In response to DNA damage, the p53 tumor suppressor can elicit either apoptosis or cell-cycle arrest and repair, but how this critical decision is made in specific cell types remains largely undefined. We investigated the mechanism by which the transcriptional repressor Slug specifically rescues hematopoietic progenitor cells from lethal doses of gamma radiation. We show that Slug is transcriptionally induced by p53 upon irradiation and then protects the damaged cell from apoptosis by directly repressing p53-mediated transcription of puma, a key BH3-only antagonist of the antiapoptotic Bcl-2 proteins. We established the physiologic significance of Slug-mediated repression of puma by demonstrating that mice deficient in both genes survive doses of total-body irradiation that lethally deplete hematopoietic progenitor populations in mice lacking only slug. Thus, Slug functions downstream of p53 in developing blood cells as a critical switch that prevents their apoptosis by antagonizing the trans-activation of puma by p53.

The Wnt signaling pathway plays a critical role in cell proliferation and differentiation, thus it is often associated with diseases such as cancers. Unfortunately, although attractive, developing anti-cancer strategy targeting Wnt signaling has been challenging given that the most attractive targets are involved in protein-protein interactions (PPIs). Here, we develop a stapled peptide inhibitor that targets the interaction between β-catenin and T cell factor/lymphoid enhancer-binding factor transcription factors, which are crucially involved in Wnt signaling. Our integrative approach combines peptide stapling to optimize proteolytic stability, with lessons learned from cell-penetrating peptide (CPP) design to maximize cellular uptake resulting in NLS-StAx-h, a selective, cell permeable, stapled peptide inhibitor of oncogenic Wnt signaling that efficiently inhibits β-catenin-transcription factor interactions. We expect that this type of integrative strategy that endows stapled peptides with CPP features will be generally useful for developing inhibitors of intracellular PPIs.

The discovery that Slug has a vital anti-apoptotic role in the normal response of hematopoietic progenitors to genotoxic stress compelled us to investigate the underlying cellular and molecular mechanism(s) of this effect. Here we show that, although the development of myeloid progenitors in Slug−/− mice is not impaired under steady-state conditions, their ability to repopulate the compartment after γ-irradiation is reduced. We demonstrate that the radiation-induced death of Slug−/− mice exclusively reflects bone marrow failure and show that Slug protects mice from γ-irradiation-induced death in a cell-autonomous manner. We also establish that Slug confers radioprotection by inhibiting the mitochondria-dependent apoptotic pathway activated by γ-irradiation in hematopoietic progenitors. We show that Slug acts as a transcriptional repressor by directly antagonizing p53-mediated upregulation of the BH3-only gene Puma, which was recently shown to encode a critical mediator of p53-induced apoptosis. Finally, we provide evidence for a novel feedback loop in the hematopoietic progenitor cells after DNA damage: Slug is itself induced by p53. Thus, the survival of hematopoietic progenitor cells after genotoxic stress relies on induction of Slug by p53 and Slug-mediated repression of Puma.

Comprehensive analysis of the cancer genome has become a standard approach to identifying new disease loci, and ultimately will guide therapeutic decisions. A key technology in this effort, single nucleotide polymorphism arrays, has been applied in hematologic malignancies to detect deletions, amplifications, and loss of heterozygosity (LOH) at high resolution. An inherent challenge of such studies lies in correctly distinguishing somatically acquired, cancer-specific lesions from patient-specific inherited copy number variations or segments of homozygosity. Failure to include appropriate normal DNA reference samples for each patient in retrospective or prospective studies makes it difficult to identify small somatic deletions not evident by standard cytogenetic analysis. In addition, the lack of proper controls can also lead to vastly overestimated frequencies of LOH without accompanying loss of DNA copies, so-called copy-neutral LOH. Here we use examples from patients with myeloid malignancies to demonstrate the superiority of matched tumor and normal DNA samples (paired studies) over multiple unpaired samples with respect to reducing false discovery rates in highresolution single nucleotide polymorphism array analysis. Comparisons between matched tumor and normal samples will continue to be critical as the field moves from high resolution array analysis to deep sequencing to detect abnormalities in the cancer genome. IntroductionGlobal profiling of DNA copy number in cancer cells using microarray platforms holds great appeal, as it offers an unparalleled opportunity to uncover the elusive genetic lesions important for tumor initiation and progression. In contrast to array comparative genomic hybridization, which allows one to record only the DNA copy number at high resolution for the whole genome, single nucleotide polymorphism (SNP) arrays permit the capture of both DNA copy number and SNP-based genotype at a submegabase resolution, facilitating the detection of small areas of genomic loss of heterozygosity (LOH) or uniparental disomy (UPD). This technology began to prove its value early in the current decade, with marked improvements in resolution and performance occurring ever since. Array platforms now interrogate the human genome at a density of 900 000 SNPs with an average intermarker distance of less than 700 bp, and nowhere has the power of genome-wide SNP array analysis been more evident than in the study of hematologic malignancies.Over the past decade, many pivotal advances in the understanding of the genetics of hematologic diseases have emerged from SNP array analysis. Large-scale analysis of SNP arrays in B-cell acute lymphocytic leukemia, for example, led to the identification of PAX5 as a key target of genetic inactivation in this disease. 1 In the same manner, the identification of TET2 as a major tumor suppressor in myelodysplastic syndromes (MDSs) was driven by SNP array analysis. 2,3 Thus, SNP arrays afford useful platforms for discovering disease alleles that can shed new light on the pa...