Regulation of WASP/WAVE proteins: making a long story short

Despite their homology, the regulation of WASP and WAVE, activators of Arp2/3-dependent actin polymerization, has always been thought to be different. Several recent studies have revealed new aspects of their regulation, highlighting its complexity and the crucial role of post-translational modifications. New data also suggest additional functions for WASP family proteins, pushing us to reconsider existing models

Inhibition of cytokinesis by wiskostatin does not rely on N-WASP/Arp2/3 complex pathway

BACKGROUND: Cytokinesis is the final step of cell division taking place at the end of mitosis during which the cytoplasmic content and replicated chromosomes of a cell are equally partitioned between the two daughter cells. This process is achieved by the formation and the ingression of an actomyosin contractile ring under the control of equatorial microtubules. The mechanisms of contractile ring formation are not fully understood but involve recruitment of preexisting actin filaments and de novo actin polymerisation. RESULTS: In this study, we evaluated the role of the actin nucleation factor, Arp2/3 complex, during cytokinesis. We found that the Arp2/3 complex is recruited late to the cleavage furrow suggesting a potential involvement of Arp2/3 complex during this process. Furthermore, wiskostatin a potent inhibitor of N-WASP activity towards the Arp2/3 complex blocked cytokinesis without affecting mitosis. Nonetheless, this inhibition could not be reproduced using alternative approaches targeting the N-WASP/Arp2/3 complex pathway. CONCLUSION: We conclude that the wiskostatin induced defective cytokinesis does not occur through the inhibition of the N-WASP/Arp2/3 pathway. Wiskostatin is likely to either directly target other proteins required for cytokinesis progression or alternately wiskostatin bound to N-WASP could affect the activity of other factors involved in cytokinesis

Subgroup II PAK-mediated phosphorylation regulates Ran activity during mitosis

Phosphorylation of the Ran GTPase on Serine-135 by PAK4 changes Ran’s association with its regulatory proteins and its ability to induce microtubule asters

La protéine tyrosine phosphatase PTPL1 (localisation et rôles dans le contrôle de la croissance cellulaire et de l'apoptose)

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Inhibition of cytokinesis by wiskostatin does not rely on N-WASP/Arp2/3 complex pathway

Abstract Background Cytokinesis is the final step of cell division taking place at the end of mitosis during which the cytoplasmic content and replicated chromosomes of a cell are equally partitioned between the two daughter cells. This process is achieved by the formation and the ingression of an actomyosin contractile ring under the control of equatorial microtubules. The mechanisms of contractile ring formation are not fully understood but involve recruitment of preexisting actin filaments and de novo actin polymerisation. Results In this study, we evaluated the role of the actin nucleation factor, Arp2/3 complex, during cytokinesis. We found that the Arp2/3 complex is recruited late to the cleavage furrow suggesting a potential involvement of Arp2/3 complex during this process. Furthermore, wiskostatin a potent inhibitor of N-WASP activity towards the Arp2/3 complex blocked cytokinesis without affecting mitosis. Nonetheless, this inhibition could not be reproduced using alternative approaches targeting the N-WASP/Arp2/3 complex pathway. Conclusion We conclude that the wiskostatin induced defective cytokinesis does not occur through the inhibition of the N-WASP/Arp2/3 pathway. Wiskostatin is likely to either directly target other proteins required for cytokinesis progression or alternately wiskostatin bound to N-WASP could affect the activity of other factors involved in cytokinesis.</p

Involvement of Rac in actin cytoskeleton rearrangements induced by MIM-B

International audienceNumerous scaffold proteins coordinate signals from the environment with actin-based protrusions during shape change and migration. Many scaffolds integrate signals from Rho-family GTPases to effect the assembly of specific actin structures. Here we investigate the mechanism of action MIM-B (missing in metastasis-B) on the actin cytoskeleton. MIM-B binds actin monomer through a WASP homology 2 motif, bundles actin filaments via an IRSp53/MIM domain, and is a long isoform of MIM, a proposed metastasis suppressor. We analysed the activity of MIM-B toward the actin cytoskeleton as well as its potential link to cancer metastasis. Endogenous MIM-B protein is widely expressed and its expression is maintained in various metastatic cell lines. MIM-B induces lamellipodia-like actin-rich protrusions. The IRSp53/MIM domain of MIM-B, as well as Rac activity are required to induce protrusions, but not the WASP homology 2 motif. MIM-B binds and activates Rac via its IRSp53/MIM domain, but this is not sufficient to induce lamellipodia. Finally, our data revealed that actin bundling and Rac-binding properties of MIM-B are not separable. Thus, MIM-B is unlikely to be a metastasis suppressor but acts as a scaffold protein that interacts with Rac, actin and actin-associated proteins to modulate lamellipodia formation

Membrane targeting of protein tyrosine phosphatase PTPL1 through its FERM domain via binding to phosphatidylinositol 4,5-biphosphate.

PTPL1 is the largest known cytoplasmic protein tyrosine phosphatase (PTP) containing a FERM (four point-1, ezrin, radixin and moesin) domain. Enzyme localization and PTP-substrate specificity are thought to play crucial roles in the regulation of PTP activity, which determines their functions. Here we report that PTPL1 is predominantly localized at the apical face of plasma membrane enriched in dorsal microvilli when expressed in HeLa cells. By comparing localization of the full-length enzyme with its FERM domain or FERM-deleted PTPL1 construct, we first concluded that PTPL1-FERM domain is necessary and sufficient to address the wild-type enzyme at the membrane. Two potential phosphatidylinositol 4,5-biphosphate [PtdIns(4,5)P2]-binding motifs were identified within the PTPL1-FERM sequence. We further showed that mutation of both sites altered PTPL1 localization similarly to FERM domain deletion, and impaired its subcellular distribution as confirmed biochemically by cell-fractionation experiments. Using protein-lipid overlays, we demonstrated an interaction of the FERM domain of PTPL1 with PtdIns(4,5)P2, which was lost after mutation of potential PtdIns(4,5)P2-binding motifs. Moreover, neomycin, which masks PtdIns(4,5)P2 polar heads, was shown to decrease by 50% the association of PTPL1 with the cytoskeletal fraction. These results identify the crucial role of the FERM domain in PTPL1 intracellular targeting and demonstrate that localization of PTPL1 is regulated by phosphoinositide metabolism

Inhibition of cytokinesis by wiskostatin does not rely on N-WASP/Arp2/3 complex pathway-1

or indicated concentrations of wiskostatin. Cells were harvested at indicated time points and DNA content determined by FACS analysis. A similar scale was used for each histogram. This result is representative of at least 3 independent experiments. B. HeLa cells synchronised as previously described were treated with vehicle (-) or 10 μM wiskostatin (+) and harvested at indicated time points. Cyclin B1, phosphorylation of Ser 10 of histone H3 and cofilin levels were determined by immunoblot analysis with specific antibodies. This result is representative of at least 5 independent experiments. C. HeLa cells stably expressing GFP-tagged histone H2B were synchronised as previously described, treated with vehicle (Control) or 10 μM wiskostatin (Wiskostatin 10 μM) and fixed after 300 minutes. F-actin was stained and nuclei per cell determined. Percentage of binucleated cells was then calculated. 536 cells treated with vehicle and 569 cells treated with wiskostatin were count from three independent experiments. Error bars represent standard error of the mean (SEM). D. Assynchronous HeLa cells stably expressing GFP-tagged histone H2B were treated with vehicle (Control) or 5 μM wiskostastin (Wiskostatin 5 μM) for 24 hours and were then fixed. Percentages of binucleated cells were determined as previously indicated. 629 cells treated with vehicle and 640 cells treated with wiskostatin were count from three independent experiments. Error bars represent SEM. Representative images from time lapse movies of HeLa cells stably expressing GFP-tagged histone H2B synchronised as previously described, treated with vehicle (E) or 10 μM wiskostatin (F). Images represent merged between DIC and fluorescent (Histone H2B) images. Time indicated as hours: minutes.<p><b>Copyright information:</b></p><p>Taken from "Inhibition of cytokinesis by wiskostatin does not rely on N-WASP/Arp2/3 complex pathway"</p><p>http://www.biomedcentral.com/1471-2121/9/42</p><p>BMC Cell Biology 2008;9():42-42.</p><p>Published online 30 Jul 2008</p><p>PMCID:PMC2527559.</p><p></p