Regulation of fibronectin splicing in sinusoidal endothelial cells from normal or injured liver

Abstract

Fn containing an extra type III domain (EIIIA in the rat, ED1 or EDA in humans) is commonly termed ''fetal'' fibronectin, but it is prominent during the injury response of adult tissues and mediates important early events in the response. This form is particularly apparent in acute liver injury, where it has been shown that sinusoidal endothelial cells produce EIIIA-fibronectin. This fibronectin isoform arises by alternative splicing of the primary transcript. In the present experiments, we have studied the regulation of fibronectin splicing in primary sinusoidal endothelial cells by transfecting a minigene containing the EIIIA exon and its flanking introns, driven by various promoters. The results indicate that fibronectin splicing in endothelial cells from normal liver is in part promoter-dependent. However, in cells from injured liver in which expression of both total and EIIIA-fibronectin is strikingly increased, promoter effects disappear. Because fibronectin splicing is known to be regulated in part by TGF␤, we also examined the effect of a soluble inhibitor of the TGF␤ type 2 receptor. This agent had no effect on splicing by normal endothelial cells. By contrast, for endothelial cells from the injured liver, the splicing pattern reverted to that of normal cells, i.e., it became promoter-dependent. We conclude that, in the setting of injury in vivo, TGF␤ overrides the promoter dependence of fibronectin splicing in normal cells. The data suggest that TGF␤ modifies the spliceosome, if not through its known signaling intermediates, then through the products of genes regulated by this cytokine. extracellular matrix ͉ fibrosis ͉ spliceosome ͉ TGF␤

Involvement of integrin-linked kinase in carbon tetrachloride–induced hepatic fibrosis in rats

“…In these animals the loss of ILK resulted in profound defects in cell spreading, adhesion, actin organization, and proliferation. 49 Therefore, on the basis of our findings as well as those of others, 36,50 we speculate that binding of HSCs to fibronectin via its integrin receptors triggers the activation of FAK, PI3K, ILK, and the AKT/PKB pathway, thus inducing activation of HSCs and enhancing their migration and proliferation. ILK also upregulates the expression of MAP and Erk 1/2 kinases, and these can further influence cell proliferation and migration.…”

Fibronectin fibrillogenesis, a cell-mediated matrix assembly process

“…However, specific functional roles for EIIIA and EIIIB have been difficult to identify. EIIIA has been implicated in cell differentiation (Chang et al, 2004) and cell adhesion (Liao et al, 2002). However, constitutive exclusion of EIIIA is not life-threatening; EIIIA À / À mice show abnormal skin wound healing (Muro et al, 2003) and smaller atherosclerotic lesions (Tan et al, 2004).…”

Fibronectin Extra Domain-A Promotes Hepatic Stellate Cell Motility but Not Differentiation Into Myofibroblasts

“…Expression of EIIIA+ cFN is minimal in the healthy liver, but TGFβ induces its upregulation within 12 hours of liver injury 12, 13 . A 1994 study showed that primary hepatic stellate cells cultured on EIIIA+ cFN express higher levels of αSMA than do those cultured on pFN 14 , suggesting that EIIIA promotes fibrosis.…”