GAP-independent functions of DLC1 in metastasis.

Metastases are responsible for most cancer-related deaths. One of the hallmarks of metastatic cells is increased motility and migration through extracellular matrixes. These processes rely on specific small GTPases, in particular those of the Rho family. Deleted in liver cancer-1 (DLC1) is a tumor suppressor that bears a RhoGAP activity. This protein is lost in most cancers, allowing malignant cells to proliferate and disseminate in a Rho-dependent manner. However, DLC1 is also a scaffold protein involved in alternative pathways leading to tumor and metastasis suppressor activities. Recently, substantial information has been gathered on these mechanisms and this review is aiming at describing the potential and known alternative GAP-independent mechanisms allowing DLC1 to impair migration, invasion, and metastasis formation.

Comprehensive Expression Analyses of Neural Cell-Type-Specific miRNAs Identify New Determinants of the Specification and Maintenance of Neuronal Phenotypes.

MicroRNAs (miRNAs) have been shown to play important roles in both brain development and the regulation of adult neural cell functions. However, a systematic analysis of brain miRNA functions has been hindered by a lack of comprehensive information regarding the distribution of miRNAs in neuronal versus glial cells. To address this issue, we performed microarray analyses of miRNA expression in the four principal cell types of the CNS (neurons, astrocytes, oligodendrocytes, and microglia) using primary cultures from postnatal d 1 rat cortex. These analyses revealed that neural miRNA expression is highly cell-type specific, with 116 of the 351 miRNAs examined being differentially expressed fivefold or more across the four cell types. We also demonstrate that individual neuron-enriched or neuron-diminished RNAs had a significant impact on the specification of neuronal phenotype: overexpression of the neuron-enriched miRNAs miR-376a and miR-434 increased the differentiation of neural stem cells into neurons, whereas the opposite effect was observed for the glia-enriched miRNAs miR-223, miR-146a, miR-19, and miR-32. In addition, glia-enriched miRNAs were shown to inhibit aberrant glial expression of neuronal proteins and phenotypes, as exemplified by miR-146a, which inhibited neuroligin 1-dependent synaptogenesis. This study identifies new nervous system functions of specific miRNAs, reveals the global extent to which the brain may use differential miRNA expression to regulate neural cell-type-specific phenotypes, and provides an important data resource that defines the compartmentalization of brain miRNAs across different cell types.

An atlas of human gene expression from massively parallel signature sequencing (MPSS).

We have used massively parallel signature sequencing (MPSS) to sample the transcriptomes of 32 normal human tissues to an unprecedented depth, thus documenting the patterns of expression of almost 20,000 genes with high sensitivity and specificity. The data confirm the widely held belief that differences in gene expression between cell and tissue types are largely determined by transcripts derived from a limited number of tissue-specific genes, rather than by combinations of more promiscuously expressed genes. Expression of a little more than half of all known human genes seems to account for both the common requirements and the specific functions of the tissues sampled. A classification of tissues based on patterns of gene expression largely reproduces classifications based on anatomical and biochemical properties. The unbiased sampling of the human transcriptome achieved by MPSS supports the idea that most human genes have been mapped, if not functionally characterized. This data set should prove useful for the identification of tissue-specific genes, for the study of global changes induced by pathological conditions, and for the definition of a minimal set of genes necessary for basic cell maintenance. The data are available on the Web at http://mpss.licr.org and http://sgb.lynxgen.com.

Functional differentiation of tbf1 orthologues in fission and budding yeasts.

In Saccharomyces cerevisiae, TBF1, an essential gene, influences telomere function but also has other roles in the global regulation of transcription. We have identified a new member of the tbf1 gene family in the mammalian pathogen Pneumocystis carinii. We demonstrate by transspecies complementation that its ectopic expression can provide the essential functions of Schizosaccharomyces pombe tbf1 but that there is no rescue between fission and budding yeast orthologues. Our findings indicate that an essential function of this family of proteins has diverged in the budding and fission yeasts and suggest that effects on telomere length or structure are not the primary cause of inviability in S. pombe tbf1 null strains.

Molecular mechanisms for the regulation of skin homeostasis

L'ubiquitination est une modification des protéines conservée, consistant en l'addition de résidus « ubiquitine » et régulant le destin cellulaire des protéines. La protéine « TRAF-interacting protein » TRAIP (ou TRIP) est une ligase E3 qui catalyse l'étape finale de l'ubiquitination. TRAIP est conservé dans l'évolution et est nécessaire au développement des organismes puisque l'ablation de TRAIP conduit à la mort embryonnaire aussi bien de la drosophile que de la souris. De plus, la réduction de l'expression de TRAIP dans des kératinocytes épidermiques humains réprime la prolifération cellulaire et induit un arrêt du cycle cellulaire en phase Gl, soulignant le lien étroit entre TRAIP et la prolifération cellulaire. Comme les mécanismes de régulation de la prolifération jouent un rôle majeur dans l'homéostasie de la peau, il est important de caractériser la fonction de TRAIP dans ces mécanismes. En utilisant des approches in vitro, nous avons déterminé que la protéine TRAIP est instable, modifiée par l'addition d'ubiquitine et ayant une demi-vie d'environ 4 heures. Nos analyses ont également révélé que l'expression de TRAIP est dépendante du cycle cellulaire, atteignant un pic d'expression en phase G2/M et que l'induction de son expression s'effectue principalement au cours de la transition Gl/S. Nous avons identifié le facteur de transcription E2F1 comme en étant le responsable, en régulant directement le promoteur de TRAIP. Aussi, TRAIP endogène ou surexprimée est surtout localisée au niveau du nucléole, une organelle nucléaire qui est désassemblée pendant la division cellulaire. Pour examiner la localisation subcellulaire de TRAIP pendant la mitose, nous avons imagé la protéine TRAIP fusionnée à une protéine fluorescente, à l'intérieur de cellules vivantes nommées HeLa, à l'aide d'un microscope confocal. Dans ces conditions, TRAIP est majoritairement localisée autour des chromosomes en début de mitose, puis est arrangée au niveau de l'ADN chromosomique en fin de mitose. La détection de TRAIP endogène à l'aide d'un anticorps spécifique a confirmé cette localisation. Enfin, l'inactivation de TRAIP dans les cellules HeLa par interférence ARN a inhibé leur capacité à s'arrêter en milieu de mitose. Nos résultats suggèrent que le mécanisme sous-jacent peut être lié au point de contrôle de l'assemblage du fuseau mitotique. - Ubiquitination of proteins is a post-translational modification which decides the cellular fate of the protein. The TRAF-interacting protein (TRAIP, TRIP) functions as an E3 ubiquitin ligase mediating addition of ubiquitin moieties to proteins. TRAIP interacts with the deubiquitinase CYLD, a tumor suppressor whose functional inactivation leads to skin appendage tumors. TRAIP is required for early embryonic development since removal of TRAIP either in Drosophila or mice by mutations or knock¬out is lethal due to aberrant regulation of cell proliferation and apoptosis. Furthermore, shRNA- mediated knock-down of TRAIP in human epidermal keratinocytes (HEK) repressed cell proliferation and induced a Gl/S phase block in the cell cycle. Additionally, TRAIP expression is strongly down- regulated during keratinocyte differentiation supporting the notion of a tight link between TRAIP and cell proliferation. We thus examined the biological functions of TRAIP in epithelial cell proliferation. Using an in vitro approach, we could determine that the TRAIP protein is unstable, modified by addition of ubiquitin moieties after translation and exhibits a half-life of 3.7+/-1-6 hours. Our analysis revealed that the TRAIP expression is modulated in a cell-cycle dependent manner, reaching a maximum expression level in G2/M phases. In addition, the expression of TRAIP was particularly activated during Gl/S phase transition and we could identify the transcription factor E2F1 as an activator of the TRAIP gene promoter. Both endogenous and over-expressed TRAIP mainly localized to the nucleolus, a nuclear organelle which is disassembled during cell division. To examine the subcellular localization of TRAIP during M phase, we performed confocal live-cell imaging of a functional fluorescent protein TRAIP-GFP in HeLa cells. TRAIP was distributed in the cytoplasm and accumulated around mitotic chromosomes in pro- and meta-phasic cells. TRAIP was then confined to chromosomal DNA location in anaphase and later phases of mitosis. Immune-detection of endogenous TRAIP protein confirmed its particular localization in mitosis. Finally, inactivating TRAIP expression in HeLa cells using RNA interference abrogated the cells ability to stop or delay mitosis progression. Our results suggested that TRAIP may involve the spindle assembly checkpoint.

Plasmacytoid dendritic cells: one-trick ponies or workhorses of the immune system?

Plasmacytoid dendritic cells (pDCs) were first described as interferon-producing cells and, for many years, their overlapping characteristics with both lymphocytes and classical dendritic cells (cDCs) created confusion over their exact ontogeny. In this Viewpoint article, Nature Reviews Immunology asks five leaders in the field to discuss their thoughts on the development and functions of pDCs--do these cells serve mainly as a major source of type I interferons or do they also make other important contributions to immune responses?

Multifaceted roles of peroxisome proliferator-activated receptors (PPARs) at the cellular and whole organism levels.

Chronic disorders, such as obesity, diabetes, inflammation, non-alcoholic fatty liver disease and atherosclerosis, are related to alterations in lipid and glucose metabolism, in which peroxisome proliferator-activated receptors (PPAR)α, PPARβ/δ and PPARγ are involved. These receptors form a subgroup of ligand-activated transcription factors that belong to the nuclear hormone receptor family. This review discusses a selection of novel PPAR functions identified during the last few years. The PPARs regulate processes that are essential for the maintenance of pregnancy and embryonic development. Newly found hepatic functions of PPARα are the mediation of female-specific gene repression and the protection of the liver from oestrogen induced toxicity. PPARα also controls lipid catabolism and is the target of hypolipidaemic drugs, whereas PPARγ controls adipocyte differentiation and regulates lipid storage; it is the target for the insulin sensitising thiazolidinediones used to treat type 2 diabetes. Activation of PPARβ/δ increases lipid catabolism in skeletal muscle, the heart and adipose tissue. In addition, PPARβ/δ ligands prevent weight gain and suppress macrophage derived inflammation. In fact, therapeutic benefits of PPAR ligands have been confirmed in inflammatory and autoimmune diseases, such as encephalomyelitis and inflammatory bowel disease. Furthermore, PPARs promote skin wound repair. PPARα favours skin healing during the inflammatory phase that follows injury, whilst PPARβ/δ enhances keratinocyte survival and migration. Due to their collective functions in skin, PPARs represent a major research target for our understanding of many skin diseases. Taken altogether, these functions suggest that PPARs serve as physiological sensors in different stress situations and remain valuable targets for innovative therapies.

Calpain 3, the "gatekeeper" of proper sarcomere assembly, turnover and maintenance.

Calpain 3 is a member of the calpain family of calcium-dependent intracellular proteases. Thirteen years ago it was discovered that mutations in calpain 3 (CAPN3) result in an autosomal recessive and progressive form of limb girdle muscular dystrophy called limb girdle muscular dystrophy type 2A. While calpain 3 mRNA is expressed at high levels in muscle and appears to have some role in developmental processes, muscles of patients and mice lacking calpain 3 still form apparently normal muscle during prenatal development; thus, a functional calpain 3 protease is not mandatory for muscle to form in vivo but it is a pre-requisite for muscle to remain healthy. Despite intensive research in this field, the physiological substrates of the calpain 3 protein (hereafter referred to as CAPN3) and its alternatively spliced isoforms remain elusive. The existence of these multiple isoforms complicates the search for the physiological functions of CAPN3 and its pathophysiological role. In this review, we summarize the genetic and biochemical evidence that point to loss of function of the full-length isoform of CAPN3, also known as p94, as the pathogenic isoform. We also argue that its natural substrates must reside in its proximity within the sarcomere where it is stored in an inactive state anchored to titin. We further propose that CAPN3 has many attributes that make it ideally suited as a sensor of sarcomeric integrity and function, involved in its repair and maintenance. Loss of these CAPN3-mediated activities can explain the "progressive" development of muscular dystrophy.