negative TRE in the promoter region of the human
TSH ß-subunit gene (Fig. 6)
(40). We next subcloned the -471/-437 and -392/-337 fragments of
the Nm23-H1 promoter into the pA3TK-Luc reporter plasmid,
and we introduced the resulting constructs, together with
ß-galactosidase and either TR1 or TRß1 expression vectors, into
COS-1 cells. Consistent with the results of the CAT reporter assay,
TR1 and TRß1 each mediated a T3-induced
inhibition of luciferase activity in cells expressing the -471/-437
construct (Table 1). In contrast,
T3 increased luciferase activity in cells
expressing the -392/-337 construct and either TR isoform. The extent
of T3- and TR-dependent repression of
transcriptional activity by the negative TRE of the Nm23-H1
promoter was similar to that observed with a promoter fragment of the
human TSH -subunit gene that also contains a negative TRE (Table 1)
(41).
|
|
1 or TRß1 and a Lys-TRE oligonucleotide as probe
(Fig. 7, lanes 1–6); probe complexes
with receptor monomers, homodimers, and heterodimers (with RXR), as
well as supershifted complexes with monoclonal antibody C4, were
detected. Reactions performed with the -471/-437 fragment as probe
and reticulocyte lysate yielded two prominent nonspecific complexes
that were not affected by monoclonal antibody C4 (Fig. 7, lanes 7–9).
However, in vitro-translated TR1 or TRß1 formed
complexes with the -471/-437 fragment that were shifted to a position
of lower mobility in the presence of antibody C4 (Fig. 7, lanes 11, 14,
16, and 19); a control antibody (MOPC21) had no such effect (Fig. 7, lanes 12 and 17). Because of the nonspecific complexes that migrated in
the expected positions of probe complexes with TR homodimers and
TR-RXR heterodimers, the participation of RXR in such complexes
was not clear. However, the intensities of the bands coinciding with
the expected positions of the heterodimer-probe complexes for reactions
containing TR and RXR (Fig. 7, lanes 13 and 18) were greater than
those for the corresponding reactions containing only TR (lanes 10 and
15), suggesting that TR-RXR heterodimers indeed interact with the
-471/-437 fragment of the Nm23-H1 promoter.
|
). However,
T3 had no substantial effect on luciferase
activity in cells expressing TRß1 mutants lacking the C (DNA binding)
domain, or the C domain and a portion of the D domain, in addition to
the A/B domain. Thus, the C domain of TRß1 seems to be required for
the inhibitory effect of the receptor on transcription from the
Nm23-H1 promoter.
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
1 in HepG2-Wt cells was about seven times that of the
endogenous protein present in the parental HepG2 cells. Stable
expression of the dominant negative mutant of TR1 in HepG2-Mt cells
allowed us to further confirm a role for endogenous TR1 in the
regulation of Nm23-H1. HepG2-Neo cells, in which the
expression and activity of TR1 were similar to those in the parental
cell line, served as an additional control. The differential expression
of TR1 in these cell lines revealed that the extent of the negative
regulation of Nm23-H1 by T3 depended
on the level of expression of TR1. The regulation of
Nm23-H1 by T3 was mediated, at least
in part, at the transcriptional level, apparently as a result of a
direct interaction of TR1 with the promoter region of the gene. As
far as we know, our data represent the first demonstration of a TR
target gene that is important in tumor metastasis.
One functional consequence of the inhibition of Nm23-H1
expression by T3 was an increase in the invasive
activity of HepG2-Wt and HepG2-Neo cells. The extent of the
T3-induced increase in invasive activity
correlated with the extent of TR1 expression. These results suggest
that T3, acting through TR1, might play an
important role in tumor metastasis. Kumar et al. (42) showed
that TH enhanced tumor growth and metastasis in two syngeneic mouse
tumor systems. Furthermore, Mishkin et al. (43) showed that
the local and metastatic growth of mouse hepatomas was inhibited and
host survival was prolonged after the induction of hypothyroidism. It
is thus possible that these in vivo effects of THs result
from TR-mediated inhibition of Nm23-H1 expression.
We have previously shown that, among various hepatocellular carcinoma
cell lines examined, SK-Hep-1 and Mahlavu cells express endogenous
TRß1 at a higher level and exhibit a higher invasive activity than do
J5, J7, and J3–28 cells (24). We have now shown that TRß1 also
induces transcriptional repression by acting at the promoter of
Nm23-H1. However, the extent of transcriptional repression
induced by TRß1 was less than that induced by TR1. The structures
of TR1 and TRß1 differ predominantly in the A/B domain. Recently,
it has been shown that the transcriptional activity of TRs is modulated
by a host of coregulatory proteins (44). It is entirely possible that
the interaction of the promoters of these two TR isoforms may be
affected differently by coregulatory proteins.
Our data indicate that a nonpalindromic half-site motif mediates the
negative action of T3 on Nm23-H1
transcription. The half-site shows substantial sequence similarity to a
negative TRE in the promoter of the human TSH ß-subunit gene (40).
EMSA analysis revealed a direct interaction of TR1 or TRß1 with
the negative TRE of the Nm23-H1 promoter. The
transcriptionally active form of TR is thought to be a heterodimer with
RXR (45). However, it was unclear from our binding data whether
RXR contributes to the interaction of TR1 or TRß1 with the
-471/-437 fragment of the Nm23-H1 promoter. We also showed
that the DNA binding domain of TRß1 is required for the repressive
effect of this receptor isoform on transcription mediated by the
Nm23-H1 promoter.
Despite its importance in tumor metastasis, little is known about the
regulation of Nm23-H1 expression. Linoleic acid and
arachidonic acid inhibit the expression of Nm23-H1, whereas
-linolenic acid increases the expression of the protein (46). The
expression of Nm23-H1 has also been shown to be reduced by
vitamin D (47), tumor necrosis factor-, and interferon- (15).
However, the underlying molecular mechanisms for these effects are
unknown. Our results show that T3, via its receptor, negatively
regulates the expression of the Nm23-H1 gene at the
transcriptional level. Thus, the present study identifies a
transcription factor which directly interacts with a gene which plays
an important role in tumor metastasis.
|
Acknowledgments |
|---|
|
Footnotes |
|---|
2 The first two authors contributed equally.
Received January 28, 2000.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
1 and ß1 receptors in a human
hepatocellular carcinoma cell line. Endocrinology 137:4073–4081[Abstract]
1 receptors from patients with hepatocellular carcinoma.
Endocrinology 138:5308–53153 gene promoter. Endocrinology 139:3423–3431This article has been cited by other articles:
 |
|
 |
|
  R.-N. Chen, Y.-H. Huang, Y.-C. Lin, C.-T. Yeh, Y. Liang, S.-L. Chen, and K.-H. Lin Thyroid Hormone Promotes Cell Invasion through Activation of Furin Expression in Human Hepatoma Cell Lines Endocrinology, August 1, 2008; 149(8): 3817 - 3831. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y.-H. Huang, C.-Y. Lee, P.-J. Tai, C.-C. Yen, C.-Y. Liao, W.-J. Chen, C.-J. Liao, W.-L. Cheng, R.-N. Chen, S.-M. Wu, et al. Indirect Regulation of Human Dehydroepiandrosterone Sulfotransferase Family 1A Member 2 by Thyroid Hormones Endocrinology, May 1, 2006; 147(5): 2481 - 2489. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C.-C. Yen, Y.-H. Huang, C.-Y. Liao, C.-J. Liao, W.-L. Cheng, W.-J. Chen, and K.-H. Lin Mediation of the inhibitory effect of thyroid hormone on proliferation of hepatoma cells by transforming growth factor-beta J. Mol. Endocrinol., February 1, 2006; 36(1): 9 - 21. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K.-H. Lin, C.-y. Chen, S.-L. Chen, C.-C. Yen, Y.-H. Huang, C.-h. Shih, J.-J. Shen, R.-C. Yang, and C.-S. Wang Regulation of fibronectin by thyroid hormone receptors J. Mol. Endocrinol., October 1, 2004; 33(2): 445 - 458. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C.-h. Shih, S.-L. Chen, C.-C. Yen, Y.-H. Huang, C.-d. Chen, Y.-S. Lee, and K.-h. Lin Thyroid Hormone Receptor-Dependent Transcriptional Regulation of Fibrinogen and Coagulation Proteins Endocrinology, June 1, 2004; 145(6): 2804 - 2814. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Weber, U. Zimmermann, H. Winter, A. Mack, I. Kopschall, K. Rohbock, H.-P. Zenner, and M. Knipper Thyroid hormone is a critical determinant for the regulation of the cochlear motor protein prestin PNAS, February 20, 2002; (2002) 52609899. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K.-H. Lin, W.-J. Wang, Y.-H. Wu, and S.-Y. Cheng Activation of Antimetastatic Nm23-H1 Gene Expression by Estrogen and Its {alpha}-Receptor Endocrinology, February 1, 2002; 143(2): 467 - 475. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K.-h. Lin and Y.-h. Wu shen-liang chen Impaired Interaction of Mutant Thyroid Hormone Receptors Associated with Human Hepatocellular Carcinoma with Transcriptional Coregulators Endocrinology, February 1, 2001; 142(2): 653 - 662. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Weber, U. Zimmermann, H. Winter, A. Mack, I. Kopschall, K. Rohbock, H.-P. Zenner, and M. Knipper Thyroid hormone is a critical determinant for the regulation of the cochlear motor protein prestin PNAS, March 5, 2002; 99(5): 2901 - 2906. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology | Recent Prog. Horm. Res. | All Endocrine Journals |
