Caldesmon Inhibits Nonmuscle Cell Contractility and Interferes with the Formation of Focal Adhesions

Abstract

Caldesmon is known to inhibit the ATPase activity of actomyosin in a Ca(2+)-calmodulin-regulated manner. Although a nonmuscle isoform of caldesmon is widely expressed, its functional role has not yet been elucidated. We studied the effects of nonmuscle caldesmon on cellular contractility, actin cytoskeletal organization, and the formation of focal adhesions in fibroblasts. Transient transfection of nonmuscle caldesmon prevents myosin II-dependent cell contractility and induces a decrease in the number and size of tyrosine-phosphorylated focal adhesions. Expression of caldesmon interferes with Rho A-V14-mediated formation of focal adhesions and stress fibers as well as with formation of focal adhesions induced by microtubule disruption. This inhibitory effect depends on the actin- and myosin-binding regions of caldesmon, because a truncated variant lacking both of these regions is inactive. The effects of caldesmon are blocked by the ionophore A23187, thapsigargin, and membrane depolarization, presumably because of the ability of Ca(2+)-calmodulin or Ca(2+)-S100 proteins to antagonize the inhibitory function of caldesmon on actomyosin contraction. These results indicate a role for nonmuscle caldesmon in the physiological regulation of actomyosin contractility and adhesion-dependent signaling and further demonstrate the involvement of contractility in focal adhesion formation.

Differential Expression of Splicing Variants of the Human Caldesmon Gene (CALD1) in Glioma Neovascularization versus Normal Brain Microvasculature

“…10 The actin cytoskeleton in eukaryotic cells operates as a tension-sensing molecular device and has an important regulatory role on cellular contractility and adhesion-dependent signaling via caldesmon modulation. 40 The contractile functions are carried out by modulating cellular tensional integrity (tensegrity) without disrupting the cel- Pilocytic astrocytoma ϩ lular structural integrity. 41 However, alterations of CALD1 expression and the molecular mechanisms leading to such alterations in the context of neoplastic angiogenesis remain unexplored.…”

“…In non-muscle cells, simulation of CALD1 overexpression by transfection of full-length l-CaD results in the inhibition of cell contractility and interferes with Rho A-mediated formation of stress fibers and focal adhesions. 40 The co-activated caldesmon isoforms induce an overexpression of the protein and could have a synergetic effect on the cellular contractility of the vascular components, enhancing the permeability of microvessels, and consequently facilitate the extravasation and migration of cancer cells. Moreover, both an increase in cellular calcium concentration and caldesmon phosphorylation cause dissociation of caldesmon from actin and results in weakening most of caldesmon's properties.…”

“…45 Taken together, caldesmon appears to be a target in a variety of signaling pathways that modulate its function and thereby its effect on cell contractility and adhesion-dependent signaling. 40 Alternative splicing of specific pre-mRNAs is controlled by cis-acting regulatory elements (exonic splicing enhancers) and trans-acting factors (SR proteins). 3 The alternative exons are commonly weakened as compared to constitutive exons by having suboptimal splice sites and length but are strengthened by the presence of exon enhancers that bind to putative splicing regulators 46 and/or activation of cryptic splice sites by mutation.…”

Cytoskeletal organization in tropomyosin-mediated reversion of ras-transformation: Evidence for Rho kinase pathway

“…Furthermore, increased expression of caldesmon stabilizes micro®laments (Warren et al, 1995(Warren et al, , 1996, and caldesmon levels are decreased in many transformed cells, as shown in Figure 3, and by others (Button et al, 1995;Novy et al, 1991). More recent studies implicate caldesmon in the regulation of actomyosin contractility and adhesion-dependent signaling in ®broblasts (Helfman et al, 1999).…”

Enhancing trabecular outflow by disrupting the actin cytoskeleton, increasing uveoscleral outflow with prostaglandins, and understanding the pathophysiology of presbyopia

“…Conversely, inhibiting the Rho pathway and myosin light chain kinase with a variety of small molecules (H-7, ML-7, Y-27632) (Epstein et al, 1999;Rao et al, 2001;Tian et al, 1998) or with bacterial toxins such as C3 (Liu et al, 2005), will uncouple actin from myosin, resulting in relaxation of the cells and disassembly of the actin cytoskeleton. In addition to small molecules and toxins, there are other proteins, such as caldesmon, that uncouple the linkage of actin and myosin II resulting in focal adhesion disassembly and loss of actomyosin contractility (Helfman et al, 1999).…”