Integrin β4 Attenuates SHP-2 and MAPK Signaling and Reduces Human Lung Endothelial Inflammatory Responses

We previously identified the marked upregulation of integrin beta 4 in human lung endothelial cells (EC) treated with simvastatin, an HMG coA-reductase inhibitor with vascular-protective and anti-inflammatory properties in murine models of acute lung injury (ALI). We now investigate the role of integrin beta 4 as a novel mediator of vascular inflammatory responses with a focus on mitogen-activated protein kinases (MAPK) signaling and the downstream expression of the inflammatory cytokines (IL-6 and IL-8) essential for the full elaboration of inflammatory lung injury. Silencing of integrin beta 4 (silTGB4) in human lung EC resulted in significant increases in both basal and LPS-induced phosphorylation of ERK 1/2, JNK, and p38 MAPK, consistent with robust integrin beta 4 regulation of MAPK activation. In addition, silTB4 increased both basal and LPS-induced expression of IL-6 and IL-8 mRNA and protein secretion into the media. We next observed that integrin beta 4 silencing increased basal and LPS-induced phosphorylation of SHP-2, a protein tyrosine phosphatase known to modulate MAPK signaling. In contrast, inhibition of SHP-2 enzymatic activity (sodium stibogluconate) abrogated the increased ERK phosphorylation associated with integrin beta 4 silencing in LPS-treated EC and attenuated the increases in levels of IL-6 and IL-8 in integrin-beta 4-silenced EC. These findings highlight a novel negative regulatory role for integrin beta 4 in EC inflammatory responses involving SHP-2-mediated MAPK signaling. Upregulation of integrin beta 4 may represent an important element of the anti-inflammatory and vascular-protective properties of statins and provides a novel strategy to limit inflammatory vascular syndromes. J. Cell. Biochem. 110: 718-724, 2010. (C) 2010 Wiley-Liss, Inc.