Integrin-Linked Kinase Mediates Bone Morphogenetic Protein 7-Dependent Renal Epithelial Cell Morphogenesis

Abstract

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.

ACKNOWLEDGMENTS

We acknowledge the expert technical assistance of Yunkai Yu, Perry Mongroo for quantifying protein expression data, and S. Dedhar (University of British Columbia) for the gift of KP-392.

S.H. is the recipient of a studentship from the Research Training Committee of the Hospital for Sick Children. This work was supported by grants from the Canadian Institutes of Health Research (CIHR) (to N.D.R. and G.E.H.), and the National Cancer Institute of Canada (to G.E.H., with funds from the Terry Fox Run). G.E.H. was a Scholar of the CIHR.