A Krox binding site regulates protease nexin-1 promoter activity in embryonic heart, cartilage and parts of the nervous system

SERPINE2/Protease Nexin-1 in vivo multiple functions: Does the puzzle make sense?

Cultures of glial cells and fibroblasts allowed and lead to the identification SERPINE2/Protease Nexin-1 (SERPINE2/PN-1). Cellular, biochemical, immunological and molecular characterization substantiated its variable expression in many organs as a function of development, adult stages, pathological situations or following injury. It is not a circulating serpin, but as other members of the family, its target specificity is influenced by components of the extracellular matrix. The challenges are to identify where and when SERPINE2/PN-1 modulatory action becomes crucial or even possibly specific in a mosaic of feasible in vivo impacts. Data providing correlations are not sufficient to satisfy this aim. Genetically modified mice, or tissue derived thereof, provide interesting in vivo models to identify and study the relevance of this serpin. This review will highlight sometimes-intriguing results indicating a crucial impact of SERPINE2/PN-1, especially in the vasculature, the nervous system or the behavior of cancer cells in vivo. Data presently available will be discussed in an attempt to define general trends in the diversity of SERPINE2/PN-1 modes of action in vivo.

The immediate early gene product EGR1 and polycomb group proteins interact in epigenetic programming during chondrogenesis

Initiation of and progression through chondrogenesis is driven by changes in the cellular microenvironment. At the onset of chondrogenesis, resting mesenchymal stem cells are mobilized in vivo and a complex, step-wise chondrogenic differentiation program is initiated. Differentiation requires coordinated transcriptomic reprogramming and increased progenitor proliferation; both processes require chromatin remodeling. The nature of early molecular responses that relay differentiation signals to chromatin is poorly understood. We here show that immediate early genes are rapidly and transiently induced in response to differentiation stimuli in vitro. Functional ablation of the immediate early factor EGR1 severely deregulates expression of key chondrogenic control genes at the onset of differentiation. In addition, differentiating cells accumulate DNA damage, activate a DNA damage response and undergo a cell cycle arrest and prevent differentiation associated hyper-proliferation. Failed differentiation in the absence of EGR1 affects global acetylation and terminates in overall histone hypermethylation. We report novel molecular connections between EGR1 and Polycomb Group function: Polycomb associated histone H3 lysine27 trimethylation (H3K27me3) blocks chromatin access of EGR1. In addition, EGR1 ablation results in abnormal Ezh2 and Bmi1 expression. Consistent with this functional interaction, we identify a number of co-regulated targets genes in a chondrogenic gene network. We here describe an important role for EGR1 in early chondrogenic epigenetic programming to accommodate early gene-environment interactions in chondrogenesis.

Serpinin: a novel chromogranin A-derived, secreted peptide up-regulates protease nexin-1 expression and granule biogenesis in endocrine cells

Previously we demonstrated that chromogranin A (CgA) promoted secretory granule biogenesis in endocrine cells by stabilizing and preventing granule protein degradation in the Golgi, through up-regulation of expression of the protease inhibitor, protease nexin-1 (PN-1). However, the mechanism by which CgA signals the increase of PN-1 expression is unknown. Here we identified a 2.9-kDa CgA-C-terminus peptide, which we named serpinin, in conditioned media from AtT-20 cells, a corticotroph cell line, which up-regulated PN-1 mRNA expression. Serpinin was secreted from AtT-20 cells upon high potassium stimulation and increased PN-1 mRNA transcription in these cells, in an actinomycin D-inhibitable manner. CgA itself and other CgA-derived peptides, when added to AtT-20 cell media, had no effect on PN-1 expression. Treatment of AtT-20 cells with 10 nm serpinin elevated cAMP levels and PN-1 mRNA expression, and this effect was inhibited by a protein kinase A inhibitor, 6-22 amide. Serpinin and a cAMP analog, 8-bromo-cAMP, promoted the translocation of the transcription factor Sp1 into the nucleus, which is known to drive PN-1 expression. Additionally, an Sp1 inhibitor, mithramycin A inhibited the serpinin-induced PN-1 mRNA up-regulation. Furthermore, a luciferase reporter assay demonstrated serpinin-induced up-regulation of PN-1 promoter activity in an Sp1-dependent manner. When added to CgB-transfected 6T3 cells, a mutant AtT20 cell line, serpinin induced granule biogenesis as evidenced by the presence of CgB puncta accumulation in the processes and tips. Our findings taken together show that serpinin, a novel CgA-derived peptide, is secreted upon stimulation of corticotrophs and plays an important autocrine role in up-regulating PN-1-dependent granule biogenesis via a cAMP-protein kinase A-Sp1 pathway to replenish released granules.

GeneChip microarrays facilitate identification of Protease Nexin-1 as a target gene of the Prx2 (S8) homeoprotein

The paired-related homeobox genes, Prx1 and Prx2, are important for normal skeletal and cardiovascular development as well as adult vascular remodeling. The identification and characterization of Prx downstream targets is crucial to understanding their function in normal developmental processes and congenital malformations. To identify Prx2 regulated genes, stably transfected NIH3T3 clones expressing Prx2 sense or antisense transcripts were generated. Expression profiles initially were established for two of the clones using Affymetrix GeneChip arrays. Over 6,400 genes were screened by the microarray approach, and approximately 500 genes differed in expression by a factor of two or more. Fifteen genes were chosen for further analysis. RT-PCR of the two transfectants used in the GeneChip analysis demonstrated that five out of the 15 genes were differentially expressed. However, after screening additional stable transfectant clones only one of the 15 genes, Protease Nexin-1 (PN-1), was differentially expressed. Subsequent Northern blot, RT-PCR, and further GeneChip analysis of additional stable transfectants confirmed that PN-1 expression is increased at least fivefold when Prx2 is overexpressed. It was demonstrated that Prx2 directly regulates PN-1 because (1) Prx2 binds to a cis element in the PN-1 promoter in vitro, and (2) Prx2 regulates the PN-1 promoter in transient transfection assays. The GeneChip analysis generated a prioritized list of other potential targets. The utility and limitations of cell culture models combined with microarray analysis for elucidating complex regulatory cascades are discussed.

Stage-specific gene expression in early differentiating oligodendrocytes

The screening of a differential library from precursor and differentiated oligodendrocytes, obtained through the representational difference analysis (RDA) technique, has generated a number of cDNA recombinants corresponding to mRNA coding for known and unknown proteins: (1) mRNA coding for proteins involved in protein synthesis, (2) mRNA coding for proteins involved in the organization of the cytoskeleton, and (3) mRNA coding for proteins of unknown function. The expression profile of the mRNA was studied by Northern blot hybridization to the poly-A(+) mRNA from primary rat progenitor and differentiated oligodendrocytes. In most cases, hybridization to the precursor was higher than hybridization to the differentiated mRNA, supporting the validity of the differential screening. Hybridization of the cDNA to rat cerebral hemisphere and brain stem poly-A(+) mRNA, isolated from 1- to 90-day-old rats, confirms the results obtained with the mRNA from differentiating oligodendrocytes. The intensity of the hybridization bands decreases as differentiation proceeds. The pattern of expression observed in oligodendrocytes is different from that found in the brain only in the case of the nexin-1 mRNA, the level of which remains essentially constant throughout differentiation both in the brain stem and in the cerebral hemispheres, in agreement with the published data. In contrast, the intensity of hybridization to the oligodendrocyte mRNA is dramatically lower in the differentiated cells compared with the progenitor oligodendrocyte cells. Some of the recombinant cDNA represent mRNA sequences present at high frequency distribution in the cells, while others belong to the rare sequences group. Six recombinants code for proteins of the ribosomal family, suggesting that of approximately 70 known ribosomal proteins, only a few are upregulated during oligodendrocyte differentiation. The third category of open reading frame (ORF) is represented by rare messengers coding for proteins of unknown functions and includes six clones: RDA 279, 11, 95, 96, 254, and 288.

Association study between two variants in the DOPA decarboxylase gene in bipolar and unipolar affective disorder

Irregularities of dopaminergic and serotonergic neurotransmission have been implicated in a variety of neuropsychiatric disorders. DOPA decarboxylase (DDC), also known as aromatic L-amino acid decarboxylase, is an enzyme involved directly in the synthesis of dopamine and serotonin and indirectly in the synthesis of noradrenaline. Therefore, the DDC gene can be considered as a candidate gene for affective disorders. Recently, two novel variants were reported in the DDC gene: a 1-bp deletion in the promoter and a 4-bp deletion in the untranslated exon 1. Subsequently, an association case-control study including 112 English patients and 80 Danish patients with bipolar affective disorder (BPAD) revealed a significant association with the 1-bp deletion. This finding prompted us to analyze whether this effect was also present in a larger and ethnically homogeneous sample of 228 unrelated German patients with BPAD (208 patients with BP I disorder, 20 patients with BP II disorder), 183 unrelated patients with unipolar affective disorder (UPAD), and 234 healthy control subjects. For both BPAD and UPAD we could not detect a genetic association with either variant. Thus, our results do not support an involvement of the 1-bp or 4-bp deletion within the DDC gene in the etiology of affective disorders.