PML::RARA and GATA2 proteins interact via DNA templates to induce aberrant self-renewal in mouse and human hematopoietic cells.

The underlying mechanism(s) by which the PML::RARA fusion protein initiates acute promyelocytic leukemia is not yet clear. We defined the genomic binding sites of PML::RARA in primary mouse and human hematopoietic progenitor cells with V5-tagged PML::RARA, using anti-V5-PML::RARA chromatin immunoprecipitation sequencing and CUT&RUN approaches. Most genomic PML::RARA binding sites were found in regions that were already chromatin-accessible (defined by ATAC-seq) in unmanipulated, wild-type promyelocytes, suggesting that these regions are "open" prior to PML::RARA expression. We found that GATA binding motifs, and the direct binding of the chromatin "pioneering factor" GATA2, were significantly enriched near PML::RARA binding sites. Proximity labeling studies revealed that PML::RARA interacts with ~250 proteins in primary mouse hematopoietic cells; GATA2 and 33 others require PML::RARA binding to DNA for the interaction to occur, suggesting that binding to their cognate DNA target motifs may stabilize their interactions. In the absence of PML::RARA, Gata2 overexpression induces many of the same epigenetic and transcriptional changes as PML::RARA. These findings suggested that PML::RARA may indirectly initiate its transcriptional program by activating Gata2 expression: Indeed, we demonstrated that inactivation of Gata2 prior to PML::RARA expression prevented its ability to induce self-renewal. These data suggested that GATA2 binding creates accessible chromatin regions enriched for both GATA and Retinoic Acid Receptor Element motifs, where GATA2 and PML::RARA can potentially bind and interact with each other. In turn, PML::RARA binding to DNA promotes a feed-forward transcriptional program by positively regulating Gata2 expression. Gata2 may therefore be required for PML::RARA to establish its transcriptional program.

Decoding the neurotoxic effects of propofol: insights into the RARα-Snhg1-Bdnf regulatory cascade.

The potential neurotoxic effects of propofol, an extensively utilized anesthetic, underline the urgency to comprehend its influence on neuronal health. Insights into the role of the retinoic acid receptor-α, small nucleolar RNA host gene 1, and brain-derived neurotrophic factor (RARα-Snhg1-Bdnf) network can offer significant advancements in minimizing these effects. The study targets the exploration of the RARα and Snhg1 regulatory network's influence on Bdnf expression in the realm of propofol-induced neurotoxicity. Harnessing the Gene Expression Omnibus (GEO) database and utilizing JASPAR and RNA-Protein Interaction Prediction (RPISeq) database for projections, the study embarks on an in-depth analysis employing both in vitro and in vivo models. The findings draw a clear link between propofol-induced neurotoxicity and the amplification of RAR signaling pathways, impacting hippocampal development and apoptosis and leading to increased RARα and Snhg1 and decreased Bdnf. Propofol is inferred to accentuate neurotoxicity by heightening RARα and Snhg1 interactions, culminating in Bdnf suppression.NEW & NOTEWORTHY This study aimed to decode propofol's neurotoxic effects on the regulatory cascade, provide insights into the RARα-Snhg1-Bdnf interaction, apply extensive validation techniques, provide a detailed analysis and exploration of propofol's neurotoxicity, and offer a comprehensive approach to understanding molecular interactions.

RAR Inhibitors Display Photo-Protective and Anti-Inflammatory Effects in A2E Stimulated RPE Cells In Vitro through Non-Specific Modulation of PPAR or RXR Transactivation.

N-retinylidene-N-retinylethanolamine (A2E) has been associated with age-related macular degeneration (AMD) physiopathology by inducing cell death, angiogenesis and inflammation in retinal pigmented epithelial (RPE) cells. It was previously thought that the A2E effects were solely mediated via the retinoic acid receptor (RAR)-α activation. However, this conclusion was based on experiments using the RAR "specific" antagonist RO-41-5253, which was found to also be a ligand and partial agonist of the peroxisome proliferator-activated receptor (PPAR)-γ. Moreover, we previously reported that inhibiting PPAR and retinoid X receptor (RXR) transactivation with norbixin also modulated inflammation and angiogenesis in RPE cells challenged in the presence of A2E. Here, using several RAR inhibitors, we deciphered the respective roles of RAR, PPAR and RXR transactivations in an in vitro model of AMD. We showed that BMS 195614 (a selective RAR-α antagonist) displayed photoprotective properties against toxic blue light exposure in the presence of A2E. BMS 195614 also significantly reduced the AP-1 transactivation and mRNA expression of the inflammatory interleukin (IL)-6 and vascular endothelial growth factor (VEGF) induced by A2E in RPE cells in vitro, suggesting a major role of RAR in these processes. Surprisingly, however, we showed that (1) Norbixin increased the RAR transactivation and (2) AGN 193109 (a high affinity pan-RAR antagonist) and BMS 493 (a pan-RAR inverse agonist), which are photoprotective against toxic blue light exposure in the presence of A2E, also inhibited PPARs transactivation and RXR transactivation, respectively. Therefore, in our in vitro model of AMD, several commercialized RAR inhibitors appear to be non-specific, and we propose that the phototoxicity and expression of IL-6 and VEGF induced by A2E in RPE cells operates through the activation of PPAR or RXR rather than by RAR transactivation.

Retinoic acid receptor α activity in proximal tubules prevents kidney injury and fibrosis.

Chronic kidney disease (CKD) is characterized by a gradual loss of kidney function and affects ~13.4% of the global population. Progressive tubulointerstitial fibrosis, driven in part by proximal tubule (PT) damage, is a hallmark of late stages of CKD and contributes to the development of kidney failure, for which there are limited treatment options. Normal kidney development requires signaling by vitamin A (retinol), which is metabolized to retinoic acid (RA), an endogenous agonist for the RA receptors (RARα, ß, γ). RARα levels are decreased in a mouse model of diabetic nephropathy and restored with RA administration; additionally, RA treatment reduced fibrosis. We developed a mouse model in which a spatiotemporal (tamoxifen-inducible) deletion of RARα in kidney PT cells of adult mice causes mitochondrial dysfunction, massive PT injury, and apoptosis without the use of additional nephrotoxic substances. Long-term effects (3 to 4.5 mo) of RARα deletion include increased PT secretion of transforming growth factor ß1, inflammation, interstitial fibrosis, and decreased kidney function, all of which are major features of human CKD. Therefore, RARα's actions in PTs are crucial for PT homeostasis, and loss of RARα causes injury and a key CKD phenotype.

Adipocyte retinoic acid receptor α prevents obesity and steatohepatitis by regulating energy expenditure and lipogenesis.

OBJECTIVE: The adipose tissue-liver axis is a major regulator of the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Retinoic acid signaling plays an important role in development and metabolism. However, little is known about the role of adipose retinoic acid signaling in the development of obesity-associated NAFLD. In this work, the aim was to investigate whether and how retinoic acid receptor alpha (RARα) regulated the development of obesity and NAFLD. METHODS: RARα expression in adipose tissue of db/db or ob/ob mice was determined. Rarαfl/fl mice and adipocyte-specific Rarα-/- (RarαAdi-/- ) mice were fed a chow diet for 1 year or high-fat diet (HFD) for 20 weeks. Primary adipocytes and primary hepatocytes were co-cultured. Metabolic regulation and inflammatory response were characterized. RESULTS: RARα expression was reduced in adipose tissue of db/db or ob/ob mice. RarαAdi-/- mice had increased obesity and steatohepatitis (NASH) when fed a chow diet or HFD. Loss of adipocyte RARα induced lipogenesis and inflammation in adipose tissue and the liver and reduced thermogenesis. In the co-culture studies, loss of RARα in adipocytes induced inflammatory and lipogenic programs in hepatocytes. CONCLUSIONS: The data demonstrate that RARα in adipocytes prevents obesity and NASH via inhibiting lipogenesis and inflammation and inducing energy expenditure.

Strategies for developing retinoic acid receptor alpha-selective antagonists as novel agents for male contraception.

Reported here are the synthesis and in vitro evaluation of a series of 26 retinoic acid analogs based on dihydronaphthalene and chromene scaffolds using a transactivation assay. Chromene amide analog 21 was the most potent and selective retinoic acid receptor α antagonist identified from this series. In vitro evaluation indicated that 21 has favorable physicochemical properties and a favorable pharmacokinetic PK profile in vivo with significant oral bioavailability, metabolic stability, and testes exposure. Compound 21 was evaluated for its effects on spermatogenesis and disruption of fertility in a mouse model. Oral administration of compound 21 at low doses showed reproducibly characteristic albeit modest effects on spermatogenesis, but no effects on fertility were observed in mating studies. The inhibition of spermatogenesis could not be enhanced by raising the dose and lengthening the duration of dosing. Thus, 21 may not be a good candidate to pursue further for effects on male fertility.

Urine Excretion, Organ Distribution, and Placental Transfer of 6PPD and 6PPD-Quinone in Mice and Potential Developmental Toxicity through Nuclear Receptor Pathways.

The rubber antioxidant 6PPD has gained significant attention due to its highly toxic transformation product, 6PPD-quinone (6PPDQ). Despite their detection in urines of pregnant women, the placental transfer and developmental toxicity of 6PPD and 6PPDQ are unknown. Here, we treated C57Bl/6 mice with 4 mg/kg 6PPD or 6PPDQ to investigate their urine excretion and placental transfer. Female and male mice exhibited sex difference in excretion profiles of 6PPD and 6PPDQ. Urine concentrations of 6PPDQ were one order of magnitude lower than those of 6PPD, suggesting lower excretion and higher bioaccumulation of 6PPDQ. In pregnant mice treated with 6PPD or 6PPDQ from embryonic day 11.5 to 15.5, 6PPDQ showed ∼1.5-8 times higher concentrations than 6PPD in placenta, embryo body, and embryo brain, suggesting higher placental transfer of 6PPDQ. Using in vitro dual-luciferase reporter assays, we revealed that 6PPDQ activated the human retinoic acid receptor α (RARα) and retinoid X receptor α (RXRα) at concentrations as low as 0.3 µM, which was ∼10-fold higher than the concentrations detected in human urines. 6PPD activated the RXRα at concentrations as low as 1.2 µM. These results demonstrate the exposure risks of 6PPD and 6PPDQ during pregnancy and emphasize the need for further toxicological and epidemiological investigations.

Deregulation of All-Trans Retinoic Acid Signaling and Development in Cancer.

Cancer stem cells are the root cause of cancer, which, in essence, is a developmental disorder. All-trans retinoic acid (ATRA) signaling via ligand-activation of the retinoic acid receptors (RARs) plays a crucial role in tissue patterning and development during mammalian embryogenesis. In adults, active RARγ maintains the pool of hematopoietic stem cells, whereas active RARα drives myeloid cell differentiation. Various findings have revealed that ATRA signaling is deregulated in many cancers. The enzymes for ATRA synthesis are downregulated in colorectal, gastric, lung, and oropharyngeal cancers. ATRA levels within breast, ovarian, pancreatic, prostate, and renal cancer cells were lower than within their normal counterpart cells. The importance is that 0.24 nM ATRA activates RARγ (for stem cell stemness), whereas 100 times more is required to activate RARα (for differentiation). Moreover, RARγ is an oncogene regarding overexpression within colorectal, cholangiocarcinoma, hepatocellular, ovarian, pancreatic, and renal cancer cells. The microRNA (miR) 30a-5p downregulates expression of RARγ, and miR-30a/miR-30a-5p is a tumor suppressor for breast, colorectal, gastric, hepatocellular, lung, oropharyngeal, ovarian, pancreatic, prostate, and renal cancer. These complementary findings support the view that perturbations to ATRA signaling play a role in driving the abnormal behavior of cancer stem cells. Targeting ATRA synthesis and RARγ has provided promising approaches to eliminating cancer stem cells because such agents have been shown to drive cell death.

RA-RAR signaling promotes mouse vaginal opening through increasing ß-catenin expression and vaginal epithelial cell apoptosis.

BACKGROUND: Retinoic acid (RA) plays important role in the maintenance and differentiation of the Müllerian ducts during the embryonic stage via RA receptors (RARs). However, the function and mechanism of RA-RAR signaling in the vaginal opening are unknown. METHOD: We used the Rarα knockout mouse model and the wild-type ovariectomized mouse models with subcutaneous injection of RA (2.5 mg/kg) or E2 (0.1 µg/kg) to study the role and mechanism of RA-RAR signaling on the vaginal opening. The effects of Rarα deletion on Ctnnb1 mRNA levels and cell apoptosis in the vaginas were analyzed by real-time PCR and immunofluorescence, respectively. The effects of RA on the expression of ß-catenin and apoptosis in the vaginas were analyzed by real-time PCR and western blotting. The effects of E2 on RA signaling molecules were analyzed by real-time PCR and western blotting. RESULTS: RA signaling molecules were expressed in vaginal epithelial cells, and the mRNA and/or protein levels of RALDH2, RALDH3, RARα and RARγ reached a peak at the time of vaginal opening. The deletion of Rarα resulted in 25.0% of females infertility due to vaginal closure, in which the mRNA (Ctnnb1, Bak and Bax) and protein (Cleaved Caspase-3) levels were significantly decreased, and Bcl2 mRNA levels were significantly increased in the vaginas. The percentage of vaginal epithelium with TUNEL- and Cleaved Caspase-3-positive signals were also significantly decreased in Rarα-/- females with vaginal closure. Furthermore, RA supplementation of ovariectomized wild-type (WT) females significantly increased the expression of ß-catenin, active ß-catenin, BAK and BAX, and significantly decreased BCL2 expression in the vaginas. Thus, the deletion of Rarα prevents vaginal opening by reducing the vaginal ß-catenin expression and epithelial cell apoptosis. The deletion of Rarα also resulted in significant decreases in serum estradiol (E2) and vagina Raldh2/3 mRNA levels. E2 supplementation of ovariectomized WT females significantly increased the expression of RA signaling molecules in the vaginas, suggesting that the up-regulation of RA signaling molecules in the vaginas is dependent on E2 stimulation. CONCLUSION: Taken together, we propose that RA-RAR signaling in the vaginas promotes vaginal opening through increasing ß-catenin expression and vaginal epithelial cell apoptosis.

Retinoic acid administration normalizes aberrant microglial activation via regulating TREM2 transcription in the PFC of valproic acid induced autism rat.

Autism spectrum disorder (ASD) is a complex neurodevelopmental disease with an unclear underlying pathogenesis. Disruption of retinoic acid (RA)-retinoic acid receptor α (RARα) signaling and aberrant microglial activation were reported to be involved in the pathogenesis of ASD. However, the effect of RA-RARα signaling on microglial activation in ASD and the underlying mechanisms are unknown. Herein, we found inhibited RA-RARα signaling and increased microglial activation in valproic acid (VPA)-induced autism rats. Furthermore, we administered RA to VPA rats and found that RA ameliorated autism-like behaviors, inhibited microglial activation and normalized microglial polarization in VPA rats. Additionally, the expression levels of RARα and triggering receptor expressed on myeloid cells 2 (TREM2) were increased in the prefrontal cortex (PFC) of VPA rats given RA. Chromatin immunoprecipitation (ChIP) and dual luciferase reporter assays confirmed that RARα can regulate the transcriptional activity of the TREM2 gene by binding to its promoter. We conclude that RA administration ameliorates autism-like behaviors in VPA rats by inhibiting microglial activation and normalizing microglial polarization through the regulation of TREM2 transcription by RARα.

All-trans retinoic acid improves NSD2-mediated RARα phase separation and efficacy of anti-CD38 CAR T-cell therapy in multiple myeloma.

BACKGROUND: Immunotherapies targeting CD38 have demonstrated salient efficacy in relapsed/refractory multiple myeloma (MM). However, loss of CD38 antigen and outgrowth of CD38 negative plasma cells have emerged as a major obstacle in clinics. All-trans retinoic acid (ATRA) has been reported to upregulate CD38 expression, but the mechanism and adaptive genetic background remain unexplored. METHODS: The efficacy of ATRA in upregulating CD38 expression in MM cells is evaluated by flow cytometry. The interaction between NSD2 and the RARα is analyzed by immunoprecipitation, and the nuclear condensation of RARα is evaluated under laser confocal microscope. A graft model of MM is established in NOD.Cg-PrkdcscidIl2rgtm1Wjl /SzJ mice, and the tumor burden is assessed by in vivo fluorescence imaging. RESULTS: We report that ATRA upregulates MM cells CD38 in a non-linear manner, which is t(4;14) translocation dependent, and t(4;14) translocation-induced NSD2 shows positive correlation with ATRA-induced level of, but not with basal level of CD38 expression. Mechanistically, NSD2 interacts with the ATRA receptor, RARα, and protects it from degradation. Meanwhile, NSD2 enhances the nuclear condensation of RARα and modifies the histone H3 dimethylation at lysine 36 on CD38 promoter. Knockdown of NSD2 attenuates the sensitization of MM against ATRA induced CD38 upregulation. Translationally, ATRA is prone to augment the efficacy of anti-CD38 CAR T cells in NSD2high MM cells in vitro and in vivo. CONCLUSION: This study elucidates a mechanism of ATRA in regulating CD38 expression and expands the clinical potential of ATRA in improving immunotherapies against CD38 in patients with MM.Cite Now.

Retinoic acid-gated BDNF synthesis in neuronal dendrites drives presynaptic homeostatic plasticity.

Homeostatic synaptic plasticity is a non-Hebbian synaptic mechanism that adjusts synaptic strength to maintain network stability while achieving optimal information processing. Among the molecular mediators shown to regulate this form of plasticity, synaptic signaling through retinoic acid (RA) and its receptor, RARα, has been shown to be critically involved in the homeostatic adjustment of synaptic transmission in both hippocampus and sensory cortices. In this study, we explore the molecular mechanism through which postsynaptic RA and RARα regulates presynaptic neurotransmitter release during prolonged synaptic inactivity at mouse glutamatertic synapses. We show that RARα binds to a subset of dendritically sorted brain-derived neurotrophic factor (Bdnf) mRNA splice isoforms and represses their translation. The RA-mediated translational de-repression of postsynaptic BDNF results in the retrograde activation of presynaptic tropomyosin receptor kinase B (TrkB) receptors, facilitating presynaptic homeostatic compensation through enhanced presynaptic release. Together, our study illustrates an RA-mediated retrograde synaptic signaling pathway through which postsynaptic protein synthesis during synaptic inactivity drives compensatory changes at the presynaptic site.

Retinoic Acid Receptor Alpha (RARα) in Macrophages Protects from Diet-Induced Atherosclerosis in Mice.

Retinoic acid signaling plays an important role in regulating lipid metabolism and inflammation. However, the role of retinoic acid receptor alpha (RARα) in atherosclerosis remains to be determined. In the current study, we investigated the role of macrophage RARα in the development of atherosclerosis. Macrophages isolated from myeloid-specific Rarα-/- (RarαMac-/-) mice showed increased lipid accumulation and inflammation and reduced cholesterol efflux compared to Rarαfl/fl (control) mice. All-trans retinoic acid (AtRA) induced ATP-binding cassette subfamily A member 1 (Abca1) and Abcg1 expression and cholesterol efflux in both RarαMac-/- mice and Rarαfl/fl mice. In Ldlr-/- mice, myeloid ablation of RARα significantly reduced macrophage Abca1 and Abcg1 expression and cholesterol efflux, induced inflammatory genes, and aggravated Western diet-induced atherosclerosis. Our data demonstrate that macrophage RARα protects against atherosclerosis, likely via inducing cholesterol efflux and inhibiting inflammation.

Deficiency of RARα Suppresses Decidualization via Downregulating CEBPB Transcription in Women With Recurrent Implantation Failure.

Background: Recurrent implantation failure (RIF) is a disease associated with endometrial receptivity dysfunction. Retinoic acid receptor alpha (RARα) is an important protein in many biological processes, such as differentiation and development. However, the exact underlying mechanism whereby RARα affects RIF remains unknown. This study investigated RARα expression and its contribution in the mid-luteal phase endometria of patients with RIF. Methods: The expression levels of RARα and CCAAT/enhancer-binding protein (C/EBP) ß in the endometria of the RIF and normal group were investigated using western blotting and immunohistochemistry. In in vitro experiments, immortal telomerase-transformed human endometrial stromal cells (T-HESCs) were incubated with medroxyprogesterone-17-acetate (MPA) and cyclic adenosine monophosphate (cAMP) for 4 days to induce decidualization. The expression levels of the decidualization markers prolactin (PRL) and insulin-like growth factor-binding protein-1 (IGFBP-1) were determined using quantitative polymerase chain reaction. RARα was knocked down using a small interfering RNA, and C/EBPß was overexpressed from an adenoviral vector. The transcriptional regulation of CEBPB by RARα was determined by chromatin immunoprecipitation (ChIP) assay and luciferase assays. Results: We found that the expression levels of RARα decreased in the mid-luteal endometria of RIF patients. After 4 days of decidualization induction in vitro, RARα knockdown impaired the decidualization of T-HESCs and downregulated the expression of C/EBPß. The restoration of C/EBPß expression rescued the RARα knockdown-induced suppression of T-HESC decidualization. In ChIP analysis of lysates from decidualized T-HESCs, the CEBPB promoter region was enriched in chromatin fragments pulled down using an anti-RARα antibody. However, the relationship between CEBPB transcription and RARα expression levels was only observed when the decidualization of T-HESCs was induced by the addition of cAMP and MPA. To identify the binding site of RARα/retinoid X receptor α, we performed luciferase assays. Mutation of the predicted binding site in CEBPB (-2,009/-1,781) decreased the transcriptional activity of the reporter. To confirm this mechanism, the expression levels of C/EBPß in the mid-luteal endometria of RIF patients were determined and found to decrease with decreased RARα expression levels. Conclusion: A deficiency of RARα expression in the mid-luteal endometrium inhibits decidualization due to the downregulation of CEBPB transcription. This is a potential mechanism contributing to RIF.

Short-Chain Fatty Acids Calibrate RARα Activity Regulating Food Sensitization.

Gut-microbiota dysbiosis links to allergic diseases. The mechanism of the exacerbation of food allergy caused by gut-microbiota dysbiosis remains unknown. Regulation of retinoic acid receptor alpha (RARα) signaling is critical for gut immune homeostasis. Here we clarified that RARα in dendritic cells (DCs) promotes Th2 cell differentiation. Antibiotics treatment stimulates retinoic acid signaling in mucosal DCs. We found microbiota metabolites short-chain fatty acids (SCFAs) maintain IGF-1 levels in serum and mesenteric lymph nodes. The IGF-1/Akt pathway is essential for regulating the transcription of genes targeted by RARα. And RARα in DCs affects type I interferon (IFN-I) responses through regulating transcription of IFN-α. Our study identifies SCFAs crosstalk with RARα in dendritic cells as a critical modulator that plays a core role in promoting Th2 cells differentiation at a state of modified/disturbed microbiome.

Convergence of distinct signaling pathways on synaptic scaling to trigger rapid antidepressant action.

Ketamine is a noncompetitive glutamatergic N-methyl-d-aspartate receptor (NMDAR) antagonist that exerts rapid antidepressant effects. Preclinical studies identify eukaryotic elongation factor 2 kinase (eEF2K) signaling as essential for the rapid antidepressant action of ketamine. Here, we combine genetic, electrophysiological, and pharmacological strategies to investigate the role of eEF2K in synaptic function and find that acute, but not chronic, inhibition of eEF2K activity induces rapid synaptic scaling in the hippocampus. Retinoic acid (RA) signaling also elicits a similar form of rapid synaptic scaling in the hippocampus, which we observe is independent of eEF2K functioni. The RA signaling pathway is not required for ketamine-mediated antidepressant action; however, direct activation of the retinoic acid receptor α (RARα) evokes rapid antidepressant action resembling ketamine. Our findings show that ketamine and RARα activation independently elicit a similar form of multiplicative synaptic scaling that is causal for rapid antidepressant action.

FMRP Interacts with RARα in Synaptic Retinoic Acid Signaling and Homeostatic Synaptic Plasticity.

The fragile X syndrome (FXS) is an X-chromosome-linked neurodevelopmental disorder with severe intellectual disability caused by inactivation of the fragile X mental retardation 1 (FMR1) gene and subsequent loss of the fragile X mental retardation protein (FMRP). Among the various types of abnormal synaptic function and synaptic plasticity phenotypes reported in FXS animal models, defective synaptic retinoic acid (RA) signaling and subsequent defective homeostatic plasticity have emerged as a major synaptic dysfunction. However, the mechanism underlying the defective synaptic RA signaling in the absence of FMRP is unknown. Here, we show that RARα, the RA receptor critically involved in synaptic RA signaling, directly interacts with FMRP. This interaction is enhanced in the presence of RA. Blocking the interaction between FMRP and RARα with a small peptide corresponding to the critical binding site in RARα abolishes RA-induced increases in excitatory synaptic transmission, recapitulating the phenotype seen in the Fmr1 knockout mouse. Taken together, these data suggest that not only are functional FMRP and RARα necessary for RA-dependent homeostatic synaptic plasticity, but that the interaction between these two proteins is essential for proper transcription-independent RA signaling. Our results may provide further mechanistic understanding into FXS synaptic pathophysiology.

Impact of RARα and miR-138 on retinoblastoma etoposide resistance.

BACKGROUND: Retinoblastoma (RB) is the most common childhood eye cancer. Chemotherapeutic drugs such as etoposide used in RB treatment often cause massive side effects and acquired drug resistances. Dysregulated genes and miRNAs have a large impact on cancer progression and development of chemotherapy resistances. OBJECTIVE: This study was designed to investigate the involvement of retinoic acid receptor alpha (RARα) in RB progression and chemoresistance as well as the impact of miR-138, a potential RARα regulating miRNA. METHODS: RARα and miR-138 expression in etoposide resistant RB cell lines and chemotherapy treated patient tumors compared to non-treated tumors was revealed by Real-Time PCR. Overexpression approaches were performed to analyze the effects of RARα on RB cell viability, apoptosis, proliferation and tumorigenesis. Besides, we addressed the effect of miR-138 overexpression on RB cell chemotherapy resistance. RESULTS: A binding between miR-138 and RARα was shown by dual luciferase reporter gene assay. The study presented revealed that RARα is downregulated in etoposide resistant RB cells, while miR-138 is endogenously upregulated. Opposing RARα and miR-138 expression levels were detectable in chemotherapy pre-treated compared to non-treated RB tumor specimen. Overexpression of RARα increases apoptosis levels and reduces tumor cell growth of aggressive etoposide resistant RB cells in vitro and in vivo. Overexpression of miR-138 in chemo-sensitive RB cell lines partly enhances cell viability after etoposide treatment. CONCLUSIONS: Our findings show that RARα acts as a tumor suppressor in retinoblastoma and is downregulated upon etoposide resistance in RB cells. Thus, RARα may contribute to the development and progression of RB chemo-resistance.

Inhibition of retinoic acid receptor α phosphorylation represses the progression of triple-negative breast cancer via transactivating miR-3074-5p to target DHRS3.

BACKGROUND: Retinoids are promising agents in the treatment of different types of neoplasia including estrogen receptor-positive breast cancers, whereas refractoriness/low sensitivity is observed in triple-negative breast cancer (TNBC) subtype. However, the reason for these diverse retinoid-sensitivity remains elusive. METHODS: Determinants of retinoid sensitivity were investigated using immunohistochemistry of primary patient samples, and identified retinoic acid receptor α (RARα) as a putative factor. The anti-tumor activity of hypo-phosphorylated RARα was investigated in TNBC cell models and a xenograft mouse model. Next, miRNA sequencing analysis was performed to identify the target miRNA of RARα, and luciferase reporter was used to confirm the direct target gene of miR-3074-5p. RESULTS: We discovered that serine-77 residue of RARα was constantly phosphorylated, which correlated with TNBC's resistance to retinoids. Overexpression of a phosphorylation-defective mutant RARαS77A mimicked activated RARα and repressed TNBC cell progression both in vitro and in vivo, via activating cell cycle arrest, apoptosis, and cytotoxic autophagy, independent of RARα agonists. We further revealed that the anti-tumor action of RARαS77A was, at least in part, mediated by the up-regulation of miR-3074-5p, which directly targeted DHRS3, a reductase negatively associated with TNBC patient survival. Our results suggest that the inhibition of RARαS77 phosphorylation by either expressing RARαS77A or inhibiting RARα's phosphokinase CDK7, can bypass RA stimuli to transactivate tumor-suppressive miR-3074-5p and reduce oncogenic DHRS3, thus overcoming the RA-resistance of TNBC. CONCLUSION: The novel regulatory network, involving RARαS77 phosphorylation, miR-3074-5p, and DHRS3, emerges as a new target for TNBC treatment.

Mechanistic effects of arsenic trioxide on acute promyelocytic leukemia and other types of leukemias.

Acute promyelocytic leukemia (APL), a subtype of acute myeloid leukemia characterized with a translocation between promyelocytic leukemia gene (PML) on chromosome 15 and retinoic acid receptor alpha gene (RARα) on chromosome 17. Transcription of this fusion gene results in PML/RARα fusion protein blocking expression of critical genes involved in differentiation of myeloid cells through interaction with RAR element. PML/RARα fusion protein prevents normal function of PML and RARα as well as inhibiting apoptosis. Arsenic trioxide (ATO) is an important agent for the treatment of relapsed and newly diagnosed APL. ATO induces apoptosis, autophagy, and partial cellular differentiation as well as inhibiting cell growth and angiogenesis. Recognition of signaling pathways and molecular mechanisms induced by ATO can be effective for discovering novel treatment strategies to target leukemia cells. Also, it can be developed for the treatment of a variety of cancer cells. This review provides a perspective on anticancerous effects of ATO on APL and leukemia cells.