Actin cytoskeleton dynamics response

Kessels, MM, Engqvist-Goldstein, AE, and Drubin, DG, Association of mouse actin-binding protein 1 (mabpl/sh3p7), an src kinase target, with dynamic regions of the cortical actin cytoskeleton in response to rad activation. Mol Biol Cell, 2000. 11(1) 393 12. 

The cellular cytoskeleton, primarily composed of microfilaments, microtubules, and intermediate filaments, provides structural support and enables cell motility. The cytoskeleton is composed of biological polymers and is not static. Rather, it is capable of dynamic reassembly in less than a minute [136], The cytoskeleton is built from three key components, the actin filaments, the intermediate filaments, and the microtubules. The filaments are primarily responsible for maintaining cell shape, whereas the microtubules can be seen as the load-bearing elements that prevent a cell from collapsing [136], The cytoskeleton protects cellular structures and connects mechanotransductive pathways. Along with mechanical support, the cytoskeleton plays a critical role in many biological processes. 

Myosins, kinesins, and dyneins move by cycling between states with different affinities for the long, polymeric macromolecules that serve as their tracks. For myosin, the molecular track is a polymeric form of actin, a 42-kd protein that is one of the most abundant proteins in eukaryotic cells, typically accounting for as much as 10% of the total protein. Actin polymers are continually being assembled and disassembled in cells in a highly dynamic manner, accompanied by the hydrolysis of ATP. On the microscopic scale, actin filaments participate in the dynamic reshaping of the cytoskeleton and the cell itself and in other motility mechanisms that do not include myosin. In muscle, myosin and actin together are the key components responsible for muscle contraction. 

A role for MAPK in the contractile responsiveness of smooth muscle may result from either of two possible mechanisms, both involving caldesmon phosphorylation. First, caldesmon phosphorylation by MAPK may lead directly to an alteration of actomyosin activity. Caldesmon may exert this effect alone, or in concert with other myofibrillar proteins such as cal-ponin. Second, phosphorylation of caldesmon may alter the dynamics of actin filament organization within the cell. Caldesmon phosphorylation may result in alterations of the cellular cytoskeleton that must occur during prolonged contractions. 

The chemotactic response of Dictyostelium cells, and certainly also of other amoeboid cells such as neutrophils, is superimposed on the spontaneous dynamics of the cytoskeleton, in particular of the actin system in the cell cortex. This system consists basically of a network of bundled actin filaments, which are continuously turned over by polymerization and depolymerization. In Dicty-ostelium the polymerization rates of actin filaments constituting the network are in the order of 3 pm/s, corresponding to the... 

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