Physiological functions of Pten in mouse tissues

The PI3K signaling pathway; from normal lymphopoiesis to lymphoid malignancies

INTRODUCTION

As a vital mechanism of survival, lymphopoiesis requires the collaboration of different signaling molecules to orchestrate each step of cell development and maturation. The PI3K pathway is considerably involved in the maturation of lymphatic cells and therefore, its dysregulation can immensely affect human well-being and cause some of the most prevalent malignancies. As a result, studies that investigate this pathway could pave the way for a better understanding of the lymphopoiesis mechanisms, the undesired changes that lead to cancer progression, and how to design drugs to solve this issue.

AREAS COVERED

The present review addresses the aforementioned aspects of the PI3K pathway and helps pave the way for future therapeutic approaches. In order to access the articles, databases such as Medicine Medline/PubMed, Scopus, Google Scholar, and Science Direct were utilized. The search formula was established by identifying main keywords including PI3K/Akt/mTOR pathway, Lymphopoiesis, Lymphoid malignancies, and inhibitors.

EXPERT OPINION

The PI3K pathway is crucial for lymphocyte development and differentiation, making it a potential target for therapeutic intervention in lymphoid cancers. Studies are focused on developing PI3K inhibitors to impede the progression of hematologic malignancies, highlighting the pathway's significance in lymphoma and lymphoid leukemia.

Cerebellar phenotypes in germline PTEN mutation carriers

PTEN hamartoma tumour syndrome (PHTS) comprises different hereditary conditions caused by germline PTEN mutations, predisposing to the development of multiple hamartomas in many body tissues and also increasing the risk of some types of cancer. Cerebellar involvement in PHTS patients has been long known due to the development of a pathognomonic cerebellar hamartoma (known as dysplastic gangliocytoma of the cerebellum or Lhermitte-Duclos disease). Recently, a crucial role of the cerebellum has been highlighted in the pathogenesis of autism spectrum disorders, now recognised as a phenotype expressed in a variable percentage of PHTS children. In addition, rare PTEN variants are indeed identified in medulloblastoma as well, even if they are less frequent than other germline gene mutations. The importance of PTEN and its downstream signalling enzymatic pathways, PI3K/AKT/mTOR, has been studied at different levels in both human clinical settings and animal models, not only leading to a better understanding of the pathogenesis of different disorders but, most importantly, to identify potential targets for specific therapies. In particular, PTEN integrity makes an important contribution to the normal development of tissue architecture in the nervous system, including the cerebellum. Thus, in patients with PTEN germline mutations, the cerebellum is an affected organ that is increasingly recognised in different disorders, whereas, in animal models, cerebellar Pten loss causes a variety of functional and histological alterations. In this review, we summarise the range of cerebellar involvement observed in PHTS and its relationships with germline PTEN mutations, along with the phenotypes expressed by murine models with PTEN deficiency in cerebellar tissue.

Regulation of the tumor suppressor PTEN in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a subtype of breast cancer (BCa) in which estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER-2) are not expressed. Although TNBC cases account for approximately 15% of all BCa cases, TNBC patients' prognosis is poor compared with that of other BCa subtypes. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) plays an important role in cell proliferation and migration by negatively regulating the PI3K/Akt pathway. PTEN is one of the most commonly inactivated tumor suppressors in BCa. PTEN inactivity is associated with larger tumor sizes, multiple lymph node metastases, and an aggressive triple-negative phenotype. This review primarily focuses on two key points: (1) PTEN and its function. (2) The regulation of tumor suppressor PTEN in TNBC. We provide a summary of genomic alterations of PTEN in BCa. We further discuss the transcriptional regulation of PTEN and how PTEN is regulated by posttranscription and posttranslational modification, as well as by protein interactions. Finally, we discuss the perspectives of the PTEN protein in TNBC.

Peroxiredoxin 6 secreted by Schwann-like cells protects neuron against ischemic stroke in rats via PTEN/PI3K/AKT pathway

Schwann cells can promote the survival of damaged neurons and axon regeneration by secreting or releasing some proteins and factors which may provide effective strategies to the remedy for ischemic stroke. The models of middle cerebral artery occlusion and oxygen-glucose deprivation (OGD) were established. Peroxiredoxin 6 (PRDX6) was found in Schwann-like cell conditioned medium (SCLC-CM) by mass spectrometry. The rehabilitative performance of SCLC-CM on focal cerebral ischemia of rats and on OGD-induced PC12 cells were assessed. SCLC-CM significantly improved neurological recovery, reducing the infarct volume of rats after stroke. PRDX6 could significantly inhibit neuron apoptosis in the OGD injury by mediating oxidative stress and activating the PTEN/PI3K/AKT pathway. In conclusion, PRDX6 secreted by Schwann-like cell protects neuron against focal cerebral ischemia, SCLC-CM might be a new effective early intervention for ischemic stroke.

Morphology and Biochemistry of Ovulation

The process of ovulation involves multiple and iterrelated genetic, biochemical, and morphological events: cessation of the proliferation of granulosa cells, resumption of oocyte meiosis, expansion of cumulus cell-oocyte complexes, digestion of the follicle wall, and extrusion of the metaphase-II oocyte. The present narrative review examines these interrelated steps in detail. The combined or isolated roles of the follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are highlighted. Genes indiced by the FSH genes are relevant in the cumulus expansion, and LH-induced genes are critical for the resumption of meiosis and digestion of the follicle wall. A non-human model for follicle-wall digestion and oocyte release was provided.

PTEN dephosphorylates Abi1 to promote epithelial morphogenesis

The tumor suppressor PTEN is essential for early development. Its lipid phosphatase activity converts PIP₃ to PIP₂ and antagonizes the PI3K–Akt pathway. In this study, we demonstrate that PTEN’s protein phosphatase activity is required for epiblast epithelial differentiation and polarization. This is accomplished by reconstitution of PTEN-null embryoid bodies with PTEN mutants that lack only PTEN’s lipid phosphatase activity or both PTEN’s lipid and protein phosphatase activities. Phosphotyrosine antibody immunoprecipitation and mass spectrometry were used to identify Abi1, a core component of the WASP-family verprolin homologous protein (WAVE) regulatory complex (WRC), as a new PTEN substrate. We demonstrate that PTEN dephosphorylation of Abi1 at Y213 and S216 results in Abi1 degradation through the calpain pathway. This leads to down-regulation of the WRC and reorganization of the actin cytoskeleton. The latter is critical to the transformation of nonpolar pluripotent stem cells into the polarized epiblast epithelium. Our findings establish a link between PTEN and WAVE-Arp2/3–regulated actin cytoskeletal dynamics in epithelial morphogenesis.

Pathophysiological significance of N-myc downstream-regulated gene 2 in cancer development through protein phosphatase 2A phosphorylation regulation

N-myc downstream-regulated gene 2 (NDRG2) is a candidate tumor suppressor in various cancers, including adult T-cell leukemia/lymphoma (ATLL). NDRG2, as a stress-responsive protein, is induced by several stress-related signaling pathways and NDRG2 negatively regulates various signal transduction pathways. Although it has not been found to function alone, NDRG2 binds serine/threonine protein phosphatase 2A (PP2A), generating a complex that is involved in the regulation of various target proteins. The main function of NDRG2 is to maintain cell homeostasis by suppressing stress-induced signal transduction; however, in cancer, genomic deletions and/or promoter methylation may inhibit the expression of NDRG2, resulting in enhanced tumor development through overactivated signal transduction pathways. A wide variety of tumors develop in Ndrg2-deficient mice, including T-cell lymphoma, liver, lung and other tumors, the characteristics of which are similar to those in Pten-deficient mice. In particular, PTEN is a target molecule of the NDRG2/PP2A complex, which enhances PTEN phosphatase activity by dephosphorylating residues in the PTEN C-terminal region. In ATLL cells, loss of NDRG2 expression leads to the failed recruitment of PP2A to PTEN, resulting in the inactivation of PTEN phosphatase with phosphorylation, ultimately leading to the activation of PI3K/AKT. Thus, NDRG2, as a PP2A adaptor, regulates the global phosphorylation of important signaling molecules. Moreover, the downregulation of NDRG2 expression by long-term stress-induced methylation is directly correlated with the development of ATLL and other cancers. Thus, NDRG2 might be important for the development of stress-induced leukemia and other cancers and has become an important target for novel molecular therapies.

PTEN Mouse Models of Cancer Initiation and Progression

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is one of the most frequently mutated, deleted, and functionally inactivated tumor suppressor genes in human cancer. PTEN is found mutated both somatically and in the germline of patients with PTEN hamartoma tumor syndrome (PHTS). PTEN encodes a dual lipid and protein phosphatase that dephosphorylates the lipid phosphatidylinositol-3,4,5-trisphosphate (PIP₃), in turn negatively regulating the oncogenic PI3K-AKT pathway, a key proto-oncogenic player in cancer development and progression. Because of importance of PTEN in tumorigenesis, a large number of sophisticated genetically engineered mouse models (GEMMs) has been designed to elucidate the underlying mechanisms by which the "PTEN pathway" promotes tumorigenesis, while simultaneously providing a well-tailored system for the identification of novel therapies and offering platforms for new drug discoveries. This review summarizes the major cancer mouse models through which the PTEN pathway has been genetically deconstructed, and outlines the rapid development of GEMMs toward more detailed functional and tissue-specific analysis.

ROS play an important role in ATPR inducing differentiation and inhibiting proliferation of leukemia cells by regulating the PTEN/PI3K/AKT signaling pathway

BACKGROUND

Acute myeloid leukemia (AML) is an aggressive and mostly incurable hematological malignancy with frequent relapses after an initial response to standard chemotherapy. Therefore, novel therapies are urgently required to improve AML clinical outcomes. 4-Amino-2-trifluoromethyl-phenyl retinate (ATPR), a novel all-trans retinoic acid (ATRA) derivative designed and synthesized by our team, has been proven to show biological anti-tumor characteristics in our previous studies. However, its potential effect on leukemia remains unknown. The present research aims to investigate the underlying mechanism of treating leukemia with ATPR in vitro.

METHODS

In this study, the AML cell lines NB4 and THP-1 were treated with ATPR. Cell proliferation was analyzed by the CCK-8 assay. Flow cytometry was used to measure the cell cycle distribution and cell differentiation. The expression levels of cell cycle and differentiation-related proteins were detected by western blotting and immunofluorescence staining. The NBT reduction assay was used to detect cell differentiation.

RESULTS

ATPR inhibited cell proliferation, induced cell differentiation and arrested the cell cycle at the G0/G1 phase. Moreover, ATPR treatment induced a time-dependent release of reactive oxygen species (ROS). Additionally, the PTEN/PI3K/Akt pathway was downregulated 24 h after ATPR treatment, which might account for the anti-AML effects of ATPR that result from the ROS-mediated regulation of the PTEN/PI3K/AKT signaling pathway.

CONCLUSIONS

Our observations could help to develop new drugs targeting the ROS/PTEN/PI3K/Akt pathway for the treatment of AML.

PTEN/FLJ10540/PI3K/Akt cascade in experimental brain stem death: A newfound role for a classical tumorigenic signaling pathway

Despite great advances in contemporary medicine, brain death still remains enigmatic and its cellular and molecular mechanisms unsettled. This review summarizes recent findings that substantiate the notion that PTEN/FLJ10540/PI3K/Akt cascade, the classical tumorigenic signaling pathway, is actively engaged in experimental brain stem death. These results were based on a clinically relevant animal model that employs the pesticide mevinphos as the experimental insult in Sprague-Dawley rats to mimic brain stem death in patients died of organophosphate poisoning. The neural substrate investigated is the rostral ventrolateral medulla (RVLM), a brain stem site classically known to maintain arterial pressure (AP) and is established to be the origin of a "life-and-death" signal detected from AP, which reflects brain stem cardiovascular dysregulation that precedes death. Activation of PI3K/Akt signaling pathway in the RVLM upregulates the nuclear factor-κB/nitric oxide synthase II/peroxynitrite cascade, resulting in impairment of brain stem cardiovascular regulation that leads to the loss of the "life-and-death" signal in experimental brain stem death. This process is reinforced by FLJ10540, a PI3K-association protein; and is counteracted by PTEN, a negative regulator of PI3K/Akt signaling. The concept that a classical signaling pathway in tumorigenesis is also an active player in cardiovascular dysregulation in brain stem death provides new ramifications for translational medicine. It promulgates the concept that rather than focusing on a particular disease condition, a new vista for future therapeutic strategy against both fatal eventualities should target at this common cellular cascade.

Nimesulide inhibits proliferation and induces apoptosis of pancreatic cancer cells by enhancing expression of PTEN

Pancreatic cancer is the fourth leading cause of cancer-associated cases of mortality worldwide. Prostaglandin-endoperoxide synthase 2 (COX-2) is considered a therapeutic target for prevention of pancreatic cancer. Nimesulide, a selective COX-2 inhibitor, can induce cell apoptosis, resulting in an anti-cancer effect. However, the mechanism underlying this effect remains to be elucidated. The present study aimed to evaluate the effects of nimesulide on proliferation of PANC-1 cells using an MTT assay. Apoptosis was evaluated by DNA laddering and Annexin V-fluorescein isothiocyanate/propidium iodide-stained flow cytometry. Furthermore, western blot analysis was used to elucidate the mechanism underlying nimesulide treatment in PANC-1 cells. It was determined that proliferation of PANC-1 cells was inhibited by nimesulide in a dose-dependent manner. Nimesulide promoted apoptosis of PANC-1 cells. Western blot analysis demonstrated that nimesulide increased expression of cleaved caspase-3 and apoptosis regulator Bax (Bcl-2 associated protein X), and decreased the expression of pro-caspase-3 and apoptosis regulator Bcl-2 (B-cell lymphoma 2). Furthermore, nimesulide enhanced expression of phosphatase and tensin homolog (PTEN), and decreased the expression level of COX-2 and vascular endothelial growth factor. In summary, the results of the present study demonstrated that nimesulide could induce apoptosis and inhibit growth of PANC-1 cells by enhancing the expression of PTEN, which indicates the potential of nimesulide to prevent tumor angiogenesis.

Region-specific role for Pten in maintenance of epithelial phenotype and integrity

Previous studies have demonstrated resistance to naphthalene-induced injury in proximal airways of mice with lung epithelial-specific deletion of the tumor-suppressor gene Pten, attributed to increased proliferation of airway progenitors. We tested effects of Pten loss following bleomycin injury, a model typically used to study distal lung epithelial injury, in conditional Pten^SFTPC-cre knockout mice. Pten-deficient airway epithelium exhibited marked hyperplasia, particularly in small bronchioles and at bronchoalveolar duct junctions, with reduced E-cadherin and β-catenin expression between cells toward the luminal aspect of the hyperplastic epithelium. Bronchiolar epithelial and alveolar epithelial type II (AT2) cells in Pten^SFTPC-cre mice showed decreased expression of epithelial markers and increased expression of mesenchymal markers, suggesting at least partial epithelial-mesenchymal transition at baseline. Surprisingly, and in contrast to previous studies, mutant mice were exquisitely sensitive to bleomycin, manifesting rapid weight loss, respiratory distress, increased early mortality (by day 5), and reduced dynamic lung compliance. This was accompanied by sloughing of the hyperplastic airway epithelium with occlusion of small bronchioles by cellular debris, without evidence of increased parenchymal lung injury. Increased airway epithelial cell apoptosis due to loss of antioxidant defenses, reflected by decreased expression of superoxide dismutase 3, in combination with deficient intercellular adhesion, likely predisposed to airway sloughing in knockout mice. These findings demonstrate an important role for Pten in maintenance of airway epithelial phenotype integrity and indicate that responses to Pten deletion in respiratory epithelium following acute lung injury are highly context-dependent and region-specific.

The PTEN/Akt Signaling Pathway Mediates Myocardial Apoptosis in Swine After Coronary Microembolization

Background/Aims:

Phosphatase and the tensin homolog deleted on chromosome ten (PTEN) has been recognized as a promoter of apoptosis in various tissues and has been shown to be upregulated in circumstances of coronary microembolization (CME). We hypothesized that the upregulation of PTEN correlates with CME-induced myocardial apoptosis.

Methods:

Swine CME was induced by an intracoronary injection of inert plastic microspheres (diameter of 42 μm) into the left anterior descending coronary, with or without pretreatment of the PTEN small-interfering RNA (siRNA). Echocardiological measurements, a pathological examination, Terminal-deoxynucleoitidyl Transferase Mediated Nick End Labeling (TUNEL) staining, and Western blotting, were performed to assess their functional, morphological, and molecular effects in CME.

Results:

PTEN was aberrantly upregulated in cardiomyocytes following CME. Downregulation of PTEN in vivo via siRNA was associated with improved cardiac function and attenuated myocardial apoptosis; concomitantly inhibited the expression of key proapoptotic proteins, such as phosphorylated Bad (p-Bad); cleaved caspase-3; and enhanced the expression of key antiapoptotic proteins, such as phosphorylated protein kinase B (p-Akt). However, there was no difference in the Akt-regulated downstream protein IκB kinases (IKKα, IKKβ, and IKKγ) among the sham, CME, and control siRNA groups.

Conclusion:

This study demonstrates, for the first time, that the PTEN/Akt signaling pathway contributes to cardiomyocyte apoptosis. The data generated from this study provide a rationale for the development of PTEN-based therapeutic strategies for CME-induced myocardial injury.

Aldehyde dehydrogenase 2 deficiency blunts compensatory cardiac hypertrophy through modulating Akt phosphorylation early after transverse aorta constriction in mice

AIMS

This study was designed to examine the impact of mitochondrial aldehyde dehydrogenase 2 (ALDH2) on transverse aorta constriction (TAC)-induced cardiac hypertrophy and related molecular mechanisms using an ALDH2 knockout (ALDH2-/-) murine model.

METHODS

Male wild-type and ALDH2-/- mice were subjected to TAC or sham operation (n=6-8 for each group). After two weeks, cardiac function was assessed by echocardiography and hemodynamic measurements. Myocardial phosphorylated and total PI3K, the catalytic subunit of PI3Ks (p110α and p110γ), Akt, and total PTEN levels were detected by Western blotting. Cardiomyocytes were stretched for 6h in vitro in the presence or absence of Alda-1 (a small-molecule activator of ALDH2) prior to assessment of phosphorylated PI3K, Akt and total PTEN expressions by Western blot.

RESULTS

Heart to body weight ratio and left ventricular posterior wall thickness as well as the cross-sectional area of cardiomyocyte were significantly lower in ALDH2-/- mice than in wild-type mice following TAC. Western blot analysis showed p110γ was upregulated post TAC in both wild-type mice and ALDH2-/- mice, phosphorylation of Akt was disrupted, PTEN expression was upregulated in ALDH2-/- mice post TAC while phosphorylated PI3K, p110α and p110γ expression was similar between ALDH2-/- and wild-type mice post TAC. In vitro, phosphorylation of Akt was significantly accentuated and PTEN expression was reduced while PI3K phosphorylation remained unchanged in stretched cardiomyocytes pretreated by Alda-1 compared to stretched cardiomyocytes treated by saline.

CONCLUSIONS

Our results show that ALDH2 deficiency attenuates compensatory cardiac hypertrophy through regulating Akt but not PI3K phosphorylation early after TAC in mice.

A PTEN translational isoform has PTEN-like activity

BACKGROUND

To identify PTEN isoform and explore its potential role in tumor suppression.

METHODS

Western blotting, over-expression, shRNA mediated knocking-down, and bioinformatic analysis were used to identify PTEN isoform and test its effect on PI3K-Akt signaling pathway. Cell proliferation, apoptosis, and migration assays were used to test PTEN isoform's biological activities.

RESULTS

The PTEN isoform is about 15 kDa bigger than PTEN and its expression is dependent on PTEN status. Immunoprecipitation for PTEN isoform followed by screening with antibodies against ISG15, SUMO1/2/3, Ubiquitin, and Nedd8 showed the identified PTEN isoform is not a general proteinaceous post-translational modification. In addition, overexpression of PTEN cDNA in cells did not generate PTEN isoform whereas knocking-down of PTEN reduced the protein levels of both PTEN and PTEN isoform in a proportional manner. Analysis of PTEN DNA sequence disclosed an alternative translational starting code (CTG) upstream of canonical PTEN coding sequence. Expression of cloned PTEN isoform generated a protein with a size about 15 kDa bigger than PTEN and suppressed PI3K-Akt signaling pathway in cells. Overexpression of PTEN isoform also led to decrease in cell growth and enhanced serum starvation-and UV irradiation-induced apoptosis through activation of Caspase 3. Finally, expression of PTEN isoform inhibited cell migration in scratch assay.

CONCLUSIONS

PTEN isoform has PTEN-like activity and might be a new tumor suppressor.

Actin dynamics is rapidly regulated by the PTEN and PIP2 signaling pathways leading to myocyte hypertrophy

Mature cardiac myocytes are terminally differentiated, and the heart has limited capacity to replace lost myocytes. Thus adaptation of myocyte size plays an important role in the determination of cardiac function. The hypothesis tested is that regulation of the dynamic exchange of actin leads to cardiac hypertrophy. ANG II was used as a hypertrophic stimulant in mouse heart and neonatal rat ventricular myocytes (NRVMs) in culture for assessment of a mechanism for regulation of actin dynamics by phosphatidylinositol 4,5-bisphosphate (PIP2). Actin dynamics in NRVMs rapidly increased in a PIP2-dependent manner, measured by imaging and fluorescence recovery after photobleaching (FRAP). A significant increase in PIP2 levels was found by immunoblotting in both adult mouse heart tissue and cultured NRVMs. Inhibition of phosphatase and tensin homolog (PTEN) in NRVMs markedly blunted ANG II-induced increases in actin dynamics, the PIP2 level, and cell size. Furthermore, PTEN activity was dramatically upregulated in ANG II-treated NRVMs but downregulated when PTEN inhibitors were used. The time course of the rise in the PIP2 level was inversely related to the fall in the PIP3 level, which was significant by 30 min in ANG II-treated NRVMs. However, significant translocation of PTEN to the plasma membrane occurred by 10 min, suggesting a crucial initial step for PTEN for the cellular responses to ANG II. In conclusion, PTEN and PIP2 signaling may play an important role in myocyte hypertrophy by the regulation of actin filament dynamics, which is induced by ANG II stimulation.

The PTEN/PI3K/AKT Pathway in vivo, Cancer Mouse Models

When PI3K (phosphatidylinositol-3 kinase) is activated by receptor tyrosine kinases, it phosphorylates PIP2 to generate PIP3 and activates the signaling pathway. Phosphatase and tensin homolog deleted on chromosome 10 dephosphorylates PIP3 to PIP2, and thus, negatively regulates the pathway. AKT (v-akt murine thymoma viral oncogene homolog; protein kinase B) is activated downstream of PIP3 and mediates physiological processes. Furthermore, substantial crosstalk exists with other signaling networks at all levels of the PI3K pathway. Because of its diverse array, gene mutations, and amplifications and also as a consequence of its central role in several signal transduction pathways, the PI3K-dependent axis is frequently activated in many tumors and is an attractive therapeutic target. The preclinical testing and analysis of these novel therapies requires appropriate and well-tailored systems. Mouse models in which this pathway has been genetically modified have been essential in understanding the role that this pathway plays in the tumorigenesis process. Here, we review cancer mouse models in which the PI3K/AKT pathway has been genetically modified.

Inhibition of mammalian target of rapamycin with rapamycin reverses hypertrophic cardiomyopathy in mice with cardiomyocyte-specific knockout of PTEN

The role of phosphatase and tensin homolog deleted from chromosome 10 (PTEN) in the maintenance of cardiac homeostasis still remains controversial. This study was designed to evaluate the role of cardiomyocyte-specific PTEN in the maintenance of cardiac homeostasis and the underlying mechanisms involved with a focus on autophagy, an evolutionarily conserved pathway for protein degradation. Cardiomyocyte-specific PTEN((flox/flox))/α-myosin heavy chain Cre mice, henceforth referred to as CM-PTENKO, were generated by crossing the floxed PTEN mice with α-myosin heavy chain Cre mice driven by a Cre recombinase promoter. The adult PTEN(-/-) mice displayed the phenotype of established hypertrophic cardiomyopathy, including unfavorable geometric, functional, and histological changes. Furthermore, cardiomyocyte-specific PTEN knockout mice exhibited increased cardiac mammalian target of rapamycin although suppressed autophagy. Treatment with rapamycin (2 mg/kg per day, IP), an inhibitor of mammalian target of rapamycin, for 1 month effectively reversed the established hypertrophic cardiomyopathy in CM-PTENKO mice. With rapamycin treatment, autophagy activity was significantly restored in the heart of CM-PTENKO mice. Taken together, our results demonstrate an essential role for cardiomyocyte PTEN in maintaining cardiac homeostasis under physiological condition. Cardiomyocyte-specific deletion of PTEN results in the development of hypertrophic cardiomyopathy possibly through a mechanism associated with mammalian target of rapamycin hyperactivation and autophagy suppression.

Manipulation of cardiac phosphatidylinositol 3-kinase (PI3K)/Akt signaling by apoptosis regulator through modulating IAP expression (ARIA) regulates cardiomyocyte death during doxorubicin-induced cardiomyopathy

PI3K/Akt signaling plays an important role in the regulation of cardiomyocyte death machinery, which can cause stress-induced cardiac dysfunction. Here, we report that apoptosis regulator through modulating IAP expression (ARIA), a recently identified transmembrane protein, regulates the cardiac PI3K/Akt signaling and thus modifies the progression of doxorubicin (DOX)-induced cardiomyopathy. ARIA is highly expressed in the mouse heart relative to other tissues, and it is also expressed in isolated rat cardiomyocytes. The stable expression of ARIA in H9c2 cardiac muscle cells increased the levels of membrane-associated PTEN and subsequently reduced the PI3K/Akt signaling and the downstream phosphorylation of Bad, a proapoptotic BH3-only protein. When challenged with DOX, ARIA-expressing H9c2 cells exhibited enhanced apoptosis, which was reversed by the siRNA-mediated silencing of Bad. ARIA-deficient mice exhibited normal heart morphology and function. However, DOX-induced cardiac dysfunction was significantly ameliorated in conjunction with reduced cardiomyocyte death and cardiac fibrosis in ARIA-deficient mice. Phosphorylation of Akt and Bad was substantially enhanced in the heart of ARIA-deficient mice even after treatment with DOX. Moreover, repressing the PI3K by cardiomyocyte-specific expression of dominant-negative PI3K (p110α) abolished the cardioprotective effects of ARIA deletion. Notably, targeted activation of ARIA in cardiomyocytes but not in endothelial cells reduced the cardiac PI3K/Akt signaling and exacerbated the DOX-induced cardiac dysfunction. These studies, therefore, revealed a previously undescribed mode of manipulating cardiac PI3K/Akt signaling by ARIA, thus identifying ARIA as an attractive new target for the prevention of stress-induced myocardial dysfunction.

Protein tyrosine phosphatase variants in human hereditary disorders and disease susceptibilities

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism to steer normal development and physiological functioning of multicellular organisms. Phosphotyrosine dephosphorylation is exerted by members of the super-family of protein tyrosine phosphatase (PTP) enzymes and many play such essential roles that a wide variety of hereditary disorders and disease susceptibilities in man are caused by PTP alleles. More than two decades of PTP research has resulted in a collection of PTP genetic variants with corresponding consequences at the molecular, cellular and physiological level. Here we present a comprehensive overview of these PTP gene variants that have been linked to disease states in man. Although the findings have direct bearing for disease diagnostics and for research on disease etiology, more work is necessary to translate this into therapies that alleviate the burden of these hereditary disorders and disease susceptibilities in man.

Conditionally ablated Pten in prostate basal cells promotes basal-to-luminal differentiation and causes invasive prostate cancer in mice

Prostate glands comprise two major epithelial cell types: luminal and basal. Luminal cells have long been considered the cellular origin of prostate cancer (CaP). However, recent evidence from a prostate regeneration assay suggests that prostate basal cells can also give rise to CaP. Here, we characterize Pten-deficient prostate lesions arising from keratin 5-expressing basal cells in a temporally controlled system in mice. Pten-deficient prostate lesions arising from basal cells exhibited luminal phenotypes with higher invasiveness, and the cell fate of Pten-deficient basal cells was traced to neoplastic luminal cells. After temporally ablating Pten in keratin 8-expressing luminal cells, luminal-derived Pten-deficient prostate tumors exhibited slower disease progression, compared with basal-derived tumors, within 13 weeks after Pten ablation. Cellular proliferation was significantly increased in basal-derived versus luminal-derived Pten-deficient prostate lesions. Increased tumor invasion into the smooth muscle layer and aberrantly regulated aggressive signatures (Smad4 and Spp1) were identified exclusively in basal-derived Pten-deficient lesions. Interestingly, p63-expressing cells, which represent basal stem and progenitor cells of basal-derived Pten-deficient prostate lesions, were significantly increased, relative to cells of the luminal-derived prostate lesion. Furthermore, castration did not suppress cellular proliferation of either basal-derived or luminal-derived Pten-deficient prostate tumors. Taken together, our data suggest that, although prostate malignancy can originate from both basal and luminal populations, these two populations differ in aggressive potential.

Conditional deletion of the Pten gene in the mouse prostate induces prostatic intraepithelial neoplasms at early ages but a slow progression to prostate tumors

The PTEN tumor suppressor gene is frequently inactivated in human prostate cancer. Using Osr1 (odd skipped related 1)-Cre mice, we generated a novel conditional Pten knockout mouse strain, Pten^LoxP:Osr1-Cre. Conditional biallelic and monoallelic Pten knockout mice were viable. Deletion of Pten expression was detected in the prostate of Pten^LoxP/LoxP:Osr1-Cre mice as early as 2 weeks of age. Intriguingly, Pten^LoxP/LoxP:Osr1-Cre mice develop high-grade prostatic intraepithelial neoplasms (PINs) with high penetrance as early as one-month of age, and locally invasive prostatic tumors after 12-months of age. Pten^LoxP/+:Osr1-Cre mice show only mild oncogenic changes after 8-weeks of age. Castration of Pten^LoxP/LoxP:Osr1-Cre mice shows no significant regression of prostate tumors, although a shift of androgen receptor (AR) staining from the nuclei to cytoplasm is observed in Pten null tumor cells of castrated mice. Enhanced Akt activity is observed in Pten null tumor cells of castrated Pten^LoxP/LoxP:Osr1-Cre. This study provides a novel mouse model that can be used to investigate a primary role of Pten in initiating oncogenic transformation in the prostate and to examine other genetic and epigenetic changes that are required for tumor progression in the mouse prostate.

Oncophagy: harnessing regulation of autophagy in cancer therapy

Autophagy is an increasingly well-characterised process of cell component auto-digestion and recycling thought necessary for cellular subsistence. As we gain a more thorough understanding of the mechanisms underlying autophagy, its relevance to human disease and therapeutic potential are being clarified. This review summarises the evidence implicating autophagy in the pathogenesis and potential treatment of malignant disease. In addition, we explore the molecular role of microRNAs as key regulators in what we propose should now become known as 'oncophagy'.

Upregulation of stromal cell-derived factor by IL-17 and IL-18 via a phosphatidylinositol 3-kinase-dependent pathway

Th17 cells that produce interleukin (IL)-17 play a key role in the pathogenesis of autoimmune inflammation. Among the various cytokines that are involved in the IL-17 pathway, members of the IL-1β family, including IL-18, have recently gained attention. In this study, we stimulated synovial fibroblasts with a combination of IL-17 and IL-18 and quantified their stromal cell-derived factor-1 (SDF-1) production by enzyme-linked immunosorbent assay and their transcript levels by reverse transcription-polymerase chain reaction. Both IL-17 and IL-18 significantly increased the level of SDF-1, not only individually but also synergistically (P< 0.05). The synergism was effectively suppressed by anti-IL-17 and -IL-18 antibodies, and a PI3K inhibitor. To the best of our knowledge, this is the first report of PI3K-dependent synergism between IL-18 and IL-17, and this work adds a novel perspective of the role of IL-18 in immune regulation. The individual effects of these two cytokines, and their interactions, suggest an interrelationship between the IL-1 family and IL-17.

Regulation of axonal growth and neuromuscular junction formation by neuronal phosphatase and tensin homologue signaling

Axonal growth and synaptogenesis are sequential events of neuronal development. Phosphatase and tensin homologue (PTEN) is expressed in motor neurons, and its disruption leads to continued axonal extension, even upon muscle contact, leading to synaptogenic suppression. Thus PTEN is involved in target-mediated cessation of axonal growth and subsequent synaptic differentiation.

During the development of the vertebrate neuromuscular junction (NMJ), motor axon tips stop growing after contacting muscle and transform into presynaptic terminals that secrete the neurotransmitter acetylcholine and activate postsynaptic ACh receptors (AChRs) to trigger muscle contraction. The neuron-intrinsic signaling that retards axonal growth to facilitate stable nerve–muscle interaction and synaptogenesis is poorly understood. In this paper, we report a novel function of presynaptic signaling by phosphatase and tensin homologue (PTEN) in mediating a growth-to-synaptogenesis transition in neurons. In Xenopus nerve–muscle cocultures, axonal growth speed was halved after contact with muscle, when compared with before contact, but when cultures were exposed to the PTEN blocker bisperoxo (1,10-phenanthroline) oxovanadate, axons touching muscle grew ∼50% faster than their counterparts in control cultures. Suppression of neuronal PTEN expression using morpholinos or the forced expression of catalytically inactive PTEN in neurons also resulted in faster than normal axonal advance after contact with muscle cells. Significantly, interference with PTEN by each of these methods also led to reduced AChR clustering at innervation sites in muscle, indicating that disruption of neuronal PTEN signaling inhibited NMJ assembly. We thus propose that PTEN-dependent slowing of axonal growth enables the establishment of stable nerve–muscle contacts that develop into NMJs.

Testosterone improves the transition of primary oocytes in artificial maturation eels (Anguilla japonica) by altering ovarian PTEN expression

In mammals, androgens appear to enhance the development of primary ovarian follicles, but PI3K (phosphoinositide 3-kinases) pathway is well recognized as one of the critical pathways in early follicular development. Roles of the PI3K were revealed by deletion of PTEN (phosphatase and tensin homolog on chromosome 10). PTEN is demonstrated to play an important role in the early stage of follicle development. In the Japanese eel, two forms of PTEN have been cloned, but what their functions on the development of early ovarian follicles are still not clear. The natural blockage and inducible of ovarian development was a benefit to address this question in the eel. Testosterone (T) shows to ameliorate the early ovarian development in the eel. The aims of this study were to elucidate the two forms of PTEN by cellular and physiological criteria and to study the effects of T on the ovarian PTEN production in the exogenous pituitary extracts-stimulated eel. Our results suggested that two forms of PTEN are existing in the Japanese eel, and eel ovarian development corresponded to the decrease in ovarian PTEN expression, vice versa. In addition, the supplement of T on eel early ovarian development can be attributed to its PTEN inhibitor role.

JNK3 maintains expression of the insulin receptor substrate 2 (IRS2) in insulin-secreting cells: functional consequences for insulin signaling

We have recently shown that silencing of the brain/islet specific c-Jun N-terminal Kinase3 (JNK3) isoform enhances both basal and cytokine-induced beta-cell apoptosis, whereas silencing of JNK1 or JNK2 has opposite effects. While it is known that JNK1 or JNK2 may promote apoptosis by inhibiting the activity of the pro-survival Akt pathway, the effect of JNK3 on Akt has not been documented. This study aims to determine the involvement of individual JNKs and specifically JNK3 in the regulation of the Akt signaling pathway in insulin-secreting cells. JNK3 silencing strongly decreases Insulin Receptor Substrate 2 (IRS2) protein expression, and blocks Akt2 but not Akt1 activation by insulin, while the silencing of JNK1 or JNK2 activates both Akt1 and Akt2. Concomitantly, the silencing of JNK1 or JNK2, but not of JNK3, potently phosphorylates the glycogen synthase kinase3 (GSK3β). JNK3 silencing also decreases the activity of the transcription factor Forkhead BoxO3A (FoxO3A) that is known to control IRS2 expression, in addition to increasing c-Jun levels that are known to inhibit insulin gene expression. In conclusion, we propose that JNK1/2 on one hand and JNK3 on the other hand, have opposite effects on insulin-signaling in insulin-secreting cells; JNK3 protects beta-cells from apoptosis and dysfunction mainly through maintenance of a normal IRS2 to Akt2 signaling pathway. It seems that JNK3 mediates its effects mainly at the transcriptional level, while JNK1 or JNK2 appear to mediate their pro-apoptotic effect in the cytoplasm.

AMP-activated protein kinase (AMPK) controls the aging process via an integrated signaling network

Efficient control of energy metabolic homeostasis, enhanced stress resistance, and qualified cellular housekeeping are the hallmarks of improved healthspan and extended lifespan. AMPK signaling is involved in the regulation of all these characteristics via an integrated signaling network. Many studies with lower organisms have revealed that increased AMPK activity can extend the lifespan. Experiments in mammals have demonstrated that AMPK controls autophagy through mTOR and ULK1 signaling which augment the quality of cellular housekeeping. Moreover, AMPK-induced stimulation of FoxO/DAF-16, Nrf2/SKN-1, and SIRT1 signaling pathways improves cellular stress resistance. Furthermore, inhibition of NF-κB signaling by AMPK suppresses inflammatory responses. Emerging studies indicate that the responsiveness of AMPK signaling clearly declines with aging. The loss of sensitivity of AMPK activation to cellular stress impairs metabolic regulation, increases oxidative stress and reduces autophagic clearance. These age-related changes activate innate immunity defence, triggering a low-grade inflammation and metabolic disorders. We will review in detail the signaling pathways of this integrated network through which AMPK controls energy metabolism, autophagic degradation and stress resistance and ultimately the aging process.

Molecular machinery of autophagy and its implication in cancer

Autophagy is an intracellular lysosome-dependent catabolic process that is indispensable for maintaining cellular homeostasis through the turnover and elimination of defective or redundant proteins and damaged or aged organelles. Recent studies suggest that autophagy may be closely associated with tumorigenesis and the response of tumor cells to chemotherapeutic drugs. This article reviews recent advances in understanding the molecular mechanisms underlying the regulation of autophagy and the role of autophagy in oncogenesis and anticancer therapy. It is paradoxical that autophagy acts as a mechanism for tumor suppression and contributes to the survival of tumors. In addition, whether autophagy in response to chemotherapies results in cell death or instead protects cancer cells from death is complicated, depending on the nature of the cancer and the drug.

Attenuation of microRNA-22 derepressed PTEN to effectively protect rat cardiomyocytes from hypertrophy

Cardiac hypertrophy, which is characterized by the enlargement of cell size, reactivation of fetal genes, remains one of the most important triggers to heart failure. Increasing evidence shows that microRNA (miRNA) is extensively involved in the pathogenesis of cardiac hypertrophy. But the effects of miRNAs on cardiomyocyte hypertrophy have not been completely solved yet. Here, we showed that a collection of miRNAs was aberrantly expressed in hypertrophic cardiomyocytes induced by phenylephrine (PE) or angiotensin II (Ang II). Among them, miR-22 was the most strikingly up-regulated miRNA. To investigate the role of miR-22 in hypertrophy, both over-expression and knock-down assays were performed on cardiomyocytes. The results showed that up-regulation of miR-22 significantly increased the cell size and markedly influenced the expression of hypertrophic markers, including induction of nppa and reduction of myh6. In contrast, reduction of miR-22 level attenuated either PE- or Ang II-induced hypertrophic reaction. Furthermore, several genes, including PTEN, were identified as potential targets of miR-22 by bioinformatic algorithms. Using luciferase analysis, miR-22 could significantly suppress the luciferase activity of reporter fused with 3' untranslated region of PTEN mRNA. Furthermore, up-regulation of miR-22 could suppress the protein level of PTEN and reduction of miR-22 level markedly increased the protein level of PTEN in cardiomyocytes by Western blot analysis, suggesting that the contribution of miR-22 to cardiomyocyte hypertrophy may be partially through targeting PTEN. Taken together, miRNAs were dynamically regulated in cardiomyocyte hypertrophy and attenuation of miR-22 in rat cardiomyocytes efficiently protected from hypertrophic effects through derepressing PTEN.

PTEN loss defines a TGF-β-induced tubule phenotype of failed differentiation and JNK signaling during renal fibrosis

We investigated the signaling basis for tubule pathology during fibrosis after renal injury. Numerous signaling pathways are activated physiologically to direct tubule regeneration after acute kidney injury (AKI) but several persist pathologically after repair. Among these, transforming growth factor (TGF)-β is particularly important because it controls epithelial differentiation and profibrotic cytokine production. We found that increased TGF-β signaling after AKI is accompanied by PTEN loss from proximal tubules (PT). With time, subpopulations of regenerating PT with persistent loss of PTEN (phosphate and tension homolog) failed to differentiate, became growth arrested, expressed vimentin, displayed profibrotic JNK activation, and produced PDGF-B. These tubules were surrounded by fibrosis. In contrast, PTEN recovery was associated with epithelial differentiation, normal tubule repair, and less fibrosis. This beneficial outcome was promoted by TGF-β antagonism. Tubule-specific induction of TGF-β led to PTEN loss, JNK activation, and fibrosis even without prior AKI. In PT culture, high TGF-β depleted PTEN, inhibited differentiation, and activated JNK. Conversely, TGF-β antagonism increased PTEN, promoted differentiation, and decreased JNK activity. Cre-Lox PTEN deletion suppressed differentiation, induced growth arrest, and activated JNK. The low-PTEN state with JNK signaling and fibrosis was ameliorated by contralateral nephrectomy done 2 wk after unilateral ischemia, suggesting reversibility of the low-PTEN dysfunctional tubule phenotype. Vimentin-expressing tubules with low-PTEN and JNK activation were associated with fibrosis also after tubule-selective AKI, and with human chronic kidney diseases of diverse etiology. By preventing tubule differentiation, the low-PTEN state may provide a platform for signals initiated physiologically to persist pathologically and cause fibrosis after injury.

Creating a pro-survival and anti-inflammatory phenotype by modulation of acetylation in models of hemorrhagic and septic shock

Shock, regardless of etiology, is characterized by decreased tissue perfusion resulting in cell death, organ dysfunction, and poor survival. Current therapies largely focus on restoring tissue perfusion through resuscitation but have failed to address the specific cellular dysfunction caused by shock. Acetylation is rapidly emerging as a key mechanism that regulates the expression of numerous genes (epigenetic modulation through activation of nuclear histone proteins), as well as functions of multiple cytoplasmic proteins involved in key cellular functions such as cell survival, repair/healing, signaling, and proliferation. Cellular acetylation can be increased immediately through the administration of histone deacetylase inhibitors (HDACI). A series of studies have been performed using: (1) cultured cells; (2) single-organ ischemia-reperfusion injury models; (3) rodent models of lethal septic and hemorrhagic shock; (4) swine models of lethal hemorrhagic shock and multi-organ trauma; and (5) tissues from severely injured trauma patients, to fully characterize the changes in acetylation that occur following lethal insults and in response to treatment with HDACI. These data demonstrate that: (1) shock causes a decrease in acetylation of nuclear and cytoplasmic proteins; (2) hypoacetylation can be rapidly reversed through the administration of HDACI; (3) normalization of acetylation prevents cell death, decreases inflammation, attenuates activation of pro-apoptotic pathways, and augments pro-survival pathways; (4) the effect of HDACI significantly improves survival in lethal models of septic shock, hemorrhagic shock, and complex poly-trauma without need for conventional fluid resuscitation or blood transfusion; and (5) improvement in survival is not due to better resuscitation but due to an enhanced ability of cells to tolerate lethal insults.As different models of hemorrhagic or septic shock have specific strengths and limitations, this chapter will summarize our attempts to create "pro-survival and anti-inflammatory phenotype" in various models of hemorrhagic shock and septic shock.

Modulation of acetylation: creating a pro-survival and anti-inflammatory phenotype in lethal hemorrhagic and septic shock

Histone deacetylases (HDACs) play a key role in homeostasis of protein acetylation in histone and nonhistone proteins and in regulating fundamental cellular activities. In this paper we review and discuss intriguing recent developments in the use of histone deacetylase inhibitors (HDACIs) to combat some critical conditions in an animal model of hemorrhagic and septic shock. HDACIs have neuroprotective, cardioprotective, renal-protective, and anti-inflammatory properties; survival improvements have been significantly shown in these models. We discuss the targets and mechanisms underlying these effects of HDACIs and comment on the potential new clinical applications for these agents in the future. This paper highlights the emerging roles of HDACIs as acetylation modulators in models of hemorrhagic and septic shock and explains some contradictions encountered in previous studies.

Decreased expression and androgen regulation of the tumor suppressor gene INPP4B in prostate cancer

Patients with metastatic prostate cancer who undergo androgen-ablation therapy invariably relapse and develop incurable castration-resistant disease. Activation of the prosurvival Akt pathway accompanies androgen ablation. We discovered that the androgen receptor induces the expression of the tumor suppressor inositol polyphosphate 4-phosphatase type II (INPP4B) but not PTEN in prostate cancer cells. Optimal induction of INPP4B by an androgen receptor required the expression of the transcriptional coactivator NCoR. INPP4B dephosphorylates phosphatidylinositol-3, 4-bisphosphate, which leads to reduced phosphorylation and activity of Akt. In support of a key role for INPP4B in Akt control, INPP4B depletion activated Akt and increased cellular proliferation. The clinical significance of INPP4B in androgen-dependent prostate cancers was determined in normal or primary tumor prostate tissues derived from radical prostatectomy specimens. In primary tumors, the expression of both INPP4B and PTEN was substantially reduced compared with normal tissue. Further, the decreased expression of INPP4B reduced the time to biochemical recurrence. Thus, androgen ablation can activate the Akt pathway via INPP4B downregulation, thereby mitigating the antitumor effects of androgen ablation. Our findings reinforce the concept that patients undergoing androgen ablation may benefit from Akt-targeting therapies.

Molecular underpinning of B-cell anergy

A byproduct of the largely stochastic generation of a diverse B-cell specificity repertoire is production of cells that recognize autoantigens. Indeed, recent studies indicate that more than half of the primary repertoire consists of autoreactive B cells that must be silenced to prevent autoimmunity. While this silencing can occur by multiple mechanisms, it appears that most autoreactive B cells are silenced by anergy, wherein they populate peripheral lymphoid organs and continue to express unoccupied antigen receptors yet are unresponsive to antigen stimulation. Here we review molecular mechanisms that appear operative in maintaining the antigen unresponsiveness of anergic B cells. In addition, we present new data indicating that the failure of anergic B cells to mobilize calcium in response to antigen stimulation is not mediated by inactivation of stromal interacting molecule 1, a critical intermediary in intracellular store depletion-induced calcium influx.

The conundrum of inhibitory signaling by ITAM-containing immunoreceptors: potential molecular mechanisms

Immunoreceptor signals must be appropriately transduced and regulated to achieve effective immunity while controlling inflammation and autoimmunity. It is generally held that these processes are mediated by the interplay of distinct activating and inhibitory receptors via conserved activating (ITAM) and inhibitory (ITIM) signaling motifs. However, recent evidence indicates that under certain conditions incomplete phosphorylation of ITAM tyrosines leads to inhibitory signaling. This new regulatory function of ITAMs has been termed ITAMi (inhibitory ITAM). Here we discuss the potential molecular mechanisms of inhibitory signaling by ITAM-containing receptors.

A limited role for PI(3,4,5)P3 regulation in controlling skeletal muscle mass in response to resistance exercise

Background

Since activation of the PI3K/(protein kinase B; PKB/akt) pathway has been shown to alter muscle mass and growth, the aim of this study was to determine whether resistance exercise increased insulin like growth factor (IGF) I/phosphoinositide 3-kinase (PI3K) signalling and whether altering PI(3,4,5)P₃ metabolism genetically would increase load induced muscle growth.

Methodology/Principal Findings

Acute and chronic resistance exercise in wild type and muscle specific PTEN knockout mice were used to address the role of PI(3,4,5)P₃ regulation in the development of skeletal muscle hypertrophy. Acute resistance exercise did not increase either IGF-1 receptor phosphorylation or IRS1/2 associated p85. Since insulin/IGF signalling to PI3K was unchanged, we next sought to determine whether inactivation of PTEN played a role in load-induced muscle growth. Muscle specific knockout of PTEN resulted in small but significant increases in heart (PTEN^+/+  = 5.00±0.02 mg/g, PTEN^−/−  = 5.50±0.09 mg/g), and TA (PTEN^+/+  = 1.74±0.04 mg/g, PTEN^−/−  = 1.89 ±0.03) muscle mass, while the GTN, SOL, EDL and PLN remain unchanged. Following ablation, hypertrophy of the PLN, SOL or EDL muscles was similar between PTEN^−/− and PTEN^+/+ animals. Even though there were some changes in overload-induced PKB and S6K1 phosphorylation, 1 hr following acute resistance exercise there was no difference in the phosphorylation state of S6K1 Thr389 between genotypes.

Conclusions/Significance

These data suggest that physiological loading does not lead to the enhanced activation of the PI3K/PKB/mTORC1 axis and that neither PI3K activation nor PTEN, and by extension PI(3,4,5)P₃ levels, play a significant role in adult skeletal muscle growth.

Cell cycle control of mammalian neural stem cells: putting a speed limit on G1

The potential to increase unlimitedly in number and to generate differentiated cell types is a key feature of somatic stem cells. Within the nervous system, cellular and environmental determinants tightly control the expansion and differentiation of neural stem cells. Importantly, a number of studies have indicated that changes in cell cycle length can influence development and physiopathology of the nervous system, and might have played a role during evolution of the mammalian brain. Specifically, it has been suggested that the length of G1 can directly influence the differentiation of neural precursors. This has prompted the proposal of a model to explain how manipulation of G1 length can be used to expand neural stem cells. If validated in non-neural systems, this model might provide the means to control the proliferation vs. differentiation of somatic stem cells, which will represent a significant advance in the field.

Evidence that inositol polyphosphate 4-phosphatase type II is a tumor suppressor that inhibits PI3K signaling

We report that knocking down the expression of inositol polyphosphate 4-phosphatase type II (INPP4B) in human epithelial cells, like knockdown of PTEN, resulted in enhanced Akt activation and anchorage-independent growth and enhanced overall motility. In xenograft experiments, overexpression of INPP4B resulted in reduced tumor growth. INPP4B preferentially hydrolyzes phosphatidylinositol-3,4-bisphosphate (PI(3,4)P(2)) with no effect on phosphatidylinositol-3.4.5-triphosphate (PI(3,4,5)P(3)), suggesting that PI(3,4)P(2) and PI(3,4,5)P(3) may cooperate in Akt activation and cell transformation. Dual knockdown of INPP4B and PTEN resulted in cellular senescence. Finally, we found loss of heterozygosity (LOH) at the INPP4B locus in a majority of basal-like breast cancers, as well as in a significant fraction of ovarian cancers, which correlated with lower overall patient survival, suggesting that INPP4B is a tumor suppressor.

Cardiac regulation by phosphoinositide 3-kinases and PTEN

The diverse effects mediated by PI3K/PTEN (phosphoinositide 3-kinase/phosphatase and tensin homologue deleted on chromosome 10) signalling in the heart clearly support an important biological and pathophysiological role for this signalling cascade. PI3Ks are a family of evolutionarily conserved lipid kinases that mediate many cellular responses to physiological and pathophysiological stimuli. Class I PI3K can be activated by either receptor tyrosine kinase/cytokine receptor activation (class IA) or G-protein-coupled receptors (class IB), leading to the generation of phosphatidyl inositol (3,4,5)P3 and recruitment and activation of Akt/protein kinase B, 3'-phosphoinositide-dependent kinase-1 (PDK1), or monomeric G-proteins, and phosphorylation of a wide range of downstream targets including glycogen synthase kinase 3beta (GSK3beta), mTOR (mammalian target of rapamycin), p70S6 kinase, endothelial nitric oxide synthase, and several anti-apoptotic effectors. Class IA (PI3Kalpha, beta, and delta) and class IB (PI3Kgamma) PI3Ks mediate distinct phenotypes in the heart under negative control by the 3'-lipid phosphatase PTEN, which dephosphorylates PtdIns(3,4,5)P3 to generate PtdIns(4,5)P2. PI3Kalpha, PI3Kgamma, and PTEN are expressed in cardiomyocytes, fibroblasts, endothelial cells, and vascular smooth muscle cells, where they modulate cell survival, hypertrophy, contractility, metabolism, and mechanotransduction. The PI3K/PTEN signalling pathways are involved in a wide variety of diseases including myocardial hypertrophy and contractility, heart failure, and preconditioning. In this review, we discuss the signalling pathways mediated by PI3K class I isoforms and PTEN and their roles in cardiac structure and function.

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.

Effects of Akt signaling on nuclear reprogramming

Reprogramming of the epigenetic state from differentiated to pluripotent cells can be attained by cell fusion of differentiated somatic cells with embryonic stem (ES) cells or transfer of the nucleus of a differentiated cell into an enucleated oocyte. Activation of Akt signaling is sufficient to maintain pluripotency of ES cells and promotes derivation of embryonic germ (EG) cells from primordial germ cells (PGCs). Here we analyzed the effects of Akt signaling on somatic cell nuclear reprogramming after cell fusion and nuclear transfer. We found that forced activation of Akt signaling stimulated reprogramming after cell fusion of ES cells with thymocytes or mouse embryonic fibroblasts. These hybrid cells showed ES cell characteristics, including in vitro and in vivo differentiation capacity. In contrast, Akt signaling significantly reduced the efficiency of reprogramming with nuclear transfer. Our results demonstrate that Akt signaling plays important roles on the nuclear reprogramming of somatic cells.

Conditional loss of uterine Pten unfailingly and rapidly induces endometrial cancer in mice

Etiology of endometrial cancer (EMC) is not fully understood. Animal models with rapidly and spontaneously developing EMC will help explore mechanisms of cancer initiation and progression. Pten(+/-) mice are currently being used as a model to study EMC. These females develop atypical endometrial hyperplasia of which approximately 20% progresses to EMC. In addition, tumors develop in other organs, complicating the use of this model to specifically study EMC. Here, we show that conditional deletion of endometrial Pten results in EMC in all female mice as early as age 1 month with myometrial invasion occurring by 3 months. In contrast, conditional deletion of endometrial p53 had no phenotype within this time frame. Whereas mice with endometrial Pten deletion had a life span of approximately 5 months, mice with combined deletion of endometrial Pten and p53 had a shorter life span with an exacerbated disease state. Such rapid development of EMC from homozygous loss of endometrial Pten suggests that this organ is very sensitive to this tumor suppressor gene for tumor development. All lesions at early stages exhibited elevated Cox-2 and phospho-Akt levels, hallmarks of solid tumors. More interestingly, levels of two microRNAs miR-199a(*) and miR-101a that posttranscriptionally inhibit Cox-2 expression were down-regulated in tumors in parallel with Cox-2 up-regulation. This mouse model in which the loxP-Cre system has been used to delete endometrial Pten and/or p53 allows us to study in detail the initiation and progression of EMC. These mouse models have the added advantage because they mimic several features of human EMC.

Total synthesis studies on macrocyclic pipecolic acid natural products: FK506, the antascomicins and rapamycin

This chapter derives its inspiration from the challenges presented to total synthesis chemists, by a particular group of macrocyclic pipecolic acid natural products. Although there is considerable emphasis on the completed syntheses of the main characters (FK506 (1), the antascomycins (4 and 5) and rapamycin (7)), the overall complexity of the molecular problem has stimulated a wealth of new knowledge, including the development of novel strategies and the invention of new synthetic methods. The ingenious and innovative approaches to these targets have enabled new generations of analogues, and provided material to further probe the biology of these fascinating molecules. With pharmaceutical application as an immunosuppressant, as well as potential use for the treatment of cancer and neurodegenerative diseases, this family of natural products continues to inspire new and interesting science while providing solutions to healthcare problems of the world.

Identification of Pax5 target genes in early B cell differentiation

The transcription factor Pax5 is essential for B cell commitment in the mouse, where it represses lineage-inappropriate gene expression while simultaneously activating the B cell gene expression program. In this study we have performed a global gene expression screen of wild-type and Pax5-deficient pro-B cells in an attempt to identify the crucial Pax5 targets in early B lymphopoiesis. These studies have identified 109 Pax5 targets comprising 61% activated and 39% repressed genes. Interestingly, Pax5 directly regulates the genes encoding a number of transcription factors that are required at the pre-B cell stage of differentiation, including Irf8, Spib, and Ikzf3 (Aiolos), suggesting that a key function of Pax5 is to activate secondary transcription factors that further reinforce the B cell program. Pax5 is also required for the expression of many genes known to be involved in adhesion and signaling, indicating that Pax5 modulates the homing and or migration properties of B cell progenitors. Finally, Pax5 also represses a cohort of genes that are involved in multiple biological processes, many of which are not typically associated with B cells. These include the repression of the adhesion molecule Embigin, which is expressed in bone marrow progenitors, T cells, and myeloid cells but is specifically repressed by Pax5 in B cells.