In addition to its classical role as a guardian of the genome, p53 functions as a developmental regulator. In the embryonic mouse kidney, p53 prevents ectopic budding from the nephric duct by antagonizing GDNF-Ret signaling. Moreover, p53 regulates expression of a subset of renal function genes (RFG) via direct binding to the target promoters. Cellular p53 levels are normally kept low via proteosomal degradation mediated by interactions with the E3 ubiquitin ligase, mdm2. Upon cellular stress (e.g., DNA damage), p53 is activated via post-translational modifications, which induce dissociation and caspase-mediated cleavage of Mdm2. The mechanisms mediating p53 stabilization and activation in the embryonic kidney are unknown. Utilizing a panel of p53 antibodies directed against phosphorylated serine/threonine or acetylated lysines, we demonstrate that embryonic kidney p53 is phosphorylated on serines S6, S9, S15, S20 and S392 and acetylated on lysines K373, K382, and K386. Site-directed mutagenesis demonstrated that some modifications are necessary, e.g., Ser15, Ser 20, Thr18, whereas others are dispensable, e.g., Ser392, K373, K382, K386, for p53 stability. Moreover, in vitro transfection experiments revealed that p53 modifications exert differential transcriptional effects on target renal differentiation genes. Chromatin Immunoprecipitation assays indicate that onset of nephron differentiation is accompanied by enhanced p53 binding to RFGs promoters. In vivo, selected p53 modifications tend to be associated with cell type-specific expression pattern; for example, p-p53S392 is enriched in differentiating proximal tubules, whereas ac-p53K373,K382/K386 is expressed in nephron progenitors and collecting ducts. In addition, embryonic p53 exists mostly in a mono-ubiquitinated form, whereas, in postnatal kidney, p53 is polyubiquitinated. This finding correlates with the developmental switch from cleaved to intact Mdm2. We conclude that factors within the embryonic microenvironment promote enhanced p53 stability via post-translational modifications / acase@tulane.edu
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_27228 |
| Date | January 2011 |
| Contributors | Aboudehen, Karam S (Author), Chen, TianJian (Thesis advisor) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Rights | Access requires a license to the Dissertations and Theses (ProQuest) database., Copyright is in accordance with U.S. Copyright law |
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