Creating a niche in the cytoskeleton: Actin reorganization by a protein kinase

Janmey, Paul A.

doi:10.1073/pnas.011601598

Cited by 16 publications

(8 citation statements)

References 19 publications

(20 reference statements)

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“…However, it is currently unclear whether formins regulate the bundling of the actin filaments directly or indirectly. The bundling of actin filaments can be caused by dimerization of F-actin-binding proteins, such as α-actinin (Ayscough, 1998;Janmey, 2001;Puius et al, 1998). It seems thus possible that, in addition to the process of actin polymerization, Fhos may be also involved in the process of F-actin bundling via the formation of a homotypic complex.…”

Section: Discussionmentioning

confidence: 99%

“…It is known that the organization of individual actin filaments into higher ordered structures is controlled by bivalent actin-crosslinking proteins that contain two discrete F-actinbinding sites or by noncovalently dimerized Factin-binding proteins (Ayscough, 1998;Janmey, 2001;Puius et al, 1998). To test the possibility that the F-actin-binding protein Fhos functions as a dimer, we expressed both GFP-and Myc-tagged Fhos proteins in HeLa cells and assessed the ability of the proteins to interact with each other.…”

Section: Fhos Forms a Homotypic Complex Via The Fh2 Domainmentioning

confidence: 99%

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Fhos, a mammalian formin, directly binds to F-actin via a region N-terminal to the FH1 domain and forms a homotypic complex via the FH2 domain to promote actin fiber formation

Takeya

Sumimoto

2003

Journal of Cell Science

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Formins constitute a family of eukaryotic proteins that are considered to function as a cytoskeleton organizer to regulate morphogenesis, cell polarity and cytokinesis. Fhos is a recently identified mammalian formin, which contains the conserved domains FH (formin homology) 1 and FH2 in the middle region and the Dia-autoregulatory domain (DAD) in the C-terminus. The role of Fhos in the regulation of cytoskeleton, however, has remained unknown. Here we show that Fhos, in an active form, induces the formation of actin stress fibers and localizes to the actin-based structure. Fhos appears to normally exist in a closed inactive form via an intramolecular interaction between the N-terminal region and the C-terminal DAD. Both FH1 and FH2 domains are required for the induction of the stress fiber formation. However, the N-terminal region of Fhos is required for the targeting of this protein to stress fibers, which is probably mediated via its F-actin-binding activity. We also show that Fhos occurs as a homotypic complex in cells. The self-association of Fhos seems to be mediated via the FH2 domain: the domains bind to each other in a direct manner. Thus, the mammalian formin Fhos, which directly binds to F-actin via the N-terminal region, forms a homotypic complex via the FH2 domain to organize actin cytoskeleton.

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Section: Discussionmentioning

confidence: 99%

Section: Fhos Forms a Homotypic Complex Via The Fh2 Domainmentioning

confidence: 99%

Fhos, a mammalian formin, directly binds to F-actin via a region N-terminal to the FH1 domain and forms a homotypic complex via the FH2 domain to promote actin fiber formation

Takeya

Sumimoto

2003

Journal of Cell Science

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“…These discoveries are particularly exciting because they indicate that MHCK A possesses the dual capacity to bring about changes in the actin-myosin II cytoskeleton directly via its actin-bundling activity and through its well-documented ability to drive myosin II bipolar-filament disassembly via myosin II heavy-chain phosphorylation. At this time, it is unclear if the bundling activity of MHCK A is involved in large-scale rearrangements of the cytoskeleton, because the estimated concentration of the kinase in a Dictyostelium cell is much lower (0.3 µM; [23]) than the concentration of actin present in actin-rich cortical structures such as forming pseudopods (> 100 µM; [42]). On the other hand, recruitment of MHCK A to specific actinrich regions of the cell [19] may result in localized increases in MHCK A concentration that are sufficient to drive in vivo bundling of actin filaments.…”

Section: Discussionmentioning

confidence: 99%

Myosin heavy-chain kinase A from Dictyostelium possesses a novel actin-binding domain that cross-links actin filaments

Russ

Croft

Ali

et al. 2006

Biochemical Journal

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Myosin heavy-chain kinase A (MHCK A) catalyses the disassembly of myosin II filaments in Dictyostelium cells via myosin II heavy-chain phosphorylation. MHCK A possesses a 'coiled-coil'-enriched domain that mediates the oligomerization, cellular localization and actin-binding activities of the kinase. F-actin (filamentous actin) binding by the coiled-coil domain leads to a 40-fold increase in MHCK A activity. In the present study we examined the actin-binding characteristics of the coiled-coil domain as a means of identifying mechanisms by which MHCK A-mediated disassembly of myosin II filaments can be regulated in the cell. Co-sedimentation assays revealed that the coiled-coil domain of MHCK A binds co-operatively to F-actin with an apparent K(D) of approx. 0.5 muM and a stoichiometry of approx. 5:1 [actin/C(1-498)]. Further analyses indicate that the coiled-coil domain binds along the length of the actin filament and possesses at least two actin-binding regions. Quite surprisingly, we found that the coiled-coil domain cross-links actin filaments into bundles, indicating that MHCK A can affect the cytoskeleton in two important ways: (1) by driving myosin II-filament disassembly via myosin II heavy-chain phosphorylation, and (2) by cross-linking/bundling actin filaments. This discovery, along with other supporting data, suggests a model in which MHCK A-mediated bundling of actin filaments plays a central role in the recruitment and activation of the kinase at specific sites in the cell. Ultimately this provides a means for achieving the robust and highly localized disruption of myosin II filaments that facilitates polarized changes in cell shape during processes such as chemotaxis, cytokinesis and multicellular development.

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“…The actin is fluorescently labeled and stabilized after polymerization. Filamin, which is a dimeric actin-binding and cross-linking protein with a forklike structure (Janmey, 2001;Nakamura, Osborn, Janmey, & Stossel, 2002;Stossel et al, 2001), is injected into the flow cell to initiate the formation of a 2D actin network (Figure 4(B)). The formation of an orthogonal network on the pillar arrays is driven by cross-linking the fluctuating extremities of the actin filaments.…”

Section: Figurementioning

confidence: 99%