Phosphorylation of caldesmon during smooth muscle contraction and cell migration or proliferation

Abstract

SummaryThe actin-binding protein caldesmon (CaD) exists both in smooth muscle (the heavy isoform, h-CaD) and non-muscle cells (the light isoform, l-CaD). In smooth muscles h-CaD binds to myosin and actin simultaneously and modulates the actomyosin interaction. In non-muscle cells l-CaD binds to actin and stabilizes the actin stress fibers; it may also mediate the interaction between actin and non-muscle myosins. Both h-and l-CaD are phosphorylated in vivo upon stimulation. The major phosphorylation sites of h-CaD when activated by phorbol ester are the Erk-specific sites, modification of which is attenuated by the MEK inhibitor PD98059. The same sites in l-CaD are also phosphorylated when cells are stimulated to migrate, whereas in dividing cells l-CaD is phosphorylated more extensively, presumably by cdc2 kinase. Both Erk and cdc2 are members of the MAPK family. Thus it appears that CaD is a downstream effector of the Ras signaling pathways. Significantly, the phosphorylatable serine residues shared by both CaD isoforms are in the C-terminal region that also contains the actin-binding sites. Biochemical and structural studies indicated that phosphorylation of CaD at the Erk sites is accompanied by a conformational change that partially dissociates CaD from actin. Such a structural change in h-CaD exposes the myosin-binding sites on the actin surface and allows actomyosin interactions in smooth muscles. In the case of non-muscle cells, the change in l-CaD weakens the stability of the actin filament and facilitates its disassembly. Indeed, the level of l-CaD modification correlates very well in a reciprocal manner with the level of actin stress fibers. Since both cell migration and cell division require dynamic remodeling of actin cytoskeleton that leads to cell shape changes, phosphorylation of CaD may therefore serve as a plausible means to regulate these processes. Thus CaD not only links the smooth muscle contractility and non-muscle motility, but also provides a common mechanism for the regulation of cell migration and cell proliferation.Abbreviations: BPM -benzophenone maleimide; CaD -caldesmon; CaM -calmodulin; EM -electron microscopy; Erk -extracellular signal-regulated kinase; FRET -fluorescence resonance energy transfer; GFP -green fluorescent protein; h-CaD -smooth muscle caldesmon; IAEDANS -5-(iodoacetamidoethyl) aminonaphthalene-1-sulfonic acid; l-CaD -non-muscle caldesmon; MAPK -mitogen activated protein kinase; MLCK -myosin light chain kinase; MS -mass spectrometry; Pak -p21-activated protein kinase; PMA -phorbol 12-myristate 13-acetate; Raf -rat aorta fibroblast cells; Tm -tropomyosin Remodeling of actin cytoskeleton plays a central role in a variety of cellular processes that involve shape change and movement. Malfunction of these processes could lead to pathological consequences, but how actin-mediated motility is regulated is only beginning to be understood. With recent

The Actin-binding Protein Caldesmon Is in Spleen and Lymph Nodes Predominately Expressed by Smooth-muscle Cells, Reticular Cells, and Follicular Dendritic Cells

“…Low-molecularmass isoforms of caldesmon (l-caldesmon, 70 to 80 kDa) are thought to be widely distributed in nonmuscle tissues, but only a few studies have used immunohistochemistry to investigate the distribution of caldesmon in selected tissues Fujita et al 1984;Ishimura et al 1984). l-Caldesmon has a role in the organization and stabilization of the microfilament network, thus regulating proliferation and migration (Kordowska et al 2006;Yokouchi et al 2006;Morita et al 2007). High-molecular-mass isoforms (h-caldesmon, 120 to 150 kDa) are predominantly expressed in differentiated smooth-muscle cells (SMCs), with only a few reported exceptions; platelets, colorectal pericryptal fibroblasts, and myoepithelial cells of galactophorous sinuses of human breast tissue contain h-caldesmon as well (Kakiuchi et al 1983;Frid et al 1992;Lazard et al 1993;Nakayama et al 1999).…”

Mechanism of Flavonoids Action in Smooth Muscle Relaxation

“…[96] In blood vessels, the endothelium plays an [97] , including endothelium-derived hyperpolarizing factor (EDHF), nitric oxide (NO), prostacyclins and epoxyeicosatrienoic acids. [98] In spite of this, it is demonstrated that the vaso-relaxation induced by FGAL is independent of EDRF, since it relaxes rat aorta both in the absence and presence of endothelium in an equipotent manner.…”

“…The phosphorylation of caldesmon by MEK/ERK seems to regulate smooth muscle contraction. [96] In this process MEK/ERK is activated by PKC which in turn is stimulated by induced by fluoride causing relaxation, thereby inhibiting Rho-kinase or MEK activity. [124] www.wjpps.com contractions and PE induced contractions at similar dose ranges.…”

Role of Protein Kinase Network in Excitation-Contraction Coupling in Smooth Muscle Cell

“…In addition, it allows an interaction between the thin and thick filaments as it is able to bind to both actin and myosin and this property seems to be involved in the sustained phase of the contractile response (Marston et al, 1991). In vitro studies have shown that caldesmon can be a substrate for several kinases (Kordowska et al, 2006).…”