TP53BP2

Gene Summary

Gene:TP53BP2; tumor protein p53 binding protein 2
Aliases: BBP, 53BP2, ASPP2, P53BP2, PPP1R13A
Location:1q41
Summary:This gene encodes a member of the ASPP (apoptosis-stimulating protein of p53) family of p53 interacting proteins. The protein contains four ankyrin repeats and an SH3 domain involved in protein-protein interactions. It is localized to the perinuclear region of the cytoplasm, and regulates apoptosis and cell growth through interactions with other regulatory molecules including members of the p53 family. Multiple transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Jul 2008]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:apoptosis-stimulating of p53 protein 2
HPRD
Source:NCBIAccessed: 17 August, 2015

Ontology:

What does this gene/protein do?
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Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 17 August 2015 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 17 August, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (3)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: TP53BP2 (cancer-related)

Wang Y, Bu F, Royer C, et al.
ASPP2 controls epithelial plasticity and inhibits metastasis through β-catenin-dependent regulation of ZEB1.
Nat Cell Biol. 2014; 16(11):1092-104 [PubMed] Related Publications
Epithelial to mesenchymal transition (EMT), and the reverse mesenchymal to epithelial transition (MET), are known examples of epithelial plasticity that are important in kidney development and cancer metastasis. Here we identify ASPP2, a haploinsufficient tumour suppressor, p53 activator and PAR3 binding partner, as a molecular switch of MET and EMT. ASPP2 contributes to MET in mouse kidney in vivo. Mechanistically, ASPP2 induces MET through its PAR3-binding amino-terminus, independently of p53 binding. ASPP2 prevents β-catenin from transactivating ZEB1, directly by forming an ASPP2-β-catenin-E-cadherin ternary complex and indirectly by inhibiting β-catenin's N-terminal phosphorylation to stabilize the β-catenin-E-cadherin complex. ASPP2 limits the pro-invasive property of oncogenic RAS and inhibits tumour metastasis in vivo. Reduced ASPP2 expression results in EMT, and is associated with poor survival in hepatocellular carcinoma and breast cancer patients. Hence, ASPP2 is a key regulator of epithelial plasticity that connects cell polarity to the suppression of WNT signalling, EMT and tumour metastasis.

Liu K, Shi Y, Guo X, et al.
CHOP mediates ASPP2-induced autophagic apoptosis in hepatoma cells by releasing Beclin-1 from Bcl-2 and inducing nuclear translocation of Bcl-2.
Cell Death Dis. 2014; 5:e1323 [PubMed] Free Access to Full Article Related Publications
Apoptosis-stimulating protein of p53-2 (ASPP2) induces apoptosis by promoting the expression of pro-apoptotic genes via binding to p53 or p73; however, the exact mechanisms by which ASPP2 induces apoptotic death in hepatoma cells are still unclear. Here, we show that the transient overexpression of ASPP2 induces autophagic apoptosis in hepatoma cells by promoting p53- or p73-independent C/EBP homologous protein (CHOP) expression. CHOP expression decreases the expression of Bcl-2; this change releases Beclin-1 from cytoplasmic Bcl-2-Beclin-1 complexes and allows it to initiate autophagy. However, transient overexpression of Beclin-1 can induce autophagy but not apoptosis. Our results show that ASPP2 induces the expression of damage-regulated autophagy modulator (DRAM), another critical factor that cooperates with free Beclin-1 to induce autophagic apoptosis. The effect of CHOP on the translocation and sequestration of Bcl-2 in the nucleus, which requires the binding of Bcl-2 to ASPP2, is also critical for ASPP2-induced autophagic apoptosis. Although the role of nuclear ASPP2-Bcl-2 complexes is still unclear, our results suggest that nuclear ASPP2 can prevent the translocation of the remaining Bcl-2 to the cytoplasm by binding to Bcl-2 in a CHOP-dependent manner, and this effect also contributes to Beclin-1-initiated autophagy. Thus, CHOP is critical for mediating ASPP2-induced autophagic apoptosis by decreasing Bcl-2 expression and maintaining nuclear ASPP2-Bcl-2 complexes. Our results, which define a mechanism whereby ASPP2 overexpression induces autophagic apoptosis, open a new avenue for promoting autophagy in treatments to cure hepatocellular carcinoma.

Turnquist C, Wang Y, Severson DT, et al.
STAT1-induced ASPP2 transcription identifies a link between neuroinflammation, cell polarity, and tumor suppression.
Proc Natl Acad Sci U S A. 2014; 111(27):9834-9 [PubMed] Free Access to Full Article Related Publications
Inflammation and loss of cell polarity play pivotal roles in neurodegeneration and cancer. A central question in both diseases is how the loss of cell polarity is sensed by cell death machinery. Here, we identify apoptosis-stimulating protein of p53 with signature sequences of ankyrin repeat-, SH3 domain-, and proline-rich region-containing protein 2 (ASPP2), a haploinsufficient tumor suppressor, activator of p53, and regulator of cell polarity, as a transcriptional target of signal transducer and activator of transcription 1 (STAT1). LPS induces ASPP2 expression in murine macrophage and microglial cell lines, a human monocyte cell line, and primary human astrocytes in vitro. LPS and IFNs induce ASPP2 transcription through an NF-κB RELA/p65-independent but STAT1-dependent pathway. In an LPS-induced maternal inflammation mouse model, LPS induces nuclear ASPP2 in vivo at the blood-cerebral spinal fluid barrier (the brain's barrier to inflammation), and ASPP2 mediates LPS-induced apoptosis. Consistent with the role of ASPP2 as a gatekeeper to inflammation, ASPP2-deficient brains possess enhanced neuroinflammation. Elevated ASPP2 expression is also observed in mouse models and human neuroinflammatory disease tissue, where ASPP2 was detected in GFAP-expressing reactive astrocytes that coexpress STAT1. Because the ability of ASPP2 to maintain cellular polarity is vital to CNS development, our findings suggest that the identified STAT1/ASPP2 pathway may connect tumor suppression and cell polarity to neuroinflammation.

Pei N, Jie F, Luo J, et al.
Gene expression profiling associated with angiotensin II type 2 receptor-induced apoptosis in human prostate cancer cells.
PLoS One. 2014; 9(3):e92253 [PubMed] Free Access to Full Article Related Publications
Increased expression of angiotensin II type 2 receptor (AT2R) induces apoptosis in numerous tumor cell lines, with either Angiotensin II-dependent or Angiotensin II-independent regulation, but its molecular mechanism remains poorly understood. Here, we used PCR Array analysis to determine the gene and microRNA expression profiles in human prostate cancer cell lines transduced with AT2R recombinant adenovirus. Our results demonstrated that AT2R over expression leads to up-regulation of 6 apoptosis-related genes (TRAIL-R2, BAG3, BNIPI, HRK, Gadd45a, TP53BP2), 2 cytokine genes (IL6 and IL8) and 1 microRNA, and down-regulation of 1 apoptosis-related gene TNFSF10 and 2 cytokine genes (BMP6, BMP7) in transduced DU145 cells. HRK was identified as an up-regulated gene in AT2R-transduced PC-3 cells by real-time RT-PCR. Next, we utilized siRNAs to silence the up-regulated genes to further determine their roles on AT2R overexpression mediated apoptosis. The results showed downregulation of Gadd45a reduced the apoptotic effect by ∼30% in DU145 cells, downregulation of HRK reduced AT2R-mediated apoptosis by more than 50% in PC-3 cells, while downregulation of TRAIL-R2 enhanced AT2R-mediated apoptosis more than 4 times in DU145 cells. We also found that the effects on AT2R-mediated apoptosis caused by downregulation of Gadd45a, TRAIL-R2 and HRK were independent in activation of p38 MAPK, p44/42 MAPK and p53. Taken together, our results demonstrated that TRAIL-R2, Gadd45a and HRK may be novel target genes for further study of the mechanism of AT2R-mediated apoptosis in prostate cancer cells.

Schittenhelm MM, Illing B, Ahmut F, et al.
Attenuated expression of apoptosis stimulating protein of p53-2 (ASPP2) in human acute leukemia is associated with therapy failure.
PLoS One. 2013; 8(11):e80193 [PubMed] Free Access to Full Article Related Publications
Inactivation of the p53 pathway is a universal event in human cancers and promotes tumorigenesis and resistance to chemotherapy. Inactivating p53 mutations are uncommon in non-complex karyotype leukemias, thus the p53-pathway must be inactivated by other mechanisms. The Apoptosis Stimulating Protein of p53-2 (ASPP2) is a damage-inducible p53-binding protein that enhances apoptosis at least in part through a p53-mediated pathway. We have previously shown, that ASPP2 is an independent haploinsufficient tumor suppressor in vivo. Now, we reveal that ASPP2 expression is significantly attenuated in acute myeloid and lymphoid leukemia - especially in patients with an unfavorable prognostic risk profile and patients who fail induction chemotherapy. In line, knock down of ASPP2 in expressing leukemia cell lines and native leukemic blasts attenuates damage-induced apoptosis. Furthermore, cultured blasts derived from high-risk leukemias fail to induce ASPP2 expression upon anthracycline treatment. The mechanisms of ASPP2 dysregulation are unknown. We provide evidence that attenuation of ASPP2 is caused by hypermethylation of the promoter and 5'UTR regions in native leukemia blasts. Together, our results suggest that ASPP2 contributes to the biology of leukemia and expression should be further explored as a potential prognostic and/or predictive biomarker to monitor therapy responses in acute leukemia.

Tordella L, Koch S, Salter V, et al.
ASPP2 suppresses squamous cell carcinoma via RelA/p65-mediated repression of p63.
Proc Natl Acad Sci U S A. 2013; 110(44):17969-74 [PubMed] Free Access to Full Article Related Publications
Squamous cell carcinoma (SCC) is highly malignant and refractory to therapy. The majority of existing mouse SCC models involve multiple gene mutations. Very few mouse models of spontaneous SCC have been generated by a single gene deletion. Here we report a haploinsufficient SCC mouse model in which exon 3 of the Tp53BP2 gene (a p53 binding protein) was deleted in one allele in a BALB/c genetic background. Tp53BP2 encodes ASPP2 (ankyrin repeats, SH3 domain and protein rich region containing protein 2). Keratinocyte differentiation induces ASPP2 and its expression is inversely correlated with p63 protein in vitro and in vivo. Up-regulation of p63 expression is required for ASPP2(Δexon3/+) BALB/c mice to develop SCC, as heterozygosity of p63 but not p53 prevents them from developing it. Mechanistically, ASPP2 inhibits ΔNp63 expression through its ability to bind IκB and enhance nuclear Rel/A p65, a component of the NF-κB transcription complex, which mediates the repression of p63. Reduced ASPP2 expression associates with tumor metastasis and increased p63 expression in human head and neck SCCs. This study identifies ASPP2 as a tumor suppressor that suppresses SCC via inflammatory signaling through NF-κB-mediated repression of p63.

Mak VC, Lee L, Siu MK, et al.
Downregulation of ASPP2 in choriocarcinoma contributes to increased migratory potential through Src signaling pathway activation.
Carcinogenesis. 2013; 34(9):2170-7 [PubMed] Related Publications
Gestational choriocarcinoma is a malignant tumor derived from placental trophoblast and the most aggressive member of gestational trophoblastic disease (GTD). Apoptosis-stimulating protein of p53-2 (ASPP2) is a member of ASPP family that transactivates p53 and thereby functions as a tumor suppressor. In this study, the expression profile of ASPP2 in choriocarcinoma was examined in comparison with normal placentas and hydatidiform moles, the latter being a type of GTD that carries malignant potential. Downregulation of ASPP2 messenger RNA and protein was demonstrated in choriocarcinoma by quantitative PCR and immunohistochemistry. ASPP2-transfected choriocarcinoma cells (JEG-3 and JAR) showed an increase in apoptosis and a decrease in cell migration as detected by TdT-mediated dUTP nick end labeling and wound healing assays, respectively, illustrating the complex action of ASPP2 on cell functions other than programmed cell death. Activated Src is known to be important in tumor progression. Transfection of ASPP2 but not ASPP1, another tumor-suppressive ASPP, was found to be related to subsequent decreased Src-pY416 phosphorylation, suggesting an inactivating effect of ASPP2 on Src. Moreover, this ASPP2-mediated inactivation of Src could be abolished by RNA interference with C-terminal Src kinase (Csk), a kinase that can inhibit Src activation. Our findings suggested that the ability of ASPP2 to attenuate Src activation was specific to ASPP2 in a Csk-dependent manner. Taken together, we demonstrated a loss of tumor-suppressive ASPP2 in choriocarcinoma with effects on cell migration and apoptosis. We also unveiled a possible mechanistic link between ASPP2 and Csk/Src signaling pathway, implicating the multiple cellular functions of ASPP2.

Alreshidi MA, Alsalamah AA, Hamat RA, et al.
Genetic variation among methicillin-resistant Staphylococcus aureus isolates from cancer patients in Saudi Arabia.
Eur J Clin Microbiol Infect Dis. 2013; 32(6):755-61 [PubMed] Related Publications
One hundred and twenty methicillin-resistant Staphylococcus aureus (MRSA) isolated from cancer and non-cancer patients in Saudi Arabia were investigated for antibiotic resistance, virulence determinants and genotypes. The majority of MRSA isolates from cancer (n = 44, 73.3 %) and non-cancer patients (n = 34, 56.7 %) were multi-resistant to more than four classes of antibiotics. Virulence gene profiling showed that all strains were commonly positive for adhesin genes, except ebps and bbp genes, which were not detected in any isolate. Although the presence of adhesin genes varied slightly among MRSA isolates from cancer and non-cancer patients, these variations were not found to be statistically significant. In contrast, the presence of the toxin genes seb, sec, seg and sei was significantly elevated in MRSA strains isolated from cancer patients. Multilocus sequence typing (MLST) detected six and nine sequence types (STs) among isolates from cancer and non-cancer patients, respectively. Using spa typing, 12 and 25 types were detected, including four new types. The ability of different MRSA clones to become multi-resistant and their ability to acquire different virulence factors may contribute to their success as pathogens in individual groups of patients.

Hsieh TH, Tsai CF, Hsu CY, et al.
n-Butyl benzyl phthalate promotes breast cancer progression by inducing expression of lymphoid enhancer factor 1.
PLoS One. 2012; 7(8):e42750 [PubMed] Free Access to Full Article Related Publications
Environmental hormones play important roles in regulating the expression of genes involved in cell proliferation, drug resistance, and breast cancer risk; however, their precise role in human breast cancer cells during cancer progression remains unclear. To elucidate the effect of the most widely used industrial phthalate, n-butyl benzyl phthalate (BBP), on cancer progression, we evaluated the results of BBP treatment using a whole human genome cDNA microarray and MetaCore software and selected candidate genes whose expression was changed by more than ten-fold by BBP compared with controls to analyze the signaling pathways in human breast cancer initiating cells (R2d). A total of 473 genes were upregulated, and 468 were downregulated. Most of these genes are involved in proliferation, epithelial-mesenchymal transition, and angiogenesis signaling. BBP induced the viability, invasion and migration, and tube formation in vitro, and Matrigel plug angiogenesis in vivo of R2d and MCF-7. Furthermore, the viability and invasion and migration of these cell lines following BBP treatment was reduced by transfection with a small interfering RNA targeting the mRNA for lymphoid enhancer-binding factor 1; notably, the altered expression of this gene consistently differentiated tumors expressing genes involved in proliferation, epithelial-mesenchymal transition, and angiogenesis. These findings contribute to our understanding of the molecular impact of the environmental hormone BBP and suggest possible strategies for preventing and treating human breast cancer.

Muret J, Hasmim M, Stasik I, et al.
Attenuation of soft-tissue sarcomas resistance to the cytotoxic action of TNF-α by restoring p53 function.
PLoS One. 2012; 7(6):e38808 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Isolated limb perfusion with TNF-α and melphalan is used with remarkable efficiency to treat unresectable limb sarcomas. Here we tested the ability of TNF-α to directly induce apoptosis of sarcoma cells. In addition, we investigated the impact of p53 in the regulation of such effect.
METHODOLOGY/PRINCIPAL FINDINGS: We first analysed the ability of TNF-α to induce apoptosis in freshly isolated tumour cells. For this purpose, sarcoma tumours (n = 8) treated ex vivo with TNF-α were processed for TUNEL staining. It revealed substantial endothelial cell apoptosis and levels of tumour cell apoptosis that varied from low to high. In order to investigate the role of p53 in TNF-α-induced cell death, human sarcoma cell lines (n = 9) with different TP53 and MDM2 status were studied for their sensitivity to TNF-α. TP53(Wt) cell lines were sensitive to TNF-α unless MDM2 was over-expressed. However, TP53(Mut) and TP53(Null) cell lines were resistant. TP53 suppression in TP53(Wt) cell lines abrogated TNF-α sensitivity and TP53 overexpression in TP53(Null) cell lines restored it. The use of small molecules that restore p53 activity, such as CP-31398 or Nutlin-3a, in association with TNF-α, potentiated the cell death of respectively TP53(Mut) and TP53(Wt)/MDM2(Ampl). In particular, CP-31398 was able to induce p53 as well as some of its apoptotic target genes in TP53(Mut) cells. In TP53(Wt)/MDM2(Ampl) cells, Nutlin-3a effects were associated with a decrease of TNF-α-induced NF-κB-DNA binding and correlated with a differential regulation of pro- and anti-apoptotic genes such as TP53BP2, GADD45, TGF-β1 and FAIM.
CONCLUSION/SIGNIFICANCE: More effective therapeutic approaches are critically needed for the treatment of unresectable limb sarcomas. Our results show that restoring p53 activity in sarcoma cells correlated with increased sensitivity to TNF-α, suggesting that this strategy may be an important determinant of TNF-α-based sarcomas treatment.

Yao M, Xie C, Constantine M, et al.
How can food extracts consumed in the Mediterranean and East Asia suppress prostate cancer proliferation?
Br J Nutr. 2012; 108(3):424-30 [PubMed] Related Publications
We have developed a blend of food extracts commonly consumed in the Mediterranean and East Asia, named blueberry punch (BBP), with the ultimate aim to formulate a chemoprevention strategy to inhibit prostate cancer progression in men on active surveillance protocol. We demonstrated previously that BBP inhibited prostate cancer cell proliferation in vitro and in vivo. The purpose of this study was to determine the molecular mechanism responsible for the suppression of prostate cancer cell proliferation by BBP. Treatment of lymph node-metastasised prostate cancer cells (LNCaP) and bone-metastasised prostate cancer cells (PC-3 and MDA-PCa-2b) with BBP (up to 0·8 %) for 72 h increased the percentage of cells at the G0/G1 phase and decreased those at the S and G2/M phases. The finding was supported by the reduction in the percentage of Ki-67-positive cells and of DNA synthesis measured by the incorporation of 5-ethynyl-2'-deoxyuridine. Concomitantly, BBP treatment decreased the protein levels of phosphorylated retinoblastoma, cyclin D1 and E, cyclin-dependent kinase (CDK) 4 and 2, and pre-replication complex (CDC6 and MCM7) in LNCaP and PC-3 cells, whereas CDK inhibitor p27 was elevated in these cell lines. In conclusion, BBP exerts its anti-proliferative effect on prostate cancer cells by modulating the expression and phosphorylation of multiple regulatory proteins essential for cell proliferation.

Qin XY, Zaha H, Nagano R, et al.
Xenoestrogens down-regulate aryl-hydrocarbon receptor nuclear translocator 2 mRNA expression in human breast cancer cells via an estrogen receptor alpha-dependent mechanism.
Toxicol Lett. 2011; 206(2):152-7 [PubMed] Related Publications
Environmental chemicals with estrogenic activity, known as xenoestrogens, may cause impaired reproductive development and endocrine-related cancers in humans by disrupting endocrine functions. Aryl-hydrocarbon receptor nuclear translocator 2 (ARNT2) is believed to play important roles in a variety of physiological processes, including estrogen signaling pathways, that may be involved in the pathogenesis and therapeutic responses of endocrine-related cancers. However, much of the underlying mechanism remains unknown. In this study, we investigated whether ARNT2 expression is regulated by a range of representative xenoestrogens in human cancer cell lines. Bisphenol A (BPA), benzyl butyl phthalate (BBP), and 1,1,1-trichloro-2,2-bis(2-chlorophenyl-4-chlorophenyl)ethane (o,p'-DDT) were found to be estrogenic toward BG1Luc4E2 cells by an E-CALUX bioassay. ARNT2 expression was downregulated by BPA, BBP, and o,p'-DDT in a dose-dependent manner in estrogen receptor 1 (ESR1)-positive MCF-7 and BG1Luc4E2 cells, but not in estrogen receptor-negative LNCaP cells. The reduction in ARNT2 expression in cells treated with the xenoestrogens was fully recovered by the addition of a specific ESR1 antagonist, MPP. In conclusion, we have shown for the first time that ARNT2 expression is modulated by xenoestrogens by an ESR1-dependent mechanism in MCF-7 breast cancer cells.

Buti L, Spooner E, Van der Veen AG, et al.
Helicobacter pylori cytotoxin-associated gene A (CagA) subverts the apoptosis-stimulating protein of p53 (ASPP2) tumor suppressor pathway of the host.
Proc Natl Acad Sci U S A. 2011; 108(22):9238-43 [PubMed] Free Access to Full Article Related Publications
Type I strains of Helicobacter pylori (Hp) possess a pathogenicity island, cag, that encodes the effector protein cytotoxin-associated gene A (CagA) and a type four secretion system. After translocation into the host cell, CagA affects cell shape, increases cell motility, abrogates junctional activity, and promotes an epithelial to mesenchymal transition-like phenotype. Transgenic expression of CagA enhances gastrointestinal and intestinal carcinomas as well as myeloid and B-cell lymphomas in mice, but the mechanism of the induced cancer formation is not fully understood. Here, we show that CagA subverts the tumor suppressor function of apoptosis-stimulating protein of p53 (ASPP2). Delivery of CagA inside the host results in its association with ASPP2. After this interaction, ASPP2 recruits its natural target p53 and inhibits its apoptotic function. CagA leads to enhanced degradation of p53 and thereby, down-regulates its activity in an ASPP2-dependent manner. Finally, Hp-infected cells treated with the p53-activating drug Doxorubicin are more resistant to apoptosis than uninfected cells, an effect that requires ASPP2. The interaction between CagA and ASPP2 and the consequent degradation of p53 are examples of a bacterial protein that subverts the p53 tumor suppressor pathway in a manner similar to DNA tumor viruses. This finding may contribute to the understanding of the increased risk of gastric cancer in patients infected with Hp CagA+ strains.

Chia YC, Rajbanshi R, Calhoun C, Chiu RH
Anti-neoplastic effects of gallic acid, a major component of Toona sinensis leaf extract, on oral squamous carcinoma cells.
Molecules. 2010; 15(11):8377-89 [PubMed] Related Publications
Extract of Toona sinensis (TS) has been reported to have various effects on cultured cell lines, including anti-proliferative activity in cancer cells. We have studied the effects of TS on various human oral squamous carcinoma cell lines (HOSCC), including UM1, UM2, SCC-4, and SCC-9. These cell lines were treated with TS leaf extract and screened for viability, apoptosis, necrosis, and apoptotic gene expression. Normal human oral keratinocytes (NHOK) served as a control for cytotoxic assays. Viability of TS-treated HOSCC was reduced, whereas that of NHOK was not affected. FACScan analysis revealed that the leaf extract induced apoptosis or a combination of apoptosis and necrosis, depending on cell type. Microarray and semi-quantitative RT-PCR analysis for apoptotic-related gene expression revealed that 3,4,5-trihydroxybenzoic acid (gallic acid, one of the major bioactive compounds purified from TS extract) up-regulated pro-apoptotic genes such TNF-α, TP53BP2, and GADD45A, and down-regulated the anti-apoptotic genes Survivin and cIAP1, resulting in cell death. This study suggests that gallic acid, the major bioactive compound present, is responsible for the anti-neoplastic effect of Toona sinensis leaf extract.

Liu WK, Jiang XY, Ren JK, Zhang ZX
Expression pattern of the ASPP family members in endometrial endometrioid adenocarcinoma.
Onkologie. 2010; 33(10):500-3 [PubMed] Related Publications
BACKGROUND: Apoptosis-stimulating protein of p53 (ASPP) family members can stimulate the apoptotic function of p53 but have no impact on its cell cycle arrest function.
MATERIAL AND METHODS: The expression pattern of the ASPP family consisting of ASPP1, ASPP2, and iASPP was examined by immunohistochemistry in 45 formalin-fixed and paraffin-embedded endometrial endometrioid adenocarcinoma (EEA) specimens and 26 normal endometrial tissue (NET) samples.
RESULTS: The expression rates of ASPP1 and ASPP2 in EEA were significantly lower than those in NET (p < 0.05). However, the iASPP expression rate in EEA was statistically higher in contrast to NET (p < 0.05). Expression of ASPP1 and iASPP in EEA had no correlation with any clinicopathological features (p > 0.05). iASPP was associated with grade, invasion, and lymph node metastasis (p < 0.05).
CONCLUSIONS: It is a novel finding that the expression pattern of the ASPP family members has respective pathological and clinical implications in EEA, and iASPP might be a candidate target for EEA therapy.

Singh J, Xie C, Yao M, et al.
Food extracts consumed in Mediterranean countries and East Asia reduce protein concentrations of androgen receptor, phospho-protein kinase B, and phospho-cytosolic phospholipase A(2)alpha in human prostate cancer cells.
J Nutr. 2010; 140(4):786-91 [PubMed] Related Publications
Active surveillance is an emerging management option for the rising number of men with low-grade, clinically localized prostate cancer. However, 30-40% of men on active surveillance will progress to high-grade disease over 5 y. With the ultimate aim of developing a food-based chemoprevention strategy to retard cancer progression in these otherwise healthy men, we have developed a blend of food extracts commonly consumed in Mediterranean countries and East Asia. The effect of the food extracts known as Blueberry Punch (BBP) on prostate cancer cell growth and key signaling pathways were examined in vitro and in vivo. BBP reduced prostate cancer cell growth in a dose-dependent manner (0.08-2.5%) at 72 h in vitro due to the reduction in cell proliferation and viability. Prostate cancer cell xenograft-bearing mice, administered 10% BBP in drinking water for 2 wk, had a 25% reduction in tumor volume compared with the control (water only). In vitro, BBP reduced protein concentrations in 3 signaling pathways necessary for the proliferation and survival of prostate cancer cells, namely androgen receptor, phospho-protein kinase B/protein kinase B, and phospho-cytosolic phospholipase A(2)alpha. The downstream effectors of these pathways, including prostate-specific antigen and glycogen synthase kinase 3beta, were also reduced. Thus, this palatable food supplement is a potential candidate for testing in clinical trials and may ultimately prove effective in retarding the progression of low-grade, early-stage prostate cancer in men managed by active surveillance.

Zhao J, Wu G, Bu F, et al.
Epigenetic silence of ankyrin-repeat-containing, SH3-domain-containing, and proline-rich-region- containing protein 1 (ASPP1) and ASPP2 genes promotes tumor growth in hepatitis B virus-positive hepatocellular carcinoma.
Hepatology. 2010; 51(1):142-53 [PubMed] Related Publications
UNLABELLED: The ankyrin-repeat-containing, SH3-domain-containing, and proline-rich-region-containing protein (ASPP) family of proteins regulates apoptosis through interaction with p53 and its family members. This study evaluated the epigenetic regulation of ASPP1 and ASPP2 in hepatitis B virus (HBV)-positive hepatocellular carcinoma (HCC) and explores the effects of down-regulation of ASPP1 and ASPP2 on the development of HCC. HCC cell lines and tissues from HCC patients were used to examine the expression and methylation of ASPP1 and ASPP2. The expression of ASPP1 and ASPP2 was diminished in HCC cells by epigenetic silence owing to hypermethylation of ASPP1 and ASPP2 promoters. Analyses of 51 paired HCC and surrounding nontumor tissues revealed that methylation of ASPP1 and ASPP2 was associated with the decreased expression of ASPP1 and ASPP2 in tumor tissues and the early development of HCC. Moreover, ASPP2 became methylated upon HBV x protein (HBx) expression. The suppressive effects on tumor growth by ASPP1 and ASPP2 were examined with RNA interference-mediated gene silence. Down-regulation of ASPP1 and ASPP2 promoted the growth of HCC cells in soft agar and in nude mice and decreased the sensitivity of HCC cells to apoptotic stimuli.
CONCLUSION: ASPP1 and ASPP2 genes are frequently down-regulated by DNA methylation in HBV-positive HCC, which may play important roles in the development of HCC. These findings provide new insight into the molecular mechanisms leading to hepatocarcinogenesis and may have potent therapeutic applications.

Dumontet C, Landi S, Reiman T, et al.
Genetic polymorphisms associated with outcome in multiple myeloma patients receiving high-dose melphalan.
Bone Marrow Transplant. 2010; 45(8):1316-24 [PubMed] Related Publications
High-dose melphalan (HDM) is an essential component in the treatment of patients with multiple myeloma (MM). Few data are available regarding genetic polymorphisms associated with patient outcome or toxicity in this setting. To identify such polymorphisms, we performed a retrospective analysis, genotyping single nucleotide polymorphisms (SNPs) with the arrayed primer extension (APEX) technology in 169 patients having received HDM for MM. We analyzed 209 SNPs in 95 genes involved in drug metabolism, DNA repair, cell cycle and apoptosis. SNPs in ABCB1, CYP3A4 and TP53BP2 were associated with response to VAD induction therapy (P<0.01). SNPs in ALDH2, GSTT2 and BRCA1 were associated with response to HDM (P<0.01). Polymorphisms in CYP1A1, RAD51 and PARP were associated with disease progression whereas polymorphisms in ALDH2 and CYP1A1 were correlated with OS. Polymorphisms in BRCA1, CDKN1A and XRCC1 were associated with the occurrence of severe mucositis after HDM. These results suggest that SNPs of genes involved in drug metabolism or DNA repair could be used to distinguish MM patient subgroups with different toxicity/efficacy profiles.

Torosyan Y, Simakova O, Naga S, et al.
Annexin-A7 protects normal prostate cells and induces distinct patterns of RB-associated cytotoxicity in androgen-sensitive and -resistant prostate cancer cells.
Int J Cancer. 2009; 125(11):2528-39 [PubMed] Related Publications
The tumor suppressor role of annexin-A7 (ANXA7) was previously demonstrated by cancer susceptibility in Anxa7(+/-)-mice and by ANXA7 loss in human cancers, especially in hormone-resistant prostate tumors. To gain mechanistic insights into ANXA7 tumor suppression, we undertook an in vitro study in which we compared wild-type (WT)-ANXA7 and dominant-negative (DN)-ANXA7 effects to a conventional tumor suppressor p53 in prostate cancer cells with different androgen sensitivity. Unlike p53 (which caused cell growth arrest and apoptosis to a noticeable extent in benign PrEC), WT-ANXA7 demonstrated profound cytotoxicityin androgen-sensitive LNCaP as well as in the androgen-resistant DU145 and PC3 prostate cancer cells, but not in PrEC. In androgen-sensitive LNCaP, WT-ANXA7 decreased low-molecular-weight (LMW) AR protein forms and maintained higher retinoblastoma 1 (RB1)/phospho-RB1 ratio. In contrast, DN-ANXA7 (which lacks phosphatidylserine liposome aggregation properties) increased LMW-AR forms and hyperphosphorylated RB1 that was consistent with the lack of DN-ANXA7 cytotoxicity. According to the microarray-based Ingenuity Pathways Analysis, a major WT-ANXA7 effect in androgen-sensitive LNCaP constituted of upregulation of the RB1-binding transcription factor E2F1 along with its downstream proapoptotic targets such as ASK1 and ASPP2. These results suggested a reversal of the RBdependent repression of the proapoptotic E2F-mediated transcription. However, DN-ANXA7 increased RB1/2 (but not E2F1) expression and induced the proliferation-promoting ERK5, thereby maintaining the RB-dependent repression of E2F-mediated apoptosis in LNcaP. On the other hand, in androgen-resistant cells, WT-ANXA7 tumor suppressor effects involved PTEN and NFkB pathways. Thus, ANXA7 revived the RB-associated cell survival control and overcame androgen resistance and dysfunctional status of major tumor suppressors commonly mutated in prostate cancer. Published 2009 UICC.

Hirata H, Hinoda Y, Nakajima K, et al.
The bcl2 -938CC genotype has poor prognosis and lower survival in renal cancer.
J Urol. 2009; 182(2):721-7 [PubMed] Related Publications
PURPOSE: A single nucleotide polymorphism (-938C/A, rs2279115) was found in the bcl2 gene, whose -938A allele is significantly associated with increased Bcl2 expression compared with that of the C allele. Bcl2 up-regulation was reported to be associated with longer survival in patients with renal cancer. However, to our knowledge there is currently no information on the role of the bcl2-938C/A single nucleotide polymorphism in renal cell carcinoma cases. Therefore, we investigated the polymorphism at the bcl2 -938C/A site and its effects on clinical characteristics in patients with renal cell carcinoma.
MATERIALS AND METHODS: We genotyped the bcl2-938C/A single nucleotide polymorphism in 216 patients with renal cancer, and in 209 healthy age and gender matched controls. We also investigated the relationship between the bcl2 -938C/A polymorphism, Bcl2 expression, proliferation and apoptosis status in renal cell carcinoma tissues using immunohistochemistry and TUNEL assay. The association of the bcl2 -938C/A single nucleotide polymorphism with survival in patients with renal cell carcinoma was also analyzed by Kaplan-Meier curves.
RESULTS: Survival in Bcl2 positive cases was significantly longer than in negative cases. On univariate and multivariate analyses the bcl2 -938CC genotype was independently associated with poor prognosis. Kaplan-Meier analysis showed that survival in patients with CC genotypes was significantly worse than in those with CA+AA genotypes. CC genotype carriers had significantly lower Bcl2 expression and higher proliferative activity in renal cancer tissues than CA+AA genotype carriers.
CONCLUSIONS: To our knowledge this is the first report to show that the bcl2 -938C/C genotype has worse prognosis and lower survival in patients with renal cell carcinoma. In addition, the bcl2 -938C/A single nucleotide polymorphism was shown to be an independent adverse prognostic factor for renal cell carcinoma.

Suri SS, Rakotondradany F, Myles AJ, et al.
The role of RGD-tagged helical rosette nanotubes in the induction of inflammation and apoptosis in human lung adenocarcinoma cells through the P38 MAPK pathway.
Biomaterials. 2009; 30(17):3084-90 [PubMed] Related Publications
The rosette nanotubes (RNTs) are a class of biologically inspired, self-assembling, metal-free, hydrophilic nanotubes, which hold tremendous potential as targeted drug delivery vehicles. We investigated the cell signaling events caused by lysine-functionalized RNTs (K-RNT) co-assembled with Arg-Gly-Asp-Ser-Lys-functionalized RNTs (RGDSK-RNT) for induction of inflammation and apoptosis in human adenocarcinoma (Calu-3) cells. When co-assembled in a ratio of 1:10 microM these composite RNTs (referred to as RGDSK/K-RNTs) rapidly induced phosphorylation of P38 mitogen-activated protein kinase (MAPK) within 2 min. Higher concentrations of RGDSK/K-RNTs (>10:100 microM) resulted in a P38 MAPK-dependent increase in secretion of TNF-alpha. RGDSK/K-RNTs (1:10-40:400 microM) also caused a concentration- and P38 MAPK-dependent increase in caspase-3 activity and DNA fragmentation in Calu-3 cells at 18 h of exposure. Over-expression of pro-apoptotic genes including caspase-3, BAK1, CIDEB, TP53BP2, FAS, TNF and FASLG supported pro-apoptotic behaviors of these RNTs. We conclude that RGDSK/K-RNTs induce phosphorylation of P38 MAPK, which regulate secretion of TNF-alpha, activation of caspase-3 and apoptosis in Calu-3 cells. These results suggest that the RNTs could be used as a drug to induce apoptosis in cancer cells or as a versatile platform to deliver a variety of biologically active molecules for cancer therapy.

Buteau-Lozano H, Velasco G, Cristofari M, et al.
Xenoestrogens modulate vascular endothelial growth factor secretion in breast cancer cells through an estrogen receptor-dependent mechanism.
J Endocrinol. 2008; 196(2):399-412 [PubMed] Related Publications
Environmental chemicals may affect human health by disrupting endocrine function. Their possible role in the mammary gland and breast tumors is still unknown. Previous studies have demonstrated that vascular endothelial growth factor (VEGF), a key factor in angiogenesis and tumor progression, is an estrogen-regulated gene. We analyzed whether VEGF expression is regulated by different xenoestrogens in several breast cancer cells, MELN (derived from MCF-7) and MELP (derived from MDA-MB-231) and stably expressing estrogen receptor alpha (ERalpha); these cell lines stably express estrogen response element (beta-globin)-luciferase. Genistein, bisphenol A (BPA), 4-(tert-octyl)phenol (OP), dieldrin, and several phthalates, including benzyl butyl phthalate (BBP) and di-ethyl-2-hexyle phthalate (DEHP), were first shown to be estrogenic. These compounds induced a dose-dependent increase of VEGF secretion in MELN and MCF-7 cells; maximal effect was observed at 1-10 microM non-cytotoxic concentrations and was inhibited by the antiestrogen ICI 182 780. VEGF increase was not observed in ERalpha-negative MDA-MB-231 cells. Most substances increased VEGF transcript levels in MELN cells. In contrast, gamma-hexachlorocyclohexane, vinclozolin, and the phthalates (mono-n-butyl ester phthalic acid, di-isononyle phthalate, and di-isodecyle phthalate) were ineffective on both VEGF secretion and estrogenic luciferase induction in these cell lines. Specific kinase inhibitors PD98059, SB203580, or LY294002 suppressed the xenoestrogen-induced VEGF response, suggesting activation of MEK, p38 kinase, and phosphatidylinositol-3-kinase pathways. Our in vitro results show for the first time that genistein and xenoestrogens (BPA, OP, dieldrin, BBP, and DEHP at high concentrations) up-regulate VEGF expression in MELN cells by an ER-dependent mechanism. Since VEGF increases capillary permeability and breast tumor angiogenesis in vivo, the physiological relevance of these findings is discussed.

Sullivan A, Lu X
ASPP: a new family of oncogenes and tumour suppressor genes.
Br J Cancer. 2007; 96(2):196-200 [PubMed] Free Access to Full Article Related Publications
The apoptosis stimulating proteins of p53 (ASPP) family consists of three members, ASPP1, ASPP2 and iASPP. They bind to proteins that are key players in controlling apoptosis (p53, Bcl-2 and RelA/p65) and cell growth (APCL, PP1). So far, the best-known function of the ASPP family members is their ability to regulate the apoptotic function of p53 and its family members, p63 and p73. Biochemical and genetic evidence has shown that ASPP1 and ASPP2 activate, whereas iASPP inhibits, the apoptotic but not the cell-cycle arrest function of p53. The p53 tumour suppressor gene, one of the most frequently mutated genes in human cancer, is capable of suppressing tumour growth through its ability to induce apoptosis or cell-cycle arrest. Thus, the ASPP family of proteins helps to determine how cells choose to die and may therefore be a novel target for cancer therapy.

Bergamaschi D, Samuels Y, Sullivan A, et al.
iASPP preferentially binds p53 proline-rich region and modulates apoptotic function of codon 72-polymorphic p53.
Nat Genet. 2006; 38(10):1133-41 [PubMed] Related Publications
iASPP is one of the most evolutionarily conserved inhibitors of p53, whereas ASPP1 and ASPP2 are activators of p53. We show here that, in addition to the DNA-binding domain, the ASPP family members also bind to the proline-rich region of p53, which contains the most common p53 polymorphism at codon 72. Furthermore, the ASPP family members, particularly iASPP, bind to and regulate the activity of p53Pro72 more efficiently than that of p53Arg72. Hence, escape from negative regulation by iASPP is a newly identified mechanism by which p53Arg72 activates apoptosis more efficiently than p53Pro72.

Li H, Rauch T, Chen ZX, et al.
The histone methyltransferase SETDB1 and the DNA methyltransferase DNMT3A interact directly and localize to promoters silenced in cancer cells.
J Biol Chem. 2006; 281(28):19489-500 [PubMed] Related Publications
DNA CpG methylation can cooperate with histone H3 lysine 9 (H3-K9) methylation in heterochromatin formation and gene silencing. Trimethylation of H3-K9 by the recently identified euchromatic histone methyltransferase SETDB1/ESET may be responsible for transcriptional repression of certain promoters. Here, we show that SETDB1 associates with endogenous DNA methyltransferase activity. SETDB1 interacts with the de novo DNA methyltransferases DNMT3A and DNMT3B but not with the maintenance methyltransferase DNMT1. The interaction of SETDB1 with DNMT3A was further characterized and confirmed by in vivo and in vitro interaction studies. A direct interaction of the two proteins occurs through the N terminus of SETDB1 and the plant homeodomain of DNMT3A. Co-expression of SETDB1 and DNMT3A was essential for repression of reporter gene expression in a Gal4-based tethering assay and resulted in their recruitment to the artificial promoter. We further demonstrate that the CpG-methylated promoters of the endogenous p53BP2 gene in HeLa cells and the RASSF1A gene in MDA-MB-231 cells are simultaneously occupied by both SETDB1 and DNMT3A proteins, which provides evidence for SETDB1 being at least partly responsible for H3-K9 trimethylation at the promoter of RASSF1A, a gene frequently silenced in human cancers. In summary, our data demonstrate the direct physical interaction and functional connection between the H3-K9 trimethylase SETDB1 and the DNA methyltransferase DNMT3A and thus contribute to a better understanding of the complexity of the self-reinforcing heterochromatin machinery operating at silenced promoters.

Cobleigh MA, Tabesh B, Bitterman P, et al.
Tumor gene expression and prognosis in breast cancer patients with 10 or more positive lymph nodes.
Clin Cancer Res. 2005; 11(24 Pt 1):8623-31 [PubMed] Related Publications
PURPOSE: This study, along with two others, was done to develop the 21-gene Recurrence Score assay (Oncotype DX) that was validated in a subsequent independent study and is used to aid decision making about chemotherapy in estrogen receptor (ER)-positive, node-negative breast cancer patients.
EXPERIMENTAL DESIGN: Patients with >or=10 nodes diagnosed from 1979 to 1999 were identified. RNA was extracted from paraffin blocks, and expression of 203 candidate genes was quantified using reverse transcription-PCR (RT-PCR).
RESULTS: Seventy-eight patients were studied. As of August 2002, 77% of patients had distant recurrence or breast cancer death. Univariate Cox analysis of clinical and immunohistochemistry variables indicated that HER2/immunohistochemistry, number of involved nodes, progesterone receptor (PR)/immunohistochemistry (% cells), and ER/immunohistochemistry (% cells) were significantly associated with distant recurrence-free survival (DRFS). Univariate Cox analysis identified 22 genes associated with DRFS. Higher expression correlated with shorter DRFS for the HER2 adaptor GRB7 and the macrophage marker CD68. Higher expression correlated with longer DRFS for tumor protein p53-binding protein 2 (TP53BP2) and the ER axis genes PR and Bcl2. Multivariate methods, including stepwise variable selection and bootstrap resampling of the Cox proportional hazards regression model, identified several genes, including TP53BP2 and Bcl2, as significant predictors of DRFS.
CONCLUSION: Tumor gene expression profiles of archival tissues, some more than 20 years old, provide significant information about risk of distant recurrence even among patients with 10 or more nodes.

Liu ZJ, Lu X, Zhong S
ASPP--Apoptotic specific regulator of p53.
Biochim Biophys Acta. 2005; 1756(1):77-80 [PubMed] Related Publications
The p53 protein is one of the best-known tumor suppressors. The recently identified ASPP family (apoptosis-stimulating protein of p53) can interfere with the working of p53. Three members of ASPP family are proved to be apoptotic specific regulators of p53. The discovery of ASPP family may answer such questions as "how cells choose to die". Understanding the ASPP status in human cancer will allow us to develop better strategies to treat cancer.

Takahashi N, Kobayashi S, Kajino S, et al.
Inhibition of the 53BP2S-mediated apoptosis by nuclear factor kappaB and Bcl-2 family proteins.
Genes Cells. 2005; 10(8):803-11 [PubMed] Related Publications
The p53 binding protein 2 (53BP2) has been identified independently as the interacting protein to p53, Bcl-2, and p65 subunit of nuclear factor kappaB (NF-kappaB). It was demonstrated that over-expression of 53BP2 (renamed as 53BP2S) induces apoptotic cell death. In this study we explored the effect of NF-kappaB activation elicited by a physiological NF-kappaB inducer, interleukin-1beta (IL-1beta), and anti-apoptotic Bcl-2 family proteins on the 53BP2S-mediated apoptosis. We found that both NF-kappaB activation and Bcl-2 family proteins could prevent the 53BP2S-mediated depression of mitochondrial transmembrane potential, activation of caspase-9, cleavage of poly ADP ribose polymerase (PARP), and cell death. These observations suggested that 53BP2S/Bbp and its directly or indirectly interacting proteins might play crucial roles in the regulation of apoptosis and contribute to carcinogenesis. It is also suggested that 53BP2S/Bbp induces apoptosis through the mitochondrial death pathway presumably by counteracting the actions of anti-apoptotic Bcl-2 family proteins. The regulatory network of the 53BP2S-mediated apoptosis cascade including its interacting proteins is discussed.

Ju H, Lee KA, Yang M, et al.
TP53BP2 locus is associated with gastric cancer susceptibility.
Int J Cancer. 2005; 117(6):957-60 [PubMed] Related Publications
We investigated the association of the TP53BP2 locus with gastric cancer susceptibility in a Korean population. We assayed 9 single nucleotide polymorphisms (SNP) in an 82.5 kb region that included the TP53BP2 locus in 233 male gastric cancer patients and 390 unaffected healthy male controls. The allelic frequencies of 4 SNP within TP53BP2, g.206692C>T, g.198267A>T, g.164895G>A and g.152389A>T, differed significantly between cases and controls (p < or = 0.0376). When compared to carriers of non-risk alleles, individuals homozygotic for each of the risk alleles had a 50% increase in risk of gastric cancer (age-adjusted odds ratio [OR] > or = 1.48; p < or = 0.0371). Furthermore, these 4 significantly associated SNP were in strong linkage disequilibrium (r2 > or = 0.51). Haplotype analysis showed that individuals with the CAGA haplotype, consisting of the risk alleles at each SNP, had a 1.55-fold higher risk for gastric cancer than individuals with the haplotype TTAT, consisting of the non-risk alleles at each SNP (OR = 1.55; 95% confidence interval [CI] = 1.13-2.14; p = 0.00705). Two other SNP were not polymorphic in the study subjects, whereas the other 3 SNP, located toward the outside of the TP53BP2 locus, were not associated with gastric cancer susceptibility. Although the location of the pathogenic variant is not yet known, our results suggest that the TP53BP2 locus is associated with susceptibility to gastric cancer in the Korean population.

Dreyfus DH, Nagasawa M, Gelfand EW, Ghoda LY
Modulation of p53 activity by IkappaBalpha: evidence suggesting a common phylogeny between NF-kappaB and p53 transcription factors.
BMC Immunol. 2005; 6:12 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: In this work we present evidence that the p53 tumor suppressor protein and NF-kappaB transcription factors could be related through common descent from a family of ancestral transcription factors regulating cellular proliferation and apoptosis. P53 is a homotetrameric transcription factor known to interact with the ankyrin protein 53BP2 (a fragment of the ASPP2 protein). NF-kappaB is also regulated by ankyrin proteins, the prototype of which is the IkappaB family. The DNA binding sequences of the two transcription factors are similar, sharing 8 out of 10 nucleotides. Interactions between the two proteins, both direct and indirect, have been noted previously and the two proteins play central roles in the control of proliferation and apoptosis.
RESULTS: Using previously published structure data, we noted a significant degree of structural alignment between p53 and NF-kappaB p65. We also determined that IkappaBalpha and p53 bind in vitro through a specific interaction in part involving the DNA binding region of p53, or a region proximal to it, and the amino terminus of IkappaBalpha independently or cooperatively with the ankyrin 3 domain of IkappaBalpha In cotransfection experiments, kappaBalpha could significantly inhibit the transcriptional activity of p53. Inhibition of p53-mediated transcription was increased by deletion of the ankyrin 2, 4, or 5 domains of IkappaBalpha Co-precipitation experiments using the stably transfected ankyrin 5 deletion mutant of kappaBalpha and endogenous wild-type p53 further support the hypothesis that p53 and IkappaBalpha can physically interact in vivo.
CONCLUSION: The aggregate results obtained using bacterially produced IkappaBalpha and p53 as well as reticulocyte lysate produced proteins suggest a correlation between in vitro co-precipitation in at least one of the systems and in vivo p53 inhibitory activity. These observations argue for a mechanism involving direct binding of IkappaBalpha to p53 in the inhibition of p53 transcriptional activity, analogous to the inhibition of NF-kappaB by kappaBalpha and p53 by 53BP2/ASPP2. These data furthermore suggest a role for ankyrin proteins in the regulation of p53 activity. Taken together, the NFkappaB and p53 proteins share similarities in structure, DNA binding sites and binding and regulation by ankyrin proteins in support of our hypothesis that the two proteins share common descent from an ancestral transcriptional factor.

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