Role of fibronectin deposition in branching morphogenesis of Madin-Darby canine kidney cells

Background. Madin-Darby canine kidney (MDCK) epithelial cells grown in coll agen gels in the presence of hepatocyte growth factor (HGF) form branching tubules. The tubule-lining epithelial cells are polarized with the basolate ral surface in contact with the collagen gel and the apical surface facing the lumen. To delineate whether MDCK branching tubules construct the basal lamina, we characterized the composition of the extracellular matrix deposi ted by MDCK tubules. The tubule-lining cells produced an apparently incompl ete basal lamina containing a discontinuous laminin substratum. In addition , a thick layer of fibronectin surrounded the basal cell surface of the bra nching tubule. In an attempt to delineate the role of fibronectin depositio n in branching morphogenesis, we conducted this study. Methods. MDCK cells cultured in collagen gel were employed. We first used a rginine-glycine-aspartate peptides containing disintegrin rhodostomin to di sturb the interactions between fibronectin and cell surface integrins. Furt hermore, we established several stable transfectants expressing fibronectin antisense RNA to examine the role of fibronectin in branching morphogenesi s directly. Results. Rhodostomin inhibited the formation of branching tubules. The tran sfectants expressing fibronectin antisense RNA exhibited relatively lower l evels of synthesized fibronectin and markedly diminished growth rates of br anching tubules than the control clone. An inhibition of branching morphoge nesis induced by the overexpression of fibronectin antisense RNA was manife sted by the decrease in cell growth rates and cell migration. Conclusion. These results indicate that the deposition of fibronectin under lying the tubule-lining epithelium serves to enhance cell proliferation and migration, and hence facilitates the branching tubulogenesis of MDCK cells .