Stromal cells mediate retinoid-dependent functions essential for renal development.
(1/3127)
The essential role of vitamin A and its metabolites, retinoids, in kidney development has been demonstrated in vitamin A deficiency and gene targeting studies. Retinoids signal via nuclear transcription factors belonging to the retinoic acid receptor (RAR) and retinoid X receptor (RXR) families. Inactivation of RARaplpha and RARbeta2 receptors together, but not singly, resulted in renal malformations, suggesting that within a given renal cell type, their concerted function is required for renal morphogenesis. At birth, RARalpha beta2(-) mutants displayed small kidneys, containing few ureteric bud branches, reduced numbers of nephrons and lacking the nephrogenic zone where new nephrons are continuously added. These observations have prompted us to investigate the role of RARalpha and RARbeta2 in renal development in detail. We have found that within the embryonic kidney, RARalpha and RARbeta2 are colocalized in stromal cells, but not in other renal cell types, suggesting that stromal cells mediate retinoid-dependent functions essential for renal development. Analysis of RARalpha beta2(-) mutant kidneys at embryonic stages revealed that nephrons were formed and revealed no changes in the intensity or distribution of molecular markers specific for different metanephric mesenchymal cell types. In contrast the development of the collecting duct system was greatly impaired in RARalpha beta2(-) mutant kidneys. Fewer ureteric bud branches were present, and ureteric bud ends were positioned abnormally, at a distance from the renal capsule. Analysis of genes important for ureteric bud morphogenesis revealed that the proto-oncogene c-ret was downregulated. Our results suggest that RARalpha and RARbeta2 are required for generating stromal cell signals that maintain c-ret expression in the embryonic kidney. Since c-ret signaling is required for ureteric bud morphogenesis, loss of c-ret expression is a likely cause of impaired ureteric bud branching in RARalpha beta2(-) mutants. (+info)
All-trans-retinoic acid inhibits Jun N-terminal kinase by increasing dual-specificity phosphatase activity.
(2/3127)
Jun N-terminal kinases (JNKs) are serine-threonine kinases that play a critical role in the regulation of cell growth and differentiation. We previously observed that JNK activity is suppressed by all-trans-retinoic acid (t-RA), a ligand for retinoic acid nuclear receptors (RARs), in normal human bronchial epithelial cells, which are growth inhibited by t-RA. In this study, we investigated the mechanism by which t-RA inhibits JNK and the possibility that this signaling event is blocked in non-small cell lung cancer (NSCLC) cells. Virtually all NSCLC cell lines are resistant to the growth-inhibitory effects of t-RA, and a subset of them have a transcriptional defect specific to retinoid nuclear receptors. We found that in NSCLC cells expressing functional retinoid receptors, serum-induced JNK phosphorylation and activity were inhibited by t-RA in a bimodal pattern, transiently within 30 min and in a sustained fashion beginning at 12 h. Retinoid receptor transcriptional activation was required for the late, but not the early, suppression of JNK activity. t-RA inhibited serum-induced JNK activity by blocking mitogen-activated protein (MAP) kinase kinase 4-induced signaling events. This effect of t-RA was phosphatase dependent and involved an increase in the expression of the dual-specificity MAP kinase phosphatase 1 (MKP-1). t-RA did not activate MKP-1 expression or inhibit JNK activity in a NSCLC cell line with retinoid receptors that are refractory to ligand-induced transcriptional activation. These findings provide the first evidence that t-RA suppresses JNK activity by inhibiting JNK phosphorylation. Retinoid receptor transcriptional activation was necessary for the sustained inhibition of JNK activity by t-RA, and this signaling event was disrupted in NSCLC cells with retinoid receptors that are refractory to ligand-induced transcriptional activation. (+info)
The Wilms' tumor suppressor gene (wt1) product regulates Dax-1 gene expression during gonadal differentiation.
(3/3127)
Gonadal differentiation is dependent upon a molecular cascade responsible for ovarian or testicular development from the bipotential gonadal ridge. Genetic analysis has implicated a number of gene products essential for this process, which include Sry, WT1, SF-1, and DAX-1. We have sought to better define the role of WT1 in this process by identifying downstream targets of WT1 during normal gonadal development. We have noticed that in the developing murine gonadal ridge, wt1 expression precedes expression of Dax-1, a nuclear receptor gene. We document here that the spatial distribution profiles of both proteins in the developing gonad overlap. We also demonstrate that WT1 can activate the Dax-1 promoter. Footprinting analysis, transient transfections, promoter mutagenesis, and mobility shift assays suggest that WT1 regulates Dax-1 via GC-rich binding sites found upstream of the Dax-1 TATA box. We show that two WT1-interacting proteins, the product of a Denys-Drash syndrome allele of wt1 and prostate apoptosis response-4 protein, inhibit WT1-mediated transactivation of Dax-1. In addition, we demonstrate that WT1 can activate the endogenous Dax-1 promoter. Our results indicate that the WT1-DAX-1 pathway is an early event in the process of mammalian sex determination. (+info)
Retinoic acid, but not arsenic trioxide, degrades the PLZF/RARalpha fusion protein, without inducing terminal differentiation or apoptosis, in a RA-therapy resistant t(11;17)(q23;q21) APL patient.
(4/3127)
Primary blasts of a t(11;17)(q23;q21) acute promyelocytic leukaemia (APL) patient were analysed with respect to retinoic acid (RA) and arsenic trioxide (As2O3) sensitivity as well as PLZF/RARalpha status. Although RA induced partial monocytic differentiation ex vivo, but not in vivo, As203 failed to induce apoptosis in culture, contrasting with t(15;17) APL and arguing against the clinical use of As203 in t(11;17)(q23;q21) APL. Prior to cell culture, PLZF/RARalpha was found to exactly co-localize with PML onto PML nuclear bodies. However upon cell culture, it quickly shifted towards microspeckles, its localization found in transfection experiments. Arsenic trioxide, known to induce aggregation of PML nuclear bodies, left the microspeckled PLZF/RARalpha localization completely unaffected. RA treatment led to PLZF/RARalpha degradation. However, this complete PLZF/RARalpha degradation was not accompanied by differentiation or apoptosis, which could suggest a contribution of the reciprocal RARalpha/PLZF fusion product in leukaemogenesis or the existence of irreversible changes induced by the chimera. (+info)
Role of retinoid receptors in the regulation of mucin gene expression by retinoic acid in human tracheobronchial epithelial cells.
(5/3127)
To investigate which retinoid receptors are critical in the regulation by all-trans-retinoic acid (RA) of the mucin genes MUC2, MUC5AC and MUC5B in cultured normal human tracheobronchial epithelial (NHTBE) cells, we used pan-RAR-, pan-RXR- and RAR- isotype (alpha, beta and gamma)-selective agonists and RARalpha- and RARgamma-selective antagonists (RAR is RA receptor and RXR is retinoid X receptor). RAR-, RARalpha- and RARgamma-selective agonists strongly induced mucin mRNAs in a dose-dependent manner, while the RARbeta-selective retinoid only weakly induced mucin gene expression at very high concentrations (1 microM). The pan-RXR-selective agonist by itself did not induce mucin gene expression, but acted synergistically with suboptimal concentrations of the pan-RAR agonist. A retinoid with selective anti-activator-protein-1 activity only marginally induced mucin gene expression. The RARalpha antagonist strongly inhibited mucin gene induction and mucous cell differentiation caused by RA and by the RARalpha- and RARgamma-selective retinoids. In contrast, the RARgamma antagonist only weakly inhibited RARalpha-selective-retinoid-induced mucin gene expression, but completely blocked mucin gene expression induced by the RARgamma-selective retinoid. Our studies indicate that RARalpha is the major retinoid receptor subtype mediating RA-dependent mucin gene expression and mucous cell differentiation, but that the RARgamma isotype can also induce mucin genes. Furthermore these studies suggest that RARbeta is probably not (directly) involved in RA-induced mucin gene expression. (+info)
Differential responses of normal, premalignant, and malignant human bronchial epithelial cells to receptor-selective retinoids.
(6/3127)
Using an in vitro lung carcinogenesis model consisting of normal, premalignant, and malignant human bronchial epithelial (HBE) cells, we analyzed the growth inhibitory effects of 26 novel synthetic retinoic acid receptor (RAR)- and retinoid X receptor (RXR)-selective retinoids. RAR-selective retinoids such as CD271, CD437, CD2325, and SR11364 showed potent activity in inhibiting the growth of either normal or premalignant and malignant HBE cells (IC50s mostly <1 microM) and were much more potent than RXR-selective retinoids. Nonetheless, the combination of RAR- and RXR-selective retinoids exhibited additive effects in HBE cells. As the HBE cells became progressively more malignant, they exhibited decreased or lost sensitivity to many retinoids. The activity of the RAR-selective retinoids, with the exception of the most potent retinoid, CD437, could be suppressed by an RAR panantagonist. These results suggest that: (a) RAR/RXR heterodimers play an important role in mediating the growth inhibitory effects of most retinoids in HBE cells; (b) CD437 may act through an RAR-independent pathway; (c) some of the RAR-selective retinoids may have the potential to be used in the clinic as chemopreventive and chemotherapeutic agents for lung cancer; and (d) early stages of lung carcinogenesis may be responsive targets for chemoprevention by retinoids, as opposed to later stages. (+info)
Convergence of transforming growth factor-beta and vitamin D signaling pathways on SMAD transcriptional coactivators.
(7/3127)
Cell proliferation and differentiation are regulated by growth regulatory factors such as transforming growth factor-beta (TGF-beta) and the liphophilic hormone vitamin D. TGF-beta causes activation of SMAD proteins acting as coactivators or transcription factors in the nucleus. Vitamin D controls transcription of target genes through the vitamin D receptor (VDR). Smad3, one of the SMAD proteins downstream in the TGF-beta signaling pathway, was found in mammalian cells to act as a coactivator specific for ligand-induced transactivation of VDR by forming a complex with a member of the steroid receptor coactivator-1 protein family in the nucleus. Thus, Smad3 may mediate cross-talk between vitamin D and TGF-beta signaling pathways. (+info)
Induction of apoptosis by N-(4-hydroxyphenyl)retinamide and its association with reactive oxygen species, nuclear retinoic acid receptors, and apoptosis-related genes in human prostate carcinoma cells.
(8/3127)
The synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR) has been shown to induce apoptosis in various malignant cells including human prostate carcinoma cells (HPC). We examined several possible mechanisms by which 4HPR could induce apoptosis in HPC cells. 4HPR exhibited concentration- and time-dependent decrease in cell number both in androgen-dependent (LNCaP) and -independent (DU145 and PC-3) cells. The 4HPR concentrations causing 50% decrease in cell number in LNCaP, DU145, and PC-3 cultures were 0.9 +/- 0.16, 4.4 +/- 0.45, and 3.0 +/- 1.0 microM, respectively, indicating that LNCaP cells were more sensitive to 4HPR than the other cells. 4HPR-induced apoptosis in all three cell lines was evidenced by increased enzymatic labeling of DNA breaks and formation of a DNA ladder. 4HPR increased the level of reactive oxygen species, especially in LNCaP cells. 4HPR-induced apoptosis could be suppressed in LNCaP cells by antioxidant and in DU145 cells by a nuclear retinoic acid receptor-specific antagonist, suggesting the involvement of reactive oxygen species or retinoic acid receptors in mediating apoptosis induced by 4HPR in the different HPC cells. Furthermore, 4HPR modulated the expression levels of some apoptosis-related gene (p21, c-myc, and c-jun), which may also contribute to the induction of apoptosis by 4HPR in HPC cells. (+info)