Jean-Jacques Michaille

miR-155: On the Crosstalk Between Inflammation and Cancer

MicroRNAs are short non-coding RNAs that posttranscriptionally modulate the expression of multiple target genes and are thus implicated in a wide array of cellular and developmental processes. miR-155 is processed from BIC, a non-coding transcript highly expressed in both activated B and T cells and in monocytes/macrophages. miR-155 levels change dynamically during both hematopoietic lineage differentiation and the course of the immune response. Different mouse models developed recently indicate that miR-155 plays a critical role during hematopoiesis and regulates lymphocyte homeostasis and tolerance. A moderate increase of miR-155 levels is observed in many types of malignancies of B cell or myeloid origin, and transgenic over-expression of miR-155 in mice results in cancer. While the high levels of miR-155 reached transiently during the course of the immune response remain unharmful for the organism, the reason why a moderate up-regulation of miR-155 can lead to cancer remains obscure. As prolonged exposure to inflammation can lead to cancer, the permanent up-regulation of miR-155 might be a link between the two. Therefore, designing miR-155 based therapies will require a better understanding of the molecular basis of its action as well as of how miR-155 levels are regulated in a cell-specific manner.

Resveratrol, MicroRNAs, Inflammation, and Cancer

MicroRNAs are short noncoding RNAs that regulate the expression of many target genes posttranscriptionally and are thus implicated in a wide array of cellular and developmental processes. The expression of miR-155 or miR-21 is upregulated during the course of the inflammatory response, but these microRNAs are also considered oncogenes due to their upregulation of expression in several types of tumors. Furthermore, it is now well established that inflammation is associated with the induction or the aggravation of nearly 25% of cancers. Therefore, the above microRNAs are thought to link inflammation and cancer. Recently, resveratrol (trans-3,4′,5-trihydroxystilbene), a natural polyphenol with antioxidant, anti-inflammatory, and anticancer properties, currently at the stage of preclinical studies for human cancer prevention, has been shown to induce the expression of miR-663, a tumor-suppressor and anti-inflammatory microRNA, while downregulating miR-155 and miR-21. In this paper we will discuss how the use of resveratrol in therapeutics may benefit from the preanalyses on the status of expression of miR-155 or miR-21 as well as of TGFβ1. In addition, we will discuss how resveratrol activity might possibly be enhanced by simultaneously manipulating the levels of its key target microRNAs, such as miR-663.

Retinoic Acid-Mediated Increase in TrkA Expression Is Sufficient to Elicit NGF-Dependent Survival of Sympathetic Neurons

Sympathetic neurons depend on the classical neurotrophin NGF for survival by the time they innervate their targets, but the mechanisms controlling the onset of NGF responsiveness in developing neuroblasts have not been defined. Immature chick sympathetic neurons are unresponsive to NGF, but express low mRNA levels of the high-affinity NGF receptor trkA. Treatment with retinoic acid (RA) leads to increased levels of both trkA mRNA and protein, a response mediated through retinoic acid receptor alpha (RAR alpha). Ectopic expression of trkA in these cells results in the ability to survive with NGF, suggesting that RA-induced trkA expression is sufficient to elicit NGF-dependent survival. Our data establish a mechanism controlling NGF responsiveness and implicate a function for RA at defined late stages of neuron development.

Initial Retinoid Requirement for Early Avian Development Coincides With Retinoid Receptor Coexpression in the Precardiac Fields and Induction of Normal Cardiovascular Development

Vitamin A requirement for early embryonic development is clearly evident in the gross cardiovascular and central nervous system abnormalities and an early death of the vitamin A‐deficient quail embryo. This retinoid knockout model system was used to examine the biological activity of various natural retinoids in early cardiovascular development. We demonstrate that all‐trans‐, 9‐cis‐, 4‐oxo‐, and didehydroretinoic acids, and didehydroretinol and all‐trans‐retinol induce and maintain normal cardiovascular development as well as induce expression of the retinoic acid receptor β2 in the vitamin A‐deficient quail embryo. The expression of RARβ2 is at the same level and at the same sites where it is expressed in the normal embryo. Retinoids provided to the vitamin A‐deficient embryo up to the 5‐somite stage of development, but not later, completely rescue embryonic development, suggesting the 5‐somite stage as a critical retinoid‐sensitive time point during early avian embryogenesis. Retinoid receptors RARα, RARγ, and RXRα are expressed in both the precardiac endoderm and mesoderm in the normal and the vitamin A‐deficient quail embryo, while the expression of RXRγ is restricted to precardiac endoderm. Vitamin A deficiency downregulates the expression of RARα and RARβ. Our studies provide strong evidence for a narrow retinoid‐requiring developmental window during early embryogenesis, in which the presence of bioactive retinoids and their receptors is essential for a subsequent normal embryonic development. Dev. Dyn. 1998;213:188–198.

Retinoid receptors and vitamin A deficiency: differential patterns of transcription during early avian development and the rapid induction of RARs by retinoic acid

The functional links of specific retinoid receptors to early developmental events in the avian embryo are not known. Before such studies are undertaken, knowledge is required of the spatiotemporal expression patterns of the receptor genes and their regulation by endogenous retinoic acid levels during the early stages of development. Here, we report the expression patterns of mRNAs for RARalpha, RARalpha2, RARbeta2, RARgamma, RARgamma2, RXRalpha, and RARgamma from neurulation to HH10 in the normal and vitamin A-deficient (VAD) quail embryo. The transcripts for all retinoid receptors are detectable at HH5, except for RXRgamma, which is detected at the beginning of HH6. At the 4/5 somite stage of HH8, when retinoid signaling is initiated in the avian embryo, mRNAs of all receptors are present, with very strong and ubiquitous expression patterns for RARalpha, RARalpha2, RARgamma, RARgamma2, and RXRalpha, a persistent expression of RARgamma in the neural tissues, a strong expression of RARbeta2 in lateral plate mesoderm and somites, and an anterior expression of RXRgamma. All retinoid receptors are expressed in the heart primordia. In the VAD quail embryo, the general pattern of retinoid receptor transcript localization is similar to that of the normal, except that the expression of RARalpha2 and RARbeta2 is severely diminished. Administration of retinol or retinoic acid to VAD embryos at or before the 4/5 somite stage rescues the expression of RARalpha2 and RARbeta2 within approximately 45 min and restores normal development. RARbeta2 expression requires the expression of RARalpha2. After neurulation, the expression of all retinoid receptors in the VAD quail embryo becomes independent of vitamin A status and is similar to that of the normal. The mRNA levels and sites of expression of the key enzyme for retinoic acid biosynthesis, Raldh-2, are not affected by vitamin A status; the expression pattern is restricted and does not correspond to that of retinoid receptors at all sites. The general patterns and intensity of retinoid receptor gene expression during early quail development are comparable to those of the mammalian and thus validate the application of results from retinoid-regulated avian development studies to those of the mammalian.

Effects of dietary phytophenols on the expression of microRNAs involved in mammalian cell homeostasis.

Besides synthesizing nutritive substances (proteins, fats and carbohydrates) for energy and growth, plants produce numerous non-energetic so-called secondary metabolites (mainly polyphenols) that allow them to protect themselves against infections and other types of hostile environments. Interestingly, these polyphenols often provide cells with valuable bioactive properties for the maintenance of their functions and homeostasis (signaling, gene regulation, protection against acquired or infectious diseases, etc.) both in humans and animals. Namely, from a nutritional point of view, and based on epidemiological data, it is now well accepted that the regular consumption of green vegetables, fruits and fibers has protective effects against the onset of cancer as well as of inflammatory, neurodegenerative, metabolic and cardiovascular diseases, and consequently increases the overall longevity. In particular, grapevine plants produce large amounts of a wide variety of polyphenols. The most prominent of those-resveratrol-has been shown to impair or delay cardiovascular alterations, cancer, inflammation, aging, etc. Until recently, the molecular bases of the pleiotropic effects of resveratrol remained largely unclear despite numerous studies on a variety of signaling pathways and the transcriptional networks that they control. However, it has been recently proposed that the protective properties of resveratrol may arise from its modulation of small non-coding regulatory RNAs, namely microRNAs. The aim of this review is to present up-to-date data on the control of microRNA expression by dietary phytophenols in different types of human cells, and their impact on cell differentiation, cancer development and the regulation of the inflammatory response.

Function of RARγ and RARα2 at the initiation of retinoid signaling is essential for avian embryo survival and for distinct events in cardiac morphogenesis

Avian embryogenesis requires retinoid receptor activation by the vitamin A active form, retinoic acid (RA), during neurulation. We conducted loss‐of‐function analysis in quail embryos by nutritional deprivation of RA and by blocking generation of retinoid receptors. Here we identify a distinct role for RARα2 in cardiac inflow tract morphogenesis and for RARγ in cardiac left/right orientation and looping morphogenesis. Blocking normal embryos with antisense oligonucleotides to RARα2 or RXRα diminishes GATA‐4 transcripts, while blocking RARγ or RXRα diminishes nodal and Pitx2 transcripts; the expression of these genes in the heart forming region resembles that of the vitamin A‐deficient embryo. Blocking the function of RARγ, RARα2, and RXRα recapitulates the complete vitamin A‐deficient phenotype. RARγ is the most potent mediator of the retinoid signal at this time of development. Our studies provide strong evidence that critical RA‐requiring developmental events in the early avian embryo are regulated by means of distinct retinoid receptor signaling pathways. Developmental Dynamics 228:697–708, 2003.

Quantitative assessment of retinoid signaling pathways in the developing eye and retina of the chicken embryo

Retinoid signaling has been implicated as an important regulator of retinal development and differentiation. We have used state of the art high‐pressure liquid chromatography to identify and quantitate biologically active retinoids, immunohistochemistry to localize the retinoic acid synthetic enzyme retinaldehyde dehydrogenase 2 (RALDH2), and nucleic acid assays to quantitate and localize retinoid receptor gene transcripts in the developing eye and retina of the chicken. Our results demonstrate spatial distinctions in retinoid synthesis and signaling that may be related to laminar differentiation in the developing retina. Retinoic acids (RAs) and their precursor retinols (ROHs) are the predominant retinoids in the developing eye. All‐trans‐RA and all‐trans‐3,4‐didehydro‐RA are present in the neuroepithelium in approximately equal amounts from early stages of neurogenesis until shortly before hatching. The retinoid X receptor (RXR) ligand 9‐cis‐RA is undetectable at all stages; if present, it cannot exceed a small percentage of the total RA content. RAs are not detected in the pigment epithelium. All‐trans‐ROH is present in the neuroepithelium and pigment epithelium, whereas all‐trans‐3,4‐didehydro‐ROH is detected only in the pigment epithelium and/or the choroid and sclera. RALDH2 immunoreactivity is intense in the choroid, low or absent in the pigment epithelium, and moderate in the neuroepithelium, where it is highest in the outer layers. Transcripts of all five chicken retinoid receptor genes are present in the neural retina and eye throughout development. During the period of neurogenesis, at least three of the receptors (RARγ, RXRγ, RXRα), exhibit dynamic patterns of differential localization within the depths of the neural retina. J. Comp. Neurol. 436:324–335, 2001.

Isolation and characterization of genomic clones of human sequences presumably coding for hair cysteine-rich proteins

The major biochemical components of the mammalian hair are the intermediate filaments or keratins and the keratin associated proteins. Keratin associated proteins are classified into two groups (high-cysteine and high glycine-tyrosine-rich polypeptides) according to the content of these amino acids. Cysteine-rich group contains high sulphur (16-24% cysteine) and ultra-high sulphur (> 30% cysteine) proteins. We report here the identification of a human sequence presumably coding for a new ultra-high sulphur protein (hUHSp21) and the isolation and characterization of four genomic clones containing six related sequences. We also discuss the possibility that all the genes encoding keratin associated proteins are evolutionary related. These human clones should provide useful molecular tools for studies of hair differentiation and understanding of the molecular basis of human trichothiodystrophy.

Promiscuous Effects of Some Phenolic Natural Products on Inflammation at Least in Part Arise from Their Ability to Modulate the Expression of Global Regulators, Namely microRNAs

Recent years have seen the exploration of a puzzling number of compounds found in human diet that could be of interest for prevention or treatment of various pathologies. Although many of these natural products (NPs) have long been used as remedies, their molecular effects still remain elusive. With the advent of biotechnology revolution, NP studies turned from chemistry and biochemistry toward global analysis of gene expression. Hope is to use genetics to identify groups of patient for whom certain NPs or their derivatives may offer new preventive or therapeutic treatments. Recently, microRNAs have gained the statute of global regulators controlling cell homeostasis by regulating gene expression through genetic and epigenetic regulatory loops. Realization that certain plant polyphenols can modify microRNA expression and thus impact gene expression globally, initiated new, mainly in vitro studies, in particular to determine phytochemicals effects on inflammatory response, whose exacerbation has been linked to several disorders including cancer, auto-immune, metabolic, cardiovascular and neuro-inflammatory diseases. However, very few mechanistic insights have been provided, given the complexity of genetic regulatory networks implicated. In this review, we will concentrate on data showing the potential interest of some plant polyphenols in manipulating the expression of pro- and anti-inflammatory microRNAs in pathological conditions.