PTEN function: how normal cells control it and tumour cells lose it

Phosphorylation of PTEN at STT motif is associated with DNA damage response

Phosphatase and tensin homolog deleted on chromosome Ten (PTEN), a tumor suppressor protein participates in multiple cellular activities including DNA repair. In this work we found a relationship between phosphorylation of carboxy (C)-terminal STT motif of PTEN and DNA damage response. Ectopic expression of C-terminal phospho-mutants of PTEN, in PTEN deficient human glioblastoma cells, U87MG, resulted in reduced viability and DNA repair after etoposide induced DNA damage compared to cells expressing wild type PTEN. Also, after etoposide treatment phosphorylation of PTEN increased at C-terminal serine 380 and threonine 382/383 residues in PTEN positive HEK293T cells and wild type PTEN transfected U87MG cells. One-step further, DNA damage induced phosphorylation of PTEN was confirmed by immunoprecipitation of total PTEN from cellular extract followed by immunobloting with phospho-specific PTEN antibodies. Additionally, phospho-PTEN translocated to nucleus after etoposide treatment as revealed by indirect immunolabeling. Further, phosphorylation dependent nuclear foci formation of PTEN was observed after ionizing radiation or etoposide treatment which colocalized with γH2AX. Additionally, etoposide induced γH2AX, Mre11 and Ku70 foci persisted for a longer period of times in U87MG cells after ectopic expression of PTEN C-terminal phospho-mutant constructs compared to wild type PTEN expressing cells. Thus, our findings strongly suggest that DNA damage induced phosphorylation of C-terminal STT motif of PTEN is necessary for DNA repair.

PI3K/AKT signaling pathway and cancer: an updated review

Despite development of novel agents targeting oncogenic pathways, matching targeted therapies to the genetic status of individual tumors is proving to be a daunting task for clinicians. To improve the clinical efficacy and to reduce the toxic side effects of treatments, a deep characterization of genetic alterations in different tumors is required. The mutational profile often evidences a gain of function or hyperactivity of phosphoinositide 3-kinases (PI3Ks) in tumors. These enzymes are activated downstream tyrosine kinase receptors (RTKs) and/or G proteins coupled receptors (GPCRs) and, via AKT, are able to induce mammalian target of rapamycin (mTOR) stimulation. Here, we elucidate the impact of class I (p110α, β, γ, and δ) catalytic subunit mutations on AKT-mediated cellular processes that control crucial mechanisms in tumor development. Moreover, the interrelation of PI3K signaling with mTOR, ERK, and RAS pathways will be discussed, exploiting the potential benefits of PI3K signaling inhibitors in clinical use.

Discovery of nanomolar phosphoinositide 3-kinase gamma (PI3Kγ) inhibitors using ligand-based modeling and virtual screening followed by in vitro analysis

Phosphoinositide 3-kinase gamma (PI3Kγ) is member of a family of enzymes involved in cancer pathogenesis. Accordingly, considerable efforts have been carried out to develop new PI3Kγ inhibitors. Towards this end we explored the pharmacophoric space of PI3Kγ using three diverse sets of inhibitors. Subsequently, we employed genetic algorithm-based QSAR analysis to select optimal combination of pharmacophoric models and physicochemical descriptors that can explain bioactivity variation within training inhibitors. Interestingly, two successful pharmacophores were selected within two statistically consistent QSAR models. The close similarity among the two binding models prompted us to merge them in a hybrid pharmacophore. The resulting model showed superior receiver operator characteristic curve (ROC) and closely resembled binding interactions seen in crystallographic ligand-PI3Kγ complexes. The resulting model was employed to screen the national cancer institute (NCI) list of compounds to search for new PI3Kγ ligands. After testing captured hits in vitro, 19 compounds showed nanomolar IC50 values against PI3Kγ. The chemical structures and purities of most potent hits were validated using NMR and MS experiments.

Interleukin-18 directly protects cortical neurons by activating PI3K/AKT/NF-κB/CREB pathways

Interleukin-18 (IL-18), a member of the IL-1 family of cytokines, was initially identified as an interferon (IFN)-γ-inducing factor. IL-18 is expressed in both immune and non-immune cells and participates in the adjustment of multitude cellular functions. Nonetheless, the effects of IL-18 on cortical neurons have not been explored. The present study was conducted to investigate the influence of IL-18 on rat primary cortical neurons and elucidate the underlying mechanisms. We proved that rrIL-18 increased the brain-derived neurotrophic factor (BDNF) expression in a time-dependent manner. Treatment with rrIL-18 (50 ng/ml) deactivated phosphatase and tensin homolog deleted on chromosome 10 (PTEN) by facilitating its phosphorylation, enhanced the expression of Phosphoinositide 3-OH kinase (PI3K) and p-Akt, standing for the activation of the PI3K/Akt pathway. As its pivotal downstream pathways, nuclear factor-kappa B (NF-κB), cAMP-responsive element binding protein (CREB)/Bcl-2 and glycogen synthase kinase-3β (GSK-3β) were examined in further steps. Our data revealed that rrIL-18 stimulated NF-κB activation, improved p-CREB and anti-apoptotic Bcl-2 expression levels. But rrIL-18 had little or no effect on GSK-3β pathway. Besides, rrIL-18 increased levels of BDNF and Bcl-2/Bax ratio and decreased cleaved caspase-3 expression to protect cortical neurons from damage induced by oxygen-glucose deprivation (OGD). These results in vitro showed the protection of IL-18 on cortical neurons. And this direct neuroprotective effect of IL-18 is crippled by PI3K inhibitor wortmannin.

Cancer cell-oriented migration of mesenchymal stem cells engineered with an anticancer gene (PTEN): an imaging demonstration

BACKGROUND

Mesenchymal stem cells (MSCs) have been considered to hold great potential as ideal carriers for the delivery of anticancer agents since the discovery of their tumor tropism. This study was performed to demonstrate the effects of phosphatase and tensin homolog (PTEN) engineering on MSCs' capacity for cancer cell-oriented migration.

METHODS

MSCs were engineered with a PTEN-bearing plasmid and the expression was confirmed with Western blotting. A human glioma cell line (DBTRG) was used as the target cell; DBTRG cell-oriented migration of MSCs was monitored with a micro speed photographic system.

RESULTS

The expression of transfected PTEN in MSCs was identified by immunoblotting analysis and confirmed with cell viability assessment of target cells. The DBTRG cell-oriented migration of PTEN-engineered MSCs was demonstrated by a real-time dynamic monitoring system, and a phagocytosis-like action of MSCs was also observed.

CONCLUSION

MSCs maintained their capacity for cancer cell-directed migration after they were engineered with anticancer genes. This study provides the first direct evidence of MSCs' tropism post-anticancer gene engineering.

Aberrant CpG island methylation of PTEN is an early event in nasopharyngeal carcinoma and a potential diagnostic biomarker

The inactivation of phosphatase and tensin homolog (PTEN) due to its CpG island hypermethylation has been observed in some types of tumors except nasopharyngeal carcinoma (NPC). In the present study, we focused on the aberrant methylation of PTEN CpG islands in NPC. The mRNA expression of PTEN was detected by quantitative PCR in 45 NPC and 22 non-tumor nasopharyngeal epithelial (NP) tissues. The methylation status of PTEN was examined by methylation-specific polymerase chain reaction and sequencing. The mRNA expression of PTEN in three NPC cell lines treated with 5-aza-2'-deoxycytidine (5-aza-dC) was also examined. PTEN was downregulated in both NPC tissues and NPC cell lines and a relatively higher methylation level of PTEN was found in NPC specimens (82.2%) relative to NP tissues (5.3%). The PTEN mRNA expression was restored in NPC cell lines by treatment with 5-aza-dC. These results first reveal an epigenetic alteration, aberrant methylation of PTEN, in NPC, which is probably an early event and may be regarded as a novel candidate biomarker for early stage of NPC detection and prevention.

Neurobiology of autism gene products: towards pathogenesis and drug targets

RATIONALE

The genetic heterogeneity of autism spectrum disorders (ASDs) is enormous, and the neurobiology of proteins encoded by genes associated with ASD is very diverse. Revealing the mechanisms on which different neurobiological pathways in ASD pathogenesis converge may lead to the identification of drug targets.

OBJECTIVE

The main objective is firstly to outline the main molecular networks and neuronal mechanisms in which ASD gene products participate and secondly to answer the question how these converge. Finally, we aim to pinpoint drug targets within these mechanisms.

METHOD

Literature review of the neurobiological properties of ASD gene products with a special focus on the developmental consequences of genetic defects and the possibility to reverse these by genetic or pharmacological interventions.

RESULTS

The regulation of activity-dependent protein synthesis appears central in the pathogenesis of ASD. Through sequential consequences for axodendritic function, neuronal disabilities arise expressed as behavioral abnormalities and autistic symptoms in ASD patients. Several known ASD gene products have their effect on this central process by affecting protein synthesis intrinsically, e.g., through enhancing the mammalian target of rapamycin (mTOR) signal transduction pathway or through impairing synaptic function in general. These are interrelated processes and can be targeted by compounds from various directions: inhibition of protein synthesis through Lovastatin, mTOR inhibition using rapamycin, or mGluR-related modulation of synaptic activity.

CONCLUSIONS

ASD gene products may all feed into a central process of translational control that is important for adequate glutamatergic regulation of dendritic properties. This process can be modulated by available compounds but may also be targeted by yet unexplored routes.

PGE2-driven expression of c-Myc and oncomiR-17-92 contributes to apoptosis resistance in NSCLC

Aberrant expression of microRNAs (miRNA) with oncogenic capacities (oncomiRs) has been described for several different malignancies. The first identified oncomiR, miR-17-92, is frequently overexpressed in a variety of cancers and its targets include the tumor suppressor PTEN. The transcription factor c-Myc (MYC) plays a central role in proliferative control and is rapidly upregulated upon mitogenic stimulation. Expression of c-Myc is frequently deregulated in tumors, facilitating proliferation and inhibiting terminal differentiation. The c-Myc-regulated network comprises a large number of transcripts, including those encoding miRNAs. Here, prostaglandin E2 (PGE2) exposure rapidly upregulates the expression of the MYC gene followed by the elevation of miR-17-92 levels, which in turn suppresses PTEN expression, thus enhancing apoptosis resistance in non-small cell lung cancer (NSCLC) cells. Knockdown of MYC expression or the miR-17-92 cluster effectively reverses this outcome. Similarly, miR-17-92 levels are significantly elevated in NSCLC cells ectopically expressing COX-2. Importantly, circulating miR-17-92 was elevated in the blood of patients with lung cancer as compared with subjects at risk for developing lung cancer. Furthermore, in patients treated with celecoxib, miR-17-92 levels were significantly reduced. These data demonstrate that PGE2, abundantly produced by NSCLC and inflammatory cells in the tumor microenvironment, is able to stimulate cell proliferation and promote resistance to pharmacologically induced apoptosis in a c-Myc and miR-17-92-dependent manner.

IMPLICATIONS

This study describes a novel mechanism, involving c-Myc and miR-17-92, which integrates cell proliferation and apoptosis resistance.

Functions and Regulation of the PTEN Gene in Colorectal Cancer

Phosphatase and TENsin homolog deleted on chromosome 10 (PTEN) is a tumor suppressor gene located at chromosome 10q23.31, encoding for a 403-amino acid protein that possesses both lipid and protein phosphatase activities. The main function of PTEN is to block the PI3K pathway by dephosphorylating phosphatidylinositol (PI) 3,4,5-triphosphate to PI-4,5-bisphosphate thus counteracting PI3K function. PTEN inactivation is a frequent event in many cancer types and can occur through various genetic alterations including point mutations, large chromosomal deletions, and epigenetic mechanisms. In colorectal cancer (CRC) PTEN is altered through mixed genetic/epigenetic mechanisms (typically: mutations and promoter hypermethylation or 10q23 LOH and promoter hypermethylation), which lead to the biallelic inactivation of the protein in 20–30% of cases. The role of PTEN as a prognostic and predictive factor in CRC has been addressed by relatively few works. This review is focused on the report and on the discussion of the studies investigating these aspects. Overall, at the moment, there are conflicting results and, therefore it has not been clarified whether PTEN might play a prognostic role in CRC. The same is valid also for the predictive role, leading to the fact that PTEN evaluation cannot be used in routinely diagnosis for the early identification of patients who might be addressed to the treatment with EGFR-targeted therapies, at odds with other genetic alterations belonging to EGFR-downstream pathways. The reason of discordant results may be attributable to several issues: (1) the size of the analyzed cohort, (2) patients inclusion criteria, (3) the methods of assessing PTEN alteration. In particular, there are no standardized methods to evaluate this marker, especially for immunohistochemistry, a technique suffering of intra and inter-observer variability due to the semi-quantitative character of such an analysis. In conclusion, much work, especially in large and homogeneous cohorts of cases from different laboratories, has to be done before the establishment of PTEN as prognostic or predictive marker in CRC.

PTEN, Longevity and Age-Related Diseases

Since the discovery of PTEN, this protein has been shown to be an effective suppressor of cancer and a contributor to longevity. This report will review, in depth, the associations between PTEN and other molecules, its mutations and regulations in order to present how PTEN can be used to increase longevity. This report will collect recent research of PTEN and use this to discuss PTEN’s role in caloric restriction, antioxidative defense of DNA-damage and the role it plays in suppressing tumors. The report will also discuss that variety of ways that PTEN can be compromised, through mutations, complete loss of alleles and its main antagonist, the PI3K/AKT pathway.

High expression of inositol polyphosphate phosphatase-like 1 associates with unfavorable survival in hepatocellular carcinoma

Inositol polyphosphate phosphatase-like 1 (INPPL1), also known as SH2-containing inositol 5'-phosphatase 2 (SHIP2), has been suggested to act downstream of the PI3K/AKT pathway and play an important function in tumor development and progression. However, the associations between SHIP2 expression and the clinical features to determine its clinicopathologic significance in hepatocellular carcinoma (HCC) have not been investigated. In the present study, one-step quantitative PCR reverse transcription-polymerase chain reaction (qPCR) and immunohistochemistry (IHC) analysis with HCC tissue microarrays (TMA) were employed to evaluate the expression of SHIP2 in HCC. The results showed that SHIP2 expression in the mRNA and protein levels was significantly higher in HCC tissue than in corresponding non-cancerous tissue (p = 0.0014 and p < 0.001, respectively). The expression of SHIP2 protein in HCC was related to tumor differentiation, α-fetoprotein level, liver cirrhosis, and five-year survival rate (all p < 0.05). Kaplan-Meier method and log-rank test indicated that high expression of SHIP2 (p = 0.017) and tumor differentiation (p = 0.036) showed significant correlations with poor prognosis of HCC patients. The data indicate that SHIP2 expression is correlated with significant characteristics of HCC, and it may be useful as an unfavorable prognostic factor in HCC.

Novel mechanism of tumor suppression by polarity gene discs large 1 (DLG1) revealed in a murine model of pediatric B-ALL

Drosophila melanogaster discs large (dlg) is an essential tumor suppressor gene (TSG) controlling epithelial cell growth and polarity of the fly imaginal discs in pupal development. A mammalian ortholog, Dlg1, is involved in embryonic urogenital morphogenesis, postsynaptic densities in neurons, and immune synapses in lymphocytes. However, a potential role for Dlg1 as a mammalian TSG is unknown. Here, we present evidence that loss of Dlg1 confers strong predisposition to the development of malignancies in a murine model of pediatric B-cell acute lymphoblastic leukemia (B-ALL). Using mice with conditionally deleted Dlg1 alleles, we identify a novel "pre-leukemic" stage of developmentally arrested early B-lineage cells marked by preeminent c-Myc expression. Mechanistically, we show that in B-lineage progenitors Dlg1 interacts with and stabilizes the PTEN protein, regulating its half-life and steady-state abundance. The loss of Dlg1 does not affect the level of PTEN mRNAs but results in a dramatic decrease in PTEN protein, leading to excessive phosphoinositide 3-kinase signaling and proliferation. Our data suggest a novel model of tumor suppression by a PDZ domain-containing polarity gene in hematopoietic cancers.

Loss of phosphatase and tensin homolog (PTEN) in myeloid cells controls inflammatory bone destruction by regulating the osteoclastogenic potential of myeloid cells

OBJECTIVE

Local bone destruction in rheumatic diseases, which often leads to disability and severely reduced quality of life, is almost exclusively mediated by osteoclasts. Therefore, it is important to understand pathways regulating the generation of osteoclasts. Here, we analysed the impact of the Phosphoinositide-3-Kinase (PI3K)/Phosphatase and tensin homolog (PTEN) axis on osteoclast generation and bone biology under basal and inflammatory conditions.

METHODS

We analysed osteoclastogenesis of wildtype (wt) and PTEN(-/-) cells in vitro and in vivo, pit resorption and qPCR of osteoclasts in vitro. Mice with a myeloid cell-specific deletion of PTEN and wt littermate mice were investigated by bone histomorphometry and clinical and histological assessment in the human tumour necrosis factor (TNF)-transgenic (hTNFtg) arthritis model.

RESULTS

We show that myeloid-specific PTEN(-/-) mice display increased osteoclastogenesis in vitro and in vivo compared to wt mice. Loss of PTEN did not affect the generation or survival of osteoclast precursor cells. However, PTEN deficiency greatly enhanced receptor activator of nuclear factor κ-B ligand (RANKL)-induced expression of the master transcription factor of osteoclastogenesis, nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), resulting in markedly increased terminal differentiation of osteoclasts in vitro. We also observed increased osteoclastogenesis under inflammatory conditions in the hTNFtg mouse model of arthritis, where hTNFtg/myeloid-specific PTEN(-/-) mice displayed enhanced local bone destruction as well as osteoclast formation in the inflamed joints. The extent of synovial inflammation, however, as well as recruitment of osteoclast precursor cells was not different between wt and myeloid-specific PTEN(-/-) mice.

CONCLUSIONS

These data demonstrate that loss of PTEN and, therefore, sustained PI3-Kinase signalling in myeloid cells especially, elevates the osteoclastogenic potential of myeloid cells, leading to enhanced inflammatory local bone destruction. Therefore, although our study allows no direct translational conclusion since we used a conditional knockout approach, the therapeutic targeting of the PI3-Kinase pathway may be of benefit in preventing structural joint damage.

A new mathematical approach for qualitative modeling of the insulin-TOR-MAPK network

In this paper we develop a novel mathematical model of the insulin-TOR-MAPK signaling network that controls growth. Most data on the properties of the insulin and MAPK signaling networks are static and the responses to experimental interventions, such as knockouts, overexpression, and hormonal input are typically reported as scaled quantities. The modeling paradigm we develop here uses scaled variables and is ideally suited to simulate systems in which much of the available data are scaled. Our mathematical representation of signaling networks provides a way to reconcile theory and experiments, thus leading to a better understanding of the properties and function of these signaling networks. We test the performance of the model against a broad diversity of experimental data. The model correctly reproduces experimental insulin dose-response relationships. We study the interaction between insulin and MAPK signaling in the control of protein synthesis, and the interactions between amino acids, insulin and TOR signaling. We study the effects of variation in FOXO expression on protein synthesis and glucose transport capacity, and show that a FOXO knockout can partially rescue protein synthesis capacity of an insulin receptor (INR) knockout. We conclude that the modeling paradigm we develop provides a simple tool to investigate the qualitative properties of signaling networks.

A secreted PTEN phosphatase that enters cells to alter signaling and survival

Phosphatase and tensin homolog on chromosome ten (PTEN) is a tumor suppressor and an antagonist of the phosphoinositide-3 kinase (PI3K) pathway. We identified a 576-amino acid translational variant of PTEN, termed PTEN-Long, that arises from an alternative translation start site 519 base pairs upstream of the ATG initiation sequence, adding 173 N-terminal amino acids to the normal PTEN open reading frame. PTEN-Long is a membrane-permeable lipid phosphatase that is secreted from cells and can enter other cells. As an exogenous agent, PTEN-Long antagonized PI3K signaling and induced tumor cell death in vitro and in vivo. By providing a means to restore a functional tumor-suppressor protein to tumor cells, PTEN-Long may have therapeutic uses.

Putative predictive biomarkers of survival in patients with metastatic pancreatic adenocarcinoma treated with gemcitabine and ganitumab, an IGF1R inhibitor

PURPOSE

This planned exploratory analysis assessed the predictive nature of baseline circulating factors of the insulin-like growth factor (IGF) axis on the treatment effect of ganitumab (monoclonal antibody inhibitor of IGF-1 receptor) plus gemcitabine in a randomized phase II study in metastatic pancreatic adenocarcinoma.

EXPERIMENTAL DESIGN

Baseline levels of IGFs/IGF binding proteins (IGFBP) were analyzed in serum or plasma. Mutations and gene expression were analyzed in archival samples. Treatment effects between biomarker subgroups were compared for overall survival (OS). Associations of tumor markers with OS were evaluated.

RESULTS

For patients with evaluable samples, ganitumab was associated with improved OS versus placebo (HR, 0.49; 95% CI: 0.28-0.87). The treatment effect on improved OS was strong in the patient subset with higher levels of IGF-1, IGF-2, or IGFBP-3, or lower levels of IGFBP-2, but not so on the other corresponding subset. Median OS of ganitumab versus placebo in patients with higher levels of IGF-1, IGF-2, and IGFBP-3 was 16 versus 6.8 months (HR, 0.25; 95% CI: 0.09-0.67), 16 versus 5.9 months (HR, 0.24; 95% CI: 0.09-0.68), and 16 versus 6.8 months (HR, 0.28; 95% CI: 0.11-0.73), and in patients with lower IGFBP-2 levels was 12.7 versus 6.6 months (HR, 0.19; 95% CI: 0.07-0.55). Interaction between treatment and IGFs/IGFBPs in multivariate analyses suggested predictive potential for IGF-2 (P = 0.002) and IGFBP-2 (P = 0.02). KRAS mutation status and PTEN expression were not associated with OS.

CONCLUSIONS

Baseline circulating factors of the IGF axis may predict OS benefit from ganitumab plus gemcitabine in metastatic pancreatic adenocarcinoma.

Hamartomatous polyposis syndromes

Hamartomas are tumour-like malformations, consisting of disorganized normal tissues, typical of the site of tumour manifestation. Familial manifestation of hamartomatous polyps can be noted in juvenile polyposis syndrome (JPS), Peutz-Jeghers’ syndrome (PJS), hereditary mixed polyposis syndrome (HMPS) and PTEN hamartoma tumour syndrome (PHTS). All the aforementioned syndromes are inherited in an autosomal dominant manner and form a rather heterogenous group both in respect to the number and localization of polyps and the risk of cancer development in the alimentary tract and other organs. Individual syndromes of hamartomatous polyposis frequently manifest similar symptoms, particularly during the early stage of the diseases when in several cases their clinical pictures do not allow for differential diagnosis. The correct diagnosis of the disease using molecular methods allows treatment to be implemented earlier and therefore more effectively since it is followed by a strict monitoring of organs that manifest a predisposition for neoplastic transformation.

Selective inactivation of PTEN in smooth muscle cells synergizes with hypoxia to induce severe pulmonary hypertension

Background

Pulmonary vascular remodeling in pulmonary hypertension (PH) is characterized by increased vascular smooth muscle cell (SMC) and adventitial fibroblast proliferation, small vessel occlusion, and inflammatory cell accumulation. The underlying molecular mechanisms driving progression remain poorly defined. We have focused on loss of the phosphatase PTEN in SMCs as a major driver of pathological vascular remodeling. Our goal was to define the role of PTEN in human PH and in hypoxia‐induced PH using a mouse model with inducible deletion of PTEN in SMCs.

Methods and Results

Staining of human biopsies demonstrated enhanced inactive PTEN selectively in the media from hypertensive patients compared to controls. Mice with induced deletion of PTEN in SMCs were exposed to normoxia or hypoxia for up to 4 weeks. Under normoxia, SMC PTEN depletion was sufficient to induce features of PH similar to those observed in wild‐type mice exposed to chronic hypoxia. Under hypoxia, PTEN depletion promoted an irreversible progression of PH characterized by increased pressure, extensive pulmonary vascular remodeling, formation of complex vascular lesions, and increased macrophage accumulation associated with synergistic increases in proinflammatory cytokines and proliferation of both SMCs and nonSMCs.

Conclusions

Chronic inactivation of PTEN selectively in SMC represents a critical mediator of PH progression, leading to cell autonomous events and increased production of factors correlated to proliferation and recruitment of adventitial and inflammatory cells, resulting in irreversible progression of the disease.

Concomitant loss of EAF2/U19 and Pten synergistically promotes prostate carcinogenesis in the mouse model

Multiple genetic alterations are associated with prostate carcinogenesis. Tumor-suppressor genes phosphatase and tensin homolog deleted on chromosome 10 (Pten) and androgen upregulated gene 19 (U19), which encodes ELL-associated factor 2 (EAF2), are frequently inactivated or downregulated in advanced prostate cancers. Previous studies showed that EAF2 knockout caused tumors in multiple organs and prostatic intraepithelial neoplasia (PIN) in mice. However, EAF2-knockout mice did not develop prostate cancer even at 2 years of age. To further define the roles of EAF2 in prostate carcinogenesis, we crossed the Pten+/- and EAF2+/- mice in the C57/BL6 background to generate EAF2-/-Pten+/-, Pten+/-, EAF2-/- and wild-type mice. The prostates from virgin male mice with the above four genotypes were analyzed at 7 weeks, 19 weeks and 12 months of age. Concomitant loss of EAF2 function and inactivation of one Pten allele induced spontaneous prostate cancer in 33% of the mice. Prostatic tissues from intact EAF2-/- Pten+/- mice exhibited higher levels of phospho-Akt, -p44/42 and microvessel density. Moreover, phospho-Akt remained high after castration. Consistently, there was a synergistic increase in prostate epithelial proliferation in both intact and castrated EAF2-/-Pten+/- mice. Using laser-capture microdissection coupled with real-time reverse transcription-PCR, we confirmed that co-downregulation of EAF2 and Pten occurred in >50% clinical prostate cancer specimens with Gleason scores of 8-9 (n=11), which is associated with poor prognosis. The above findings together demonstrated synergistic functional interactions and clinical relevance of concurrent EAF2 and Pten downregulation in prostate carcinogenesis.

PTEN plasticity: how the taming of a lethal gene can go too far

PTEN loss drives many cancers and recent genetic studies reveal that often PTEN is antagonised at the protein level without alteration of DNA or RNA expression. This scenario can already cause malignancy, because PTEN is haploinsufficient. We here review normally occurring mechanisms of PTEN protein regulation and discuss three processes where PTEN plasticity is needed: ischaemia, development, and wound healing. These situations demand transient PTEN suppression, whereas cancer exploits them for continuous proliferation and survival advantages. Therefore, increased understanding of PTEN plasticity may help us better interpret tumour development and ultimately lead to drug targets for PTEN supporting cancer therapy.

High-frequency electrical stimulation reveals a p38-mTOR signaling module correlated with force-time integral

High-frequency electrical stimulation (HFES) leads to muscle hypertrophy, and attention has been drawn to the high forces involved. However, both mechanical and metabolic stresses occur simultaneously, and both stimuli influence signaling cascades related to protein synthesis. This study aimed to identify the immediate signaling correlates of contraction-induced force and metabolic stresses under the hypothesis that HFES induces growth-related signaling through mechanical stimulation. Force-time integral (FTI) signaling in mouse tibialis anterior muscle was examined by separately manipulating the time of contraction to emphasize the metabolic aspect or the force of contraction to emphasize the mechanical aspect. When FTI was manipulated by changing the total time of activation, phosphorylation of p54 JNK, ERK and p70S6k(T421/S424) was independent of FTI, while phosphorylation of acetyl-CoA carboxylase and p38 correlated with FTI. When FTI was manipulated by changing the force of contraction, p54 JNK, ERK and p70S6k(T421/S424) were again independent of FTI, while phosphorylation of p38 and FAK correlated with FTI. Factor analysis identified a p38-mTOR signaling module that correlated with FTI in both experiments. The consistent link among p38, mTOR and FTI suggests that they form a connected signaling module sensitive to the mechanical aspects of FTI, separate from markers of metabolic load.

p110δ PI3 kinase pathway: emerging roles in cancer

Class IA PI3Ks consists of three isoforms of the p110 catalytic subunit designated p110α, p110β, and p110δ which are encoded by three separate genes. Gain-of-function mutations on PIK3CA gene encoding for p110α isoform have been detected in a wide variety of human cancers whereas no somatic mutations of genes encoding for p110β or p110δ have been reported. Unlike p110α and p110β which are ubiquitously expressed, p110δ is highly enriched in leukocytes and thus the p110δ PI3K pathway has attracted more attention for its involvement in immune disorders. However, findings have been accumulated showing that the p110δ PI3K plays a seminal role in the development and progression of some hematologic malignancies. A wealth of knowledge has come from studies showing the central role of p110δ PI3K in B-cell functions and B-cell malignancies. Further data have documented that wild-type p110δ becomes oncogenic when overexpressed in cell culture models and that p110δ is the predominant isoform expressed in some human solid tumor cells playing a prominent role in these cells. Genetic inactivation of p110δ in mice models and highly-selective inhibitors of p110δ have demonstrated an important role of this isoform in differentiation, growth, survival, motility, and morphology with the inositol phosphatase PTEN to play a critical role in p110δ signaling. In this review, we summarize our understanding of the p110δ PI3K signaling pathway in hematopoietic cells and malignancies, we highlight the evidence showing the oncogenic potential of p110δ in cells of non-hematopoietic origin and we discuss perspectives for potential novel roles of p110δ PI3K in cancer.

RFP-mediated ubiquitination of PTEN modulates its effect on AKT activation

The PTEN tumor suppressor is a lipid phosphatase that has a central role in regulating the phosphatidylinositol-3-kinase (PI3K) signal transduction cascade. Nevertheless, the mechanism by which the PTEN activity is regulated in cells needs further elucidation. Although previous studies have shown that ubiquitination of PTEN can modulate its stability and subcellular localization, the role of ubiquitination in the most critical aspect of PTEN function, its phosphatase activity, has not been fully addressed. Here, we identify a novel E3 ubiquitin ligase of PTEN, Ret finger protein (RFP), that is able to promote atypical polyubiquitinations of PTEN. These ubiquitinations do not lead to PTEN instability or relocalization, but rather significantly inhibit PTEN phosphatase activity and therefore modulate its ability to regulate the PI3K signal transduction cascade. Indeed, RFP overexpression relieves PTEN-mediated inhibitory effects on AKT activation; in contrast, RNAi-mediated knockdown of endogenous RFP enhances the ability of PTEN to suppress AKT activation. Moreover, RFP-mediated ubiquitination of PTEN inhibits PTEN-dependent activation of TRAIL expression and also suppresses its ability to induce apoptosis. Our findings demonstrate a crucial role of RFP-mediated ubiquitination in controlling PTEN activity.

Parameter space exploration within dynamic simulations of signaling networks

We started offering an introduction to very basic aspects of molecular biology, for the reader coming from computer sciences, information technology, mathematics. Similarly we offered a minimum of information about pathways and networks in graph theory, for a reader coming from the bio-medical sector. At the crossover about the two different types of expertise, we offered some definition about Systems Biology. The core of the article deals with a Molecular Interaction Map (MIM), a network of biochemical interactions involved in a small signaling-network sub-region relevant in breast cancer. We explored robustness/sensitivity to random perturbations. It turns out that our MIM is a non-isomorphic directed graph. For non physiological directions of propagation of the signal the network is quite resistant to perturbations. The opposite happens for biologically significant directions of signal propagation. In these cases we can have no signal attenuation, and even signal amplification. Signal propagation along a given pathway is highly unidirectional, with the exception of signal-feedbacks, that again have a specific biological role and significance. In conclusion, even a relatively small network like our present MIM reveals the preponderance of specific biological functions over unspecific isomorphic behaviors. This is perhaps the consequence of hundreds of millions of years of biological evolution.

Collective epithelial and mesenchymal cell migration during gastrulation

Gastrulation, the process that puts the three major germlayers, the ectoderm, mesoderm and endoderm in their correct topological position in the developing embryo, is characterised by extensive highly organised collective cell migration of epithelial and mesenchymal cells. We discuss current knowledge and insights in the mechanisms controlling these cell behaviours during gastrulation in the chick embryo. We discuss several ideas that have been proposed to explain the observed large scale vortex movements of epithelial cells in the epiblast during formation of the primitive streak. We review current insights in the control and execution of the epithelial to mesenchymal transition (EMT) underlying the formation of the hypoblast and the ingression of the mesendoderm cells through the streak. We discuss the mechanisms by which the mesendoderm cells move, the nature and dynamics of the signals that guide these movements, as well as the interplay between signalling and movement that result in tissue patterning and morphogenesis. We argue that instructive cell-cell signaling and directed chemotactic movement responses to these signals are instrumental in the execution of all phases of gastrulation.

Interleukin-18 augments growth ability of primary human melanocytes by PTEN inactivation through the AKT/NF-κB pathway

Normal human skin relies on melanocytes to provide photoprotection and thermoregulation by producing melanin. The growth and behavior of melanocytes are controlled by many factors. Interleukin-18 (IL-18) is expressed in both immune and non-immune cells and participates in the adjustment of multitude cellular functions. Nonetheless, the regulative roles of IL-18 in melanogenesis and growth of melanocytes have not been explored. The present study was conducted to investigate the effects of IL-18 on melanocytes and elucidate the underlying mechanisms. We proved that IL-18 increased the tyrosinase activity and melanin content in normal human foreskin-derived epidermal melanocytes (NHEM). Treatment with IL-18 (20 ng/ml) enhanced the expression of c-Kit, microphtalmia-associated transcription factor (MITF) and its downstream tyrosinase-related protein 1 (TRP-1), and TRP-2. In addition, IL-18 induced NHEM migration at concentration of 20 ng/ml. These results indicated a promotive action of IL-18 on melanogenesis in NHEM. Our data revealed that IL-18 stimulated ERK1/2 and NF-κB activation, improved p-Akt, p70 S6K and anti-apoptotic Bcl-2 levels, and deactivated phosphatase and tensin homolog deleted on chromosome 10 (PTEN) in NHEM. Besides, IL-18 increased level of PTEN phosphorylation to protect NHEM from damage induced by H(2)O(2). These results in vitro showed the accommodation of IL-18 in melanocytes growth. Therefore, we suggested an important regulating action of IL-18 to melanogenesis and cell growth ability of skin melanocytes.

Salvianolic acid A positively regulates PTEN protein level and inhibits growth of A549 lung cancer cells

Salvianolic acid A (Sal A) is an effective compound extracted from Salvia miltiorrhiza which has been used in the treatment of various diseases. Preliminary data indicate that Sal A treatment has a specific anti-lung cancer effect. However, the manner in which Sal A regulates cancer growth remains unknown. In this study, the A549 lung cancer cell line and its response to Sal A treatment was examined. Results showed that Sal A treatment significantly decreased A549 cell growth, promoted partial apoptosis and increased mitochondrial membrane permeability. Western blot analysis showed that Sal A upregulated the phosphatase and tensin homolog (PTEN) protein level, while consistently downregulating Akt phosphorylation. These results indicate that Sal A negatively mediates A549 lung cancer cell line growth or apoptosis, most likely by positively regulating PTEN protein level.

Phosphoproteomics: A possible route to novel biomarkers of breast cancer

Proteomics is rapidly transforming the way that cancer and other pathologies are investigated. The ability to identify hundreds of proteins and to compare their abundance in different clinical samples presents a unique opportunity for direct identification of novel disease markers. Furthermore, recent advances allow us to analyse and compare PTMs. This gives an additional dimension for defining a new class of protein biomarker based not only on abundance and expression but also on the occurrence of covalent modifications specific to a disease state or therapy response. Such modifications are often a consequence of the activation/inactivation of a particular disease related pathway. In this review we evaluate the available information on breast cancer related protein-phosphorylation events, illustrating the rationale for investigating this PTM as a target for breast cancer research with eventual clinical relevance. We present a critical survey of the published experimental strategies to study protein phosphorylation on a system wide scale and highlight recent specific advances in breast cancer phosphoproteomics. Finally we discuss the feasibility of establishing novel biomarkers for breast cancer based on the detection of patterns of specific protein phosphorylation events.

Analysis of PTEN expression in large intestine polyps and its relation to the recognized histopathological and clinical risk factors for cancer development in this location

AIM OF THE STUDY

PTEN is an important gene whose protein product is double specific phosphatase holding key regulatory functions in sending signals from membrane receptors for growth factors into the cell downstreams. Its participation, mainly by PI3K/AKT signaling pathway in the pathomechanism of many malignant cancers was unambiguously confirmed. The PTEN function gets disturbed on many levels and for various reasons. Disorders of PTEN protein expression seem to be even more common in many carcinomas. The aim of the study is to enquire the meaning of PTEN expression in the cancer transformation process in large intestine glandular polyps.

MATERIAL AND METHODS

The group includes 40 patients, 21 men and 19 women, age median 64 years (51-83) qualified to endoscopic removal of large intestine polyp. Tissue material obtained during polyp removal endoscopy was immediately fixed in 4% buffered formalin solution with the mixture of phosphatase activity inhibitors (PhosStop Roche). Time of fixation 24-48 h. After fixation, the material was embedded in paraffin. PTEN visualization was based on specific rabbit monoclonal antibodies (Cell Signaling). The expression of PTEN protein in large intestine and rectum polyps was marked by a semi-quantitative method and an attempt to correlate the results with the acknowledged clinical and histopathological malignancy risk factors was undertaken.

RESULTS

Loss or weakening of protein expression was found in 45% cases. Moreover, the relationship between polyp diameter and a loss of PTEN expression was proved. The received results can indicate a significant participation of PTEN gene in early oncogenesis stages of large intestine cancer.

Effect of the IGF-1/PTEN/Akt/FoxO signaling pathway in the duodenal mucosa of rats subjected to water immersion and restraint stress

The insulin growth factor 1/phosphatase and tensin homologue deleted on chromosome 10/Akt/forkhead box (IGF-1/PTEN/Akt/FoxO) signaling pathway reportedly exhibits gastroprotective effects by reducing water immersion and restraint stress (WRS)-induced gastric mucosal cell apoptosis. We examined the expression and localization of IGF-1, PTEN, Akt, and FoxO proteins, caspase-3 activity, and the number of apoptotic cells in the duodenal mucosa of rats subjected to WRS to confirm whether the IGF-1/PTEN/Akt/FoxO signaling pathway has a role in the duodenal mucosa. The results indicated that WRS enhanced cell apoptosis in the duodenal mucosa. In addition, in normal rats, PTEN was found mainly in the cellular cytoplasm of the duodenal glands and lamina propria of villi. IGF-1 and total Akt were observed in the cellular cytoplasm of the duodenal glands. In addition, total Akt was found in the cellular cytoplasm of the myenteric plexus. FoxO3a and FoxO4 were primarily concentrated in the cellular cytoplasm of the lamina propria. Specifically, PTEN, FoxO3a and FoxO4 were also localized in the cellular cytoplasm of lamina propria of restituted villi in the duodenal mucosa of rat subjected to WRS. In addition, messenger RNA transcript levels of IGF-1, PTEN, Akt1, Akt2, FoxO3, and FoxO4 were upregulated in the duodenal mucosa, with a peak between the 4th and 8th day after 7 h of WRS. Furthermore, the results also suggested that Akt3 messenger RNA transcript levels in the duodenal mucosa of rats after WRS showed no significant differences compared with those in the non-WRS group. Collectively, our results implied that the IGF-1/ PTEN/Akt/FoxO signaling pathway was effective in regulating cellular apoptosis in the duodenal mucosa of rats after WRS.

Voltage-Controlled Enzymes: The New JanusBifrons

The Ciona intestinalis voltage-sensitive phosphatase, Ci-VSP, was the first Voltage-controlled Enzyme (VEnz) proven to be under direct command of the membrane potential. The discovery of Ci-VSP conjugated voltage sensitivity and enzymatic activity in a single protein. These two facets of Ci-VSP activity have provided a unique model for studying how membrane potential is sensed by proteins and a novel mechanism for control of enzymatic activity. These facets make Ci-VSP a fascinating and versatile enzyme. Ci-VSP has a voltage sensing domain (VSD) that resembles those found in voltage-gated channels (VGC). The VSD resides in the N-terminus and is formed by four putative transmembrane segments. The fourth segment contains charged residues which are likely involved in voltage sensing. Ci-VSP produces sensing currents in response to changes in potential, within a defined range of voltages. Sensing currents are analogous to “gating” currents in VGC. As known, these latter proteins contain four VSDs which are entangled in a complex interaction with the pore domain – the effector domain in VGC. This complexity makes studying the basis of voltage sensing in VGC a difficult enterprise. In contrast, Ci-VSP is thought to be monomeric and its catalytic domain – the VSP’s effector domain – can be cleaved off without disrupting the basic electrical functioning of the VSD. For these reasons, VSPs are considered a great model for studying the activity of a VSD in isolation. Finally, VSPs are also phosphoinositide phosphatases. Phosphoinositides are signaling lipids found in eukaryotes and are involved in many processes, including modulation of VGC activity and regulation of cell proliferation. Understanding VSPs as enzymes has been the center of attention in recent years and several reviews has been dedicated to this area. Thus, this review will be focused instead on the other face of this true JanusBifrons and recapitulate what is known about VSPs as electrically active proteins.

The impact of PTEN tumor suppressor gene on acquiring resistance to tamoxifen treatment in breast cancer patients

Tamoxifen is a standard therapeutical treatment in patients with estrogen receptor positive breast carcinoma. However, less than 50% of estrogen receptor positive breast cancers do not respond to tamoxifen treatment whereas 40% of tumors that initially respond to treatment develop resistance over time. The underlying mechanisms for tamoxifen resistance are probably multifactorial but remain largely unknown. The primary aim of this study was to investigate the impact of PTEN tumor suppressor gene on acquiring resistance to tamoxifen by analyzing loss of heterozygosity (LOH) and immunohystochemical expression of PTEN in 49 primary breast carcinomas of patients treated with tamoxifen as the only adjuvant therapy. The effect of PTEN inactivation on breast cancer progression and disease outcome was also analyzed. Reduced or completely lost PTEN expression was observed in 55.1% of samples, while 63.3% of samples displayed LOH of PTEN gene. Inactivation of PTEN immunoexpression significantly correlated with the PTEN loss of heterozygosity, suggesting LOH as the most important genetic mechanism for the reduction or complete loss of PTEN expression in primary breast carcinoma. Most importantly, LOH of PTEN and consequential reduction of its immunoexpression showed significant correlation with the recurrence of the disease. Besides, our study revealed that LOH of PTEN tumor suppressor was significantly associated with shorter disease free survival, breast cancer specific survival and overall survival. In summary, our results imply that LOH of PTEN could be used as a good prognostic characteristic for the outcome of breast cancer patients treated with tamoxifen.

Metastasis-associated protein 1/histone deacetylase 4-nucleosome remodeling and deacetylase complex regulates phosphatase and tensin homolog gene expression and function

Metastasis-associated protein 1 (MTA1) is widely overexpressed in human cancers and is associated with malignant phenotypic changes contributing to morbidity in the associated diseases. Here we discovered for the first time that MTA1, a master chromatin modifier, transcriptionally represses the expression of phosphatase and tensin homolog (PTEN), a tumor suppressor gene, by recruiting class II histone deacetylase 4 (HDAC4) along with the transcription factor Yin-Yang 1 (YY1) onto the PTEN promoter. We also found evidence of an inverse correlation between the expression levels of MTA1 and PTEN in physiologically relevant breast cancer microarray datasets. We found that MTA1 up-regulation leads to a decreased expression of PTEN protein and stimulation of PI3K as well as phosphorylation of its signaling targets. Accordingly, selective down-regulation of MTA1 in breast cancer cells increases PTEN expression and inhibits stimulation of the PI3K/AKT signaling. Collectively, these findings provide a mechanistic role for MTA1 in transcriptional repression of PTEN, leading to modulation of the resulting signaling pathways.

Phenotype selection reveals coevolution of muscle glycogen and protein and PTEN as a gate keeper for the accretion of muscle mass in adult female mice

We have investigated molecular mechanisms for muscle mass accretion in a non-inbred mouse model (DU6P mice) characterized by extreme muscle mass. This extreme muscle mass was developed during 138 generations of phenotype selection for high protein content. Due to the repeated trait selection a complex setting of different mechanisms was expected to be enriched during the selection experiment. In muscle from 29-week female DU6P mice we have identified robust increases of protein kinase B activation (AKT, Ser-473, up to 2-fold) if compared to 11- and 54-week DU6P mice or controls. While a number of accepted effectors of AKT activation, including IGF-I, IGF-II, insulin/IGF-receptor, myostatin or integrin-linked kinase (ILK), were not correlated with this increase, phosphatase and tensin homologue deleted on chromosome 10 (PTEN) was down-regulated in 29-week female DU6P mice. In addition, higher levels of PTEN phosphorylation were found identifying a second mechanism of PTEN inhibition. Inhibition of PTEN and activation of AKT correlated with specific activation of p70S6 kinase and ribosomal protein S6, reduced phosphorylation of eukaryotic initiation factor 2α (eIF2α) and higher rates of protein synthesis in 29-week female DU6P mice. On the other hand, AKT activation also translated into specific inactivation of glycogen synthase kinase 3ß (GSK3ß) and an increase of muscular glycogen. In muscles from 29-week female DU6P mice a significant increase of protein/DNA was identified, which was not due to a reduction of protein breakdown or to specific increases of translation initiation. Instead our data support the conclusion that a higher rate of protein translation is contributing to the higher muscle mass in mid-aged female DU6P mice. Our results further reveal coevolution of high protein and high glycogen content during the selection experiment and identify PTEN as gate keeper for muscle mass in mid-aged female DU6P mice.

Effect of the IGF-1/PTEN/Akt/FoxO signaling pathway on the development and healing of water immersion and restraint stress-induced gastric ulcers in rats

Insulin-like growth factor 1 (IGF-1) and Akt [also known as protein kinase B (PKB)] proteins have been reported to exhibit gastroprotective effects by reducing water immersion and restraint stress (WRS)-induced gastric mucosal cellular apoptosis. To confirm whether the IGF-1/PTEN/Akt/FoxO signaling pathway is effective in protecting against gastric ulcers, our current study was conducted to examine the expression and localization of IGF-1, phosphatase and tensin homologue deleted on chromosome 10 (PTEN), Akt and O subfamily of forkhead box (FoxO) proteins, caspase-3 activity and the number of apoptotic cells in gastric mucosa of rats subjected to WRS. Our results demonstrated that WRS induced gastric ulcers by enhancing cell apoptosis in rat gastric mucosa. In addition, in normal rat gastric mucosa, PTEN, total Akt and FoxO1 were found mainly in the cell cytoplasm of fundic glands in the lamina propria close to the muscularis mucosa. In addition, strong staining of IGF-1, FoxO3a and FoxO4 in the gastric mucosa was primarily concentrated in the cell cytoplasm of the fundic glands in whole lamina propria. However, in rat gastric ulcers, IGF-1, total Akt, FoxO3a and FoxO4 were localized in proximity to the base of the ulcer margin and were also present in the granulation tissues of the gastric ulcers. Moreover, in the rat gastric ulcers, the mRNA transcript levels of IGF-1, PTEN, Akt-1, Akt-2, FoxO3 and FoxO4 were upregulated in the gastric ulcer margin, with a peak between Days 4 and 8 following 7 h of WRS. In conclusion, our results imply that the IGF-1/PTEN/Akt/FoxO signaling pathway plays a certain role(s) in the protection against ulceration through the regulation of cellular apoptosis as observed in the development and healing of rat gastric ulcers.

PTEN gene: a model for genetic diseases in dermatology

PTEN gene is considered one of the most mutated tumor suppressor genes in human cancer, and it's likely to become the first one in the near future. Since 1997, its involvement in tumor suppression has smoothly increased, up to the current importance. Germline mutations of PTEN cause the PTEN hamartoma tumor syndrome (PHTS), which include the past-called Cowden, Bannayan-Riley-Ruvalcaba, Proteus, Proteus-like, and Lhermitte-Duclos syndromes. Somatic mutations of PTEN have been observed in glioblastoma, prostate cancer, and brest cancer cell lines, quoting only the first tissues where the involvement has been proven. The negative regulation of cell interactions with the extracellular matrix could be the way PTEN phosphatase acts as a tumor suppressor. PTEN gene plays an essential role in human development. A recent model sees PTEN function as a stepwise gradation, which can be impaired not only by heterozygous mutations and homozygous losses, but also by other molecular mechanisms, such as transcriptional regression, epigenetic silencing, regulation by microRNAs, posttranslational modification, and aberrant localization. The involvement of PTEN function in melanoma and multistage skin carcinogenesis, with its implication in cancer treatment, and the role of front office in diagnosing PHTS are the main reasons why the dermatologist should know about PTEN.

Comparison of growth factor signalling pathway utilisation in cultured normal melanocytes and melanoma cell lines

BACKGROUND

The phosphatidylinositol-3-kinase (PI3K-PKB), mitogen activated protein kinase (MEK-ERK) and the mammalian target of rapamycin (mTOR- p70S6K), are thought to regulate many aspects of tumour cell proliferation and survival. We have examined the utilisation of these three signalling pathways in a number of cell lines derived from patients with metastatic malignant melanoma of known PIK3CA, PTEN, NRAS and BRAF mutational status.

METHODS

Western blotting was used to compare the phosphorylation status of components of the PI3K-PKB, MEK-ERK and mTOR-p70S6K signalling pathways, as indices of pathway utilisation.

RESULTS

Normal melanocytes could not be distinguished from melanoma cells on the basis of pathway utilisation when grown in the presence of serum, but could be distinguished upon serum starvation, where signalling protein phosphorylation was generally abrogated. Surprisingly, the differential utilisation of individual pathways was not consistently associated with the presence of an oncogenic or tumour suppressor mutation of genes in these pathways.

CONCLUSION

Utilisation of the PI3K-PKB, MEK-ERK and mTOR-p70S6K signalling pathways in melanoma, as determined by phosphorylation of signalling components, varies widely across a series of cell lines, and does not directly reflect mutation of genes coding these components. The main difference between cultured normal melanocytes and melanoma cells is not the pathway utilisation itself, but rather in the serum dependence of pathway utilisation.

The significance of PTEN and AKT aberrations in pediatric T-cell acute lymphoblastic leukemia

BACKGROUND

PI3K/AKT pathway mutations are found in T-cell acute lymphoblastic leukemia, but their overall impact and associations with other genetic aberrations is unknown. PTEN mutations have been proposed as secondary mutations that follow NOTCH1-activating mutations and cause cellular resistance to γ-secretase inhibitors.

DESIGN AND METHODS

The impact of PTEN, PI3K and AKT aberrations was studied in a genetically well-characterized pediatric T-cell leukemia patient cohort (n=146) treated on DCOG or COALL protocols.

RESULTS

PTEN and AKT E17K aberrations were detected in 13% and 2% of patients, respectively. Defective PTEN-splicing was identified in incidental cases. Patients without PTEN protein but lacking exon-, splice-, promoter mutations or promoter hypermethylation were present. PTEN/AKT mutations were especially abundant in TAL- or LMO-rearranged leukemia but nearly absent in TLX3-rearranged patients (P=0.03), the opposite to that observed for NOTCH1-activating mutations. Most PTEN/AKT mutant patients either lacked NOTCH1-activating mutations (P=0.006) or had weak NOTCH1-activating mutations (P=0.011), and consequently expressed low intracellular NOTCH1, cMYC and MUSASHI levels. T-cell leukemia patients without PTEN/AKT and NOTCH1-activating mutations fared well, with a cumulative incidence of relapse of only 8% versus 35% for PTEN/AKT and/or NOTCH1-activated patients (P=0.005).

CONCLUSIONS

PI3K/AKT pathway aberrations are present in 18% of pediatric T-cell acute lymphoblastic leukemia patients. Absence of strong NOTCH1-activating mutations in these cases may explain cellular insensitivity to γ-secretase inhibitors.

S-Glutathionylation signaling in cell biology: progress and prospects

S-Glutathionylation is a mechanism of signal transduction by which cells respond effectively and reversibly to redox inputs. The glutathionylation regulates most cellular pathways. It is involved in oxidative cellular response to insult by modulating the transcription factor Nrf2 and inducing the expression of antioxidant genes (ARE); it contributes to cell survival through nuclear translocation of NFkB and activation of survival genes, and to cell death by modulating the activity of caspase 3. It is involved in mitotic spindle formation during cell division by binding cytoskeletal proteins thus contributing to cell proliferation and differentiation. Glutathionylation also interfaces with the mechanism of phosphorylation by modulating several kinases (PKA, CK) and phosphatases (PP2A, PTEN), thus allowing a cross talk between the two processes of signal transduction. Also, skeletal RyR1 channels responsible of muscle excitation-contraction coupling appear to be sensitive to glutathionylation. Members of the ryanodine receptor super family, responsible for Ca(2) release from endoplasmic reticulum stores, contain sulfhydryl groups that function as a redox "switch", which either induces or inhibits Ca(2) release. Finally, but very importantly, glutathionylation of proteins may also act on cell metabolism by modulating enzymes involved in glycosylation, in the Krebs cycle and in mitochondrial oxidative phosphorylation. In this review, we propose a greater role for glutathionylation in cell biology: not only a cellular response to oxidative stress, but an elegant and sensitive mechanism able to respond even to subtle changes in redox balance in the different cellular compartments. Given the wide spectrum of redox-sensitive proteins, we discuss the possibility that different pathways light up by glutathionylation under various pathological conditions. The feature of reversibility of this process also makes it prone to develop targeted drug therapies and monitor the pharmacological effectiveness once identified the sensor proteins involved.

New insights in the activity of voltage sensitive phosphatases

The Ciona intestinalis voltage sensitive phosphatase (Ci-VSP) was the first proven enzyme to be under direct control of the membrane potential. Ci-VSP belongs to a family of proteins known as Protein Tyrosine Phosphatases (PTP), which are a group of enzymes that catalyze the removal of phosphate groups from phosphatidylinositides and phosphorylated tyrosine residues on proteins. What makes Ci-VSP and similar phosphatases unique is the presence of a Voltage Sensing Domain (VSD) in their N-terminus. The VSD of Ci-VSP shares high homology with those from voltage-gated channels and confers voltage sensitivity to these enzymes. The catalytic domain of Ci-VSP displays extraordinary structural and functional similarities to PTEN. This latter protein is encoded by the Phosphatase and Tensin homolog deleted from chromosome 10 gene, thus its name, and it is known as a tumor suppressor. The resemblance between these proteins has prompted the use of PTEN as a template for the study of Ci-VSP and produced a rapid advance in our understanding of the mechanism of activity of Ci-VSP. This review will be focused on discussing recent advances in the understanding of the activation mechanism for these molecules known as electrochemical coupling.

Akt: a double-edged sword in cell proliferation and genome stability

The Akt family of serine/threonine protein kinases are key regulators of multiple aspects of cell behaviour, including proliferation, survival, metabolism, and tumorigenesis. Growth-factor-activated Akt signalling promotes progression through normal, unperturbed cell cycles by acting on diverse downstream factors involved in controlling the G1/S and G2/M transitions. Remarkably, several recent studies have also implicated Akt in modulating DNA damage responses and genome stability. High Akt activity can suppress ATR/Chk1 signalling and homologous recombination repair (HRR) via direct phosphorylation of Chk1 or TopBP1 or, indirectly, by inhibiting recruitment of double-strand break (DSB) resection factors, such as RPA, Brca1, and Rad51, to sites of damage. Loss of checkpoint and/or HRR proficiency is therefore a potential cause of genomic instability in tumor cells with high Akt. Conversely, Akt is activated by DNA double-strand breaks (DSBs) in a DNA-PK- or ATM/ATR-dependent manner and in some circumstances can contribute to radioresistance by stimulating DNA repair by nonhomologous end joining (NHEJ). Akt therefore modifies both the response to and repair of genotoxic damage in complex ways that are likely to have important consequences for the therapy of tumors with deregulation of the PI3K-Akt-PTEN pathway.

Evaluation of PTEN immunoexpression in oral submucous fibrosis: role in pathogenesis and malignant transformation

Oral submucous fibrosis (OSMF) is a chronic debilitating disease and a premalignant condition of the oral cavity characterized by generalized submucosal fibrosis. Despite its precancerous nature, the molecular biology regarding its malignant potential has not been extensively studied. PTEN, a known tumor suppressor gene is mutated in a majority of human cancers and has also been implicated in several fibrotic disorders. The present study aims to evaluate the expression of PTEN in OSMF and oral squamous cell carcinoma (OSCC) and correlate it with the pathogenesis and malignant transformation of OSMF. 60 cases total of OSMF (30) and OSCC (30) were subjected to immunohistochemistry using PTEN antibody. Ten normal oral mucosa (NOM) specimens were also stained as controls. There was progressive loss of PTEN expression from normal mucosa to OSMF and OSCC (p ≤ 0.001). Significant differences were observed for PTEN expression between NOM and OSMF, OSMF and OSCC as well as NOM and OSCC. Though a progressive loss of PTEN was noticed between early OSMF and advanced OSMF, the variation did not reach statistical significance (p ≥ 0.001). Data suggest that there is a significant loss of PTEN expression in OSMF as compared to normal oral mucosa and that this trend increased from OSMF to OSCC. Thus, alteration of PTEN is likely an important molecular event in OSMF pathogenesis and oral carcinogenesis.

High levels of p110δ PI3K expression in solid tumor cells suppress PTEN activity, generating cellular sensitivity to p110δ inhibitors through PTEN activation

Class IA PI3K isoforms have divergent, nonredundant cell biological roles. In untransformed cells and tissues, p110α and p110β are ubiquitously expressed, whereas p110δ expression is highly enriched in leukocytes. High levels of p110δ expression have been documented in some solid tumor cell lines, but the functional role is unknown. This study aimed to elucidate the link between elevated expression of p110δ PI3K and cancer. We report that in breast and prostate cancer cells that contain leukocyte levels of p110δ, p110δ activity dampens the activity of the PTEN tumor suppressor. Indeed, inactivation of p110δ in these cells led to PTEN activation, suppression of Akt phosphorylation, and inhibition of cell proliferation, with inhibition of PTEN activity being able to counterbalance p110δ inactivation. Likewise, forced overexpression of p110δ in cells with low p110δ expression reduced PTEN activity, resulting in increased Akt phosphorylation. Our data indicate that the oncogenic potential of p110δ PI3K overexpression might at least partially act through PTEN inactivation, and that p110δ-selective PI3K inhibitors can have a dual antitumor mechanism, namely by directly inhibiting p110δ signaling and by a broader inhibition of class I PI3K activity through PTEN activation. These data may have important implications in the intervention of breast cancer.

Cancer biomarkers: selecting the right drug for the right patient

This Perspective highlights biomarkers that are expressed as a consequence of cancer development and progression. We focus on those biomarkers that are most relevant for identifying patients who are likely to respond to a given therapy, as well as those biomarkers that are most effective for measuring patient response to therapy. These two measures are necessary for selecting the right drug for the right patient, regardless of whether the setting is in drug development or in the post-approval use of the drug for patients with cancer. We also discuss the innovative designs of clinical trials and methodologies that are used to validate and qualify biomarkers for use in specific contexts. Furthermore, we look ahead to the promises and challenges in the field of cancer biomarkers.