Rho and basic fibroblast growth factor involvement in centrosome redistribution and actin microfilament remodeling during early endothelial wound repair

Surfing the big WAVE: Insights into the role of WAVE3 as a driving force in cancer progression and metastasis

WAVE3 belongs to the WASP/WAVE family of actin cytoskeleton remodeling proteins. These proteins are known to be involved in several biological functions ranging from controlling cell shape and movement, to being closely associated with pathological conditions such as cancer progression and metastasis. Last decade has seen an explosion in the literature reporting significant scientific advances on the molecular mechanisms whereby the WASP/WAVE proteins are regulated both in normal physiological as well as pathological conditions. The purpose of this review is to present the major findings pertaining to how WAVE3 has become a critical player in the regulation of signaling pathways involved in cancer progression and metastasis. The review will conclude with suggesting options for the potential use of WAVE3 as a therapeutic target to prevent the progression of cancer to the lethal stage that is the metastatic disease.

Down-regulation of WAVE3, a metastasis promoter gene, inhibits invasion and metastasis of breast cancer cells

The expression of WAVE3, an actin-cytoskeleton and reorganization protein, is elevated in malignant human breast cancer, yet the role of WAVE3 in promoting tumor progression remains undefined. We have recently shown that knockdown of WAVE3 expression in human breast adenocarcinoma MDA-MB-231 cells using small interfering RNA resulted in a significant reduction of cell motility, migration, and invasion, which correlated with a reduction in the levels of active p38 mitogen-activated protein kinase. Here, we investigated the effect of stable suppression of WAVE3 by short hairpin RNA on tumor growth and metastasis in xenograft models. Breast cancer MDA-MB-231 cells expressing short hairpin RNA to WAVE3 (shWAVE3) showed a significant reduction in Matrigel invasion and formation of lung colonies after tail-vein injection in SCID mice. In the orthotopic model, we observed a reduction in growth rate of the primary tumors, as well as in the metastases to the lungs. We also show that suppression of p38 mitogen-activated protein kinase activity by dominant-negative p38 results in comparable phenotypes to the knockdown of WAVE3. These studies provide direct evidence that the WAVE3-p38 pathway contributes to breast cancer progression and metastasis.

Actin filament organization regulates the induction of lens cell differentiation and survival

The actin cytoskeleton has the unique capability of integrating signaling and structural elements to regulate cell function. We have examined the ability of actin stress fiber disassembly to induce lens cell differentiation and the role of actin filaments in promoting lens cell survival. Three-dimensional mapping of basal actin filaments in the intact lens revealed that stress fibers were disassembled just as lens epithelial cells initiated their differentiation in vivo. Experimental disassembly of actin stress fibers in cultured lens epithelial cells with either the ROCK inhibitor Y-27632, which destabilizes stress fibers, or the actin depolymerizing drug cytochalasin D induced expression of lens cell differentiation markers. Significantly, short-term disassembly of actin stress fibers in lens epithelial cells by cytochalasin D was sufficient to signal lens cell differentiation. As differentiation proceeds, lens fiber cells assemble actin into cortical filaments. Both the actin stress fibers in lens epithelial cells and the cortical actin filaments in lens fiber cells were found to be necessary for cell survival. Sustained cytochalasin D treatment of undifferentiated lens epithelial cells suppressed Bcl-2 expression and the cells ultimately succumbed to apoptotic cell death. Inhibition of Rac-dependent cortical actin organization induced apoptosis of differentiating lens fiber cells. Our results demonstrate that disassembly of actin stress fibers induced lens cell differentiation, and that actin filaments provide an essential survival signal to both lens epithelial cells and differentiating lens fiber cells.

Atherosclerosis and acute coronary syndromes

In the past 20 years, there has been much new knowledge discovered on the pathogenesis of atherosclerosis and complicated and vulnerable plaques leading to a better understanding of acute coronary syndromes (ACS). The role of thrombosis, lipid metabolism, and inflammation has been investigated at the cellular and molecular levels, resulting in important new diagnostic and therapeutic strategies. The characterization of the role of hemodynamic shear stress and its regulation of cytoskeletal function in endothelial repair and the discovery of endothelial precursor cells (EPCs) derived from the bone marrow have provided new insight into vascular repair. Thus, our knowledge continues to increase, leading to improved prevention, diagnosis, and treatment of ACS.

A possible role for membrane depolarization in epithelial wound healing

Linear narrow wounds produced on cultured bovine corneal endothelial monolayers heal by actin cable formation at the wound border and lamellar crawling of cells into the injured area. We report the novel finding that membrane potential depolarization occurs at the leading edge of wounds and gradually extends inward toward the neighboring cells. We have determined that the replacement of extracellular Na+by choline and the incorporation of phenamil, an inhibitor of the epithelial Na+channel (ENaC), provoke a decrease in the actin cable and depolarization areas and in the lamellar activity of the wound edges. To the contrary, extracellular Li+can successfully replace Na+in the determination of the depolarization and cytoskeletal responses. This finding supports the idea that membrane depolarization, not the increase in intracellular Na+concentration, is responsible for the formation of the actin cable, a result that is in agreement with previous evidence showing that nonspecific depolarization of the plasma membrane potential (PMP) of epithelial cells may promote characteristic cytoskeletal rearrangements per se (Chifflet S, Hernández JA, Grasso S, and Cirillo A. Exp Cell Res 282: 1–13, 2003). We suggest that spontaneous depolarization of the PMP of the cells at the wound borders determined by a rise in the ENaC activity of these cells constitutes an additional factor in the intermediate cellular processes leading to wound healing in some epithelia.

Towards understanding acute destabilization of vulnerable atherosclerotic plaques

BACKGROUND

The current wisdom is that destabilization of human atheromatous fibroinflammatory plaques may result in thrombosis and is responsible for most acute ischemic syndromes. This paradigm has led to vigorous research to understand the pathogenesis of plaque vulnerability and subsequent rupture, to find reliable systemic serological markers and to identify imaging techniques in order to determine vulnerability of individual plaques.

METHODS

Research examining the pathobiology of the vulnerable plaque and its subsequent destabilization is described. Investigations are based on the current understanding of vascular cell and molecular biology and clinical paradigms of acute coronary syndromes.

RESULTS

It is apparent that there are three steps that need to be considered. These are transformation of a stable plaque into a vulnerable plaque, destabilization of a vulnerable plaque and regulation of the complications following destabilization, the most serious being acute occlusive thrombosis. In vitro cell and molecular vascular biology studies, and animal model studies that alter specific gene(s) expression, have provided new knowledge on putative mechanisms leading to plaque vulnerability and on subsequent destabilization of the plaque. These studies show that several local and systemic factors, including inflammation, matrix disruption, lipid deposition, cell necrosis and apoptosis are likely to play a role in vulnerability, destabilization and clinical syndromes.

CONCLUSION

Plaque vulnerability and destabilization is of multifactoral etiology with inflammation, cap matrix and necrotic lipid core remodeling being important pathobiological processes associated with vulnerability and destabilization. Identifying gene-environment interactions, improving imaging techniques and improving our understanding of the mechanisms underlining plaque pathogenesis via animal models are essential elements for understanding human plaque vulnerability and destabilization.

Thrombospondin signaling through the calreticulin/LDL receptor-related protein co-complex stimulates random and directed cell migration

The matricellular extracellular matrix protein thrombospondin-1 (TSP1) stimulates focal adhesion disassembly through a sequence (known as the hep I peptide) in its heparin-binding domain. This mediates signaling through a receptor co-complex involving calreticulin and low-density lipoprotein (LDL) receptor-related protein (LRP). We postulate that this transition to an intermediate adhesive state enhances cellular responses to dynamic environmental conditions. Since cell adhesion dynamics affect cell motility, we asked whether TSP1/hep I-induced intermediate adhesion alters cell migration. Using both transwell and Dunn chamber assays, we demonstrate that TSP1 and hep I gradients stimulate endothelial cell chemotaxis. Treatment with focal adhesion-labilizing concentrations of TSP1/hep I in the absence of a gradient enhances endothelial cell random migration, or chemokinesis, associated with an increase in cells migrating, migration speed, and total cellular displacement. Calreticulin-null and LRP-null fibroblasts do not migrate in response to TSP1/hep I, nor do endothelial cells treated with the LRP inhibitor receptor-associated protein (RAP). Furthermore, TSP1/hep I-induced focal adhesion disassembly is associated with reduced chemotaxis to basic fibroblast growth factor (bFGF) but enhanced chemotaxis to acidic (a)FGF, suggesting differential modulation of growth factor-induced migration. Thus, TSP1/hep I stimulation of intermediate adhesion regulates the migratory phenotype of endothelial cells and fibroblasts, suggesting a role for TSP1 in remodeling responses.