While Wnt and Hgf signaling pathways are known to regulate epithelial cell responses during kidney injury and repair, whether they exhibit functional cross-talk is not well defined. Canonical Wnt signaling is initiated by the phosphorylation of the Lrp5/6 co-receptors and culminates in stabilization of (β-catenin, its translocation to the nucleus and activation of gene transcription. In the current study we demonstrate that Hgf stimulates the Met-dependent and Wnt-independent phosphorylation of Lrp5/6 at 3 separate activation motifs in murine renal epithelial cells. This Hgf-induced phosphorylation of Lrp5/6 was restricted to subconfluent, de-differentiated mouse proximal tubular (MPT) cells and down-regulated as the cells become more confluent. We then pursued the mechanism of Hgf-induced Lrp5/6 phosphorylation. This phosphorylation was found to be Gsk3-dependent and Hgf treatment stimulated the selective association of `active' (tyrosine phosphorylated) Gsk3 with Lrp5/6. In contrast, Akt-phosphorylated `inactive' Gsk3 is excluded from this association. Subsequently, we conducted studies to determine the significance of our findings. After knocking down Lrp5 and 6 in MPT cells, we found that Hgf mediated Lrp5/6 phosphorylation led to (β-catenin stabilization, its nuclear accumulation and increased expression of the Wnt target gene c-myc. We also find that Hgf protects against epithelial cell apoptosis in an Lrp5/6 dependent fashion and increased Survivin gene expression. In vivo , the increase in Lrp5/6 phosphorylation and (β-catenin stabilization on the first day after renal ischemic injury was significantly reduced in mice lacking Met receptor in the renal proximal tubule. Our results thus identify Hgf as an important transactivator of canonical Wnt signaling that is mediated by Met-stimulated, Gsk3-dependent Lrp5/6 phosphorylation.
|Advisor:||Cantley, Lloyd Garnet|
|School Location:||United States -- Connecticut|
|Source:||DAI-B 76/07(E), Dissertation Abstracts International|
|Subjects:||Molecular biology, Cellular biology, Physiology|
|Keywords:||Gsk3, Hgf, Kidney, Repair, Signaling, Wnt|
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