Role of α₃β₁ integrin in tubulogenesis of Madin-Darby canine kidney cells

Background. We isolated several Madin-Darby canine kidney (MDCK) subclones that exhibit different degrees of branching tubulogenesis in lower concentrations of collagen gel. The M634 clone formed cell aggregates in 0.3% collagen gel, but developed branching tubules vigorously in 0.1% collagen gel. In contrast, the Y224 clone formed cysts in 0.3% collagen gel and displayed fewer branching structures in 0.1% collagen gel. Morphologically, M634 cells exhibited higher levels of cell scattering as well as collagen-induced cell migration than Y224. We conducted this study to delineate the underlying mechanism of branching tubulogenesis in M634 cells. Methods. Components of the focal contact machinery were analyzed in both cell lines, including the extracellular matrix glycoproteins fibronectin, laminin, and vitronectin; cytoskeleton-associated elements α-actinin, talin, and vinculin; and receptors for extracellular matrix and α₂, α₃, α₅, α_v, β₁, and β₃ integrins. Furthermore, we established several stable transfectants of α₃ integrin antisense RNA in M634 cells to examine the role of α₃β₁ integrin in branching morphogenesis directly. Results. There were no obvious differences in levels of the focal adhesion complex proteins between M634 and Y224 cells, except that the content of the α₃ and β₁ integrins were 1.2- and 0.6-fold higher in M634 cells, respectively. The expression of α₃ integrin antisense RNA significantly lowered the levels of α₃ integrin mRNA and protein. The potential of cell scattering, migration, and branching tubulogenesis in M634 cells was inhibited according to the decrease in α₃ integrin expression. Conclusion. Our data indicate that expression of α₃β₁ integrin regulates cell scattering, migration, and branching tubulogenesis of MDCK cells, possibly via adhesion to or serving as a signaling molecule for type I collagen.