Mounia Chami

Calcium and apoptosis: facts and hypotheses

Although longstanding experimental evidence has associated alterations of calcium homeostasis to cell death, only in the past few years the role of calcium in the signaling of apoptosis has been extensively investigated. In this review, we will summarize the current knowledge, focusing on (i) the effect of the proteins of the Bcl-2 family on ER Ca2+ levels, (ii) the action of the proteolytic enzymes of apoptosis on the Ca2+ signaling machinery, (iii) the ensuing alterations on the signaling patterns of extracellular stimuli, and (iv) the intracellular targets of ‘apoptotic’ Ca2+ signals, with special emphasis on the mitochondria and cytosolic Ca2+-dependent enzymes.

Hepatitis B virus-related insertional mutagenesis occurs frequently in human liver cancers and recurrently targets human telomerase gene

Integration of Hepatitis B Virus (HBV) DNA into liver cell DNA has been well established, but its implication in liver carcinogenesis is still being debated. In particular, insertion of the viral genome into cellular genes has been viewed as a rare event. By using HBV-Alu PCR, we have now isolated, from nine hepatocellular carcinomas, nine HBV-DNA integration sites showing that the viral genome mutates key regulatory cellular genes: neurotropic tyrosin receptor kinase 2 (NTRK2) gene, IL-1R-associated kinase 2 (IRAK2) gene, p42 mitogen-activated protein kinase 1 (p42MAPK1) gene, inositol 1,4,5-triphosphate receptor type 2 (IP3R2) gene, inositol 1,4,5-triphosphate receptor (IP3R) type 1 (IP3R1) gene, alpha 2,3 sialyltransferase (ST3GAL VI or SITA) gene, thyroid hormone uncoupling protein (TRUP) gene, EMX2-like gene, and human telomerase reverse transcriptase (hTERT) gene. This result brings to 15 the total number of genes targeted by HBV in a study of 22 human liver cancers. Overall, we found that both the inositol 1,4,5-triphosphate receptor gene and the telomerase gene were targeted by HBV in two different tumors. Thus, HBV frequently targets cellular genes involved in cell signalling and some of them may be preferential targets of the viral integration.

Hepatitis C virus core triggers apoptosis in liver cells by inducing ER stress and ER calcium depletion.

Hepatitis C virus (HCV) core, known to be involved in liver carcinogenesis, is processed in the endoplasmic reticulum (ER). We thus investigated the impact of three HCV core isolates on ER stress, ER calcium signalling and apoptosis. We show that HCV core constructs trigger hyperexpression of Grp78/BiP, Grp 94, calreticulin and sarco/endoplasmic reticulum calcium ATPase, inducing ER stress. By using the ER-targeted aequorin calcium probe, we found that ER calcium depletion follows ER stress in core-expressing cells. HCV core induces apoptosis through overexpression of the CHOP/GADD153 proapoptotic factor, Bax translocation to mitochondria, mitochondrial membrane depolarization, cytochrome c release, caspase-3 and PARP cleavage. Furthermore, reversion of HCV core-induced ER calcium depletion (by transfection of SERCA2) completely abolished mitochondrial membrane depolarization, suggesting that both ER stress (through CHOP overexpression) and calcium signalling play a major role in the HCV core-mediated control of apoptosis. ER stress and apoptosis were also found in a proportion of HCV-full-length replicon-expressing cells and in the liver of HCV core transgenic mice. In conclusion, our data demonstrate that HCV core deregulates the control of apoptosis by inducing ER stress and ER calcium depletion providing new elements to understand the mechanisms involved in HCV-related liver chronic diseases.

Identification of human cancer-related genes by naturally occurring Hepatitis B Virus DNA tagging.

Proviral tagging has been used in animals as a powerful tool for cancer genetics. We show that a similar approach is possible in patients with hepatocellular carcinoma (HCC) infected by Hepatitis B Virus (HBV), a human pararetrovirus which may act by insertional mutagenesis. In this work, the HBV genome is used as a probe to identify cancer-related genes. By using HBV-Alu-PCR, we obtained 21 HBV/cellular DNA junctions from 18 different patients. In six of 21, we found the HBV DNA integrated into a cellular gene: (1) Sarco/Endoplasmic Reticulum Calcium ATPase1 Gene; (2) Thyroid Hormone Receptor Associated Protein 150 alpha Gene; (3) Human Telomerase Reverse Transcriptase Gene; (4) Minichromosome Maintenance Protein (MCM)-Related Gene; (5) FR7, a new gene expressed in human liver and cancer tissues; and (6) Nuclear Matrix Protein p84 Gene. Seven junctions contained unique cellular sequences. In the remaining eight, the HBV DNA was next to repetitive sequences, five of them of LINE1 type. The cellular genes targeted by HBV are key regulators of cell proliferation and viability. Our results show that studies on HBV-related HCCs allow to identify cellular genes involved in cancer. We therefore propose this approach as a valuable tool for functional cancer genomic studies in humans.

Hepatitis B virus-related insertional mutagenesis implicates SERCA1 gene in the control of apoptosis

We have used the Hepatitis B Virus DNA genome as a probe to identify genes clonally mutated in vivo, in human liver cancers. In a tumor, HBV-DNA was found to be integrated into the gene encoding Sarco/Endoplasmic Reticulum Calcium ATPase (SERCA), which pumps calcium, an important intracellular messenger for cell viability and growth, from the cytosol to the endoplasmic reticulum. The HBV X gene promoter cis-activates chimeric HBV X/SERCA1 transcripts, with splicing of SERCA1 exon 11, encoding C-terminally truncated SERCA1 proteins. Two chimeric HBV X/SERCA1 proteins accumulate in the tumor and form dimers. In vitro analyses have demonstrated that these proteins localize to the ER, determine its calcium depletion and induce cell death. We have also shown that these biological effects are related to expression of the SERCA, rather than of the viral moiety. This report involves for the first time the expression of mutated SERCA proteins in vivo in a tumor cell proliferation and in vitro in the control of cell viability.

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.

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.

Calcium signalling-dependent mitochondrial dysfunction and bioenergetics regulation in respiratory chain Complex II deficiency

Despite advanced knowledge on the genetic basis of oxidative phosphorylation-related diseases, the molecular and/or cellular determinants for tissue-specific dysfunction are not completely understood. Here, we report the cellular events associated with mitochondrial respiratory Complex II deficiency occurring before cell death. Mutation or chronic inhibition of Complex II determined a large increase of basal and agonist-evoked Ca2+ signals in the cytosol and the mitochondria, in parallel with mitochondrial dysfunction characterized by membrane potential (Δψmit) loss, [ATP] reduction and increased reactive oxygen species production. Cytosolic and mitochondrial Ca2+ overload are linked to increased endoplasmic reticulum (ER) Ca2+ leakage, and to SERCA2b and PMCA proteasome-dependent degradation. Increased [Ca2+]mit is also contributed by decreased mitochondrial motility and increased ER-mitochondria contact sites. Interestingly, increased intracellular [Ca2+] activated on the one hand a compensatory Ca2+-dependent glycolytic ATP production and determined on the second hand mitochondrial pathology. These results revealed the primary function for Ca2+ signalling in the control of mitochondrial dysfunction and cellular bioenergetics outcomes linked to respiratory chain Complex II deficiency.

Nuclear Factor-κB Regulates βAPP and β- and γ-Secretases Differently at Physiological and Supraphysiological Aβ Concentrations

Nuclear factorB regulates APP and and -secretases differently at physiological and supraphysiological A concentrations. Linda Chami, Virginie Buggia-Prévot, Eric Duplan, Dolores Del Prete, Mounia Chami, Jean-François Peyron, and Frédéric Checler Dr. Del Prete’s name was misspelled. The correct spelling is Dolores Del Prete, as shown in the author line. THE JOURNAL OF BIOLOGICAL CHEMISTRY VOL. 290, NO. 50, p. 29758, December 11, 2015

Localization and Processing of the Amyloid-β Protein Precursor in Mitochondria-Associated Membranes

Alteration of mitochondria-associated membranes (MAMs) has been proposed to contribute to the pathogenesis of Alzheimer’s disease (AD). We studied herein the subcellular distribution, the processing, and the protein interactome of the amyloid-β protein precursor (AβPP) and its proteolytic products in MAMs. We reveal that AβPP and its catabolites are present in MAMs in cellular models overexpressing wild type AβPP or AβPP harboring the double Swedish or London familial AD mutations, and in brains of transgenic mice model of AD. Furthermore, we evidenced that both β- and γ-secretases are present and harbor AβPP processing activities in MAMs. Interestingly, cells overexpressing APPswe show increased ER-mitochondria contact sites. We also document increased neutral lipid accumulation linked to Aβ production and reversed by inhibiting β- or γ-secretases. Using a proteomic approach, we show that AβPP and its catabolites interact with key proteins of MAMs controlling mitochondria and ER functions. These data highlight the role of AβPP processing and proteomic interactome in MAMs deregulation taking place in AD.

Ryanodine receptors: dual contribution to Alzheimer disease?

ISSN: 1933-6950 (Print) 1933-6969 (Online) Journal homepage: http://www.tandfonline.com/loi/kchl20 Ryanodine receptors Mounia Chami & Frédéric Checler To cite this article: Mounia Chami & Frédéric Checler (2014) Ryanodine receptors, Channels, 8:3, 168-168, DOI: 10.4161/chan.29000 To link to this article: http://dx.doi.org/10.4161/chan.29000 Copyright