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O gene nuclear GAL1 de Saccharomyces cerevisiae codifica uma galactoquinase induzida por galactose e reprimida por glicose. Três evidências indicam que a transcrição de GAL1 é dependente da atividade mitocondrial. Linhagens petite, com deleção no DNA da organela (ρ-) ou rompimento em gene nuclear, que codifica a farnesil transferase mitocondrial, são incapazes de induzir GAL1. Os inibidores de respiração antimicina-A e azoteto de sódio (NaN3), que atuam, respectivamente, nos complexos III e IV da cadeia de transporte de elétrons, impedem a indução de GAL1. Em células crescidas em glicose ou glicerol, o oligômero formado pela proteína URF13, na presença de metomil, produz um poro na membrana mitocondrial interna que reduz o potencial de membrana ΔΨ e os níveis do mRNA de GAL1. A regulação dependente da atividade da mitocôndria ocorre a nível transcricional, pois o gene repórter GUS, sob controle de GAL1, não é induzido na presença de galactose, após tratamento prévio das células com antimicina-A ou NaN3. Mig1p é um repressor que atua diretamente no promotor de GAL1 e inibe a transcrição da galactoquinase. Os resultados obtidos indicam que Mig1p media a repressão da indução de GAL1, na presença do inibidor da cadeia respiratória antimicina-A. / The nuclear gene GAL1 of Saccharomyces cerevisiae encodes a galactokinase induced by galactose and repressed by glucose. Three lines of evidence indicate that expression of GAL1 transcript is dependent on mitochondrial activity. Petite strains in which mitochondrial DNA was partialy deleted (ρ-) or cells containing a disruption in the nuclear gene COX10, which encodes the mitochondrial farnesil transferase, are unable to induce GAL1. Respiratory inhibitors such as antimycin-A or sodium azide (NaN3), that inhibit complexes III and IV of the electron transport chain, respectively, affect GAL1 induction. Functional expression of the maize protein URF13, which is translocated to the mitochondrial inner membrane, forming a pore that leads to a reduction of the mitochondrial membrane potential ΔΨ and reduces the leveis of GAL1 transcripts. Experiments using a heterologous gene fusion showed that the inhibition of GAL1 expresion, by treatment of cells with antimycin-A or NaN3, controls the expression of GAL1 at the transcrptional level. Mig1p is a repressor that binds GAL1 promoter. Our results indicate that Mig1p mediates the represion of GAL1 induction, observed in the presence of the mitochondrial inhibitor antimycin-A.

O gene nuclear GAL1 de Saccharomyces cerevisiae codifica uma galactoquinase induzida por galactose e reprimida por glicose. Três evidências indicam que a transcrição de GAL1 é dependente da atividade mitocondrial. Linhagens petite, com deleção no DNA da organela (ρ-) ou rompimento em gene nuclear, que codifica a farnesil transferase mitocondrial, são incapazes de induzir GAL1. Os inibidores de respiração antimicina-A e azoteto de sódio (NaN3), que atuam, respectivamente, nos complexos III e IV da cadeia de transporte de elétrons, impedem a indução de GAL1. Em células crescidas em glicose ou glicerol, o oligômero formado pela proteína URF13, na presença de metomil, produz um poro na membrana mitocondrial interna que reduz o potencial de membrana ΔΨ e os níveis do mRNA de GAL1. A regulação dependente da atividade da mitocôndria ocorre a nível transcricional, pois o gene repórter GUS, sob controle de GAL1, não é induzido na presença de galactose, após tratamento prévio das células com antimicina-A ou NaN3. Mig1p é um repressor que atua diretamente no promotor de GAL1 e inibe a transcrição da galactoquinase. Os resultados obtidos indicam que Mig1p media a repressão da indução de GAL1, na presença do inibidor da cadeia respiratória antimicina-A. / The nuclear gene GAL1 of Saccharomyces cerevisiae encodes a galactokinase induced by galactose and repressed by glucose. Three lines of evidence indicate that expression of GAL1 transcript is dependent on mitochondrial activity. Petite strains in which mitochondrial DNA was partialy deleted (ρ-) or cells containing a disruption in the nuclear gene COX10, which encodes the mitochondrial farnesil transferase, are unable to induce GAL1. Respiratory inhibitors such as antimycin-A or sodium azide (NaN3), that inhibit complexes III and IV of the electron transport chain, respectively, affect GAL1 induction. Functional expression of the maize protein URF13, which is translocated to the mitochondrial inner membrane, forming a pore that leads to a reduction of the mitochondrial membrane potential ΔΨ and reduces the leveis of GAL1 transcripts. Experiments using a heterologous gene fusion showed that the inhibition of GAL1 expresion, by treatment of cells with antimycin-A or NaN3, controls the expression of GAL1 at the transcrptional level. Mig1p is a repressor that binds GAL1 promoter. Our results indicate that Mig1p mediates the represion of GAL1 induction, observed in the presence of the mitochondrial inhibitor antimycin-A.

La protéine p97/VCP est un membre de la famille des ATPase AAA+ et joue un rôle majeur dans de nombreux processus cellulaires tel que le contrôle de l’homéostasie protéique ou de fonctions associées à la chromatine (transcription, réplication, dommage à l’ADN, progression du cycle cellulaire). De plus, la protéine p97/VCP est impliquée dans un nombre croissant de maladies dont les cancers où il a été montré qu’elle contribue à l’homéostasie protéique et l’adaptation au stress oncogéniques. En effet, l’expression de la protéine p97/VCP est augmentée dans de nombreux cancers et dans certains cas corrèle avec une récurrence de la tumeur et un mauvais pronostique pour les patients. Cependant, le mécanisme moléculaire précis par lequel la protéine p97/VCP régule l’homéostasie protéique des cellules tumorales reste incertain. Pour remédier à cela, nous avons démontré un rôle de la protéine p97/VCP dans le contrôle de l’expression des gènes lors du stress du Réticulum Endoplasmique (RE). Nous avons trouvé que en conditions basales, la protéine RuvBL2 fait partie d’un complexe remodeleur de la chromatine qui contient les protéines HDAC1 et mSin3A et agit comme un répresseur des gènes de stress du RE. De plus, nous avons identifié le gène Gli1, un effecteur connu de la voie de signalisation Hedgehog comme cible de la protéine p97/VCP et du complexe RuvBL2-HDAC1-mSin3A. Ainsi en condition de stress du RE, la voie de signalisation Hedgehog qui a été impliqué dans le développement de cancers est activée. Globalement, nos travaux indiquent que p97/VCP agit comme un interrupteur moléculaire pour inactiver le complexe répresseur RuvBL2-HDAC1 en condition de stress du RE et ainsi activer les gènes de stress du RE et de la voie de signalisation Hedhehog de façon non-canonique. / P97/VCP is a member of the AAA+ ATPase family that plays major roles in various cellular processes including control of protein homeostasis and chromatin-associated functions (transcription, replication, DNA damage, cellular cycle progression). Moreover, p97/VCP is involved in a growing number of diseases including cancers in which it has been shown to contribute to protein homeostasis and adaptation to oncogenic stresses. Indeed, p97/VCP expression is increased in numerous cancers and in some cases correlates with tumor recurrence and poor prognosis for patients. However, the precise mechanism by which p97/VCP regulates tumor cell proteostasis remains unclear. To address this, we demonstrated a role of p97/VCP in gene expression control upon endoplasmic reticulum (ER) stress. We found that in basal conditions, RuvBL2 is part of chromatin remodeler complex that included HDAC1 and mSin3A and act as a repressor of ER stress genes. However under ER stress, ubiquitinylated RuvBL2 is degraded by p97/VCP thus causing activation of ER stress genes. Moreover, we have identified GLI1, a known effector of Hedgehog signaling, as a target of the p97/VCP and RuvBL2-HDAC1-mSin3A complex. As a result under ER stress conditions, the Hedgehog pathway which have been linked to cancer development is non-canonically activated. Overall, our work indicated that p97/VCP acts as a molecular switch to inactivate RuvBL2-HDAC1 repressor complex under ER stress thus activating ER stress genes and Hedgehog genes in a non-canonical manner.