Faculty Opinions recommendation of The F-BAR domain of srGAP2 induces membrane protrusions required for neuronal migration and morphogenesis.

Filopodia are actin-filled membrane protrusions that play essential roles in cell motility and cell–cell communication and act as precursors of dendritic spines. IRSp53 is an essential regulator of filopodia formation, which couples Rho-GTPase signaling to actin cytoskeleton and membrane remodeling. IRSp53 has three major domains: an N-terminal inverse-BAR (I-BAR) domain, a Cdc42- and SH3-binding CRIB-PR domain, and an SH3 domain that binds downstream cytoskeletal effectors. Phosphorylation sites in the region between the CRIB-PR and SH3 domains mediate the binding of 14-3-3. Yet the mechanism by which 14-3-3 regulates filopodia formation and dynamics and its role in cell migration are poorly understood. Here, we show that phosphorylation-dependent inhibition of IRSp53 by 14-3-3 counters activation by Cdc42 and cytoskeletal effectors, resulting in down-regulation of filopodia dynamics and cancer cell migration. In serum-starved cells, increased IRSp53 phosphorylation triggers 14-3-3 binding, which inhibits filopodia formation and dynamics, irrespective of whether IRSp53 is activated by Cdc42 or downstream effectors (Eps8, Ena/VASP). Pharmacological activation or inhibition of AMPK, respectively, increases or decreases the phosphorylation of two of three sites in IRSp53 implicated in 14-3-3 binding. Mutating these phosphorylation sites reverses 14-3-3-dependent inhibition of filopodia dynamics and cancer cell chemotaxis.

Download Full-text

Dimerization is necessary for MIM-mediated membrane deformation and endocytosis

Biochemical Journal ◽

10.1042/bj20120329 ◽

2012 ◽

Vol 446 (3) ◽

pp. 469-475 ◽

Cited By ~ 9

Author(s):

Meng Cao ◽

Tailan Zhan ◽

Min Ji ◽

Xi Zhan

Keyword(s):

Metastasis Suppressor ◽

Intracellular Protein ◽

High Potency ◽

Membrane Deformation ◽

Bar Domain ◽

Membrane Protrusions ◽

Metastasis Suppressor 1 ◽

Intrinsic Capacity ◽

Transferrin Uptake

MIM [missing in metastasis; also called MTSS1 (metastasis suppressor 1)] is an intracellular protein that binds to actin and cortactin and has an intrinsic capacity to sense and facilitate the formation of protruded membranous curvatures implicated in cell-ular polarization, mobilization and endocytosis. The N-terminal 250 amino acids of MIM undergo homodimerization and form a structural module with the characteristic of an I-BAR [inverse BAR (Bin/amphiphysin/Rvs)] domain. To discern the role of the dimeric configuration in the function of MIM, we designed several peptides able to interfere with MIM dimerization in a manner dependent upon their lengths. Overexpression of one of the peptides effectively abolished MIM-mediated membrane protrusions and transferrin uptake. However, a peptide with a high potency inhibiting MIM dimerization failed to affect its binding to actin and cortactin. Thus the results of the present study indicate that the dimeric configuration is essential for MIM-mediated membrane remodelling and serves as a proper target to develop antagonists specifically against an I-BAR-domain-containing protein.

Download Full-text

Ezrin enrichment on curved membranes requires a specific conformation or interaction with a curvature-sensitive partner

10.1101/297895 ◽

2018 ◽

Author(s):

Feng-Ching Tsai ◽

Aurélie Bertin ◽

Hugo Bousquet ◽

John Manzi ◽

Yosuke Senju ◽

...

Keyword(s):

Cell Biology ◽

Membrane Curvature ◽

Bar Domain ◽

Negatively Curved ◽

Current Cell ◽

Bar Domain Proteins ◽

Membrane Protrusions ◽

Curved Membranes ◽

Curved Membrane

AbstractOne challenge in current cell biology is to decipher the biophysical mechanisms governing protein enrichment on curved membranes and the resulting membrane deformation. The ERM protein ezrin is abundant and associated with cellular membranes that are flat or with positive or negative curvatures. Using in vitro and cell biology approaches, we assess mechanisms of ezrin’s enrichment on curved membranes. We evidence that ezrin (ezrinWT) and its phosphomimetic mutant T567D (ezrinTD) do not deform membranes but self-assemble anti-parallelly, zipping adjacent membranes. EzrinTD’s specific conformation reduces intermolecular ezrin interactions, allows binding to actin filaments, and promotes ezrin binding to positively curved membranes. While neither ezrinTD nor ezrinWT senses negative membrane curvature alone, we demonstrate that interacting with curvature sensors I-BAR-domain proteins facilitates ezrin enrichment in negatively curved membrane protrusions. Overall, our work reveals new mechanisms, specific conformation or binding to a curvature sensor partner, for targeting curvature insensitive proteins to curved membranes.

Download Full-text

Missing-in-metastasis and IRSp53 deform PI(4,5)P2-rich membranes by an inverse BAR domain–like mechanism

The Journal of Cell Biology ◽

10.1083/jcb.200609176 ◽

2007 ◽

Vol 176 (7) ◽

pp. 953-964 ◽

Cited By ~ 262

Author(s):

Pieta K. Mattila ◽

Anette Pykäläinen ◽

Juha Saarikangas ◽

Ville O. Paavilainen ◽

Helena Vihinen ◽

...

Keyword(s):

Mammalian Cells ◽

Membrane Curvature ◽

Membrane Dynamics ◽

Actin Dynamics ◽

Actin Binding ◽

Tubular Structures ◽

Membrane Deformation ◽

Bar Domain ◽

Membrane Protrusions ◽

Induce Plasma

The actin cytoskeleton plays a fundamental role in various motile and morphogenetic processes involving membrane dynamics. We show that actin-binding proteins MIM (missing-in-metastasis) and IRSp53 directly bind PI(4,5)P2-rich membranes and deform them into tubular structures. This activity resides in the N-terminal IRSp53/MIM domain (IMD) of these proteins, which is structurally related to membrane-tubulating BAR (Bin/amphiphysin/Rvs) domains. We found that because of a difference in the geometry of the PI(4,5)P2-binding site, IMDs induce a membrane curvature opposite that of BAR domains and deform membranes by binding to the interior of the tubule. This explains why IMD proteins induce plasma membrane protrusions rather than invaginations. We also provide evidence that the membrane-deforming activity of IMDs, instead of the previously proposed F-actin–bundling or GTPase-binding activities, is critical for the induction of the filopodia/microspikes in cultured mammalian cells. Together, these data reveal that interplay between actin dynamics and a novel membrane-deformation activity promotes cell motility and morphogenesis.

Download Full-text

Ezrin enrichment on curved membranes requires a specific conformation or interaction with a curvature-sensitive partner

eLife ◽

10.7554/elife.37262 ◽

2018 ◽

Vol 7 ◽

Cited By ~ 17

Author(s):

Feng-Ching Tsai ◽

Aurelie Bertin ◽

Hugo Bousquet ◽

John Manzi ◽

Yosuke Senju ◽

...

Keyword(s):

Cell Biology ◽

Bar Domain ◽

Curvature Sensing ◽

Negatively Curved ◽

Bar Domain Proteins ◽

Membrane Tethering ◽

Membrane Protrusions ◽

Curved Membranes ◽

Curved Membrane

One challenge in cell biology is to decipher the biophysical mechanisms governing protein enrichment on curved membranes and the resulting membrane deformation. The ERM protein ezrin is abundant and associated with cellular membranes that are flat, positively or negatively curved. Using in vitro and cell biology approaches, we assess mechanisms of ezrin’s enrichment on curved membranes. We evidence that wild-type ezrin (ezrinWT) and its phosphomimetic mutant T567D (ezrinTD) do not deform membranes but self-assemble anti-parallelly, zipping adjacent membranes. EzrinTD’s specific conformation reduces intermolecular interactions, allows binding to actin filaments, which reduces membrane tethering, and promotes ezrin binding to positively-curved membranes. While neither ezrinTD nor ezrinWT senses negative curvature alone, we demonstrate that interacting with curvature-sensing I-BAR-domain proteins facilitates ezrin enrichment in negatively-curved membrane protrusions. Overall, our work demonstrates that ezrin can tether membranes, or be targeted to curved membranes, depending on conformations and interactions with actin and curvature-sensing binding partners.

Download Full-text