Abstract
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 approximately 40% 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 Ca2+-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.
Highlights
Of “actin-dynamizing proteins.” These proteins play a critical role in the rapid adaptation of the actin cytoskeleton to localized cellular functions [1,2,3]
Our results demonstrate that Actin-depolymerizing factor (ADF)/ cofilin undergoes dephosphorylation in response to contractile stimulation in smooth muscle tissues and that ADF/cofilin dephosphorylation is necessary for both actin polymerization
We conclude that the activation of ADF/cofilin is a necessary step for the dynamic reorganization of actin that occurs during the contraction of smooth muscle tissues
Summary
Of “actin-dynamizing proteins.” These proteins play a critical role in the rapid adaptation of the actin cytoskeleton to localized cellular functions [1,2,3]. Dephosphorylation of ADF/cofilin and its activation in tracheal Stimulation with ACh caused a significant decrease in the smooth muscle tissues.
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