ProjectMembrane transport and actin cytoskeleton

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► Small G proteins Arf are involved in intracellular transport, but their exact function remains poorly defined. We have shown that activation of the β2-adrenergic receptor induces the activation of Arf6 by its exchange factor EFA6, leading to the inhibition of receptor recycling and its targeting into the degradation pathway. Furthermore, we have demonstrated a direct interaction between EFA6 and a protein with a BAR (Bin, Amphiphysin and Rvs) domain, a domain capable of sensing and/or inducing membrane curvature and thus participating in the formation of transport vesicles and regulating vesicular trafficking. Taken together, this work allows us to define the molecular basis of the role of the small G protein Arf6 and its activator EFA6 in vesicular transport processes.

 Diagram of the role of Arf6 in the intracellular transport of a GPCR

► Actin cytoskeleton reorganization is necessary for intracellular transport processes as well as for the performance of numerous cellular functions, such as establishing epithelial polarity and cell migration. In epithelial cells, we have shown that EFA6/Arf6 regulate the assembly and maintenance of tight junctions. Furthermore, EFA6 and its partner alpha-actinin play a crucial role in lumen formation and extension. These proteins act by regulating lipid membrane transport and the contractility of the actomyosin system located at the apical pole.

 EFA6/Arf6 regulate tight junctions, luminogenesis, and epithelial polarity.

► Primary cilium assembly, or ciliogenesis, is another example of cell polarization. We have shown the essential role of the EFA6A/Arf6 pair in the early stages of cilium assembly, and particularly in the fusion processes of the first membrane vesicles that attach to the mother centriole to give rise to the ciliary vesicle and then to the cilium.

Diagram of the role of EFA6 in primary cilium assembly
► The EFA6 protein is capable of inducing a strong reorganization of the actin cytoskeleton. We have shown that its C-terminal end interacts directly with actin filaments, inhibiting polymerization at the barbed ends and inducing the formation of actin cables.

Diagram of the role of the C-terminal domain of EFA6

in the formation of plasma membrane extensions

► In collaboration with Dr. Tâm Mignot's team (Mediterranean Institute of Microbiology, Marseille), we have demonstrated that the rapid change in cell polarity during motility in the bacterium Myxococcus xanthus is regulated by a small G protein homologous to the Arf family, the MglA protein, and its GAP (GTPase Activating Protein), the MglB protein. Similar to eukaryotes, this motility requires a connection between this small G protein MglA and MreB, a protein analogous to eukaryotic actin.

Diagram of the role of the small G protein MglA
   in the mobility of the bacteria Mr. xanthus

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