Biomedical subjects

Etienne Boulter

Publications and source records attributed to Etienne Boulter.

4 recordsLinked to original sources

PubMed2006

Regulation of cell-matrix adhesion dynamics and Rac-1 by integrin linked kinase.

Extracellular matrix (ECM) receptors of the integrin family initiate changes in cell shape and motility by recruiting signaling components that coordinate these events. Integrin-linked kinase (ILK) is one such partner of beta1 integrins that participates in dynamic rearrangement of cell-matrix adhesions and cell spreading by mechanisms that are not well understood. To further elucidate the role of ILK in these events, we engineered a chimeric molecule comprising ILK fused to a membrane-targeted green fluorescent protein (ILK-GFP-F). ILK-GFP-F is highly enriched in cell-matrix adhesions, and its expression in fibroblasts leads to an accumulation of focal adhesions (2-5 microm) and elongated adhesions (>5 microm). ILK-GFP-F enhances cell spreading on fibronectin and induces a constitutive increase in the levels of GTP-bound Rac-1. Conversely, ILK knock-down by siRNA transfection decreases active Rac-1. Endogenous ILK was found to associate with PKL (paxillin kinase linker) and the Rac/Cdc42 guanine nucleotide exchange factor betaPIX. Further, expression of a dominant negative betaPIX mutant reversed the increase in active Rac-1 levels of ILK-GFP-F-expressing cells, thus placing betaPIX in the pathway leading from ILK to Rac-1 activation. However, expression of constitutively active Rac only partially restores the spreading defects of ILK-depleted cells, suggesting that an additional ILK-dependent signal is required for cell spreading.

Animals↗

PubMed2005

Integrin-linked kinase and its partners: a modular platform regulating cell-matrix adhesion dynamics and cytoskeletal organization.

Integrin-linked kinase (ILK) represents a key component of integrin signaling complexes that functions in concert with multiple binding partners to transmit cues from the extracellular matrix environment to the actin cytoskeleton. Both gain- and loss-of-function approaches to study ILK have confirmed the essential role of this protein in regulating cell-matrix adhesion dynamics and cytoskeletal organization.

Actin Cytoskeleton↗

PubMed2004

ILK is required for the assembly of matrix-forming adhesions and capillary morphogenesis in endothelial cells.

Integrins play a key role in regulating endothelial cell survival, migration and differentiated function during angiogenic blood-vessel remodeling. Integrin-linked kinase (ILK) is a multidomain protein that interacts with the cytoplasmic tail of integrin beta subunits and is thought to participate in integrin-mediated signal transduction. We report here that attenuation of ILK expression in cultured bovine aortic endothelial cells by RNA interference had marked effects on surface distribution of alpha5beta1 integrin and the organization of cell-matrix adhesions characterized by the disappearance of fibrillar (3D-like) adhesions that are rich in alpha5beta1 and paxillin, and associated fibrillar fibronectin matrix. This defect was not caused by a decrease in fibronectin mRNA levels or by intracellular retention of the protein. Adhesion to surface-adsorbed matrix proteins based on beta1 and beta3 integrin was enhanced following ILK depletion, whereas cell spreading, migration and multilayer alignment into capillary-like structures on Matrigel were impaired. We conclude that ILK is an important regulator of the endothelial phenotype and vascular network formation by directing the assembly and/or maturation of alpha5beta1-competent matrix-forming adhesions.

Actins↗

PubMed2002

Distinct signals via Rho GTPases and Src drive shape changes by thrombin and sphingosine-1-phosphate in endothelial cells.

Soluble mediators such as thrombin and sphingosine-1-phosphate regulate morphological changes in endothelial cells that affect vascular permeability and new blood vessel formation. Although these ligands activate a similar set of heterotrimeric G proteins, thrombin causes cell contraction and rounding whereas sphingosine-1-phosphate induces cell spreading and migration. A functional requirement for Rho family GTPases in the cytoskeletal responses to both ligands has been established, yet the dynamics of their regulation and additional signaling mechanisms that lead to such opposite effects remain poorly understood. Using a pull-down assay to monitor the activity of Rho GTPases in human umbilical vein endothelial cells, we find significant temporal and quantitative differences in RhoA and Rac1 activation. High levels of active RhoA rapidly accumulate in cells in response to thrombin whereas Rac1 is inhibited. In contrast, sphingosine-1-phosphate addition leads to comparatively weak and delayed activation of RhoA and it activates Rac1. In addition, we show here that sphingosine-1-phosphate treatment activates a Src family kinase and triggers recruitment of the F-actin-binding protein cortactin to sites of actin polymerization at the rim of membrane ruffles. Both Src and Rac pathways are essential for lamellipodia targeting of cortactin. Further, Src plays a determinant role in sphingosine-1-phosphate-induced cell spreading and migration. Taken together these data demonstrate that the thrombin-induced contractile and immobile phenotype in endothelial cells reflects both robust RhoA activation and Rac inhibition, whereas Src- and Rac-dependent events couple sphingosine-1-phosphate receptors to the actin polymerizing machinery that drives the extension of lamellipodia and cell migration.

Actins↗