Retinoids are produced by glia in the lateral ganglionic eminence and regulate striatal neuron differentiation.
(1/5913)
In order to identify molecular mechanisms involved in striatal development, we employed a subtraction cloning strategy to enrich for genes expressed in the lateral versus the medial ganglionic eminence. Using this approach, the homeobox gene Meis2 was found highly expressed in the lateral ganglionic eminence and developing striatum. Since Meis2 has recently been shown to be upregulated by retinoic acid in P19 EC cells (Oulad-Abdelghani, M., Chazaud, C., Bouillet, P., Sapin, V., Chambon, P. and Dolle, P. (1997) Dev. Dyn. 210, 173-183), we examined a potential role for retinoids in striatal development. Our results demonstrate that the lateral ganglionic eminence, unlike its medial counterpart or the adjacent cerebral cortex, is a localized source of retinoids. Interestingly, glia (likely radial glia) in the lateral ganglionic eminence appear to be a major source of retinoids. Thus, as lateral ganglionic eminence cells migrate along radial glial fibers into the developing striatum, retinoids from these glial cells could exert an effect on striatal neuron differentiation. Indeed, the treatment of lateral ganglionic eminence cells with retinoic acid or agonists for the retinoic acid receptors or retinoid X receptors, specifically enhances their striatal neuron characteristics. These findings, therefore, strongly support the notion that local retinoid signalling within the lateral ganglionic eminence regulates striatal neuron differentiation. (+info)
All-trans-retinoic acid inhibits Jun N-terminal kinase by increasing dual-specificity phosphatase activity.
(2/5913)
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)
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.
(3/5913)
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.
(4/5913)
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)
Regulation of UDP-N-acetylglucosamine:dolichyl-phosphate N-acetylglucosamine-1-phosphate transferase by retinoic acid in P19 cells.
(5/5913)
UDP-N-acetylglucosamine:dolichyl-phosphate N-acetylglucosamine-1-phosphate transferase (GPT) is the first enzyme in the dolichol pathway of protein N-glycosylation, and is implicated in the developmental programmes of a variety of eukaryotes. In the present study we describe the effects of all-trans-retinoic acid (RA) on the levels of GPT protein and enzymic activity, and on the transcription rate of the GPT gene, in mouse P19 teratocarcinoma cells. RA caused a dose-dependent and protein-synthesis-dependent induction of enzyme activity. The maximum induction of GPT activity (about 3-fold) required 2 days of exposure to 1 microM RA. Induced GPT activity also resulted in an increase in the rate of incorporation of [3H]mannose into Glc3Man9GlcNAc2. Enzymic activities paralleled GPT gene expression. The GPT gene was induced (2-fold) after 7 h of RA treatment. An approx. 3-fold increase in a 48 kDa GPT protein and approx. 4-fold increases in the levels of three GPT transcripts (1.8, 2.0 and 2.2 kb) were observed after 2 days of RA treatment. The enhanced levels of GPT protein and mRNAs began to decline 3 days after the initiation of differentiation, and GPT expression was down-regulated during cellular differentiation. GPT activity decreased about 2. 8-fold to a constant level in differentiated P19 cells. The results indicate that the RA-induced enzyme activity was mainly determined by increased transcription of the GPT gene. RA-treated P19 cells were about 4-fold more resistant to tunicamycin, a fungal antibiotic which inhibits GPT, than were control cells. In addition, GPT activity in membranes from RA-treated P19 cells exhibited approx. 4-fold increased resistance to tunicamycin compared with activity in membranes from untreated control cells, demonstrating that resistance to tunicamycin is correlated with induced GPT activity. Furthermore, increased GPT activity had regulatory significance with regard to the rate of incorporation of [3H]mannose into Glc3Man9GlcNAc2-P-P-dolichol and into glycoproteins. Together, the data provide additional insights into the hormonal regulation of GPT and present evidence that the RA-mediated induction of GPT has a regulatory impact on the dolichol pathway. (+info)
Retinoic acid stimulates the expression of 11beta-hydroxysteroid dehydrogenase type 2 in human choriocarcinoma JEG-3 cells.
(6/5913)
The syncytiotrophoblasts of the human placenta express high levels of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), the enzyme responsible for the inactivation of glucocorticoids. It has been proposed that the placental 11beta-HSD2 serves as a barrier to protect the fetus from high levels of maternal cortisol. To examine the hypothesis that nutritional signals regulate the expression of 11beta-HSD2 in placental syncytiotrophoblasts, we investigated the effects of retinoic acids (RAs), the major metabolites of vitamin A, on the expression of 11beta-HSD2 using human choriocarcinoma JEG-3 cells as a model. This trophoblast-like cell line displays a number of functional similarities to the syncytiotrophoblast. Treatment for 24 h with all-trans RA (1-1000 nM) resulted in a dose-dependent increase in 11beta-HSD2 activity with a maximal effect (increase to 3-fold) at 100 nM. The effect of all-trans RA (100 nM) was also time-dependent in that the effect was detectable at 6 h and reached its maximum by 48 h. Similar increases in 11beta-HSD2 activity were observed when the cells were treated with 9-cis RA. Results from semi-quantitative reverse transcription-polymerase chain reaction demonstrated that there was a corresponding increase in 11beta-HSD2 mRNA after RA treatment. Moreover, treatment with actinomycin D (100 ng/ml) abrogated the increase in 11beta-HSD2 mRNA induced by RA, indicating an effect on transcription. In conclusion, the present study has demonstrated for the first time that RA, at physiological concentrations, induces 11beta-HSD2 gene expression and enzyme activity in JEG-3 cells. If this occurs in vivo, the present finding suggests that high expression of 11beta-HSD2 in the human placenta may be maintained, at least in part, by dietary intake of vitamin A. (+info)
Constitutive degradation of PML/RARalpha through the proteasome pathway mediates retinoic acid resistance.
(7/5913)
PML/RARalpha is the leukemogenetic protein of acute promyelocytic leukemia (APL). Treatment with retinoic acid (RA) induces degradation of PML/RARalpha, differentiation of leukaemic blasts, and disease remission. However, RA resistance arises during RA treatment of APL patients. To investigate the phenomenon of RA resistance in APL, we generated RA-resistant sublines from APL-derived NB4 cells. The NB4.007/6 RA-resistant subline does not express the PML/RARalpha protein, although its mRNA is detectable at levels comparable to those of the parental cell line. In vitro degradation assays showed that the half-life of PML/RARalpha is less than 30 minutes in NB4.007/6 and longer than 3 hours in NB4. Treatment of NB4.007/6 cells with the proteasome inhibitors LLnL and lactacystin partially restored PML/RARalpha protein expression and resulted in a partial release of the RA-resistant phenotype. Similarly, forced expression of PML/RARalpha, but not RARalpha, into the NB4/007.6 cells restored sensitivity to RA treatment to levels comparable to those of the NB4 cells. These results indicate that constitutive degradation of PML/RARalpha protein may lead to RA resistance and that PML/RARalpha expression is crucial to convey RA sensitivity to APL cells. (+info)
Differential expression and phosphorylation of CTCF, a c-myc transcriptional regulator, during differentiation of human myeloid cells.
(8/5913)
CTCF is a transcriptional repressor of the c-myc gene. Although CTCF has been characterized in some detail, there is very little information about the regulation of CTCF activity. Therefore we investigated CTCF expression and phosphorylation during induced differentiation of human myeloid leukemia cells. We found that: (i) both CTCF mRNA and protein are down-regulated during terminal differentiation in most cell lines tested; (ii) CTCF down-regulation is retarded and less pronounced than that of c-myc; (iii) CTCF protein is differentially phosphorylated and the phosphorylation profiles depend on the differentiation pathway. We concluded that CTCF expression and activity is controlled at transcriptional and post-transcriptional levels. (+info)