A proposed mechanism for cell polarization with no external cues

Bernstein, Ben C.; Bamburg, James R.

doi:10.1002/cm.20001

Cited by 18 publications

(15 citation statements)

References 66 publications

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“…the actin depolymerization and severing caused by ADF/cofilin; thus tropomyosins may serve to spatially segregate stable actin filaments from dynamic subsets of actin filaments (35)(36)(37)(38)(39)(40)(41). In smooth muscle, most of the filamentous actin that is associated with myosin is believed to be bound to tropomyosin (42); thus, it is likely that ADF/cofilin associates with a pool of actin that is not part of the contractile apparatus.…”

Section: Discussionmentioning

confidence: 99%

Actin Depolymerization Factor/Cofilin Activation Regulates Actin Polymerization and Tension Development in Canine Tracheal Smooth Muscle

Zhao

Huang

et al. 2008

Journal of Biological Chemistry

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The contractile activation of airway smooth muscle tissues stimulates actin polymerization, and the inhibition of actin polymerization inhibits tension development. Actin-depolymerizing factor (ADF) and cofilin are members of a family of actin-binding proteins that mediate the severing of F-actin when activated by dephosphorylation at serine 3. The role of ADF/cofilin activation in the regulation of actin dynamics and tension development during the contractile activation of smooth muscle was evaluated in intact canine tracheal smooth muscle tissues. Two-dimensional gel electrophoresis revealed that ADF and cofilin exist in similar proportions in the muscle tissues, and that ϳ40% of the total ADF/cofilin in unstimulated tissues is phosphorylated. Phospho-ADF/cofilin decreased concurrently with tension development in response to stimulation with acetylcholine (ACh) or potassium depolarization indicating the activation of ADF/cofilin. Expression of an inactive phospho-cofilin mimetic (cofilin S3E) but not wild type cofilin in the smooth muscle tissues inhibited endogenous ADF/cofilin dephosphorylation and ACh-induced actin polymerization. Expression of cofilin S3E in the tissues depressed tension development in response to ACh, but it did not affect myosin light chain phosphorylation. The ACh-induced dephosphorylation of ADF/cofilin required the Ca 2؉ -dependent activation of calcineurin (PP2B). The results indicate that the activation of ADF/ cofilin is regulated by contractile stimulation in tracheal smooth muscle and that cofilin activation is required for actin polymerization and tension development in response to contractile stimulation.

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Section: Discussionmentioning

confidence: 99%

Actin Depolymerization Factor/Cofilin Activation Regulates Actin Polymerization and Tension Development in Canine Tracheal Smooth Muscle

Zhao

Huang

et al. 2008

Journal of Biological Chemistry

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“…In root hairs (Bibikova et al, 1998), root caps (Fasano et al, 2001), and columella cells (Scott and Allen, 1999) of Arabidopsis thaliana, cytoplasmic pH changes are recognized as important signals that mediate directional growth and root gravity perception. Studies in animal cells also reveal that pH microdomains and actin polymerization play important roles in controlling cell polarity and growth (Bernstein et al, 2000;Bernstein and Bamburg, 2004;Ghosh et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

Oscillatory Increases in Alkalinity Anticipate Growth and May Regulate Actin Dynamics in Pollen Tubes of Lily

et al. 2006

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Lily (Lilium formosanum or Lilium longiflorum) pollen tubes, microinjected with a low concentration of the pH-sensitive dye bis-carboxyethyl carboxyfluorescein dextran, show oscillating pH changes in their apical domain relative to growth. An increase in pH in the apex precedes the fastest growth velocities, whereas a decline follows growth, suggesting a possible relationship between alkalinity and cell extension. A target for pH may be the actin cytoskeleton, because the apical cortical actin fringe resides in the same region as the alkaline band in lily pollen tubes and elongation requires actin polymerization. A pH-sensitive actin binding protein, actin-depolymerizing factor (ADF), together with actin-interacting protein (AIP) localize to the cortical actin fringe region. Modifying intracellular pH leads to reorganization of the actin cytoskeleton, especially in the apical domain. Acidification causes actin filament destabilization and inhibits growth by 80%. Upon complete growth inhibition, the actin fringe is the first actin cytoskeleton component to disappear. We propose that during normal growth, the pH increase in the alkaline band stimulates the fragmenting activity of ADF/AIP, which in turn generates more sites for actin polymerization. Increased actin polymerization supports faster growth rates and a proton influx, which inactivates ADF/AIP, decreases actin polymerization, and retards growth. As pH stabilizes and increases, the activity of ADF/AIP again increases, repeating the cycle of events.

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“…Among the extensive array of proteins that interact directly or indirectly with actin (2) and regulate the dynamics and assembly of actin filaments, the Tms play an essential role. Tms stabilize actin filaments by modulating the interaction of actinbinding proteins responsible for the regulation of actin dynamics (3)(4)(5)(6)(7)(8). The majority of the ϳ40 mammalian Tm isoforms (9 -12) are found associated with actin filaments of the cytoskeleton (known as cytoskeletal Tms), whereas three Tm isoforms (striated muscle or sarcomeric Tms) are exclusively expressed in striated muscle and associate with actin in the thin filament of the sarcomere (13).…”

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confidence: 99%

Divergent Regulation of the Sarcomere and the Cytoskeleton

Schevzov

Fath

Vrhovski

et al. 2008

Journal of Biological Chemistry

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The existence of a feedback mechanism regulating the precise amounts of muscle structural proteins, such as actin and the actin-associated protein tropomyosin (Tm), in the sarcomeres of striated muscles is well established. However, the regulation of nonmuscle or cytoskeletal actin and Tms in nonmuscle cell structures has not been elucidated. Unlike the thin filaments of striated muscles, the actin cytoskeleton in nonmuscle cells is intrinsically dynamic. Given the differing requirements for the structural integrity of the actin thin filaments of the sarcomere compared with the requirement for dynamicity of the actin cytoskeleton in nonmuscle cells, we postulated that different regulatory mechanisms govern the expression of sarcomeric versus cytoskeletal Tms, as key regulators of the properties of the actin cytoskeleton. Comprehensive analyses of tissues from transgenic and knock-out mouse lines that overexpress the cytoskeletal Tms, Tm3 and Tm5NM1, and a comparison with sarcomeric Tms provide evidence for this. Moreover, we show that overexpression of a cytoskeletal Tm drives the amount of filamentous actin.Actin microfilaments are present in a variety of cellular structures that are specialized for different functions (1). In muscle cells, actin filaments are arranged into the thin filaments of sarcomeres to provide contractile force. Proper functioning of the sarcomere requires an invariant organization of this structure. A mechanism is in place that maintains strict stoichiometric expression of the components of the sarcomere, such as actin and Tms, 2 and thus sarcomeric integrity. In contrast, actin microfilaments in nonmuscle cells are involved in a wide range of cellular architectures and functions, including motility, membrane ruffling, adhesion, cytokinesis, and transport. The diverse activities of the actin microfilaments involved in these cellular processes is made possible due to the dynamic nature of the actin cytoskeleton, where actin filaments undergo rapid assembly and disassembly through monomeric to filamentous actin conversion. Among the extensive array of proteins that interact directly or indirectly with actin (2) and regulate the dynamics and assembly of actin filaments, the Tms play an essential role. Tms stabilize actin filaments by modulating the interaction of actinbinding proteins responsible for the regulation of actin dynamics (3-8). The majority of the ϳ40 mammalian Tm isoforms (9 -12) are found associated with actin filaments of the cytoskeleton (known as cytoskeletal Tms), whereas three Tm isoforms (striated muscle or sarcomeric Tms) are exclusively expressed in striated muscle and associate with actin in the thin filament of the sarcomere (13).A number of studies have established the existence of a feedback mechanism in striated muscles such that forced overexpression or knockdown of genes encoding sarcomere-associated contractile proteins results in translational compensation that maintains a fixed amount for a given sarcomeric protein (14 -24). This is evident in the regulation...

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A proposed mechanism for cell polarization with no external cues

Cited by 18 publications

References 66 publications

Actin Depolymerization Factor/Cofilin Activation Regulates Actin Polymerization and Tension Development in Canine Tracheal Smooth Muscle

Actin Depolymerization Factor/Cofilin Activation Regulates Actin Polymerization and Tension Development in Canine Tracheal Smooth Muscle

Oscillatory Increases in Alkalinity Anticipate Growth and May Regulate Actin Dynamics in Pollen Tubes of Lily

Divergent Regulation of the Sarcomere and the Cytoskeleton

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