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Contrôle de la mort cellulaire par la voie des MAPK1/3 (ERK2/1)

Abstract : Programmed cell death or"apoptosis"is an evolutionary conserved feature of multicellular organisms necessary for normal development and tissue homeostasis. In living cells, the activity of the proteases that execute the apoptotic cell death program, the caspases, is controlled by survival signals emanating from the cellular environment. The regulatory components of the caspase cascade, caspase 9 and caspase 8, are activated respectively by the apoptosome and by death receptors. Survival signals elicited by extracellular matrix or growth factors activate signaling pathways that control the cell death machinery. The MAPK1/3 signaling pathway is a kinase cascade comprising Raf, MEK1/2 and MAPK1/3 (ERK1/2 or p42/p44 MapKinases) regulated by the proto-oncogene Ras. The MAPK1/3 pathway is implicated in cell proliferation and differentiation and plays an essential role in cell survival. This thesis objective was to characterize the molecular mechanisms involved in the control of cell death by MAPK1/3 pathway. This study relies on the use of an inducible form of Raf-1 kinase (DeltaRaf-1:ER) those strong and persistent activation leads to a pathological induction of MAPK1/3 activity. We have been able to show that, depending on the cell type, Raf-1:ER activation favors cell survival or induces cell death. In the lung fibroblastic cell line CCL39, Raf-1:ER activation prevents cell death induced by serum withdrawal from the tissue culture medium. Under this experimental setting, we could show that Raf-1:ER stimulation inhibits caspase 9 activation but did not prevent cytochrome c release, APAF1 oligomerization and caspase 9 recruitment in the apoptosome. This novel mechanism of cell death inhibition at a post-mitochondrial level requires ongoing protein synthesis and continuous MEK kinase activity. In HEK293, an embryonic kidney cell line that bares properties of neuronal lineage cells, sustained activation of the MAPK1/3 pathway in response to Raf-1:ER induces massive cell death. Cell death is characterized by caspases activation and DNA fragmentation. It is a slow process, detectable more than 24 hours after Raf-1:ER stimulation and maximal at 48 hours. Cell death induction needs protein synthesis only during the early stage of activation but requires a continuous activity of the MEK/MAPK module. Cell death results from caspase 8 activation and does not require the mitochondrial pathway of apoptosis. It is characterized by the formation of vacuoles in the cytoplasm that evoke paraptosis, a particular form of apoptosis. Functional inactivation of the death receptor Fas or its adaptator FADD indicates that the activation process of caspase 8 is independent of the death receptor pathway. Altogether, these results extend our understanding on the role of the Raf/MAPk pathway in the control of cell death. We have shown that in different cellular context, this signaling pathway can either promote cell survival or induce cell death. In both cases, cell death control requires protein synthesis and post-traductionnal modifications. Molecular mechanisms that respond to prolonged MAPK1/3 activation could be involved in tumor resistance to proapoptotic treatments as well as in the development of neurodegenerative diseases.
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https://tel.archives-ouvertes.fr/tel-00104792
Contributor : Jean-Claude Chambard <>
Submitted on : Monday, October 9, 2006 - 2:21:26 PM
Last modification on : Wednesday, October 14, 2020 - 4:24:02 AM
Long-term archiving on: : Thursday, September 20, 2012 - 11:31:31 AM

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  • HAL Id : tel-00104792, version 1

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Sébastien Cagnol. Contrôle de la mort cellulaire par la voie des MAPK1/3 (ERK2/1). Biologie cellulaire. Université Nice Sophia Antipolis, 2005. Français. ⟨tel-00104792⟩

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