The Homeodomain Protein Cux1 Is Regulated By The Notch Signaling Pathway In The Developing Kidney
Notch signaling is a highly conserved cell-cell communication pathway that is important for the development of most organisms. Cux1 is the murine homologue of the Drosophila gene Cut. In Drosophila, multiple genetic interactions between Cut and the Notch and Wingless signaling pathways occur during development. Cux1 is upregulated in rat kidney epithelial cells expressing a constitutively active Notch1 (Notch1ic), and interacts with the groucho homologue Grg4 to regulate p27 expression in the developing kidney. Moreover, Cux1 co-localizes with several components of the Notch signaling pathway during kidney development. To further evaluate whether Cux1 is an effector of the Notch signaling pathway we used the gamma-secretase inhibitor DAPT to block all Notch signaling in kidney organ cultures. DAPT treatment significantly inhibited growth of wild-type metanephroi. In contrast, Cux1 transgenic kidney cultures treated with DAPT were not growth inhibited, but showed high levels of cell proliferation in the nephrogenic zone, and ureteric bud branching was similar to vehicle treated kidney cultures. Notch1ic cells showed an increase in cell proliferation compared to wild type RKE cells, however, antisense knockdown of Cux1 in the Notch1ic cells reduced cell proliferation to the same level as wild type cells. Finally, the targeted deletion of RBPJ/k, a transcription factor required for canonical Notch signaling, in the developing ureteric bud and collecting duct, resulted in the complete absence of Cux1 protein specifically in the ureteric bud and collecting duct cells. Taken together, these results suggest that Notch signaling regulates the expression of Cux1 in the developing kidney.