Heparin II domain of fibronectin mediates contractility through an alpha4beta1 co-signaling pathway.

PubMed ID: 20302860

Author(s): Schwinn MK, Gonzalez JM Jr, Gabelt BT, Sheibani N, Kaufman PL, Peters DM. Heparin II domain of fibronectin mediates contractility through an alpha4beta1 co-signaling pathway. Exp Cell Res. 2010 May 15;316(9):1500-12. doi: 10.1016/j.yexcr.2010.03.010. Epub 2010 Mar 17. PMID 20302860

Journal: Experimental Cell Research, Volume 316, Issue 9, May 2010

In the trabecular meshwork (TM) of the eye, regulation of tissue contractility by the PPRARI sequence within the Heparin II (HepII) domain of fibronectin is believed to control the movement of aqueous humor and dictate the level of intraocular pressure. This study shows that the HepII domain utilizes activated alpha4beta1 integrin and collagen to mediate a co-signaling pathway that down-regulates contractility in TM cells. siRNA silencing of alpha4beta1 integrin blocked the actin disrupting effects of both PPRARI and the HepII domain. The down-regulation of the actin cytoskeleton and contractility did not involve syndecan-4 or other heparan sulfate proteoglycans (HSPGs) since siRNA silencing of syndecan-4 expression or heparitinase removal of cell surface HSPGs did not prevent the HepII-mediated disruption of the actin cytoskeleton. HepII-mediated disruption of the cytoskeleton depended upon the presence of collagen in the extracellular matrix, and cell binding studies indicated that HepII signaling involved cross-talk between alpha4beta1 and alpha1/alpha2beta1 integrins. This is the first time that the PPRARI sequence in the HepII domain has been shown to serve as a physiological alpha4beta1 ligand, suggesting that alpha4beta1 integrin may be a key regulator of tissue contractility.