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

Regulating tumor suppressor genes: post-translational modifications

Tumor suppressor genes cooperate with each other in tumors. Three important tumor suppressor proteins, retinoblastoma (Rb), p53, phosphatase, and tensin homolog deleted on chromosome ten (PTEN) are functionally associated and they regulated by post-translational modification (PTMs) as well. PTMs include phosphorylation, SUMOylation, acetylation, and other novel modifications becoming growing appreciated. Because most of PTMs are reversible, normal cells use them as a switch to control the state of cells being the resting or proliferating, and PTMs also involve in cell survival and cell cycle, which may lead to abnormal proliferation and tumorigenesis. Although a lot of studies focus on the importance of each kind of PTM, further discoveries shows that tumor suppressor genes (TSGs) form a complex "network" by the interaction of modification. Recently, there are several promising strategies for TSGs for they change more frequently than carcinogenic genes in cancers. We here review the necessity, characteristics, and mechanisms of each kind of post-translational modification on Rb, p53, PTEN, and its influence on the precise and selective function. We also discuss the current antitumoral therapies of Rb, p53 and PTEN as predictive, prognostic, and therapeutic target in cancer.

Epigenetics of Renal Development and Disease

An understanding of epigenetics is indispensable to our understanding of gene regulation under normal and pathological states. This knowledge will help with designing better therapeutic approaches in regenerative tissue medicine. Epigenetics allows us to parse out the mechanisms by which transcriptional regulators gain access to specific gene loci thereby imprinting epigenetic information affecting chromatin function. This epigenetic memory forms the basis of cell lineage specification in multicellular organisms. Post-translational modifications to DNA and histones in the nucleosome core form characteristic epigenetic codes which are distinct for self-renewing and primed progenitor cell populations. Studies of chromatin modifiers and modifications in renal development and disease have been gaining momentum. Both congenital and adult renal diseases have a gene-environment component, which involves alterations to the epigenetic information imprinted during development. This epigenetic memory must be characterized to establish optimal treatment of both acute and chronic renal diseases.

Genome-wide analysis of gestational gene-environment interactions in the developing kidney

The G protein-coupled bradykinin B2 receptor (Bdkrb2) plays an important role in regulation of blood pressure under conditions of excess salt intake. Our previous work has shown that Bdkrb2 also plays a developmental role since Bdkrb2(-/-) embryos, but not their wild-type or heterozygous littermates, are prone to renal dysgenesis in response to gestational high salt intake. Although impaired terminal differentiation and apoptosis are consistent findings in the Bdkrb2(-/-) mutant kidneys, the developmental pathways downstream of gene-environment interactions leading to the renal phenotype remain unknown. Here, we performed genome-wide transcriptional profiling on embryonic kidneys from salt-stressed Bdkrb2(+/+) and Bdkrb2(-/-) embryos. The results reveal significant alterations in key pathways regulating Wnt signaling, apoptosis, embryonic development, and cell-matrix interactions. In silico analysis reveal that nearly 12% of differentially regulated genes harbor one or more Pax2 DNA-binding sites in their promoter region. Further analysis shows that metanephric kidneys of salt-stressed Bdkrb2(-/-) have a significant downregulation of Pax2 gene expression. This was corroborated in Bdkrb2(-/-);Pax2(GFP+/tg) mice, demonstrating that Pax2 transcriptional activity is significantly repressed by gestational salt-Bdkrb2 interactions. We conclude that gestational gene (Bdkrb2) and environment (salt) interactions cooperate to impact gene expression programs in the developing kidney. Suppression of Pax2 likely contributes to the defects in epithelial survival, growth, and differentiation in salt-stressed BdkrB2(-/-) mice.

Histone deacetylases in kidney development: implications for disease and therapy

Histone deacetylases (HDACs) are an evolutionarily conserved group of enzymes that regulate a broad range of biological processes through removal of acetyl groups from histones as well as non-histone proteins. Recent studies using a variety of pharmacological inhibitors and genetic models of HDACs have revealed a central role of HDACs in control of kidney development. These findings provide new insights into the epigenetic mechanisms underlying congenital anomalies of the kidney and urinary tract (CAKUT) and implicate the potential of HDACs as therapeutic targets in kidney diseases, such as cystic kidney diseases and renal cell cancers. Determining the specific functions of individual HDAC members would be an important task of future research.

p53 and MDM2 are involved in the regulation of osteocalcin gene expression

Osteocalcin (OC) is a major noncollagenous bone matrix protein and an osteoblast marker whose expression is limited to mature osteoblasts during the late differentiation stage. In previous studies we have shown osteosarcomas to lose p53 function with a corresponding loss of osteocalcin gene expression. Introduction of wild type p53 resulted in re expression of the osteocalcin gene. Using gel shift and chromatin immunoprecipitation assays, we have identified a putative p53 binding site within the rat OC promoter region and observed an increase in OC promoter activity when p53 accumulates using a CAT assay. The p53 inducible gene Mdm2 is a well-known downstream regulator of p53 levels. Our results showed a synergistic increase in the OC promoter activity when both p53 and MDM2 were transiently overexpressed. We further demonstrate that p53 is not degraded during overexpression of MDM2 protein. Increased OC expression was observed with concomitantly increased p53, VDR, and MDM2 levels in ROS17/2.8 cells during treatment with differentiation promoting (DP) media, but was significantly decreased when co-treated with DP media and the small molecule inhibitor of MDM2-p53 interaction, Nutlin-3. We have also observed a dramatic increase of the OC promoter activity in the presence of p53 and Mdm2 with inclusion of Cbfa-1 and p300 factors. Our results suggest that under some physiological conditions the oncoprotein MDM2 may cooperate with p53 to regulate the osteocalcin gene during osteoblastic differentiation.

Ontogeny of bradykinin B1 receptors in the mouse kidney

Kinins are vasoactive peptides that stimulate two G-protein coupled bradykinin receptors (B1R and B2R). B2R-knockout mice are salt sensitive and develop renal dysgenesis and hypertension if salt stressed during embryogenesis. B1R-knockout mice, on the other hand, are protected from inflammation and fibrosis. This study examined the spatiotemporal expression of B1R during renal organogenesis. The segmental nephron identity of B1R immunoreactivity was determined by costaining with markers of the collecting duct (Dolichos biflorus), proximal tubule (Dolichos tetraglonus), and nephron progenitors (Pax2). At E14.5, the B1R was confined to few cells in the metanephric mesenchyme. Abundance of B1R increased progressively during development. On E17.5, B1R was enriched in differentiating proximal tubular cells and by postnatal day 1, B1R was clearly expressed on the luminal aspect of the proximal tubule. Quantitative real-time PCR revealed that the levels of B1R mRNA more than double during renal maturation. We conclude that 1) B1R expression correlates closely with nephron maturation; 2) lack of B1R in nephron progenitors suggests that B1R is unlikely to play a role in early nephrogenesis; and 3) enrichment of B1R in maturing proximal tubule suggests a potential role for this receptor in terminal differentiation of the proximal nephron.

Cell and molecular biology of kidney development

Abnormalities of kidney and urinary tract development are the most common cause of end-stage kidney failure in childhood in the United States. Over the past 20 years, the advent of mutant and transgenic mice and the manipulation of gene expression in other animal models has resulted in major advances in identification of the cellular and molecular mechanisms that direct kidney morphogenesis, providing insights into the pathophysiology of renal and urologic anomalies. This review focuses on the molecular mechanisms that define kidney progenitor cell populations, induce nephron formation within the metanephric mesenchyme, initiate and organize ureteric bud branching, and participate in terminal differentiation of the nephron. Highlighted are common signaling pathways that function at multiple stages during kidney development, including signaling via Wnts, bone morphogenic proteins, fibroblast growth factor, sonic hedgehog, RET/glial cell-derived neurotrophic factor, and notch pathways. Also emphasized are the roles of transcription factors Odd1, Eya1, Pax2, Lim1, and WT-1 in directing renal development. Areas requiring future investigation include the factors that modulate signaling pathways to provide temporal and site-specific effects. The evolution of our understanding of the cellular and molecular mechanisms of kidney development may provide methods for improved diagnosis of renal anomalies and, hopefully, targets for intervention for this common cause of childhood end-stage kidney disease.