Expression of β1 integrins changes during transformation of avian lens epithelium to mesenchyme in collagen gels

Abstract

Remarkably, a number of definitive epithelia, such as that of the anterior lens, give rise when suspended within 3D gels of type I collagen, to elongate, bipolar shaped cells that exhibit the ultrastructure, polarity, and migratory ability of mesenchymal cells. They begin producing type I collagen and stop producing crystallins, type IV collagen, and laminin. Here, we investigated changes in p l integrins and their extracellular matrix (ECM) ligands during this transdifferentiation. The former free surface of the lens epithelium that is now in contact with collagen begins within a day to stain intensely for p l and it is this surface rather than the surface facing the basement membranc that gives rise to mesenchyma1 cells. Immunoprecipitation experiments reveal a large increase in the pl integrin subunit on mesenchymal cells as compared to the epithelium of origin. The a 5 integrin subunit, which is barely detectable in the lens, increases in the mesenchyma1 cells and a3 continues to be expressed at about the same level as in the epithelium. 016, the epithelial integrin subunit, and laminin, its ECM ligand, are not detected immunohistochemically or biochemically in the mesenchyme. Rather, the mesenchymal cells secrete abundant fibronectin, the major ECM ligand for a5pl. RGD peptides do not inhibit the transformation but antibodies to p l do perturb the emigration of mesenchymal cells from the lens apical surface. We conclude that the p l integrins newly expressed on the apical epithelial surface interact with the surrounding 3D collagen gel to help bring about this unusual epithelial-mesenchymal transition. o

Tumor cell invasiveness correlates with changes in integrin expression and localization

“…Our finding that a functional a5b1 integrin is indeed required for TGFb-induced EMT provides strong support for this notion, in line with findings by others (Putz et al, 1999;Reeves et al, 2001). Interestingly, fibronectin receptors like a5b1 were also (Zuk and Hay, 1994). A further important finding of this paper is that the a6 integrin subunit is subject to regulation during Ras transformation and EMT, both by upregulation in response to Ras and by delocalization to the entire plasma membrane during TGFb-induced EMT.…”

Proteomics Profiling of Madin-Darby Canine Kidney Plasma Membranes Reveals Wnt-5a Involvement during Oncogenic H-Ras/TGF-β-mediated Epithelial-Mesenchymal Transition

“…This result is in agreement with oncogenic Ras/TGF-␤ EMT studies in EpH4 cells (60) where integrins ␣5␤1 and ␣V␤3 were found to be involved in cell migration and cell signaling (65). In addition, the well known EMT marker fibronectin (49, 66) was found to be up-regulated (Rsc, 13.48) in 21D1 cells (67). The contribution of the integrin ␣5␤1 and fibronectin interaction during cell migration is exemplified in a study by White et al (68) where tubular epithelial cells undergoing EMT demonstrate enhanced motility when cultured on fibronectin; when the ␣5 subunit was knocked down using siRNA, cell movement was attenuated.…”

TGF-β-induced EMT: mechanisms and implications for fibrotic lung disease

“…Injury to lens epithelial cells and retinal pigment epithelial cells leads to EMT with resultant fibrosis (25,86,122). EMT has been observed in animal models of renal fibrosis as well as in biopsies of diseased human kidneys (29,81,95,118).…”