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

Institute of Signaling, Developmental Biology and Cancer Research, CNRS-UMR6543, Centre Antoine Lacassagne, Nice, France

¹Correspondence: Institute of Signaling, Developmental Biology and Cancer Research, CNRS-UMR6543, Centre Antoine Lacassagne, 33 Ave. de Valombrose, Nice 06189, France. E-mail: vanobber{at}unice.fr

ABSTRACT

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 ß1 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 µm) and elongated adhesions (>5 µm). 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 ßPIX. Further, expression of a dominant negative ßPIX mutant reversed the increase in active Rac-1 levels of ILK-GFP-F-expressing cells, thus placing ßPIX 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.—Boulter, E., Grall, D., Cagnol, S., and Van Obberghen-Schilling, E. Regulation of cell-matrix adhesion dynamics and Rac-1 by integrin linked kinase.

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