Shwachman-Diamond syndrome is a congenital bone marrow failure disorder characterized by debilitating neutropenia. The disease is associated with loss-of-function mutations in the SBDS gene, ...implicated in ribosome biogenesis, but the cellular and molecular events driving cell specific phenotypes in ribosomopathies remain poorly defined. Here, we established what is to our knowledge the first mammalian model of neutropenia in Shwachman-Diamond syndrome through targeted downregulation of Sbds in hematopoietic stem and progenitor cells expressing the myeloid transcription factor CCAAT/enhancer binding protein α (Cebpa). Sbds deficiency in the myeloid lineage specifically affected myelocytes and their downstream progeny while, unexpectedly, it was well tolerated by rapidly cycling hematopoietic progenitor cells. Molecular insights provided by massive parallel sequencing supported cellular observations of impaired cell cycle exit and formation of secondary granules associated with the defect of myeloid lineage progression in myelocytes. Mechanistically, Sbds deficiency activated the p53 tumor suppressor pathway and induced apoptosis in these cells. Collectively, the data reveal a previously unanticipated, selective dependency of myelocytes and downstream progeny, but not rapidly cycling progenitors, on this ubiquitous ribosome biogenesis protein, thus providing a cellular basis for the understanding of myeloid lineage biased defects in Shwachman-Diamond syndrome.
Puma encodes a BH3-only protein that is induced by the p53 tumor suppressor and other apoptotic stimuli. To assess its physiological role in apoptosis, we generated
Puma knockout mice by gene ...targeting. Here we report that Puma is essential for hematopoietic cell death triggered by ionizing radiation (IR), deregulated c-Myc expression, and cytokine withdrawal. Puma is also required for IR-induced death throughout the developing nervous system and accounts for nearly all of the apoptotic activity attributed to p53 under these conditions. These findings establish Puma as a principal mediator of cell death in response to diverse apoptotic signals, implicating Puma as a likely tumor suppressor.
Tumor necrosis factor- alpha (TNF- alpha ) is a cytokine that has an important role in immunity and inflammation by inducing cellular responses such as apoptosis. The transcription factor nuclear ...factor- Kappa B (NF- Kappa B) can paradoxically suppress and promote apoptosis in response to TNF- alpha . In this study, we found that p53 upregulated modulator of apoptosis (PUMA), a p53 downstream target and a BH3-only Bcl-2 family member, is directly regulated by NF- Kappa B in response to TNF- alpha . TNF- alpha treatment led to increases in PUMA mRNA and protein levels in human colon cancer cells. The induction of PUMA was p53 independent, and mediated by the p65 component of NF- Kappa B through a Kappa B site in the PUMA promoter. The apoptotic effect of PUMA induction by TNF- alpha was unmasked by depleting the antiapoptotic protein Bcl-X sub(L). In mice, PUMA was also induced by TNF- alpha in an NF- Kappa B-dependent manner. TNF- alpha -induced apoptosis in a variety of tissues and cell types, including small intestinal epithelial cells, hepatocytes, and thymocytes, was markedly reduced in PUMA-deficient mice. Collectively, these results demonstrated that PUMA is a direct target of NF- Kappa B and mediates TNF- alpha -induced apoptosis in vitro and in vivo.Cell Death and Differentiation (2009) 16, 1192-1202; doi:10.1038/cdd.2009.51; published online 15 May 2009
The incidence of pediatric adrenal cortical carcinoma (ACC) in southern Brazil is 10-15 times higher than that of pediatric ACC worldwide. Because childhood ACC is associated with Li-Fraumeni ...syndrome, we examined the cancer history and p53 status of 36 Brazilian patients and their families. Remarkably, 35 of 36 patients had an identical germ-line point mutation of p53 encoding an R337H amino acid substitution. Differences within intragenic polymorphic markers demonstrated that at least some mutant alleles arose independently, thus eliminating a founder effect. In tumor cells, the wild-type allele was deleted, and mutant p53 protein accumulated within the nuclei. Although these features are consistent with Li-Fraumeni syndrome-associated adrenal tumors, there was no history of increased cancer incidence among family members. Therefore, this inherited R337H p53 mutation represents a low-penetrance p53 allele that contributes in a tissue-specific manner to the development of pediatric ACC.
The tumor suppressor p53 plays a central role in the protection against DNA damage and other forms of physiological stress primarily by inducing cell cycle arrest or apoptosis. Mutation of p53, which ...is the most frequent genetic alteration detected in human cancers, inactivates these growth regulatory functions and causes a loss of tumor suppressor activity. In some cases, mutation also confers tumor-promoting functions, such as the transcriptional activation of genes involved in cell proliferation, cell survival and angiogenesis. Consequently, cells expressing some forms of mutant p53 show enhanced tumorigenic potential with increased resistance to chemotherapy and radiation. Our current understanding of these activities is summarized in this review. By dissecting out mechanistic differences between wild-type and mutant p53 activities, it may be possible to develop therapeutics that restore tumor suppressor function to mutant p53 or that selectively inactivate mutant p53 tumor-promoting functions.
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 γ 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.
Background: An inherited germline P53 mutation has been identified in cases of childhood adrenocortical carcinoma (ACT), a neoplasm with a high incidence in southern Brazil. The penetrance of ACT in ...carriers of the point mutation, which encodes an arginine-to-histidine substitution at codon 337 of TP53 (R337H), has not been determined. Objective: To investigate the penetrance of childhood ACT in carriers of the R337H TP53 mutation. Methods: The family histories of 30 kindreds of 41 southern Brazilian children with ACT were obtained. A PCR based assay was used to detect this P53 mutation in a large number of relatives of children with ACT. In all, 927 individuals were tested for the mutation, 232 from the non-carrier and 695 (including the 40 probands) from the carrier parental lines. Results: 40 children with ACT carried the TP53 R337H mutation; the remaining child with ACT was not tested. There was no evidence of Li-Fraumeni syndrome in any of the kindreds; however, seven met the criteria for Li-Fraumeni-like syndrome. The carrier parental line was identified in each kindred. Of the 695 individuals tested in the carrier parental line, 240 (34.5%) were positive for the mutation, while none of the 232 individuals in the other parental line carried the mutation. The penetrance of ACT was 9.9% (95% confidence interval, 8.7% to 11.1%). Conclusions: The TP53 R337H mutation dramatically increases predisposition to childhood ACT but not to other cancers, and explains the increased frequency of ACT observed in this geographic region.
BH3-only proteins function at a proximal point in a conserved cell death pathway by binding, through their BH3 domains, to other Bcl-2 family members and triggering mitochondrial events associated ...with apoptosis. Here, we describe a strongly pro-apoptotic BH3-only protein, designated Bbc3, whose expression increases in response to diverse apoptotic stimuli. bbc3 mRNA levels were induced by exposure to DNA-damaging agents and by wild-type p53, which mediates DNA damage-induced apoptosis. p53 transactivated bbc3 through consensus p53 binding sites within the bbc3 promoter region, indicating that bbc3 is a direct target of p53. Additionally, bbc3 mRNA was induced by p53-independent apoptotic stimuli, including dexamethasone treatment of thymocytes, and serum deprivation of tumor cells. Insulin-like growth factor-1 and epidermal growth factor, growth factors with broad anti-apoptotic activity, were each sufficient to suppress Bbc3 expression in serum-starved tumor cells. These results suggest that the transcriptional regulation of bbc3 contributes to the transduction of diverse cell death and survival signals.
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