|Cell Polarity and Migration - CNRS URA 2592|
|HEAD||ETIENNE-MANNEVILLE Sandrine / firstname.lastname@example.org|
|MEMBERS||Dr. CAMAND Emeline / DUPIN Isabelle/ JEHANNO Muguette / Dr. MZALI Rym / OSMANI Naël / Dr. SAKAMOTO Yasuhisa
Our research focuses on the control cell polarization and migration. We use primary rat astrocytes and astrocyte derived tumors to develop in vitro models of cell migration and polarization. In these systems, we investigate the role (i) of cell-cell contacts and cadherin signaling (ii) of different tumor suppressors (APC, LKB1, PTEN, Dlg, Scrib) (iii) and of the cytoskeletal elements.
i) 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. Using calcium depletion or RNA interference, we show that N-cadherin and β-catenin are involved in cell-cell contact regulated polarity. These adherens junctions proteins control, via the small GTPase Rho, (i) the actin cytoskeleton to drag the nucleus and centrosome complex in proximity to cell-cell contacts and (ii) the microtubule cytoskeleton to orient the centrosome-nucleus axis towards free cell edges.
During cell migration, N-cadherin also modulate the integrin signaling pathway that controls cell polarization and migration. Our ongoing work focuses on the molecular mechanisms by which N-cadherin modulates Scrib-Cdc42 polarity pathway.
ii) 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 al., 2003; Manneville et al., 2005). We have shown that Scrib, the mammalian orthologue of the Drosophila tumor suppressor and polarity protein Scribble, binds the exchange factor β-PIX to control Cdc42 localisation and activity and regulate astrocyte polarity (Osmani et al., 2006; see figure). Localization of Scrib and further association with βPIX induce Cdc42. We now show that Scrib and bPIX form a complext with GIT1 a GAP for the small GTPase Arf6. Arf6 is activated during cell migration and controls the recycling of membrane-bound Cdc42 to precisely regulate the localization of the active protein.
LKB1 is a serine/threonine kinase involved in Peutz-Jegher syndrome. It is also the closest homologue of the C. elegans polarity protein PAR-4. We have shown that LKB1 was required for centrosome reorientation during astrocyte migration and that both its catalytic and its carboxy-terminal domains are essential for this function (Forcet et al., 2005). We now aim at characterizing the regulatory mechanisms and the downstream targets of LKB1 during cell polarization.
iii) The cytoskeleton is composed of actin microfilaments, microtubules and intermediate filaments composed, in astrocytes, of nestin and GFAP mainly. The microtubule network plays a key role in astrocyte polarization and migration. We have shown that microtubules of the leading edge of migrating cells were anchored at the basal plasma membrane. We investigate the role of the microtubule-associated motor dynein in this event and show that the Cdc42 polarity pathway control dynein association with microtubules through Dlg and GKAP.
Our results extend our knowledge of polarity signaling pathways and their regulation in migrating cells. They also further confirm the functional conservation of several polarity proteins such as Scrib, N-cadherin or LKB1.
Keywords: Polarity, migration, astrocytes, Rho GTPases, tumor suppressor genes, cytoskeleton, microtubules, centrosome
Activity Reports 2007 - Institut Pasteur
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