Retinoic acid

Dev Biol. 2014 Nov 15;395(2):199-208.

Identification of novel retinoic acid target genes.[Pubmed: 25251699]

Retinoic acid is required for diverse ontogenic processes and as such identification of the genes and pathways affected by Retinoic acid is critical to understanding these pleiotropic effects. The presomitic mesoderm of the E8.5 mouse embryo is composed of undifferentiated cells that are depleted of Retinoic acid, yet are competent to respond to the retinoid signal.
METHODS AND RESULTS:
We have exploited these properties to use this tissue to identify novel Retinoic acid-responsive genes, including candidate target genes, by treating E8.5 embryos with Retinoic acid and assessing changes in gene expression in the presomitic mesoderm by microarray analysis. This exercise yielded a cohort of genes that were differentially expressed in response to exogenous Retinoic acid exposure. Among these were a number of previously characterized Retinoic acid targets, validating this approach. In addition, we recovered a number of novel candidate target genes which were confirmed as Retinoic acid-responsive by independent analysis. Chromatin immunoprecipitation assays revealed Retinoic acid receptor occupancy of the promoters of certain of these genes. We further confirmed direct Retinoic acid regulation of the F11r gene, a new RA target, using tissue culture models.
CONCLUSIONS:
Our results reveal a significant number of potential RA targets implicated in embryonic development and offer a novel in vivo system for better understanding of retinoid-dependent transcription.

J Nutr Biochem. 2014 Sep;25(9):964-76.

A RARE of hepatic Gck promoter interacts with RARα, HNF4α and COUP-TFII that affect retinoic acid- and insulin-induced Gck expression.[Pubmed: 24973045]

The expression of hepatic glucokinase gene (Gck) is regulated by hormonal and nutritional signals. How these signals integrate to regulate the hepatic Gck expression is unclear. We have shown that the hepatic Gck expression is affected by Vitamin A status and synergistically induced by insulin and retinoids in primary rat hepatocytes.
METHODS AND RESULTS:
We hypothesized that this is mediated by a Retinoic acid responsive element (RARE) in the hepatic Gck promoter. Here, we identified the RARE in the hepatic Gck promoter using standard molecular biology techniques. The single nucleotide mutations affecting the promoter activation by Retinoic acid (RA) were also determined for detail analysis of protein and DNA interactions. We have optimized experimental conditions for performing electrophoresis mobility shift assay and demonstrated the interactions of the Retinoic acid receptor α (RARα), retinoid X receptor α (RXRα), hepatocyte nuclear factor 4α (HNF4α) and chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) in the rat nuclear extract with this RARE, suggesting their roles in the regulation of Gck expression. Chromatin immunoprecipitation assays demonstrated that recombinant adenovirus-mediated overexpression of RARα, HNF4α and COUP-TFII, but not RXRα, significantly increased their occupancy in the hepatic Gck promoter in primary rat hepatocytes. Overexpression of RARα, HNF4α and COUP-TFII, but not RXRα, also affected the Retinoic acid- and insulin-mediated Gck expression in primary rat hepatocytes.
CONCLUSIONS:
In summary, this hepatic Gck promoter RARE interacts with RARα, HNF4α and COUP-TFII to integrate Vitamin A and insulin signals.

Acta Histochem. 2014 Jun;116(5):810-9.

Retinoic acid induced repair in the lung of adult hyperoxic mice, reducing transforming growth factor-β1 (TGF-β1) mediated abnormal alterations.[Pubmed: 24576683]

The aim of the study was to determine the effects of Retinoic acid on lung alveolar repair in adult hyperoxic mice and to investigate the relationship between TGF-β1 and Retinoic acid during the repair processes.
METHODS AND RESULTS:
Adult mice were divided into 4 groups. Two groups were given daily intraperitoneal injections of peanut oil/dimethylsulfoxide mixture and Retinoic acid (50mg/kg body weight, 50 μl of volume) dissolved in peanut oil/dimethylsulfoxide mixture for 12 days with a 2-day break on days 6 and 7. Following hyperoxia (100% oxygen) for 72 h the remaining two groups were treated in the same manner as already described: peanut oil/dimethylsulfoxide mixture and Retinoic acid. Lung structure was investigated by light microscopy. TGF-β1 and Smad protein expressions in the lung were assayed by biochemical methods. Hyperoxic mice exhibited damage to the alveolar walls, increased cell proliferation and induced Smad3/TGF-β1 signaling. Smad2 and phospho-Smad2 protein expressions were unchanged in all groups. Retinoic acid administration improved the degenerative alterations caused by hyperoxia and helped in alveolar repair. This positive effect of Retinoic acid resulted from the inhibition of Smad3/TGF-β1 signaling via reduced Smad4 mRNA and increased Smad7 protein expression. Retinoic acid also induced alveolarization and restricted Smad3/TGF-β1 signaling by decreasing Smad4 mRNA in healthy mice.
CONCLUSIONS:
Thus, Retinoic acid helped repair Smad3/TGF-β1-induced lung damage in hyperoxic mice.

J Neurochem. 2014 Dec;131(6):731-42.

MicroRNA-302b-inhibited E2F3 transcription factor is related to all trans retinoic acid-induced glioma cell apoptosis.[Pubmed: 25040912]

All-trans Retinoic acid (ATRA), a derivative of retinoid, is involved in the onset of differentiation and apoptosis in a wide variety of normal and cancer cells. MicroRNAs (miRNAs) are small non-coding RNAs that control gene expression. Several miRNAs were identified to participate in ATRA-mediated cell differentiation. However, no studies have demonstrated whether miRNA can enhance ATRA cytotoxicity, thereby resulting in cell apoptosis. This study investigated the effects of ATRA-mediated miRNA expression in activating apoptotic pathways in glioblastoma.
METHODS AND RESULTS:
First, we found that high-dose ATRA treatment significantly reduced cell viability, caspase-dependent apoptosis, endoplasmic reticular (ER) stress activation, and intracellular reactive oxygen species accumulation. From microarray data, miR-302b was analyzed as a putative downstream regulator upon ATRA treatment. Furthermore, we found that ATRA up-regulated miR-302b expression in a dose- and time-dependent manner through Retinoic acid receptor α-mediated pathway. Overexpression and knockdown of miR-302b significantly influenced ATRA-mediated cytotoxicity. E2F3, an important transcriptional regulator of glioma proliferation, was validated to be a direct target gene of miR-302b. The miR-302b-reduced E2F3 levels were also identified to be associated with ATRA-mediated glioma cell death.
CONCLUSIONS:
These results emphasize that an ATRA-mediated miR-302b network may provide novel therapeutic strategies for glioblastoma therapy. We propose that high-dose all-trans Retinoic acid (ATRA) treatment, a derivative of retinoid, significantly induces glioblastoma cell apoptosis via caspase-dependent apoptosis, endoplasmic reticular (ER) stress, and intracellular reactive oxygen species (ROS) accumulation. The miR-302b overexpression enhanced by ATRA-mediated Retinoic acid receptor (RAR)α pathway was also identified. The E2F3 repression, a novel target gene of miR-302b, was involved in ATRA-induced glioblastoma cell cytotoxicity.

Hum Immunol. 2014 Aug;75(8):923-9.

Retinoic acid acts as a selective human IgA switch factor.[Pubmed: 24994461]

Retinoic acid (RA) is known to have several functions that lead to a potent mucosal IgA response. Nevertheless, its exact role in human IgA synthesis has yet to be elucidated. Thus, we investigated the role of RA in promoting IgA isotype switching in human B cells.
METHODS AND RESULTS:
We found that RA increased IgA production and the expression of germ-line IgA1 and IgA2 transcripts (GLTα1 and GLTα2). This induction occurred alongside an increase in the frequency of IgA1-secreting B cell clones, as assessed by limiting dilution analysis. Under the same conditions, RA did not increase IgM and IgG production. Am80, an agonist of RA receptor α (RARα), increased IgA production. In addition, RA activity was abrogated by LE540, an antagonist of RAR, suggesting that the RAR pathway is involved in RA-induced IgA production.
CONCLUSIONS:
Taken together, these results indicate that RA induces IgA isotype switching mainly through RARα in human B cells.