The focus of our labis to decipher the molecular mechanisms controlling cell polarization and migration in health and disease. We study polarization in migrating astrocytes to characterize the signalling pathways involved in the regulation of cell migration. Astrocytes are major glial cells of the central nervous system and they fulfill many different functions allowing the development, survival and functions of neurons. Although immobile in normal situations, astrocytes can become motile in response to inflammatory situations accompanying cerebral lesions, infections or neurogenerative diseases. Astrocyte migration is, in these cases, a key event to define the brain regions accessible to neuronal regeneration. Moreover, astrocytes can give rise to tumors, called gliomas which are characterized by their invasiveness into the brain parenchyma. Their invasive properties render these tumors particulary resistant to classical cancer treatment.

Our goal is to better define the fundamental signalling pathways controlling normal astrocyte polarization and migration during inflammatory situations. We want to determine what are the mechanisms controlling astrocyte migration during inflammatory situation and if alteration of these pathways can lead to the invasive properties of astrocyte-derived tumors. We thereby hope to identify therapeutic targets that will allow a better control of astrocyte migration in various pathological situations. We focus on evolutionary conserved polarity proteins and tumor suppressor genes in sensing polarity cues or in intracellular signalling pathways leading to cytoskeleton and vesicle trafficking regulation.

Some of the current issues being addressed are

• Intercellular contacts as polarity cues: N-cadherin based adherens junctions are the main type of cell-cell junctions in astrocytes. Using adhesive micropatterns, we show that in absence of cell migration, the geometry of intercellular contacts controls centrosome and nucleus positioning as well as cell polarity. During cell migration, N-cadherin also modulates the integrin signaling pathway that controls cell polarization and migration.

• Integrin-induced polarity pathways: Integrin activation is one of the first events leading to cell polarization and migration via a signaling pathway involving the small GTPase Cdc42 (Etienne-Manneville et Hall, 2003; Manneville et al., 2005). Cdc42 is a key player in cell polarity in a wide range of organisms and biological situation (Etienne-Manneville, 2004). During cell migration and cell polarization, Cdc42 is activated in a time and space-restricted manner. We aim at understanding the mechanisms that control Cdc42 activity and localization and the role of integrin signalling in these events.

• Evolutionary conserved polarity proteins: The role of polarity proteins such as Par proteins (including Par3, Par6, and the Par4 orthologue LKB1), proteins of the Scrib complex (Scrib, Dlg and Lgl) in astrocyte migration is investigated. While they all are involved in centrosome positioning and in directed migration (Etienne-Manneville et Hall, 2001; Forcet et al. 2004; Osmani et al. 2006; Etienne-Manneville et al. 2005), our current goal is to characterize their regulatory mechanisms and their downstream targets during the process of cell polarization. Our results extend our knowledge of polarity signalling pathways and their regulation in migrating cells.

• Cytoskeleton regulation: The cytoskeleton is composed of actin microfilaments, microtubules and intermediate filaments which, in astrocytes, mainly include nestin, GFAP and vimentin. Actin, microtubule and intermediate filaments are all essential for astrocyte and glioma cell migration and all of them acquire a polarized organization during directed cell migration. We investigate how polarity pathways co-ordinately control the 3 cytoskeletal elements.

• Alteration of polarity pathways in glioma: In vitro analysis of cell migration shows that glioma cells migrate faster than normal cells but that they are unable to undergo persistent directed migration. Our hypothesis is that polarity pathways are fundamentally perturbed in tumor cells leading to uncontrolled migration and invasion in vivo. Using microarray analysis of polarity gene expression in glioma cells (In collaboration with Pr. P-Y Delattre, Pitié-Salpétrière), we analyse whether polarity protein expression is altered in these cells and what is the consequences of such alteration. We hope that this approach will help us to find new diagnostic and prognostic factors and to identify potential therapeutic targets to prevent glioma cell infiltration.

Our approaches

In vitro cell polarity and cell migration models- Cell biology and microscopy techniques – Biochemistry - Molecular biology - Global transcriptomic approach of human tumors.

Keywords: Polarity, migration, astrocytes, gliomas, Rho GTPases, tumor suppressor genes, cytoskeleton, microtubules, centrosome

S. Etienne-Manneville, J.-B. Manneville, S. Nicholls , A. Ferenczi, A. Hall. 2005. Cdc42 and Par6-PKC  regulate the spatially localized association of Dlg1 and APC to control cell polarization. J.Cell Biol. 170: 895-901.

C. Forcet, S. Etienne-Manneville (Equal contribution), H. Gaude, L. Fournier, S. Debilly, M. Salmi, A. Baas, S. Olschwang, H. Clevers, M. Billaud. 2005. Functional analysis of Peutz-Jeghers mutations reveals that the carboxy-terminal region of LKB1 exerts a crucial role in the control of cell polarity. Hum. Mol. Gen. 14 : 1283-1292

N. Osmani, N. Vitale, J.-P. Borg, S. Etienne-Manneville. 2006. Scrib controls Cdc42 localization and activity to promote cell polarization during astrocyte migration. Curr. Biol. 16:2395-405

S. Etienne-Manneville. Polarity proteins in migration and invasion. 2008. Oncogene. 27(55):6970-80

S. Etienne-Manneville. Polarity proteins in glial cell functions. 2008. Curr. Opin. Neurobiol. 18(5):488-94.