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Al Haj A.,Ruhr University Bochum | Mazur A.J.,Ruhr University Bochum | Mazur A.J.,Wroclaw University | Buchmeier S.,TU Braunschweig | And 10 more authors.

F-actin treadmilling plays a key part in cell locomotion. Because immunofluorescence showed colocalisation of thymosin beta4 (Tβ4) with cofilin-1 and Arp2/3 complex in lamellipodia, we analyzed combinations of these proteins on F-actin-adenosine triphosphate (ATP)-hydrolysis, which provides a measure of actin treadmilling. Actin depolymerising factor (ADF)/cofilin stimulated treadmilling, while Tβ4 decreased treadmilling, presumably by sequestering monomers. Tβ4 added together with ADF/cofilin also inhibited the treadmilling, relative to cofilin alone, but both the rate and extent of depolymerization were markedly enhanced in the presence of both these proteins. Arp2/3 complex reversed the sequestering activity of Tβ4 when equimolar to actin, but not in the additional presence of cofilin-1 or ADF. Transfection experiments to explore the effects of changing the intracellular concentration of Tβ4 in HeLa cells showed that an increase in Tβ4 resulted in reduced actin filaments bundles and narrower lamellipodia, and a conspicuous decrease of cell migration as seen by two different assays. In contrast, cells transfected with a vector leading to Tβ4 knockdown by small interfering RNA (siRNA) displayed prominent actin filament networks within the lamellipodia and the leading lamella and enhanced migration. The experiments reported here demonstrate the importance of the interplay of these different classes of actin-binding proteins on cell behaviour. © 2013 Wiley Periodicals, Inc. Source

Machaidze G.,Maurice E Muller Institute For Structural Biology | Sokoll A.,Ruhr University Bochum | Shimada A.,Max Planck Institute of Molecular Physiology | Lustig A.,Maurice E Muller Institute For Structural Biology | And 5 more authors.
Journal of Molecular Biology

Mouse Diaphanous-related formins (mDias) are members of the formin protein family that nucleate actin polymerization and subsequently promote filamentous actin (F-actin) elongation by monomer addition to fast-growing barbed ends. It has been suggested that mDias preferentially recruit actin complexed to profilin due to their proline-rich FH1 domains. During filament elongation, dimeric mDias remain attached to the barbed ends by their FH2 domains, which form an anti-parallel ring-like structure enclosing the filament barbed ends. Dimer formation of mDia-FH2 domains is dependent on their N-terminal lasso and linker subdomains (connector). Here, we investigated the effect of isolated FH2 domains on actin polymerization using mDia1-FH2 domain plus connector, as well as core mDia1, mDia2, and mDia3 missing the connector, by cosedimentation and electron microscopy after negative staining. Analytical ultracentrifugation showed that core FH2 domains of mDia1 and mDia2 exhibited a low degree of dimer formation, whereas mDia3-FH2 minus connector and mDia1-FH2 plus connector readily dimerized. Only core mDia3-FH2 was able to nucleate actin polymerization. However, all tested core FH2 domains decorated and bundled F-actin, as demonstrated by electron microscopy after negative staining. Bundling activity was highest for mDia3-FH2, decreased for mDia2-FH2, and further decreased for mDia1-FH2. The mDia1-FH2 domain plus connector induced actin polymerization also in the absence of profilin, but failed to induce F-actin deformation and bundling. We also tested whether mDia1-FH2 was able to repolymerize actin in complex with different proteins that stabilize globular actin. The data obtained demonstrated that mDia1-FH2 induced actin repolymerization only from the actin/cofilin-1 complex, but not when complexed to actin depolymerizing factor, gelsolin segment 1, vitamin D binding protein, or deoxyribonuclease I. © 2010 Elsevier Ltd. Source

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