Fee Arrangements and Fee Shifting: Lessons From the Experience in Ontario

About one-third of oestrogen receptor alpha-positive breast cancer patients treated with tamoxifen relapse. Here we identify the nuclear receptor retinoic acid receptor alpha as a marker of tamoxifen resistance. Using quantitative mass spectrometry-based proteomics, we show that retinoic acid receptor alpha protein networks and levels differ in a tamoxifen-sensitive (MCF7) and a tamoxifen-resistant (LCC2) cell line. High intratumoural retinoic acid receptor alpha protein levels also correlate with reduced relapse-free survival in oestrogen receptor alpha-positive breast cancer patients treated with adjuvant tamoxifen solely. A similar retinoic acid receptor alpha expression pattern is seen in a comparable independent patient cohort. An oestrogen receptor alpha and retinoic acid receptor alpha ligand screening reveals that tamoxifen-resistant LCC2 cells have increased sensitivity to retinoic acid receptor alpha ligands and are less sensitive to oestrogen receptor alpha ligands compared with MCF7 cells. Our data indicate that retinoic acid receptor alpha may be a novel therapeutic target and a predictive factor for oestrogen receptor alpha-positive breast cancer patients treated with adjuvant tamoxifen

Studies on the mechanism of retinoid-induced pattern duplications in the early chick limb bud: temporal and spatial aspects.

All-trans-retinoic acid causes striking digit pattern changes when it is continuously released from a bead implanted in the anterior margin of an early chick wing bud. In addition to the normal set of digits (234), extra digits form in a mirror-symmetrical arrangement, creating digit patterns such as a 432234. These retinoic acid-induced pattern duplications closely mimic those found after grafts of polarizing region cells to the same positions with regard to dose-response, timing, and positional effects. To elucidate the mechanism by which retinoic acid induces these pattern duplications, we have studied the temporal and spatial distribution of all-trans-retinoic acid and its potent analogue TTNPB in these limb buds. We find that the induction process is biphasic: there is an 8-h lag phase followed by a 6-h duplication phase, during which additional digits are irreversibly specified in the sequence digit 2, digit 3, digit 4. On average, formation of each digit seems to require between 1 and 2 h. The tissue concentrations, metabolic pattern, and spatial distribution of all-trans-retinoic acid and TTNPB in the limb rapidly reach a steady state, in which the continuous release of the retinoid is balanced by loss from metabolism and blood circulation. Pulse-chase experiments reveal that the half-time of clearance from the bud is 20 min for all-trans-retinoic acid and 80 min for TTNPB. Manipulations that change the experimentally induced steep concentration gradient of TTNPB suggest that a graded distribution of retinoid concentrations across the limb is required during the duplication phase to induce changes in the digit pattern. The extensive similarities between results obtained with retinoids and with polarizing region grafts raise the possibility that retinoic acid serves as a natural "morphogen" in the limb

Unexpected evolutionary proximity of eukaryotic and cyanobacterial enzymes responsible for biosynthesis of retinoic acid and its oxidation

Biosynthesis of retinoic acid from retinaldehyde (retinal) is catalysed by an aldehyde dehydrogenase (ALDH) and its oxidation by cytochrome P450 enzymes (CYPs). Herein we show by phylogenetic analysis that the ALDHs and CYPs in the retinoic acid pathway in animals are much closer in evolutionary terms to cyanobacterial orthologs than would be expected from the standard models of evolution

Proliferation versus Differentiation: Redefining Retinoic Acids Role.

Retinoic acid is commonly used in culture to differentiate stem cells into neurons and has established neural differentiation functions in vivo in developing and adult organisms. In this issue of Stem Cell Reports, Mishra et al. (2018) broaden its role in stem cell functions, showing that retinoic acid is necessary for stem and progenitor cell proliferation in the adult brain

Retinoids cause apoptosis in pancreatic cancer cells via activation of RAR-γ and altered expression of Bcl-2/Bax

All-trans-retinoic acid and 9-cis-retinoic acid have been reported to have inhibitory effects on pancreatic adenocarcinoma cells and we have shown that this is partly due to induction of apoptosis. In this study, the mechanisms whereby 9-cis-retinoic acid induces apoptosis in these cells were investigated. An involvement of the Bcl-2 family of proteins was shown, such that 9-cis-retinoic acid causes a decrease in the Bcl-2/Bax ratio. Overexpression of Bcl-2 also resulted in inhibition of apoptosis induced by 9-cis-retinoic acid. Furthermore, two broad-range caspase inhibitors blocked DNA fragmentation induced by 9-cis-retinoic acid, but had no effect on viability defined by mitochondrial activity. Using synthetic retinoids, which bind selectively to specific retinoic acid receptor subtypes, we further established that activation of retinoic acid receptor-γ is essential for induction of apoptosis. Only pan-retinoic acid receptor and retinoic acid receptor-γ selective agonists reduced viability and a cell line expressing very low levels of retinoic acid receptor-γ is resistant to the effects of 9-cis-retinoic acid. A retinoic acid receptor-β/γ selective antagonist also suppressed the cytotoxic effects of 9-cis-retinoic acid in a dose-dependent manner. This study provides important insight into the mechanisms involved in suppression of pancreatic tumour cell growth by retinoids. Our results encourage further work evaluating the clinical use of receptor subtype selective retinoids in pancreatic carcinoma

Expression of ski can act as a negative feedback mechanism on retinoic acid signaling

Background: Retinoic acid signaling is essential for many aspects of early development in vertebrates. To control the levels of signaling, several retinoic acid target genes have been identified that act to suppress retinoic acid signaling in a negative feedback loop. The nuclear protein Ski has been extensively studied for its ability to suppress transforming growth factor-beta (TGF-β) signaling but has also been implicated in the repression of retinoic acid signaling. Results: We demonstrate that ski expression is up-regulated in response to retinoic acid in both early Xenopus embryos and in human cell lines. Blocking retinoic acid signaling using a retinoic acid antagonist results in a corresponding decrease in the levels of ski mRNA. Finally, overexpression of SKI in human cells results in reduced levels of CYP26A1 mRNA, a known target of retinoic acid signaling. Conclusions: Our results, coupled with the known ability of Ski to repress retinoic acid signaling, demonstrate that Ski expression is a novel negative feedback mechanism acting on retinoic acid signaling. Developmental Dynamics 242:604-613, 2013. © 2013 Wiley Periodicals, Inc

Retinoic Acid Regulation of Aromatase Expression in the Ovary

Retinoic acid is the active derivative of vitamin-A in the body. Retinoic acid is essential in normal embryonic development, and studies from the Kipp laboratory have also demonstrated its importance in the developing ovary. Aromatase, encoded by the gene Cyp19a1, is an enzyme that converts androgens to estrogens, and is primarily expressed in the granulosa cells of the ovary. Previous studies have suggested that retinoic acid influences aromatase expression in a few different tissue types; however, how retinoic acid may regulate aromatase expression in the ovary is not known. Therefore, the purpose of this study was to examine the role of retinoic acid in regulating aromatase expression in granulosa cells from the mouse ovary. Granulosa cells were isolated and treated with retinoic acid, a retinoic acid metabolism blocking agent R115866, a pan-retinoic acid receptor inhibitor AGN193109, and combinations of these treatments. Cells were treated for 24- and 72- hours, after which mRNA and proteins were collected for RT-PCR and western blot analyses, respectively. The results showed that retinoic acid or R115866 treatment increased Cyp19a1 mRNA levels at 24-hours. The stimulatory effects were specific as they were abolished by AGN193109. AGN193109 continued to suppress Cyp19a1 mRNA levels after 72-hours, but no stimulatory effect by retinoic acid was observed, possibly due to the short half-life of the mRNA. Retinoic acid and R115866 also increased aromatase protein expression at 24- and 72- hours. It was observed that 19-day MT-α transgenic mice had increased levels of Cyp26b1 mRNA, which encodes an enzyme that metabolizes retinoic acid, and decreased levels of Cyp19a1 mRNA, suggesting retinoic acid signaling is important in aromatase expression in vivo. Overall, this study provides strong evidence that further supports an important role of retinoic acid in ovarian development, as it demonstrates that retinoic acid regulates ovarian aromatase expression

Interaction between cellular retinoic acid-binding protein II and histone hypoacetylation in renal cell carcinoma

Renal cell carcinoma is a rare but serious malignancy. Since a reduction in the level of retinoic acid receptor beta 2 (RARbeta2) expression in cancer cells due in part to histone hypoacetylation which is controlled by histone deacetylase (HD), the study on the interaction between cellular retinoic acid-binding proteins II (CRABP II), which is proposed to have its potential influence on retinoic acid (RA) response, and HD can be useful. Comparing to CARBP II and HD, the CARBP II-HD poses the same function and biological process as HD. This can confirm that HD has a significant suppressive effect on the expression of CARBP II. Therefore, reduction in the level of RARbeta2 expression in cancer cells can be expected and this can lead to failure in treatment of renal cell carcinoma with RA. The author hereby purpose that additional HD inhibitor should be added into the regiment of RA to increase the effectiveness of treatment

Effects of localized application of retinoic acid on Xenopus laevis development

In order to more accurately determine the mechanism by which retinoic acid causes embryonic defects, we have developed a simple method of locally applying retinoic acid rather than immersing the whole embryo in retinoic acid solutions. Retinoic acid was suspended in corn oil and then injected between the surface and the deep ectodermal layers of an early gastrula Xenopus embryo. When droplets containing retinoic acid were injected into the presumptive head region, the embryos exhibited inhibited development of anterior structures near the injection site. Development of the eye, cement gland, hatching gland, olfactory pits, and expression of engrailed protein were all disrupted near the injection site. Inhibited development of anterior structures was far greater on the injected side of the embryo than on the uninjected side. The retinoic acid droplet did not cause an anterior shift of structures on the injected side relative to the uninjected side. These experiments suggest that retinoic acid does not cause global respecification of axial level in the head, but rather suppresses development of anterior structures. Retinoic acid injected into presumptive trunk regions had no discernible effect