BID, BIM, and PUMA are essential for activation of the BAX- and BAK-dependent cell death program

Although the proteins BAX and BAK are required for initiation of apoptosis at the mitochondria, how BAX and BAK are activated remains unsettled. We provide in vivo evidence demonstrating an essential role of the proteins BID, BIM, and PUMA in activating BAX and BAK. Bid, Bim, and Puma triple-knockout mice showed the same developmental defects that are associated with deficiency of Bax and Bak, including persistent interdigital webs and imperforate vaginas. Genetic deletion of Bid, Bim, and Puma prevented the homo-oligomerization of BAX and BAK, and thereby cytochrome c-mediated activation of caspases in response to diverse death signals in neurons and T lymphocytes, despite the presence of other BH3-only molecules. Thus, many forms of apoptosis require direct activation of BAX and BAK at the mitochondria by a member of the BID, BIM, or PUMA family of proteins.

Familial predisposition to adrenocortical tumors: clinical and biological features and management strategies

The incidence of adrenocortical tumors (ACTs) is increased in several familial cancer syndromes resulting from abnormalities in genes that encode transcription factors implicated in cell proliferation, differentiation, senescence, apoptosis, and genomic instability. These include P53, MEN1, APC, and PRKAR1A. Adenomas are the most common ACTs, but adrenocortical carcinomas occur rarely as well. The clinical manifestations of ACTs, which result from increased secretion of adrenocortical hormones, are similar in the familial and sporadic forms of the disease. However, their management may differ because of unique aspects of the constitutional syndromes. The analysis of gene expression profiles of ACTs in these constitutional syndromes have contributed to our understanding of adrenal tumorigenesis and revealed new molecular diagnostic and prognostic markers and candidate genes for targeted therapies. This chapter summarizes the clinical and biological features, pathogenesis, and management strategies for ACTs that develop in patients with familial cancer syndrome.

Regulation of insulin-like growth factor-mammalian target of rapamycin signaling by microRNA in childhood adrenocortical tumors

MicroRNAs (miRNAs) act at the posttranscriptional level to control gene expression in virtually every biological process, including oncogenesis. Here, we report the identification of a set of miRNAs that are differentially regulated in childhood adrenocortical tumors (ACT), including miR-99a and miR-100. Functional analysis of these miRNAs in ACT cell lines showed that they coordinately regulate expression of the insulin-like growth factor-mammalian target of rapamycin (mTOR)-raptor signaling pathway through binding sites in their 3'-untranslated regions. In these cells, the active Ser(2448)-phosphorylated form of mTOR is present only in mitotic cells in association with the mitotic spindle and midbody in the G(2)-M phases of the cell cycle. Pharmacologic inhibition of mTOR signaling by everolimus greatly reduces tumor cell growth in vitro and in vivo. Our results reveal a novel mechanism of regulation of mTOR signaling by miRNAs, and they lay the groundwork for clinical evaluation of drugs inhibiting the mTOR pathway for treatment of adrenocortical cancer.

Stepwise activation of BAX and BAK by tBID, BIM, and PUMA initiates mitochondrial apoptosis

While activation of BAX/BAK by BH3-only molecules (BH3s) is essential for mitochondrial apoptosis, the underlying mechanisms remain unsettled. Here we demonstrate that BAX undergoes stepwise structural reorganization leading to mitochondrial targeting and homo-oligomerization. The alpha1 helix of BAX keeps the alpha9 helix engaged in the dimerization pocket, rendering BAX as a monomer in cytosol. The activator BH3s, tBID/BIM/PUMA, attack and expose the alpha1 helix of BAX, resulting in secondary disengagement of the alpha9 helix and thereby mitochondrial insertion. Activator BH3s remain associated with the N-terminally exposed BAX through the BH1 domain to drive homo-oligomerization. BAK, an integral mitochondrial membrane protein, has bypassed the first activation step, explaining why its killing kinetics are faster than those of BAX. Furthermore, death signals initiated at ER induce BIM and PUMA to activate mitochondrial apoptosis. Accordingly, deficiency of Bim/Puma impedes ER stress-induced BAX/BAK activation and apoptosis. Our study provides mechanistic insights regarding the spatiotemporal execution of BAX/BAK-governed cell death.

JNK1-dependent PUMA expression contributes to hepatocyte lipoapoptosis

Free fatty acids (FFA) induce hepatocyte lipoapoptosis by a c-Jun N-terminal kinase (JNK)-dependent mechanism. However, the cellular processes by which JNK engages the core apoptotic machinery during lipotoxicity, especially activation of BH3-only proteins, remain incompletely understood. Thus, our aim was to determine whether JNK mediates induction of BH3-only proteins during hepatocyte lipoapoptosis. The saturated FFA palmitate, but not the monounsaturated FFA oleate, induces an increase in PUMA mRNA and protein levels. Palmitate induction of PUMA was JNK1-dependent in primary murine hepatocytes. Palmitate-mediated PUMA expression was inhibited by a dominant negative c-Jun, and direct binding of a phosphorylated c-Jun containing the activator protein 1 complex to the PUMA promoter was identified by electrophoretic mobility shift assay and a chromatin immunoprecipitation assay. Short hairpin RNA-targeted knockdown of PUMA attenuated Bax activation, caspase 3/7 activity, and cell death. Similarly, the genetic deficiency of Puma rendered murine hepatocytes resistant to lipoapoptosis. PUMA expression was also increased in liver biopsy specimens from patients with non-alcoholic steatohepatitis as compared with patients with simple steatosis or controls. Collectively, the data implicate JNK1-dependent PUMA expression as a mechanism contributing to hepatocyte lipoapoptosis.

PUMA regulates intestinal progenitor cell radiosensitivity and gastrointestinal syndrome

Radiation is one of the most effective cancer treatments. However, gastrointestinal (GI) syndrome is a major limiting factor in abdominal and pelvic radiotherapy. The loss of crypt stem cells or villus endothelial cells has been suggested to be responsible for radiation-induced intestinal damage. We report here a critical role of the BH3-only protein p53 upregulated modulator of apoptosis (PUMA) in the radiosensitivity of intestinal epithelium and pathogenesis of GI syndrome. PUMA was induced in a p53-dependent manner and mediated radiation-induced apoptosis via the mitochondrial pathway in the intestinal mucosa. PUMA-deficient mice exhibited blocked apoptosis in the intestinal progenitor and stem cells, enhanced crypt proliferation and regeneration, and prolonged survival following lethal doses of radiation. Unexpectedly, PUMA deficiency had little effect on radiation-induced intestinal endothelial apoptosis. Suppressing PUMA expression by antisense oligonucleotides provided significant intestinal radioprotection. Therefore, PUMA-mediated apoptosis in the progenitor and stem cell compartments is crucial for radiation-induced intestinal damage.

Induction of apoptosis promoted by Bang52; a small molecule that downregulates Bcl-x(L)

Cancer cells evade death by over-producing specific proteins that inhibit apoptosis. One such group of proteins is the Bcl-2 family, of which Bcl-x(L) is an important member. This protein binds and inhibits BAK, another protein that promotes apoptosis. While the development of chemical inhibitors that block Bcl-x(L)-BAK association have been the focus of intense research efforts, we demonstrate in this manuscript an alternative strategy to downregulate Bcl-x(L). We have identified a small molecule (Bang52) that induces apoptosis in a lymphoblast-derived cell line by lowering levels of Bcl-x(L). Since Bang52 bears no resemblance to any chemical binder of Bcl-x(L) we believe that degradation of the protein is stimulated by a new type of pathway. These findings highlight a novel approach to the development of small molecules that promote apoptosis.

Assays to measure p53-dependent and -independent apoptosis

Paramount to the maintenance of normal tissue homeostasis is the induction of programmed cell death, otherwise known as apoptosis. Several disease states, including cancer, are characterized by an inability to remove unwanted cells due to a failure to commit to apoptosis. What is more, apoptosis is the central functional response behind many agents utilized in the treatment of cancer. Many of these antitumorigenic agents rely on the activation of the tumor suppressor p53. As the physiological "guardian of the genome," p53's normal function is to sense stressed or damaged cells and arrest proliferation, allowing time for cellular repair. However, if the damage is excessive, cells are removed prior to the onset of malignancy through apoptosis. Current chemotherapeutic strategies manipulate this property by damaging cells and turning on p53's transcriptional function, which consequently upregulates the expression of proapoptotic proteins such as Puma. We have also demonstrated that Puma is capable of inducing apoptosis independent of p53. In this regard, defects in the apoptotic machinery or in p53 function itself lead to a resistant phenotype that in cancer results in chemotherapeutic failure, and more often than not, poor prognosis. This chapter describes protocols for the determination of p53-dependent and -independent apoptosis utilizing primary cells from genetically altered mice.

Association of the germline TP53 R337H mutation with breast cancer in southern Brazil

Background

The germline TP53-R337H mutation is strongly associated with pediatric adrenocortical tumors (ACT) in southern Brazil; it has low penetrance and limited tissue specificity in most families and therefore is not associated with Li-Fraumeni syndrome. However, other tumor types, mainly breast cancer, have been observed in carriers of several unrelated kindreds, raising the possibility that the R337H mutation may also contribute to breast tumorigenesis in a genetic background-specific context.

Methods

We conducted a case-control study to determine the prevalence of the R337H mutation by sequencing TP53 exon 10 in 123 women with breast cancer and 223 age- and sex-matched control subjects from southern Brazil. Fisher's test was used to compare the prevalence of the R337H.

Results

The R337H mutation was found in three patients but in none of the controls (p = 0.0442). Among the carriers, two had familial history of cancer meeting the Li-Fraumeni-like criteria. Remarkably, tumors in each of these three cases underwent loss of heterozygosity by eliminating the mutant TP53 allele rather than the wild-type allele. Polymorphisms were identified within the TP53 (R72P and Ins16) and MDM2 (SNP309) genes that may further diminish TP53 tumor suppressor activity.

Conclusion

These results demonstrate that the R337H mutation can significantly increase the risk of breast cancer in carriers, which likely depends on additional cooperating genetic factors. These findings are also important for understanding how low-penetrant mutant TP53 alleles can differentially influence tumor susceptibility.

High frequency of loss of heterozygosity at 11p15 and IGF2 overexpression are not related to clinical outcome in childhood adrenocortical tumors positive for the R337H TP53 mutation

A germline TP53 R337H mutation is present in childhood adrenocortical tumors (ACT) from southern Brazil. Other genetic alterations are also frequently found in these tumors. This study was designed to assess whether alterations of the 11p15 region exist in childhood ACT, accounting for IGF2 overexpression in these tumors, and how they are related to clinical outcome. Tumor DNA of 12 children with ACT (4 adenomas and 8 carcinomas) and from the blood of their parents was analyzed. All patients showed 11p15 loss of heterozygosity (LOH) in the tumor. In contrast to the single case of paternal LOH, IGF2 was overexpressed in tumors with maternal allele loss. Our data show that 11p15 LOH is a widespread finding in childhood ACT not related with malignancy, contrary to adult ACT. Alterations in the expression of other genes in the same region (e.g., CDKN1C) may contribute to ACT tumorigenesis.

Identification of a novel TP53 germline mutation E285V in a rare case of paediatric adrenocortical carcinoma and choroid plexus carcinoma

Paediatric choroid plexus carcinomas (CPC) and adrenocortical carcinomas (ACC) are exceedingly rare tumours, each occurring at an annual rate of 0.3 cases per million children or less. Although both tumour types are associated with Li-Fraumeni syndrome (LFS), the penetrance of germline TP53 mutations in CPC remains to be established. We report here a young boy without a family history of cancer who presented with CPC and subsequently ACC. Genetic testing revealed a novel de novo germline TP53 mutation (E285V). Neither tumour underwent loss of heterozygosity. Consistent with this observation, functional analyses demonstrated that E285V acts as a dominant negative mutant that is defective in regulating target gene expression, growth suppression and apoptosis. These results further strengthen the association between germline TP53 mutations and childhood CPC, even when occurring in the absence of familial tumour susceptibility.

The p53 mutation "gradient effect" and its clinical implications

The p53 tumor suppressor-signaling pathway is inactivated in most human cancers. Depending on how p53 is targeted during tumorigenesis impacts whether partial or full tumor suppressor activity is lost. The degree of remaining p53 activity, if any, intuitively impacts the tumor phenotype. This review focuses on recent findings from human cancer studies and genetically engineered mouse models to highlight a p53 functional "gradient effect" and its clinical implications.

Increased steroidogenic factor-1 dosage triggers adrenocortical cell proliferation and cancer

Steroidogenic factor-1 (SF-1/Ad4BP; NR5A1), a nuclear receptor transcription factor, has a pivotal role in adrenal and gonadal development in humans and mice. A frequent feature of childhood adrenocortical tumors is SF-1 amplification and overexpression. Here we show that an increased SF-1 dosage can by itself augment human adrenocortical cell proliferation through concerted actions on the cell cycle and apoptosis. This effect is dependent on an intact SF-1 transcriptional activity. Gene expression profiling showed that an increased SF-1 dosage regulates transcripts involved in steroid metabolism, the cell cycle, apoptosis, and cell adhesion to the extracellular matrix. Consistent with these results, increased SF-1 levels selectively modulate the steroid secretion profile of adrenocortical cells, reducing cortisol and aldosterone production and maintaining dehydroepiandrosterone sulfate secretion. As a model to understand the mechanisms of transcriptional regulation by increased SF-1 dosage, we studied FATE1, coding for a cancer-testis antigen implicated in the control of cell proliferation. Increased SF-1 levels increase its binding to a consensus site in FATE1 promoter and stimulate its activity through modulation of the recruitment of specific cofactors. On the other hand, sphingosine, which can compete with phospholipids for binding to SF-1, had no effect on the SF-1 dosage-dependent increase of adrenocortical cell proliferation and expression of the FATE1 promoter. In mice, increased Sf-1 dosage produces adrenocortical hyperplasia and formation of tumors expressing gonadal markers (Amh, Gata-4), which originate from the subcapsular region of the adrenal cortex. Gene expression profiling revealed that genes involved in cell adhesion and the immune response and transcription factor signal transducer and activator of transcription-3 (Stat3) are differentially expressed in Sf-1 transgenic mouse adrenals compared with wild-type adrenals. Our studies reveal a critical role for SF-1 dosage in adrenocortical tumorigenesis and constitute a rationale for the development of drugs targeting SF-1 transcriptional activity for adrenocortical tumor therapy.

Nephroblastoma overexpressed/cysteine-rich protein 61/connective tissue growth factor/nephroblastoma overexpressed gene-3 (NOV/CCN3), a selective adrenocortical cell proapoptotic factor, is down-regulated in childhood adrenocortical tumors

CONTEXT

Childhood adrenocortical tumors (ACTs) have a fetal adrenal phenotype and overexpress steroidogenic factor-1 (SF-1). Nephroblastoma overexpressed (NOV)/cysteine-rich protein 61/connective tissue growth factor/nephroblastoma overexpressed gene-3 mRNA is significantly down-regulated in childhood ACTs.

OBJECTIVE

The objective of the study was to measure NOV protein levels in childhood ACTs and characterize NOV expression regulation and biological function in human adrenocortical cells.

DESIGN AND SETTING

Protein extracts from ACT and normal adrenal cortex samples, human adrenocortical carcinoma H295R, primary adrenocortical tumors and fetal adrenal cultures, tissue culture supernatants, and cell lysates from H295R cells overexpressing SF-1 in an inducible fashion were used.

MAIN OUTCOME MEASURES

NOV protein levels were measured by enzyme-linked immunoassay and immunoblot. Transient transfection assays were used to study the activity of NOV promoter. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling, caspase assays, and flow cytometry were used to assess the proapoptotic activity of NOV on cells in culture.

RESULTS

NOV mRNA and protein expression is lower in childhood ACTs than in normal adrenal cortex. No significant difference was observed between adenomas and carcinomas. SF-1 overexpression down-regulates NOV at the transcriptional level. NOV has a selective proapoptotic activity toward human adrenocortical cells. The C-terminal domain of NOV is responsible for its proapoptotic effect. NOV protein is expressed in DAX-1-positive human fetal adrenal cells.

CONCLUSIONS

NOV is a selective proapoptotic factor for human adrenocortical cells. Reduced expression of NOV in ACTs may play an important role in the process of childhood ACT tumorigenesis, accounting at least in part for the defect of apoptotic regression of the fetal adrenal that has been proposed to be responsible for tumor formation.

p53 independent induction of PUMA mediates intestinal apoptosis in response to ischaemia-reperfusion

BACKGROUND

The small intestine is highly sensitive to ischaemia-reperfusion (I/R) induced injury which is associated with high morbidity and mortality. Apoptosis, or programmed cell death, is a major mode of cell death occurring during I/R induced injury. However, the mechanisms by which I/R cause apoptosis in the small intestine are poorly understood. p53 upregulated modulator of apoptosis (PUMA) is a p53 downstream target and a member of the BH3-only group of Bcl-2 family proteins. It has been shown that PUMA plays an essential role in apoptosis induced by a variety of stimuli in different tissues through a mitochondrial pathway.

AIMS

The role of PUMA in I/R induced injury and apoptosis in the small intestine was investigated. The mechanisms by which PUMA is regulated in I/R induced intestinal apoptosis were also studied.

METHODS

Ischaemia was induced by superior mesenteric artery occlusion in the mouse small intestine. Induction of PUMA in response to ischaemia alone, or ischaemia followed by reperfusion (I/R), was examined. I/R induced intestinal apoptosis and injury were compared between PUMA knockout and wild-type mice. The mechanisms of I/R induced and PUMA mediated apoptosis were investigated through analysis of caspase activation, cytosolic release of mitochondrial cytochrome c and alterations of the proapoptotic Bcl-2 family proteins Bax and Bak. To determine whether PUMA is induced by reactive oxygen species and/or reactive nitrogen species generated by I/R, superoxide dismutase (SOD) and N-nitro-l-arginine methyl ester (L-NAME) were used to treat animals before I/R. To determine whether p53 is involved in regulating PUMA during I/R induced apoptosis, PUMA induction and apoptosis in response to I/R were examined in p53 knockout mice.

RESULTS

PUMA was markedly induced following I/R in the mucosa of the mouse small intestine. I/R induced intestinal apoptosis was significantly attenuated in PUMA knockout mice compared with that in wild-type mice. I/R induced caspase 3 activation, cytochrome c release, Bax mitochondrial translocation and Bak multimerisation were also inhibited in PUMA knockout mice. SOD or L-NAME significantly blunted I/R induced PUMA expression and apoptosis. Furthermore, I/R induced PUMA expression and apoptosis in the small intestine were not affected in the p53 knockout mice.

CONCLUSIONS

Our data demonstrated that PUMA is activated by oxidative stress in response to I/R to promote p53 independent apoptosis in the small intestine through the mitochondrial pathway. Inhibition of PUMA is potentially useful for protecting against I/R induced intestinal injury and apoptosis.

Clinical and molecular characteristics of malignant transformation of low-grade glioma in children

PURPOSE

To analyze the clinical and molecular characteristics of malignant transformation (MT) of low-grade glioma (LGG) in children.

PATIENTS AND METHODS

The clinical, radiologic, and histologic characteristics of children treated at our institution who experienced MT of LGG were reviewed. Molecular alterations in these tumors were analyzed by fluorescent in situ hybridization, immunohistochemistry, and TP53 sequencing. Cumulative incidence estimate and risk factors for MT were determined for 65 patients with grade 2 astrocytoma treated at our institution during the study interval.

RESULTS

Eleven patients who experienced MT were identified (median age at diagnosis of LGG, 13.3 years). Initial diagnoses were grade 2 astrocytoma (n = 6) and other grade 1/2 gliomas (n = 5). The median latency of MT was 5.1 years. Histologic diagnoses after MT were glioblastoma (n = 7) and other high-grade gliomas (n = 4). The 15-year cumulative incidence estimate of MT among 65 patients with grade 2 astrocytoma was 6.7% +/- 3.9%; no risk factor analyzed, including radiotherapy, was associated with MT. Tissue was available for molecular analysis in all patients, including nine with samples obtained before and after MT. TP53 overexpression was more common after MT. Deletions of RB1 and/or CDKN2A were observed in 71% of LGGs and in 90% of tumors after MT. PTEN pathway abnormalities occurred in 76% of patients. One of five oncogenes analyzed (PDGFRA) was amplified in one patient.

CONCLUSION

The molecular abnormalities that occur during MT of LGG in children are similar to those observed in primary and secondary glioblastoma in adults.

Gene expression profiling of childhood adrenocortical tumors

Pediatric adrenocortical tumors (ACT) are rare and often fatal malignancies; little is known regarding their etiology and biology. To provide additional insight into the nature of ACT, we determined the gene expression profiles of 24 pediatric tumors (five adenomas, 18 carcinomas, and one undetermined) and seven normal adrenal glands. Distinct patterns of gene expression, validated by quantitative real-time PCR and Western blot analysis, were identified that distinguish normal adrenal cortex from tumor. Differences in gene expression were also identified between adrenocortical adenomas and carcinomas. In addition, pediatric adrenocortical carcinomas were found to share similar patterns of gene expression when compared with those published for adult ACT. This study represents the first microarray analysis of childhood ACT. Our findings lay the groundwork for establishing gene expression profiles that may aid in the diagnosis and prognosis of pediatric ACT, and in the identification of signaling pathways that contribute to this disease.

Hierarchical regulation of mitochondrion-dependent apoptosis by BCL-2 subfamilies

Although the BCL-2 family constitutes a crucial checkpoint in apoptosis, the intricate interplay between these family members remains elusive. Here, we demonstrate that BIM and PUMA, similar to truncated BID (tBID), directly activate BAX-BAK to release cytochrome c. Conversely, anti-apoptotic BCL-2-BCL-X(L)-MCL-1 sequesters these 'activator' BH3-only molecules into stable complexes, thus preventing the activation of BAX-BAK. Extensive mutagenesis of BAX-BAK indicates that their activity is not kept in check by BCL-2-BCL-X(L)-MCL-1. Anti-apoptotic BCL-2 members are differentially inactivated by the remaining 'inactivator' BH3-only molecules including BAD, NOXA, BMF, BIK/BLK and HRK/DP5. BAD displaces tBID, BIM or PUMA from BCL-2-BCL-X(L) to activate BAX-BAK, whereas NOXA specifically antagonizes MCL-1. Coexpression of BAD and NOXA killed wild-type but not Bax, Bak doubly deficient cells or Puma deficient cells with Bim knockdown, indicating that activator BH3-only molecules function downstream of inactivator BH3-only molecules to activate BAX-BAK. Our data establish a hierarchical regulation of mitochondrion-dependent apoptosis by various BCL-2 subfamilies.

Identification of a novel germ line variant hotspot mutant p53-R175L in pediatric adrenal cortical carcinoma

Hotspot mutations in the p53 tumor suppressor gene result in the disruption of DNA contact points or alter the overall structure of the protein to prevent DNA binding. When inherited, hotspot mutants are associated with Li-Fraumeni syndrome (LFS), a familial cancer predisposition. One of the most common hotspot mutations occurs at codon 175, resulting in an arginine to histidine substitution. We have identified a novel germ line variant of the 175 mutant (Arg to Leu; R175L) in a pediatric patient who developed adrenal cortical carcinoma. Surprisingly, the family is not tumor prone or associated with LFS. In vitro, the R175L mutant displayed an attenuated tumor suppressor activity in the regulation of transcription, colony formation, and apoptosis when compared with wild-type p53 and the R175H mutant. These findings suggest that p53-R175L retains sufficient activity to suppress LFS, but not adrenal cortical carcinoma. Therefore, not all hotspot mutants are functionally equivalent and the biochemical nature of the mutant may significantly influence clinical outcome. The implications of these results for genetic counseling are discussed.

Skeletons in the p53 tumor suppressor closet: genetic evidence that p53 blocks bone differentiation and development

A series of in vitro tissue culture studies indicated that the p53 tumor suppressor promotes cellular differentiation, which could explain its role in preventing cancer. Quite surprisingly, however, two new in vivo studies (Lengner et al., 2006; Wang et al., 2006) provide genetic evidence that p53 blocks osteoblast differentiation and bone development. These interesting results and their biological and clinical implications are the focus of this comment.

Slug antagonizes p53-mediated apoptosis of hematopoietic progenitors by repressing puma

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.

Targeted deletion of Puma attenuates cardiomyocyte death and improves cardiac function during ischemia-reperfusion

The p53-upregulated modulator of apoptosis (Puma), a BH3-only member of the Bcl-2 protein family, is required for p53-dependent and -independent forms of apoptosis and has been implicated in the pathomechanism of several diseases, including cancer, acquired immunodeficiency syndrome, and ischemic brain disease. The role of Puma in cardiomyocyte death, however, has not been analyzed. On the basis of the ability of Puma to integrate diverse cell death stimuli, we hypothesized that Puma might be critical for cardiomyocyte death upon ischemia-reperfusion (I/R) of the heart. Here we show that hypoxia-reoxygenation of isolated cardiomyocytes led to an increase in Puma mRNA and protein levels. Moreover, if Puma was delivered by an adenoviral construct, cardiomyocytes died by apoptosis. Under ATP-depleted conditions, however, Puma overexpression primarily induced necrosis, suggesting that Puma is involved in the development of both types of cell death. Consistent with these findings, targeted deletion of Puma in a mouse model attenuated both apoptosis and necrosis. When the Langendorff ex vivo I/R model was used, infarcts were approximately 50% smaller in Puma(-/-) than in wild-type mice. As a result, after I/R, cardiac function was significantly better preserved in Puma(-/-) mice than in their wild-type littermates. Our study thus establishes Puma as an essential mediator of cardiomyocyte death upon I/R injury and offers a novel therapeutic target to limit cell loss in ischemic heart disease.

Biology, clinical characteristics, and management of adrenocortical tumors in children

Childhood adrenocortical tumors (ACT) are very aggressive endocrine neoplasms whose incidence is quite low. Little is known about their pathogenesis, clinical presentation, and optimal treatment. In recent years, however, new information has been derived from the International Pediatric Adrenocortical Tumor Registry (IPACTR), and new clues to its pathogenesis have emerged. To provide an overview of the available data that may apply to pediatric ACT, we reviewed the epidemiology, pathogenesis, and treatment of ACT in adults and in children. Germline TP53 mutation is almost always the predisposing factor in childhood ACT. A unique germline mutation (TP53-R337H) has been described in Southern Brazil, where the incidence of ACT is 10-15 times the general incidence. Childhood ACT typically present during the first 5 years of life and has female predominance. Hormone hyperproduction is almost universal, and most patients present with virilization. Two-thirds of patients have resectable tumors. Surgery is the definitive treatment for ACT, and a curative complete resection should always be attempted. Cisplatin-based chemotherapy with mitotane is indicated for unresectable or metastatic disease, although its impact on overall outcome is slight. In childhood ACT, age, tumor size, and tumor resectability are the most important prognostic indicators. Outcome is stage-dependent; patients with small, resectable tumors have survival rates in excess of 80%, whereas the outcome for patients with unresectable disease is dismal. Patients with large, resectable tumors have an intermediate outcome. Childhood ACT are rare, but their unique epidemiology appear to implicate novel oncogenic pathways that are unique to the pediatric population. Multi-institutional and prospective studies are necessary to further our understanding of the pathogenesis and to improve outcomes.