Submitted on June 20, 2008
Revised on July 27, 2008
Accepted on August 23, 2008
Bradykinin B2 receptor null mice harboring a Ser23-to-Ala substitution in the p53 gene are protected from renal dysgenesis
Samir S. El-Dahr1*, Karam Aboudehen2, and Susana Dipp2
1 Tulane University Health Sciences Center
2 Tulane University School of Medicine
* To whom correspondence should be addressed. E-mail: seldahr{at}tulane.edu.
A physiological cross-talk operates between the tumor suppressor protein, p53, and the bradykinin B2 receptor (BdkrB2) during renal organogenesis. Thus, while BdkrB2 is a target for p53-mediated transcriptional activation, BdkrB2 is required to restrict p53 pro-apoptotic 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 to wild-type kidneys, BdkrB2-/- express abnormally high levels of the Checkpoint kinase, Chk1, which activates p53 via Serine 23 (S23) phosphorylation. In order to define the functional relevance of p53S23 phosphorylation, we generated a compound strain of BdkrB2-/- mice harboring a homozygous serine-to-alanine (S23A) mutation in the p53 gene by crossing BdkrB2-/- to p53S23A knock-in 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 had 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 AQP-2, NCC, NKCC2, NBC1, and Sglt1. We conclude that p53 phosphorylation on serine 23 is an essential step in the signaling pathway mediating the susceptibility of Bdkrb2-/- mutants to renal dysgenesis.
