Cadmium Induces Retinoic Acid Signaling by Regulating Retinoic Acid Metabolic Gene Expression
ABSTRACT The transition metal cadmium is an environmental teratogen. In addition, cadmium and retinoic acid can act synergistically to induce forelimb malformations. The molecular mechanism underlying the teratogenicity of cadmium and the synergistic effect with retinoic acid has not been addressed. An evolutionarily conserved gene, beta,beta-carotene 15,15'-monooxygenase (BCMO), which is involved in retinoic acid biosynthesis, was studied in both Caenorhabditis elegans and murine Hepa 1-6 cells. In C. elegans, bcmo-1 was expressed in the intestine and was cadmium inducible. Similarly, in Hepa 1-6 cells, Bcmo1 was induced by cadmium. Retinoic acid-mediated signaling increased after 24-h exposures to 5 and 10 microm cadmium in Hepa 1-6 cells. Examination of gene expression demonstrated that the induction of retinoic acid signaling by cadmium may be mediated by overexpression of Bcmo1. Furthermore, cadmium inhibited the expression of Cyp26a1 and Cyp26b1, which are involved in retinoic acid degradation. These results indicate that cadmium-induced teratogenicity may be due to the ability of the metal to increase the levels of retinoic acid by disrupting the expression of retinoic acid-metabolizing genes.
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ABSTRACT: Because all-trans retinoic acid (atRA) is teratogenic in all species tested and many of the specific defects induced are common across the phylogenetic spectrum, it would be logical to predict that murine strain differences in teratology to this agent are minimal. However, for specific defects, strain susceptibilities are vastly different. Studies with atRA have shown stark differences between C57BL/6 and SWV mouse strains in susceptibility to postaxial forelimb ectrodactyly and ectopic hindlimb formation, with the C57 strain being more susceptible for both defects. Various approaches were used to determine why these strains differ in susceptibility, but the mechanisms remain unknown. Hindlimb duplications were hypothesized to be caused by the formation of ectopic posterior body axes. For forelimb ectrodactyly, a locus on chromosome 11, Rafar, has linkage to the strain difference, and mRNA localization has shown that specific genes (Fgf8, Dlx3, Bmp4, and Sp8) in the postaxial preAER (prior to formation of the apical ectodermal ridge) of the developing limb bud (the site of the defect) were downregulated hours after atRA administration more in the susceptible C57 than in the SWV strain. Because both atRA and divalent cadmium induce postaxial forelimb ectrodactyly (right-sided predominance) at a high rate in C57BL/6 and low in the SWV strain, there is debate as to whether they share a common mechanism. These teratogens cause a greater-than-additive level of forelimb ectrodactyly when coadministered at low doses, but cadmium does not induce ectopic hindlimb formation. The hypothesis is that these agents have separate molecular pathologic pathways that converge to perturb a common anatomic structure.Birth Defects Research Part A Clinical and Molecular Teratology 10/2010; 88(10):863-82. DOI:10.1002/bdra.20712 · 2.21 Impact Factor
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ABSTRACT: To incorporate genomics data into environmental assessments a mechanistic perspective of interactions between chemicals and induced biological processes needs to be developed. Since chemical compounds with structural similarity often induce comparable biological responses in exposed animals, gene expression signatures can serve as a starting point for the assessment of chemicals and their toxicity, but only when relevant and stable gene panels are available. To design such a panel, we isolated differentially expressed gene fragments from the soil arthropod Folsomia candida, a species often used for ecotoxicological testing. Animals were exposed to two chemically distinct compounds, being a metal (cadmium) and a polycyclic aromatic hydrocarbon (phenanthrene). We investigated the affected molecular responses resulting from either treatment and developed and validated 44 qPCR assays for their responses using a high throughput nano-liter RT-qPCR platform for the analysis of the samples. Suppressive subtractive hybridization (SSH) was used to retrieve stress-related gene fragments. SSH libraries revealed pathways involved in mitochondrial dysfunction and protein degradation for cadmium and biotransformation for phenanthrene to be overrepresented. Amongst a small cluster of SSH-derived cadmium responsive markers were an inflammatory response protein and an endo-glucanase. Conversely, cytochrome P450 family 6 or 9 was specifically induced by phenanthrene. Differential expressions of these candidate biomarkers were also highly significant in the independently generated test sample set. Toxicity levels in different training samples were not reflected by any of the markers' intensity of expressions. Though, a model based on partial least squares differential analysis (PLS-DA) (with RMSEPs between 9 and 22% and R(2)s between 0.82 and 0.97) using gene expressions of 25 important qPCR assays correctly predicted the nature of exposures of test samples. For the application of molecular bio-indication in environmental assessments, multivariate analyses obviously have an added value over univariate methods. Our results suggest that compound discrimination can be achieved by PLS-DA, based on a hard classification of the within-class rankings of samples from a test set. This study clearly shows that the use of high throughput RT-qPCR could be a valuable tool in ecotoxicology combining high throughput with analytical sensitivity.BMC Molecular Biology 03/2011; 12:11. DOI:10.1186/1471-2199-12-11 · 2.06 Impact Factor