Rho/Rho Kinase Pathway Regulates Maintenance of the Differentiated Tubular Epithelial Cell Phenotype on Laminin-1

Abstract

Background: Maintenance of a polarized tubular epithelium by appropriate intracellular signaling and extracellular matrix is critical both in normal renal function as well as in acute and chronic tubular injury. We examined the hypothesis that maintenance of a differentiated epithelial phenotype on the basement membrane glycoprotein laminin-1 is controlled by the Rho/Rho kinase pathway. Methods: Using the tubular epithelial cell lines LLC-PK1 and MDCK which were cultured on laminin-1 vs. collagen IV, we analyzed cell morphology and motility (cohort migration assay) as well as expression of differentiation and dedifferentiation markers (immunofluorescence microscopy). Results: Cohort migration of LLC-PK1 cells was significantly slowed down on laminin-1 (10.7 ± 2.2 m.u. (migratory units)) compared with collagen IV (16.6 ± 2.3 m.u.; BSA control: 2.8 ± 2.5 m.u.). Inhibition of the Rho/Rho kinase pathway by C3 exotoxin (1 µg/ml) or the Rho kinase inhibitor Y27632 (10 µ M) significantly augmented cohort migration on laminin-1 (14.5 ± 1.4 and 16.0 ± 1.8 m.u. vs. 10.7 ± 2.2 m.u.). In parallel to the increased migratory activity, inhibition of the Rho/Rho kinase pathway resulted in a more mesenchymal phenotype of LLC-PK1 cells on laminin-1 with increased formation of lamellopodia and filopodia, distinct loss of focal contacts and stress fibers, upregulation of the dedifferentiation marker vimentin, and loss of cell-cell contacts with translocation of β-catenin from the adherens junctions to the cytosol and nucleus. Similarly, cohort migration of MDCK cells was retarded on laminin-1 when compared with collagen IV, and addition of the Rho kinase inhibitor Y27632 resulted in enhanced motility and a change in cell morphology. Conclusion: The study demonstrates that the Rho/Rho kinase pathway is required to maintain a non-migratory epithelial phenotype of cultured renal tubular LLC-PK1 and MDCK cells on the basement membrane glycoprotein laminin-1.