Nanoencapsulation of MDM2 Inhibitor RG7388 and Class-I HDAC Inhibitor Entinostat Enhances their Therapeutic Potential Through Synergistic Antitumor Effects and Reduction of Systemic Toxicity

Inhibitors of the p53-MDM2 interaction such as RG7388 have been developed to exploit latent tumor suppressive properties in p53 in 50% of tumors in which p53 is wild-type. However, these agents for the most part activate cell cycle arrest rather than death, and high doses in patients elicit on-target dose-limiting neutropenia. Recent work from our group indicates that combination of p53-MDM2 inhibitors with the class-I HDAC inhibitor Entinostat (which itself has dose-limiting toxicity issues) has the potential to significantly augment cell death in p53 wild-type colorectal cancer cells. We investigated whether coencapsulation of RG7388 and Entinostat within polymeric nanoparticles (NPs) could overcome efficacy and toxicity limitations of this drug combination. Combinations of RG7388 and Entinostat across a range of different molar ratios resulted in synergistic increases in cell death when delivered in both free drug and nanoencapsulated formats in all colorectal cell lines tested. Importantly, we also explored the in vivo impact of the drug combination on murine blood leukocytes, showing that the leukopenia induced by the free drugs could be significantly mitigated by nanoencapsulation. Taken together, this study demonstrates that formulating these agents within a single nanoparticle delivery platform may provide clinical utility beyond use as nonencapsulated agents.

miR-34c-5p inhibited fibroblast proliferation, differentiation and epithelial-mesenchymal transition in benign airway stenosis via MDMX/p53 pathway

Benign airway stenosis (BAS) means airway stenosis or obstruction that results from a variety of non-malignant factors, including tuberculosis, trauma, benign tumors, etc. In consideration of the currently limited research on microRNAs in BAS, this study aimed to explore the role and mechanism of miR-34c-5p in BAS. The expression of miR-34c-5p in BAS granulation tissues showed a significant down-regulation compared with the normal control group. Moreover, miR-34c-5p mimics suppressed the proliferation and differentiation of human bronchial fibroblasts (HBFs) and the epithelial-mesenchymal transition (EMT) of human bronchial epithelial cells (HBE). Conversely, miR-34c-5p inhibitors aggravated those effects. A dual-luciferase reporter assay confirmed that miR-34c-5p can target MDMX rather than Notch1. The over-expression of MDMX can reverse the inhibiting effect of miR-34c-5p on HBFs proliferation, differentiation and EMT. Furthermore, the expressions of tumor protein (p53) and PTEN were down-regulated following the over-expression of MDMX. In addition, the expressions of PI3K and AKT showed an up-regulation. In conclusion, miR-34c-5p was down-regulated in BAS and may inhibit fibroblast proliferation differentiation and EMT in BAS via the MDMX/p53 signaling axis. These findings expand the understanding of the role of miR-34c-5p and will help develop new treatment strategies for BAS.

MDM2 provides TOP2 poison resistance by promoting proteolysis of TOP2βcc in a p53-independent manner

DNA topoisomerase II (TOP2) is an enzyme that performs a critical function in manipulating DNA topology during replication, transcription, and chromosomal compaction by forming a vital intermediate known as the TOP2-DNA cleavage complex (TOP2cc). Although the TOP2cc is often transient, stabilization can be achieved by TOP2 poisons, a family of anti-cancer chemotherapeutic agents targeting TOP2, such as etoposide (VP-16), and then induce double-strand breaks (DSBs) in cellular DNA. TOP2cc first needs to be proteolyzed before it can be processed by TDP2 for the removal of these protein adducts and to produce clean DNA ends necessary for proper repair. However, the mechanism by which TOP2βcc is proteolyzed has not been thoroughly studied. In this study, we report that after exposure to VP-16, MDM2, a RING-type E3 ubiquitin ligase, attaches to TOP2β and initiates polyubiquitination and proteasomal degradation. Mechanistically, during exposure to VP-16, TOP2β binds to DNA to form TOP2βcc, which promotes MDM2 binding and subsequent TOP2β ubiquitination and degradation, and results in a decrease in TOP2βcc levels. Biologically, MDM2 inactivation abrogates TOP2β degradation, stabilizes TOP2βcc, and subsequently increases the number of TOP2β-concealed DSBs, resulting in the rapid death of cancer cells via the apoptotic process. Furthermore, we demonstrate the combination activity of VP-16 and RG7112, an MDM2 inhibitor, in the xenograft tumor model and in situ lung cancer mouse model. Taken together, the results of our research reveal an underlying mechanism by which MDM2 promotes cancer cell survival in the presence of TOP2 poisons by activating proteolysis of TOP2βcc in a p53-independent manner, and provides a rationale for the combination of MDM2 inhibitors with TOP2 poisons for cancer therapy.

The DNA damage sensor ATM kinase interacts with the p53 mRNA and guides the DNA damage response pathway

BACKGROUND

The ATM kinase constitutes a master regulatory hub of DNA damage and activates the p53 response pathway by phosphorylating the MDM2 protein, which develops an affinity for the p53 mRNA secondary structure. Disruption of this interaction prevents the activation of the nascent p53. The link of the MDM2 protein-p53 mRNA interaction with the upstream DNA damage sensor ATM kinase and the role of the p53 mRNA in the DNA damage sensing mechanism, are still highly anticipated.

METHODS

The proximity ligation assay (PLA) has been extensively used to reveal the sub-cellular localisation of the protein-mRNA and protein-protein interactions. ELISA and co-immunoprecipitation confirmed the interactions in vitro and in cells.

RESULTS

This study provides a novel mechanism whereby the p53 mRNA interacts with the ATM kinase enzyme and shows that the L22L synonymous mutant, known to alter the secondary structure of the p53 mRNA, prevents the interaction. The relevant mechanistic roles in the DNA Damage Sensing pathway, which is linked to downstream DNA damage response, are explored. Following DNA damage (double-stranded DNA breaks activating ATM), activated MDMX protein competes the ATM-p53 mRNA interaction and prevents the association of the p53 mRNA with NBS1 (MRN complex). These data also reveal the binding domains and the phosphorylation events on ATM that regulate the interaction and the trafficking of the complex to the cytoplasm.

CONCLUSION

The presented model shows a novel interaction of ATM with the p53 mRNA and describes the link between DNA Damage Sensing with the downstream p53 activation pathways; supporting the rising functional implications of synonymous mutations altering secondary mRNA structures.

Design-rules for stapled peptides with in vivo activity and their application to Mdm2/X antagonists

Although stapled α-helical peptides can address challenging targets, their advancement is impeded by poor understandings for making them cell permeable while avoiding off-target toxicities. By synthesizing >350 molecules, we present workflows for identifying stapled peptides against Mdm2(X) with in vivo activity and no off-target effects. Key insights include a clear correlation between lipophilicity and permeability, removal of positive charge to avoid off-target toxicities, judicious anionic residue placement to enhance solubility/behavior, optimization of C-terminal length/helicity to enhance potency, and optimization of staple type/number to avoid polypharmacology. Workflow application gives peptides with >292x improved cell proliferation potencies and no off-target cell proliferation effects ( > 3800x on-target index). Application of these 'design rules' to a distinct Mdm2(X) peptide series improves ( > 150x) cellular potencies and removes off-target toxicities. The outlined workflow should facilitate therapeutic impacts, especially for those targets such as Mdm2(X) that have hydrophobic interfaces and are targetable with a helical motif.

Delivery versus Potency in Treating Brain Tumors: BI-907828, a MDM2-p53 Antagonist with Limited BBB Penetration but Significant In Vivo Efficacy in Glioblastoma

MDM2-p53 inhibition may be effective in glioblastoma (GBM). This study evaluates the pharmacokinetics/pharmacodynamics of BI-907828, a potent antagonist of MDM2, in GBM, and demonstrates a translational paradigm with a focus on a unified "Delivery - Potency - Efficacy" relationship in drug development for central nervous system(CNS) tumors. BI-907828 was tested for cytotoxicity and MDM2-p53 pathway inhibition. Systemic pharmacokinetics and transport mechanisms controlling CNS distribution were evaluated in mice. BI-907828 free fractions in cell media, mouse and human specimens were measured to determine "active" unbound concentrations. Efficacy measures, including overall survival and target expression were assessed in mouse orthotopic GBM xenografts. BI-907828 exhibited potent inhibition of MDM2-p53 pathway and promoted cell death in GBM TP53 wild-type cells. MDM2-amplified cells are highly sensitive to BI-907828, with an effective unbound concentration of 0.1 nmol/L. The CNS distribution of BI-907828 is limited by blood-brain barrier (BBB) efflux mediated by P-gp, resulting in a Kp,uu_brain of 0.002. Despite this seemingly "poor" BBB penetration, weekly administration of 10 mg/kg BI-907828 extended median survival of orthotopic GBM108 xenografts from 28 to 218 days (P < 0.0001). This excellent efficacy can be attributed to high potency, resulting in a limited, yet effective, exposure in the CNS. These studies show that efficacy of BI-907828 in orthotopic models is related to high potency even though its CNS distribution is limited by BBB efflux. Therefore, a comprehensive understanding of all aspects of the "Delivery - Potency - Efficacy" relationship is warranted in drug discovery and development, especially for treatment of CNS tumors.

Hydrogen sulfide inhibits alveolar type II cell senescence and limits pulmonary fibrosis via promoting MDM2-mediated p53 degradation

AIM

Senescence of alveolar type II (AT2) cells is an important driver of pulmonary fibrosis. This study aimed to investigate whether and how dysregulation of hydrogen sulfide (H2 S) production affected AT2 cell senescence, and then explored the effect of H2 S on the communication between AT2 and fibroblasts.

METHODS

ICR mice were intratracheally administered with bleomycin (3 mg/kg). Sodium hydrosulfide (NaHS, 28 μmol/kg/d) was intraperitoneally injected for 2 weeks. The H2 S-generating enzyme cystathionine-β-synthase (CBS) knockout heterozygous (CBS+/- ) mice were used as a low H2 S production model.

RESULTS

Analysis of microarray datasets revealed downregulation of H2 S-generating enzymes in lung tissues of patients with pulmonary fibrosis. Decreased H2 S production was correlated with higher levels of cell senescence markers p53 and p21 in bleomycin-induced lung fibrosis. CBS+/- mice exhibited increased levels of p53 and p21. The numbers of AT2 cells positive for p53 and p21 were increased in CBS+/- mice as compared to control mice. H2 S donor NaHS attenuated bleomycin-induced AT2 cell senescence both in vivo and in vitro. H2 S donor suppressed bleomycin-induced senescence-associated secretory phenotype (SASP) of AT2 cells via inhibiting p53/p21 pathway, consequently suppressing proliferation and myofibroblast transdifferentiation of fibroblasts. Mechanically, H2 S suppressed p53 expression by enhancing the mouse double-minute 2 homologue (MDM2)-mediated ubiquitination and degradation of p53.

CONCLUSION

H2 S inactivated p53-p21 pathway, consequently suppressing AT2 cell senescence as well as cell communication between senescent AT2 cells and fibroblasts. Aberrant H2 S synthesis may contribute to the development of pulmonary fibrosis through promoting the activation loop involving senescent AT2 cells and activated fibroblasts.

The Antiproliferative and Proapoptotic Effects of Cucurbitacin B on BPH-1 Cells via the p53/MDM2 Axis

Cucurbitacin B (Cu B), a triterpenoid compound, has anti-inflammatory and antioxidant activities. Most studies only focus on the hepatoprotective activity of Cu B, and little effort has been geared toward exploring the effect of Cu B on the prostate. Our study identified that Cu B inhibited the proliferation of the benign prostatic hyperplasia epithelial cell line (BPH-1). At the molecular level, Cu B upregulated MDM2 and thrombospondin 1 (THBS1) mRNA levels. Immunocytochemistry results revealed that the protein expressions of p53 and MDM2 were upregulated in BPH-1 cells. Furthermore, Cu B upregulated THBS1 expression and downregulated COX-2 expression in the BPH-1 cell supernatant. Altogether, Cu B may inhibit prostate cell proliferation by activating the p53/MDM2 signaling cascade and downregulating the COX-2 expression.

A GPX4 non-enzymatic domain and MDM2 targeting peptide PROTAC for acute lymphoid leukemia therapy through ferroptosis induction

Ferroptosis, an emerging form of programmed cell death, has garnered substantial attention as a potential target for cancer therapy. However, despite the potential promise, no ferroptosis-related therapies have progressed to clinical trials. Identifying disease types sensitive to ferroptosis and developing specific ferroptosis-targeting drugs are critical focal points in the field of ferroptosis-based treatment. In this study, we conducted a comprehensive database analysis and presented compelling evidence indicating a high expression of GPX4 in patients with acute lymphoblastic leukemia (ALL), significantly correlating with poor prognosis. Notably, elevated GPX4 expression is closely associated with ALL relapse, a major challenge in the treatment of this disease. Building upon these findings, we devised a novel peptide-based Proteolysis Targeting Chimeras (PROTAC) drug targeting GPX4 through computer-aided design. In contrast to existing drugs that target the conjugative enzyme active site, our design focused on a peptide drug targeting the non-active site of GPX4. Furthermore, we strategically selected MDM2, an E3 ligase highly expressed in ALL, for the PROTAC drug design. This deliberate choice amplifies the drug's effect on cancer cells while minimizing its impact on normal cells, achieving desirable selectivity for cancer cells. Leveraging nanogold delivery, we successfully facilitated intracellular action of the GPX4-targeting peptide PROTAC drug, denoted as Au-PGPD (peptide GPX4 PROTAC drug). Au-PGPD effectively induced GPX4 degradation and inhibited ALL cell proliferation. Remarkably, Au-PGPD exhibited significantly less efficacy on normal cells, underscoring the selectivity and safety of our design.

The MDM2-p53 Antagonist Brigimadlin (BI 907828) in Patients with Advanced or Metastatic Solid Tumors: Results of a Phase Ia, First-in-Human, Dose-Escalation Study

Brigimadlin (BI 907828) is an oral MDM2-p53 antagonist that has shown encouraging antitumor activity in vivo. We present phase Ia results from an open-label, first-in-human, phase Ia/Ib study investigating brigimadlin in patients with advanced solid tumors (NCT03449381). Fifty-four patients received escalating doses of brigimadlin on day 1 of 21-day cycles (D1q3w) or days 1 and 8 of 28-day cycles (D1D8q4w). Based on dose-limiting toxicities during cycle 1, the maximum tolerated dose was selected as 60 mg for D1q3w and 45 mg for D1D8q4w. The most common treatment-related adverse events (TRAE) were nausea (74.1%) and vomiting (51.9%); the most common grade ≥3 TRAEs were thrombocytopenia (25.9%) and neutropenia (24.1%). As evidence of target engagement, time- and dose-dependent increases in growth differentiation factor 15 levels were seen. Preliminary efficacy was encouraging (11.1% overall response and 74.1% disease control rates), particularly in patients with well-differentiated or dedifferentiated liposarcoma (100% and 75% disease control rates, respectively).

SIGNIFICANCE

We report phase Ia data indicating that the oral MDM2-p53 antagonist brigimadlin has a manageable safety profile and shows encouraging signs of efficacy in patients with solid tumors, particularly those with MDM2-amplified advanced/metastatic well-differentiated or dedifferentiated liposarcoma. Further clinical investigation of brigimadlin is ongoing. See related commentary by Italiano, p. 1765. This article is highlighted in the In This Issue feature, p. 1749.

A small HDM2 antagonist peptide and a USP7 inhibitor synergistically inhibit the p53-HDM2-USP7 circuit

HDM2, an E3 ubiquitin ligase, is a crucial regulator of many proliferation-related pathways. It is also one of the primary regulators of p53. USP7, a deubiquitinase, also plays a key role in the regulation of both p53 and HDM2, thus forming a small regulatory network with them. This network has emerged as an important drug target. Development of a synergistic combination targeting both proteins is desirable and important for regulating this module. We have developed a small helically constrained peptide that potently inhibited p53-HDM2 interaction and exerted anti-proliferative effects on p53+/+ cells. A combination of this peptide-when attached to cell entry and nuclear localization tags-and a USP7 inhibitor showed synergistic anti-proliferative effects against cells harboring wild-type alleles of p53. Synergistic inhibition of two important drug targets may lead to novel therapeutic strategies.

[A case report of adult primary soft tissue sarcoma of the head and neck]

Head and neck primary soft tissue sarcoma is a rare adult connective tissue malignant tumor derived from mesenchymal tissue, which can occur in the paranasal sinuses, throat or neck space.The clinical manifestations are local spread masses in the head and neck or difficulty breathing, swallowing, etc al. MRI and enhanced CT examination are the most commonly used to diagnose such diseases. Pathological diagnosis requires immunohistochemistry combined with FISH to detect MDM2 and CDK4. In this report，two cases of primary soft tissue sarcoma were reported,one is parotid high-differentiated liposarcoma and the other is laryngeal dedifferentiated leiomyosarcoma, introducing the characteristics diagnosis and treatment, and reviewing the relevant literature.

Aglianico Grape Seed Semi-Polar Extract Exerts Anticancer Effects by Modulating MDM2 Expression and Metabolic Pathways

Grapevine (Vitis vinifera L.) seeds are rich in polyphenols including proanthocyanidins, molecules with a variety of biological effects including anticancer action. We have previously reported that the grape seed semi-polar extract of Aglianico cultivar (AGS) was able to induce apoptosis and decrease cancer properties in different mesothelioma cell lines. Concomitantly, this extract resulted in enriched oligomeric proanthocyanidins which might be involved in determining the anticancer activity. Through transcriptomic and metabolomic analyses, we investigated in detail the anticancer pathway induced by AGS. Transcriptomics analysis and functional annotation allowed the identification of the relevant causative genes involved in the apoptotic induction following AGS treatment. Subsequent biological validation strengthened the hypothesis that MDM2 could be the molecular target of AGS and that it could act in both a p53-dependent and independent manner. Finally, AGS significantly inhibited tumor progression in a xenograft mouse model of mesothelioma, confirming also in vivo that MDM2 could act as molecular player responsible for the AGS antitumor effect. Our findings indicated that AGS, exerting a pro-apoptotic effect by hindering MDM2 pathway, could represent a novel source of anticancer molecules.

In Vitro/In Vivo Translation of Synergistic Combination of MDM2 and MEK Inhibitors in Melanoma Using PBPK/PD Modelling: Part I

Translation of the synergy between the Siremadlin (MDM2 inhibitor) and Trametinib (MEK inhibitor) combination observed in vitro into in vivo synergistic efficacy in melanoma requires estimation of the interaction between these molecules at the pharmacokinetic (PK) and pharmacodynamic (PD) levels. The cytotoxicity of the Siremadlin and Trametinib combination was evaluated in vitro in melanoma A375 cells with MTS and RealTime-Glo assays. Analysis of the drug combination matrix was performed using Synergy and Synergyfinder packages. Calculated drug interaction metrics showed high synergy between Siremadlin and Trametinib: 23.12%, or a 7.48% increase of combined drug efficacy (concentration-independent parameter β from Synergy package analysis and concentration-dependent δ parameter from Synergyfinder analysis, respectively). In order to select the optimal PD interaction parameter which may translate observed in vitro synergy metrics into the in vivo setting, further PK/PD studies on cancer xenograft animal models coupled with PBPK/PD modelling are needed.

Pharmacokinetics and Macrophage Inhibitory Cytokine-1 Pharmacodynamics of the Murine Double Minute 2 Inhibitor, Navtemadlin (KRT-232) in Fed and Fasted Healthy Subjects

This single 60-mg dose, 4-period crossover study assessed the effect of food and formulation change on navtemadlin (KRT-232) pharmacokinetics (PK) and macrophage inhibitory cytokine-1 (MIC-1) pharmacodynamics. Healthy subjects (N = 30) were randomized to 3 treatment sequences, A: new tablet, fasted (reference, dosed twice); B: new tablet, 30 minutes after a high-fat meal (test 1); C: old tablet, fasted (test 2). PK/pharmacodynamic parameters were measured over 0 to 96 hours. Adverse events were mild without any discontinuations. No serious adverse events or deaths occurred. In treatment A, navtemadlin mean (coefficient of variation) maximum concentration (Cmax ) was 525 (66) ng/mL, at median time to maximum concentration (tmax ) of 2 hours. Mean (coefficient of variation) area under the plasma concentration-time curve from time 0 to time t (AUC0-t ) was 3392 (63.3) ng • h/mL, and arithmetic mean terminal half-life was 18.6 hours. Acyl glucuronide metabolite (M1)/navtemadlin AUC0-t ratio was 0.2, and urine excretion of navtemadlin was negligible. After a meal (B vs A), navtemadlin tmax was delayed by 1 hour. Geometric least squares means ratios (90%CI) for navtemadlin Cmax and AUC0-t were 102.7% (87.4-120.6) and 81.4% (76.2-86.9), respectively. Old vs new tablet fasted formulations (C vs A) had geometric least squares means ratios (90%CI) of 78.4% (72.0-85.3) for Cmax and 85.9% (80.5-91.7) for AUC0-t . MIC-1 Cmax and AUC were comparable across groups; tmax was delayed relative to navtemadlin tmax by ≈8 hours. Navtemadlin AUC0-t and MIC-1 AUC0-t correlated significantly. In conclusion, navtemadlin can be administered safely with or without food; the new formulation does not affect navtemadlin PK. The 60-mg navtemadlin dose elicited a reproducible and robust MIC-1 response that correlated well with navtemadlin exposure, indicating that murine double minute 2 target engagement leads to p53 activation.

PPM1D mutations are oncogenic drivers of de novo diffuse midline glioma formation

The role of PPM1D mutations in de novo gliomagenesis has not been systematically explored. Here we analyze whole genome sequences of 170 pediatric high-grade gliomas and find that truncating mutations in PPM1D that increase the stability of its phosphatase are clonal driver events in 11% of Diffuse Midline Gliomas (DMGs) and are enriched in primary pontine tumors. Through the development of DMG mouse models, we show that PPM1D mutations potentiate gliomagenesis and that PPM1D phosphatase activity is required for in vivo oncogenesis. Finally, we apply integrative phosphoproteomic and functional genomics assays and find that oncogenic effects of PPM1D truncation converge on regulators of cell cycle, DNA damage response, and p53 pathways, revealing therapeutic vulnerabilities including MDM2 inhibition.

[Regulatory mechanism of interferon regulatory factor 1 by α-synuclein in mouse Parkinson's disease model]

OBJECTIVE

To investigate the molecular mechanism by which α-synuclein (α-Syn) regulates interferon regulatory factor 1 (IRF-1) expression.

METHODS

SH-SY5Y cells overexpressing α-Syn and transgenic mouse model carrying human α-Syn gene with A53T mutation (3 and 6 months old) were examined for IRF-1 mRNA and protein expressions using real-time PCR and Western blotting, respectively. The subcellular localization of IRF-1 was determined with immunofluorescence staining and cytoplasmic/nuclear protein isolation. The optimal concentrations of the proteasome inhibitor MG132 (0.01-2.0 μmol/L) and lysosomal inhibitor chloroquine (5-200 μmol/L) for treatment of SH-SY5Y cells for 24 h were determined by examining the cell viability. SH-SY5Y cells were treated with 0.2 μmol/L MG132 and 30 μmol/L chloroquine for 24 h (the maximum dose that did not cause cell damage), and the changes of IRF-1 protein expressions was analyzed. The effects of α-Syn on MDM2 protein expression and IRF-1 ubiquitylation were analyzed using Western blotting and ubiquitylation assay.

RESULTS

α-Syn overexpression did not affect the mRNA level of IRF-1 but significantly increased its protein level (P < 0.01). In α-Synoverexpressing SH-SY5Y cells, IRF-1 translocation was observed from the cytoplasm to the nucleus (P < 0.001). Treatment of the cells with 0.2 μmol/L MG132 significantly aggravated α-Syn-induced increase of IRF-1 protein expression (P < 0.01) while 30 μmol/L chloroquine produced no significant changes in IRF-1 level. α-Syn overexpression caused an obvious decrease of MDM2 protein level and further inhibited the ubiquitylation of IRF-1 (P < 0.01).

CONCLUSION

α-Syn blocks MDM2-mediated ubiquitylation of IRF-1 through ubiquitin proteasome pathway, thereby enhancing IRF-1 protein expression.

Mdm2 Promotes Odontoblast-like Differentiation by Ubiquitinating Dlx3 and p53

Dentin is an important structural component of the tooth. Odontoblast differentiation is an essential biological process that guarantees normal dentin formation, which is precisely regulated by various proteins. Murine double minute 2 (Mdm2) is an E3 ubiquitin ligase, and it plays a pivotal role in the differentiation of different cell types, such as osteoblasts and myoblasts. However, whether Mdm2 plays a role in odontoblast differentiation remains unknown. Here, we investigated the spatiotemporal expression of Mdm2 by immunostaining and found that Mdm2 was highly expressed in the odontoblasts and slightly in the dental papilla cells of mouse incisors and molars. Gene knockdown and overexpression experiments verified that Mdm2 promoted the odontoblast-like differentiation of mouse dental papilla cells (mDPCs). Intranuclear colocalization and physical interaction between Mdm2 and distal-less 3 (Dlx3), a transcription factor important for odontoblast differentiation, was found during the odontoblast-like differentiation of mDPCs by double immunofluorescence and immunoprecipitation. Mdm2 was proved to monoubiquitinate Dlx3, which enhanced the expression of Dlx3 target gene Dspp. In addition, p53, the canonical substrate of Mdm2, was validated to be also ubiquitinated but degraded by Mdm2 during the odontoblast-like differentiation of mDPCs. Gene knockdown experiments confirmed that p53 inhibited the odontoblast-like differentiation of mDPCs. p53 and Mdm2 double knockdown partially rescued the reduced odontoblast-like differentiation by knockdown of Mdm2 alone. Taken together, our study revealed that Mdm2 promoted the odontoblast-like differentiation of mDPCs by ubiquitinating both Dlx3 and p53. On one hand, the monoubiquitination of Dlx3 by Mdm2 led to upregulation of Dspp, which is a marker of the odontoblast differentiation. On the other hand, ubiquitination of p53 by Mdm2 resulted in its degradation, which eliminated the inhibitory effect of p53 on the odontoblast-like differentiation of mDPCs.

Untangling the Role of Polycomb Complexes in Chemotherapy Resistance

In this issue, Maganti and colleagues described an epigenetic link between reduced abundance of Polycomb-related protein MTF2 and chemotherapy resistance in refractory acute myeloid leukemia. MTF2 deficiency impaired expression of the PRC2 complex and deposition of H3K27me3 at many genes, including the key target gene MDM2, leading to increased MDM2 expression that in turn depleted p53 and thereby conferred chemoresistance. Cancer Discov; 8(11); 1348-51. ©2018 AACR See related article by Maganti et al., p. 1376.

MDM2-TP53 Crossregulation: An Underestimated Target to Promote Loss of TP53 Function and Cell Survival

Half of human cancers bear inactivating mutations of the tumor suppressor gene TP53, but the other half do not. In a recent issue of Cancer Cell, Dhar et al. and Zhu et al. reported that, in liver cancer and medulloblastoma, MDM2 is constitutively activated, causing a loss of TP53 function that does not require TP53 mutation. On theoretical grounds, such cancer would be amenable to treatment with MDM2 inhibitors.

Prognostic value of p53 and MDM2 Expression in Bilharziasis-Associated Squamous Cell Carcinoma of the Urinary Bladder

The aim of this study was to elucidate the associations between immunostaining for MDM2 and p53, their respective expression in squamous cell carcinoma of the urinary bladder, and the value of these variables for predicting treatment outcome after cystectomy. Inactivation of TP53 might play a role in the development and progression of bladder cancer. Complex formation with the MDM2 product is one mechanism that inactivates the p53 protein. Therefore, the MDM2 and the p53 protein were investigated to study potential interactions in bladder cancer. Fifty archival bladder tissue specimens were immunohistochemically stained using monoclonal antibodies against p53 and MDM2. Staining for p53 was observed in 48% of the specimens and staining for MDM2 in 20%. Univariate analysis demonstrated a significant correlation between p53 accumulation and survival (p=0.0101), while the correlation between MDM2 and survival was not significant (p=0.7183). The combined expression of MDM2 and p53 doest not add to the prognostic information provided by p53 alone.

Stressing Out PanIN: NRF2 Pushes over the Edge

The mechanisms by which chronic stress promote the development of pancreatic ductal adenocarcinoma (PDAC) are poorly defined. In this issue of Cancer Cell, Todoric et al. discover a role for impaired autophagy in the development of PDAC through p62-mediated activation of NRF2.

Assay for Ubiquitin Ligase Activity: High-Throughput Screen for Inhibitors of HDM2

An assay for the autoubiquitination activity of the E3 ligaseHDM2 (Mdm2) was developed and adapted to a high-throughput format to identify inhibitors of this activity. The assay can also be used tomeasure the activity of other E3s andmay be useful in finding both inhibitors and activators of a wide range of different ubiquitin ligases.

[p14ARF enhances cisplatin-induced apoptosis in human osteosarcoma cells in p53-independent pathway]

OBJECTIVE

To study effect of tumor suppressor p14ARF on cisplatin-induced apoptosis in human osteosarcoma cells with its molecular mechanisms to provide evidences for increasing chemosensitivity of osteosarcoma.

METHODS

pcDNA3.1-p14ARF plasmid was stable transfected into MG63 cells lack of p14ARF expression. Expression of p14ARF on mRNA and protein level was evaluated with RT-PCR and Western blot. MG63, MG63-vec and MG63-ARF cells were treated with cisplatin. Cell growth inhibition and IC50 were determined through MTT assay. Apoptosis was detected using fluorescence-activated cell sorting and Hoechst33258 staining. The expression of p53, Bax, p21, Mdm2, Fas, Caspase-3, caspase-9 and PARP was detected with Western blot. RNAi was used to silence p53. Cells were pre-treated with Caspase-9 specific inhibitor Z-LEHD-FMK to determine whether the effect was Caspase-9-dependent.

RESULTS

There was no expression of p14ARF in MG63 and MG63-vec cells but obvious expression in MG63-ARF cells on mRNA and protein level. Cell viability was 84.2%±4.3%, 80.8%±4.3% and 58.9%±5.4% in MG63, MG63-vec, and MG63-ARF cells after treatment of cisplatin for 72 h. IC50 was (11.1±0.6), (10.7±0.9) and (7.2±0.7) µmol/L. The apoptotic rate was 13.6%, 18.5% and 35.9% in groups, There were more obvious apoptotic more changes in MG63-ARF cells than MG63 and MG63-vec cells, and activation of Caspase-3, 9 and PARP on higher level in U2OS-ARF cells after stimulation with cisplatin for 72 h. The expression of p53, Bax, p21, Mdm2 and Fas, in MG63-vec and MG63-ARF cells did not changed (P>0.05). The expression of p53 was effectively and continuously suppressed by p53-siRNA in U2OS-vec and U2OS-ARF cells. The p53 silencing did not alter the cytotoxicity mediated by cisplatin treatment for 72 h (P>0.05). Cell viability was 96.8%±3.6%, 54.1%±5.7% and 89.5%±5.1% in Z-LEHD-FMK, cisplatin and Z-LEHD-FMK+cisplatin groups.

CONCLUSION

p14ARF enhances cisplatin-induced apoptosis in human osteosarcoma MG63 cells in p53-independent caspase-9-dependent pathway, in which the intrinsic mitochondrial apoptotic pathway is involved.

Subcellular Localization of Proteins Responding to Mitoxantrone-Induced DNA Damage in Leukaemic Cells

The aim of the present study was to investigate the subcellular localization of proteins participating in the double-strand break response pathway - p53, Mdm2, p21 and Chk2. MOLT-4 cells were pre-treated with mitoxantrone in concentrations 1 nmol/l and 5 nmol/l. The trypan blue technique was used to determine cell viability and proliferation. Western blotting was used to evaluate changes in p53, Mdm2 and Chk2 protein expression and sandwich ELISA was used to evaluate changes in the p21 protein amount. After 1 nmol/l mitoxantrone cells did not die, but their ability to proliferate was decreased. The p53 protein was activated and phosphorylated at serines 15 and 392 and accumulated in the nucleus after 24 and 48 h. The Mdm2 protein was present in the cytoplasm with its maximal level after 8 and 16 h. The p21 protein was detected in the nucleus after 24 and 48 h. Increased levels of phosphorylated Chk2 at threonine 68 were observed in the cytoplasmic fraction after 24 and 48 h of mitoxantrone treatment. We used mitoxantrone as an inducer of double-strand breaks to bring new data about the subcellular distribution of proteins responding to DNA damage. In MOLT-4 cells, the p53 protein was activated. p53 was phosphorylated at serines 15 and 392 and accumulated in the nucleus. The Mdm2 protein was activated in advance to p53 and occurred in the cytoplasm. The p21 protein was present in the nucleus. Chk2 kinase was activated by the phosphorylation at threonine 68 and we observed increased levels of this protein in the cytoplasmic fraction.

[p14ARF enhances chemosensitivity to cisplatin in human osteosarcoma U2OS cells through p53 apoptotic pathway]

OBJECTIVE

To explore the effects of tumor suppressor p14ARF on chemosensitivity of human osteosarcoma U2OS cells to cisplatin and elucidate its molecular mechanism.

METHODS

U2OS cells expressing no p14ARF and U2OS-ARF cells expressing p14ARF stably through stable transfection were treated with cisplatin. Cell viability and IC50 were assayed with methyl thiazolyl tetrazolium (MTT). Apoptosis was examined by fluorescence-activated cell sorting and Hoechst33258 staining. The expressions of p53, Bax, p21, Mdm2 and Fas were detected by Western blot. And colorimetry was used to determine the activities of caspase-3, caspase-8 and caspase-9.

RESULTS

The viability was 84.8% ± 4.4%, 86.9% ± 5.0% and 66.7% ± 4.6% respectively in U2OS, U2OS-vec and U2OS-ARF cells. The values of IC50 were (15.8 ± 0.9) µmol/L, (16.3 ± 0.6) and (8.9 ± 0.8) µmol/L respectively in U2OS, U2OS-vec and U2OS-ARF cells. The levels of viability and IC50 obviously decreased in U2OS-ARF cells in response to cisplatin (P < 0.05). There were higher apoptotic rate and more obvious apoptotic morphological changes in U2OS-ARF cells than U2OS and U2OS-vec cells. The basal levels of p53, Mdm2 and p21 in U2OS-ARF cells were slightly higher than those in U2OS-vec cells. Cisplatin up-regulated p53, Mdm2 and p21 in both cell lines. However, the up-regulation was more pronounced in U2OS-ARF cells. Cisplatin did not change the levels of Bax and Fas in U2OS-vec cells. Bax protein was up-regulated in U2OS-ARF cells while the level of Fas remained constant. p14ARF also enhanced the activities of caspase-9 and caspase-3 in response to cisplatin.

CONCLUSION

p14ARF enhances the chemosensitivity to cisplatin in human osteosarcoma U2OS cells through p53 apoptotic pathway. And intrinsic mitochondrial apoptosis is involved.

The Novel Yeast PAS Kinase Rim15 Orchestrates G0-Associated Antioxidant Defense Mechanisms

The hdm2 protein, upon binding to p53, inhibits its tumor suppressor activity. The inhibition of the p53-hdm2 interaction represents therefore a new therapeutic strategy to activate wild type p53 in tumors. Potent low molecular weight compounds inhibiting this protein-protein interaction, which are active in vivo, have just been identified. This offers new perspectives and hopes in this research area.

The p53 paddy wagon: COP1, Pirh2, and MDM2 are found resisting apoptosis and growth arrest

For years, the growth inhibitory effects of the tumor suppressor p53 were thought to be antagonized predominantly by the ubiquitin ligase, MDM2. It has long been established that MDM2 physically associates with p53 and targets this tumor suppressor for proteasomal degradation. In light of recent findings, it now appears that MDM2 may not be the only ubiquitin ligase that negatively controls p53 function. Two recently discovered proteins, Pirh2 and COP1, are also believed to facilitate p53 degradation via the ubiquitin-proteasome pathway. Both proteins are upregulated by p53 as well as genotoxic stress and each has been found to directly promote p53 ubiquitination and degradation. Future studies in this field will now face the challenge of elucidating the physiological significance of three molecules all apparently able to independently facilitate p53 degradation and abrogate its function.

UVB-induced cell death signaling is associated with G1-S progression and transcription inhibition in primary human fibroblasts

DNA damage induced by ultraviolet (UV) radiation can be removed by nucleotide excision repair through two sub-pathways, one general (GGR) and the other specific for transcribed DNA (TCR), and the processing of unrepaired lesions trigger signals that may lead to cell death. These signals involve the tumor suppressor p53 protein, a central regulator of cell responses to DNA damage, and the E3 ubiquitin ligase Mdm2, that forms a feedback regulatory loop with p53. The involvement of cell cycle and transcription on the signaling to apoptosis was investigated in UVB-irradiated synchronized, DNA repair proficient, CS-B (TCR-deficient) and XP-C (GGR-deficient) primary human fibroblasts. Cells were irradiated in the G1 phase of the cell cycle, with two doses with equivalent levels of apoptosis (low and high), defined for each cell line. In the three cell lines, the low doses of UVB caused only a transient delay in progression to the S phase, whereas the high doses induced permanent cell cycle arrest. However, while accumulation of Mdm2 correlated well with the recovery from transcription inhibition at the low doses for normal and CS-B fibroblasts, for XP-C cells this protein was shown to be accumulated even at UVB doses that induced high levels of apoptosis. Thus, UVB-induced accumulation of Mdm2 is critical for counteracting p53 activation and apoptosis avoidance, but its effect is limited due to transcription inhibition. However, in the case of XP-C cells, an excess of unrepaired DNA damage would be sufficient to block S phase progression, which would signal to apoptosis, independent of Mdm2 accumulation. The data clearly discriminate DNA damage signals that lead to cell death, depending on the presence of UVB-induced DNA damage in replicating or transcribing regions.

Rapid detection of SNP (c.309T>G) in the MDM2 gene by the Duplex SmartAmp method

Background

Genetic polymorphisms in the human MDM2 gene are suggested to be a tumor susceptibility marker and a prognostic factor for cancer. It has been reported that a single nucleotide polymorphism (SNP) c.309T>G in the MDM2 gene attenuates the tumor suppressor activity of p53 and accelerates tumor formation in humans.

Methodology

In this study, to detect the SNP c.309T>G in the MDM2 gene, we have developed a new SNP detection method, named “Duplex SmartAmp,” which enabled us to simultaneously detect both 309T and 309G alleles in one tube. To develop this new method, we introduced new primers i.e., nBP and oBPs, as well as two different fluorescent dyes that separately detect those genetic polymorphisms.

Results and Conclusions

By the Duplex SmartAmp method, the genetic polymorphisms of the MDM2 gene were detected directly from a small amount of genomic DNA or blood samples. We used 96 genomic DNA and 24 blood samples to validate the Duplex SmartAmp by comparison with results of the conventional PCR-RFLP method; consequently, the Duplex SmartAmp results agreed totally with those of the PCR-RFLP method. Thus, the new SNP detection method is considered useful for detecting the SNP c.309T>G in the MDM2 gene so as to judge cancer susceptibility against some cellular stress in the clinical setting, and also to handle a large number of samples and enable rapid clinical diagnosis.

Harmonic oscillations in homeostatic controllers: Dynamics of the p53 regulatory system

Homeostatic mechanisms are essential for the protection and adaptation of organisms in a changing and challenging environment. Previously, we have described molecular mechanisms that lead to robust homeostasis/adaptation under inflow or outflow perturbations. Here we report that harmonic oscillations occur in models of such homeostatic controllers and that a close relationship exists between the control of the p53/Mdm2 system and that of a homeostatic inflow controller. This homeostatic control model of the p53 system provides an explanation why large fluctuations in the amplitude of p53/Mdm2 oscillations may arise as part of the homeostatic regulation of p53 by Mdm2 under DNA-damaging conditions. In the presence of DNA damage p53 is upregulated, but is subject to a tight control by Mdm2 and other factors to avoid a premature apoptotic response of the cell at low DNA damage levels. One of the regulatory steps is the Mdm2-mediated degradation of p53 by the proteasome. Oscillations in the p53/Mdm2 system are considered to be part of a mechanism by which a cell decides between cell cycle arrest/DNA repair and apoptosis. In the homeostatic inflow control model, harmonic oscillations in p53/Mdm2 levels arise when the binding strength of p53 to degradation complexes increases. Due to the harmonic character of the oscillations rapid fluctuating noise can lead, as experimentally observed, to large variations in the amplitude of the oscillation but not in their period, a behavior which has been difficult to simulate by deterministic limit-cycle models. In conclusion, the oscillatory response of homeostatic controllers may provide new insights into the origin and role of oscillations observed in homeostatically controlled molecular networks.

Abundant Expression of Spliced HDM2 in Hodgkin Lymphoma Cells does not Interfere with p14ARFand p53 Binding

Recently, comparative genomic hybridization (CGH)- and fluorescence in situ hybridization (FISH)-analyses of native Hodgkin and Reed-Sternberg (H&RS) cells extracted from Hodgkin lymphoma (HL) revealed a recurrent amplification of the HDM2 locus on chromosome 12. HDM2 is known to target, inactivate and to degrade p53. Wild type (wt) p53 protein is detected in high levels in HL. Simultaneously, stabilized wt p53 and spliced hdm2 transcripts have been observed in different tumors. Therefore, we examined the expression and structure of HDM2 in HL cell lines and possible effects on components of the p53 pathway. DNA integrity and induction potential of p53 was verified by DNA sequencing and detection of potential effector proteins (p21(WAF/CIP), HDM2) using immunofluorescence, respectively. All HL cell lines show an overexpression of HDM2 protein. Furthermore, several different spliced hdm2 transcripts (mdm-sv) including five new variants lacking a functional p53 binding site were characterized. If expressed, corresponding proteins were shown to be not restricted to the nucleus. Co-localization of the potential binding partners HDM2/p14(ARF) and HDM2/p53 was found in HL cell lines. We suggest that HDM2-sv have no significant disturbing influence on the interaction of these proteins.

Differing effects of breast cancer 1, early onset (BRCA1) and ataxia‐telangiectasia mutated (ATM) mutations on cellular responses to ionizing radiation

PURPOSE

The ataxia-telangiectasia mutated (ATM) gene encodes a protein kinase, the activation of which is an early event in the cellular response to ionizing radiation. One of the many substrates of ATM is BRCA1 (breast cancer 1, early onset gene), which has been associated with susceptibility to breast and ovarian cancer, and has been implicated in DNA repair processes. Various cellular responses to radiation were analysed in cells with mutations in ATM or BRCA1 in an attempt to clarify which effects of ATM can be mediated through BRCA1.

MATERIALS AND METHODS

The response to radiation of cells with mutations in ATM or BRCA1 was examined, as were BRCA1-mutant tumour cells transfected with an exogenous wild-type BRCA1 allele. Assays included cell-survival curves, studies of potentially lethal damage repair, measurement of chromosomal aberrations and of G1 arrest, and Western blot analysis of lysates of irradiated cells to determine the phosphorylation of the product of the human Mdm2 gene (HDM2).

RESULTS

Both ATM and BRCA1 mutations were associated with sensitivity to ionizing radiation, deficient repair of potentially lethal damage and markedly increased chromosomal aberrations. A BRCA1-mutated tumour cell line HCC1937, like ATM mutant cells, did not exhibit a normal G1 arrest but, unlike ATM mutant cells, did exhibit phosphorylation of HDM2. Expression of wild-type BRCA1 in HCC1937 cells partially restored radioresistance, restored repair of potentially lethal damage and markedly reduced radiation-induced chromosomal aberrations. G1 arrest, however, was not restored by expression of BRCA1.

CONCLUSIONS

The results are consistent with a model in which ATM phosphorylation of BRCA1 regulates DNA repair functions, particularly those involved in potentially lethal damage repair and chromosomal integrity, but not other aspects of the cellular response to radiation such as G1 cell cycle arrest. To the authors' knowledge, this is the first demonstration of the ability of exogenously expressed BRCA1 to restore the ability to perform potentially lethal damage repair and maintain chromosomal integrity in irradiated cells.

Induction of endoreduplication by a JNK inhibitor SP600125 in human lung carcinoma A 549 cells

The effect of the pan c-Jun N-terminal kinase (JNK) inhibitor SP600125 on the proliferation of human lung carcinoma A549 cells has been evaluated. We have shown that SP600125 completely inhibited the proliferation of A549 cells, the cycle arrest being in G2/M phase. When cells were treated with SP600125 for >12h, a cell population with DNA content of 4n to 8n was detected. Moreover, the effect of SP600125 on the expression of cell cycle related proteins was an upregulation of p53 protein accompanied by an increase in its molecular mass. Prolonged SP600125 treatment downregulated p21, Bax and Mdm2 expression, but increased the level of the cellular p53-Mdm2 complex. Taken together, we show that SP600125 could induce G2/M cell cycle arrest and endoreduplication in a p21 independent manner, and that SP600125 could also post-translationally modify p53 to modify its function. Our data show that basic JNK activity plays an important role in the progression of the cell cycle at G2/M cell phase.

NKX3.1 stabilizes p53, inhibits AKT activation, and blocks prostate cancer initiation caused by PTEN loss

We demonstrate that PTEN loss causes reduced NKX3.1 expression in both murine and human prostate cancers. Restoration of Nkx3.1 expression in vivo in Pten null epithelium leads to decreased cell proliferation, increased cell death, and prevention of tumor initiation. Whereas androgen receptor (AR) positively regulates NKX3.1 expression, NKX3.1 negatively modulates AR transcription and consequently the AR-associated signaling events. Consistent with its tumor suppressor functions, NKX3.1 engages cell cycle and cell death machinery via association with HDAC1, leading to increased p53 acetylation and half-life through MDM2-dependent mechanisms. Importantly, overexpression of Nkx3.1 has little effect on Pten wild-type epithelium, suggesting that PTEN plays a predominant role in PTEN-NKX3.1 interplay. Manipulating NKX3.1 expression may serve as a therapeutic strategy for treating PTEN-deficient prostate cancers.

Preferential inactivation of the p53 tumor suppressor pathway and lack of EGFR amplification distinguish de novo high grade pediatric astrocytomas from de novo adult astrocytomas

Classification of high grade astrocytomas of children into genetic subtypes similar to the adult remains to be defined. Here we report an extensive characterization of 29 high grade pediatric astrocytomas, 7 WHO grade III and 22 WHO grade IV, for genetic alterations frequently observed in high grade adult astrocytomas occurring in either the p53/MDM2/p14ARF or Rb/CDK4/p16INK4a tumor suppressor pathways. In addition, we have assessed the contribution of EGFR overexpression and amplification and LOH for chromosome 10, two genetic alterations commonly associated with the development of de novo adult glioblastoma for their roles in the development of de novo astrocytomas of childhood. Our results suggest two major differences in the genetic pathway(s) leading to the formation of de novo high grade astrocytomas in children compared with those of the adult. Our findings show preferential inactivation of the p53 tumor suppressor pathway in >95% of pediatric astrocytomas versus inactivation of the Rb tumor suppressor pathway in <25% of the same tumors. In addition, de novo high grade pediatric astrocytomas lack amplification of the EGFR gene compared with EGFR amplification in one-third of adult glioblastomas. Since drug treatments and gene therapy strategies exploit specific genetic alterations in tumor cells, our findings have important implications for the future development of treatments for high grade pediatric astrocytomas.

Survival of patients with glioblastoma multiforme is not influenced by altered expression of p16, p53, EGFR, MDM2 or Bcl-2 genes

Deregulated expression of one or more growth control genes including p16, p53, EGF receptor (EGFR), MDM2 or Bcl-2 may contribute to the treatment resistance phenotype of GBM and generally poor patient survival. Clinically, GBM have been divided into two major groups defined by (1) histologic progression from a low grade tumor ("progressive" or "secondary" GBM) contrasted with (2) those which show initial clinical presentation without a prior history ("de novo" or "primary" GBM). Using molecular genetic analysis for p53 gene mutations together with immunophenotyping for overexpression of EGFR, up to four GBM variants can be distinguished, including the p53+/EGFR- progressive or the p53-/EGFR+ de novo variant. We examined the survival of 80 adult patients diagnosed with astrocytic GBM stratified by age category (>40, 41-60 or 61-80) to determine whether alterations in any one given growth control gene or whether different genetic variants of GBM (progressive versus de novo) were associated with different survival outcomes. Survival testing using Kaplan-Meier plots for GBM patients with or without altered expression of p16, p53, EGFR, MDM2 or Bcl-2 showed no significant differences by age group or by gene expression indicating a lack of prognostic value for GBM. Also the clinical outcome among patients with GBM showed no significant differences within each age category for any GBM variant including the progressive and de novo GBM variants indicating similar biologic behavior despite different genotypes. Using a pairwise comparison, one-third of the GBM with normal p16 expression showed accumulation of MDM2 protein and this association approached statistical significance (0.01 < P < 0.05) using the Bonferroni procedure. These GBM may represent a variant in which the p19ARF/MDM2/p53 pathway may be deregulated rather than the p16/cyclin D-CDK4/Rb pathway.

Immunohistochemical Status of p53, MDM2, bcl2, bax, and ER in Invasive Ductal Breast Carcinoma in Tunisian Patients

TP53 gene alterations have been associated with sporadic breast cancer. To assess the role of p53 in invasive ductal carcinoma (IDC) of the breast among Tunisian patients, p53 protein status was studied by immuno-histochemical analysis. The p53 protein was expressed in 41 of 70 (58%) tumors. Study of the status of its target gene expression showed that MDM2 was overexpressed in 43 tumors (61%), bcl2 in 29 (41%), and bax in only 9 (12%). Estrogen receptor (ER) was detected in 38 tumor tissues (54%). The accumulated p53 was significantly associated with MDM2-positive, bcl2-negative, and ER-negative tumors (P = 0.024, P = 0.000027, and P = 0.000008, respectively), whereas with bax the correlaton was not significant. Bcl2 immunostaining displayed a positive correlation with ER (P = 0.001). A significantly higher fraction of p53-positive cells was observed in ER-negative SBRII-SBRIII tumors than in ER-positive SBRI-SBRII tumors (P = 0.000066). bcl2-positive tumors were significantly correlated with ER-positive/SBRI-SBRII tumors (P = 0.007), but negatively correlated with p53/bax (P = 0000004). MDM2 immunostaining displayed the same phenotype as p53 in the correlation with bcl2 and ER (P = 0.003), strengthened by significant associations between MDM2-positive/p53-positive and bcl2-negative or ER-negative, respectively (P = 0.00005 and P = 0.000001, respectively). MDM2-positive cells were significantly correlated with the p53-positive/bax-negative phenotype (P = 0.04). These results suggest that p53 accumulated in these tumor tissues is associated with bad prognostic markers (ER-negative, SBRIII) of IDC. MDM2 overexpression might be responsible for the accumulated p53 value in IDC. Regulation of the apoptotic process is involved in IDC; bcl2 is associated with a good prognostic marker (ER-positive and SBRI-II), whereas the regulation of bax is complex and does not necessarily correlate with the overexpression of p53.

Activated AKT regulates NF-kappaB activation, p53 inhibition and cell survival in HTLV-1-transformed cells

AKT activation enhances resistance to apoptosis and induces cell survival signaling through multiple downstream pathways. We now present evidence that AKT is activated in HTLV-1-transformed cells and that Tax activation of AKT is linked to NF-kappaB activation, p53 inhibition and cell survival. Overexpression of AKT wild type (WT), but not a kinase dead (KD) mutant, resulted in increased Tax-mediated NF-kappaB activation. Blocking AKT with the PI3K/AKT inhibitor LY294002 or AKT SiRNA prevented NF-kappaB activation and inhibition of p53. Treatment of C81 cells with LY294002 resulted in an increase in the p53-responsive gene MDM2, suggesting a role for AKT in the Tax-mediated regulation of p53 transcriptional activity. Further, we show that LY294002 treatment of C81 cells abrogates in vitro IKKbeta phosphorylation of p65 and causes a reduction of p65 Ser-536 phosphorylation in vivo, steps critical to p53 inhibition. Interestingly, blockage of AKT function did not affect IKKbeta phosphorylation of IkappaBalpha in vitro suggesting selective activity of AKT on the IKKbeta complex. Finally, AKT prosurvival function in HTLV-1-transformed cells is linked to expression of Bcl-xL. We suggest that AKT plays a role in the activation of prosurvival pathways in HTLV-1-transformed cells, possibly through NF-kappaB activation and inhibition of p53 transcription activity.

Murine double minute 2 as a therapeutic target for radiation sensitization of lung cancer

Murine double minute 2 (MDM2) inhibits p53-mediated functions, which are essential for therapies using DNA-damaging agents. The purpose of this study was to determine whether MDM2 inhibition enhances the radiosensitivity of a lung cancer model. The effects of MDM2 inhibition on tumor vasculature were also studied. Transient transfection of H460 lung cancer cells and human umbilical vascular endothelial cells (HUVEC) with antisense oligonucleotides (ASODN) against MDM2 resulted in a reduced level of MDM2 and increased levels of p21 and p53. Clonogenic assays showed that inhibition of MDM2 greatly decreased cell survival following irradiation. Quantification of apoptotic cells by 7-aminoactinomycin D staining and of senescent cells by X-gal staining showed that both processes were significantly increased in H460 cells treated with MDM2-specific ASODN and radiation. H460 xenografts that were treated with MDM2 ASODN plus radiotherapy also showed significant growth delay (P < 0.001) and increased apoptosis by terminal deoxynucleotidyl transferase-mediated nick end labeling staining. HUVECs transfected with MDM2-specific ASODN showed impaired viability and migration with decreased tube formation. Doppler studies showed that tumor blood flow was compromised when H460 xenografts were treated with MDM2-specific ASODN and radiation. A combination of radiotherapy and inhibition of MDM2 through the antisense approach results in improved tumor control in the H460 lung cancer model. This implies that a similar strategy should be investigated among patients with locally advanced lung cancer, receiving thoracic radiotherapy.

Regulation of ubiquitin ligase dynamics by the nucleolus

Cellular pathways relay information through dynamic protein interactions. We have assessed the kinetic properties of the murine double minute protein (MDM2) and von Hippel-Lindau (VHL) ubiquitin ligases in living cells under physiological conditions that alter the stability of their respective p53 and hypoxia-inducible factor substrates. Photobleaching experiments reveal that MDM2 and VHL are highly mobile proteins in settings where their substrates are efficiently degraded. The nucleolar architecture converts MDM2 and VHL to a static state in response to regulatory cues that are associated with substrate stability. After signal termination, the nucleolus is able to rapidly release these proteins from static detention, thereby restoring their high mobility profiles. A protein surface region of VHL's β-sheet domain was identified as a discrete [H+]-responsive nucleolar detention signal that targets the VHL/Cullin-2 ubiquitin ligase complex to nucleoli in response to physiological fluctuations in environmental pH. Data shown here provide the first evidence that cells have evolved a mechanism to regulate molecular networks by reversibly switching proteins between a mobile and static state.

The time-dependent serial gene response to Zeocin treatment involves caspase-dependent apoptosis in HeLa cells

Zeocin, a member of the bleomycin/phleomycin family of antibiotics, is known to bind DNA and to induce apoptosis in cervical cancer cells, but the mechanism underlying this apoptotic response is poorly understood. The present study was undertaken to elucidate time-dependent serial transcript patterns in the HeLa cervical carcinoma cell line, following treatment with Zeocin. The HeLa cell proliferation rate was found to gradually decrease following Zeocin exposure, in a time-and dose-dependent manner. RNA transcript level measurements, for time-dependent serial gene expression profiling, were determined at 0, 6, 12, 18 and 24 hr using a 0.5 k apoptosis functional microarray chip. Further statistical analysis, using a significance test at a 95% confidence level, for transcripts with a greater than 2-fold change on the array chips, identified 49 up-regulated and 57 down-regulated genes. Our gene expression profile data indicate that Zeocin treatment induces an initial release of cytochrome c, the down-regulation of Bcl-X (L), ENDOG, DAXX and MDM2, and the up-regulation of CASP and BID. This suggests that a p53-independent mitochondrial caspase cascade pathway is primarily involved in Zeocin-induced apoptosis. Such caspasedependent cytotoxic activity also implies that this cell death pathway occurs via the caspase 8 and BID genes. However, disruption of either FAS or TNFR1 signaling did not interfere with the Zeocin induced apoptotic response in our experimental system. We hypothesize that Zeocin could be active against cervical cancer cell resistance to conventional chemotherapy and postulate that Zeocin is a novel candidate for the development of new chemotherapeutic treatments of gynecological cancers.

Control of p53 nuclear accumulation in stressed cells

Wild-type p53 accumulates in the nucleus following stress. Current models suggest this nuclear accumulation involves phosphorylation at p53 N-terminal sites, and inhibition of murine double minute (MDM)2-dependent nuclear export. We monitored the effects of stress on MDM2-dependent nuclear export of wild-type p53 and a mutant lacking N-terminal phosphorylation sites. Etoposide and ionizing radiation inhibited nuclear export of wild-type p53 and the phosphor-mutant to comparable extents, indicating nuclear export inhibition does not require N-terminal phosphorylation. Cytoplasmic p53 accumulated in the nucleus of transfected cells treated with the nuclear export-inhibitor leptomycin B (LMB). Interestingly, LMB caused less p53 nuclear accumulation than stress treatment, suggesting stress-induced nuclear accumulation of p53 does not result solely from inhibited nuclear export.

Apigenin inhibits VEGF and HIF-1 expression via PI3K/AKT/p70S6K1 and HDM2/p53 pathways

Apigenin is a nontoxic dietary flavonoid that has been shown to possess anti-tumor properties and therefore poses special interest for the development of a novel chemopreventive and/or chemotherapeutic agent for cancer. Ovarian cancer is one of the most common causes of cancer death among women. Here we demonstrate that apigenin inhibits expression of vascular endothelial growth factor (VEGF) in human ovarian cancer cells. VEGF plays an important role in tumor angiogenesis and growth. We found that apigenin inhibited VEGF expression at the transcriptional level through expression of hypoxia-inducible factor 1alpha (HIF-1alpha). Apigenin inhibited expression of HIF-1alpha and VEGF via the PI3K/AKT/p70S6K1 and HDM2/p53 pathways. Apigenin inhibited tube formation in vitro by endothelial cells. These findings reveal a novel role of apigenin in inhibiting HIF-1 and VEGF expression that is important for tumor angiogenesis and growth, identifying new signaling molecules that mediate this regulation.

Increased expression of MDM2, cyclin D1, and p27Kip1 in carcinogen-induced rat mammary tumors

It is thought that environmental pollutants, such as polycyclic aromatic hydrocarbons (PAH), contribute to human breast tumorigenesis, yet their roles remain incompletely elucidated. The prototypical PAH 7,12-dimethylbenz(alpha)anthracene (DMBA) specifically and effectively induces mammary tumor formation in rodent models. In an attempt to explore the molecular mechanisms by which PAH initiates and promotes mammary tumorigenesis, we examined the expression of several cell cycle regulators in rat mammary tumors induced by DMBA. Expression of cyclin D1, murine double minute-2 (MDM2), and Akt was up-regulated in tumors in comparison to normal mammary glands, as indicated by RT-PCR, Western blot analysis, and immunohistochemical staining. Expression of p27Kip1 protein was also elevated in the tumors with increased cytoplasmic localization. However, RB protein remained hyperphosphorylated. To directly test the effects of DMBA, the MCF-7 human breast cancer cells were treated. DMBA induced MDM2 expression in a dose- and time-dependent fashion in the MCF-7 cells, and this activation appeared to be p53 dependent. These data suggest that activation of cyclin D1, MDM2, and AKT as well as increased expression and cytoplasmic localization of p27Kip1 may play a role in this model of environmental pollutant-induced mammary tumorigenesis.

Molecular features of adult glioma associated with patient race/ethnicity, age, and a polymorphism in O6-methylguanine-DNA-methyltransferase

BACKGROUND

Risk factors for adult glioma in the San Francisco Bay Area include well-known demographic features such as age and race/ethnicity, and our previous studies indicated that these characteristics are associated with the TP53 mutation status of patients' tumors. We enlarged our study to assess the relationships of risk factors with TP53 as well as epidermal growth factor receptor (EGFR) and murine double minute-2 (MDM2) gene amplification and expression and the germ line Leu84Phe polymorphism in the DNA repair protein O6-methylguanine-DNA-methyltransferase (MGMT). MGMT expression may depend on the TP53 status of cells.

METHODS

Molecular analyses were carried out on 556 incident astrocytic tumors. MGMT genotype data were collected on germ line DNA from 260 of these cases.

RESULTS

The tumor data confirm the inverse relationships between TP53 mutation and MDM2 (P = 0.04) or EGFR (P = 0.004) amplification and that patients whose tumors contain TP53 mutations are younger than those without (P < 0.001). Although there was little difference in age of patient by EGFR amplification or expression among glioblastoma multiforme cases, EGFR gene amplification was associated with much older age of onset of anaplastic astrocytoma; for example, EGFR-amplified anaplastic astrocytoma cases were on average 63 years old compared with 48 years for nonamplified cases (P = 0.005). An increased prevalence of TP53 mutation positive glioblastoma multiforme was noted among nonwhites (African American and Asian) compared with whites (Latino and non-Latino; P = 0.004). Carriers of the MGMT variant 84Phe allele were significantly less likely to have tumors with TP53 overexpression (odds ratio, 0.30; 95% confidence interval, 0.13-0.71) and somewhat less likely to have tumors with any TP53 mutation (odds ratio, 0.47; 95% confidence interval, 0.13-1.69) after adjusting for age, gender, and ethnicity. Interestingly, EGFR gene amplification and EGFR protein overexpression were also inversely associated with the MGMT 84Phe allele.

CONCLUSIONS

Our results are consistent with ethnic variation in glioma pathogenesis. The data on MGMT show that an inherited factor involving the repair of methylation and other alkylation damage, specifically to the O6 position of guanine, may be associated with the development of tumors that proceed in their development without TP53 mutations or accumulation of TP53 protein and possibly also those that do not involve amplification of the EGFR locus.

HAUSP, a deubiquitinating enzyme for p53, is polyubiquitinated, polyneddylated, and dimerized

The tumor suppressor protein p53 is ubiquitinated and neddylated by MDM2 and then degraded by 26S proteasome. However, p53 is stabilized by the HAUSP (Herpes-virus-associated ubiquitin-specific protease) deubiquitinating enzyme. In this study, we discovered that rat HAUSP (rHAUSP) is polyubiquitinated, polyneddylated, and dimerized using co-immunoprecipitation assays. This suggests that rHAUSP may function as a dimer or multimer and is also degraded through the proteasome-mediated degradation. Transfection of rHAUSP into RGC-Lac-Z cell line with the integrated p53 response element revealed that rHAUSP contributed to p53 stabilization, and a rHAUSP (C224S) mutant contributed to p53 destabilization in a dose-dependent manner.

Structure-based design of potent non-peptide MDM2 inhibitors

A successful structure-based design of a class of non-peptide small-molecule MDM2 inhibitors targeting the p53-MDM2 protein-protein interaction is reported. The most potent compound 1d binds to MDM2 protein with a Ki value of 86 nM and is 18 times more potent than a natural p53 peptide (residues 16-27). Compound 1d is potent in inhibition of cell growth in LNCaP prostate cancer cells with wild-type p53 and shows only a weak activity in PC-3 prostate cancer cells with a deleted p53. Importantly, 1d has a minimal toxicity to normal prostate epithelial cells. Our studies provide a convincing example that structure-based strategy can be employed to design highly potent, non-peptide, cell-permeable, small-molecule inhibitors to target protein-protein interaction, which remains a very challenging area in chemical biology and drug design.