M
TP53-Associated Pediatric Malignancies
Emilia M. Pinto1,2, Raul C. Ribeiro1,3,4, Bonald C. Figueiredo5, and Gerard P. Zambetti2,4
Genes & Cancer 2(4) 485-490 @ The Author(s) 2011 Reprints and permission: sagepub.com/journalsPermissions.nav DOI: 10.1177/1947601911409745
http://ganc.sagepub.com SSAGE
Abstract
Although the majority of pediatric malignancies express wild-type p53, it is well established that germline TP53 mutations or functional inactivation of this pathway by other means contribute to childhood cancer. Epidemiology studies have revealed the existence of diverse inherited mutant TP53 alleles that display different levels of tumor suppressor activity, which correlate with cancer risk in terms of penetrance, age of onset, and tumor types. In this monograph, the authors describe those childhood cancers associated with functional inactivation of TP53 focusing on adrenocortical carcinoma as a model for tissues that are highly sensitive to loss of p53 activity.
Keywords: p53 mutation, adrenocortical tumors, Arg337His
Introduction
Pediatric malignancies are rare, com- plex, and heterogeneous disorders. Alto- gether they represent only about 1% to 2% of all human malignancies.1 If we assume that childhood cancer is a devel- opmental genetic disorder, it is reason- able to postulate that a combination of alterations crippling one or more signal- ing pathways is sufficient to initiate a cascade of events establishing a malig- nant clone. As a group, TP53 mutations are among the most common genetic alterations observed in human cancers and occur in about 50% of unselected sporadic tumors.2,3
When TP53 mutations are inherited, carriers have an increased lifetime predis- position to cancer.4 Although the spec- trum of tumor types in these individuals is similar to that found in the sporadic counterpart, they tend to develop tumors much earlier in life. The anticipation of tumor development, particularly in certain tissues, suggests that cells with constitutional TP53 mutations are less dependent on naturally occurring events, such as aging or environmental carcino- gens (e.g., UV, benzo[a]pyrene) for initi- ating tumorigenesis. Therefore, it can be postulated that additional constitutional genetic polymorphisms, mutations, and
other epigenetic mechanisms cooperate with p53 insufficiency to promote tumor development. If this premise is correct, the study of pediatric tumors associated with TP53 mutations provides an impor- tant opportunity to uncover these cooper- ating events for establishing the cancer phenotype. It is also plausible that these same constitutional genetic alterations play a role in the development of spo- radic tumors later in life.
For many years, our clinical and laboratory efforts have focused on improving the outcome of children with a rare malignancy, adrenocortical tumors (ACT), which are usually associated with TP53 mutations. Understanding the changes in incidence over time and dif- ferences between different groups (e.g., gender and ethnicity) provides essential clues to the etiology of disease, particu- larly the balance between genetic factors versus environment in the causation of the disease. We approached this task first by creating a tumor registry to col- lect demographic, epidemiologic, and clinical information, including family history of cancer, outcome, and long- term follow up data of families with a proband with ACT. Second, we estab- lished uniform treatment guidelines for the management of these patients. Finally, we have been conducting
extensive cellular and molecular studies of p53 and its associated pathways to learn more about the mechanisms driv- ing adrenocortical tumorigenesis with the goal of developing more effective therapies for these patients.
TP53 Tumor Suppression Function
p53 (encoded by human gene TP53) functions primarily as a tetrameric tran- scription factor within a signaling path- way that is essential for maintaining normal cell growth and survival. Cell stress caused by DNA damaging agents, deregulation of oncogenes, or other environmental insults, such as hypoxia, can activate p53, resulting in cell cycle
1International Outreach Program, St. Jude Children’s Research Hospital, Memphis, TN, USA
2Department of Biochemistry, St. Jude Children’s Research Hospital, Memphis, TN, USA 3Department of Oncology, St. Jude Children’s Research Hospital, Memphis, TN, USA 4Department of Pediatrics, University of Tennessee College of Medicine, Memphis, TN, USA 5Instituto de Pesquisa Pelé Pequeno Príncipe, Curitiba, Brazil
Corresponding Author:
Gerard P. Zambetti, PhD, Biochemistry, MS 340 Room D4063E, St. Jude Children’s Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105-3678, USA
Email: gerard.zambetti@stjude.org
·
arrest, cellular senescence, and/or apop- tosis. In addition, p53 can affect glyco- lytic pathways, DNA repair, angiogenesis, longevity, and aging.5 Upon cellular stress, p53 undergoes posttranslational modifications that stabilize and activate the protein to induce the expression of its downstream target genes.6 These p53- responsive genes are differentially regu- lated depending on cell context, the extent of damage, and various other yet unidentified parameters.7
Mutational Inactivation of TP53
During tumorigenesis, strong selective pressures prevent the activation of p53.8 About 50% of all human tumors sustain TP53 mutations, whereas the remaining cases acquire other genetic or epigenetic alterations that compromise p53 func- tion.9 The majority of tumor-derived TP53 mutations are single-nucleotide substitutions clustering within the DNA binding domain (DBD), resulting in the expression of a missense protein that is defective in sequence-specific binding, transactivation, and growth inhibition.10 In addition, p53 can be functionally inactivated through the loss of upstream inducers (ATM, p14ARF) or downstream mediators (caspase 9, APAF1) or by overexpressing negative regulators (Mdm2, Mdm4, human papilloma virus E6), for example.11
Approximately 80% of TP53 muta- tions occur within DBD,12 with the majority occurring at 6 hot spot codons (175, 245, 248, 249, 273, and 282). These specific sites account for about 40% of all TP53 missense mutations and are naturally selected during tumorigen- esis due to their deleterious effects on p53’s ability to bind DNA and regulate transcription.9 However, an increasing number of studies highlight the impor- tance of mutations outside of this domain. 13-15
Most missense p53 proteins are sta- ble and expressed at high levels in human tumors.8 It has been shown that some p53 mutants exhibit a dominant- negative phenotype by binding the
normal p53 monomer (expressed by the wild-type allele), resulting in an inactive heterodimer and tetramer.16,17 Consistent with these findings, human cancers that express mutant p53 while retaining the wild-type TP53 allele have been described.18 Similarly, mice that are het- erozygous for a dominant-negative TP53 point mutation develop tumors without loss of the wild-type TP53 allele.19 Partial inactivation of wild-type p53 function by mutant p53 might allow for some selec- tive advantage during tumor progression. However, many tumors that harbor TP53 point mutations also show loss of hetero- zygosity (LOH)13,14 by eliminating the wild-type allele through either deletion or other mechanisms.
Negative Regulators of p53
p53 tumor suppressor activity is limited primarily by Mdm2, which binds and conceals the N-terminus of p53. Conse- quently, Mdm2 inhibits p53 transcrip- tion function and, through its E3 ubiquitin ligase activity, targets p53 for proteasomal degradation. Notably, Mdm2 forms an elegant negative- feedback loop with p53, as Mdm2 tran- scription can be directly positively regulated by p53.20,21 The importance of this interaction in regulating p53-depen- dent tumor suppression is highlighted by the following findings: 1) Studies in ani- mal models have shown that the embry- onic lethality of Mdm2 knockout mice can be fully rescued by deleting p53, 2) Mdm2 transgenic mice are tumor prone, 3) MDM2 is frequently amplified and overexpressed in human tumors that retain wild-type TP53 alleles, and 4) Nutlin, an MDM2 inhibitor, can reacti- vate p53 function in tumors expressing wild-type TP53 alleles.22
A single-nucleotide polymorphism (SNP) within the MDM2 promoter at nucleotide 309T>G (rs2279744) has been shown to enhance MDM2 tran- scription, resulting in the accumulation of MDM2 protein and consequently the attenuation of p53 function.23 Consistent with these findings, the MDM2 SNP309
G allele is associated with earlier age of onset of tumors among patients with Li- Fraumeni syndrome (LFS).24
p53 inactivation in human cancers can also occur through the amplification and overexpression of MDM4, which shares homology with MDM2.25,26 MDM4 is genetically amplified in a sub- set of breast, colon, and lung carcino- mas; gliomas; and approximately 65% of children with retinoblastoma.27 A general consensus is emerging that in addition to Nutlin and derivative com- pounds, an MDM4-specific inhibitor will need to be developed to effectively treat retinoblastoma and other tumors that retain expression of wild-type p53.26
Familial Mutant p53 Syndromes
Germline inherited TP53 mutations cause a rare type of familial cancer pre- disposition known as LFS, in which family members can present with diverse tumor types occurring over a wide age range, including during childhood. This syndrome is characterized by the fol- lowing criteria: a proband with a sar- coma aged less than 45 years, a first-degree relative younger than 45 years with any cancer, plus an additional first- or second-degree relative in the same lineage with any cancer before age 45 years or a sarcoma at any age.28
Individuals with LFS have a greater risk for cancer at younger ages than those in the general population. It is esti- mated that 50% of LFS-associated malignancies occur by age 30 years.29 LFS is associated with increased suscep- tibility to diverse malignancies such as soft tissue sarcomas, osteosarcomas, brain tumors, choroid plexus carcino- mas (CPC), and pediatric ACT, as well as multiple primary tumors.3º In particu- lar, women with LFS are at a signifi- cantly high risk of premenopausal breast cancer.31 In assessing families for LFS, an unusually young age at diagnosis may be as important a variable as the specific type of malignancy.
More inclusive clinical classification schemes have been described that
characterize Li-Fraumeni-like syndrome (LFL) as having features of LFS without fulfilling its strict requirements.32 Addi- tional criteria by Chompret and col- leagues33 allow for the possibility of a proband with an LFS-related tumor but a negative family history of cancer.
TP53 is the only gene known to date to be strongly associated with LFS and LFL. Clinical testing involves sequence analysis of the entire TP53 coding region. This method detects about 95% of TP53 mutations, most of which are missense mutations. It is estimated that 70% of individuals with LFS and 8% to 22% of individuals with LFL have detectable TP53 mutations.34,35 The fre- quency of de novo mutations in LFS ranges between 7% and 20%.3º It is not too surprising that the inherited TP53 mutations associated with LFS are local- ized to the same hot spot sites found in sporadic tumors. One of the most com- monly inherited TP53 mutations is Arg175His. This mutant fails to fold properly, bind DNA, activate transcrip- tion, or suppress cell growth. Carriers of this mutation, which is considered to be highly penetrant, are at greater risk for cancer at early ages.1
Pediatric Cancers Associated with TP53 Mutations
Compared with the cancer incidence in adults, pediatric tumors are rare, accounting for only 3.0% of all cases in the United States. However, cancer is the primary cause of disease-related deaths in children.36 Childhood tumors comprise a variety of malignancies with incidences varying worldwide by age, sex, ethnicity, and geography, and these factors can provide important insights into cancer etiology.3
Pediatric ACT is rare and occurs at an estimated incidence of 0.3 per million in individuals younger than 15 years.1 ACT is associated with isolated hemi- hypertrophy or Beckwith-Wiedemann syndrome38 and rarely occurs in children with multiple endocrine neoplasia type 1.39 However, pediatric ACT may also be
c.151_156 del CCGCCCGGCACCC
IVS4+1G>A
c.134_135 insT
c.108_110 dupl GTTTCCG
IVS10-2A>G
c51_53 del CAAT ins GACCTG
R196X
1
4
5
6
7
R
10
11
G245C
R248W
R213Q
| V157F | G266E | 1332F | |
|---|---|---|---|
| R158L | R273C | G334R | |
| R175L | R282W | R337C | |
| R175H | R283H | R337H | |
| E285V | |||
Figure 1. TP53 mutations in childhood adrenocortical tumors. Blood and tumor samples were banked through the St. Jude Children’s Research Hospital International Pediatric Adrenocortical Tumor Registry (institutional review board approved). In a cohort of 48 patients with adrenocortical tumors, 36 TP53 mutations were detected (75%) within and outside the DNA binding domain. Three mutations were detected in multiple cases (Arg175His, Arg273Cys, and Arg337His). Most mutations represent single-nucleotide substitutions (red), although non-sense and complex mutations were also observed (black). The schematic outlines the coding region of TP53 spanning exons 1 to 11 (colors represent functional domains).
the first indication of a germline TP53 mutation and LFS within a family.28 Sporadic cases of ACT have also been noted,40 and approximately 80% have atypical germline mutations of TP53 associated with a lower but increased cancer risk in relatives. 14,41
Affected children with ACT typically present with symptoms related to exces- sive production of adrenal cortex steroids, and virilization and Cushing syndrome are the most common endocrine manifesta- tions. Disease stage, which includes tumor size, is the most important predictor of outcome. Patients who have residual dis- ease after incomplete tumor resection or metastatic disease have a dismal prognosis.42
Tumor Registry
We have established an International Pediatric Adrenocortical Tumor Regis- try (IPACTR) at St. Jude Children’s Research Hospital, which collects clini- cal information and biological speci- mens, including blood and tumor. Our data (manuscript in preparation) show
that approximately 75% of ACTs are positive for TP53 mutations (8% somatic and 92% germline). In our cohort of 48 ACTs, we detected 23 independent TP53 mutations within and outside the DBD, and of these, only 3 were detected more than once (Arg175His, Arg273Cys, and Arg337His; Figure 1). In our cohort, we also identified a novel germline variant, Arg175Leu.43 Surprisingly, the family is not tumor prone or associated with LFS. In vitro, the Arg175Leu mutant dis- played intermediate tumor suppressor activity in the regulation of transcrip- tion, colony formation, and apoptosis when compared to wild-type and hot spot mutant Arg175His. These findings sug- gest that Arg175Leu retains sufficient activity to suppress LFS but not ACT. Therefore, not all TP53 mutations are functionally equivalent, and the biochem- ical nature of the mutant may signifi- cantly influence clinical outcome.11,43
Pediatric ACT is frequently associ- ated with LFS families carrying high- penetrance TP53 mutations. However, there is growing evidence that low- penetrance TP53 mutations, such as the
M
| Cases | ||
|---|---|---|
| Number | % | |
| Sex | ||
| Female | 53 | 67.1 |
| Male | 26 | 32.9 |
| Age at diagnosis, y | ||
| 0-4 | 36 | 46.6 |
| 5-9 | 14 | 17.7 |
| 10-14 | 11 | 14.0 |
| 15-19 | 18 | 22.7 |
| Disease stage | ||
| Local | 37 | 34.2 |
| Regional | 10 | 46.8 |
| Distant metastasis | 27 | 12.7 |
| Unknown | 5 | 6.3 |
one found in southern Brazil, increases the predisposition for childhood ACT but not that of other Li-Fraumeni core component tumors.44 On the basis of these observations, we propose that the adrenal cortex is particularly vulnerable to TP53 loss of function.
According to the National Cancer Institute (Surveillance Epidemiology and End Results [SEER]), 79 cases of pediatric ACT were reported from 17 geographic areas in the United States during a 34-year period (1973-2007) (Table 1). Remarkably, the number of cases in the SEER database represents approximately 60% of the cases treated at a single institution in southern Brazil (n = 124; Hospital das Clínicas de Curi- tiba) during a similar time period (1966- 2003) and time span (37 years).45
The predisposition for childhood ACT in southern Brazil is associated with the germline TP53-Arg337His mutation.13,14 This mutation lies within the p53 tetramerization domain (amino acids 336-353). Specifically, arginine-337 of one subunit forms a salt bridge with aspartate-352 in the corre- sponding monomer to stabilize the com- plex. Structural studies have shown that the Arg337His mutant is unstable and
does not efficiently dimerize at physio- logic pH in vitro14,46 but was found to dis- play wild-type p53 activity when ectopically expressed in fibroblasts and osteosarcoma cells.14 These observations could explain the lack of association of Arg337His with LFS. In contrast, the substitution of cysteine at codon 337 has a very different biochemical and clinical outcome.47 The Arg337Cys mutant improperly folds irrespective of pH and exhibits only partial biological activi- ties.48 Consistent with this significant loss of functional activity, carriers of a germ- line Arg337Cys mutation are susceptible to multiple tumor types, including breast carcinoma.47 Therefore, Arg337His in most cases has a markedly less severe impact on tumor predisposition than Arg337Cys, and this difference correlates with the relative degree of activity that can be measured in the laboratory.” These observations support the concept that single-site mutations, depending on the amino acid substitution, have differ- ent consequences on the structure, func- tion, and degree of activity that, in turn, affects tumor susceptibility.”
The TP53-Arg337His mutation is the most common germline mutation reported in the International Agency for Research on Cancer (IARC) database (http://www .iarc.fr/). Although Arg337His was ini- tially observed in pediatric ACT,14 detailed studies of families with this mutation also revealed an association with choroid plexus carcinoma in children49 and breast and stomach tumors in young adults.50 The Arg337His mutation was also observed in 7% of pediatric osteosarco- mas in southern Brazil.49,51 This frequency is much higher than that reported for the general population of the region (0.3%) and is greater than that reported for non- selected North American patients with osteosarcoma who had any constitu- tional TP53 mutation (3%).52 These findings implicate genetic background and cooperating factors that could influ- ence tumor susceptibility in the presence of Arg337His.
Although it is recognized that indi- viduals with certain TP53 mutations
(i.e., Arg175His) are at high risk for can- cer at early ages and multiple tumors, this is not the case for Arg337His. In fact, many carriers remain asymptom- atic.14,53 The incomplete penetrance of Arg337His in pediatric ACT (2%-10% of carriers develop disease) may be related to its inability to act as a domi- nant negative regulator of wild-type p53. This is consistent with nearly 100% of the ACT cases undergoing LOH by eliminating the wild-type p53 allele. 14,49,54
Molecular studies identify the same haplotype for the TP53 locus in individ- uals carrying the Arg337His mutation, indicating a common origin for this mutation (founder effect).55 The major- ity of the population in the southern region of Brazil is of European extrac- tion (Portuguese, Italians, Spanish, and Germans) with native Brazilian Indian and African influence.56 The high inci- dence of ACT in patients from this region is therefore explained by the presence of the germline Arg337His mutation, which was likely inherited from a common founder.55 Nevertheless, Arg337His has been detected in isolated ACT cases outside of Brazil but not yet as a common TP53 mutation in other populations.
Cooperating Factors in Pediatric ACT
Additional factors that have been impli- cated in ACT include defects in imprint- ing and overexpression of insulin-like growth factor-2 (IGF-2). Gene expres- sion profiling of sporadic human ACT revealed dysregulation of the 11p15.5 region, and several studies have shown IGF-2 to be the single most up-regulated transcript in 80% to 90% of ACTs. IGF-2 mainly elicits its cellular effects through the ubiquitously expressed type 1 IGF receptor (IGF-1R). Interestingly, during organ development in the human fetus, the adrenal gland has one of the highest levels of IGF-2 expression, which subsequently declines after birth.60 These observations suggest that
M
activation of the IGF pathway is a common pathological mechanism used by tumor cells during adrenocortical tumorigenesis.
Using comparative genomic hybrid- ization, it has been shown that childhood ACTs are characterized by a high fre- quency of chromosomal aberrations, especially involving amplification of 9q33-q34.61 This chromosomal region harbors the human steroidogenic factor 1 (SF-1) gene, and an increased SF-1 copy number was detected in 8 of 9 Brazilian pediatric ACTs using fluorescence in situ hybridization, suggesting an association between SF-1 gene amplification and childhood adrenocortical tumorigene- sis.62 Consistent with these findings, each case of ACT overexpressed SF-1 pro- tein.63 SF-1 is an orphan member of the nuclear receptor family of transcription factors and plays an important role in endocrine function, including the regula- tion of steroid hydroxylases, develop- ment and function of the adrenal cortex, and male sexual differentiation.64 Fur- thermore, increased SF-1 dosage pro- motes cell proliferation and triggers tumorigenesis in mice.65 Based on these observations, SF1 functions as an onco- gene that contributes to the development of ACT.
Inhibin-a (Inha) was found to be an important determinant of cortical adre- nal tumor development in mice.66 Molecular analysis of Brazilian child- hood ACTs identified mutations in INHIBIN-a. (INHA), and LOH was observed in 8 of 9 tumors, suggesting INHA functions as a tumor suppressor of ACT in carriers of the Arg337His TP53 mutation.67 Therefore, in keeping with a multihit model for tumorigenesis, the incomplete penetrance of ACT in carri- ers of the Arg337His mutation may be explained by the apparent requirement for loss of relevant tumor suppressors (e.g., INHA) and activation of cooperat- ing oncogenes (e.g., SF1 and IGF2).
Concluding Remarks
It is becoming clear that most human cancers have acquired defects within the
p53 tumor suppressor signaling path- way, either by TP53 mutation or by deregulation of upstream regulators or downstream effectors. Our clinical and molecular studies of pediatric ACT have advanced our understanding of the basic biology of p53 in these tumors. We have uncovered important genotype- phenotype relationships between the biochemical consequence of germline TP53 mutations on p53 function and their association with inherent cancer risk. These findings have important implications for genetic counseling and clinical management. By focusing on a rare childhood cancer, such as ACT, it is possible to learn not only a great deal regarding how p53 functions as a tumor suppressor but also about the disease itself and ultimately how to improve long-term outcome.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of inter- est with respect to the research, authorship, and/or publication of this article.
Funding
This work was supported in part by grant CA-21765 from the National Institutes of Health (U.S. Department of Health and Human Services), by a Center of Excellence grant from the State of Tennessee, and by the American Lebanese Syrian Associated Charities (ALSAC).
References
1. Altekruse SF, Kosary CL, Krapcho M, et al., editors. SEER Cancer Statistics Review, 1975- 2007, based on November 2009 SEER data submis- sion, posted to the SEER web site, 2010. Bethesda, MD: National Cancer Institute. http://seer.cancer .gov/csr/1975_2007/
2. Strong LC, Williams WR, Tainsky MA. The Li-Fraumeni syndrome: from clinical epidemi- ology to molecular genetics. Am J Epidemiol. 1992;135:190-9.
3. Birch JM, Blair V, Kelsey AM, et al. Cancer phe- notype correlates with constitutional TP53 geno- type in families with the Li-Fraumeni syndrome. Oncogene. 1998;17:1061-8.
4. Bennett WP, Hussain SP, Vahakangas KH, Khan MA, Shields PG, Harris CC. Molecular epidemi- ology of human cancer risk: gene-environment interactions and p53 mutation spectrum in human lung cancer. J Pathol. 1999;187:8-18.
5. Vousden KH, Lane DP. p53 in health and disease. Nat Rev Mol Cell Biol. 2007;8:275-83.
6. Brosh R, Rotter V. When mutants gain new pow- ers: news from the mutant p53 field. Nat Rev Cancer. 2009;9:701-13.
7. Oren M. Decision making by p53: life, death and cancer. Cell Death Differ. 2003;10:431-42.
8. Vousden KH, Lu X. Live or let die: the cell’s response to p53. Nat Rev Cancer. 2002;2:594- 604.
9. Weisz L, Oren M, Rotter V. Transcription regula- tion by mutant p53. Oncogene. 2007;26:2202-11.
10. Yan W, Chen X. Characterization of functional domains necessary for mutant p53 gain of func- tion. J Biol Chem. 2010;285:14229-38.
11. Zambetti GP. The p53 mutation “gradient effect” and its clinical implications. J Cell Physiol. 2007;213:370-3.
12. Petitjean A, Mathe E, Kato S, et al. Impact of mutant p53 functional properties on TP53 muta- tion patterns and tumor phenotype: lessons from recent developments in the IARC TP53 database. Hum Mutat. 2007;28:622-9.
13. Latronico AC, Pinto EM, Domenice S, et al. An inherited mutation outside the highly conserved DNA-binding domain of the p53 tumor suppres- sor protein in children and adults with sporadic adrenocortical tumors. J Clin Endocrinol Metab. 2001;86:4970-3.
14. Ribeiro RC, Sandrini F, Figueiredo B, et al. An inherited p53 mutation that contributes in a tissue-specific manner to pediatric adrenal cortical carcinoma. Proc Natl Acad Sci U S A. 2001;98:9330-5.
15. Pinto EM, Ribeiro RC, Kletter GB, et al. Inher- ited germline TP53 mutation encodes a protein with an aberrant C-terminal motif in a case of pediatric adrenocortical tumor. Fam Cancer. 2011;10:141-6.
16. Milner J, Medcalf EA. Cotranslation of activated mutant p53 with wild type drives the wild-type p53 protein into the mutant conformation. Cell. 1991;65:765-74.
17. de Vries A, Flores ER, Miranda B, et al. Targeted point mutations of p53 lead to dominant-negative inhibition of wild-type p53 function. Proc Natl Acad Sci U S A. 2002;99:2948-53.
18. Russell-Swetek A, West AN, Mintern JE, et al. Identification of a novel TP53 germline mutation E285V in a rare case of paediatric adrenocortical carcinoma and choroid plexus carcinoma. J Med Genet. 2008;45:603-6.
19. Liu G, McDonnell TJ, Montes de Oca Luna R, et al. High metastatic potential in mice inheriting a targeted p53 missense mutation. Proc Natl Acad Sci U S A. 2000;97:4174-9.
20. Momand J, Zambetti GP, Olson DC, George D, Levine AJ. The mdm-2 oncogene product forms a complex with the p53 protein and inhibits p53- mediated transactivation. Cell. 1992;69:1237-45.
21. Haupt Y, Maya R, Kazaz A, Oren M. Mdm2 promotes the rapid degradation of p53. Nature. 1997;387:296-9.
22. Wade M, Wahl GM. Targeting Mdm2 and Mdmx in cancer therapy: better living through medicinal chemistry? Mol Cancer Res. 2009;7:1-11.
23. Bond GL, Hu W, Bond EE, et al. A single nucle- otide polymorphism in the MDM2 promoter attenuates the p53 tumor suppressor pathway and accelerates tumor formation in humans. Cell. 2004;119:591-602.
24. Bougeard G, Baert-Desurmont S, Tournier I, et al. Impact of the MDM2 SNP309 and p53 Arg72Pro polymorphism on age of tumour onset in Li- Fraumeni syndrome. J Med Genet. 2006;43:531-3.
M
25. Shvarts A, Steegenga WT, Riteco N, et al. MDMX: a novel p53-binding protein with some functional properties of MDM2. EMBO J. 1996;15:5349-57.
26. Reed D, Shen Y, Shelat AA, et al. Identifica- tion and characterization of the first small molecule inhibitor of MDMX. J Biol Chem. 2010;285:10786-96.
27. Laurie NA, Donovan SL, Shih CS, et al. Inac- tivation of the p53 pathway in retinoblastoma. Nature. 2006; 444:61-6.
28. Li FP, Fraumeni JF Jr, Mulvihill JJ, et al. A can- cer family syndrome in twenty-four kindreds. Cancer Res. 1998;48:5358-62.
29. Lustbader ED, Williams WR, Bondy ML, Strom S, Strong LC. Segregation analysis of cancer in families of childhood soft-tissue-sarcoma patients. Am J Hum Genet. 1992;51:344-56.
30. Gonzalez KD, Noltner KA, Buzin CH, et al. Beyond Li Fraumeni syndrome: clinical charac- teristics of families with p53 germline mutations. J Clin Oncol. 2009;27:1250-6.
31. Olivier M, Goldgar DE, Sodha N, et al. Li-Frau- meni and related syndromes: correlation between tumor type, family structure, and TP53 genotype. Cancer Res. 2003;63:6643-50.
32. Birch JM. Familial cancer syndromes and clus- ters. Br Med Bull. 1994;50:624-39.
33. Chompret A, Abel A, Stoppa-Lyonnet D, et al. Sensitivity and predictive value of criteria for p53 germline mutation screening. J Med Genet. 2001;38:43-7.
34. Birch JM, Hartley AL, Tricker KJ, et al. Preva- lence and diversity of constitutional mutations in the p53 gene among 21 Li-Fraumeni families. Cancer Res. 1994;54:1298-304.
35. Varley JM. Germline TP53 mutations and Li- Fraumeni syndrome. Hum Mutat. 2003;21:313-20.
36. Jemal A, Murray T, Samuels A, Ghafoor A, Ward E, Thun MJ. 2003 Cancer statistics, 2003. CA Cancer J Clin. 2003;53:5-26.
37. Munir CS, Nectoux J. International patterns of cancer. In: Schottenfeld D, Fraumeni JF Jr, edi- tors. Cancer epidemiology and prevention. 2nd ed. New York: Oxford University Press; 1996. p. 141-67.
38. Teinturier C, Pauchard MS, Brugieres L, Landais P, Chaussain JL, Bougneres PF. Clinical and prog- nostic aspects of adrenocortical neoplasms in child- hood. Med Pediatr Oncol. 1999;32:106-11.
39. Langer P, Cupisti K, Bartsch DK, et al. Adrenal involvement in multiple endocrine neoplasia type 1. World J Surg. 2002;26:891-6.
40. Rosati R, Cerrato F, Doghman M, et al. High frequency of loss of heterozygosity at 11p15 and IGF2 overexpression are not related to clini- cal outcome in childhood adrenocortical tumors positive for the R337H TP53 mutation. Cancer Genet Cytogenet. 2008;186:19-24.
41. Wagner J, Portwine C, Rabin K, Leclerc JM, Narod SA, Malkin D. High frequency of germ- line p53 mutations in childhood adrenocortical cancer. J Natl Cancer Inst. 1994;86:1707-10.
42. Michalkiewicz E, Sandrini R, Figueiredo B, et al. Clinical and outcome characteristics of chil- dren with adrenocortical tumors: a report from the International Pediatric Adrenocortical Tumor Registry. J Clin Oncol. 2004;22:838-45.
43. West AN, Ribeiro RC, Jenkins J, et al. Identifica- tion of a novel germ line variant hotspot mutant p53-R175L in pediatric adrenal cortical carci- noma. Cancer Res. 2006;66:5056-62.
44. Varley JM, McGown G, Thorncroft M, et al. Are there low-penetrance TP53 alleles? Evidence from childhood adrenocortical tumors. Am J Hum Genet. 1999;65:995-1006.
45. Pianovski MA, Maluf EM, de Carvalho DS, et al. Mortality rate of adrenocortical tumors in chil- dren under 15 years of age in Curitiba, Brazil. Pediatr Blood Cancer. 2006;47:56-60.
46. DiGiammarino EL, Lee AS, Cadwell C, et al. A novel mechanism of tumorigenesis involving pH-dependent destabilization of a mutant p53 tetramer. Nat Struct Biol. 2002;9:12-6.
47. Lomax ME, Barnes DM, Hupp TR, Picksley SM, Camplejohn RS. Characterization of p53 oligo- merization domain mutations isolated from Li- Fraumeni and Li-Fraumeni like family members. Oncogene. 1998;17:643-9.
48. Davison TS, Yin P, Nie E, Kay C, Arrowsmith CH. Characterization of the oligomerization defects of two p53 mutants found in families with Li-Fraumeni and Li-Fraumeni-like syndrome. Oncogene. 1998;7:651-6.
49. Seidinger AL, Mastellaro MJ, Fortes FP, et al. Association of the highly prevalent TP53 R337H mutation with pediatric choroid plexus carci- noma and osteosarcoma in southeast Brazil. Cancer. 2010 Dec 29. [Epub ahead of print]
50. Assumpcao JG, Seidinger AL, Mastellaro MJ, et al. Association of the germline TP53 R337H mutation with breast cancer in southern Brazil. BMC Cancer. 2008;8:357.
51. Oliveira CR, Mendonca BB, Camargo OP, et al. Classical osteoblastoma, atypical osteoblastoma, and osteosarcoma: a comparative study based on clinical, histological, and biological parameters. Clinics (Sao Paulo). 2007;62:167-74.
52. McIntyre JF, Smith-Sorensen B, Friend SH, et al. Germline mutations of the p53 tumor suppres- sor gene in children with osteosarcoma. J Clin Oncol. 1994;12:925-30.
53. Figueiredo BC, Sandrini R, Zambetti GP, et al. Penetrance of adrenocortical tumours associated with the germline TP53 R337H mutation. J Med Genet. 2006;43:91-6.
54. Pinto EM, Billerbeck AE, Fragoso MC, Men- donca BB, Latronico AC. Deletion mapping of
chromosome 17 in benign and malignant adre- nocortical tumors associated with the Arg337His mutation of the p53 tumor suppressor protein. J Clin Endocrinol Metab. 2005;90:2976-81.
55. Pinto EM, Billerbeck AE, Villares MC, Domenice S, Mendonca BB, Latronico AC. Founder effect for the highly prevalent R337H mutation of tumor suppressor p53 in Brazilian patients with adrenocortical tumors. Arq Bras Endocrinol Metabol. 2004;48:647-50.
56. Parra FC, Amado RC, Lambertucci JR, Rocha J, Antunes CM, Pena SD. Color and genomic ancestry in Brazilians. Proc Natl Acad Sci U S A. 2003;100:177-82.
57. Giordano TJ, Thomas DG, Kuick R, et al. Dis- tinct transcriptional profiles of adrenocortical tumors uncovered by DNA microarray analysis. Am J Pathol. 2003;162:521-31.
58. Velazquez-Fernandez D, Laurell C, Geli J, et al. Expression profiling of adrenocortical neoplasms suggests a molecular signature of malignancy. Surgery. 2005;138:1087-94.
59. West AN, Neale GA, Pounds S, et al. Gene expression profiling of childhood adrenocortical tumors. Cancer Res. 2007;67:600-8.
60. Han VK, Lund PK, Lee DC, D’Ercole AJ. Expression of somatomedin/insulin-like growth factor messenger ribonucleic acids in the human fetus: identification, characterization, and tissue distribution. J Clin Endocrinol Metab. 1998;66: 422-9.
61. Figueiredo BC, Stratakis CA, Sandrini R, et al. Comparative genomic hybridization analysis of adrenocortical tumors of childhood. J Clin Endo- crinol Metab. 1999;84:1116-21.
62. Figueiredo BC, Cavalli LR, Pianovski MA, et al. Amplification of the steroidogenic factor 1 gene in childhood adrenocortical tumors. J Clin Endo- crinol Metab. 2005;90:615-9.
63. Pianovski MA, Cavalli LR, Figueiredo BC, et al. SF-1 overexpression in childhood adrenocortical tumours. Eur J Cancer. 2006;42:1040-3.
64. Parker KL, Schimmer BP. Steroidogenic factor 1: a key determinant of endocrine development and function. Endocr Rev. 1997;18:361-77.
65. Doghman M, Karpova T, Rodrigues GA, et al. Increased steroidogenic factor-1 dosage triggers adrenocortical cell proliferation and cancer. Mol Endocrinol. 2007;21:2968-87.
66. Matzuk MM, Finegold MJ, Mather JP, Krummen L, Lu H, Bradley A. Development of cancer cachexia-like syndrome and adrenal tumors in inhibin-deficient mice. Proc Natl Acad Sci U S A. 1994;91:8817-21.
67. Longui CA, Lemos-Marini SH, Figueiredo B, et al. Inhibin alpha-subunit (INHA) gene and locus changes in paediatric adrenocortical tumours from TP53 R337H mutation heterozy- gote carriers. J Med Genet. 2004;41:354-9.