Inhibition of MDM2 homodimerization by XIAP IRES stabilizes MDM2, influencing cancer cell survival

An MDM2 degrader shows potent cytotoxicity to MDM2-overexpressing acute lymphoblastic leukemia cells with minimal toxicity to normal cells/tissues

The MDM2 oncogene is amplified and/or overexpressed in various human cancers and elevated expression of MDM2 protein acts as a survival factor promoting cancer progression through both p53-dependent and -independent pathways. Here, we report a novel small-molecule chemical compound (MX69-102) that we identified to induce MDM2 protein degradation, resulting in reactivation of p53, inhibition of XIAP, and potent cell growth inhibition and apoptosis in MDM2-overexpressing acute lymphoblastic leukemia (ALL) in vitro and in vivo. We have previously identified a compound (MX69) that binds to the MDM2 C-terminal RING domain and induces MDM2 protein degradation. In the present study, we performed structural modifications of MX69 and selected analog MX69-102, showing increased MDM2-targeting activity. MX69-102 exhibited significantly enhanced inhibitory and apoptotic effects on a group of MDM2-overexpressing ALL cell lines in vitro with IC50 values of about 0.2 μM, representing an approximately 38-fold increase in activity compared to MX69. MX69-102 also showed effective inhibition on xenografted human MDM2-overexpressing ALL in SCID mice. Importantly, MX69-102 had minimal or no inhibitory effect on normal human hematopoiesis in vitro and was very well tolerated in vivo in animal models. Based on the strong inhibitory and apoptotic activity against MDM2-overexpressing ALL, along with minimal or no toxicity to normal cells/tissues, MX69-102 is a candidate for further development as a novel MDM2-targeted therapeutic drug for refractory/MDM2-overexpressing ALL.

Identification of MDM2 as a prognostic and immunotherapeutic biomarker in a comprehensive pan-cancer analysis: A promising target for breast cancer, bladder cancer and ovarian cancer immunotherapy

BACKGROUND

The murine double minute 2 (MDM2) gene is a crucial factor in the development and progression of various cancer types. Multiple rigorous scientific studies have consistently shown its involvement in tumorigenesis and cancer progression in a wide range of cancer types. However, a comprehensive analysis of the role of MDM2 in human cancer has yet to be conducted.

METHODS

We used various databases, including TIMER2.0, TCGA, GTEx and STRING, to analyze MDM2 expression and its correlation with clinical outcomes, interacting genes and immune cell infiltration. We also investigated the association of MDM2 with immune checkpoints and performed gene enrichment analysis using DAVID tools.

RESULTS

The pan-cancer MDM2 analysis found that MDM2 expression and mutation status were observably different in 25 types of cancer tissue compared with healthy tissues, and prognosis analysis showed that there was a significant correlation between MDM2 expression and patient prognosis. Furthermore, correlation analysis showed that MDM2 expression was correlated with tumor mutational burden, microsatellite instability and drug sensitivity in certain cancer types. We found that there was an association between MDM2 expression and immune cell infiltration across cancer types, and MDM2 inhibitors might enhance the effect of immunotherapy on breast cancer, bladder cancer and ovarian cancer.

CONCLUSIONS

The first systematic pan-cancer analysis of MDM2 was conducted, and it demonstrated that MDM2 was a reliable prognostic biomarker and was closely related to cancer immunity, providing a potential immunotherapeutic target for breast cancer, bladder cancer and ovarian cancer.

Synthesis and biological evaluation of dual MDM2/XIAP inhibitors based on the tetrahydroquinoline scaffold

Overexpression of both human murine double minute 2 (MDM2) and X-linked inhibitor of apoptosis protein (XIAP) is detected in tumor cells from several cancer types, including childhood acute leukemia lymphoma (ALL), neuroblastoma (NB), and prostate cancer, and is associated with disease progression and treatment resistance. In this report, we described the design and syntheses of a series of dual MDM2/XIAP inhibitors based on the tetrahydroquinoline scaffold from our previously reported lead compound JW-2-107 and tested their cytotoxicity in a panel of human cancer cell lines. The best compound identified in this study is compound 3e. Western blot analyses demonstrated that treatments with 3e decreased MDM2 and XIAP protein levels and increased expression of p53, resulting in cancer cell growth inhibition and cell death. Furthermore, compound 3e effectively inhibited tumor growth in vivo when tested using a human 22Rv1 prostate cancer xenograft model. Collectively, results in this study strongly suggest that the tetrahydroquinoline scaffold, represented by 3e and our earlier lead compound JW-2-107, has abilities to dual target MDM2 and XIAP and is promising for further preclinical development.

Combined inhibition of XIAP and autophagy induces apoptosis and differentiation in acute myeloid leukaemia

Perturbations in autophagy, apoptosis and differentiation have greatly affected the progression and therapy of acute myeloid leukaemia (AML). The role of X-linked inhibitor of apoptosis (XIAP)-related autophagy remains unclear in AML therapeutics. Here, we found that XIAP was highly expressed and associated with poor overall survival in patients with AML. Furthermore, pharmacologic inhibition of XIAP using birinapant or XIAP knockdown via siRNA impaired the proliferation and clonogenic capacity by inducing autophagy and apoptosis in AML cells. Intriguingly, birinapant-induced cell death was aggravated in combination with ATG5 siRNA or an autophagy inhibitor spautin-1, suggesting that autophagy may be a pro-survival signalling. Spautin-1 further enhanced the ROS level and myeloid differentiation in THP-1 cells treated with birinapant. The mechanism analysis showed that XIAP interacted with MDM2 and p53, and XIAP inhibition notably downregulated p53, substantially increased the AMPKα1 phosphorylation and downregulated the mTOR phosphorylation. Combined treatment using birinapant and chloroquine significantly retarded AML progression in both a subcutaneous xenograft model injected with HEL cells and an orthotopic xenograft model injected intravenously with C1498 cells. Collectively, our data suggested that XIAP inhibition can induce autophagy, apoptosis and differentiation, and combined inhibition of XIAP and autophagy may be a promising therapeutic strategy for AML.

MYCN mRNA degradation and cancer suppression by a selective small-molecule inhibitor in MYCN-amplified neuroblastoma

Amplification of the MYCN gene leads to its overexpression at both the mRNA and protein levels. Overexpression of MYCN mRNA may also have an important role in promoting neuroblastoma (NB) beyond the translation of MYCN protein. In the present study, we report a small molecule compound (MX25-1) that was able to bind to the 3'UTR of MYCN mRNA and induce MYCN mRNA degradation; this resulted in potent cell-growth inhibition and cell death specifically in MYCN-amplified or MYCN 3'UTR overexpressing NB cells. To evaluate the role of MYCN 3'UTR-mediated signals in contributing to the anticancer activity of MX25-1, we examined the status and activation of the tumor suppressor microRNA (miRNA) let-7, which is a target of MYCN 3'UTR in MYCN-amplified NB. We first observed that overexpression of MYCN mRNA was associated with high-level expression of the let-7 oncogenic targets DICER1, ARID3B and HMGA2. Following MYCN mRNA degradation, the expression of DICER1, ARID3B and HMGA2 was downregulated in MX25-1-treated cells. Inhibition of let-7 reversed the downregulation of these oncogenic mRNAs and significantly increased resistance of NB cells to MX25-1. Our results from this study supported the notion that overexpression of MYCN mRNA due to gene amplification has an independent function in NB cell growth and disease progression and suggest that targeting MYCN mRNA may represent an attractive strategy for therapy of MYCN amplified NB, both by inhibiting MYCN's cell-survival effects and activating the tumor-suppressor effect of let-7.

Killing by Degradation: Regulation of Apoptosis by the Ubiquitin-Proteasome-System

Apoptosis is a cell suicide process that is essential for development, tissue homeostasis and human health. Impaired apoptosis is associated with a variety of human diseases, including neurodegenerative disorders, autoimmunity and cancer. As the levels of pro- and anti-apoptotic proteins can determine the life or death of cells, tight regulation of these proteins is critical. The ubiquitin proteasome system (UPS) is essential for maintaining protein turnover, which can either trigger or inhibit apoptosis. In this review, we will describe the E3 ligases that regulate the levels of pro- and anti-apoptotic proteins and assisting proteins that regulate the levels of these E3 ligases. We will provide examples of apoptotic cell death modulations using the UPS, determined by positive and negative feedback loop reactions. Specifically, we will review how the stability of p53, Bcl-2 family members and IAPs (Inhibitor of Apoptosis proteins) are regulated upon initiation of apoptosis. As increased levels of oncogenes and decreased levels of tumor suppressor proteins can promote tumorigenesis, targeting these pathways offers opportunities to develop novel anti-cancer therapies, which act by recruiting the UPS for the effective and selective killing of cancer cells.

The roles and regulation of MDM2 and MDMX: it is not just about p53

In this review, Klein et al. discuss the p53-independent roles of MDM2 and MDMX. First, they review the structural and functional features of MDM2 and MDMX proteins separately and together that could be relevant to their p53-independent activities. Following this, they summarize how these two proteins are regulated and how they can function in cells that lack p53.

Most well studied as proteins that restrain the p53 tumor suppressor protein, MDM2 and MDMX have rich lives outside of their relationship to p53. There is much to learn about how these two proteins are regulated and how they can function in cells that lack p53. Regulation of MDM2 and MDMX, which takes place at the level of transcription, post-transcription, and protein modification, can be very intricate and is context-dependent. Equally complex are the myriad roles that these two proteins play in cells that lack wild-type p53; while many of these independent outcomes are consistent with oncogenic transformation, in some settings their functions could also be tumor suppressive. Since numerous small molecules that affect MDM2 and MDMX have been developed for therapeutic outcomes, most if not all designed to prevent their restraint of p53, it will be essential to understand how these diverse molecules might affect the p53-independent activities of MDM2 and MDMX.

Discovery of N-(3,4-Dimethylphenyl)-4-(4-isobutyrylphenyl)-2,3,3a,4,5,9b-hexahydrofuro[3,2-c]quinoline-8-sulfonamide as a Potent Dual MDM2/XIAP Inhibitor

Murine double minute 2 (MDM2) and X-linked inhibitor of apoptosis protein (XIAP) are important cell survival proteins in tumor cells. As a dual MDM2/XIAP inhibitor reported previously, compound MX69 has low potency with an IC50 value of 7.5 μM against an acute lymphoblastic leukemia cell line EU-1. Herein, we report the structural optimization based on the MX69 scaffold, leading to the discovery of a 25-fold more potent analogue 14 (IC50 = 0.3 μM against EU-1). We demonstrate that 14 maintains its mode of action by dual targeting of MDM2 and XIAP through inducing MDM2 protein degradation and inhibiting XIAP mRNA translation, respectively, which resulted in cancer cell growth inhibition and cell death. The results strongly suggest that the scaffold based on 14 is promising for further optimization to develop a new therapeutic agent for leukemia and possibly other cancers where MDM2 and XIAP are dysregulated.

Regulation of p53 stability as a therapeutic strategy for cancer

The tumor suppressor protein p53 participates in the control of key biological functions such as cell death, metabolic homeostasis and immune function, which are closely related to various diseases such as tumors, metabolic disorders, infection and neurodegeneration. The p53 gene is also mutated in approximately 50% of human cancer cells. Mutant p53 proteins escape from the ubiquitination-dependent degradation, gain oncogenic function and promote the carcinogenesis, malignant progression, metastasis and chemoresistance. Therefore, the stability of both wild type and mutant p53 needs to be precisely regulated to maintain normal functions and targeting the p53 stability is one of the therapeutic strategies against cancer. Here, we focus on compound-induced degradation of p53 by both the ubiquitination-dependent proteasome and autophagy-lysosome degradation pathways. We also review other posttranslational modifications which control the stability of p53 and the biological functions involved in these processes. This review provides the current theoretical basis for the regulation of p53 abundance and its possible applications in different diseases.

Molecular and Biochemical Techniques for Deciphering p53-MDM2 Regulatory Mechanisms

The p53 and Mouse double minute 2 (MDM2) proteins are hubs in extensive networks of interactions with multiple partners and functions. Intrinsically disordered regions help to adopt function-specific structural conformations in response to ligand binding and post-translational modifications. Different techniques have been used to dissect interactions of the p53-MDM2 pathway, in vitro, in vivo, and in situ each having its own advantages and disadvantages. This review uses the p53-MDM2 to show how different techniques can be employed, illustrating how a combination of in vitro and in vivo techniques is highly recommended to study the spatio-temporal location and dynamics of interactions, and to address their regulation mechanisms and functions. By using well-established techniques in combination with more recent advances, it is possible to rapidly decipher complex mechanisms, such as the p53 regulatory pathway, and to demonstrate how protein and nucleotide ligands in combination with post-translational modifications, result in inter-allosteric and intra-allosteric interactions that govern the activity of the protein complexes and their specific roles in oncogenesis. This promotes elegant therapeutic strategies that exploit protein dynamics to target specific interactions.

Targeting Mouse Double Minute 2: Current Concepts in DNA Damage Repair and Therapeutic Approaches in Cancer

Defects in DNA damage repair may cause genome instability and cancer development. The tumor suppressor gene p53 regulates cell cycle arrest to allow time for DNA repair. The oncoprotein mouse double minute 2 (MDM2) promotes cell survival, proliferation, invasion, and therapeutic resistance in many types of cancer. The major role of MDM2 is to inhibit p53 activity and promote its degradation. In this review, we describe the influence of MDM2 on genomic instability, the role of MDM2 on releasing p53 and binding DNA repair proteins to inhibit repair, and the regulation network of MDM2 including its transcriptional modifications, protein stability, and localization following DNA damage in genome integrity maintenance and in MDM2-p53 axis control. We also discuss p53-dependent and p53 independent oncogenic function of MDM2 and the outcomes of clinical trials that have been used with clinical inhibitors targeting p53-MDM2 to treat certain cancers.

Cadmium induces mitochondrial ROS inactivation of XIAP pathway leading to apoptosis in neuronal cells

Cadmium (Cd), a heavy metal pollutant, contributes to neurodegenerative disorders. Recently, we have demonstrated that Cd induction of reactive oxygen species (ROS) causes apoptosis in neuronal cells. Whether X-linked inhibitor of apoptosis protein (XIAP) is involved in Cd-induced ROS-dependent neuronal apoptosis remains unclear. Here, we show that Cd-induced ROS reduced the expression of XIAP, which resulted in up-regulation of murine double minute 2 homolog (MDM2) and down-regulation of p53, leading to apoptosis in PC12 cells and primary neurons. Inhibition of MDM2 with Nutlin-3a reversed Cd-induced reduction of p53 and substantially rescued cells from excess ROS-dependent death. Overexpression of XIAP protected against Cd induction of ROS-dependent neuronal apoptosis. Inhibition of XIAP by Embelin strengthened Cd-induced ROS and apoptosis in the cells. Furthermore, we found that Cd inactivation of XIAP pathway was attributed to Cd induction of mitochondrial ROS, as evidenced by using a mitochondrial superoxide indicator MitoSOX and a mitochondria-targeted antioxidant Mito-TEMPO. Taken together, these results indicate that Cd induces mitochondrial ROS inactivation of XIAP-MDM2-p53 pathway leading to apoptosis in neuronal cells. Our findings suggest that activators of XIAP or modulation of XIAP-MDM2-p53 pathway by antioxidants may be exploited for the prevention of Cd-induced oxidative stress and neurodegenerative diseases.

Alternative Mechanisms of mRNA Translation Initiation in Cellular Stress Response and Cancer

Throughout evolution, eukaryotic cells have devised different mechanisms to cope with stressful environments. When eukaryotic cells are exposed to stress stimuli, they activate adaptive pathways that allow them to restore cellular homeostasis. Most types of stress stimuli have been reported to induce a decrease in overall protein synthesis accompanied by induction of alternative mechanisms of mRNA translation initiation. Here, we present well-studied and recent examples of such stress responses and the alternative translation initiation mechanisms they induce, and discuss the consequences of such regulation for cell homeostasis and oncogenic transformation.

Inhibition of IAP's and activation of p53 leads to caspase-dependent apoptosis in gastric cancer cells treated with Scutellarein

Gastric cancer is the fifth most common cancer and the third leading cause of cancer deaths worldwide. South Korea is in first place with 9,180 death alone attributed to gastric cancer in 2013. Plenty of literature suggests the evasion of apoptosis is implicated in neurodegeneration, autoimmune diseases, and tumors development due to dysregulation in the apoptotic mechanism. Reduced apoptosis or its resistance in cancer cells plays a significant role in carcinogenesis. It’s imperative to understand apoptosis, which provides the basis for novel targeted therapies that can induce cancer cell death or sensitize them to cytotoxic agents by regulating key factors like IAPs, MDM2, p53, caspases and much more. Studies have demonstrated that Scutellarein have the ability to inhibit several cancer cells by inducing apoptosis with both: Scutellarein monomers as well as scutellarein containing flavonoids. MTT results revealed that scutellarein inhibited cell viability in both dose and time dependent manner. Flow cytometry and western blot analysis showed that scutellarein induces apoptosis in both AGS and SNU-484 human gastric cancer cells and G2/M phase cell cycle arrest in SNU-484 cells. This study demonstrated that the Scutellarein on AGS and SNU-484 cells significantly inhibits cell proliferation and induces apoptotic cell death via down regulating MDM2 and activated the tumor suppresser protein p53, subsequently down regulating the IAP family proteins (cIAP1, cIAP2, and XIAP) leading to caspase-dependent apoptosis in AGS and SNU-484 cells.

Identification of XBP1-u as a novel regulator of the MDM2/p53 axis using an shRNA library

Cell cycle progression is a tightly controlled fundamental process in living cells, with any defects being closely linked to various abnormalities. The tumor suppressor p53/p21 axis is a core pathway controlling cell cycle progression; however, its regulatory mechanism has not been fully elucidated. In an effort to unravel this crucial network, we screened a short hairpin RNA expression vector library and identified unspliced X-box binding protein 1 (XBP1-u) as a novel and critical regulator of the p53/p21 axis. Specifically, XBP1-u negatively regulates the p53/p21 axis by enhancing p53 ubiquitination, which in turn down-regulates p21 expression. We show that XBP1-u suppression induces G₀-G₁ phase arrest and represses cell proliferation. We further report that the carboxyl terminus of XBP1-u, which differs from that of its spliced form (XBP1-s) due to a codon shift, binds and stabilizes mouse double minute homolog 2 (MDM2) protein, a negative regulator of p53, by inhibiting its self-ubiquitination. Concomitantly, XBP-u overexpression enhances tumorigenesis by positively regulating MDM2. Together, our findings suggest that XBP1-u functions far beyond being merely a precursor of XBP1-s and, instead, is involved in fundamental biological processes. Furthermore, this study provides new insights regarding the regulation of the MDM2/p53/p21 axis.

More than just scanning: the importance of cap-independent mRNA translation initiation for cellular stress response and cancer

The scanning model for eukaryotic mRNA translation initiation states that the small ribosomal subunit, along with initiation factors, binds at the cap structure at the 5' end of the mRNA and scans the 5' untranslated region (5'UTR) until an initiation codon is found. However, under conditions that impair canonical cap-dependent translation, the synthesis of some proteins is kept by alternative mechanisms that are required for cell survival and stress recovery. Alternative modes of translation initiation include cap- and/or scanning-independent mechanisms of ribosomal recruitment. In most cap-independent translation initiation events there is a direct recruitment of the 40S ribosome into a position upstream, or directly at, the initiation codon via a specific internal ribosome entry site (IRES) element in the 5'UTR. Yet, in some cellular mRNAs, a different translation initiation mechanism that is neither cap- nor IRES-dependent seems to occur through a special RNA structure called cap-independent translational enhancer (CITE). Recent evidence uncovered a distinct mechanism through which mRNAs containing N 6-methyladenosine (m6A) residues in their 5'UTR directly bind eukaryotic initiation factor 3 (eIF3) and the 40S ribosomal subunit in order to initiate translation in the absence of the cap-binding proteins. This review focuses on the important role of cap-independent translation mechanisms in human cells and how these alternative mechanisms can either act individually or cooperate with other cis-acting RNA regulons to orchestrate specific translational responses triggered upon several cellular stress states, and diseases such as cancer. Elucidation of these non-canonical mechanisms reveals the complexity of translational control and points out their potential as prospective novel therapeutic targets.

Gossypol has anti-cancer effects by dual-targeting MDM2 and VEGF in human breast cancer

Background

Mouse double minute 2 (MDM2) and vascular endothelial growth factor (VEGF) are important molecules involved in tumor progression. We researched potential inhibitors that simultaneously target MDM2 and VEGF. In our recent study involving the performance of high-throughput screening with a fluorescence polarization assay, gossypol was identified as one of the top hits that inhibit protein-RNA binding activity. Because MDM2 is an RNA-binding protein and its targets include VEGF mRNA, we investigated whether gossypol has an inhibitory effect on MDM2-VEGF.

Methods

UV cross-linking and RNA binding assay, isothermal titration calorimetry assay, and ubiquitination assay were performed to determine mechanisms by which gossypol functions as a dual inhibitor of MDM2 and VEGF. The effect of gossypol on MDM2 and VEGF expression, cancer cell apoptosis, tumor growth and VEGF-mediated angiogenesis were studied in vitro and in vivo in different human breast cancer models with a different p53 status.

Results

We observed that gossypol inhibited expression of both MDM2 and VEGF in human breast cancer cells with either wild-type or mutant p53. A nechanistic study further demonstrated that, through disrupting the interaction between MDM2 protein and VEGF mRNA, gossypol induced MDM2 self-ubiquitination and decreased VEGF translation simultaneously, which resulted in both apoptosis and anti-angiogenesis effects. In vitro, regardless of p53 status, gossypol induced cancer cell apoptosis. In nude mouse xenograft in vivo models, gossypol suppressed tumor growth and VEGF-mediated angiogenesis.

Conclusion

Gossypol has anti-cancer effects by dual-targeting MDM2 and VEGF in human breast cancer. Our study reveals a novel mechanism by which gossypol functions as an anticancer agent. We believe that MDM2-VEGF targeting represents a novel strategy for improving cancer outcome.

WSB1 overcomes oncogene-induced senescence by targeting ATM for degradation

Oncogene-induced senescence (OIS) or apoptosis through the DNA-damage response is an important barrier of tumorigenesis. Overcoming this barrier leads to abnormal cell proliferation, genomic instability, and cellular transformation, and finally allows cancers to develop. However, it remains unclear how the OIS barrier is overcome. Here, we show that the E3 ubiquitin ligase WD repeat and SOCS box-containing protein 1 (WSB1) plays a role in overcoming OIS. WSB1 expression in primary cells helps the bypass of OIS, leading to abnormal proliferation and cellular transformation. Mechanistically, WSB1 promotes ATM ubiquitination, resulting in ATM degradation and the escape from OIS. Furthermore, we identify CDKs as the upstream kinase of WSB1. CDK-mediated phosphorylation activates WSB1 by promoting its monomerization. In human cancer tissue and in vitro models, WSB1-induced ATM degradation is an early event during tumorigenic progression. We suggest that WSB1 is one of the key players of early oncogenic events through ATM degradation and destruction of the tumorigenesis barrier. Our work establishes an important mechanism of cancer development and progression in premalignant lesions.

Discovery of Dual Inhibitors of MDM2 and XIAP for Cancer Treatment

MDM2 and XIAP are mutually regulated. Binding of MDM2 RING protein to the IRES region on XIAP mRNA results in MDM2 protein stabilization and enhanced XIAP translation. In this study, we developed a protein-RNA fluorescence polarization (FP) assay for high-throughput screening (HTS) of chemical libraries. Our FP-HTS identified eight inhibitors that blocked the MDM2 protein-XIAP RNA interaction, leading to MDM2 degradation. The compound-induced MDM2 downregulation resulted not only in inhibition of XIAP expression, but also in activation of p53, which contributed to cancer cell apoptosis in vitro and inhibition of cancer cell proliferation in vivo. Importantly, one of the MDM2/XIAP inhibitors, MX69, showed minimal inhibitory effect on normal human hematopoiesis in vitro and was very well tolerated in animal models.

FKBP12 enhances sensitivity to chemotherapy-induced cancer cell apoptosis by inhibiting MDM2

The FK506-binding protein 12 (FKBP12) is a cytoplasmic protein and has been reported to possess multiple functions in signaling transduction based on its interaction with different cellular targets. Here, we report that FKBP12 interacts with oncoprotein MDM2 and induces MDM2 degradation. We demonstrate that FKBP12 degrades MDM2 through binding to MDM2 protein, disrupting MDM2/MDM4 interaction and inducing MDM2 self-ubiquitination. The FKBP12-mediated MDM2 degradation was significantly enhanced when the transfected MDM2 was localized in the cytoplasm. The endogenous MDM2, when it was induced by p53 subjecting to DNA-damaging stimuli such as treatment with doxorubicin, was also significantly inhibited by FKBP12. This is due to translocation of p53-induced MDM2 from the nucleus to the cytoplasm, which facilitates interaction with cytoplasmic FKBP12. Furthermore, the enhanced level of MDM2 following p53 activation in nutlin-3 treated cells was also inhibited by FKBP12. The FKBP12-mediated downregulation of MDM2 in response to doxorubicin or nutlin-3 results in continuing and constitutive activation of p53, inhibition of XIAP and sensitization of cancer cells to apoptosis. These results identify a novel function for FKBP12 in downregulating MDM2, which directly enhances sensitivity of cancer cells to chemotherapy and nutlin-3 treatment.

Glioblastomas with copy number gains in EGFR and RNF139 show increased expressions of carbonic anhydrase genes transformed by ENO1

Background

Prominence of glycolysis in glioblastomas may be non-specific or a feature of oncogene-related subgroups (i.e. amplified EGFR, etc.). Relationships between amplified oncogenes and expressions of metabolic genes associated with glycolysis, directly or indirectly via pH, were therefore investigated.

Methods

Using multiplex ligation-dependent probe amplification, copy numbers (CN) of 78 oncogenes were quantified in 24 glioblastomas. Related expressions of metabolic genes encoding lactate dehydrogenases (LDHA, LDHC), carbonic anhydrases (CA3, CA12), monocarboxylate transporters (SLC16A3 or MCT4, SLC16A4 or MCT5), ATP citrate lyase (ACLY), glycogen synthase1 (GYS1), hypoxia inducible factor-1A (HIF1A), and enolase1 (ENO1) were determined in 22 by RT-qPCR. To obtain supra-glycolytic levels and adjust for heterogeneity, concurrent ENO1 expression was used to mathematically transform the expression levels of metabolic genes already normalized with delta-delta crossing threshold methodology.

Results

Positive correlations with EGFR occurred for all metabolic genes. Significant differences (Wilcoxon Rank Sum) for oncogene CN gains in tumors of at least 2.00-fold versus less than 2.00-fold occurred for EGFR with CA3's expression (p < 0.03) and for RNF139 with CA12 (p < 0.004). Increased CN of XIAP associated negatively. Tumors with less than 2.00-fold CN gains differed from those with gains for XIAP with CA12 (p < 0.05). Male gender associated with CA12 (p < 0.05).

Conclusions

Glioblastomas with CN increases in EGFR had elevated CA3 expression. Similarly, tumors with RNF149 CN gains had elevated CA12 expression.

General significance

In larger studies, subgroups of glioblastomas may emerge according to oncogene-related effects on glycolysis, such as control of pH via effects on carbonic anhydrases, with prognostic and treatment implications.

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PCR of glioblastomas show oncogene copy numbers relate to metabolic gene expressions.

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ENO1(ENOLASE1) transformations yielded “supra-glycolytic” metabolic gene expressions.

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EGFR, RNF139, and XIAP associated with expressions of two carbonic anhydrase genes.

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Male gender associated (+) with the transformed expression of carbonic anhydrase 12.

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Oncogene amplifications may aid control of pH to protect glycolysis in glioblastomas.