Pregnane X Receptor Expression in Human Pancreatic Adenocarcinoma: Associations With Clinicopathologic Parameters, Tumor Proliferative Capacity, Patients' Survival, and Retinoid X Receptor Expression

OBJECTIVES

Pregnane X receptor (PXR) has been involved in human malignancy, either by directly affecting carcinogenesis or by inducing drug-drug interactions and chemotherapy resistance. The present study aimed to assess the clinical significance of PXR in pancreatic adenocarcinoma.

METHODS

Pregnane X receptor and its heterodimers' PXR/retinoid X receptor α (RXR-α), RXR-β, and RXR-γ expression were assessed immunohistochemically on tumoral samples from 55 pancreatic adenocarcinoma patients and were associated with clinicopathologic parameters, tumor proliferative capacity, and patients' survival.

RESULTS

Enhanced PXR expression was noted in 24 (43.6%) of 55 pancreatic adenocarcinoma cases. Pancreatic adenocarcinoma patients presenting increased histological grade of tumor differentiation showed a significant increased incidence of elevated PXR expression (P = 0.023). Enhanced PXR/RXR-β expression was significantly associated with smaller tumor size and earlier clinical stage (P = 0.005 and P = 0.003, respectively). Elevated PXR/RXR-γ expression was significantly associated with smaller tumor size and earlier clinical stage (P = 0.012 and P = 0.014, respectively) and borderline with the absence of lymph node metastases (P = 0.056). In addition, pancreatic adenocarcinoma patients presenting enhanced PXR/RXR-γ expression showed marginally longer survival times compared with those with decreased expression (log-rank test, P = 0.053).

CONCLUSIONS

This study supported evidence that PXR and its copartners' overexpression may be associated with favorable clinicopathologic parameters and better outcome in pancreatic adenocarcinoma.

Retinoic acid differentially affects in vitro proliferation, differentiation and mineralization of two fish bone-derived cell lines: different gene expression of nuclear receptors and ECM proteins

Retinoic acid (RA), the main active metabolite of vitamin A, regulates vertebrate morphogenesis through signaling pathways not yet fully understood. Such process involves the specific activation of retinoic acid and retinoid X receptors (RARs and RXRs), which are nuclear receptors of the steroid/thyroid hormone receptor superfamily. Teleost fish are suitable models to study vertebrate development, such as skeletogenesis. Cell systems capable of in vitro mineralization have been developed for several fish species and may provide new insights into the specific cellular and molecular events related to vitamin A activity in bone, complementary to in vivo studies. This work aims at investigating the in vitro effects of RA (0.5 and 12.5 μM) on proliferation, differentiation and extracellular matrix (ECM) mineralization of two gilthead seabream bone-derived cell lines (VSa13 and VSa16), and at identifying molecular targets of its action through gene expression analysis. RA induced phenotypic changes and cellular proliferation was inhibited in both cell lines in a cell type-dependent manner (36-59% in VSa13 and 17-46% in VSa16 cells). While RA stimulated mineral deposition in VSa13 cell cultures (50-62% stimulation), it inhibited the mineralization of extracellular matrix in VSa16 cells (11-57% inhibition). Expression of hormone receptor genes (rars and rxrs), and extracellular matrix-related genes such as matrix and bone Gla proteins (mgp and bglap), osteopontin (spp1) and type I collagen (col1a1) were differentially regulated upon exposure to RA in proliferating, differentiating and mineralizing cultures of VSa13 and VSa16 cells. Altogether, our results show: (i) RA affects proliferative and mineralogenic activities in two fish skeletal cell types and (ii) that during phenotype transitions, specific RA nuclear receptors and bone-related genes are differentially expressed in a cell type-dependent manner.

[Expression of nuclear hormone receptors PPAR, LXR and RXR in the liver and lipid and glucose levels in blood in susceptible and resistant to hepatocarcinogenesis mice strains]

Earlier it was shown that male mice of the DD/He strain were highly susceptible to ortho-aminoasotoluene (OAT) induced hepatocarcinogenesis, and resistant to spontaneous liver tumor development as compared to the CC57BR/Mv strain. In the present work we have made a comparative investigation of peroxisome proliferator-activated receptor (PPAR), liver X-receptor (LXR) and retinoic X-receptor (RXR) mRNA levels in liver as well as concentrations of corticosterone, glucose, lipids and insulin in blood of male DD/He and CC57BR/Mv mice. Using the multiplex RT-PCR method it was found that PPAR-alpha, PPAR-gamma, RXR-alpha and RXR-beta mRNA content was essentially decreased in the liver of DD mice as compared to mice of the CC57BR strain. No significant interstrain differences of LXR-alpha and LXR-beta mRNA content were found. In DD micetere was more then the 3-fold decrease of blood content of corticosterone, which is involved in PPAR and RXR regulation. DD mice demonstrated a significant decrease in blood serum glucose and insulin concentrations as well as higher reactivity to insulin as compared with CC57BR mice. Elevated blood total cholesterol and cholesterol HDL level were found in DD mice whereas triglyceride content was basically the same in both mouse strains. It is known that glucocorticoids, PPAR and RXR play crucial role in transcription regulation of inflammation response. Therefore our data allow to suggest that decreased corticosterone level in blood, PPAR and RXR mRNA content in liver of the DD strain may lead to induction of inflammation by OAT exposure, resulting in a high incidence of tumorigenesis in this strain.

Genistein aglycone does not affect thyroid function: results from a three-year, randomized, double-blind, placebo-controlled trial

CONTEXT AND OBJECTIVE

Genistein aglycone positively affects postmenopausal symptoms. However, questions about its long-term safety on the thyroid gland still remain.

DESIGN

The parent study was a randomized, double-blind, placebo-controlled trial involving 389 osteopenic, postmenopausal women for 24 months. A subcohort (138 patients) continued therapy for an additional year.

SETTING

Patients received ambulatory care.

PATIENTS AND INTERVENTIONS

Participants received 54 mg of genistein aglycone daily (n = 71) or placebo (n = 67), plus calcium and vitamin D(3) at therapeutic doses. Circulating thyroid hormones (TSH, free T(3), free T(4)) and autoantibodies (thyroid peroxidase, thyroglobulin, and thyroid microsomal antigen) were assessed in 40 genistein and 37 placebo subjects who completed 3 yr. Thyroid hormone receptor (THRalpha and THRbeta) and retinoid receptor (RARalpha, RARgamma, and RXRalpha) expression from peripheral blood monocytes was also evaluated at baseline, 12, 24, and 36 months in all 3-yr completers.

RESULTS

Genistein administration over 3 yr did not affect serum thyroid hormones or autoantibodies. In addition, there were no differences in THRalpha, THRbeta, RARalpha, RARgamma, or RXRalpha mRNA expression between groups.

CONCLUSION

These data suggest that genistein aglycone intake does not significantly increase the risk of clinical or subclinical hypothyroidism at the dose of 54 mg/d.

Retinoic acid receptor and retinoid X receptor subtype expression for the differential diagnosis of thyroid neoplasms

BACKGROUND

Although differential expression of retinoic acid receptor (RAR) subtypes between benign and malignant thyroid tissues has been described, their diagnostic value has not been reported.

AIM

To investigate the diagnostic accuracy of RAR and retinoid X receptor (RXR) subtype protein expression for the differential diagnosis of thyroid neoplasms.

METHODS

We used a tissue array containing 93 benign thyroid tissues (normal thyroid, multinodular goiter, and follicular adenoma (FA)) and 77 thyroid carcinomas (papillary thyroid carcinoma (PTC), follicular thyroid carcinoma, and follicular variant of PTC (FVPTC)). Immunostaining was done for RAR and RXR subtypes. Staining was analyzed semiquantitatively based on receiver operating curve analyses and using hierarchical cluster analysis.

RESULTS

We found increased expression of cytoplasmic (c) RARA, cRARG, cRXRB and decreased expression of nuclear (n) RARB, nRARG, and nRXRA in thyroid carcinomas compared with benign tissues. We found three proteins differently expressed between FA and FTC and five proteins differentially expressed between FA and FVPTC, with high diagnostic accuracies. Using cluster analysis, the combination of negative staining of membranous RXRB and positive staining for cRXRB had a high positive predictive value (98%) for malignant thyroid disease, whereas the combination of positive nRXRA and negative cRXRB staining had a high predictive value (91%) for benign thyroid lesions.

CONCLUSION

We conclude that differences in RAR and RXR subtype protein expression may be valuable for the differential diagnosis of thyroid neoplasms. The results of this study and especially the value of cluster analysis have to be confirmed in subsequent studies.

Isolation and expression of the retinoid X receptor from last instar nymphs and adult females of the soft tick Ornithodoros moubata (Acari: Argasidae)

Retinoid X receptors (RXR) exist broadly from invertebrates to vertebrates, and play essential roles in physiological processes of these organisms. In arthropods, RXRs form a complex with the ecdysteroid receptor (EcR) and ecdysteroids to mediate the regulation of ecdysis and reproduction. Compared to EcR, RXR and its homologue ultraspiracle (USP) are much less well understood. Therefore, we identified RXR of the soft tick Ornithodoros moubata (OmRXR) and used real-time PCR to examine the expression of OmRXR. This is the first report of RXR from a soft tick. OmRXR showed higher homology to hard tick, crustacean and vertebrate RXRs than insect RXRs and USPs. OmRXR expression was observed during molting in the last instar nymphs coinciding with EcR expression and increases in ecdysteroid titers. Tick vitellogenesis normally occurs soon after engorgement and OmRXR expression coinciding with EcR expression and ecdysteroid titers in engorged females occurred before vitellogenin (Vg) synthesis and egg maturation. The ecdysteroid/EcR/RXR complex appears to be important in the regulation of molting and vitellogenesis of soft ticks.

Retinoid X receptor gene expression and protein content in tissues of the rock shell Thais clavigera

To elucidate the role of retinoid X receptor (RXR) in the development of imposex caused by organotin compounds in gastropod molluscs, we investigated RXR gene expression and RXR protein content in various tissues of male and female wild rock shells (Thais clavigera). Quantitative real-time polymerase chain reaction, Western blotting, and immunohistochemistry with a commercial antibody against human RXR alpha revealed that RXR gene expression was significantly higher in the penises of males and imposex-exhibiting females than in the penis-forming areas of normal females (P<0.01 and P<0.05, respectively). Western blotting demonstrated that the antibody could detect rock shell RXR and showed that the male penis had the highest content of RXR protein among the analyzed tissues of males and normal females. Immunohistochemical staining revealed nuclear localization of RXR protein in the epithelial and smooth muscle cells of the vas deferens and in the interstitial or connective tissues and epidermis of the penis in males and imposex-exhibiting females. RXR could be involved in the mechanism of induction of male-type genitalia (penis and vas deferens) by organotin compounds in female rock shells.

Cloning and characterization of the retinoid X receptor from a primitive crustacean Daphnia magna

Terpenoid hormones function as morphogens throughout the animal kingdom and many of these activities are mediated through members of the retinoid X group of nuclear receptors (RXR; NR2B). In the present study, RXR was cloned from the water flea Daphnia magna, a primitive crustacean of the class Branchiopoda, and characterized with respect to phylogeny, developmental expression, and hormonal regulation. The full length daphnid RXR cDNA was cloned by initial PCR amplification of a cDNA fragment from the highly conserved DNA-binding domain followed by extension of the fragment using RACE PCR. The full length cDNA was 1888 base pairs in length and coded for a 400 amino acid protein that exhibited the five-domain structure of a nuclear receptor superfamily member. The RXR protein shared significant identity with other NR2B group members. Phylogenetic analyses of the ligand-binding domain of the receptor revealed that daphnid RXR clustered with RXR from decapod crustaceans on a branch of the phylogenetic tree that was distinct from RXRs known to bind retinoic acids and juvenile hormones. Daphnid RXR mRNA levels were greatest in embryos that were early in development and progressively declined through the initial five stages of embryo development. Adult females expressed higher levels of RXR mRNA than did males and exposure of females to the terpenoid mimic pyriproxyfen reduced RXR mRNA to levels approaching levels in males. RXR mRNA levels in males were refractory to pyriproxyfen. These results show that branchiopod crustaceans dynamically express RXR which should be evaluated as a candidate receptor for the terpenoid hormone methyl farnesoate which functions as a sex determinant in these organisms.

Activation of p53 as a causal step for atherosclerosis induced by polycyclic aromatic hydrocarbons

This study was performed to prove our hypothesis that the metabolite(s) of polycyclic aromatic hydrocarbons (PAHs) caused the activation or phosphorylation of p53 via DNA damage to suppress the liver X receptor (LXR)-mediated signal transductions as a probably more direct mechanism. We found that LXR-mediated trans-activation was inhibited by 3-methylchoranthrene (MC) and doxorubicin (Dox) in HepG2 cells carrying wild-type p53, but not in Hep3B cells possessing mutant p53. The exogenous expression of wild-type p53 suppressed the LXR-mediated trans-activation in Hep3B cells. The expression of mRNA for ATP binding cassette A1 was suppressed by MC and Dox in HepG2 cells. The protein expression of retinoid X receptor (RXR), a partner of LXR to form a heterodimer, was suppressed by MC and Dox in HepG2 cells.

Chemoprevention of prostate cancer by cholecalciferol (vitamin D3): 25-hydroxylase (CYP27A1) in human prostate epithelial cells

The 20-30 year latency period for prostate cancer provides an important opportunity to prevent the development of invasive cancer. A logical approach for chemoprevention to reduce incidence is to identify agents, such as, vitamin D, which can inhibit cell proliferation and induce differentiation, are safe, and readily available to the public at low cost. Epidemiological evidence suggests that vitamin D deficiency is associated with increased risk for prostate cancer. We examined the ability and mechanisms of action of cholecalciferol (vitamin D(3)), a precursor of the most biologically active hormone calcitriol, to block or reverse premalignant changes. The immortalized, non-tumorigenic, RWPE-1 human prostate epithelial cell line, was used. Results show that cholecalciferol, at physiological levels: (i) inhibits anchorage-dependent growth (ii) induces differentiation by increasing PSA expression and (iii) exerts its effects by up-regulating vitamin D receptor (VDR), retinoid-X receptors (RXRs), and androgen receptor (AR). Furthermore, we discovered that human prostate epithelial cells constitutively express appreciable levels of 25-hydroxylase CYP27A1 protein, the enzyme which catalyzes the conversion of cholecalciferol to 25(OH)D(3), and that CYP27A1 is up-regulated by cholecalciferol. Recent studies show that human mitochondrial CYP27A1 can also catalyze 1alpha-hydroxylation of 25(OH)D(3) to calcitriol. The presence of 25-hydroxylase in human prostate epithelial cells has not previously been shown. Since human prostate epithelial cells have the necessary enzymes and the rare ability to locally convert cholecalciferol to the active hormone calcitriol, we propose that they are a prime target for chemoprevention of prostate cancer with cholecalciferol whose safety is well established as a supplement in vitamins and fortified foods.

Retinoic acid via RARalpha inhibits the expression of 24-hydroxylase in human prostate stromal cells

25-Hydroxyvitamin D(3)-24-hydroxylase (24-hydroxylase) is an important inactivating enzyme and its expression is induced by 25-hydroxyvitamin D3 (25OHD3) and 1alpha,25-dihydroxyvitamin D3 (1alpha,25-(OH)2D3) through action of heterodimers of vitamin D receptor (VDR) and retinoid X receptor (RXR). RXRs also act as heterodimer partners for retinoic acid receptors (RARs), mediating the action of all-trans-retinoic acid (ATRA). Prostate stroma plays a crucial role in prostate cancer development and benign prostatic hyperplasia. We demonstrate here that ATRA markedly reduced the expression of 24-hydroxylase mRNA induced by 25OHD3 and 1alpha,25-(OH)2D3 in human prostatic stromal cells P29SN and P32S but not in epithelial cells PrEC or cancer cells LNCaP. By using transfection and RAR-selective ligands, we found that the inhibitory effect of ATRA on 24-hydroxylase expression in stromal cells was mediated by RARalpha but not by RARbeta. Moreover, the ATRA-induced expression of RARbeta was also mediated by RARalpha. The combined treatment of 1alpha,25-(OH)2D3 and RARalpha agonist Am80 at 10 nM exhibited strong growth-inhibitory effect whereas either alone had no effect. Our data suggest that ATRA suppresses 24-hydroxylase expression through RARalpha-dependent signaling pathway and can enhance vitamin D action in suppression of cell growth.

Inhibition of apolipoprotein AI gene expression by 1, 25-dihydroxyvitamin D3

Members of the steroid receptor superfamily are known to alter the transcription of apolipoprotein AI (apo AI), the major apoprotein of high-density lipoprotein (HDL). To assess the role of vitamin D receptor (VDR) in apo AI gene expression, we investigated the effect of 1alpha, 25-dihydroxycholecalciferol (1, 25-(OH)2 D3) as well as the vitamin D antagonist ZK-191784 (ZK), on apo AI gene expression and promoter activity in the human hepatoma cell line HepG2. Apo AI secretion and mRNA levels were both suppressed in a dose-dependent manner in HepG2 cells treated 1, 25-(OH)2 D3. This was accompanied by a similar decrease in apo AI promoter activity. Mapping of the vitamin D response element showed that suppression required a region of the apo AI gene promoter identified previously to contain site A. However, vitamin D treatment had no effect on nuclear factor binding to site A of the apo AI promoter. Treatment with vitamin D receptor antagonist ZK inhibited the ability of 1, 25-(OH)2 D3 to repress apo AI promoter activity, while higher doses of ZK increased apo AI promoter activity. ZK did not alter estradiol stimulated apo AI promoter activity. The VDR antisense ODN had no effect on apo AI promoter activity in control cells, however, it reversed the repression normally seen in cells treated with 1, 25-(OH)2D3. It is concluded that 1, 25-(OH)2 D3 suppresses apo A1 gene expression at the transcriptional level, possibly by altering coactivators or corepressors. This effect requires the VDR as well as a vitamin D response element in the apo AI promoter.

Cholecalciferol (Vitamin D3) Inhibits Growth and Invasion by Up-regulating Nuclear Receptors and 25-Hydroxylase (CYP27A1) in Human Prostate Cancer Cells

Epidemiological evidence suggests an inverse relationship between prostate cancer and serum vitamin D levels. We examined the ability of cholecalciferol (vitamin D(3)), a calcitriol precursor, to inhibit or reverse cellular changes associated with malignant transformation and invasion and explored its mechanisms of action. The RWPE2-W99 human prostate epithelial cell line, which forms slow-growing tumors in nude mice, was used because it mimics the behavior of the majority of primary human prostate cancers. Cholecalciferol, at physiological levels: (i) inhibited anchorage-dependent and -independent growth; (ii) induced differentiation by decreasing vimentin expression with a concomitant decrease in motility/chemotaxis; (iii) decreased MMP-9 and MMP-2 activity with concomitant decrease in invasion; and (iv) exerted its effects by up-regulating vitamin D receptor (VDR), retinoid-X receptor-alpha (RXR-alpha), and androgen receptor (AR) in a dose-dependent manner. Furthermore, we found that RWPE2-W99 prostate cancer cells, similar to RWPE-1 cells (Tokar and Webber. Clin Exp Metast 2005; 22: 265-73), constitutively express the enzyme 25-hydroxylase CYP27A1 which is markedly up-regulated by cholecalciferol. Cholecalciferol has effects similar to those of calcitriol on growth, MMP activity, and VDR. The ability of CYP27A1 to catalyze the conversion of cholecalciferol to 25(OH)D(3) and of 25(OH)D(3) to calcitriol has been reported. RWPE2-W99 cells, similar to RWPE-1 cells, appear to have the rare ability to locally convert cholecalciferol to the active hormone calcitriol. Because it can inhibit cellular changes associated with malignant transformation and invasion, we propose that cholecalciferol may be an effective agent for the treatment of prostate cancer.

Unliganded RXR acts as an inhibitory factor on troglitazone-induced activation

Troglitazone (TZ), a thiazolidinedione derivative, is a specific ligand for the peroxisome proliferator-activated receptor (PPAR) gamma and improves insulin sensitivity. PPARgamma regulates the expression of genes by binding to PPAR response element in promoter regions of regulator genes as heterodimers with a retinoid X receptor (RXR). We report here that PPARgamma activation by TZ depends on the expression levels of RXR. A transient transfection study in CV-1 cells revealed that the activation by TZ was suppressed by increasing amounts of expression of RXR, but not PPARgamma. Northern blot analysis revealed that PPARgamma and RXR were not expressed in CV-1 cells, and TZ did not induce PPARgamma or RXR mRNA in CV-1 cells indicating that RXR suppression is not related to these endogenous receptor expressions. Electrophoretic mobility shift assay revealed that the increasing amount of RXR did not compete with the DNA binding of the PPARgamma/RXR heterodimer in the presence or absence of TZ. Transfected co-activators enhanced the TZ-dependent gene transcription, and this activation was inhibited by excessive amounts of RXR, indicating that unliganded RXR may recruit the specific coactivators from the PPARgamma/RXR heterodimer.

Retinoic acid reverses the PTU related decrease in neurogranin level in mice brain

Recent data have shown that fine regulation of retinoid mediated gene expression is fundamentally important for optimal brain functioning in aged mice. Nevertheless, alteration of the thyroid hormone signalling pathway may be a limiting factor, which impedes retinoic acid (RA) from exerting its modulating effect. Mild hypothyroidism is often described in the elderly. Thus, in the present study, it was of interest to determine if RA exerts its neurological modulating effect in mild hypothyroidism. To obtain further insight into this question, mice were submitted to a low propylthiouracyl (PTU) drink (0.05%) in order to slightly reduce the serum level of triiodothyronine (T3). A quantitative evaluation of RA nuclear receptors (RAR, RXR), T3 nuclear receptor (TR) and of neurogranin (RC3, a RA target gene which codes for a protein considered as a good marker of synaptic plasticity) in PTU treated mice injected with vehicle or RA or T3 was carried out. The PTU-related decrease in expression of RAR, RXR and RC3 was restored following RA or T3 administration, as observed in aged mice. The amount of TR mRNA, which was not affected in PTU treated mice, was increased only after T3 treatment as observed in overt hypothyroidism. These results suggest that neurobiological alterations observed in aged mice are probably related to RA and T3 signalling pathway modifications associated, in part, with mild changes in thyroid function.