The 2A proteins of three diverse picornaviruses are related to each other and to the H-rev107 family of proteins involved in the control of cell proliferation.
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The 2A protein appears to be diverse among picornaviruses, in contrast to the other non-structural proteins, which have homologous structures and functions. In enteroviruses and rhinoviruses, 2A is a trypsin-like protease involved in protein processing and in shut-off of host-cell macromolecular synthesis. The aphthovirus and cardiovirus 2A is associated with an unusual processing event at the 2A/2B junction. It is shown here that the 2A protein of several diverse picornaviruses, the human parechoviruses, Aichi virus and avian encephalomyelitis virus, possess previously unrecognized conserved motifs and are likely to have a common function. Moreover, these motifs, a conserved histidine and flanking amino acids, an asparagine-cysteine dipeptide and a putative transmembrane domain, are characteristic of a family of cellular proteins, at least two of which are involved in the control of cell growth. These observations have important implications for an understanding of picornavirus genome structure and evolution, as well as pointing to possible functions of 2A in these viruses. (+info)
hH-Rev107, a class II tumor suppressor gene, is expressed by post-meiotic testicular germ cells and CIS cells but not by human testicular germ cell tumors.
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By systematic analysis of a human testis library, we have isolated the hH-Rev107-3 cDNA, identical to hH-Rev107-1 cDNA, which was previously described as a class II tumor suppressor gene. In this study, two transcripts (1 and 0.8 kb) were detected by Northern blot in all human tissues, excepted in thymus. The strongest expression was found in testis, skeletal muscle and heart. These two mRNA are probably transcribed from only one gene that we mapped to the q12-q13 region of the chromosome 11. In human testis, hH-Rev107 gene expression was localized, by in situ hybridization, within the round spermatids. To investigate a possible role for hH-Rev107 protein in testicular malignant growth, we examined the expression of this gene in germ cell tumors. A strong hH-Rev107 gene expression was observed in normal testis as well as in samples with preinvasive carcinoma in situ but was completely absent in overt tumors, both seminomas and non-seminomas. By in situ hybridization, CIS was found hH-Rev107 positive and tumor negative. A semi-quantitative assessment of hH-Rev107 mRNA level in testicular germ cell tumors, by RT-PCR, exhibited a ninefold decrease in the gene expression. No gross structural aberrations of hH-Rev107 gene were detected in these human primary tumors. The results suggest that down-regulation of hH-Rev107 may be associated with invasive progression of testicular germ cell tumors. (+info)
The class II tumour suppressor gene H-REV107-1 is a target of interferon-regulatory factor-1 and is involved in IFNgamma-induced cell death in human ovarian carcinoma cells.
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H-rev107-1 is a growth inhibitory RAS target gene capable of suppressing anchorage independent growth in vitro and in vivo. Using a tumour tissue array with 241 matched tumour and normal tissue cDNA pools, we found down-regulation of H-REV107-1 in 7 out of 14 ovary-derived cDNAs. RT-PCR analysis and immunohistochemical investigation confirmed expression of H-REV107-1 in normal ovarian epithelial cells but down-regulation in high grade ovarian carcinomas. H-REV107-1 is also strongly expressed in immortalized rat and human ovarian epithelial cells in vitro, but suppressed in transformed cells by two different mechanisms. KRAS-transformed rat ovarian cells and PA1 teratocarcinoma cells, reversibly repress H-REV107-1 via MAP/ERK signaling. In contrast, treatment of A27/80 and OVCAR-3 epithelial ovarian cancer cells with IFNgamma stimulated H-REV107-1 expression. In NIH3T3 cells harbouring an estrogen-inducible IRF-1, H-rev107-1 is directly induced after activation of IRF-1, indicating that H-rev107-1 is a target of IRF-1. Stimulation of H-REV107-1 expression was also observed in ovarian epithelial cells suggesting that IRF-1 is involved in H-REV107-1 regulation in human ovarian epithelium. In the IFNgamma-sensitive cell line A27/80, H-REV107-1 suppresses colony formation. A27/80 and OVCAR-3 cells overexpressing H-REV107-1 protein underwent apoptosis. These results demonstrate down-regulation of the class II tumour suppressor H-REV107-1 in human ovarian carcinomas and suggest an involvement of H-REV107-1 in interferon-dependent cell death. (+info)
Silencing of the mouse H-rev107 gene encoding a class II tumor suppressor by CpG methylation.
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H-rev107 is a tumor suppressor originally isolated in revertants of H-ras-transformed cell lines. The gene is ubiquitously expressed in normal tissues but down-regulated in primary carcinomas or in many cell lines derived from tumors, including WEHI 7.1 lymphoma cells. Here, we show that unlike in H-rev107-expressing cells or tissues the 5'-end of H-rev107 containing a CpG-rich region of 421 bp is highly methylated in WEHI 7.1 lymphoma cells, correlating with silencing of this gene. Repression of H-rev107 transcription in these cells could be relieved by chemically induced hypomethylation with 5-aza-dC. In addition, upon in vitro methylation, expression of the luciferase reporter gene driven by the H-rev107 promoter decreased by 80% in WEHI 7.1 and 293 cells. Furthermore, co-transfection of the methyl-CpG binding proteins, MeCP2 and MBD2, inhibited H-rev107 promoter activity up to 70% in SL2 cells when the promoter was methylated. By chromatin immunoprecipitation assays, we observed in vivo binding of MeCP2 and MBD2 to the 5'-end of H-rev107 in WEHI 7.1 cells, which was reduced to undetectable levels upon 5-aza-dC treatment, concluding that MeCP2 and MBD2 might be involved in silencing the methylated H-rev107 gene in lymphoma cells and probably certain tumors. (+info)
H-REV107-1 stimulates growth in non-small cell lung carcinomas via the activation of mitogenic signaling.
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H-REV107-1, a known member of the class II tumor suppressor gene family, is involved in the regulation of differentiation and survival. We analyzed H-REV107-1 in non-small cell lung carcinomas, in normal lung, and in immortalized and tumor-derived cell lines. Sixty-eight percent of lung tumors revealed positive H-REV107-1-specific staining. Furthermore, survival analysis demonstrated a significant association of cytoplasmic H-REV107-1 with decreased patient survival. This suggested that H-REV107-1, known as a tumor suppressor, plays a different role in non-small cell lung carcinomas. Knock-down of H-REV107-1 expression in lung carcinoma cells inhibited anchorage-dependent and anchorage-independent growth whereas overexpression of H-REV107-1 induced tumor cell proliferation. Consistent with results of the survival analysis, cytoplasmic localization of the protein was essential for this growth-inducing function. Analysis of signaling pathways potentially involved in this process demonstrated that overexpression of H-REV107-1 stimulated RAS-GTPase activity, ERK1,2 phosphorylation, and caveolin-1 expression in the cell lines analyzed. These results indicate that H-REV107-1 is deficient in its function as a tumor suppressor in non-small cell lung carcinomas and is required for proliferation and anchorage-independent growth in cells expressing high levels of the protein, thus contributing to tumor progression in a subset of non-small cell lung carcinomas. (+info)
Mechanisms of the HRSL3 tumor suppressor function in ovarian carcinoma cells.
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HRSL3 (also known as H-REV107-1) belongs to a class II tumor suppressor gene family and is downregulated in several human tumors including ovarian carcinomas. To unravel the mechanism of HRSL3 tumor suppressor action, we performed a yeast two-hybrid screen and identified the alpha-isoform of the regulatory subunit A of protein phosphatase 2A (PR65alpha) as a new interaction partner of HRSL3. Interaction between HRSL3 and PR65alpha was confirmed in vitro and by co-immunoprecipitation in mammalian cells. We demonstrate that HRSL3 binds to the endogenous PR65alpha, thereby partially sequestering the catalytic subunit PR36 from the PR65 protein complex, and inhibiting PP2A catalytic activity. Furthermore, binding of HRSL3 to PR65 induces apoptosis in ovarian carcinoma cells in a caspase-dependent manner. Using several mutant HRSL3 constructs, we identified the N-terminal proline-rich region within the HRSL3 protein as the domain that is relevant for both binding of PR65alpha and induction of programmed cell death. This suggests that the negative impact of HRSL3 onto PP2A activity is important for the HRSL3 pro-apoptotic function and indicates a role of PP2A in survival of human ovarian carcinomas. The analysis of distinct PP2A target molecules revealed PKCzeta as being involved in HRSL3 action. These data implicate HRSL3 as a signaling regulatory molecule, which is functionally involved in the oncogenic network mediating growth and survival of ovarian cancer cells. (+info)
Reticulocyte-secreted exosomes bind natural IgM antibodies: involvement of a ROS-activatable endosomal phospholipase iPLA2.
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Reticulocytes release small membrane vesicles termed exosomes during their maturation into erythrocytes. It has been suggested that reticulocytes remodel the plasma membrane of the immature red cell during erythropoiesis by specifically eliminating various proteins. We report here that exosome release is associated with a physiologic cascade induced by the expression of a 15-lipoxygenase at the reticulocyte stage. We found that the phospholipase iPLA2 specifically associated with the endosomal and exosomal membranes could be activated by reactive oxygen species (ROSs) produced during mitochondria degeneration induced by 15-lipoxygenase. Since iPLA2 has recently been demonstrated to participate in the clearance of apoptotic cells, we investigated its role in vesicle removal. We found that exosomes isolated directly from the blood of an anemic rat or released during in vitro maturation of rat reticulocytes bind IgM antibodies on their surface, in contrast to immature and mature red cells. These natural IgM antibodies recognize lysophosphatidylcholine and are able to specifically bind to apoptotic cells. Finally, evidence of C3 deposition on the exosome surface leads us to hypothesize that this cascade may favor the clearance of exosomes by cells once released into the bloodstream, via a mechanism similar to that involved in the elimination of apoptotic cells. (+info)
Role of Ca2+-independent phospholipase A2 and store-operated pathway in urocortin-induced vasodilatation of rat coronary artery.
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Urocortin has been shown to produce vasodilatation in several arteries, but the precise mechanism of its action is still poorly understood. Here we demonstrate the role of store operated Ca2+ entry (SOCE) regulated by Ca2+-independent phospholipase A2 (iPLA2) in phenylephrine hydrochloride (PE)-induced vasoconstriction, and we present the first evidence that urocortin induces relaxation by the modulation of SOCE and iPLA2 in rat coronary artery. Urocortin produces an endothelium independent relaxation, and its effect is concentration-dependent (IC50 approximately = 4.5 nmol/L). We show in coronary smooth muscle cells (SMCs) that urocortin inhibits iPLA2 activation, a crucial step for SOC channel activation, and prevents Ca2+ influx evoked by the emptying of the stores via a cAMP and protein kinase A (PKA)-dependent mechanism. Lysophophatidylcholine and lysophosphatidylinositol, products of iPLA2, exactly mimic the effect of the depletion of the stores in presence of urocortin. Furthermore, we report that long treatment with urocortin downregulates iPLA2 mRNA and proteins expression in rat coronary smooth muscle cells. In summary, we propose a new mechanism of vasodilatation by urocortin which involves the regulation of iPLA2 and SOCE via the stimulation of a cAMP/PKA-dependent signal transduction cascade in rat coronary artery. (+info)