ERK-regulated double cortin-like kinase (DCLK)-short phosphorylation and nuclear translocation stimulate POMC gene expression in endocrine melanotrope cells

We tested whether double cortin-like kinase-short (DCLK-short), a microtubule-associated Ser/Thr kinase predominantly expressed in the brain, is downstream of the ERK signaling pathway and is involved in proopiomelanocortin gene (POMC) expression in endocrine pituitary melanotrope cells of Xenopus laevis. Melanotropes form a well-established model to study physiological aspects of neuroendocrine plasticity. The amphibian X. laevis adapts its skin color to the background light intensity by the release of α-MSH from the melanotrope cell. In frogs on a white background, melanotropes are inactive but they are activated during adaptation to a black background. Our results show that melanotrope activation is associated with an increase in DCLK-short mRNA and with phosphorylation of DCLK-short at serine at position 30 (Ser-30). Upon cell activation phosphorylated Ser-30-DCLK-short was translocated from the cytoplasm into the nucleus, and the ERK blocker U0126 inhibited this process. The mutation of Ser-30 to alanine also inhibited the translocation and reduced POMC expression, whereas overexpression stimulated POMC expression. This is the first demonstration of DCLK-short in a native endocrine cell. We conclude that DCLK-short is physiologically regulated at both the level of its gene expression and protein phosphorylation and that the kinase is effectively regulating POMC gene expression upon its ERK-mediated phosphorylation.

Temporal and functional dynamics of the transcriptome during nerve growth factor-induced differentiation

The rat pheochromocytoma cell line (PC12) is an extensively used model to study neuronal differentiation. The initial signaling cascades triggered by nerve growth factor (NGF) stimulation have been subject to thorough investigation and are well characterized. However, knowledge of temporal transcriptomal regulation during NGF-induced differentiation of PC12 cells remains far from complete. We performed a microarray study that characterized temporal and functional changes of the transcriptome during 4 subsequent days of differentiation of Neuroscreen-1 PC12 cells. By analyzing the transcription profiles of 1595 NGF-regulated genes, we show a large diversity of transcriptional regulation in time. Also, we quantitatively identified 26 out of 243 predefined biological process and 30 out of 255 predefined molecular function classes that are specifically regulated by NGF. Combining the temporal and functional transcriptomal data revealed that NGF selectively exerts a temporally coordinated regulation of genes implicated in protein biosynthesis, intracellular signaling, cell structure, chromatin packaging and remodeling, intracellular protein traffic, mRNA transcription, and cell cycle. We will discuss how NGF-induced changes may modulate the transcriptional response to NGF itself during differentiation.

Lentivirus-mediated transgene delivery to the hippocampus reveals sub-field specific differences in expression

Background

In the adult hippocampus, the granule cell layer of the dentate gyrus is a heterogeneous structure formed by neurons of different ages, morphologies and electrophysiological properties. Retroviral vectors have been extensively used to transduce cells of the granule cell layer and study their inherent properties in an intact brain environment. In addition, lentivirus-based vectors have been used to deliver transgenes to replicative and non-replicative cells as well, such as post mitotic neurons of the CNS. However, only few studies have been dedicated to address the applicability of these widespread used vectors to hippocampal cells in vivo. Therefore, the aim of this study was to extensively characterize the cell types that are effectively transduced in vivo by VSVg-pseudotyped lentivirus-based vectors in the hippocampus dentate gyrus.

Results

In the present study we used Vesicular Stomatitis Virus G glycoprotein-pseudotyped lentivirual vectors to express EGFP from three different promoters in the mouse hippocampus. In contrast to lentiviral transduction of pyramidal cells in CA1, we identified sub-region specific differences in transgene expression in the granule cell layer of the dentate gyrus. Furthermore, we characterized the cell types transduced by these lentiviral vectors, showing that they target primarily neuronal progenitor cells and immature neurons present in the sub-granular zone and more immature layers of the granule cell layer.

Conclusion

Our observations suggest the existence of intrinsic differences in the permissiveness to lentiviral transduction among various hippocampal cell types. In particular, we show for the first time that mature neurons of the granule cell layer do not express lentivirus-delivered transgenes, despite successful expression in other hippocampal cell types. Therefore, amongst hippocampal granule cells, only adult-generated neurons are target for lentivirus-mediated transgene delivery. These properties make lentiviral vectors excellent systems for overexpression or knockdown of genes in neuronal progenitor cells, immature neurons and adult-generated neurons of the mouse hippocampus in vivo.

Chromatin immunoprecipitation scanning identifies glucocorticoid receptor binding regions in the proximal promoter of a ubiquitously expressed glucocorticoid target gene in brain

While the actions of glucocorticoids on brain functions have been comprehensively studied, the underlying genomic mechanisms are poorly understood. In this study, we show that glucocorticoid-induced leucine zipper (GILZ) mRNA is strongly and ubiquitously induced in rat brain. To decipher the molecular mechanisms underlying these genomic effects, it is of interest to identify the regulatory sites in the promoter region. Alignment of the rat GILZ promoter with the well-characterized human promoter resulted in poor sequence homology. Consequently, we analyzed the rat 5' flanking sequence by Matrix REDUCE and identified two high-affinity glucocorticoid response elements (GRE) located 2 kb upstream of the transcription start site. These findings were corroborated using the glucocorticoid receptor (GR) expressing Ns-1 PC12 rat cell-line. In these cells, dexamethasone treatment leads to a progressive increase of GILZ mRNA expression levels via a GR-dependent mechanism. Subsequently, using chromatin immunoprecipitation assays we show that the two high-affinity GREs are located within the GR-binding regions. Lastly, we demonstrate using multiple tissue in situ hybridization a marked increase in mRNA expression levels in spleen, thymus, heart, lung, liver, muscle, testis, kidney, colon, ileum, as well as in brain and conclude that the GILZ gene can be used to study glucocorticoid effects in many additional rodent tissues.

The microtubule-associated protein doublecortin-like regulates the transport of the glucocorticoid receptor in neuronal progenitor cells

In neuronal cells, activated glucocorticoid receptor (GR) translocates to the nucleus guided by the cytoskeleton. However, the detailed mechanisms underlying GR translocation remain unclear. Using gain and loss of function studies, we report here for the first time that the microtubule-associated protein doublecortin-like (DCL) controls GR translocation to the nucleus. DCL overexpression in COS-1 cells, neuroblastoma cells, and rat hippocampus organotypic slice cultures impaired GR translocation and decreased GR-dependent transcriptional activity, measured by a specific reporter gene assay, in COS-1 cells. Moreover, DCL and GR directly interact on microtubule bundles formed by DCL overexpression. A C-terminal truncated DCL with conserved microtubule-bundling activity did not influence GR translocation. In N1E-115 mouse neuroblastoma cells and neuronal progenitor cells in rat hippocampus organotypic slice cultures, laser-scanning confocal microscopy showed colabeling of endogenously expressed DCL and GR. In these systems, RNA-interference-mediated DCL knockdown hampered GR translocation. Thus, we conclude that DCL expression is tightly regulated to adequately control GR transport. Because DCL is primarily expressed in neuronal progenitor cells, our results introduce this microtubule-associated protein as a new modulator of GR signaling in this cell type and suggest the existence of cell-specific mechanisms regulating GR translocation to the nucleus.

Steroid receptor coactivator-1 splice variants differentially affect corticosteroid receptor signaling

The mechanisms of receptor- and cell-specific effects of the adrenal corticosteroid hormones via mineralo- (MRs) and glucocorticoid receptors (GRs) are still poorly understood. Because the expression levels of two splice variants of the steroid receptor coactivator-1 (SRC-1) 1a and 1e, can differ significantly in certain cell populations, we tested the hypothesis that their relative abundance could determine cell- and receptor-specific effects of corticosteroid receptor-mediated transcription. In transient transfections, we demonstrate three novel types of SRC-1a- and SRC-1e-specific effects for corticosteroid receptors. One is promoter dependence: SRC-1e much more potently coactivated transcription from several multiple response element-containing promoters. Mammalian 1-hydrid studies indicated that this likely does not involve promoter-specific coactivator recruitment. Endogenous phenylethanolamine-N-methyltransferase mRNA induction via GRs was also differentially affected by the splice variants. Another type is receptor specificity: responses mediated by the N-terminal part of the MR, but not the GR, were augmented by SRC-1e at synergizing response elements. SRC fragment SRC(988-1240) by the MR but not the GR N-terminal fragment in a 1-hybrid assay. The last type, for GRs, is ligand dependence. Due to effects on partial agonism of RU486-activated GRs, different ratios of SRC-1a and 1e can lead to large differences in the extent of antagonism of RU486 on GR-mediated transcription. Furthermore, we show that SRC-1e but not SRC-1a mRNA expression was regulated in the pituitary by corticosterone. We conclude that the cellular differences in SRC-1a to SRC-1e ratio demonstrated in vivo might be involved in cell-specific responses to corticosteroids in a promoter- and ligand-dependent way.