Lipid Membrane Shape Evolution and the Actin Cytoskeleton

Vertebrate cell growth, division, migration, morphogenesis, and development, rely on the dynamic interactions of cells with components the extracellular matrix (ECM) via cell surface complexes. These focal adhesions (FAs) are comprised of integrin receptors, associated signaling molecules, and talin, which is required for "inside-out" signaling that stabilizes contacts of integrin receptors with the ECM by linking FAs to the actin cytoskeleton by binding to vinculin. The highly dynamic interactions with the actin cytoskeleton are also essential for the formation of membrane protrusions (lamellopodia and filopodia). Second messengers are found at the plasma cell membrane and include signaling lipids such as phosphoinositides, which play essential roles in signal transduction pathways and in directing the oligomerization of cytoskeletal proteins that function as essential links of FAs to the actin cytoskeleton. Notably, the most abundant phosphoinositide, phosphatidyl (4,5) bisphosphate (PIP2), directly binds to key cytoskeletal proteins, where it triggers homotypic and heterotypic interactions that amplify binding to the actin network. Binding of the inositol head group and the hydrophobic acyl chain pose difficulties in generating protein/PIP2 complex crystals and here we present the only second non-membrane protein structure of such a complex. Our crystal structure and biochemical approaches define the roles of PIP2 in controlling the oligomerization of cytoskeletal proteins and their binding to adhesion receptors and to the actin cytoskeleton. Importantly, we also determined the contribution of PIP2-directed oligomerization of cytoskeletal proteins to the formation and stabilization of adhesion complexes. These studies provide important new insights into how dynamic interactions of cytoskeletal proteins with the lipid membrane, adhesion complexes, and the actin network direct the mechanical behaviors of cells.

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Encapsulated actomyosin patterns drive cell-like membrane shape changes

10.1101/2021.10.20.465228 ◽

2021 ◽

Author(s):

Yashar Bashirzadeh ◽

Hossein Moghimianavval ◽

Allen P Liu

Keyword(s):

Lipid Membrane ◽

Animal Cell ◽

Cell Cortex ◽

Cortical Actin ◽

Membrane Bound ◽

Actin Nucleator ◽

Lipid Bilayer Vesicles ◽

Network Patterns ◽

Membrane Shape ◽

Shape Changes

Cell shape changes from locomotion to cytokinesis are, to a large extent, driven by myosin-driven remodeling of cortical actin patterns. Passive crosslinkers such as α-actinin and fascin as well actin nucleator Arp2/3 complex largely determine the architecture and connectivity of actin network patterns; consequently, they regulate network remodeling and membrane shape changes. Membrane constriction in animal cell cytokinesis proceeds by assembly and contraction of a contractile ring pattern rich in α-actinin and myosin at the equator of the cell cortex, with which the ring is contiguous. Here we reconstitute actomyosin networks inside cell-sized lipid bilayer vesicles and show that, depending on vesicle size and concentrations of α-actinin and fascin, actomyosin networks assemble into ring and aster-like patterns. Anchoring actin to the membrane enhances the interaction of the contractile networks with lipid membrane but does not change the architecture of the patterns. A membrane-bound actomyosin ring exerts force and constricts the membrane. An Arp2/3 complex-mediated actomyosin cortex is shown to assemble a ring-like pattern at the equatorial cortex and contribute to myosin-driven clustering of the cortex and consequently membrane deformation. An active gel theory unifies a model for the observed membrane constriction and protrusion induced by the membrane-bound actomyosin networks.

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A role for the actin cytoskeleton in the hormonal and growth-factor-mediated activation of protein kinase B

Biochemical Journal ◽

10.1042/0264-6021:3530735v ◽

2001 ◽

Vol 353 (3) ◽

pp. 735

Author(s):

K. PEYROLLIER ◽

E. HAJDUCH ◽

A. GRAY ◽

G. J. LITHERLAND ◽

A. R. PRESCOTT ◽

...

Keyword(s):

Growth Factor ◽

Protein Kinase ◽

Actin Cytoskeleton ◽

Protein Kinase B

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Spatial control of actin-based motility through plasmalemmal PtdIns(4,5)P2-rich raft assemblies.

Biochemical Society Symposium ◽

10.1042/bss0720119 ◽

2005 ◽

Vol 72 ◽

pp. 119-127 ◽

Cited By ~ 19

Author(s):

Tamara Golub ◽

Caroni Pico

Keyword(s):

Protein Kinase ◽

Cell Surface ◽

Actin Cytoskeleton ◽

Lipid Rafts ◽

Patch Clustering ◽

Pkc Protein Kinase C ◽

Membrane Bound ◽

And Function ◽

Cytoskeleton Dynamics ◽

Syndrome Protein

The interactions of cells with their environment involve regulated actin-based motility at defined positions along the cell surface. Sphingolipid- and cholesterol-dependent microdomains (rafts) order proteins at biological membranes, and have been implicated in most signalling processes at the cell surface. Many membrane-bound components that regulate actin cytoskeleton dynamics and cell-surface motility associate with PtdIns(4,5)P2-rich lipid rafts. Although raft integrity is not required for substrate-directed cell spreading, or to initiate signalling for motility, it is a prerequisite for sustained and organized motility. Plasmalemmal rafts redistribute rapidly in response to signals, triggering motility. This process involves the removal of rafts from sites that are not interacting with the substrate, apparently through endocytosis, and a local accumulation at sites of integrin-mediated substrate interactions. PtdIns(4,5)P2-rich lipid rafts can assemble into patches in a process depending on PtdIns(4,5)P2, Cdc42 (cell-division control 42), N-WASP (neural Wiskott-Aldrich syndrome protein) and actin cytoskeleton dynamics. The raft patches are sites of signal-induced actin assembly, and their accumulation locally promotes sustained motility. The patches capture microtubules, which promote patch clustering through PKA (protein kinase A), to steer motility. Raft accumulation at the cell surface, and its coupling to motility are influenced greatly by the expression of intrinsic raft-associated components that associate with the cytosolic leaflet of lipid rafts. Among them, GAP43 (growth-associated protein 43)-like proteins interact with PtdIns(4,5)P2 in a Ca2+/calmodulin and PKC (protein kinase C)-regulated manner, and function as intrinsic determinants of motility and anatomical plasticity. Plasmalemmal PtdIns(4,5)P2-rich raft assemblies thus provide powerful organizational principles for tight spatial and temporal control of signalling in motility.

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