Mutational spectra of PTEN/MMAC1 gene: a tumor suppressor with lipid phosphatase activity

A new role for PTEN in regulating transient receptor potential canonical channel 6-mediated Ca2+ entry, endothelial permeability, and angiogenesis

Phosphatase and tensin homologue (PTEN) is a dual lipid-protein phosphatase that catalyzes the conversion of phosphoinositol 3,4,5-triphosphate to phosphoinositol 4,5-bisphosphate and thereby inhibits PI3K-Akt-dependent cell proliferation, migration, and tumor vascularization. We have uncovered a previously unrecognized role for PTEN in regulating Ca(2+) entry through transient receptor potential canonical channel 6 (TRPC6) that does not require PTEN phosphatase activity. We show that PTEN tail-domain residues 394-403 permit PTEN to associate with TRPC6. The inflammatory mediator thrombin promotes this association. Deletion of PTEN residues 394-403 prevents TRPC6 cell surface expression and Ca(2+) entry. However, PTEN mutant, C124S, which lacks phosphatase activity, did not alter TRPC6 activity. Thrombin failed to increase endothelial monolayer permeability in the endothelial cells, transducing the Δ394-403 PTEN mutant. Paradoxically, we also show that thrombin failed to induce endothelial cell migration and tube formation in cells transducing the Δ394-403 PTEN mutant. Our results demonstrate that PTEN, through residues 394-403, serves as a scaffold for TRPC6, enabling cell surface expression of the channel. Ca(2+) entry through TRPC6 induces an increase in endothelial permeability and directly promotes angiogenesis. Thus, PTEN is indicated to play a role beyond suppressing PI3K signaling.

PI(3)king apart PTEN's role in cancer

The tumor suppressor phosphatase and tensin homolog (PTEN) is a nonredundant phosphatase, counteracting one of the most critical cancer-promoting pathways: the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. In addition to the canonical function of dephosphorylation of phosphatidylinositol-3,4,5-trisphosphate (PIP3), recent studies showed the intriguing roles of PTEN in regulating genomic instability, DNA repair, stem cell self-renewal, cellular senescence, and cell migration and/or metastasis. Clinically, PTEN mutations and deficiencies are prevalent in many types of human cancers. Severe PTEN deficiency is also associated with advanced tumor stage and therapeutic resistance, such as the resistance to trastuzumab, an anti-HER2 therapy. Currently, targeting the deregulated PI3K/PTEN-Akt signaling axis has emerged as one of the major tenets in anticancer drug development. In this review, we highlight our current knowledge of PTEN function and the recent discoveries in dissecting the PTEN signaling pathway. The deregulations of PTEN in cancers, clinical lessons, and new prospects of rationally designed PI3K/Akt-targeted therapy for effective cancer treatment are also discussed.

Phosphoinositide phosphatases in cell biology and disease

Phosphoinositides are essential signaling molecules linked to a diverse array of cellular processes in eukaryotic cells. The metabolic interconversions of these phospholipids are subject to exquisite spatial and temporal regulation executed by arrays of phosphatidylinositol (PtdIns) and phosphoinositide-metabolizing enzymes. These include PtdIns- and phosphoinositide-kinases that drive phosphoinositide synthesis, and phospholipases and phosphatases that regulate phosphoinositide degradation. In the past decade, phosphoinositide phosphatases have emerged as topics of particular interest. This interest is driven by the recent appreciation that these enzymes represent primary mechanisms for phosphoinositide degradation, and because of their ever-increasing connections with human diseases. Herein, we review the biochemical properties of six major phosphoinositide phosphatases, the functional involvements of these enzymes in regulating phosphoinositide metabolism, the pathologies that arise from functional derangements of individual phosphatases, and recent ideas concerning the involvements of phosphoinositide phosphatases in membrane traffic control.

Molecular mechanisms of necrosis in glioblastoma: the role of glutamate excitotoxicity

Glioblastomas continue to rank among the most lethal primary human tumors. Despite treatment with the most rigorous surgical interventions along with the most optimal chemotherapeutic and radiation regimens, the median survival is just 12-15 mo for patients with glioblastoma. Among the histological hallmarks of glioblastoma, necrosis has been demonstrated to be a powerful predictor of poor patient prognosis. Over the years, there have been many advances in our understanding of the molecular mechanisms underlying glioblastoma formation, yet the mechanisms that lead to tumor necrosis remain unclear. One pathway that may lead to necrosis in glioblastoma involves the neurotransmitter, glutamate, which has been shown to accumulate in the peritumoral fluid as a result of decreased cellular uptake by glioblastoma cells. This accumulation leads to subsequent glutamate excitotoxicity and probable necrosis through a massive elevation of intracellular Ca(2+) and reduction in cellular ATP levels. We propose that a pathway involving tumor necrosis factor-alpha (TNFalpha), astrocyte-elevated gene-1 (AEG-1) and nuclear factor-kappaB (NFkappaB) leads to decreased glutamate uptake through coordinated downregulation of the excitatory amino acid transporter 2 (EAAT2), the glutamate transporter responsible for the majority of glutamate uptake in the human brain. In addition, we suggest that AEG-1 signaling, loss of phosphatase and tensin homolog (PTEN), and ionotropic glutamate receptor activity lead to AKT pathway activation, which results in nutrient overconsumption and necrosis. Together, these pathways provide a new perspective on glioblastoma necrosis involving the process of glutamate excitotoxicity. Future research should address the components of these molecular pathways in order to better understand the mechanism of necrosis in glioblastoma and to begin to develop targeted therapies that may improve patient prognosis in the future.

Mutational and immunohistochemical study of the PI3K/Akt pathway in papillary thyroid carcinoma in Greece

PI3K/Akt signaling pathway plays critical role in many cell processes. There is indication that enhanced activation of PI3K/Akt cascade is implicated in thyroid tumors. Aim of this study was to evaluate the mutational status and expression of PI3K/Akt pathway mediators in papillary thyroid carcinoma in Greece. We evaluated the presence of mutations in PIK3CA (exons 9 and 20), AKT1 (exons 6-11), AKT2 (exons 6-11), AKT3 (exons 5-10), PTEN (exons 3-8), and PDPK1 (exons 4-10) genes in 83 papillary thyroid carcinomas by DNA sequencing. The expression levels of phospho-Akt and insulin-like growth factor I receptor (IGF-IR) were evaluated by immunohistochemistry. PIK3CA mutations were found in three samples. The analysis of AKT1 revealed one silent mutation in exon 9 (G726A) in 16 samples. One specimen carried an AKT3 mutation. One missense mutation was found in one sample in PTEN. No mutations were found in AKT2 and PDPK1. Increased levels of phosphorylated total Akt and IGF-IR were identified in some papillary cancers. Our findings indicate that PI3K/Akt signaling pathway is activated in some papillary tumors. However, mutations in genes coding most mediators of the pathway have not been proven to be the major modus of enhanced activation. These data suggest a potential role for PI3K/Akt-mediated signaling in papillary thyroid tumors.

A pharmacodynamic study of rapamycin in men with intermediate- to high-risk localized prostate cancer

PURPOSE

Given discrepancies between preclinical and clinical observations of mammalian target of rapamycin (mTOR) inhibition in prostate cancer, we sought to determine the pharmacodynamic effects of the mTOR/TORC1 inhibitor rapamycin in men with intermediate- to high-risk prostate cancer undergoing radical prostatectomy.

EXPERIMENTAL DESIGN

Rapamycin was given at 3 or 6 mg orally for 14 days before radical prostatectomy in men with multifocal Gleason sum > or =7 prostate cancer; 10 untreated control subjects were included. The primary outcome was inhibition of phosphorylation of ribosomal S6 in posttreatment radical prostatectomy versus pretreatment biopsy tumor tissue, evaluated using a Simon two-stage design for pharmacodynamic efficacy.

RESULTS

Thirty-two subjects were accrued: 20 at 3 mg, 2 at 6 mg, and 10 controls. No dose-limiting toxicities were observed at 3 mg; however, two of two men enrolled at 6 mg experienced dose-limiting toxicities including thrombocytopenia and fever with grade 3 stomatitis. Adverse events observed at 3 mg included stomatitis, rash, ileus, and neutropenia. Pharmacodynamic studies showed tumor S6 phosphorylation inhibition in 50% of 10 evaluable rapamycin-treated men with sufficient paired tissue [median 58% inhibition (P = 0.049) versus 2% inhibition in controls (P = 0.75)] with no significant effect on AKT activity. We observed no change in Ki-67 or caspase-3 cleavage but noted a reduction in cytoplasmic p27 staining with increased nuclear localization with rapamycin treatment. Prostate tissue rapamycin concentrations were 3- to 4-fold higher than blood.

CONCLUSIONS

At 3 mg daily, rapamycin successfully and safely inhibited prostate cancer S6 phosphorylation and achieved relatively high prostate tissue concentrations. No effect on AKT phosphorylation, tumor proliferation, or apoptosis was observed.

Bis(morpholino-1,3,5-triazine) derivatives: potent adenosine 5'-triphosphate competitive phosphatidylinositol-3-kinase/mammalian target of rapamycin inhibitors: discovery of compound 26 (PKI-587), a highly efficacious dual inhibitor

The PI3K/Akt signaling pathway is a key pathway in cell proliferation, growth, survival, protein synthesis, and glucose metabolism. It has been recognized recently that inhibiting this pathway might provide a viable therapy for cancer. A series of bis(morpholino-1,3,5-triazine) derivatives were prepared and optimized to provide the highly efficacious PI3K/mTOR inhibitor 1-(4-{[4-(dimethylamino)piperidin-1-yl]carbonyl}phenyl)-3-[4-(4,6-dimorpholin-4-yl-1,3,5-triazin-2-yl)phenyl]urea 26 (PKI-587). Compound 26 has shown excellent activity in vitro and in vivo, with antitumor efficacy in both subcutaneous and orthotopic xenograft tumor models when administered intravenously. The structure-activity relationships and the in vitro and in vivo activity of analogues in this series are described.

Phosphoinositide signalling in cancer: beyond PI3K and PTEN

There are numerous studies that suggest multiple links between the cellular phosphoinositide system and cancer. As key roles in cancer have been established for PI3K and PTEN - enzymes that regulate the levels of phosphatidylinositol-3,4,5-trisphosphate - compounds targeting this pathway are entering the clinic at a rapid pace. Several other phosphoinositide-modifying enzymes, including phosphoinositide kinases, phosphatases and phospholipase C enzymes, have been implicated in the generation and progression of tumours. Studies of these enzymes are providing new insights into the mechanisms and the extent of their involvement in cancer, highlighting new potential targets for therapeutic intervention.

Hepatic cancer stem cells and drug resistance: Relevance in targeted therapies for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of most common malignancies in the world. Systemic treatments for HCC, particularly for advanced stages, are limited by the drug resistance phenomenon which ultimately leads to therapy failure. Recent studies have indicated an association between drug resistance and the existence of the cancer stem cells (CSCs) as tumor initiating cells. The CSCs are resistant to conventional chemotherapies and might be related to the mechanisms of the ATP Binding Cassette (ABC) transporters and alterations in the CSCs signaling pathways. Therefore, to contribute to the development of new HCC treatments, further information on the characterization of CSCs, the modulation of the ABC transporters expression and function and the signaling pathway involved in the self renewal, initiation and maintenance of the cancer are required. The combination of transporters modulators/inhibitors with molecular targeted therapies may be a potent strategy to block the tumoral progression. This review summarizes the association of CSCs, drug resistance, ABC transporters activities and changes in signaling pathways as a guide for future molecular therapy for HCC.

Faithfull modeling of PTEN loss driven diseases in the mouse

A decade of work has indisputably defined PTEN as a pivotal player in human health and disease. Above all, PTEN has been identified as one of the most commonly lost or mutated tumor suppressor genes in human cancers. For this reason, the generation of a multitude of mouse models has been an invaluable strategy to dissect the function and consequences-of-loss of this essential, evolutionary conserved lipid phosphatase in tumor initiation and progression.In this chapter, we will summarize the mouse models that have allowed us to faithfully recapitulate features of human cancers and to highlight the network of connections between the PTEN signaling cascade and other oncogenic or tumor suppressive pathways.Notably, PTEN represents one of the most extensively modeled genes involved in human cancer and exemplifies the strength of genetic mouse modeling as an approach to gain information aimed to improve our understanding of and ability to alleviate human disease.

Formation of primordial follicles and immunolocalization of PTEN, PKB and FOXO3A proteins in the ovaries of fetal and neonatal pigs

The assembly of primordial follicles and subsequent development and transition of the primordial follicle to the primary follicle are critical processes in ovarian biology. In order to examine follicle formation and development in fetal and neonatal pigs, ovarian samples were obtained from a famous local breed of Chinese pigs, Erhualian pigs, ranging in age from 50 days postcoitum to 1 day postpartum in our current study. Morphological changes in the ovaries of the fetal and neonatal pigs indicated that egg nests were the earliest recognizable gamete cells. The proportion of egg nests decreased from 98.4 to 25.6% and the proportion of single follicles increased from 1.6 to 74.4% between 70 and 90 days postcoitum. The proportions of primordial follicles increased between 70 and 90 days postcoitum but decreased from 90 days postcoitum to 1 day postpartum. Our results suggested that the key stage of primordial follicle formation was between 70 and 90 days postcoitum and that the major stage of transition from primordial follicles into primary follicles was between 90 days postcoitum and 1 day postpartum. Experiments were also conducted to examine the localization of PTEN, PKB and FOXO3A proteins in the porcine ovaries by immunohistochemistry and immunoblotting. The results indicated that PTEN, PKB and FOXO3A were localized in the germ cells of egg nests, cytoplasm of oocytes and granulosa cells of follicles ranging from the primordial to secondary stages and that the staining intensity was weak in granulosa cells but strong in oocytes. The different staining patterns of PTEN, FOXO3A and PKB suggested that these proteins were expressed in a stage- and cell-specific manner during ovarian follicle formation and development in the fetal and neonatal pig.

Peroxiredoxin 1 and its role in cell signaling

Peroxiredoxins (Prdxs) are a family of small (22-27 kDa) nonseleno peroxidases currently known to possess six mammalian isoforms. Although their individual roles in cellular redox regulation and antioxidant protection are quite distinct, they all catalyze peroxide reduction of H(2)O(2), organic hydroperoxides and peroxynitrite. They are found to be expressed ubiquitously and in high levels, suggesting that they are both an ancient and important enzyme family. Prdxs can be divided into three major subclasses: typical 2-cysteine (2-Cys) Prdxs (Prdx1-4), atypical 2-Cys Prdx (Prdx 5) and 1-Cys Prdx (Prdx 6). Recent evidence suggests that 2-Cys peroxiredoxins are more than "just simple peroxidases". This hypothesis has been discussed elegantly in recent review articles, considering "over"-oxidation of the protonated thiolate peroxidatic cysteine and post-translational modification of Prdxs as processes initiating a mechanistic switch from peroxidase to chaperon function. The process of over-oxidation of the peroxidatic cysteine (C(P)) occurs during catalysis in the presence of thioredoxin (Trx), thus rendering the sulfenic moiety to sulfinic acid, which can be reduced by sulfiredoxin (Srx). However, further oxidation to sulfonic acid is believed to promote Prdx degradation or, as recently shown, the formation of oligomeric peroxidase-inactive chaperones with questionable H(2)O(2)-scavenging capacity. In the light of this and given that Prdx1 has recently been shown by us and by others to interact directly with signaling molecules, we will explore the possibility that H(2)O(2) regulates signaling in the cell in a temporal and spatial fashion via oxidizing Prdx1. Therefore, this review will focus on H(2)O(2) modulating cell signaling via Prdxs by discussing: (1) the activity of Prdxs towards H(2)O(2); (2) sub cellular localization and availability of other peroxidases, such as catalase or glutathione peroxidases; (3) the availability of Prdxs reducing systems, such as thioredoxin and sulfiredoxin and lastly, (4) Prdx1 interacting signaling molecules.

Novel imidazolopyrimidines as dual PI3-Kinase/mTOR inhibitors

This article describes the syntheses and SAR of a series of imidazolopyrimidine derivatives, which are evaluated as inhibitors of PI3-Kinase (PI3K) and mTOR. These compounds were found to be ATP competitive with good tumor cell growth inhibition, and suppression of pathway specific biomakers such as phosphorylation of Akt at T308.

Nuclear PTEN levels and G2 progression in melanoma cells

The phosphatase and tensin homolog (PTEN) exerts its function, in part, by negatively regulating the well-known phosphatidylinositol-3-kinase/AKT signaling pathway. Previous histological work has suggested that alterations in the nuclear/cytoplasmic compartmentalization of PTEN may play a role in the development and progression of melanoma. In this study, we examined the nuclear/cytoplasmic compartmentalization of PTEN in melanoma cell lines and its correlation with the cell cycle. Studies were performed in melanoma cells lines using classic cell biological techniques. In contrast to breast cancer cell lines, we found that increased levels of nuclear PTEN levels correlate with G2 rather than with G1 arrest. In WM164 and SKmel28 cells, overexpression of PTEN protein did not significantly increase the number of cells in the G2 phase. Differential CDC2 phosphorylation levels in cells that overexpressed PTEN compared with those where PTEN was downregulated suggest some involvement of PTEN in G2 checkpoint regulation. The data suggest that although nuclear PTEN levels correlate with the G2 phase, the role of PTEN in modulating G2/M arrest is not limiting. Further, the specific cell cycle phase regulated by nuclear PTEN is cell-type dependent. Taken together, our observations suggest that in melanoma, nuclear PTEN is involved in G2 progression possibly through the modulation of CDC2, opening up a new arena for investigation.

Main roads to melanoma

The characterization of the molecular mechanisms involved in development and progression of melanoma could be helpful to identify the molecular profiles underlying aggressiveness, clinical behavior, and response to therapy as well as to better classify the subsets of melanoma patients with different prognosis and/or clinical outcome. Actually, some aspects regarding the main molecular changes responsible for the onset as well as the progression of melanoma toward a more aggressive phenotype have been described. Genes and molecules which control either cell proliferation, apoptosis, or cell senescence have been implicated. Here we provided an overview of the main molecular changes underlying the pathogenesis of melanoma. All evidence clearly indicates the existence of a complex molecular machinery that provides checks and balances in normal melanocytes. Progression from normal melanocytes to malignant metastatic cells in melanoma patients is the result of a combination of down- or up-regulation of various effectors acting on different molecular pathways.

Selective deletion of PTEN in dopamine neurons leads to trophic effects and adaptation of striatal medium spiny projecting neurons

The widespread distribution of the tumor suppressor PTEN in the nervous system suggests a role in a broad range of brain functions. PTEN negatively regulates the signaling pathways initiated by protein kinase B (Akt) thereby regulating signals for growth, proliferation and cell survival. Pten deletion in the mouse brain has revealed its role in controlling cell size and number. In this study, we used Cre-loxP technology to specifically inactivate Pten in dopamine (DA) neurons (Pten KO mice). The resulting mutant mice showed neuronal hypertrophy, and an increased number of dopaminergic neurons and fibers in the ventral mesencephalon. Interestingly, quantitative microdialysis studies in Pten KO mice revealed no alterations in basal DA extracellular levels or evoked DA release in the dorsal striatum, despite a significant increase in total DA tissue levels. Striatal dopamine receptor D1 (DRD1) and prodynorphin (PDyn) mRNA levels were significantly elevated in KO animals, suggesting an enhancement in neuronal activity associated with the striatonigral projection pathway, while dopamine receptor D2 (DRD2) and preproenkephalin (PPE) mRNA levels remained unchanged. In addition, PTEN inactivation protected DA neurons and significantly enhanced DA-dependent behavioral functions in KO mice after a progressive 6OHDA lesion. These results provide further evidence about the role of PTEN in the brain and suggest that manipulation of the PTEN/Akt signaling pathway during development may alter the basal state of dopaminergic neurotransmission and could provide a therapeutic strategy for the treatment of Parkinson's disease, and other neurodegenerative disorders.

Analysis of PTEN complex assembly and identification of heterogeneous nuclear ribonucleoprotein C as a component of the PTEN-associated complex

PTEN (phosphatase and tensin homolog deleted on chromosome 10) is well characterized for its role in antagonizing the phosphoinositide 3-kinase pathway. Previous studies using size-exclusion chromatography demonstrated PTEN recruitment into high molecular mass complexes and hypothesized that PTEN phosphorylation status and PDZ binding domain may be required for such complex formation. In this study, we set out to test the structural requirements for PTEN complex assembly and identify the component(s) of the PTEN complex(es). Our results demonstrated that the PTEN catalytic function and PDZ binding domain are not absolutely required for its complex formation. On the other hand, PTEN phosphorylation status has a significant impact on its complex assembly. Our results further demonstrate enrichment of the PTEN complex in nuclear lysates, suggesting a mechanism through which PTEN phosphorylation may regulate its complex assembly. These results prompted further characterization of other protein components within the PTEN complex(es). Using size-exclusion chromatography and two-dimensional difference gel electrophoresis followed by mass spectrometry analysis, we identified heterogeneous nuclear ribonucleoprotein C (hnRNP C) as a novel protein recruited to higher molecular mass fractions in the presence of PTEN. Further analysis indicates that endogenous hnRNP C and PTEN interact and co-localize within the nucleus, suggesting a potential role for PTEN, alongside hnRNP C, in RNA regulation.

PTEN identified as important risk factor of chronic obstructive pulmonary disease

Common genetic variation may play an important role in altering chronic obstructive pulmonary disease (COPD) risk. In Xuanwei, China, the COPD rate is more than twice the Chinese national average, and COPD is strongly associated with in-home coal use. To identify genetic variation that may be associated with COPD in a population with substantial in-home coal smoke exposures, we evaluated 1261 single nucleotide polymorphisms (SNPs) in 380 candidate genes potentially relevant for cancer and other human diseases in a population-based case-control study in Xuanwei (53 cases; 107 controls). PTEN was the most significantly associated gene with COPD in a minP analysis using 20,000 permutations (P=0.00005). SNP-based analyses found that homozygote variant carriers of PTEN rs701848 (OR(TT)=0.12, 95% CI=0.03-0.47) had a significant decreased risk of COPD. PTEN, or phosphatase and tensin homolog, is an important regulator of cell cycle progression and cellular survival via the AKT signaling pathway. Our exploratory analysis suggests that genetic variation in PTEN may be an important risk factor of COPD in Xuanwei. However, due to the small sample size, additional studies are needed to evaluate these associations within Xuanwei and other populations with coal smoke exposures.

PTEN and the PI3-kinase pathway in cancer

PI3-kinase and PTEN are major positive and negative regulators, respectively, of the PI3-kinase pathway, which regulates growth, survival, and proliferation. These key signaling components are two of the most frequently mutated proteins in human cancers, resulting in unregulated activation of PI3K signaling and providing irrefutable genetic evidence of the central role of this pathway in tumorigenesis. PTEN regulates PI3K signaling by dephosphorylating the lipid signaling intermediate PIP(3), but PTEN may have additional phosphatase-independent activities, as well as other functions in the nucleus. In this review, we highlight current work showing cancer-relevant complexities in the regulation of PTEN and PI3K activity, potential novel functions for PTEN, and feedback regulation within the pathway. The significance and complexity of PI3K signaling make it an important but challenging therapeutic target for cancer.

Pharmacological inhibition of mTORC1 suppresses anatomical, cellular, and behavioral abnormalities in neural-specific Pten knock-out mice

PTEN (phosphatase and tensin homolog deleted on chromosome ten) is a lipid phosphatase that counteracts the function of phosphatidylinositol-3 kinase (PI3K). Loss of function of PTEN results in constitutive activation of AKT and downstream effectors and correlates with many human cancers, as well as various brain disorders, including macrocephaly, seizures, Lhermitte-Duclos disease, and autism. We previously generated a conditional Pten knock-out mouse line with Pten loss in limited postmitotic neurons in the cortex and hippocampus. Pten-null neurons developed neuronal hypertrophy and loss of neuronal polarity. The mutant mice exhibited macrocephaly and behavioral abnormalities reminiscent of certain features of human autism. Here, we report that rapamycin, a specific inhibitor of mammalian target of rapamycin complex 1 (mTORC1), can prevent and reverse neuronal hypertrophy, resulting in the amelioration of a subset of PTEN-associated abnormal behaviors, providing evidence that the mTORC1 pathway downstream of PTEN is critical for this complex phenotype.

Cdc6 and cyclin E2 are PTEN-regulated genes associated with human prostate cancer metastasis

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is frequently inactivated in metastatic prostate cancer, yet the molecular consequences of this and their association with the metastatic phenotype are incompletely understood. We performed transcriptomic analysis and identified genes altered by conditional PTEN reexpression in C4-2, a human metastatic prostate cancer cell line with inactive PTEN. PTEN-regulated genes were disproportionately represented among genes altered in human prostate cancer progression and metastasis but not among those associated with tumorigenesis. From the former set, we identified two novel putative PTEN targets, cdc6 and cyclin E2, which were overexpressed in metastatic human prostate cancer and up-regulated as a function of PTEN depletion in poorly metastatic DU145 human prostate cancer cells harboring a wild type PTEN. Inhibition of cdc6 and cyclin E2 levels as a consequence of PTEN expression was associated with cell cycle G(1) arrest, whereas use of PTEN activity mutants revealed that regulation of these genes was dependent on PTEN lipid phosphatase activity. Computational and promoter-reporter evaluations implicated the E2F transcription factor in PTEN regulation of cdc6 and cyclin E2 expression. Our results suggest a hypothetical model whereby PTEN loss upregulates cell cycle genes such as cdc6 and cyclin E2 that in turn promote metastatic colonization at distant sites.

Genetic variations in the PI3K/PTEN/AKT/mTOR pathway are associated with clinical outcomes in esophageal cancer patients treated with chemoradiotherapy

PURPOSE

The phosphoinositide-3-kinase (PI3K), phosphatase and tensin homolog (PTEN), v-akt murine thymoma viral oncogene homolog (AKT), and mammalian target of rapamycin (mTOR) signaling pathway has been implicated in resistance to several chemotherapeutic agents. In this retrospective study, we determined whether common genetic variations in this pathway are associated with clinical outcomes in esophageal cancer patients with adenocarcinoma or squamous cell carcinoma who have undergone chemoradiotherapy and surgery.

PATIENTS AND METHODS

Sixteen tagging single nucleotide polymorphisms (SNPs) in PIK3CA, PTEN, AKT1, AKT2, and FRAP1 (encoding mTOR) were genotyped in these patients and analyzed for associations with response to therapy, survival, and recurrence.

RESULTS

We observed an increased recurrence risk with genetic variations in AKT1 and AKT2 (hazard ratio [HR], 2.21; 95% CI, 1.06 to 4.60; and HR, 3.30; 95% CI, 1.64 to 6.66, respectively). This effect was magnified with an increasing number of AKT adverse genotypes. In contrast, a predictable protective effect by PTEN genetic variants on recurrence was evident. Survival tree analysis identified higher-order interactions that resulted in variation in recurrence-free survival from 12 to 42 months, depending on the combination of SNPs. Genetic variations in AKT1, AKT2, and FRAP1 were associated with survival. Patients homozygous for either of the FRAP1 SNPs assayed had a more than three-fold increased risk of death. Two genes--AKT2 and FRAP1--were associated with a poor treatment response, while a better response was associated with heterozygosity for AKT1:rs3803304 (odds ratio, 0.50; 95% CI, 0.25 to 0.99).

CONCLUSION

These results suggest that common genetic variations in this pathway modulate clinical outcomes in patients who undergo chemoradiotherapy. With further validation, these results may be used to build a model of individualized therapy for the selection of the optimal chemotherapeutic regimen.

PI3K/mTORC1 activation in hamartoma syndromes: therapeutic prospects

Dysregulated activity of phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin complex 1 (mTORC1) is characteristic feature of hamartoma syndromes. Hamartoma syndromes, dominantly inherited cancer predisposition disorders, affect multiple organs and are manifested by benign tumors consisting of various cell types native to the tissues in which they arise. In the past few years, three inherited hamartoma syndromes, Cowden syndrome (CS), tuberous sclerosis complex (TSC) syndrome, and Peutz-Jeghens syndrome (PJS), have all been linked to a common biochemical pathway: the hyperactivation of PI3K/mTORC1 intracellular signaling. Three tumor suppressors, PTEN (phosphatases and tensin homolog), tuberous sclerosis complex TSC1/TSC2, and LKB1, are negative regulators of PI3K/mTORC1 signaling; disease-related inactivation of these tumor suppressors results in the development of PTEN-associated hamartoma syndromes, TSC and PJS, respectively. The goal of this review is to provide a roadmap for navigating the inherently complex regulation of PI3K/mTORC1 signaling while highlighting the progress that has been made in elucidating the cellular and molecular mechanisms of hamartoma syndromes and identificating potential therapeutic targets for their treatment. Importantly, because the PI3K/mTORC1 pathway is activated in the majority of common human cancers, the identification of novel molecular target(s) for the treatment of hamartoma syndromes may have a broader translational potential, and is critically important not only for therapeutic intervention in hamartoma disorders, but also for the treatment of cancers.

Genetic modelling of the PTEN/AKT pathway in cancer research

The focus on targeted therapies has been fuelled by extensive research on molecular pathways and their role in tumorigenesis. Novel models of human cancer have been created to evaluate the role of specific genes in the different stages of cancer. Currently, mouse modelling of human cancer is possible through the expression of oncogenes, specific genetic mutations or the inactivation of tumour suppressor genes, and these models have begun to provide us with an understanding of the molecular pathways involved in tumour initiation and progression at the physiological level. Additionally, these mouse models serve as an excellent system to evaluate the efficacy of currently developed molecular targeted therapies and identify new potential targets for future therapies. The PTEN/AKT pathway is implicated in signal transduction through tyrosine kinase receptors and heterotrimeric G protein-linked receptors. Deregulation of the PTEN/AKT pathway is a common event in human cancer. Despite the abundant literature, the physiological role of each element of the pathway has begun to be uncovered thanks to genetically engineered mice. This review will summarise some of the key animal models which have helped us to understand this signalling network and its contribution to tumorigenesis.

FoxO1 mediates PTEN suppression of androgen receptor N- and C-terminal interactions and coactivator recruitment

FoxO (mammalian forkhead subclass O) proteins are transcription factors acting downstream of the PTEN (phosphatase and tensin homolog deleted on chromosome 10) tumor suppressor. Their activity is negatively regulated by AKT-mediated phosphorylation. Our previous studies showed that the transcriptional activity of the androgen receptor (AR) was inhibited by PTEN in an AKT-sensitive manner. Here, we report the repression of the activity of the full-length AR and its N-terminal domain by FoxO1 and the participation of FoxO1 in AR inhibition by PTEN. Ectopic expression of active FoxO1 decreased the transcriptional activity of AR as well as androgen-induced cell proliferation and production of prostate-specific antigen. FoxO1 knock down by RNA interference increased the transcriptional activity of the AR in PTEN-intact cells and relieved its inhibition by ectopic PTEN in PTEN-null cells. Mutational analysis revealed that FoxO1 fragment 150-655, which contains the forkhead box and C-terminal activation domain, was required for AR inhibition. Mammalian two-hybrid and glutathione-S-transferase pull-down assays demonstrated that the inhibition of AR activity by PTEN through FoxO1 involved the interference of androgen-induced interaction of the N- and C-termini of the AR and the recruitment of the p160 coactivators to its N terminus and to the androgen response elements of natural AR target genes. These studies reveal new mechanisms for the inhibition of AR activity by PTEN-FoxO axis and establish FoxO proteins as important nuclear factors that mediate the mutual antagonism between AR and PTEN tumor suppressor in prostate cancer cells.

PTEN deficiency is a common defect in juvenile myelomonocytic leukemia

The biological hallmark of juvenile myelomonocytic leukemia (JMML) is selective GM-CSF hypersensitivity. We hypothesized that PTEN protein deficiency might lead to insufficient negative growth signals to counter the hyperactive Ras signaling and therefore aid in the acceleration of the malignant transformation of JMML. In screening 34 JMML patients we found: (1) decreased PTEN protein in 67% of patients; (2) significantly lower PTEN mRNA levels in patients compared to controls (p<0.01); (3) a hypermethylated PTEN promoter in 77% of patients; and (4) constitutive-hyperactive Akt and MAPK in 55% and 73% of patients, respectively. These findings suggest that PTEN deficiency is very common in JMML and is in part due to hypermethylation of the PTEN gene promoter.

PTEN: a default gate-keeping tumor suppressor with a versatile tail

The tumor suppressor PTEN controls a variety of biological processes including cell proliferation, growth, migration, and death. As a master cellular regulator, PTEN itself is also subjected to deliberated regulation to ensure its proper function. Defects in PTEN regulation have a profound impact on carcinogenesis. In this review, we briefly discuss recent advances concerning PTEN regulation and how such knowledge facilitates our understanding and further exploration of PTEN biology. The carboxyl-tail of PTEN, which appears to be associated with multiple types of posttranslational regulation, will be under detailed scrutiny. Further, a comparative analysis of PTEN and p53 suggests while p53 needs to be activated to suppress tumorigenesis (a dormant gatekeeper), PTEN is probably a constitutive surveillant against cancer development, thus a default gatekeeper.

Class I PI3K in oncogenic cellular transformation

Class I phosphoinositide 3-kinase (PI3K) is a dimeric enzyme, consisting of a catalytic and a regulatory subunit. The catalytic subunit occurs in four isoforms designated as p110 alpha, p110 beta, p110 gamma and p110 delta. These isoforms combine with several regulatory subunits; for p110 alpha, beta and delta, the standard regulatory subunit is p85, for p110 gamma, it is p101. PI3Ks play important roles in human cancer. PIK3CA, the gene encoding p110 alpha, is mutated frequently in common cancers, including carcinoma of the breast, prostate, colon and endometrium. Eighty percent of these mutations are represented by one of the three amino-acid substitutions in the helical or kinase domains of the enzyme. The mutant p110 alpha shows a gain of function in enzymatic and signaling activity and is oncogenic in cell culture and in animal model systems. Structural and genetic data suggest that the mutations affect regulatory inter- and intramolecular interactions and support the conclusion that there are at least two molecular mechanisms for the gain of function in p110 alpha. One of these mechanisms operates largely independently of binding to p85, the other abolishes the requirement for an interaction with Ras. The non-alpha isoforms of p110 do not show cancer-specific mutations. However, they are often differentially expressed in cancer and, in contrast to p110 alpha, wild-type non-alpha isoforms of p110 are oncogenic when overexpressed in cell culture. The isoforms of p110 have become promising drug targets. Isoform-selective inhibitors have been identified. Inhibitors that target exclusively the cancer-specific mutants of p110 alpha constitute an important goal and challenge for current drug development.

Post-translational regulation of PTEN

PTEN (phosphatase and tensin homolog deleted on chromosome 10) tumor suppressor regulates a variety of cellular processes including cell proliferation, growth, migration and death. This master regulator itself is also under deliberative regulation. Although the evidence for PTEN regulation and its significance in normal biology and disease is overwhelming, the mechanisms and exact functional consequences of PTEN regulation are far from clear. In this review, we discuss recent advances concerning post-translational regulation of PTEN in general, and in more detail about its regulation by ubiquitination. We also discuss some unsolved questions in the field and how they might be addressed in the future. We propose that the complex regulatory mechanisms of PTEN dictate how this tumor suppressor executes its distinct biological functions.

The role of PTEN signaling perturbations in cancer and in targeted therapy

The PTEN tumor suppressor was discovered by its homozygous deletion and other mutations in cancer. Since then, PTEN has been shown to be a non-redundant, evolutionarily conserved phosphatase whose function affects diverse cellular progresses such as cell cycle progression, cell proliferation, chemotaxis, apoptosis, aging, muscle contractility, DNA damage response, angiogenesis and cell polarity. In accordance with its ability to influence multiple crucial cellular processes, PTEN has a major role in the pathogenesis of numerous diseases such as diabetes, autism and almost every cancer examined. This review will discuss the diverse ways in which PTEN signaling is modified in cancer, and how these changes correlate with and might possibly affect the action of targeted chemotherapy.

PTEN posttranslational inactivation and hyperactivation of the PI3K/Akt pathway sustain primary T cell leukemia viability

Mutations in the phosphatase and tensin homolog (PTEN) gene leading to PTEN protein deletion and subsequent activation of the PI3K/Akt signaling pathway are common in cancer. Here we show that PTEN inactivation in human T cell acute lymphoblastic leukemia (T-ALL) cells is not always synonymous with PTEN gene lesions and diminished protein expression. Samples taken from patients with T-ALL at the time of diagnosis very frequently showed constitutive hyperactivation of the PI3K/Akt pathway. In contrast to immortalized cell lines, most primary T-ALL cells did not harbor PTEN gene alterations, displayed normal PTEN mRNA levels, and expressed higher PTEN protein levels than normal T cell precursors. However, PTEN overexpression was associated with decreased PTEN lipid phosphatase activity, resulting from casein kinase 2 (CK2) overexpression and hyperactivation. In addition, T-ALL cells had constitutively high levels of ROS, which can also downmodulate PTEN activity. Accordingly, both CK2 inhibitors and ROS scavengers restored PTEN activity and impaired PI3K/Akt signaling in T-ALL cells. Strikingly, inhibition of PI3K and/or CK2 promoted T-ALL cell death without affecting normal T cell precursors. Overall, our data indicate that T-ALL cells inactivate PTEN mostly in a nondeletional, posttranslational manner. Pharmacological manipulation of these mechanisms may open new avenues for T-ALL treatment.

Crucial role of the C-terminus of PTEN in antagonizing NEDD4-1-mediated PTEN ubiquitination and degradation

PTEN (phosphatase and tensin homologue deleted on chromosome 10), a potent tumour suppressor and multifunctional signalling protein, is under intricate regulation. In the present study, we have investigated the mechanism and regulation of PTEN ubiquitination catalysed by NEDD4-1 (neural-precursor-cell-expressed, developmentally down-regulated 4-1), a ubiquitin ligase for PTEN we identified recently. Using the reconstituted assay and cellular analysis, we demonstrated that NEDD4-1-mediated PTEN ubiquitination depends on its intact HECT (homologous to E6-associated protein C-terminus) domain. Instead of using its WW domains (protein-protein interaction domains containing two conserved tryptophan residues) as a protein interaction module, NEDD4-1 interacts with PTEN through its N-terminal region containing a C2 domain as well as the HECT domain. Strikingly, we found that a C-terminal truncated PTEN fragment binds to NEDD4-1 with higher affinity than the full-length PTEN, suggesting an intrinsic inhibitory effect of the PTEN C-terminus on PTEN-NEDD4-1 interaction. Moreover, the C-terminal truncated PTEN is more sensitive to NEDD4-1-mediated ubiquitination and degradation. Therefore the present study reveals that the C-terminus of PTEN plays a critical role in stabilizing PTEN via antagonizing NEDD4-1-induced PTEN protein decay; conversely, truncation of the PTEN C-terminus results in rapid NEDD4-1-mediated PTEN degradation, a possible mechanism accounting for attenuation of PTEN function by certain PTEN mutations in human cancers.

Pten haploinsufficiency accelerates formation of high-grade astrocytomas

We previously reported that central nervous system (CNS) inactivation of Nf1 and p53 tumor suppressor genes in mice results in the development of low-grade to high-grade progressive astrocytomas. When the tumors achieve high grade, they are frequently accompanied by Akt activation, reminiscent of the frequent association of PTEN mutations in human high-grade glioma. In the present study, we introduced CNS heterozygosity of Pten into the Nf1/p53 astrocytoma model. Resulting mice had accelerated morbidity, shortened survival, and full penetrance of high-grade astrocytomas. Haploinsufficiency of Pten accelerated formation of grade 3 astrocytomas, whereas loss of Pten heterozygosity and Akt activation coincided with progression into grade 4 tumors. These data suggest that successive loss of each Pten allele may contribute to de novo formation of high-grade astrocytoma and progression into glioblastoma, respectively, thus providing insight into the etiology of primary glioblastoma. The presence of ectopically migrating neural stem/progenitor lineage cells in presymptomatic Pten-deficient mutant brains supports the notion that these tumors may arise from stem/progenitor cells.

Enhanced effects of xanthohumol plus honokiol on apoptosis in 3T3-L1 adipocytes

OBJECTIVE

To study the effects of xanthohumol (XN), a flavonoid found in hops (Humulus lupulus) and honokiol (HK), a lignan isolated from Magnolia officinalis, alone and in combination, on apoptotic signaling in 3T3-L1 adipocytes.

METHODS AND PROCEDURES

3T3-L1 mature adipocytes were incubated with various concentrations of XN and HK alone and in combination. Viability and apoptosis were quantified using an MTS-based cell viability assay and single-stranded DNA assay, respectively. Expression of apoptosis related proteins including cleaved poly(ADP-ribose) polymerase (PARP), cytochrome c, Bcl-2, caspase-3/7, phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and Akt was analyzed by western blotting.

RESULTS

Combinations of XN and HK significantly decreased viability and induced apoptosis in a dose-dependent manner and more than the additive responses to XN and HK alone. Western blot analysis showed an increase in cleaved PARP and cytochrome c release and decrease in expression of Bcl-2 protein by XN plus HK, whereas XN and HK individually had no effect. Furthermore, the combination of XN and HK activated PTEN and inactivated Akt by decreasing levels of phosphorylated PTEN and phosphorylated Akt.

DISCUSSION

We demonstrated that although XN and HK showed little or no effect as individual compounds, in combination (XN plus HK) they showed enhanced activity in inducing apoptosis via the cytochrome c/caspase-3/PARP and PTEN/Akt pathways in 3T3-L1 adipocytes.

Tenets of PTEN tumor suppression

Since its discovery as the elusive tumor suppressor gene at the frequently mutated 10q23 locus, PTEN has been identified as lost or mutated in several sporadic and heritable tumor types. A decade of work has established that PTEN is a nonredundant phosphatase that is essential for regulating the highly oncogenic prosurvival PI3K/AKT signaling pathway. This review discusses emerging modes of PTEN function and regulation, and speculates about how manipulation of PTEN function could be used for cancer therapy.

The tumour suppressor PTEN mediates a negative regulation of the E3 ubiquitin-protein ligase Nedd4

The tumour suppressor PTEN (phosphatase and tensin homologue deleted on chromosome 10; a phosphatidylinositol 3-phosphatase) is a multifunctional protein deregulated in many types of cancer. It is suggested that a number of proteins that relate with PTEN functionally or physically have not yet been found. In order to search for PTEN-interacting proteins that might be crucial in the regulation of PTEN, we exploited a proteomics-based approach. PTEN-expressing NIH 3T3 cell lysates were used in affinity chromatography and then analysed by LC–ESI–MS/MS (liquid chromatography–electrospray ionization–tandem MS). A total of 93 proteins were identified. Among the proteins identified, we concentrated on the E3 ubiquitin-protein ligase Nedd4 (neural-precursor-cell-expressed, developmentally down-regulated gene 4), and performed subsequent validation experiments using HeLa cells. Nedd4 inhibited PTEN-induced apoptotic cell death and, conversely, the Nedd4 level was down-regulated by PTEN. The down-regulation effect was diminished by a mutation (C124S) in the catalytic site of PTEN. Nedd4 expression was also decreased by a PI3K (phosphoinositide 3-kinase) inhibitor, LY294002, suggesting that the regulation is dependent on the phosphatase-kinase activity of the PTEN-PI3K/Akt pathway. Semi-quantitative real-time PCR analysis revealed that Nedd4 was transcriptionally regulated by PTEN. Thus our results have important implications regarding the roles of PTEN upon the E3 ubquitin ligase Nedd4 as a negative feedback regulator as well as a substrate.

Lipid signalling in disease

Signalling lipids such as eicosanoids, phosphoinositides, sphingolipids and fatty acids control important cellular processes, including cell proliferation, apoptosis, metabolism and migration. Extracellular signals from cytokines, growth factors and nutrients control the activity of a key set of lipid-modifying enzymes: phospholipases, prostaglandin synthase, 5-lipoxygenase, phosphoinositide 3-kinase, sphingosine kinase and sphingomyelinase. These enzymes and their downstream targets constitute a complex lipid signalling network with multiple nodes of interaction and cross-regulation. Imbalances in this network contribute to the pathogenesis of human disease. Although the function of a particular signalling lipid is traditionally studied in isolation, this review attempts a more integrated overview of the key role of these signalling lipids in inflammation, cancer and metabolic disease, and discusses emerging strategies for therapeutic intervention.

The aryl hydrocarbon receptor (AhR) inhibits vanadate-induced vascular endothelial growth factor (VEGF) production in TRAMP prostates

Hypoxia-inducible factor-1 alpha (HIF-1alpha) and aryl hydrocarbon receptor nuclear translocator (ARNT) are basic helix-loop-helix/per-arnt-sim (PAS) family transcription factors. During angiogenesis and tumor growth, HIF-1alpha dimerizes with ARNT, inducing expression of many genes, including vascular endothelial growth factor (VEGF). ARNT also dimerizes with the aryl hydrocarbon receptor (AhR). AhR-null (Ahr(-/-)) transgenic adenocarcinoma of the mouse prostate (TRAMP) mice develop prostate tumors with greater frequency than AhR wild-type (Ahr(+/+)) TRAMP mice, even though prevalence of prostate epithelial hyperplasia is not inhibited. This suggests that Ahr inhibits prostate carcinogenesis. In TRAMP mice, prostatic epithelial hyperplasia results in stabilized HIF-1alpha, inducing expression of VEGF, a prerequisite for tumor growth and angiogenesis. Since ARNT is a common dimerization partner of AhR and HIF-1alpha, we hypothesized that the AhR inhibits prostate tumor formation by competing with HIF-1alpha for ARNT, thereby limiting VEGF production. Prostates from Ahr(+/+), Ahr(+/-) and Ahr(-/-) C57BL/6J TRAMP mice were cultured in the presence of graded concentrations of vanadate, an inducer of VEGF through the HIF-1alpha-ARNT pathway. Vanadate induced VEGF protein in a dose-dependent fashion in Ahr(+/-) and Ahr(-/-) TRAMP cultures, but not in Ahr(+/+) cultures. However, vanadate induced upstream proteins in the phosphatidylinositol 3-kinase-signaling cascade to a similar extent in TRAMPs of each Ahr genotype, evidenced by v-akt murine thymoma viral oncogene homolog (Akt) phosphorylation. These findings suggest that AhR sequesters ARNT, decreasing interaction with HIF-1alpha reducing VEGF production. Since VEGF is required for tumor vascularization and growth, these studies further suggest that reduction in VEGF correlates with inhibited prostate carcinogenesis in Ahr(+/+) TRAMP mice.

PTEN nuclear localization is regulated by oxidative stress and mediates p53-dependent tumor suppression

The tumor suppressor gene PTEN (phosphatase and tensin homologue deleted on chromosome 10) is frequently mutated or deleted in various human cancers. PTEN localizes predominantly to the cytoplasm and functions as a lipid phosphatase, thereby negatively regulating the phosphatidylinositol 3-kinase-AKT signaling pathway. PTEN can also localize to the nucleus, where it binds and regulates p53 protein level and transcription activity. However, the precise function of nuclear PTEN and the factors that control PTEN nuclear localization are still largely unknown. In this study, we identified oxidative stress as one of the physiological stimuli that regulate the accumulation of nuclear PTEN. Specifically, oxidative stress inhibits PTEN nuclear export, a process depending on phosphorylation of its amino acid residue Ser-380. Nuclear PTEN, independent of its phosphatase activity, leads to p53-mediated G(1) growth arrest, cell death, and reduction of reactive oxygen species production. Using xenografts propagated from human prostate cancer cell lines, we reveal that nuclear PTEN is sufficient to reduce tumor progression in vivo in a p53-dependent manner. The data outlined in this study suggest a unique role of nuclear PTEN to arrest and protect cells upon oxidative damage and to regulate tumorigenesis. Since tumor cells are constantly exposed to oxidative stress, our study elucidates the cooperative roles of nuclear PTEN with p53 in tumor suppression.

Temporally controlled ablation of PTEN in adult mouse prostate epithelium generates a model of invasive prostatic adenocarcinoma

Studies of prostate cancer pathogenesis and development of new therapies have been hampered by a lack of appropriate mouse models. We have generated PSA-Cre-ER(T2) mice that express the tamoxifen-dependent Cre-ER(T2) recombinase selectively in prostatic epithelium, thus allowing us to target floxed genes selectively in epithelial cells of fully differentiated prostate of adult mice and to modulate the number of genetically altered cells. Our present mouse model, in which prostate carcinogenesis is initiated through Cre-ER(T2)-mediated somatic biallelic ablation of the tumor suppressor gene PTEN after puberty, closely mimics the course of human cancer formation. Indeed, mutant mice developed prostate epithelium hyperplasia within 4 weeks after PTEN ablation and prostatic intraepithelial neoplasia (PIN) in all lobes within 2-3 months, with the highest incidence in the dorsolateral lobe, which is considered to be the most similar to the peripheral zone of the human prostate, in which adenocarcinoma is preferentially localized. Eight to 10 months after PTEN ablation some PINs of the dorsolateral lobe had progressed to adenocarcinoma, but no distant metastases were found up to 20 months after PTEN ablation, indicating that progression to metastasis requires an additional mutation or mutations. Interestingly, monoallelic Cre-ER(T2)-mediated PTEN ablation in epithelial cells of adult prostate also generated focal hyperplasia and PINs, but exclusively in the dorsolateral lobe, and in much lower number and after a longer latency. However, no progression to adenocarcinoma was observed. Because PTEN expression was undetectable in epithelial cells from these PINs, loss of PTEN function appears to act as a permissive event for uncontrolled cell proliferation.

Targeting the PI3K/Akt/mTOR pathway: effective combinations and clinical considerations

The PI3K/Akt/mTOR pathway is a prototypic survival pathway that is constitutively activated in many types of cancer. Mechanisms for pathway activation include loss of tumor suppressor PTEN function, amplification or mutation of PI3K, amplification or mutation of Akt, activation of growth factor receptors, and exposure to carcinogens. Once activated, signaling through Akt can be propagated to a diverse array of substrates, including mTOR, a key regulator of protein translation. This pathway is an attractive therapeutic target in cancer because it serves as a convergence point for many growth stimuli, and through its downstream substrates, controls cellular processes that contribute to the initiation and maintenance of cancer. Moreover, activation of the Akt/mTOR pathway confers resistance to many types of cancer therapy, and is a poor prognostic factor for many types of cancers. This review will provide an update on the clinical progress of various agents that target the pathway, such as the Akt inhibitors perifosine and PX-866 and mTOR inhibitors (rapamycin, CCI-779, RAD-001) and discuss strategies to combine these pathway inhibitors with conventional chemotherapy, radiotherapy, as well as newer targeted agents. We will also discuss how the complex regulation of the PI3K/Akt/mTOR pathway poses practical issues concerning the design of clinical trials, potential toxicities and criteria for patient selection.