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Bradykinin B₂ receptor null mice harboring a Ser²³-to-Ala substitution in the p53 gene are protected from renal dysgenesis

Department of Pediatrics, Tulane University School of Medicine, New Orleans, Louisiana

Submitted 20 June 2008 ; accepted in final form 23 August 2008

A physiological cross talk operates between the tumor suppressor protein p53 and the bradykinin B₂ receptor (BdkrB2) during renal organogenesis. Thus, although BdkrB2 is a target for p53-mediated transcriptional activation, BdkrB2 is required to restrict p53 proapoptotic activity. We previously demonstrated that BdkrB2^–/– embryos exposed to gestational salt stress develop renal dysgenesis as a result of p53-mediated apoptosis of nephron progenitors and repression of the terminal differentiation program. Compared with wild-type kidneys, BdkrB2^–/– express abnormally high levels of the Checkpoint kinase (Chk1), which activates p53 via Ser²³ phosphorylation. To define the functional relevance of p53^S23 phosphorylation, we generated a compound strain of BdkrB2^–/– mice harboring a homozygous Ser²³-to-Ala (S23A) mutation in the p53 gene by crossing BdkrB2^–/– with p53^S23A knockin mice. Unlike salt-stressed BdkrB2^–/– pups, which exhibit renal dysgenesis, homozygous S23A;BdkrB2^–/– littermates are protected and have normal renal development. Heterozygous S23A;BdkrB2^–/– mice have an intermediate phenotype. The p53-S23A substitution was associated with amelioration of apoptosis and restored markers of nephrogenesis and tubulogenesis. Real-time quantitative RT-PCR of terminal differentiation genes demonstrated that the S23A substitution restored normal expression patterns of aquaporin-2, Na-Cl cotransporter, Na-K-2Cl cotransporter, Na-bicarbonate cotransporter, and Sglt1. We conclude that p53 phosphorylation on Ser²³ is an essential step in the signaling pathway mediating the susceptibility of BdkrB2^–/– mutants to renal dysgenesis.

gene knockin; gene knockout; kidney development; nephrogenesis