Wilms tumor suppressor, WT1, suppresses epigenetic silencing of the ß-catenin gene.

The mammalian kidney is derived from progenitor cells in intermediate mesoderm. During embryogenesis, progenitor cells expressing the Wilms tumor suppressor gene, WT1, are induced to differentiate in response to WNT signals from the ureteric bud. In hereditary Wilms tumors, clonal loss of WT1 precludes the ß-catenin pathway response and leads to precancerous nephrogenic rests. We hypothesized that WT1 normally primes progenitor cells for differentiation by suppressing the enhancer of zeste2 gene (EZH2), involved in epigenetic silencing of differentiation genes. In human amniotic fluid-derived mesenchymal stem cells, we show that exogenous WT1B represses EZH2 transcription. This leads to a dramatic decrease in the repressive lysine 27 trimethylation mark on histone H3 that silences ß-catenin gene expression. As a result, amniotic fluid mesenchymal stem cells acquire responsiveness to WNT9b and increase expression of genes that mark the onset of nephron differentiation. Our observations suggest that biallelic loss of WT1 sustains the inhibitory histone methylation state that characterizes Wilms tumors.

Endothelial activation by angiotensin II through NFkappaB and p38 pathways: Involvement of NFkappaB-inducible kinase (NIK), free oxygen radicals, and selective inhibition by aspirin.

Angiotensin-II (AII), the dominant effector of the renin-angiotensin system, is involved in the pathogenesis of cardiovascular diseases, such as atherosclerosis. Upregulation of the adhesion molecules VCAM-1, ICAM-1, and E-selectin in endothelial cells by inflammatory cytokines through nuclear factor kappa B (NFkappaB) activation is implicated in formation and progression of atherosclerotic plaque. Here we show that AII induces NFkappaB-dependent transcription in primary endothelial cell lines, leading to the upregulation of ICAM-1 and VCAM-1 expression. NFkappaB activation by AII is mediated by the NFkappaB-inducing kinase (NIK), a common mediator of NFkappaB activation by inflammatory cytokines, such as TNF-alpha. However, NFkappaB stimulation by AII differs from that of TNF-alpha since a TNF-receptor associated factor 2 (TRAF-2) dominant negative mutant does not prevent AII-mediated NFkappaB activation. In analogy with TNF-alpha-dependent activation of NFkappaB, treatment with either the anti-oxidant N-acetyl cysteine (NAC) or the cyclooxygenase (COX) inhibitor acetyl salicylic acid (aspirin), but not indometacin, prevents the induction of NFkappaB-dependent transcription by AII. Thus, production of reactive oxygen species, aspirin (asp)-sensitive enzymes of the arachidonate metabolism, and NIK are common transducers of AII- and TNF-dependent pathways to NFkappaB. AII also activates the inflammatory p38 kinase in endothelial cells, an effect inhibited by exposure to either NAC or asp. Pharmacological interference of the p38 pathway, with the inhibitor SB 202190, prevented AII-mediated activation of the NFkappaB target V-CAM, without affecting degradation of IkappaBalpha. These results support a pro-inflammatory effect of the vasoactive peptide AII in endothelial cells, through at least two pathways-NFkappaB and p38-both of which are sensitive to asp and antioxidants.