PTEN has tumor-promoting properties in the setting of gain-of-function p53 mutations

ATM kinase inhibition preferentially sensitizes p53-mutant glioma to ionizing radiation

PURPOSE

Glioblastoma multiforme (GBM) is the most lethal form of brain cancer with a median survival of only 12 to 15 months. Current standard treatment consists of surgery followed by chemoradiation. The poor survival of patients with GBM is due to aggressive tumor invasiveness, an inability to remove all tumor tissue, and an innate tumor chemo- and radioresistance. Ataxia-telangiectasia mutated (ATM) is an excellent target for radiosensitizing GBM because of its critical role in regulating the DNA damage response and p53, among other cellular processes. As a first step toward this goal, we recently showed that the novel ATM kinase inhibitor KU-60019 reduced migration, invasion, and growth, and potently radiosensitized human glioma cells in vitro.

EXPERIMENTAL DESIGN

Using orthotopic xenograft models of GBM, we now show that KU-60019 is also an effective radiosensitizer in vivo. Human glioma cells expressing reporter genes for monitoring tumor growth and dispersal were grown intracranially, and KU-60019 was administered intratumorally by convection-enhanced delivery or osmotic pump.

RESULTS

Our results show that the combined effect of KU-60019 and radiation significantly increased survival of mice 2- to 3-fold over controls. Importantly, we show that glioma with mutant p53 is much more sensitive to KU-60019 radiosensitization than genetically matched wild-type glioma.

CONCLUSIONS

Taken together, our results suggest that an ATM kinase inhibitor may be an effective radiosensitizer and adjuvant therapy for patients with mutant p53 brain cancers.

AMPK activation by oncogenesis is required to maintain cancer cell proliferation in astrocytic tumors

5'-AMP-activated protein kinase (AMPK) is an energy sensor that controls cell metabolism, and it has been related to apoptosis and cell-cycle arrest. Although its role in metabolic homeostasis is well documented, its function in cancer is much less clear. In this study, we examined the role of AMPK in a mouse model of astrocytoma driven by oncogenic H-Ras(V12) and/or with PTEN deletion based on the common constitutive activation of the Raf/MEK/ERK and PI3K/AKT cascades in human astrocytomas. We also evaluated the activity and role of AMPK in human glioblastoma cells and xenografts. AMPK was constitutively activated in astrocytes expressing oncogenic H-Ras(V12) in parallel with high cell division rates. Genetic deletion of AMPK or attenuation of its activity in these cells was sufficient to reduce cell proliferation. The levels of pAMK were always related to the levels of phosphorylated retinoblastoma (Rb) at Ser804, which may indicate an AMPK-mediated phosphorylation of Rb. We confirmed this AMPK-Rb relationship in human glioblastoma cell lines and xenografts. In clinical specimens of human glioblastoma, elevated levels of activated AMPK appeared especially in areas of high proliferation surrounding the blood vessels. Together, our findings indicate that the initiation and progression of astrocytic tumors relies upon AMPK-dependent control of the cell cycle, thereby identifying AMPK as a candidate therapeutic target in this setting.

R280T mutation of p53 gene promotes proliferation of human glioma cells through GSK-3β/PTEN pathway

p53 mutation is associated with "gain-of-function" capabilities of human cancers. We aim to identify p53 mutations in human glioma cells and to explore the potential mechanism for mutant p53-promoted cellular growth. Whole genomic DNA was isolated from SWO-38, a human glioma cell line and amplified for the region of exons 5, 6, and 8 in p53 gene using polymerase chain reaction (PCR). By means of direct sequencing of PCR products and alignment analysis using BLAST database, a mutation of G to C transition at codon 280 of p53 exon 8 (AGA→ACA), i.e. R280T was detected in SWO-38 cells. Knockdown of R280T mutant p53 by RNA interference inhibited the GSK-3β/PTEN associated cell proliferation, and PI3K/Akt but not Wnt/β-catenin signaling pathway was involved in this process. Furthermore, depletion or overexpression of PTEN alone did not affect cell proliferation and cell cycle, implicating the impairment of PTEN function in SWO-38 cells. However, knockdown of both PTEN and p53 mutation could significantly rescue the p53 depletion-mediated growth inhibition, suggesting that the R280T mutation in glioma may promote the proliferation through an underlying mechanism related to PTEN. Our observations indicate that the R280T mutation of p53 regulates the proliferation of human glioma cells related to the GSK-3β/PTEN pathway. These findings provide valuable insights for better understanding the molecular mechanism of uncontrolled growth of glioma cells.

Evolutionary pathways in BRCA1-associated breast tumors

BRCA1-associated breast tumors display loss of BRCA1 and frequent somatic mutations of PTEN and TP53. Here we describe the analysis of BRCA1, PTEN, and p53 at the single cell level in 55 BRCA1-associated breast tumors and computational methods to predict the relative temporal order of somatic events, on the basis of the frequency of cells with single or combined alterations. Although there is no obligatory order of events, we found that loss of PTEN is the most common first event and is associated with basal-like subtype, whereas in the majority of luminal tumors, mutation of TP53 occurs first and mutant PIK3CA is rarely detected. We also observed intratumor heterogeneity for the loss of wild-type BRCA1 and increased cell proliferation and centrosome amplification in the normal breast epithelium of BRCA1 mutation carriers. Our results have important implications for the design of chemopreventive and therapeutic interventions in this high-risk patient population.

Cooperation between c-Met and focal adhesion kinase family members in medulloblastoma and implications for therapy

We previously showed the involvement of the tyrosine kinase receptor c-Met in medulloblastoma malignancy. The nonreceptor tyrosine kinases focal adhesion kinase (FAK) and Pyk2 are key players in the progression of different cancers. However, their role in medulloblastoma malignancy is not well understood. In this study, using a protein array approach, we found that c-Met induces FAK and Pyk2 phosphorylation in medulloblastoma cells. We therefore studied the interactions between c-Met and FAK/Pyk2 and their implications for medulloblastoma therapy. We found that c-Met activates FAK and Pyk2 in several medulloblastoma cell lines. We also found that FAK and Pyk2 mediate the malignant effects of c-Met on medulloblastoma cell proliferation, migration, and invasion. On the basis of these findings, we hypothesized that combined c-Met and FAK inhibitions would have additive effects on the inhibition of medulloblastoma malignancy. To test this hypothesis, we assessed the effects on medulloblastoma malignancy parameters of single or combined treatments of medulloblastoma cells with c-Met and FAK small-molecule kinase inhibitors. We found a significant increase in the inhibitory effect of both inhibitors on medulloblastoma cell migration and cell invasion as compared with single inhibitions (P < 0.05). In addition, oral gavage treatment with c-Met inhibitor of mice bearing medulloblastoma xenografts significantly reduced in vivo tumor growth. Therefore, combining c-Met inhibitors with FAK inhibitors constitutes a new potential strategy for medulloblastoma therapy. Altogether, our study describes a role for FAK and Pyk2 in medulloblastoma malignancy, uncovers new interactions between c-Met and FAK/Pyk2, and proposes for the first time combining anti-c-Met and anti-FAK inhibitors as a new strategy for medulloblastoma therapy.

Phase 2 randomized study of p53 antisense oligonucleotide (cenersen) plus idarubicin with or without cytarabine in refractory and relapsed acute myeloid leukemia

BACKGROUND

The p53 antisense oligonucleotide cenersen has been shown to sensitize acute myeloid leukemia (AML) stem cells to DNA damaging agents.

METHODS

To determine whether cenersen merits testing in larger efficacy studies, an exploratory study of cenersen in combination with idarubicin either alone or with 1 of 2 doses of cytarabine was performed in first-salvage AML patients. Patients who either had failed to respond to a single induction course or had responded to induction but relapsed within 12 months were enrolled. Stopping rules based on an expected 14% complete response (CR) rate were applied to each treatment arm.

RESULTS

Fifty-three patients were treated, and none of the arms was terminated for lack of activity. Nearly all patients received a single course unless they responded. Ten of the 53 (19%) patients responded (8 CR and 2 CR with incomplete platelet recovery). There was a positive trend for a better response rate with increasing intensity of chemotherapy in the patients refractory to front-line treatment compared with those who had relapsed previously. One-third (17/53) of the patients received cenersen inhibitors (acetaminophen and/or high dose antioxidants) during treatment, and none of these responded to treatment. No unique toxicity was attributed to cenersen.

CONCLUSION

The results of this study suggested that the combination of cenersen with chemotherapy may have clinical efficacy, and additional studies are warranted to explore its full potential.

Coalterations of p53 and PTEN tumor suppressor genes in non-small cell lung carcinoma patients

The inactivation of p53 and PTEN tumor suppressor genes is a common genetic event in lung cancer. However, data on the effect of the joint inactivation of tumor-suppressor genes in non-small cell lung carcinoma (NSCLC) are lacking. The purpose of this study was to investigate the alterations in PTEN and p53 genes, as well as to evaluate their mutual role in NSCLC pathogenesis and their impact on survival rate. To that end, polymerase chain reaction single-strand conformational polymorphism (PCR-SSCP), sequencing, methylation-specific PCR, and fragment analysis were used. The results obtained were correlated with clinicopathologic parameters, the level of genomic instability, and patient survival. Overall, 13% of specimens had aberrant p53 only, 13% had inactive PTEN only, and 50% of samples had both genes altered. Correlation analyses showed that the mutual inactivation of p53 and PTEN was a frequent event that was associated significantly with the increased level of genomic instability and lymph node invasion implying their synergistic effect in promoting metastatic phenotype of this kind of cancer. In addition, our results revealed a significant association of joint alterations of these genes with dramatically shortened survival indicating that aberrant p53 and PTEN could be used as an adverse prognostic factor for NSCLC patients' outcome. Our findings established the relevance of the combinatorial inactivation of p53 and PTEN in NSCLC progression and identified a subgroup of patients with a particularly aggressive disease.

PTEN tumor suppressor plays less prognostic role than P53 tumor suppressor in diffuse large B-cell lymphoma

The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and P53 tumor suppressors are among the most commonly inactivated or mutated genes in human cancers, whose pathways cross-talk and interact in a complementary mode. In order to understand their roles and relationship in diffuse large B-cell lymphoma (DLBCL), we examined their expression and evaluated their prognostic significance in 62 patients with DLBCL treated with standard chemotherapy. Results showed that PTEN protein was lost in 23 (37.1%) cases, and the loss was associated with the activation of PI3K/AKT pathway, but was not associated with patient's clinical outcome. P53 mutation protein was detected in 30 (48.4%) cases and was associated with poor survival. Results of multivariate analysis showed that P53 mutation but not PTEN loss is associated with short survival in patients with DLBCL. PTEN status has no effect on P53 mutation-associated poor survival. We conclude that PTEN may play less prognostic role than P53 and that P53 mutation protein should be considered as a predictive factor of the need for a more aggressive therapy in patients with DLBCL who express P53.

Mutant p53 gain-of-function in cancer

In its wild-type form, p53 is a major tumor suppressor whose function is critical for protection against cancer. Many human tumors carry missense mutations in the TP53 gene, encoding p53. Typically, the affected tumor cells accumulate excessive amounts of the mutant p53 protein. Various lines of evidence indicate that, in addition to abrogating the tumor suppressor functions of wild-type p53, the common types of cancer-associated p53 mutations also endow the mutant protein with new activities that can contribute actively to various stages of tumor progression and to increased resistance to anticancer treatments. Collectively, these activities are referred to as mutant p53 gain-of-function. This article addresses the biological manifestations of mutant p53 gain-of-function, the underlying molecular mechanisms, and their possible clinical implications.

PTEN and p53 cross-regulation induced by soy isoflavone genistein promotes mammary epithelial cell cycle arrest and lobuloalveolar differentiation

The tumor suppressors phosphatase and tensin homologue deleted on chromosome ten (PTEN) and p53 are closely related to the pathogenesis of breast cancer, yet pathway-specific mechanisms underlying their participation in mediating the protective actions of dietary bioactive components on breast cancer risk are poorly understood. We recently showed that dietary exposure to the soy isoflavone genistein (GEN) induced PTEN expression in mammary epithelial cells in vivo and in vitro, consistent with the breast cancer preventive effects of soy food consumption. Here, we evaluated PTEN and p53 functional interactions in the nuclear compartment of mammary epithelial cells as a mechanism for mammary tumor protection by GEN. Using the non-tumorigenic human mammary epithelial cells MCF10-A, we demonstrate that GEN increased PTEN expression and nuclear localization. We show that increased nuclear PTEN levels initiated an autoregulatory loop involving PTEN-dependent increases in p53 nuclear localization, PTEN-p53 physical association, PTEN-p53 co-recruitment to the PTEN promoter region and p53 transactivation of PTEN promoter activity. The PTEN-p53 cross talk induced by GEN resulted in increased cell cycle arrest; decreased pro-proliferative cyclin D1 and pleiotrophin gene expression and the early formation of mammary acini, indicative of GEN promotion of lobuloalveolar differentiation. Our findings provide support to GEN-induced PTEN as both a target and regulator of p53 action and offer a mechanistic basis for PTEN pathway activation to underlie the antitumor properties of dietary factors, with important implications for reducing breast cancer risk.

PTEN augments SPARC suppression of proliferation and inhibits SPARC-induced migration by suppressing SHC-RAF-ERK and AKT signaling

SPARC (secreted protein acidic and rich in cysteine) is expressed in all grades of astrocytoma, including glioblastoma (GBM). SPARC suppresses glioma growth but promotes migration and invasion by mediating integrin and growth factor receptor-regulated kinases and their downstream effectors. PTEN (phosphatase and tensin homolog deleted on chromosome 10), which is commonly lost in primary GBMs, negatively regulates proliferation and migration by inhibiting some of the same SPARC-mediated signaling pathways. This study determined whether PTEN reconstitution in PTEN-mutant, SPARC-expressing U87MG cells could further suppress proliferation and tumor growth but inhibit migration and invasion in SPARC-expressing cells in vitro and in vivo, and thereby prolong survival in animals with xenograft tumors. In vitro, PTEN reduced proliferation and migration in both SPARC-expressing and control cells, with a greater suppression in SPARC-expressing cells. PTEN reconstitution suppressed AKT activation in SPARC-expressing and control cells but suppressed the SHC-RAF-ERK signaling pathway only in SPARC-expressing cells. Importantly, coexpression of SPARC and PTEN resulted in the smallest, least proliferative tumors with reduced invasive capacity and longer animal survival. Furthermore, direct inhibition of the AKT and SHC-RAF-ERK signaling pathways suppressed the proliferation and migration of SPARC-expressing cells in vitro. These findings demonstrate that PTEN reconstitution or inhibition of signaling pathways that are activated by the loss of PTEN provide potential therapeutic strategies to inhibit SPARC-induced invasion while enhancing the negative effect of SPARC on tumor growth.

Driver mutations in TP53 are ubiquitous in high grade serous carcinoma of the ovary

Numerous studies have tested the association between TP53 mutations in ovarian cancer and prognosis but these have been consistently confounded by limitations in study design, methodology, and/or heterogeneity in the sample cohort. High-grade serous (HGS) carcinoma is the most clinically important histological subtype of ovarian cancer. As these tumours may arise from the ovary, Fallopian tube or peritoneum, they are collectively referred to as high-grade pelvic serous carcinoma (HGPSC). To identify the true prevalence of TP53 mutations in HGPSC, we sequenced exons 2-11 and intron-exon boundaries in tumour DNA from 145 patients. HGPSC cases were defined as having histological grade 2 or 3 and FIGO stage III or IV. Surprisingly, pathogenic TP53 mutations were identified in 96.7% (n = 119/123) of HGPSC cases. Molecular and pathological review of mutation-negative cases showed evidence of p53 dysfunction associated with copy number gain of MDM2 or MDM4, or indicated the exclusion of samples as being low-grade serous tumours or carcinoma of uncertain primary site. Overall, p53 dysfunction rate approached 100% of confirmed HGPSCs. No association between TP53 mutation and progression-free or overall survival was found. From this first comprehensive mapping of TP53 mutation rate in a homogeneous group of HGPSC patients, we conclude that mutant TP53 is a driver mutation in the pathogenesis of HGPSC cancers. Because TP53 mutation is almost invariably present in HGPSC, it is not of substantial prognostic or predictive significance.

An extensive invasive intracranial human glioblastoma xenograft model: role of high level matrix metalloproteinase 9

The lack of an intracranial human glioma model that recapitulates the extensive invasive and hypervascular features of glioblastoma (GBM) is a major hurdle for testing novel therapeutic approaches against GBM and studying the mechanism of GBM invasive growth. We characterized a high matrix metalloproteinase-9 (MMP-9) expressing U1242 MG intracranial xenograft mouse model that exhibited extensive individual cells and cell clusters in a perivascular and subpial cellular infiltrative pattern, geographic necrosis and infiltrating tumor-induced vascular proliferation closely resembling the human GBM phenotype. MMP-9 silencing cells with short hairpin RNA dramatically blocked the cellular infiltrative pattern, hypervascularity, and cell proliferation in vivo, and decreased cell invasion, colony formation, and cell motility in vitro, indicating that a high level of MMP-9 plays an essential role in extensive infiltration and hypervascularity in the xenograft model. Moreover, epidermal growth factor (EGF) failed to stimulate MMP-9 expression, cell invasion, and colony formation in MMP-9-silenced clones. An EGF receptor (EGFR) kinase inhibitor, a RasN17 dominant-negative construct, MEK and PI3K inhibitors significantly blocked EGF/EGFR-stimulated MMP-9, cell invasion, and colony formation in U1242 MG cells, suggesting that MMP-9 is involved in EGFR/Ras/MEK and PI3K/AKT signaling pathway-mediated cell invasion and anchorage-independent growth in U1242 MG cells. Our data indicate that the U1242 MG xenograft model is valuable for studying GBM extensive invasion and angiogenesis as well as testing anti-invasive and anti-angiogenic therapeutic approaches.

Driver mutations in TP53 are ubiquitous in high grade serous carcinoma of the ovary

Numerous studies have tested the association between TP53 mutations in ovarian cancer and prognosis but these have been consistently confounded by limitations in study design, methodology, and/or heterogeneity in the sample cohort. High-grade serous (HGS) carcinoma is the most clinically important histological subtype of ovarian cancer. As these tumours may arise from the ovary, Fallopian tube or peritoneum, they are collectively referred to as high-grade pelvic serous carcinoma (HGPSC). To identify the true prevalence of TP53 mutations in HGPSC, we sequenced exons 2-11 and intron-exon boundaries in tumour DNA from 145 patients. HGPSC cases were defined as having histological grade 2 or 3 and FIGO stage III or IV. Surprisingly, pathogenic TP53 mutations were identified in 96.7% (n = 119/123) of HGPSC cases. Molecular and pathological review of mutation-negative cases showed evidence of p53 dysfunction associated with copy number gain of MDM2 or MDM4, or indicated the exclusion of samples as being low-grade serous tumours or carcinoma of uncertain primary site. Overall, p53 dysfunction rate approached 100% of confirmed HGPSCs. No association between TP53 mutation and progression-free or overall survival was found. From this first comprehensive mapping of TP53 mutation rate in a homogeneous group of HGPSC patients, we conclude that mutant TP53 is a driver mutation in the pathogenesis of HGPSC cancers. Because TP53 mutation is almost invariably present in HGPSC, it is not of substantial prognostic or predictive significance.

Driver mutations in TP53 are ubiquitous in high grade serous carcinoma of the ovary

Numerous studies have tested the association between TP53 mutations in ovarian cancer and prognosis but these have been consistently confounded by limitations in study design, methodology, and/or heterogeneity in the sample cohort. High-grade serous (HGS) carcinoma is the most clinically important histological subtype of ovarian cancer. As these tumours may arise from the ovary, Fallopian tube or peritoneum, they are collectively referred to as high-grade pelvic serous carcinoma (HGPSC). To identify the true prevalence of TP53 mutations in HGPSC, we sequenced exons 2-11 and intron-exon boundaries in tumour DNA from 145 patients. HGPSC cases were defined as having histological grade 2 or 3 and FIGO stage III or IV. Surprisingly, pathogenic TP53 mutations were identified in 96.7% (n = 119/123) of HGPSC cases. Molecular and pathological review of mutation-negative cases showed evidence of p53 dysfunction associated with copy number gain of MDM2 or MDM4, or indicated the exclusion of samples as being low-grade serous tumours or carcinoma of uncertain primary site. Overall, p53 dysfunction rate approached 100% of confirmed HGPSCs. No association between TP53 mutation and progression-free or overall survival was found. From this first comprehensive mapping of TP53 mutation rate in a homogeneous group of HGPSC patients, we conclude that mutant TP53 is a driver mutation in the pathogenesis of HGPSC cancers. Because TP53 mutation is almost invariably present in HGPSC, it is not of substantial prognostic or predictive significance.

microRNA-34a is tumor suppressive in brain tumors and glioma stem cells

We recently found that microRNA-34a (miR-34a) is downregulated in human glioma tumors as compared to normal brain, and that miR-34a levels in mutant-p53 gliomas were lower than in wildtype-p53 tumors. We showed that miR-34a expression in glioma and medulloblastoma cells inhibits cell proliferation, G1/S cell cycle progression, cell survival, cell migration and cell invasion, but that miR-34a expression in human astrocytes does not affect cell survival and cell cycle. We uncovered the oncogenes c-Met, Notch-1 and Notch-2 as direct targets of miR-34a that are inhibited by miR-34a transfection. We found that c-Met levels in human glioma specimens inversely correlate with miR-34a levels. We showed that c-Met and Notch partially mediate the inhibitory effects of miR-34a on cell proliferation and cell death. We also found that mir-34a expression inhibits in vivo glioma xenograft growth. We concluded that miR-34a is a potential tumor suppressor in brain tumors that acts by targeting multiple oncogenes. In this extra view, we briefly review and discuss the implications of these findings and present new data on the effects of miR-34a in glioma stem cells. The new data show that miR-34a expression inhibits various malignancy endpoints in glioma stem cells. Importantly, they also show for the first time that miR-34a expression induces glioma stem cell differentiation. Altogether, the data suggest that miR-34a is a tumor suppressor and a potential potent therapeutic agent that acts by targeting multiple oncogenic pathways in brain tumors and by inducing the differentiation of cancer stem cells.

Slit2 inhibits glioma cell invasion in the brain by suppression of Cdc42 activity

Acquisition of insidious invasiveness by malignant glioma cells involves multiple genetic alterations in signaling pathways. Slit2, a chemorepulsive factor, controls cell migration of neuronal and glial cells during development and inhibits chemotaxic migration of various types of cells in vitro. However, the role of Slit2 in vitro remains controversial, and the biological significance of Slit2 expression in cancer cell invasion in vivo has not yet been determined. In the present study, we characterized the effects of Slit2 expression on the migration and invasion of invasive glioma cells in vitro and in vivo. By reverse transcriptase polymerase chain reaction (PCR) analyses, Slit2 was found to be expressed at lower levels in primary glioma specimens and invasive glioma cells compared with normal human brain cells and astrocytes. Ectopic expression of Slit2 or treatment with recombinant Slit2 on glioma cells attenuates cell migration and invasion through inhibition of Cdc42 activity in vitro. Cellular depletion of Robo1, a cognate receptor for Slit2, prevented Slit2 inhibition of Cdc42 activity and glioma cell migration. In vivo, expression of Slit2 by invasive SNB19 glioma cells markedly inhibited glioma cell infiltration into the brain of mice. Moreover, impediment of glioma cell invasion by Slit2 did not affect the expression of N-cadherin and beta-catenin in glioma cells. These results provide the first evidence demonstrating that Slit2-Robo1 inhibits glioma invasion through attenuating Cdc42 activity in vitro and in the brain. Understanding the mechanisms of Slit2-Robo1 inhibition of glioma cell invasion will foster new treatments for malignant gliomas.

The novel estrogen-induced gene EIG121 regulates autophagy and promotes cell survival under stress

We previously identified a novel estrogen-induced gene, EIG121, as being differentially regulated in endometrioid and nonendometrioid endometrial carcinoma. The function of EIG121 was unknown. Using a tetracycline-inducible system, we found that overexpression of EIG121, but not of LacZ, caused a profound suppression of cell growth. Subcellular fractionation and immunofluroscent labeling indicated that EIG121 was a transmembrane protein localized in the plasma membrane-late endosome–lysosome compartments. Deletion of the putative transmembrane domain abolished the membrane association. In cells overexpressing EIG121, cytoplasmic vacuoles accumulated after EIG121 induction, and the autophagosome marker LC3 translocated into punctuate, dot-like structures. Electron microscopy revealed that in cells overexpressing EIG121, autophagosomes were markedly increased. Overexpression of EIG121 also increased the cells containing acidic vesicles and induced lysosomal degradation of long-lived proteins. In MCF-7 cells, both EIG121 and LC3 were rapidly degraded by a lysosomal mechanism after starvation. Knockdown of EIG121 blocked starvation-induced LC3 degradation. By itself, knockdown of EIG121 did not affect cell survival. When combined with starvation or cytotoxic agents, EIG121 knockdown greatly increased apoptosis. Our results suggest that EIG121 is associated with the endosome–lysosome compartments and may have an important role in autophagy. Under unfavorable conditions such as starvation and exposure to cytotoxic agents, EIG121 may protect cells from cell death by upregulating the autophagy pathway.

Targeting the insulin-like growth factor-1 receptor by picropodophyllin as a treatment option for glioblastoma

Glioblastoma (GB) is the most common malignant brain tumor in adults. It has limited treatment opportunities and is almost exclusively fatal. Owing to the central role the insulin-like growth factor-1 receptor (IGF-1R) plays in malignant cells, it has been suggested as a target for anticancer therapy including GB. The cyclolignan picropodophyllin (PPP) inhibits IGF-1R without affecting the highly homologous insulin receptor. Here, we show that PPP inhibits growth of human GB cell lines along with reduced phosphorylation of IGF-1R and AKT. In vivo, PPP-treatment causes dramatic tumor regression not only in subcutaneous xenografts but also in intracerebral xenografts, indicating passage of PPP across the blood-brain barrier.

Improved ATM kinase inhibitor KU-60019 radiosensitizes glioma cells, compromises insulin, AKT and ERK prosurvival signaling, and inhibits migration and invasion

Ataxia telangiectasia (A-T) mutated (ATM) is critical for cell cycle checkpoints and DNA repair. Thus, specific small molecule inhibitors targeting ATM could perhaps be developed into efficient radiosensitizers. Recently, a specific inhibitor of the ATM kinase, KU-55933, was shown to radiosensitize human cancer cells. Herein, we report on an improved analogue of KU-55933 (KU-60019) with K(i) and IC(50) values half of those of KU-55933. KU-60019 is 10-fold more effective than KU-55933 at blocking radiation-induced phosphorylation of key ATM targets in human glioma cells. As expected, KU-60019 is a highly effective radiosensitizer of human glioma cells. A-T fibroblasts were not radiosensitized by KU-60019, strongly suggesting that the ATM kinase is specifically targeted. Furthermore, KU-60019 reduced basal S473 AKT phosphorylation, suggesting that the ATM kinase might regulate a protein phosphatase acting on AKT. In line with this finding, the effect of KU-60019 on AKT phosphorylation was countered by low levels of okadaic acid, a phosphatase inhibitor, and A-T cells were impaired in S473 AKT phosphorylation in response to radiation and insulin and unresponsive to KU-60019. We also show that KU-60019 inhibits glioma cell migration and invasion in vitro, suggesting that glioma growth and motility might be controlled by ATM via AKT. Inhibitors of MEK and AKT did not further radiosensitize cells treated with KU-60019, supporting the idea that KU-60019 interferes with prosurvival signaling separate from its radiosensitizing properties. Altogether, KU-60019 inhibits the DNA damage response, reduces AKT phosphorylation and prosurvival signaling, inhibits migration and invasion, and effectively radiosensitizes human glioma cells.

When mutants gain new powers: news from the mutant p53 field

Ample data indicate that mutant p53 proteins not only lose their tumour suppressive functions, but also gain new abilities that promote tumorigenesis. Moreover, recent studies have modified our view of mutant p53 proteins, portraying them not as inert mutants, but rather as regulated proteins that influence the cancer cell transcriptome and phenotype. This influence is clinically manifested as association of TP53 mutations with poor prognosis and drug resistance in a growing array of malignancies. Here, we review recent studies on mutant p53 regulation, gain-of-function mechanisms, transcriptional effects and prognostic association, with a focus on the clinical implications of these findings.

MicroRNA-34a inhibits glioblastoma growth by targeting multiple oncogenes

MicroRNA-34a (miR-34a) is a transcriptional target of p53 that is down-regulated in some cancer cell lines. We studied the expression, targets, and functional effects of miR-34a in brain tumor cells and human gliomas. Transfection of miR-34a down-regulated c-Met in human glioma and medulloblastoma cells and Notch-1, Notch-2, and CDK6 protein expressions in glioma cells. miR-34a expression inhibited c-Met reporter activities in glioma and medulloblastoma cells and Notch-1 and Notch-2 3'-untranslated region reporter activities in glioma cells and stem cells. Analysis of human specimens showed that miR-34a expression is down-regulated in glioblastoma tissues as compared with normal brain and in mutant p53 gliomas as compared with wild-type p53 gliomas. miR-34a levels in human gliomas inversely correlated to c-Met levels measured in the same tumors. Transient transfection of miR-34a into glioma and medulloblastoma cell lines strongly inhibited cell proliferation, cell cycle progression, cell survival, and cell invasion, but transfection of miR-34a into human astrocytes did not affect cell survival and cell cycle status. Forced expression of c-Met or Notch-1/Notch-2 transcripts lacking the 3'-untranslated region sequences partially reversed the effects of miR-34a on cell cycle arrest and cell death in glioma cells and stem cells, respectively. Also, transient expression of miR-34a in glioblastoma cells strongly inhibited in vivo glioma xenograft growth. Together, these findings represent the first comprehensive analysis of the role of miR-34a in gliomas. They show that miR-34a suppresses brain tumor growth by targeting c-Met and Notch. The results also suggest that miR-34a could serve as a potential therapeutic agent for brain tumors.

Promyelocytic leukemia protein is required for gain of function by mutant p53

Mutations in the p53 tumor suppressor are the most common genetic events in human cancer. These mutations not only result in a loss of wild-type p53 activity, but can also lead to a gain of new oncogenic properties. Understanding how these gained functions are regulated is in its infancy. In this study, we show that the promyelocytic leukemia (PML) protein is an important regulator of mutant p53. We show that PML interacts with mutant p53. Importantly, PML enhances the transcriptional activity of mutant p53. Unexpectedly, PML is required for the proliferation and colony formation of cancer cells bearing mutant p53. Down-regulation of PML expression inhibits the growth of mutant p53-expressing cancer cells, predominantly by promoting cell cycle arrest. Our results suggest that the tumor suppression function of PML depends on the status of p53. In the context of mutant p53, PML enhances its cancer-promoting activities.

PTEN suppression of YY1 induces HIF-2 activity in von-Hippel-Lindau-null renal-cell carcinoma

Despite recent advances in cancer therapies, metastatic renal cell carcinoma (RCC) remains difficult to treat. Most RCCs result from inactivation of the von Hippel Lindau (VHL) tumor suppressor, leading to stable expression of Hypoxia-Inducible Factor-alpha (HIF-1alpha, -2alpha, -3alpha) and the induction of downstream target genes, including those responsible for angiogenesis and metastasis. While VHL is inactivated in the majority of RCC cases, expression of the PTEN tumor suppressor is reduced in about 30% of cases. PTEN functions to antagonize PI3K/Akt/mTOR signaling, thereby controlling cell growth and survival. Activation of PI3K/Akt/mTOR leads to increased HIF-1alpha expression in certain cancer cells, supporting the rationale of using mTOR inhibitors as anti-cancer agents. Notably, HIF-2alpha, rather than HIF-1alpha, has been shown to play a critical role in renal tumorigenesis. To investigate whether HIF-2alpha is similarly regulated by the PI3K pathway in VHL(-/-)RCC cells, we manipulated PI3K signaling using PTEN overexpression and siRNA knockdown studies and pharmacologic inhibition of PI3K or Akt. Our data support a novel role for wild-type PTEN in promoting HIF-2alpha activity in VHL null RCC cells. This mechanism is unique to the cellular environment in which HIF-2alpha expression is deregulated, resulting from the loss of VHL function. Our data show that PTEN induces HIF-2alpha transcriptional activity by inhibiting expression of Yin Yang 1 (YY1), which acts as a novel corepressor of HIF-2alpha. Further, PTEN suppression of YY1 is mediated through antagonism of PI3K signaling. We conclude that wild-type PTEN relieves the repressive nature of YY1 at certain HIF-2alpha target promoters and that this mechanism may promote early renal tumorigenesis resulting from VHL inactivation by increasing HIF-2alpha activity.

Interactions between PTEN and the c-Met pathway in glioblastoma and implications for therapy

The tyrosine kinase receptor c-Met and its ligand hepatocyte growth factor (HGF) are frequently overexpressed and the tumor suppressor PTEN is often mutated in glioblastoma. Because PTEN can interact with c-Met-dependent signaling, we studied the effects of PTEN on c-Met-induced malignancy and associated molecular events and assessed the potential therapeutic value of combining PTEN restoration approaches with HGF/c-Met inhibition. We studied the effects of c-Met activation on cell proliferation, cell cycle progression, cell migration, cell invasion, and associated molecular events in the settings of restored or inhibited PTEN expression in glioblastoma cells. We also assessed the experimental therapeutic effects of combining anti-HGF/c-Met approaches with PTEN restoration or mTOR inhibition. PTEN significantly inhibited HGF-induced proliferation, cell cycle progression, migration, and invasion of glioblastoma cells. PTEN attenuated HGF-induced changes of signal transduction proteins Akt, GSK-3, JNK, and mTOR as well as cell cycle regulatory proteins p27, cyclin E, and E2F-1. Combining PTEN restoration to PTEN-null glioblastoma cells with c-Met and HGF inhibition additively inhibited tumor cell proliferation and cell cycle progression. Similarly, combining a monoclonal anti-HGF antibody (L2G7) with the mTOR inhibitor rapamycin had additive inhibitory effects on glioblastoma cell proliferation. Systemic in vivo delivery of L2G7 and PTEN restoration as well as systemic in vivo deliveries of L2G7 and rapamycin additively inhibited intracranial glioma xenograft growth. These preclinical studies show for the first time that PTEN loss amplifies c-Met-induced glioblastoma malignancy and suggest that combining anti-HGF/c-Met approaches with PTEN restoration or mTOR inhibition is worth testing in a clinical setting.

Interactions between PTEN and receptor tyrosine kinase pathways and their implications for glioma therapy

Gliomas are the most common and deadly form of malignant primary brain tumors. Loss of the tumor-suppressor PTEN and activation of the receptor tyrosine kinases (RTKs) EGF receptor, c-Met, PDGF receptor and VEGF receptor are among the most common molecular dysfunctions associated with glioma malignancy. PTEN interacts with RTK-dependent signaling at multiple levels. These include the ability of PTEN to counteract PI3K activation by RTKs, as well as possible effects of PTEN on RTK activation of the MAPK pathway and RTK-dependent gene-expression regulation. Consequently, PTEN expression affects RTK-induced malignancy. Importantly, the PTEN status was recently found to be critical for the outcome of RTK-targeted clinical therapies that have been developed recently. Combining RTK-targeted therapies with therapies aimed at counteracting the effects of PTEN loss, such as mTOR inhibition, might also have therapeutic advantage. This article reviews the known molecular and functional interactions between PTEN and RTK pathways and their implications for glioma therapy.

Applications of emerging molecular technologies in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults. Median survival from the time of diagnosis is less than a year, with less than 5% of patients surviving 5 years. These tumors are thought to arise through two different pathways. Primary GBMs represent de novo tumors, while secondary GBMs represent the malignant progression of lower-grade astrocytomas. Moreover, despite improvements in deciphering the complex biology of these tumors, the overall prognosis has not changed in the past three decades. The hope for improving the outlook for these glial-based malignancies is centered on the successful clinical application of current high-throughput technologies. For example, the complete sequencing of the human genome has brought both genomics and proteomics to the forefront of cancer research as a powerful approach to systematically identify large volumes of data that can be utilized to study the molecular and cellular basis of oncology. The organization of these data into a comprehensive view of tumor growth and progression translates into a unique opportunity to diagnose and treat cancer patients. In this review, we summarize current genomic and proteomic alterations associated with GBM and how these modalities may ultimately impact treatment and survival.

Targeting prostate cancer based on signal transduction and cell cycle pathways

Prostate cancer remains a leading cause of death in men despite increased capacity to diagnose at earlier stages. After prostate cancer has become hormone independent, which often occurs after hormonal ablation therapies, it is difficult to effectively treat. Prostate cancer may arise from mutations and dysregulation of various genes involved in regulation signal transduction (e.g., PTEN, Akt, etc.,) and the cell cycle (e.g., p53, p21(Cip1), p27(Kip1), Rb, etc.,). This review focuses on the aberrant interactions of signal transduction and cell cycle genes products and how they can contribute to prostate cancer and alter therapeutic effectiveness.