Integrin-linked kinase mediates bone morphogenetic protein 7-dependent renal epithelial cell morphogenesis

Bone morphogenetic protein 7 (BMP7) stimulates renal branching morphogenesis via p38 mitogen-activated protein kinase (p38^MAPK) and activating transcription factor 2 (ATF-2) (M. C. Hu, D. Wasserman, S. Hartwig, and N. D. Rosenblum, J. Biol. Chem. 279:12051-12059, 2004). Here, we demonstrate a novel role for integrin-linked kinase (ILK) in mediating renal epithelial cell morphogenesis in embryonic kidney explants and identify p38^MAPK as a target of ILK signaling in a cell culture model of renal epithelial morphogenesis. The spatial and temporal expression of ILK in embryonic mouse kidney cells suggested a role in branching morphogenesis. Adenovirus-mediated expression of ILK stimulated and expression of a dominant negative ILK mutant inhibited ureteric bud branching in embryonic mouse kidney explants. BMP7 increased ILK kinase activity in inner medullary collecting duct 3 (IMCD-3) cells, and adenovirus-mediated expression of ILK increased IMCD-3 cell morphogenesis in a three-dimensional culture model. In contrast, treatment with a small molecule ILK inhibitor or expression of a dominant negative-acting ILK (ILK^E359K) inhibited epithelial cell morphogenesis. Further, expression of ILK^E359K abrogated BMP7-dependent stimulation. To investigate the role of ILK in BMP7 signaling, we showed that ILK overexpression increased basal and BMP7-induced levels of phospho-p38^MAPK and phospho-ATF-2. Consistent with its inhibitory effects on IMCD-3 cell morphogenesis, expression of ILK^E359K blocked BMP7-dependent increases in phospho-p38^MAPK and phospho-ATF-2. Inhibition of p38^MAPK activity with the specific inhibitor, SB203580, failed to inhibit BMP7-dependent stimulation of ILK activity, suggesting that ILK functions upstream of p38^MAPK during BMP7 signaling. We conclude that ILK functions in a BMP7/p38^MAPK/ATF-2 signaling pathway and stimulates epithelial cell morphogenesis.