Overexpression of the Mitochondrial T3 Receptor p43 Induces a Shift in Skeletal Muscle Fiber Types

In previous studies, we have characterized a new hormonal pathway involving a mitochondrial T3 receptor (p43) acting as a mitochondrial transcription factor and consequently stimulating mitochondrial activity and mitochondrial biogenesis. We have established the involvement of this T3 pathway in the regulation of in vitro myoblast differentiation.We have generated mice overexpressing p43 under control of the human α-skeletal actin promoter. In agreement with the previous characterization of this promoter, northern-blot and western-blot experiments confirmed that after birth p43 was specifically overexpressed in skeletal muscle. As expected from in vitro studies, in 2-month old mice, p43 overexpression increased mitochondrial genes expression and mitochondrial biogenesis as attested by the increase of mitochondrial mass and mt-DNA copy number. In addition, transgenic mice had a body temperature 0.8°C higher than control ones and displayed lower plasma triiodothyronine levels. Skeletal muscles of transgenic mice were redder than wild-type animals suggesting an increased oxidative metabolism. In line with this observation, in gastrocnemius, we recorded a strong increase in cytochrome oxidase activity and in mitochondrial respiration. Moreover, we observed that p43 drives the formation of oxidative fibers: in soleus muscle, where MyHC IIa fibers were partly replaced by type I fibers; in gastrocnemius muscle, we found an increase in MyHC IIa and IIx expression associated with a reduction in the number of glycolytic fibers type IIb. In addition, we found that PGC-1α and PPARδ, two major regulators of muscle phenotype were up regulated in p43 transgenic mice suggesting that these proteins could be downstream targets of mitochondrial activity. These data indicate that the direct mitochondrial T3 pathway is deeply involved in the acquisition of contractile and metabolic features of muscle fibers in particular by regulating PGC-1α and PPARδ

Bases moléculaires de l'induction de la transformation des fibroblastes du derme humain après surexpression du récepteur mitonchondrial de la triiodothyronine

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Mise en évidence d'une relation entre la protéine Damaged DNA-Binding 2 et le facteur de transcription NF-kB (conséquences sur les capacités migratrices et invasives des tumeurs mammaires)

La protéine Damaged DNA-Binding 2 (DDB2) est connue pour son rôle dans la réparation de l'ADN lésé par les UV. Cependant, le laboratoire a montré que cette protéine est surexprimée naturellement dans les cellules tumorales mammaires non métastatiques et active leur prolifération, en favorisant leur entrée en phase de transition G1/S du cycle cellulaire. Il a été montré que cette nouvelle activité biologique de DDB2 dépend de sa capacité à intervenir dans la transcription de gènes cibles, comme celui codant l'enzyme anti-oxydante, la superoxyde dismutase à manganèse (SOD Mn). Sur la base que DDB2 est peu ou pas exprimée dans les cellules tumorales mammaires métastatiques, ce travail a consisté à étudier le rôle de cette protéine dans les capacités invasives de ces cellules. Dans un 1er temps, nous avons montré que les cellules tumorales mammaires hautement métastatiques (MDA-MB231 et SKBR3), lorsqu'elles surexpriment DDB2 après introduction de son gène, ont des capacités migratrices et invasives in vitro, ainsi que des propriétés in vivo à développer des métastases pulmonaires, fortement réduites, en association avec une diminution importante de l'expression de la métalloprotéase matricielle 9 (MMP-9). De même, lors d'une analyse rétrospective sur 92 échantillons cliniques provenant de patientes, une corrélation inverse entre l'expression de DDB2 et le haut grade (SBR>=3) des tumeurs mammaires est observée. Dans un 2ème temps, nous avons identifié le mécanisme moléculaire par lequel DDB2 agit négativement sur les capacités invasives des cellules tumorales mammaires. Nous avons montré que DDB2 intervient positivement sur l'expression du gène codant I kappa B alpha (IkBa), en se fixant sur une séquence d'ADN localisée dans la région proximale du promoteur, qui entraîne en conséquence une forte diminution de l'activité du facteur de transcription NF-kB. Ce dernier est connu pour son rôle dans les capacités invasives et migratrices des cellules tumorales mammaires métastatiques, en régulant de nombreux gènes cibles comme celui codant la MMP-9. Nous avons montré, que l'inhibition de l'expression d'IkBa, par ARN interférence restaure en partie les propriétés invasives des cellules tumorales mammaires métastatiques surexprimant DDB2, en association avec une réexpression de MMP-9. Dans un 3ème temps, nous avons également montré dans les cellules tumorales mammaires métastatiques, que l'expression constitutivement élevée de la SOD Mn, en l'absence de DDB2, dépend de l'activité conjointe des facteurs de transcription NF-kB et Sp1, révélant ainsi un autre mécanisme moléculaire impliqué dans les propriétés invasives de ces cellules. L'ensemble de ce travail contribue ainsi à mieux comprendre comment les cellules tumorales mammaires progressent vers un statut invasif et renforce également l'idée que DDB2 présente un intérêt clinique potentiel, comme marqueur prédictif de la progression métastatique des tumeurs mammaires. Enfin, la relation entre la DDB2, NF-kB et la SOD Mn représente une voie intéressante pour le développement de nouvelles thérapies anticancéreusesThe Damaged DNA-Binding 2 protein (DDB2) is known to play a role in repair of UV-induced DNA damages. However, the laboratory has shown that this protein is overexpressed in nonmetastatic breast tumor cells and stimulates their proliferation by favouring their entry in G1/S transition phase of cell cycle. This novel biological activity of DDB2 depends on its ability to modulate transcription of target genes, such as that encoding the manganese superoxide dismutase (MnSOD) antioxidant enzyme. The fact that DDB2 is not expressed in metastatic breast tumor cells led us to focuse this work on the role of DDB2 in the invasive abilities of these cells. In a 1st time, we have shown that highly metastatic breast tumor cells (MDA-MB231 et SKBR3), when they overexpress DDB2 after introduction of its gene, have a strong decrease in their in vitro migratory and invasive abilities, and in their properties to develop in vivo lung metastasis, associated with a highly reduced expression of matrix metalloprotease 9 (MMP-9). In addition, DDB2 expression was analyzed in a cohort of 92 breast samples from patients. An inverse correlation is observed between DDB2 level and the high-grade (SBR>=3) breast tumors. In a 2nd time, we identified the molecular mechanism by which DDB2 controls negatively the invasive abilities of breast tumor cells. We have shown that DDB2 plays a positive role in the expression of gene encoding I kappa B alpha gene (IkBa), though its binding to a specific DNA sequence localized in the proximal promoter, and which promotes a strong decrease in the NF-kB activity. This transcription factor is well known to play a role in migratory and invasive abilities of metastatic breast tumor cells by regulating many target genes, such as that encoding MMP-9. We have shown that inhibition by RNA interference of IkBa expression restores in part the invasive properties of DDB2-overexpressing metastatic breast tumor cells, associated with an induction of MMP-9 gene expression. In a 3rd time, we have also shown in metastatic breast tumor cells, that the high basal MnSOD expression, when DDB2 is lacking, depends on the related activity of the NF-kB and Sp1 transcription factors, considering that this other molecular mechanism is involved in invasive properties of these cells. Taken together, this work contributes to a better understanding how breast tumor cells progress toward an invasive phenotype and underlines also the idea that DDB2 has a clinical relevance as a good potential marker for predicting breast tumor progression toward metastasis. Finally, the relationship between DDB2, NF-kB and MnSOD may be considered as an interesting pathway for development of new anticancer therapiesMETZ-SCD (574632105) / SudocNANCY1-Bib. numérique (543959902) / SudocNANCY2-Bibliotheque electronique (543959901) / SudocNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Mitochondrial dynamics and cancer

Mitochondrial morphology is regulated by continuous fusion and fission events that are essential for maintaining a normal mitochondrial function. If the last years have witnessed major discoveries in the characterization of the fission and fusion machineries, little is known about the physiological role of mitochondrial dynamics. In this review we report the results showing evidences of relationships between mitochondrial dynamics and cellular metabolism, autophagy or apoptosis. We discuss how different mitochondrial alterations observed in cancer cells could be linked to unbalanced mitochondrial fission or fusion events and how this could impinge on key essential cellular processes, thereby contributing to tumorigenesis

Cooperative effects of cytosine methylation on DNA structure and dynamics

International audienceThe behavior of the structural parameters of DNA considering different level of methylation in CpG islands is studied by means of full-atom molecular dynamics simulations and electronic circular dichroism, both in an artificial model system and in a gene promoter sequence. It is demonstrated that methylation although intrinsically brings quite local perturbations may, if its level is high enough, induce cooperative effects that strongly modify the DNA backbone torsional parameters altering the helicity as compared to the non-methylated case. Since methylation of CpG island is correlated with the regu-lation of gene expression, understanding the struc-tural modifications induced in DNA is crucial to char-acterize all the fine equilibria into play in epigenetics phenomena

From non-covalent binding to irreversible DNA lesions: Nile blue and nile red as photosensitizing agents

We report a molecular modeling study, coupled with spectroscopy experiments, on the behavior of two well known organic dyes, nile blue and nile red, when interacting with B-DNA. In particular, we evidence the presence of two competitive binding modes, for both drugs. However their subsequent photophysical behavior is different and only nile blue is able to induce DNA photosensitization via an electron transfer mechanism. Most notably, even in the case of nile blue, its sensitization capabilities strongly depend on the environment resulting in a single active binding mode: the minor groove. Fluorescence spectroscopy confirms the presence of competitive interaction modes for both sensitizers, while the sensitization via electron transfer, is possible only in the case of nile blue

Delta2-Troglitazone alters energetic metabolism in triple-negative breast cancer cells: a mechanism to sensitize cancer cells to chemotherapy?

National audienc

Joint analysis of flow cytometry data and fluorescence spectra as a non-negative array factorization problem

International audienceThe paper presents a novel approach to the processing of flow cytometry data sequences. It consists in decomposing a sequence of multidimensional probability density functions by using multilinear block tensor decomposition approach. Also a formal link between flow cytometry data and fluorescence spectra is provided allowing the joint processing of both data. To illustrate the effectiveness of the approach, a study of the T47D cell line mitochondrial membrane potential as a function of the CCCP decoupling agent concentration is performed. The main advantages of the method are : (i) the flow cytometry data compensation is no longer necessary, (ii) the cell sorting capacity of the method is significantly improved as compared to classical clustering methods. As a byproduct, it was possible to observe directly on the result of the processing, the dependence of the cell mitochondrial membrane potential with respect to the cell cycle phase. The proposed method is quite general provided that it is possible to design an experiment allowing to observe the response of cell populations to an environmental/chemical/biological parameter