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Background: Angiogenesis is an essential physiological process for growth and maintenance of the body. Especially its role becomes indispendable during the embryonic development stage but lacks in adults with some exceptions like while wound repair and menstrual cycle. It is a tightly regulated process and relies on the cascade of several molecular signaling pathways with the involvement of many effectors like vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), insulin-like growth factor (IGF) etc., Methods: Related literature/ information were retrieved, analyzed and compiled from the online published resources available in Medline, Pubmed, Pubmed Central, Science Direct and other scientific databases., Results: Excessive angiogenesis leads to disorders like tumor, atherosclerosis, rheumatoid arthritis, diabetic retinopathy, endometriosis, psoriasis, and adiposity. While, reduced angiogenesis also results in several ailments like cardiac ischemia, low capillary density in brain of Alzheimer's patients and delayed wound healing. Therefore, both angio-proliferative and anti-angiogenic approaches may be of use in developing novel therapeutics. Bacterial toxins are known for modulating the process of angiogenesis by mimicking pro-angiogenic factors and/ or competing with them. Furthermore, they inactivate the receptors or keep them in ON status, hence can be used to treat angiogenic disorders. The ease in handling, cultivation and manipulating the toxins structure has enabled the use of bacteria as an ideal choice for novel therapeutic developments., Conclusion: This review intends to elucidate the molecular mechanisms through which certain bacteria may alter the level of angiogenesis and consequently can work as therapeutics against angiogenic disorders., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

Actin stress fibers are fundamental components of the actin cytoskeleton that produce contractile force in non-muscle cells. The formation of stress fibers is controlled by the small GTPase RhoA and two highly related proteins, RhoB and RhoC. Together, this subgroup of actin-regulatory proteins represents the canonical pathway of stress-fiber formation. Here, we show that the Rif GTPase is an alternative trigger of stress-fiber formation in epithelial cells. Rif is distantly related to RhoA; however, we show that the two proteins share a common downstream partner in stress-fiber formation - the Diaphanous-related formin mDia1. Rif-induced stress fibers also depend on the activity of the ROCK protein kinase. Unlike RhoA, Rif does not raise ROCK activity in cells, instead Rif appears to regulate the localization of myosin light chain phosphorylation. This study establishes Rif as a general regulator of Diaphanous-related formins and shows how non-classical Rho family members can access classical Rho pathways to create new signaling interfaces in cytoskeletal regulation. [ABSTRACT FROM AUTHOR]

Cell adhesion to the extracellular matrix (ECM) is mediated by the integrin family of transmembrane receptors. Integrins link ECM ligands to the cytoskeleton, providing strong attachment to enable cell-shape change and tissue integrity. This connection is made possible by an intracellular complex of proteins, which links to actin filaments and controls signalling cascades that regulate cytoskeletal rearrangements. We have identified stress-fibre-associated focal adhesions that change their composition during tissue morphogenesis. Early expression of αPS1βPS integrin decreases the levels of the actin-nucleating factors Enabled, Diaphanous and profilin, as well as downregulating the amount of F-actin incorporated into the stress fibres. As follicle cells mature in their developmental pathway and become squamous, the integrin in the focal adhesions changes from αPS1βPS to αPS2βPS. During the switch, stress fibres increase their length and change orientation, first changing by 90° and then reorienting back. The normal rapid reorientation requires new expression of αPS2βPS, which also permits recruitment of the adaptor protein tensin. Unexpectedly, it is the extracellular portion of the αPS2 subunit that provides the specificity for intracellular recruitment of tensin. Molecular variation of the integrin complex is thus a key component of developmentally programmed morphogenesis. [ABSTRACT FROM AUTHOR]

We compared a non-metastasising sarcoma cell population with three related populations of increasing metastatic potential. The metastatic cells in vitro exhibited a significantly reduced incidence of actin stress fibres but enhanced motility and chemotaxis. We also investigated gene expression underlying progression to a metastatic phenotype by performing a microarray analysis of the four sarcoma populations. We identified a subset of genes with significantly altered expression levels between non-metastasising and metastasising cells in tissue culture and in primary tumours. One such gene, encoding protein 4.1B, is downregulated in the metastatic sarcoma populations. To investigate possible roles of 4.1B in the mechanisms of metastasis, we used RNA interference (RNAi) to reduce its expression in the non-metastatic cells. Cells with reduced 4.1B expression displayed an altered F-actin morphology, with significantly fewer stress fibres. We also found that the 4.1B RNAi cells migrated at twice the speed of the untreated cells. Metastatic cells exogenously expressing 4.1B migrated at half the speed of control metastatic cells and displayed suppressed chemotaxis. Therefore, we propose that the reduction of 4.1B in the metastatic cells promotes the metastatic phenotype as a result of inducing a loss of actin stress fibres and a concomitant increase in cell motility. [ABSTRACT FROM AUTHOR]

Syndecan-4 is a ubiquitously expressed transmembrane heparan sulphate proteoglycan acting in concert with integrins in the formation of focal adhesions and stress fibres. Signalling events studied thus far suggest the formation of a ternary complex between syndecan-4, phosphatidylinositol 4,5-bisphosphate and protein kinase C alpha; (PKCα). Syndecan-4 clustering at the cell surface has also been associated with RhoA-dependent signalling, but the relationship between PKCα and RhoA has not been resolved. Here we present evidence that syndecan-4, PKCα and RhoA are in a linear pathway necessary for the formation and maintenance of stress fibres in primary rat embryo fibroblasts. Inhibition of PKC activity through the use of specific pharmacological inhibitors, a dominant-negative construct, or siRNA downregulation of protein levels, attenuated focal adhesion formation and the maintenance of stress fibres. However, these effects could be bypassed through independent activation of RhoA with lysophosphatidic acid, but not by clustering of syndecan-4 with ligand. Furthermore, inhibition of PKCα could block the increase in the GTP levels of RhoA induced by clustering of syndecan-4 at the cell surface. All these data point to a mechanism whereby syndecan-4 signals to RhoA in a PKCα-dependent manner and PKCα directly influences RhoA activity. [ABSTRACT FROM AUTHOR]

Haemodynamic forces applied at the apical surface of vascular endothelial cells (ECs) provide the mechanical signals at intracellular organelles and through the inter-connected cellular network. The objective of this study is to quantify the intracellular and intercellular stresses in a confluent vascular EC monolayer. A novel three-dimensional, multiscale and multicomponent model of focally adhered ECs is developed to account for the role of potential mechanosensors (glycocalyx layer, actin cortical layer, nucleus, cytoskeleton, focal adhesions (FAs) and adherens junctions (ADJs)) in mechanotransmission and EC deformation. The overriding issue addressed is the stress amplification in these regions, which may play a role in subcellular localization of mechanotransmission. The model predicts that the stresses are amplified 250-600-fold over apical values at ADJs and 175-200-fold at FAs for ECs exposed to a mean shear stress of 10 dyne cm(-2). Estimates of forces per molecule in the cell attachment points to the external cellular matrix and cell-cell adhesion points are of the order of 8 pN at FAs and as high as 3 pN at ADJs, suggesting that direct force-induced mechanotransmission by single molecules is possible in both. The maximum deformation of an EC in the monolayer is calculated as 400 nm in response to a mean shear stress of 1 Pa applied over the EC surface which is in accord with measurements. The model also predicts that the magnitude of the cell-cell junction inclination angle is independent of the cytoskeleton and glycocalyx. The inclination angle of the cell-cell junction is calculated to be 6.6° in an EC monolayer, which is somewhat below the measured value (9.9°) reported previously for ECs subjected to 1.6 Pa shear stress for 30 min. The present model is able, for the first time, to cross the boundaries between different length scales in order to provide a global view of potential locations of mechanotransmission., (© 2014 The Author(s) Published by the Royal Society. All rights reserved.)

Prostaglandin E2 is a pleiotropic bioactive lipid that controls cytoskeletal alterations, although the precise G-protein coupled EP receptor signalling mechanisms remain ill defined. We adopted a phosphoproteomic approach to characterize post-receptor downstream signalling substrates using antibodies that selectively recognize and immunoprecipitate phosphorylated substrates of a number of kinases. Using human synovial fibroblasts in monolayer cell culture, PGE2 induced rapid and sustained changes in cellular morphology and reduction in cytoplasmic volume that were associated with disassembly of the phalloidin-stained stress fibres as judged by light and confocal microscopy. Furthermore, PGE2 induced a rapid dephosphorylation of myosin light chain II (MLC) at S19 under basal or cytokine-induced conditions that was linked to an activation of myosin light chain phosphatase. The use of specific synthetic EP agonists suggested that the response was mediated by EP2 receptors, as other EP agonists did not manifest the same effect on MLC phosphorylation. In addition, PGE2 induced sustained Y118 dephosphorylation of phospho-paxillin and loss of focal adhesions as observed by confocal microscopy and Western analysis. Phosphoproteomic analysis of PGE2 /GPCR/PKA phosphosubstrates identified a unique, non-redundant, phosphorylated (>30-fold) site on rho-associated coiled coil-containing kinase 2 (ROCK2) at S1379. Analysis of ROCK2 mutant behaviour (e.g. S1379A) in overexpression studies revealed that PGE2 -dependent phosphorylation of ROCK2 resulted in the inhibition of the kinase, since induced MLC phosphorylation was no longer blocked by PGE2 nor could PGE2 induce disassembly of stress fibres. Thus, PGE2 -dependent blockade of actomyosin fibre formation, characteristic of myofibroblasts, may be mediated through specific ROCK2 S1379 phosphorylation., (© 2014 Wiley Periodicals, Inc.)

Dynamic remodelling of actin stress fibres (SFs) allows non-muscle cells to adapt to applied forces such as uniaxial cell shortening. However, the mechanism underlying rapid and selective disassembly of SFs oriented in the direction of shortening remains to be elucidated. Here, we investigated how myosin crossbridge cycling induced by MgATP is associated with SF disassembly. Moderate concentrations of MgATP, or [MgATP], induced SF contraction. Meanwhile, at [MgATP] slightly higher than the physiological level, periodic actin patterns emerged along the length of SFs and dispersed within seconds. The actin fragments were diverse in length, but comparable to those in characteristic sarcomeric units of SFs. These results suggest that MgATP-bound non-muscle myosin II dissociates from the individual actin filaments that constitute the sarcomeric units, resulting in unbundling-induced disassembly rather than end-to-end actin depolymerization. This rapid SF disassembly occurred independent of dephosphorylation of myosin light chain. In terms of effects on actin-myosin interactions, a rise in [MgATP] is functionally equivalent to a temporal decrease in the total number of actin-myosin crossbridges. Actin-myosin crossbridges are known to be reduced by an assisting load on myosin. Thus, the present study suggests that reducing the number of actin-myosin crossbridges promotes rapid and orientation-dependent disassembly of SFs after cell shortening.