Hepatocyte growth factor upregulates α2β1 integrin in Madin-Darby canine kidney cells: Implications in tubulogenesis

It has been well established that hepatocyte growth factor (HGF) induces branching tubule formation of Madin-Darby canine kidney (MDCK) cells cultured in collagen gel. Tubulogenesis per se requires the involvement of cell proliferation, migration, focalization proteolysis, cell-cell interaction and differentiation. However, signaling pathways and proteins involved in HGF-induced tubulogenesis by MDCK cells have not been thoroughly studied. Because cell-matrix interactions play important roles in tubulogenesis, we analyzed whether HGF altered the expression of extracellular matrix receptor (α2, α3, β1 and αvβ3 integrin). We found that among those proteins examined, α2β1 integrin levels were enhanced by HGF. HGF-induced upregulation of α2β1 integrin was mediated via upregulation of α2 integrin mRNA abundance. Cycloheximide blocked the HGF-induced increase in α2 integrin mRNA expression. To understand the signaling pathways leading to an HGF-induced increase in α2β1 integrin levels, PD98059 (MEK1 inhibitor), LY294002 (PI3-kinase inhibitor), and GF109203X (PKC inhibitor) were used. We found that PD98059 blocked the HGF-induced increase in α2β1 integrin expression. Furthermore, 5E8 (specific anti-α2β1 integrin antibody) was employed to elucidate the potential role of HGF-induced upregulation of α2β1 integrin in branching morphogenesis. 5E8 did not alter HGF-induced scattering effects but disrupted HGF-induced branching tubulogenesis in collagen gel via inhibition of cell-cell interactions and growth. Taken together, HGF upregulates α2β1 integrin expression via an indirect pathway, the results of which contribute to the regulation of cell-cell interactions and cell growth during branching morphogenesis in collagen gel.