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Thirty two thiourea derivatives were prepared and their agonistic activities on the retinoic acid receptor-related orphan receptor α (RORα) were evaluated. The replacement of the 3-allyl-2-imino-thiazolidin-4-one moiety of the lead compound CGP52608 (1) with various functional group substituted aromatic rings, improved the agonistic activity of RORα. Among the prepared derivatives, 1-methyl-3-(4-phenoxy-benzyl)-thiourea (32) showed 2.6-fold higher agonistic activity than CGP52608 in the RORα-activation assay.

Multiple cellular signaling pathways that control metabolism and survival are activated when cell are incubated under hypoxic conditions. Activation of the hypoxia inducible factor (HIF)-1 promotes expression of genes that increase the capacity to cope with the stress imposed by a reduced oxygen environment. Here we show that the orphan nuclear receptor estrogen related receptor gamma (ERR gamma) plays a critical role in hypoxia-mediated activation of pyruvate dehydrogenase kinase 4 (PDK4) gene expression. ERR gamma mRNA and protein levels were increased by hypoxia or desferrioxamine (DFO) treatment in hepatoma cell lines. Co-expression of HIF-1 alpha and beta increased ERRc promoter activity as well as mRNA expression, while knockdown of endogenous HIF-1 alpha reduced the hypoxia-mediated induction of ERR gamma. In addition, hypoxia also increased the promoter activity and mRNA level of PDK4 in HepG2 cells. Adenovirus mediated-overexpression of ERR gamma specifically increased PDK4 gene expression, while ablation of endogenous ERR gamma significantly decreased hypoxia-mediated induction of PDK4 gene expression. Finally, GSK5182, an inverse agonist of ERR gamma, strongly inhibited the hypoxia-mediated induction of PDK4 protein and promoter activity. Regulation of the transcriptional activity of ERR gamma may provide a therapeutic approach for the regulation of PDK4 gene expression under hypoxia.

Retinoids regulate a broad range of biological processes and affect cell growth and differentiation of many cell types, including the immune system. Recently, it was reported that human immunodeficiency virus type 1 (HIV-1) expression in macrophages is enhanced by retinoic acid (RA). Retinoid signals are mediated by the RA receptors (RARs) and retinoid X receptors (RXRs) that bind to specific RA responsive elements (RAREs) in the promoter region of susceptible genes. Here, we report on a RARE in the long terminal repeat (LTR) region that allows activation of the HIV-1 LTR. The RARE is composed of two consensus RARE half-sites (A/GGGTCA) arranged as a palindrome separated by 9 nucleotides and is activated by both RAR/RXR heterodimers and RXR homodimers. We show that the COUP (chicken ovalbumin upstream promoter) orphan receptors also bind to the HIV-1 RARE and repress the retinoid response of the HIV-1 RARE or the HIV-1 LTR. Furthermore, a newly discovered synthetic retinoid is shown to be a potent inhibitor of retinoid-induced activation of the HIV-1 RARE. These observations suggest additional approaches for the inhibition of HIV replication.

The retinoid X receptor (RXR) heterodimerizes with a variety of nuclear receptors. In addition, RXR forms homodimers in the presence of its ligand, 9-cis-retinoic acid. From deletion and point mutation analysis we present evidence that a short region (amino acids 413 to 443) in the carboxy terminus of RXR alpha is critical for both homo- and heterodimeric interactions as well as for diverse functional activities. In addition, we present evidence that homo- and heterodimer functions can be separated. The deletion of 19 amino acids from the C-terminal end of RXR dramatically reduced the transcriptional activation function of RXR. The removal of 10 additional amino acids resulted in a receptor (delta RXR3) that had completely lost its ligand-dependent homodimer function but retained its heterodimer activities. Heterodimer function was abolished by the deletion of an additional 20 amino acids. Single amino acid substitutions in the region generated receptors with altered RXR homodimer DNA binding, while simultaneous mutation of three Leu residues (Leu-418, -419 and -422) completely abolished both RXR homodimer and heterodimer DNA binding activities. Mutation of Leu-430 to Phe (L430-F) resulted in a receptor that bound to DNA strongly as homodimers in a ligand-independent manner, while another single amino acid exchange (L422-Q) led to a mutant that behaved in a manner exactly opposite to that of wild-type RXR in that the homodimerization of the mutant occurred in the absence of ligand and was inhibited by 9-cis-retinoic acid. In transfection assays, both L422-Q and L430-F failed to act as homodimers but retained their heterodimer function. Our studies demonstrate the unique properties of the RXR ligand binding domain and point to specific residues that mediate homo- and heterodimer activities and ligand-induced conformational switches.

All-trans-retinoic acid mediates cell growth and differentiation by binding to and then activating nuclear retinoid receptor proteins that regulate gene transcription. Recombinant human retinoic acid receptor beta was cloned and expressed in Escherichia coli as a fusion protein rMBP-RAR beta with maltose-binding protein to facilitate purification. After isolation from bacterial lysates, rMBP-RAR beta was used for binding with selected retinoids. Scatchard analysis with [11,12-3H2]all-trans-retinoic acid gave a Kd of 0.34 nM. Competitive binding studies with a series of conformationally restricted aromatic retinoids indicated that the Ki values for binding to rMBP-RAR beta correlated with the logs of the EC50 values for gene transcriptional activation (p < or = 0.05) and with those for the relative activation compared to that of all-trans-retinoic acid (p < or = 0.01). Inspection of binding-activation correlation diagrams indicates candidate structures for improved retinoid agonists or antagonists.

Thyroid hormone receptors (TRs) form heterodimers with retinoid X receptors (RXRs). Heterodimerization is required for efficient TR DNA binding to most response elements and transcriptional activation by thyroid hormone. RXRs also function as auxiliary proteins for several other receptors. In addition, RXR alpha can be induced by specific ligands to form homodimers. Here we report that RXR-specific retinoids that induce RXR homodimers are effective repressors of the T3 response. We provide evidence that this repression by RXR-specific ligands occurs by sequestering of RXR from TR-RXR heterodimers into RXR homodimers. This ligand-induced squelching may represent an important mechanism by which RXR-specific retinoids and 9-cis retinoic acid mediate hormonal cross talk among a subfamily of nuclear receptors activated by structurally unrelated ligands.

In order to address the hypoglycemic mechanism of brazilin, effects on glucose metabolism in epididymal adipose tissue from diabetic KK-mice were investigated. Brazilin remarkably lowered non fasting plasma glucose level without any changes in plasma insulin level. Brazilin significantly increased the rate of glucose oxidation and lipogenesis only in the presence of insulin. Activities of glucose-6 phosphate dehydrogenase and fatty acid synthetase, involved in glucose oxidation and lipogenesis respectively, were significantly increased. These results suggest that brazilin might exert hypoglycemic action in insulin resistance state by, at least in part, regulating the enzymatic reaction process involved in glucose metabolism.

Objective— To explore whether α-lipoic acid (ALA), a naturally occurring antioxidant, inhibits neointimal hyperplasia by inducing apoptosis of vascular smooth muscle cells and to examine its potential effects on reendothelialization and platelet aggregation. Methods and Results— Restenosis and late stent thrombosis, caused by neointimal hyperplasia and delayed reendothelialization, are significant clinical problems of balloon angioplasty and drug-eluting stents. ALA treatment strongly induced apoptosis of vascular smooth muscle cells and enhanced the expression and cytoplasmic localization of Nur77, which triggers intrinsic apoptotic events. Small interfering RNA–mediated downregulation of Nur77 diminished this proapoptotic effect of ALA. Moreover, ALA increased p38 mitogen-activated protein kinase phosphorylation, and inhibition of p38 mitogen-activated protein kinase completely blocked ALA-induced vascular smooth muscle cell apoptosis and Nur77 induction and cytoplasmic localization. In balloon-injured rat carotid arteries, ALA enhanced Nur77 expression and increased TUNEL-positive apoptotic cells in the neointima, leading to inhibition of neointimal hyperplasia. This preventive effect of ALA was significantly reduced by infection of an adenovirus encoding Nur77 small hairpin (sh)RNA. Furthermore, ALA reduced basal apoptosis of human aortic endothelial cells and accelerated reendothelialization after balloon injury. ALA also suppressed arachidonic acid–induced platelet aggregation. Conclusion— ALA could be a promising therapeutic agent to prevent restenosis and late stent thrombosis after angioplasty and drug-eluting stent implantation.

The oxysterol nuclear receptors, LXRα (liver X receptor α; NR1H3) and LXRβ (NR1H2), coordinately regulate the expression of genes involved in lipid metabolism, anti-inflammation, and cholesterol transport. Previous studies have demonstrated that ligands of LXRα are important in the maintenance of the normal epidermal barrier function and keratinocyte differentiation. In this study, we examined whether LXRα and its ligands regulate lipid synthesis in HaCaT cells, a spontaneously transformed human keratinocyte cell line. When HaCaT cells were treated with the LXRα ligand TO901317, lipid droplets accumulated in the majority of cells, which were stained by Oil Red O. A luciferase reporter construct containing the LXR response element was activated about fourfold in HaCaT cells by TO901317 treatment, suggesting that LXR has a role in lipid synthesis in these cells. The expression of LXRα target genes, such as those encoding sterol regulatory binding protein and fatty acid synthase, were induced time dependently by TO901317, as measured by RT-PCR and western blotting. The expression of PPAR-α, -β, and -γ which regulate lipid metabolism, was also increased by TO901317 treatment. In contrast, TO901317 reduced the lipopolysaccharide-induced expression of cyclooxygenase 2 and inducible nitric oxide synthase in HaCaT cells. These results indicate that LXRα activation leads to lipogenesis in keratinocytes, which may enhance the epidermal barrier function of the skin.

Although the roles of Nur77, an orphan member of the nuclear hormone receptor superfamily, in the control of cellular proliferation, apoptosis, inflammation, and glucose metabolism, are well recognized, the molecular mechanism regulating the activity and expression of Nur77 is not fully understood. Acetylation of transcription factors has emerged recently as a major post-translational modification that regulates protein stability and transcriptional activity. Here, we examined whether Nur77 is acetylated, and we characterized potential associated factors. First, Nur77 was found to be an acetylated protein when examined by immunoprecipitation and western blotting using acetyl protein-specific antibodies. Second, expression of p300, which possesses histone acetyltransferase activity, enhanced the acetylation and protein stability of Nur77. Treatment with a histone deacetylase (HDAC) inhibitor, trichostatin A, also increased Nur77 acetylation. Among the several types of HDACs, HDAC1 was found as the major enzyme affecting protein level of Nur77. HDAC1 decreased the acetylation level, protein level, and transcriptional activity of Nur77. Interestingly, overexpression of Nur77 induced expression of both p300 and HDAC1. Finally, the expression of Nur77 increased along with that of p300, but decreased with induction of HDAC1 after treatment with epithelial growth factor, nerve growth factor, or 6-mercaptopurine, suggesting that the self-control of the acetylation status contributes to the transient induction of Nur77 protein. Taken together, these results demonstrate that acetylation of Nur77 is modulated by p300 and HDAC1, and suggest that acetylation is an important post-translational modification for the rapid turnover of Nur77 protein.

Hypoxia-inducible factor-1α (HIF-1α) induces tumor proliferation, angiogenesis and metastasis. Reactive oxygen species, hypoxia, and growth factor stimulation induce HIF-1α, and the augmented HIF-1α activity confers upon cancer cells the ability to adapt to microenvironments. Oltipraz is a cancer chemopreventive agent and has an inhibitory effect on angiogenesis and tumor growth. Nonetheless, the molecular mechanism of tumor inhibition is as yet unclear. This study investigated whether oltipraz and its congeners inhibit HIF-1α activity and, if so, the molecular basis of inhibition. Oltipraz and other 1,2-dithiole-3-thiones have the ability to prevent insulin- or hypoxia-induced HIF-1α expression through an increase in ubiquitination, thereby accelerating HIF-1α degradation and inhibiting HIF-1α–dependent gene transcription. Transfection of cells with a constitutively active mutant of p70 ribosomal S6 kinase-1 (CA-S6K1) increased the basal and insulin-inducible HIF-1α activity. CA-S6K1 overexpression reversed HIF-1α inhibition by rapamycin (a mammalian target of rapamycin/S6K1 inhibitor). However, the inhibitory effect of oltipraz on HIF-1α was not reversed by CA-S6K1 despite its S6K1 inhibition. The failure of dominant negative mutant AMP-activated protein kinase-α to restore the ability of insulin to increase HIF-1α against oltipraz excluded the possible role of AMP-activated protein kinase activation in the action of oltipraz. Oltipraz treatment abrogated insulin-induced H2O2 production, thereby preventing H2O2-enhanced HIF-1α expression and promoting its ubiquitination and degradation. In an animal model, tumor regression by oltipraz was accompanied by decreases in microvessel density and vascular endothelial growth factor induction. Oltipraz inhibits HIF-1α activity and HIF-1α–dependent tumor growth, which may result from a decrease in HIF-1α stability through S6K1 inhibition in combination with an H2O2-scavenging effect. [Mol Cancer Ther 2009;8(10):2791–802]

Chronic consumption of ethanol can cause cumulative liver damage that can ultimately lead to cirrhosis. To explore the mechanisms of alcoholic steatosis, we investigated the global intrahepatic gene expression profiles of livers from mice administered alcohol. Ethanol was administered by feeding the standard Lieber-DeCarli diet, of which 36% (high dose) and 3.6% (low dose) of the total calories were supplied from ethanol for 1, 2, or 4 weeks. Histopathological evaluation of the liver samples revealed fatty changes and punctate necrosis in the high-dose group and ballooning degeneration in the low-dose group. In total, 292 genes were identified as ethanol responsive, and several of these differed significantly in expression compared to those of control mice (two-way ANOVA; p

Objective— Hypoxia-inducible factor 1α (HIF-1α) is primarily involved in the adapting of cells to changes in oxygen levels, which is essential for normal vascular function. Recently, physiological roles for retinoic acid–related orphan receptor α (RORα) have been implicated in cardiovascular diseases such as atherosclerosis. In this study, we have investigated the potential roles of RORα in the hypoxia signaling pathway in connection with activation of HIF-1α. Methods and Results— Under hypoxic conditions, expression of RORα was induced. When RORα was introduced exogenously, protein level as well as transcriptional activity of HIF-1α was enhanced. Putative ligands of RORα, such as melatonin and cholesterol sulfate, induced transcriptional activity for HIF-1α, which was abolished by RNA interference against RORα. RORα was physically associated with HIF-1α through DNA binding domain, which was required to the RORα-induced stabilization and transcriptional activation of HIF-1α. Finally, either infection with adenovirus encoding RORα or treatment with ROR ligands enhanced the formation of capillary tubes by human umbilical vascular endothelial cells. Conclusions— Our results provide a new insight for the function of RORα in amplification of hypoxia signaling and suggest a potential application of RORα ligands for the therapy of hypoxia-associated vascular diseases.

A toxicogenomics study was performed in the mouse liver after treatment of a bile-duct–damaging chemical, 4,4′-methylene dianiline (MDA), across multiple doses and sampling times in an acute phase using the AB Expression Array System. Imprinting control region (ICR) mice were given a single oral administration of a low (10 mg/kg b.w.) or high (100 mg/kg b.w.) dose of MDA. Mice were sacrificed six, twenty-four, and seventy-two hours after treatment for serum chemistry, histopathology, and mRNA preparation from liver samples. Treatment with MDA increased liver-toxicity–related enzymes in blood and induced bile-duct cell injury, followed by regeneration. To explore potential biomarker gene profiles, the altered genes were categorized into four expression patterns depending on dose and time. Numerous functionally defined and unclassified genes in each category were up- or down-regulated throughout the period from cellular injury to the recovery phase, verified by RT-PCR. Many genes associated with liver toxicity and diseases belonged to one of these categories. The chemokine-mediated Th1 pathway was implicated in the inflammatory process. The genes associated with oxidative stress, apoptosis, and cell-cycle regulation were also dynamically responsive to MDA treatment. The Wnt/β-catenin signaling pathway was likely responsible for the reconstitution process of the MDA-injured liver.

Kaempferol is the major flavonol in green tea and exhibits many biomedically useful properties such as antioxidative, cytoprotective and anti-apoptotic activities. To elucidate its effects on the skin, we investigated the transcriptional profiles of kaempferol-treated HaCaT cells using cDNA microarray analysis and identified 147 transcripts that exhibited significant changes in expression. Of these, 18 were up-regulated and 129 were down-regulated. These transcripts were then classified into 12 categories according to their functional roles: cell adhesion/cytoskeleton, cell cycle, redox homeostasis, immune/defense responses, metabolism, protein biosynthesis/modification, intracellular transport, RNA processing, DNA modification/ replication, regulation of transcription, signal transduction and transport. We then analyzed the promoter sequences of differentially-regulated genes and identified over-represented regulatory sites and candidate transcription factors (TFs) for gene regulation by kaempferol. These included c-REL, SAP-1, Ahr-ARNT, Nrf-2, Elk-1, SPI-B, NF-kappaB and p65. In addition, we validated the microarray results and promoter analyses using conventional methods such as real-time PCR and ELISA-based transcription factor assay. Our microarray analysis has provided useful information for determining the genetic regulatory network affected by kaempferol, and this approach will be useful for elucidating gene-phytochemical interactions.

Expression level of metastasis-associated protein 1 (MTA1) is closely related to tumor growth and metastasis in various cancers. Although increased expression level of MTA1 was observed in hepatocellular carcinoma (HCC), role of MTA1 complex containing histone deacetylase (HDAC) in hepatitis B virus (HBV)-associated hepatocarcinogenesis has not been studied. Here, we demonstrated that HBx strongly induced the expression of MTA1 and HDAC1 genes at transcription level. MTA1 and HDAC1/2 physically associated with hypoxia-inducible factor-1 alpha (HIF-1 alpha) in vivo in the presence of HBx, which was abolished by knockdown of MTA1 by short interfering RNA (siRNA). HBx induced deacetylation of the oxygen-dependent degradation domain of HIF-1 alpha, which was accompanied with dissociation of prolyl hydroxylases and von Hippel-Lindau tumor suppressor from HIF-1 alpha. These results indicate that HBx-induced deacetylation is important for proteasomal degradation of HIF-1 alpha. Further, we observed that protein levels of MTA1 and HDAC1 were increased in the liver of HBx-transgenic mice. Also, there was a higher expression of HDAC1 in HCC than in the adjacent non-tumorous cirrhotic nodules in 10 out of 12 human HBV-associated HCC specimens. Together, our data indicate a positive cross talk between HBx and the MTA1/HDAC complex in stabilizing HIF-1 alpha, which may play a critical role in angiogenesis and metastasis of HBV-associated HCC.

Formaldehyde has been identified as the most prevalent cause of sick building syndrome (SBS), which has become a major social problem, especially in developing urban areas. However, studies on the molecular mechanisms associated with formaldehyde toxicity have been limited, probably because it is difficult to relate the experimental results obtained from in vitro studies to human exposure in vivo. Using polymerase chain reaction-based suppression subtractive hybridization, we recently identified 27 different formaldehyde-inducible genes including platelet-derived growth factor receptor alpha gene (PDGFRA) and mouse double minute 2 (MDM2) gene which were increased significantly in both formaldehyde-exposed human trachea cells, 680. Tr, and rat tracheas. To establish a possible relationship between induction of these formaldehyde-inducible genes and symptoms of SBS, we examined expression levels of these genes in peripheral lymphocytes of residents of new apartments. Here, we report that the expression of PDGFRA and MDM2 transcripts was significantly higher in peripheral blood lymphocytes obtained from 15 residents in new buildings than in seven control individuals. Our results suggest that the elevated levels of PDGFRA and MDM2 may be associated with the formaldehyde-induced pathophysiology that is closely related with SBS, and that they deserve evaluation as potential biomarkers for formaldehyde intoxication.

Differentiation of sebocytes is strongly associated with enhanced lipid synthesis and accumulation in the cells. Liver X receptors (LXRs) are members of the nuclear receptor superfamily, which play a critical role in cholesterol homeostasis and lipid metabolism. We examined whether LXRalpha regulated lipid synthesis in the immortalized human sebaceous gland cell line SZ95. When the SZ95 sebocytes were treated with the ligand of LXR such as TO901317 or 22(R)-hydroxycholesterol, lipid droplets were accumulated in the majority of cells when examined by Oil Red O staining. The expression of the known LXR targets, such as fatty acid synthase and sterol regulatory-binding protein-1, was induced by TO901317. TO901317 treatment increased expression of LXRalpha but not that of LXRbeta. Transfection of antisense LXRalpha significantly decreased TO901317-induced target gene expression and lipid droplet accumulation, suggesting a major role of LXRalpha in differentiation of sebocytes. Further, TO901317 decreased the expression of cyclooxygenase-2 and inducible nitric oxide synthase that was induced by lipopolysaccharide treatment. Together, these results indicate that important roles of LXRalpha in differentiation and inflammatory signaling in sebaceous glands. Thus, we suggest that LXR ligands could provide a new class of therapeutic agents for sebaceous gland-associated disorders such as seborrhea and acne.

Formaldehyde is frequently used in indoor household and occupational environments. Inhalation of formaldehyde invokes an inflammatory response, including a variety of allergic signs and symptoms. Therefore, formaldehyde has been considered as the most prevalent cause of sick building syndrome, which has become a major social problem, especially in developing urban areas. Further formaldehyde is classified as a genotoxicant in the respiratory tract of rats and humans. To better understand the molecular mechanisms involved in formaldehyde intoxication, we sought differentially regulated genes by formaldehyde exposure to Hs 680.Tr human trachea cells, using polymerase chain reaction (PCR)-based suppression subtractive hybridization. We identified 27 different formaldehyde-inducible genes, including those coding for the major histocompatibility complex, class IA, calcyclin, glutathione S-transferase pi, mouse double minute 2 (MDM2), platelet-derived growth factor receptor alpha, and which are known to be associated with cell proliferation and differentiation, immunity and inflammation, and detoxification. Induction of these genes by formaldehyde treatment was confirmed by reverse transcription PCR and western blot analysis. Further, the expression of calcyclin, glutathione S-transferase pi, PDGFRA and MDM2 were significantly induced in the tracheal epithelium of Sprague Dawley rats after formaldehyde inhalation. Our results suggest that the elevated levels of these genes may be associated with the formaldehyde-induced toxicity, and that they deserve evaluation as potential biomarkers for formaldehyde intoxication.

Valproic acid (VPA) is used clinically to treat epilepsy, however it induces hepatotoxicity such as microvesicular steatosis. Acute hepatotoxicity of VPA has been well documented by biochemical studies and microarray analysis, but little is known about the chronic effects of VPA in the liver. In the present investigation, we profiled gene expression patterns in the mouse liver after subchronic treatment with VPA. VPA was administered orally at a dose of 100 mg/kg/day or 500 mg/kg/day to ICR mice, and the livers were obtained after 1, 2, or 4 weeks. The activities of serum liver enzymes did not change, whereas triglyceride concentration increased significantly. Microarray analysis revealed that 1325 genes of a set of 32,996 individual genes were VPA responsive when examined by two-way ANOVA (P0.05) and fold change (1.5). Consistent with our previous results obtained using an acute VPA exposure model (Lee et al., Toxicol Appl Pharmacol. 220:45-59, 2007), the most significantly over-represented biological terms for these genes included lipid, fatty acid, and steroid metabolism. Biological pathway analysis suggests that the genes responsible for increased biosynthesis of cholesterol and triglyceride, and for decreased fatty acid beta-oxidation contribute to the abnormalities in lipid metabolism induced by subchronic VPA treatment. A comparison of the VPA-responsive genes in the acute and subchronic models extracted 15 commonly altered genes, such as Cyp4a14 and Adpn, which may have predictive power to distinguish the mode of action of hepatotoxicants. Our data provide a better understanding of the molecular mechanisms of VPA-induced hepatotoxicity and useful information to predict steatogenic hepatotoxicity.

Inhibitor of DNA binding 1 (Id-1) has been implicated in tumor angiogenesis by regulating the expression of vascular endothelial growth factor (VEGF), but its molecular mechanism has not been fully understood. Here, we show the cross talk between Id-1 and hypoxia-inducible factor-1α (HIF-1α), that Id-1 induces VEGF by enhancing the stability and activity of HIF-1α in human endothelial and breast cancer cells. Although both the transcript and proteins levels of VEGF were induced by Id-1, only the protein expression of HIF-1α was induced without transcriptional changes in both human umbilical endothelial cells and MCF7 breast cancer cells. Such induction of the HIF-1α protein did not require de novo protein synthesis but was dependent on the active extracellular response kinase (ERK) pathway. In addition, stability of the HIF-1α protein was enhanced in part by the reduced association of the HIF-1α protein with von Hippel-Lindau protein in the presence of Id-1. Furthermore, Id-1 enhanced nuclear translocation and the transcriptional activity of HIF-1α. Transcriptional activation of HIF-1–dependent promoters was dependent on the active ERK pathway, and the association of HIF-1α protein with cyclic AMP-responsive element binding protein was enhanced by Id-1. Finally, Id-1 induced tube formation in human umbilical endothelial cells, which also required active ERK signaling. In conclusion, we provide the molecular mechanism of the cross talk between HIF-1α and Id-1, which may play a critical role in tumor angiogenesis. (Mol Cancer Res 2007;5(4):321–9)

This study evaluated HIF-1 alpha inhibitors under different hypoxic conditions, physiological hypoxia (5% O-2) and severe hypoxia (0.1% O-2). We found that chenodeoxy cholic acid (CDCA) reduced the amount of HIF-1 alpha protein only under physiological hypoxia but not under severe hypoxia without decreasing its mRNA level. By using a proteasome inhibitor MG132 and a translation inhibitor cyclohexamide, we showed that CDCA reduced HIF-1 alpha protein by decreasing its translation but not by enhancing its degradation. The following findings indicated that farnesoid X receptor (FXR), a CDCA receptor and its target gene, Small heterodimer partner (SHP) are not involved in this effect of CDCA. Distinctly from CDCA, MG132 prevented SHP and an exogenous FXR agonist, GW4064 from reducing HIF-1 alpha protein. Furthermore a FXR antagonist, guggulsterone failed to prevent CDCA from decreasing HIF-1 alpha protein. Furthermore, guggulsterone by itself reduced HIF-1 alpha protein even in the presence of MG132. These findings suggested that CDCA and guggulsterone reduced the translation of HIF-1 alpha in a mechanism which FXR and SHP are not involved. This study reveals novel therapeutic functions of traditional nontoxic drugs, CDCA and guggulsterone, as inhibitors of HIF-1 alpha protein.

Microarray analysis of RNA from d-galactosamine (GalN)-administered mouse livers was performed to establish a global gene expression profile during injury and regeneration stages at two different doses. A single dose of GalN at 266 or 26.6 mg/kg body weight was given intraperitoneally, and the liver samples were obtained after 6, 24, and 72 h. Histopathologic studies enabled the classification of the d-galactosamine effect into injury (6, 24 h) and regeneration (72 h) stages. By using the Applied Biosystems mouse genome survey microarray, a total of 7267 out of 33,315 (21.8%) genes were found to be statistically reliable at p < 0.05 by two-way ANOVA, and 1469 (4.4%) probes at false discovery rate

The expression of metastasis-associated protein 1 (MTA1) correlates well with tumor metastases; however, the associated molecular mechanism is not fully understood. Here, we explored the possibility of cross-talk between MTA1 and hypoxia-inducible factor-1alpha (HIF-1alpha), a key regulator of angiogenic factors. We observed that the expression of MTA1 was strongly induced under hypoxia in breast cancer cell lines such as MCF-7 and MDA-MB-231. When MTA1 was overexpressed, the transcriptional activity and stability of HIF-1alpha protein were enhanced. MTA1 and HIF-1alpha are physically associated in vivo and they were localized completely in the nucleus when coexpressed. MTA1 induced the deacetylation of HIF-1alpha by increasing the expression of histone deacetylase 1 (HDAC1). MTA1 counteracted to the action of acetyltransferase, ARD1, and it did not stabilize the HIF-1alpha mutant that lacks the acetylation site, K532R. These results indicate that acetylation is the major target of MTA1/HDAC1 function. Collectively, our data provide evidence of a positive cross-talk between HIF-1alpha and MTA1, which is mediated by HDAC1 recruitment, and indicate a close connection between MTA1-associated metastasis and HIF-1-induced tumor angiogenesis.

The binding of sphingoid bases to peroxisome proliferator-activated receptor (PPAR) has been detected in a solid-phase binding assay. However, sphingoid base-induced changes in PPAR transactivation activity have not been examined. In this report, we show by reporter gene analyses that phytosphingosine (PS), a natural sphingoid base, activates the transcriptional activity of PPARs in the immortalized human keratinocyte, HaCaT. Real-time PCR analyses showed that the mRNA level of PPARgamma was increased after PS treatment in HaCaT cells in a dose- and time-dependent manner. Because PPARs play important roles in skin barrier homeostasis by regulating epidermal cell growth, terminal differentiation, and inflammatory response, we examined the effect of PS on normal human epidermal keratinocytes (NHEKs) and mouse skin. PS increased the production of cornified envelope in NHEKs by approximately 1.8-fold compared with controls. Epidermal differentiation marker proteins such as involucrin, loricrin, and keratin1 were also increased in PS-treated NHEKs, by ELISA or Western blotting analysis. A [(3)H]thymidine incorporation assay showed that PS inhibited DNA synthesis in NHEKs to 20% compared with controls. The antiproliferative and anti-inflammatory effects of PS were examined in a mouse model of irritant contact dermatitis produced by topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA). PS blocked epidermal thickening and edema and the infiltration of inflammatory cells into the dermis in the skin of TPA-treated hairless mice. The anti-inflammatory effects of PS were confirmed by the observation that PS blocked the TPA-induced generation of prostaglandin E(2) in peripheral mononuclear leukocytes. Taken together, our results provide an insight into the multiple regulatory roles of PS in epidermal homeostasis, and furthermore point to the potential use of PS as a therapeutic agent in the treatment of inflammatory and proliferative cutaneous diseases.

A presynaptic membrane disturbance is an essential process for the release of various neurotransmitters. Ceramide, which is a tumor suppressive lipid, has been shown to act as a channel-forming molecule and serve as a precursor of ceramide-1-phosphate, which can disturb the cellular membrane. This study found that while permeable ceramide increases the rate of dopamine release in the presence of a Ca(2+)-ionophore, A23187, permeable ceramide-1-phosphate provoked its release even without the ionophore. The treatment of PC12 cells with the ionophore at concentrations < 2 microM produced ceramide via the sphingomyelin (SM) pathway with a concomitant release of dopamine, and no cell damage was observed. The addition of a Ca(2+) chelator, EGTA, to the medium inhibited the increase in the release of both the ceramide and dopamine. This suggests that ceramide might be produced by Ca(2+) and is implicated in the membrane disturbance associated with the release of dopamine as a result of its conversion to ceramide-1-phosphate. Consistent with these results, this study detected a membrane-associated and neutral pH optimum sphingomyelinase (SMase) whose activity was increased by Ca(2+). Together, these results demonstrate that ceramide can be produced via the activation of a neutral form of SMase through Ca(2+), and is involved in the dopamine release in concert with Ca(2+).

Nur77, an orphan nuclear receptor, has been implicated in apoptosis of a variety of cell types, including hepatocytes. The small heterodimer partner (SHP) binds and inhibits the function of many nuclear receptors. Here, we investigated cross-talk between Nur77 and SHP during anti-Fas antibody (CH11)-mediated apoptosis of hepatic cells. Expression of SHP decreased, whereas antisense SHP enhanced, the transcriptional activity of Nur77 in HepG2 cells. SHP and Nur77 were physically associated in vivo and colocalized in the nucleus. SHP decreased the transactivation function of the N-terminal domain of Nur77 that recruits coactivators. Nur77 and SHP competitively bound to cAMP response element-binding protein-binding protein and the expression of coactivators, such as cAMP response element-binding protein-binding protein and activating signal cointegrator-2, recovered the decreased function of Nur77 caused by SHP. Finally, SHP was differentially expressed in hepatoma cell lines in that it was not detected in the interferon-gamma (IFNgamma)/CH11-sensitive SNU354, whereas it was significantly expressed in the IFNgamma/CH11-resistant HepG2. Interestingly, a stable SNU354 cell line that expressed SHP became resistant to the IFNgamma/CH11-induced apoptosis. Together, our results suggest that SHP plays a key role in the regulation of Nur77 activation and thereby in Nur77-mediated apoptosis in the liver.

Hypoxia-inducible factor-1alpha (HIF-1alpha) plays a central role in oxygen homeostasis by inducing the expression of a broad range of genes in a hypoxia-dependent manner. Here, we show that the orphan nuclear receptor Nur77 is an important regulator of HIF-1alpha. Under hypoxic conditions, Nur77 protein and transcripts were induced in a time-dependent manner. When Nur77 was exogenously introduced, it enhanced the transcriptional activity of HIF-1, whereas the dominant negative Nur77 mutant abolished the function of HIF-1. The HIF-1alpha protein was greatly increased and completely localized in the nucleus when coexpressed with Nur77. The N-terminal transactivation domain of Nur77 was required and sufficient for the activation of HIF-1alpha. The association of HIF-1alpha with von Hippel-Lindau protein was not affected, whereas that with mouse double minute 2 (MDM2) was greatly reduced in the presence of Nur77. Further we found that the expression of MDM2 was repressed at transcription level in the presence of Nur77 as well as under hypoxic conditions. Finally, PD98059 decreased Nur77-induced HIF-1alpha stability and recovered MDM2 expression, indicating that the extracellular signal-regulated kinase pathway is critical in the Nur77-induced activation of HIF-1alpha. Together, our results demonstrate a novel function for Nur77 in the stabilization of HIF-1alpha and suggest a potential role for Nur77 in tumor progression and metastasis.

Hepatitis B virus X protein (HBx) of the hepatitis B virus is strongly implicated in angiogenesis and metastasis during hepatocarcinogenesis. Previously, we reported that HBx enhances activity of hypoxia-inducible factor-1alpha (HIF-1alpha), a potent transactivator that induces angiogenic factors. Here, we delineate the structural region of HBx that potentiates HIF-1alpha. The carboxy-terminus of HBx increased the stability of HIF-1alpha protein, probably through inhibiting interaction with von Hippel-Lindau protein. Further, the carboxy-terminus of HBx enhanced the transactivation function of HIF-1alpha by enhancing its association with CREB binding protein (CBP). Finally, we demonstrated the physical association of HBx with the basic helix-loop-helix/PER-ARNT-SIM domain, the inhibitory domain, and the carboxy-terminal transactivation domain of HIF-1alpha in vivo.

Cadmium is an environmentally widely dispersed and highly toxic heavy metal that has been classified as a human carcinogen. Using the suppression subtractive hybridization technique, we identified previously 29 cadmium-inducible genes, primarily involved in inflammation, cell survival and apoptosis. Among these genes, we are particularly interested in Nor-1, because this gene belongs to the Nur77 family, which plays a key role in the apoptotic processes of a variety of cells and tissues, including the lung. In the present study, we characterized the induction of the Nur77 family genes in the lungs after cadmium exposure. Nur77, Nor-1 and Nurr1 were all induced after cadmium treatment in a dose- and time-dependent manner in WI-38 and A549 lung cell lines. Treatment with inhibitors of signaling pathways, such as PD98059 and H89, almost completely blocked the expression of Nur77, indicating that the extracellular signal-regulated kinase and protein kinase A signaling pathways are important in cadmium-induced Nur77 expression. When a plasmid encoding dominant-negative Nur77 was transfected into A549 cells, cadmium-induced apoptotic changes, such as chromosomal condensation and Bax expression, were significantly reduced, suggesting that the expression of Nur77 plays an important role in cadmium-induced apoptosis. Furthermore, the number of apoptotic cells and the expression of Nur77 was increased in lung tissues collected from cadmium-treated (30 micromol/kg body wt) Wistar rats. Taken together, these results demonstrate that cadmium induces the expression of Nur77 family genes, leading to apoptosis in lung cells, which may cause pulmonary toxicity in response to cadmium exposure.

Although evidences are emerging that dietary isoflavones have beneficial effects in treatment of hyperlipidemia and cardiovascular diseases, the underlying molecular mechanism has not yet been extensively characterized. In this report, we showed that genistein, one of the major isoflavones, increased expression of genes involved in lipid catabolism such as carnitine palmitoyltransferase 1, liver form (CPT1L) in HepG2 cells, when assayed by real-time reverse-transcriptase polymerase chain reactions as well as Western blotting analysis. The increase in mRNA-level of CPT1L after genistein treatment was not changed in the presence of ICI182780, a potent inhibitor of estrogen receptor, suggesting that this effect of genistein was estrogen receptor-independent. Since these genes involved in fatty acid catabolism are considered putative downstream target genes of peroxisome proliferators-activated receptor alpha (PPARalpha), we examined whether expression of PPARalpha was modulated by genistein treatment. Interestingly, genistein induced expression of PPARalpha at both mRNA- and protein-level. Further, genistein activated transcriptional activity of PPARalpha, when determined by reporter gene analysis, suggesting genistein as a potential ligand for PPARalpha. Taken together, this study provides a picture of the regulatory action of genistein, as an activator of PPARalpha in fatty acid catabolism and potential use of genistein as lipid-lowering agent.

HBx (hepatitis B virus X) viral oncoprotein is a multifunctional protein of which the cellular level may be one of the important factors in determining HBV-mediated pathological progression of liver diseases, chronic hepatitis, and hepatocellular carcinoma. Our previous work revealed that adriamycin, a chemotherapeutic agent, caused a marked increase in the intracellular level of HBx by retarding its rapid degradation. In the present study, modulation of HBx expression was found to be confined to adriamycin but not to other chemotherapeutic agents, cisplatin and 5-fluorouracil. Interestingly, adriamycin caused a rapid increase of reactive oxygen species (ROS) and its accumulation continued until 24h. In contrast, two other agents had little effect on ROS generation, suggesting the possible involvement of ROS in the HBx regulation. In fact, direct addition of H(2)O(2) to the cells significantly increased the level of HBx protein in HBx-expressing ChangX-34 cells as well as in hepatitis B virus-related hepatoma cells, PLC/PRF/5 and HepG2.2.15 cells. Furthermore, antioxidants, N-acetyl-cysteine and pyrrolidinedithiocarbamate (PDTC), completely abolished the increase of HBx protein induced by adriamycin, indicating that adriamycin modulates the intracellular HBx level via ROS generation. Together, these findings provide a novel aspect of HBx regulation by cellular ROS level. Therefore, intracellular microenvironments generating ROS such as severe inflammation may aggravate the pathogenesis of liver disease by accumulating the HBx level.

We previously reported that the retinoic acid (RA) insensitivity of RARbeta induction is a general feature of human colon cancer cells (Biochem. Pharmacol., 59: 485-496, 2000). In the present investigation, we analyzed potential transcriptional defects associated with the expression of the RARbeta gene in colon cancer cells. Transfection of reporter constructs containing the RARbeta gene promoter as well as truncated fragments of the promoter showed a significant induction of reporter activity by RA treatment in RA-sensitive HCT-15 cells, but not in RA-resistant DLD-1 cells. The results suggest that the transcriptional defect of RARbeta expression may not be due to the presence of a specific cis-element in the RARbeta promoter. Next we examined whether coactivators and core-pressors of nuclear receptors were involved in the RA sensitivity of colon cancer cells. Transfection of coactivators such as CREB binding protein (CBP) and p300 up-regulated the RA-responsive element present in the RARbeta promoter (betaRARE) in DLD-1 cells up to the level in HCT-15, while coexpression of the nuclear receptor corepressor (NCoR) suppressed the betaRARE activity in HCT-15 cells. The expression level of CBP protein was consistently higher in HCT-15, while that of NCoR and Sin3A was higher in DLD-1 cells. Treatment with the histone deacetvlase inhibitor trichostatin A (TSA) increased both basal and RA-induced betaRARE activity in DLD-1, indicating that histone deacetylase is involved in the regulation of RARbeta gene expression. Taken together, our results show that differential function of coactivators and corepressors may determine the level of RARbeta induction that may mediate retinoid action in colon cancer cells.

Background/Aims : The hepatitis B virus X protein (HBx), a major viral transactivator, is implicated in hepatic inflammation, since it induces many pro-inflammatory cytokines at transcriptional level. The aim of this study was to investigate role of HBx in expression of interleukin 18 (IL-18), a newly identified cytokine that up-regulates Fas ligand (FasL) expression. Methods : Chang X-34 that expressing HBx under the control of a doxycycline-inducible promoter, and hepatitis B virus (HBV)-integrated hepatoma cell lines were examined for IL-18 expression by Northern and Western blotting analysis. To test the role of IL-18 produced by hepatoma cells, FasL expression was examined by flow cytometry after treatment with neutralizing anti-IL-18 antibodies. Further, IL-18 expression was examined in the liver tissues of HBx-transgenic mice. Results : Induction of IL-18 following HBx expression in Chang X-34 and the pattern of IL-18 expression in HBV-integrated cell lines, implicated that HBx transcriptionally induces IL-18 expression. Neutralizing anti-IL-18 antibodies blocked the expression of FasL, suggesting that IL-18 plays a critical role in FasL expression. Further, IL-18 expression in the HBx-transgenic liver, was correlated with the degree of hepatitis. Conclusions : Our results demonstrated that HBx induces IL-18 expression in liver, which may be associated with hepatic injury by amplifying FasL expression during HBV infection.

Retinoids are potent immune modulators that inhibit Fas ligand (FasL) expression and thereby repress the activation-induced apoptosis of immature thymocytes and T-cell hybridomas. In this study, we demonstrate that all-trans-retinoic acid (all-trans-RA) directly represses the transcriptional activity of the nuclear factors of activated T-cells (NFAT), which is an important transactivator of the FasL promoter. The analysis of reporter constructs containing the FasL promoter and wild-type or mutant NFAT binding-sites indicated that all-trans-RA repression was mediated via an NFAT binding element located in the promoter. A reporter construct comprising the NFAT binding sequence linked to a heterologous SV-40 promoter showed that NFAT transcriptional activity was significantly inhibited by all-trans-RA. Furthermore, all-trans-RA inhibited activation of the distal NFAT binding motif present in the interleukin (IL)-2 promoter, suggesting that the inhibition of NFAT function by all-trans-RA was not specific to the FasL promoter. Gel shift assays corroborated the results of the gene reporter studies by showing that all-trans-RA decreased the NFAT binding to DNA. All-trans-RA blocked translocation of NFATp from the cytosol into the nucleus, which was induced by PMA/ionomycin treatment in HeLa cells transfected with a Flag-tagged NFATp. Taken together, our results indicate that FasL inhibition by all-trans-RA involves a novel mechanism whereby the transcriptional function of NFAT is blocked.

Nur77 (NGFI-B) is an orphan nuclear receptor that has been implicated in activation-induced T-cell apoptosis. Retinoids, potent immune modulators, were shown to inhibit the activation-induced apoptosis of immature thymocytes and T-cell hybridomas. To illustrate the mechanism of the inhibition, we examined the effects of retinoic acid (RA) on the expression and transactivation functions of Nur77 in the human peripheral blood mononuclear cells and the human T-cell leukemia, Jurkat. All- trans -RA remarkably repressed the DNA binding and transcriptional induction of Nur77. Among the two potential trans -acting factors that activate Nur77 gene promoter, i.e., AP-1 and related serum response factor (RSRF), all- trans -RA repressed DNA binding and reporter gene activity of AP-1 but not that of RSRF, suggesting that the inhibition may be mediated through AP-1. We also demonstrated a posttranscriptional regulation of Nur77 function by retinoid receptors by showing that transactivation activity of Nur77 was significantly inhibited by cotransfection of RARα or RXRα. Nur77 bound RARα or RXRα in both yeast and mammalian two-hybrid tests, suggesting that direct protein–protein interaction between these receptors may mediate the inhibition. Taken all together, we demonstrated that RA repressed Nur77 function through multiple mechanisms that may provide the basis for RA inhibition on the apoptosis of activated T-lymphocytes.

To elucidate the molecular action of the NFkappaB inhibitor IkappaBbeta, we isolated a number of IkappaBbeta interactors using the yeast two-hybrid system. These include the retinoid X receptor (RXR), whose interaction with IkappaBbeta is significantly stimulated by the RXR ligand 9-cis-retinoic acid, as shown in the yeast system as well as the glutathione S-transferase pull down assays. RXR is a nuclear protein, whereas IkappaBbeta accumulates in the nucleus only in cells stimulated with lipopolysaccharide or other inducers that result in prolonged activation of NFkappaB. Consistent with this, cotransfection with IkappaBbeta specifically repressed the 9-cis-RA-induced transcriptional activities of RXR in an lipopolysaccharide-dependent manner. These results suggest a novel IkappaBbeta-mediated antagonism between the signaling pathways of NFkappaB and RXR.

The diverse function of retinoic acid (RA) is mediated by its nuclear receptors, the retinoic acid receptors (RARs) and retinoid X receptors (RXRs). However, the RA response is often lost in cancer cells that express the receptors. Previously, it was demonstrated that the RA response is regulated by the COUP-TF orphan receptors. Here, we present evidence that nur77, another orphan receptor whose expression is highly induced by phorbol esters and growth factors, is involved in modulation of the RA response. Expression of nur77 enhances ligand-independent transactivation of RA response elements (RAREs) and desensitizes their RA responsiveness. Conversely, expression of COUP-TF sensitizes RA responsiveness of RAREs by repressing their basal transactivation activity. Unlike the effect of COUP-TFs, the function of nur77 does not require direct binding of nur77 to the RAREs, but is through interaction between nur77 and COUP-TFs. The interaction occurs in solution and results in inhibition of COUP-TF RARE binding and transcriptional activity. Unlike other nuclear receptors, a large portion of the carboxy-terminal end of nur77 is not required for its interaction with COUP-TF. In human lung cancer cell lines, COUP-TF is highly expressed in RA-sensitive cell lines while nur77 expression is associated with RA resistance. Stable expression of COUP-TF in nur77-positive, RA-resistant lung cancer cells enhances the inducibility of RARbeta gene expression and growth inhibition by RA. These observations demonstrate that a dynamic equilibrium between orphan receptors nur77 and COUP-TF, through their heterodimerization that regulates COUP-TF RARE binding, is critical for RA responsiveness of human lung cancer cells.

Numerous factors that promote movement of macromolecules in and out of the nucleus have now been identified. These include both soluble cytoplasmic and nucleoplasmic proteins and proteins of the nuclear pore complex (NPC). Genetic analyses of the nuclear transport process in the model organism, the budding yeastSaccharomyces cerevisiae,have revealed remarkable conservation of all of these factors. In addition, important clues as to how these factors promote the unique bidirectional movement across the NPC have emerged from studies of yeast. We summarize the characterization and genetic interactions of the soluble transport factors and present data to illustrate how genetic experiments can be used to further define the import and export pathways.

Retinoids regulate a broad range of biological processes through two subfamilies of nuclear retinoid receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs). Recently, we reported a novel type of retinoic acid antagonist (SR11335) and showed that this compound can inhibit retinoic acid (RA)-induced activation of a human immunodeficiency virus type 1 (HIV-1) promoter construct that contains a special RA response element (RARE). We have now further characterized the antagonism mediated by SR11335 and of newly synthesized structurally related compounds. Two compounds, SR11330 and SR11334, which are poor transactivators, also showed antagonist activities, inhibiting all-trans-RA (tRA) and 9-cis-RA. The retinoids inhibited transcriptional activation of RAR/RXR heterodimers effectively, while inhibition of RXR homodimers was less efficient. Inhibition was observed on several RAREs, including the TREpal, betaRARE, apoAI-RARE, and CRBPI-RARE. In addition, the antagonists inhibited tRA-induced differentiation of HL-60 cells. The antagonist did not interfere with DNA binding of the receptors. In limited proteolytic digestion assays, SR11335 induced resistance of the receptors to proteolysis, but the pattern of the degradation was not altered from that induced by tRA, suggesting that these antagonists induce their biological effects by competing with agonists for binding to RARs, thereby preventing the induction of conformational changes of the receptors necessary for transcriptional activation.

Retinoids are known to inhibit the growth of hormone-dependent but not that of hormone-independent breast cancer cells. We investigated the involvement of retinoic acid (RA) receptors (RARs) in the differential growth-inhibitory effects of retinoids and the underlying mechanism. Our data demonstrate that induction of RAR beta by RA correlates with the growth-inhibitory effect of retinoids. The hormone-independent cells acquired RA sensitivity when the RAR beta expression vector was introduced and expressed in the cells. In addition, RA sensitivity of hormone-dependent cells was inhibited by a RAR beta-selective antagonist and the expression of RAR beta antisense RNA. Introduction of RAR alpha also restored RA sensitivity in hormone-independent cells, but this restoration was accomplished by the induction of endogenous RAR beta expression. Furthermore, we show that induction of apoptosis contributes to the growth-inhibitory effect of RAR beta. Thus, RAR beta can mediate retinoid action in breast cancer cells by promoting apoptosis. Loss of RAR beta, therefore, may contribute to the tumorigenicity of human mammary epithelial cells.

Retinoids, the natural and synthetic vitamin A derivatives, are known to inhibit the proliferation of lung cancer and breast cancer cells and the growth of carcinogen-induced bronchogenic squamous cell carcinoma and mammary tumors, and have been used as chemoprevention agents against both types of cancer. However, clinical trials of retinoids in patients with advanced lung cancer and breast cancer have not been successful. In studying how retinoid sensitivity is lost in cancer cells, we have found that lack of the retinoic acid receptor beta (RAR beta) gene expression and its abnormal regulation by retinoic acid (RA) are common features in human lung cancer and breast cancer cells. The absence and abnormal RA regulation of RAR beta correlates with the loss of anti-proliferation effect of RA in hormone-independent breast cancer cells, and is due to different abnormalities found in cancer cells. Furthermore, expression of RAR beta gene in hormone-independent breast cancer cells restores their RA sensitivity. These data demonstrate that RAR beta can mediate the growth inhibitory effect of RA and suggest that the lack of RAR beta may contribute to retinoid resistance in certain cancer cells.

The natural retinoid 9-cis-retinoic acid is an activating ligand for both the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs), which are members of the retinoid/thyroid hormone/steroid hormone family of nuclear receptor proteins that activate gene transcription through specific response elements. The pharmacophoric groups necessary to confer RXR selectivity were established by evaluating the ability of 21 conformationally restricted retinoids to activate the TREpal retinoic acid receptor response element for gene transcription in the presence of one of the three RAR subtypes or RXR alpha. In contrast to those retinoids selective for the RARs, these RXR-selective retinoids have one less atom in the bridge linking the hydrophobic and carboxylic acid termini of the retinoid skeleton. Therefore, a one-carbon bridge replaces the 19-methyl group and 9E-double bond of 9-cis-retinoic acid and is further functionalized by inclusion in an isopropylidene group, a dioxolane ring, or a cyclopropane ring for optimal RXR alpha activity and selectivity. In addition, the beta-geranylidene and 20-methyl-(11E,13E)-dienoic acid groups of 9-cis-retinoic acid are replaced by a 5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl ring and a 4-carboxylphenyl ring, respectively, for optimal activation and selectivity. RXR alpha selectivity is reduced on replacement of the 4-carboxylphenyl group by a 2-carboxyl-5-thienyl group or the 9-cis-retinoic acid methylpentadienoic acid terminus.

Expression of metastasis-associated protein 1 (MTA1) gene correlates with the degree of invasion and metastasis in hepatocellular carcinoma (HCC). Expression of MTA1 is induced by hepatitis B virus X protein (HBx); however, little is known about the transcriptional regulation of MTA1 gene expression. Here, we report that the 5′-flanking region of the human MTA1 promoter contains two CpG islands. Transient expression of HBx in Chang liver cells increased the methylation of the CpG island1 from 18 to 49% when measured by bisulfite-modified direct sequencing. Chromatin immunoprecipitation showed that HBx recruited DNA methyltransferase 3a (DNMT3a) and DNMT3b to the CpG island1. In silico analysis of CpG island1 predicted the existence of putative p53-binding sequences. p53 was pulled down by a DNA probe encoding the p53-binding sequences but not by the methylated DNA probe. The mouse MTA1 promoter also contains a CpG island encoding a p53-binding sequence of which p53 binding was decreased in the presence of HBx, and the expression of MTA1 and DNMT3 was increased in the liver of HBx-transgenic mice. Comparison of MTA1 and DNMT3a expression in the human normal liver and HCC specimens produced a significant correlation coefficient >0.5 (r=0.5686, P=0.0001) for DNMT3a, and a marginally significant coefficient (r=0.3162, P=0.0103) for DNMT3b. These data show that HBx induces methylation of CpG island in the MTA1 promoter, which interferes with DNA binding of p53 in the specific DNA region. This result may explain the molecular mechanism responsible for the induction of MTA1 gene expression by HBx.

Hepatitis B virus (HBV) is strongly associated with the development of hepatocellular carcinoma (HCC). Among the HBV viral proteins, X protein (HBx) is regarded as a major risk factor of HCC. HBx contributes to HCC development through regulating expression of many host or viral genes and interacting with other cellular proteins. In this study, proteins that interact with HBx were analyzed by immunoprecipitation and subsequent LC/MS/MS. We identified 60 HBx interacting proteins that function in a wide spectrum of biology. Among these proteins, we were interested in PARP1, Poly (ADP-ribose) polymerase, a crucial factor in base excision repair (BER) pathway, since HBx was known to inhibit DNA repair capacity in cancer cells. Therefore, we characterized the cross-talk between HBx and PARP-1. HBx and PARP-1 colocalized in the nucleus and they are physically associated. Coimmunoprecipitation experiments revealed that the catalytic domain of PARP-1 bound to HBx. Chromatin immunoprecipitation showed that HBx inhibited the recruitment of DNA damage induced by paraquat treatment. HBx overexpression significantly inhibited the protein expression of the DNA damage response factors that respond to the paraquat-induced oxidative stress. Finally, HBx further enhanced the level of 8-OHdG, the marker of DNA damage, under oxidative stress. Together, these data suggest that the interaction between HBx and PARP1 inhibits DNA repair, which could result in onset of hepatocarcinogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2120. doi:1538-7445.AM2012-2120

Although metastasis-associated protein 1 (MTA1) is known to play roles in angiogenesis and metastasis in various human cancers, the molecular mechanism of regulation of MTA1 gene expression remains unclear. Therefore, we searched potential regulators of MTA1 expression in this study. Treatment of 5-fluorouracil (5-FU), a traditional anti-cancer drug in HepG2, MCF7 and LNCaP cells, expressing wild-type p53, decreased the protein and mRNA expression of MTA1. However, the MTA1 expression levels were not altered in response to 5-FU treatment in Hep3B, MDA-MB-231 and PC3 cells which lack functional p53. The specific knockdown of p53 in HepG2 and MCF7 cells recovered the level of MTA1 after 5-FU treatment. This observation indicates that p53 mediates the repression of MTA1. Next, we virtually analyzed the promoter region of the human MTA1 gene and identified several potential consensus binding sequences of p53. Indeed, chromatin immunoprecipitation and pull-down assays showed that p53 directly bound to the MTA1 promoter region. These findings suggest that p53 is transcriptionally associated with regulation of MTA1 gene expression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 210. doi:10.1158/1538-7445.AM2011-210