Question: 

The Wilms' tumor gene product (Wt1) functions as a transcription factor and tumor suppressor in the kidneys. In the absence of Wt1 outgrowth of the uretic bud is impaired and the metanephric mesenchyme becomes apoptotic at an early developmental stage. Here we investigated the role of Wt1 in regulating the expression of the diamine oxidase amiloride-binding protein 1 (Abp1) during kidney development. Abp1 catalyzes the breakdown of the polyamine putrescine, which is important for normal cell growth and proliferation.

Methods and results: 

Silencing of Wt1 by RNA interference reduced Abp1 mRNA levels by approximately 60% in embryonic kidney-derived M15 cells. Binding of Wt1 protein to the Abp1 promoter in M15 cells in vivo was demonstrated by chromatin immunoprecipitation (ChIP) analysis. Luciferase reporter constructs carrying different Abp1 promoter sequences were significantly stimulated by co-transfection of a Wt1 expression construct. Incubation of embryonic (E13.5) murine kidney explants with the Abp1 inhibitor aminoguanidine (AG, 1mM) reduced ureteric bud branching by approximately 12%, and increased branching morphogenesis by 25% in E11.5 embryonic kidneys. Consistently, the number of ureteric bud branching points was reduced by approximately 9% in organ cultures of embryonic kidneys incubated in the presence of 1mg/ml diamine oxidase Abp1.

Conclusions: 

These findings identify the Abp1 gene as a novel transcriptional target of the Wilms' tumor protein, Wt1. Furthermore, through regulating the expression of Abp1, Wt1 bears on putrescine metabolism. It is suggested that Wt1-dependent control of putrescine breakdown contributes to normal kidney development.