Nuclear PTEN controls DNA repair and sensitivity to genotoxic stress

PTEN Methylation by NSD2 Controls Cellular Sensitivity to DNA Damage

The function of PTEN in the cytoplasm largely depends on its lipid-phosphatase activity, though which it antagonizes the PI3K-AKT oncogenic pathway. However, molecular mechanisms underlying the role of PTEN in the nucleus remain largely elusive. Here, we report that DNA double-strand breaks (DSB) promote PTEN interaction with MDC1 upon ATM-dependent phosphorylation of T/S398-PTEN. Importantly, DNA DSBs enhance NSD2 (MMSET/WHSC1)-mediated dimethylation of PTEN at K349, which is recognized by the tudor domain of 53BP1 to recruit PTEN to DNA-damage sites, governing efficient repair of DSBs partly through dephosphorylation of γH2AX. Of note, inhibiting NSD2-mediated methylation of PTEN, either through expressing methylation-deficient PTEN mutants or through inhibiting NSD2, sensitizes cancer cells to combinatorial treatment with a PI3K inhibitor and DNA-damaging agents in both cell culture and in vivo xenograft models. Therefore, our study provides a novel molecular mechanism for PTEN regulation of DSB repair in a methylation- and protein phosphatase-dependent manner. SIGNIFICANCE: NSD2-mediated dimethylation of PTEN is recognized by the 53BP1 tudor domain to facilitate PTEN recruitment into DNA-damage sites, governing efficient repair of DNA DSBs. Importantly, inhibiting PTEN methylation sensitizes cancer cells to combinatorial treatment with a PI3K inhibitor combined with DNA-damaging agents in both cell culture and in vivo xenograft models.This article is highlighted in the In This Issue feature, p. 1143.

Precise definition of PTEN C-terminal epitopes and its implications in clinical oncology

Anti-PTEN monoclonal antibodies (mAb) are arising as important tools for immunohistochemistry (IHC) and protein quantification routine analysis in clinical oncology. Although an effort has been made to document the reliability of tumor tissue section immunostaining by anti-PTEN mAb, and to standardize their IHC use in research and in the clinical practice, the precise topological and biochemical definition of the epitope recognized by each mAb has been conventionally overlooked. In this study, six commercial anti-PTEN mAb have been validated and characterized for sensitivity and specificity by IHC and FISH, using a set of prostate and urothelial bladder tumor specimens, and by immunoblot, using PTEN positive and PTEN negative human cell lines. Immunoblot precise epitope mapping, performed using recombinant PTEN variants and mutations, revealed that all mAb recognized linear epitopes of 6–11 amino acid length at the PTEN C-terminus. Tumor-associated or disease-associated mutations at the PTEN C-terminus did not affect subcellular localization or PIP3 phosphatase activity of PTEN in cells, although resulted in specific loss of reactivity for some mAb. Furthermore, specific mimicking-phosphorylation mutations at the PTEN C-terminal region also abolished binding of specific mAb. Our study adds new evidence on the relevance of a precise epitope mapping in the validation of anti-PTEN mAb for their use in the clinics. This will be substantial to provide a more accurate diagnosis in clinical oncology based on PTEN protein expression in tumors and biological fluids.

The Tumor Immune Contexture of Prostate Cancer

One in seven men in North America is expected to be diagnosed with prostate cancer (PCa) during their lifetime (1, 2). While a wide range of treatment options including surgery, radiation, androgen deprivation and chemotherapy have been in practice for the last few decades, there are limited treatment options for metastatic and treatment resistant disease. Immunotherapy targeting T-cell associated immune checkpoints such as CTLA-4, PD-L1, and PD-1 have not yet proven to be efficacious in PCa. Tumor mutational burden, mutations in DNA damage repair genes, immune cell composition and density in combination with their spatial organization, and expression of immune checkpoint proteins are some of the factors influencing the success of immune checkpoint inhibitor therapies. The paucity of these features in PCa potentially makes them unresponsive to contemporary immune checkpoint inhibition. In this review, we highlight the hallmark events in the PCa tumor immune microenvironment and provide insights into the current state of knowledge in this field with a focus on the role of tumor cell intrinsic events that potentially regulate immune related events and determine therapeutic outcomes. We surmise that the cumulative impact of factors such as the pre-treatment immune status, PTEN expression, DNA damage repair gene mutations, and the effects of conventionally used treatments on the anti-tumor immune response should be considered in immunotherapy trial design in PCa.

Inhibition of Nuclear PTEN Tyrosine Phosphorylation Enhances Glioma Radiation Sensitivity through Attenuated DNA Repair

Ionizing radiation (IR) and chemotherapy are standard-of-care treatments for glioblastoma (GBM) patients and both result in DNA damage, however, the clinical efficacy is limited due to therapeutic resistance. We identified a mechanism of such resistance mediated by phosphorylation of PTEN on tyrosine 240 (pY240-PTEN) by FGFR2. pY240-PTEN is rapidly elevated and bound to chromatin through interaction with Ki-67 in response to IR treatment and facilitates the recruitment of RAD51 to promote DNA repair. Blocking Y240 phosphorylation confers radiation sensitivity to tumors and extends survival in GBM preclinical models. Y240F-Pten knockin mice showed radiation sensitivity. These results suggest that FGFR-mediated pY240-PTEN is a key mechanism of radiation resistance and is an actionable target for improving radiotherapy efficacy.

PTEN arginine methylation by PRMT6 suppresses PI3K-AKT signaling and modulates pre-mRNA splicing

Arginine methylation is a ubiquitous posttranslational modification that regulates critical cellular processes including signal transduction and pre-mRNA splicing. Here, we report that the tumor-suppressor PTEN is methylated by protein arginine methyltransferase 6 (PRMT6). Mass-spectrometry analysis reveals that PTEN is dimethylated at arginine 159 (R159). We found that PTEN is mutated at R159 in cancers, and the PTEN mutant R159K loses its capability to inhibit the PI3K-AKT cascade. Furthermore, PRMT6 is physically associated with PTEN, promotes asymmetrical dimethylation of PTEN, and regulates the PI3K-AKT cascade through PTEN R159 methylation. In addition, using transcriptome analyses, we found that PTEN R159 methylation is involved in modulation of pre-mRNA alternative splicing. Our results demonstrate that PTEN is functionally regulated by arginine methylation. We propose that PTEN arginine methylation modulates pre-mRNA alternative splicing and influences diverse physiologic processes.

Non-canonical role of cancer-associated mutant SEC23B in the ribosome biogenesis pathway

SEC23B is a component of coat protein complex II (COPII) vesicles that transport secretory proteins from the endoplasmic reticulum (ER) to the Golgi apparatus. Loss-of-function SEC23B mutations cause a rare form of anemia, resulting from decreased SEC23B levels. We recently identified germline heterozygous SEC23B variants as potentially cancer-predisposing. Mutant SEC23B associated with ER stress-mediated tumorigenesis, without decreased SEC23B expression. However, our understanding of the processes behind these observations remain limited. Here, we show mutant SEC23B exists within nucleoli, in addition to classical distribution at the ER/Golgi. This occurs independent of other COPII proteins and does not compromise secretory function. Mutant cells have increased ribosomal protein and translation-related gene expression, and enhanced translational capacity, in the presence of ER stress. We show that mutant SEC23B binds to UBF transcription factor, with increased UBF transcription factor binding at the ribosomal DNA promoter. Our data indicate SEC23B has potential non-canonical COPII-independent function, particularly within the ribosome biogenesis pathway, and that may contribute to the pathogenesis of cancer-predisposition.

Unique properties of PTEN-L contribute to neuroprotection in response to ischemic-like stress

Phosphatase and tensin homolog (PTEN) signalling might influence neuronal survival after brain ischemia. However, the influence of the less studied longer variant termed PTEN-L (or PTENα) has not been studied to date. Therefore, we examined the translational variant PTEN-L in the context of neuronal survival. We identified PTEN-L by proteomics in murine neuronal cultures and brain lysates and established a novel model to analyse PTEN or PTEN-L variants independently in vitro while avoiding overexpression. We found that PTEN-L, unlike PTEN, localises predominantly in the cytosol and translocates to the nucleus 10-20 minutes after glutamate stress. Genomic ablation of PTEN and PTEN-L increased neuronal susceptibility to oxygen-glucose deprivation. This effect was rescued by expression of either PTEN-L indicating that both PTEN isoforms might contribute to a neuroprotective response. However, in direct comparison, PTEN-L replaced neurons were protected against ischemic-like stress compared to neurons expressing PTEN. Neurons expressing strictly nuclear PTEN-L NLS showed increased vulnerability, indicating that nuclear PTEN-L alone is not sufficient in protecting against stress. We identified mutually exclusive binding partners of PTEN-L or PTEN in cytosolic or nuclear fractions, which were regulated after ischemic-like stress. GRB2-associated-binding protein 2, which is known to interact with phosphoinositol-3-kinase, was enriched specifically with PTEN-L in the cytosol in proximity to the plasma membrane and their interaction was lost after glutamate exposure. The present study revealed that PTEN and PTEN-L have distinct functions in response to stress and might be involved in different mechanisms of neuroprotection.

Roles of PI3K/AKT/GSK3 Pathway Involved in Psychiatric Illnesses

Psychiatric illnesses may be qualified to the cellular impairments of the function for survival or death in neurons, which may consequently appear as abnormalities in the neuroplasticity. The molecular mechanism has not been well understood, however, it seems that PI3K, AKT, GSK3, and their downstream molecules have crucial roles in the pathogenesis. Through transducing cell surviving signal, the PI3K/AKT/GSK3 pathway may organize an intracellular central network for the action of the synaptic neuroplasticity. In addition, the pathways may also regulate cell proliferation, cell migration, and apoptosis. Several lines of evidence have supported a role for this signaling network underlying the development and treatment for psychiatric illnesses. Indeed, the discovery of molecular biochemical phenotypes would represent a breakthrough in the research for effective treatment. In this review, we summarize advances on the involvement of the PI3K/AKT/GSK3 pathways in cell signaling of neuronal cells. This study may provide novel insights on the mechanism of mental disorder involved in psychiatric illnesses and would open future opportunity for contributions suggesting new targets for diagnostic and/or therapeutic procedures.

Synthetic lethality of a cell-penetrating anti-RAD51 antibody in PTEN-deficient melanoma and glioma cells

PTEN is a tumor suppressor that is highly mutated in a variety of human cancers. Recent studies have suggested a link between PTEN loss and deficiency in the non-homologous end-joining (NHEJ) pathway of DNA double strand break (DSB) repair. As a means to achieve synthetic lethality in this context, we tested the effect of 3E10, a cell-penetrating autoantibody that inhibits RAD51, a key factor in the alternative pathway of DSB repair, homology dependent repair (HDR). We report here that treatment of PTEN-deficient glioma cells with 3E10 leads to an accumulation of DNA damage causing decreased proliferation and increased cell death compared to isogenic PTEN proficient controls. Similarly, 3E10 was synthetically lethal to a series of PTEN-deficient, patient-derived primary melanoma cell populations. Further, 3E10 was found to synergize with a small molecule inhibitor of the ataxia telangiectasia and Rad3-related (ATR) protein, a DNA damage checkpoint kinase, in both PTEN-deficient glioma cells and primary melanoma cells. These results point to a targeted synthetic lethal strategy to treat PTEN-deficient cancers through a combination designed to disrupt both DNA repair and DNA damage checkpoint signaling.

Signaling control of antibody isotype switching

Class switch recombination (CSR) generates isotype-switched antibodies with distinct effector functions essential for mediating effective humoral immunity. CSR is catalyzed by activation-induced deaminase (AID) that initiates DNA lesions in the evolutionarily conserved switch (S) regions at the immunoglobulin heavy chain (Igh) locus. AID-initiated DNA lesions are subsequently converted into DNA double stranded breaks (DSBs) in the S regions of Igh locus, repaired by non-homologous end-joining to effect CSR in mammalian B lymphocytes. While molecular mechanisms of CSR are well characterized, it remains less well understood how upstream signaling pathways regulate AID expression and CSR. B lymphocytes express multiple receptors including the B cell antigen receptor (BCR) and co-receptors (e.g., CD40). These receptors may share common signaling pathways or may use distinct signaling elements to regulate CSR. Here, we discuss how signals emanating from different receptors positively or negatively regulate AID expression and CSR.

Mechanisms of PTEN loss in cancer: It's all about diversity

PTEN is a phosphatase which metabolises PIP₃, the lipid product of PI 3-Kinase, directly opposing the activation of the oncogenic PI3K/AKT/mTOR signalling network. Accordingly, loss of function of the PTEN tumour suppressor is one of the most common events observed in many types of cancer. Although the mechanisms by which PTEN function is disrupted are diverse, the most frequently observed events are deletion of a single gene copy of PTEN and gene silencing, usually observed in tumours with little or no PTEN protein detectable by immunohistochemistry. Accordingly, with the exceptions of glioblastoma and endometrial cancer, mutations of the PTEN coding sequence are uncommon (<10%) in most types of cancer. Here we review the data relating to PTEN loss in seven common tumour types and discuss mechanisms of PTEN regulation, some of which appear to contribute to reduced PTEN protein levels in cancers.

PTEN-opathies: from biological insights to evidence-based precision medicine

The tumor suppressor phosphatase and tensin homolog (PTEN) classically counteracts the PI3K/AKT/mTOR signaling cascade. Germline pathogenic PTEN mutations cause PTEN hamartoma tumor syndrome (PHTS), featuring various benign and malignant tumors, as well as neurodevelopmental disorders such as autism spectrum disorder. Germline and somatic mosaic mutations in genes encoding components of the PI3K/AKT/mTOR pathway downstream of PTEN predispose to syndromes with partially overlapping clinical features, termed the "PTEN-opathies." Experimental models of PTEN pathway disruption uncover the molecular and cellular processes influencing clinical phenotypic manifestations. Such insights not only teach us about biological mechanisms in states of health and disease, but also enable more accurate gene-informed cancer risk assessment, medical management, and targeted therapeutics. Hence, the PTEN-opathies serve as a prototype for bedside to bench, and back to the bedside, practice of evidence-based precision medicine.

Expression of PTEN-long nephritis and its effect on renal inflammation

Based on the important functions of phosphatase and tensin homolog (PTEN)-Long for renal diseases, the present study aimed to investigate the expression of PTEN-Long in patients and mice with nephritis and its effect on nephritis. Expression levels of PTEN-Long in serum of patients with nephritis, renal cell carcinoma (RCC) as well as normal controls, and in serum and renal tissues of mice were measured by western blotting. PTEN-Long knock-in and knock-out mice were constructed via the CRISPR-Cas9 technique. Intraperitoneal injection of lipopolysaccharide+renal homogenate was performed to construct a mouse nephritis model. Mice were divided into control group, model group, knock-in group and knock-out group. A Bio-Plex system was used to detect secretion of serum inflammatory factors. Expression of inflammatory factors in renal tissues of different groups was detected by reverse transcription semi-quantitative polymerase chain reaction. Hematoxylin and eosin staining was used to observe the pathological changes of renal tissue. PTEN-Long was downregulated in patients with nephritis and RCC compared with controls, whereas the expression levels of inflammatory factors were increased. PTEN-long knock-in significantly reduced the serum content and expression levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β and IL-18. PTEN-long knock-out also decreased the expression levels of TNF-α and IL-6 but exhibited no effects on expression of IL-1β and IL-18. Compared with knock-out and model groups, renal tissue inflammation was significantly reduced in knock-in group. The protein level of PTEN-Long was significantly lower in serum than in renal tissue. These findings suggest that PTEN-long can inhibit the progression of nephritis by interacting with inflammatory factors to protect kidney.

Signaling through non-membrane nuclear phosphoinositide binding proteins in human health and disease

Phosphoinositide membrane signaling is critical for normal physiology, playing well-known roles in diverse human pathologies. The basic mechanisms governing phosphoinositide signaling within the nucleus, however, have remained deeply enigmatic owing to their presence outside the nuclear membranes. Over 40% of nuclear phosphoinositides can exist in this non-membrane state, held soluble in the nucleoplasm by nuclear proteins that remain largely unidentified. Recently, two nuclear proteins responsible for solubilizing phosphoinositides were identified, steroidogenic factor-1 (SF-1; NR5A1) and liver receptor homolog-1 (LRH-1; NR5A2), along with two enzymes that directly remodel these phosphoinositide/protein complexes, phosphatase and tensin homolog (PTEN; MMAC) and inositol polyphosphate multikinase (IPMK; ipk2). These new footholds now permit the assignment of physiological functions for nuclear phosphoinositides in human diseases, such as endometriosis, nonalcoholic fatty liver disease/steatohepatitis, glioblastoma, and hepatocellular carcinoma. The unique nature of nuclear phosphoinositide signaling affords extraordinary clinical opportunities for new biomarkers, diagnostics, and therapeutics. Thus, phosphoinositide biology within the nucleus may represent the next generation of low-hanging fruit for new drugs, not unlike what has occurred for membrane phosphatidylinositol 3-kinase drug development. This review connects recent basic science discoveries in nuclear phosphoinositide signaling to clinical pathologies, with the hope of inspiring development of new therapies.

Regulation and modulation of PTEN activity

PTEN (Phosphatase and tensin homolog deleted on chromosome ten) is a tumor suppressor that is frequently mutated in most human cancers. PTEN is a lipid and protein phosphatase that antagonizes PI3K/AKT pathway through lipid phosphatase activity at the plasma membrane. More recent studies showed that, in addition to the putative role of PTEN as a PI(3,4,5)P3 3-phosphatase, it is a PI(3,4)P2 3-phosphatase during stimulation of class I PI3K signaling pathway by growth factor. Although PTEN tumor suppressor function via it's lipid phosphatase activity occurs primarily in the plasma membrane, it can also be found in the nucleus, in cytoplasmic organelles and extracellular space. PTEN has also shown phosphatase independent functions in the nucleus. PTEN can exit from the cell through exosomal export or secretion and has a tumor suppressor function in adjacent cells. PTEN has a critical role in growth, the cell cycle, protein synthesis, survival, DNA repair and migration. Understanding the regulation of PTEN function, activity, stability, localization and its dysregulation outcomes and also the intracellular and extracellular role of PTEN and paracrine role of PTEN-L in tumor cells as an exogenous therapeutic agent can help to improve clinical conceptualization and treatment of cancer.

Nuclear Excluded Autism-Associated Phosphatase and Tensin Homolog Mutations Dysregulate Neuronal Growth

BACKGROUND

Phosphatase and tensin homolog (PTEN) negatively regulates downstream protein kinase B signaling, resulting in decreased cellular growth and proliferation. PTEN is mutated in a subset of children with autism spectrum disorder (ASD); however, the mechanism by which specific point mutations alter PTEN function is largely unknown. Here, we assessed how ASD-associated single-nucleotide variations in PTEN (ASD-PTEN) affect function.

METHODS

We used viral-mediated molecular substitution of human PTEN into Pten knockout mouse neurons and assessed neuronal morphology to determine the functional impact of ASD-PTEN. We employed molecular cloning to examine how PTEN's stability, subcellular localization, and catalytic activity affect neuronal growth.

RESULTS

We identified a set of ASD-PTEN mutations displaying altered lipid phosphatase function and subcellular localization. We demonstrated that wild-type PTEN can rescue the neuronal hypertrophy, while PTEN H93R, F241S, D252G, W274L, N276S, and D326N failed to rescue this hypertrophy. A subset of these mutations lacked nuclear localization, prompting us to examine the role of nuclear PTEN in regulating neuronal growth. We found that nuclear PTEN alone is sufficient to regulate soma size. Furthermore, forced localization of the D252G and W274L mutations into the nucleus partially restores regulation of soma size.

CONCLUSIONS

ASD-PTEN mutations display decreased stability, catalytic activity, and/or altered subcellular localization. Mutations lacking nuclear localization uncover a novel mechanism whereby lipid phosphatase activity in the nucleus can regulate mammalian target of rapamycin signaling and neuronal growth.

Novel nuclear translocation of inositol polyphosphate 4-phosphatase is associated with cell cycle, proliferation and survival

Inositol polyphosphate 4 phosphatase type I enzyme (INPP4A) has a well-documented function in the cytoplasm where it terminates the phosphatidylinositol 3-kinase (PI 3-K) pathway by acting as a negative regulator. In this study, we demonstrate for the first time that INPP4A shuttles between the cytoplasm and the nucleus. Nuclear INPP4A is enzymatically active and in dynamic equilibrium between the nucleus and cytoplasm depending on the cell cycle stage, with highest amounts detected in the nucleus during the G0/G1 phase. Moreover, nuclear INPP4A is found to have direct proliferation suppressive activity. Cells constitutively overexpressing nuclear INPP4A exhibit massive apoptosis. In human tissues as well as cell lines, lower nuclear localization of INPP4A correlate with cancerous growth. Together, our findings suggest that nuclear compartmentalization of INPP4A may be a mechanism to regulate cell cycle progression, proliferation and apoptosis. Our results imply a role for nuclear-localized INPP4A in tumor suppression in humans.

Stromal PTEN determines mammary epithelial response to radiotherapy

The importance of the tumor-associated stroma in cancer progression is clear. However, it remains uncertain whether early events in the stroma are capable of initiating breast tumorigenesis. Here, we show that in the mammary glands of non-tumor bearing mice, stromal-specific phosphatase and tensin homolog (Pten) deletion invokes radiation-induced genomic instability in neighboring epithelium. In these animals, a single dose of whole-body radiation causes focal mammary lobuloalveolar hyperplasia through paracrine epidermal growth factor receptor (EGFR) activation, and EGFR inhibition abrogates these cellular changes. By analyzing human tissue, we discover that stromal PTEN is lost in a subset of normal breast samples obtained from reduction mammoplasty, and is predictive of recurrence in breast cancer patients. Combined, these data indicate that diagnostic or therapeutic chest radiation may predispose patients with decreased stromal PTEN expression to secondary breast cancer, and that prophylactic EGFR inhibition may reduce this risk.

Chk1 inhibition as a novel therapeutic strategy in melanoma

Melanoma patients respond poorly to chemotherapies because they acquire drug resistance. Therapies that can overcome the resistance to inhibitors of the mutated BRAF protein kinase in melanoma are urgently needed. Chk1 protein kinase is a central component of the DNA damage response and plays a crucial role in controlling cell cycle progression. Analyses indicate that low mRNA expression of Chk1 is significantly associated with good overall survival of melanoma patients. To evaluate the effectiveness of Chk1 inhibitors in melanoma therapy, we have generated BRAF inhibitor (PLX4032 or vemurafenib) resistant melanoma cell lines (A375-PLX-R and WM9-PLX-R) from A375 and WM9, respectively. We observe that AKT (protein kinase B) is constitutively activated in A375-PLX-R, but not in WM9-PLX-R cells, suggesting that these cells develop resistance to PLX4032 through different mechanisms. We show that a potent and specific inhibitor of Chk1 (PF477736) is effective in reducing cell viability and colony formation of PLX4032-resistant cells. Even more impressively, PF477736 triggers PLX4032-resistant melanoma cells to regain sensitivity to the PLX4032. Mouse xenograft studies show that treating A375-PLX-R derived tumors with combined PLX4032 and PF477736 significantly reduce tumor growth. Combined treatments with PLX4032 and PF477736 reduce the levels of total Chk1 protein and alter Chk1 phosphorylation at several sites in both PLX4032 sensitive and resistant melanoma cells. Combinatorial treatments with PLX4032 and PF477736 to melanoma cells substantially induce DNA damage and cell death. Our results suggest that Chk1 inhibitors may provide new therapy options for melanoma patients.

PTEN Physically Interacts with and Regulates E2F1-mediated Transcription in Lung Cancer

PTEN phosphorylation at its C-terminal (C-tail) serine/threonine cluster negatively regulates its tumor suppressor function. However, the consequence of such inhibition and its downstream effects in driving lung cancer remain unexplored. Herein, we ascertain the molecular mechanisms by which phosphorylation compromises PTEN function, contributing to lung cancer. Replacement of the serine/threonine residues with alanine generated PTEN-4A, a phosphorylation-deficient PTEN mutant, which suppressed lung cancer cell proliferation and migration. PTEN-4A preferentially localized to the nucleus where it suppressed E2F1-mediated transcription of cell cycle genes. PTEN-4A physically interacted with the transcription factor E2F1 and associated with chromatin at gene promoters with E2F1 DNA-binding sites, a likely mechanism for its transcriptional suppression function. Deletion analysis revealed that the C2 domain of PTEN was indispensable for suppression of E2F1-mediated transcription. Further, we uncovered cancer-associated C2 domain mutant proteins that had lost their ability to suppress E2F1-mediated transcription, supporting the concept that these mutations are oncogenic in patients. Consistent with these findings, we observed increased PTEN phosphorylation and reduced nuclear PTEN levels in lung cancer patient samples establishing phosphorylation as a bona fide inactivation mechanism for PTEN in lung cancer. Thus, use of small molecule inhibitors that hinder PTEN phosphorylation is a plausible approach to activate PTEN function in the treatment of lung cancer. Abbreviations AKT V-Akt Murine Thymoma Viral Oncogene CA Cancer adjacent CDK1 Cyclin dependent kinase 1 CENPC-C Centromere Protein C ChIP Chromatin Immunoprecipitation co-IP Co-immunoprecipitation COSMIC Catalog of Somatic Mutations In Cancer CREB cAMP Responsive Element Binding Protein C-tail Carboxy terminal tail E2F1 E2F Transcription Factor 1 ECIS Electric Cell-substrate Impedance Sensing EGFR Epidermal Growth Factor Receptor GSI Gamma Secretase Inhibitor HDAC1 Histone Deacetylase 1 HP1 Heterochromatin protein 1 KAP1/TRIM28 KRAB-Associated Protein 1/Tripartite Motif Containing 28 MAF1 Repressor of RNA polymerase III transcription MAF1 homolog MCM2 Minichromosome Maintenance Complex Component 2 miRNA micro RNA MTF1 Metal-Regulatory Transcription Factor 1 PARP Poly(ADP-Ribose) Polymerase PD-1 Programmed Cell Death 1 PD-L1 Programmed Cell Death 1 Ligand 1 PI3K Phosphatidylinositol-4,5-Bisphosphate 3-Kinase PLK Polo-like Kinase pPTEN Phosphorylated PTEN PTEN Phosphatase and Tensin Homolog deleted on chromosome ten PTM Post Translational Modification Rad51 RAD51 Recombinase Rad52 RAD52 Recombinase RPA1 Replication protein A SILAC Stable Isotope Labeling with Amino Acids in Cell Culture SRF Serum Response Factor TKI Tyrosine Kinase inhbitors TMA Tissue Microarray TOP2A DNA Topoisomerase 2A.

The Mfge8-α8β1-PTEN pathway regulates airway smooth muscle contraction in allergic inflammation

Asthma affects ∼300 million people worldwide. Despite multiple treatment options, asthma treatment remains unsatisfactory in a subset of patients. Airway obstruction is a hallmark of allergic asthma and is largely due to airway smooth muscle hypercontractility induced by airway inflammation. Identification of molecular pathways that regulate airway smooth muscle hypercontractility is of considerable therapeutic interest. We previously identified roles for milk fat globule epidermal growth factor-like 8 (Mfge8) in opposing the effects of allergic inflammation on increasing airway smooth muscle contractile force. In this study, we delineate the signaling pathway by which Mfge8 mediates these effects. By using genetic and pharmacologic approaches, we show that the α8β1 integrin and the phosphatase and tensin homolog (PTEN) mediate the effects of Mfge8 on preventing IL-13-induced increases in airway contractility. Tracheal rings from mice with smooth muscle-specific deletion of α8β1 or PTEN have enhanced contraction in response to treatment with IL-13. Enhanced IL-13-induced tracheal ring contraction in Mfge8-/- mice was abolished by treatment with the PI3K inhibitor. Mechanistically, IL-13 induces ubiquitination and degradation of PTEN protein. Our findings identify a role for the Mfge8-α8β1-PTEN pathway in regulating the force of airway smooth muscle contraction in the setting of allergic inflammation.-Khalifeh-Soltani, A., Gupta, D., Ha, A., Podolsky, M. J., Datta, R., Atabai, K. The Mfge8-α8β1-PTEN pathway regulates airway smooth muscle contraction in allergic inflammation.

PTEN Regulates Nonhomologous End Joining By Epigenetic Induction of NHEJ1/XLF

DNA double-strand breaks (DSB) are the most cytotoxic DNA lesions, and up to 90% of DSBs require repair by nonhomologous end joining (NHEJ). Functional and genomic analyses of patient-derived melanomas revealed that PTEN loss is associated with NHEJ deficiency. In PTEN-null melanomas, PTEN complementation rescued the NHEJ defect; conversely, suppression of PTEN compromised NHEJ. Mechanistic studies revealed that PTEN promotes NHEJ through direct induction of expression of XRCC4-like factor (NHEJ1/XLF), which functions in DNA end bridging and ligation. PTEN was found to occupy the NHEJ1 gene promoter and to recruit the histone acetyltransferases, PCAF and CBP, inducing XLF expression. This recruitment activity was found to be independent of its phosphatase activity, but dependent on K128, a site of regulatory acetylation on PTEN. These findings define a novel function for PTEN in regulating NHEJ DSB repair, and therefore may assist in the design of individualized strategies for cancer therapy.Implications: PTEN is the second most frequently lost tumor suppressor gene. Here it is demonstrated that PTEN has a direct and novel regulatory role in NHEJ, a key DNA repair pathway in response to radiation and chemotherapy. Mol Cancer Res; 16(8); 1241-54. ©2018 AACR.

Nuclear PTEN deficiency causes microcephaly with decreased neuronal soma size and increased seizure susceptibility

Defects in phosphatase and tensin homolog (PTEN) are associated with neurological disorders and tumors. PTEN functions at two primary intracellular locations: the plasma membrane and the nucleus. At the membrane, PTEN functions as a phosphatidylinositol (3,4,5)-trisphosphate phosphatase and suppresses PI 3-kinase signaling that drives cell growth and tumorigenesis. However, the in vivo function of nuclear PTEN is unclear. Here, using CRISPR/Cas9, we generated a mouse model in which PTEN levels in the nucleus are decreased. Nuclear PTEN-deficient mice were born with microcephaly and maintained a small brain during adulthood. The size of neuronal soma was significantly smaller in the cerebellum, cerebral cortex, and hippocampus. Also, these mice were prone to seizure. No changes in PI 3-kinase signaling were observed. By contrast, the size of other organs was unaffected. Therefore, nuclear PTEN is essential for the health of the brain by promoting the growth of neuronal soma size during development.

SUMOylation regulates germinal vesicle breakdown and the Akt/PKB pathway during mouse oocyte maturation

SUMOylation, a process of posttranslational modification of proteins by the small ubiquitin-related modifier (SUMO) family of proteins, is known to be involved in yeast and mammalian somatic cell-cycle regulation. However, the identities of the SUMO-modified oocyte targets are largely unknown and the functional role(s) for SUMOylation during mammalian oocyte maturation remains unclear. On the basis of studies in non-germline cells, protein kinase B/Akt is a potential SUMOylation target in the mouse oocyte, where it plays an essential role in cell-cycle resumption and progression during maturation. This study investigated the temporal patterns and prospective role(s) for interactions between SUMOylation and Akt serine-phosphorylation during oocyte meiotic resumption. Pharmacological inhibition of SUMOylation significantly decreased follicular fluid meiosis-activating sterol-induced cell-cycle resumption in oocytes matured in vitro and negatively affected the phosphorylation and nuclear translocation of Akt. Similarly, nuclear localization of cyclin D1, a downstream target of Akt activation, was significantly decreased following SUMOylation inhibition. Together these data show that SUMO and the posttranslational process of SUMOylation are involved in cell-cycle resumption during murine oocyte maturation and exert a regulatory influence on the Akt pathway during germinal vesicle breakdown.

Novel function of HATs and HDACs in homologous recombination through acetylation of human RAD52 at double-strand break sites

The p300 and CBP histone acetyltransferases are recruited to DNA double-strand break (DSB) sites where they induce histone acetylation, thereby influencing the chromatin structure and DNA repair process. Whether p300/CBP at DSB sites also acetylate non-histone proteins, and how their acetylation affects DSB repair, remain unknown. Here we show that p300/CBP acetylate RAD52, a human homologous recombination (HR) DNA repair protein, at DSB sites. Using in vitro acetylated RAD52, we identified 13 potential acetylation sites in RAD52 by a mass spectrometry analysis. An immunofluorescence microscopy analysis revealed that RAD52 acetylation at DSBs sites is counteracted by SIRT2- and SIRT3-mediated deacetylation, and that non-acetylated RAD52 initially accumulates at DSB sites, but dissociates prematurely from them. In the absence of RAD52 acetylation, RAD51, which plays a central role in HR, also dissociates prematurely from DSB sites, and hence HR is impaired. Furthermore, inhibition of ataxia telangiectasia mutated (ATM) protein by siRNA or inhibitor treatment demonstrated that the acetylation of RAD52 at DSB sites is dependent on the ATM protein kinase activity, through the formation of RAD52, p300/CBP, SIRT2, and SIRT3 foci at DSB sites. Our findings clarify the importance of RAD52 acetylation in HR and its underlying mechanism.

Therapeutic inhibition of USP7-PTEN network in chronic lymphocytic leukemia: a strategy to overcome TP53 mutated/deleted clones

Chronic Lymphocytic Leukemia (CLL) is a lymphoproliferative disorder with either indolent or aggressive clinical course. Current treatment regiments have significantly improved the overall outcomes even if higher risk subgroups - those harboring TP53 mutations or deletions of the short arm of chromosome 17 (del17p) - remain highly challenging. In the present work, we identified USP7, a known de-ubiquitinase with multiple roles in cellular homeostasis, as a potential therapeutic target in CLL. We demonstrated that in primary CLL samples and in CLL cell lines USP7 is: i) over-expressed through a mechanism involving miR-338-3p and miR-181b deregulation; ii) functionally activated by Casein Kinase 2 (CK2), an upstream interactor known to be deregulated in CLL; iii) effectively targeted by the USP7 inhibitor P5091. Treatment of primary CLL samples and cell lines with P5091 induces cell growth arrest and apoptosis, through the restoration of PTEN nuclear pool, both in TP53-wild type and -null environment. Importantly, PTEN acts as the main tumor suppressive mediator along the USP7-PTEN axis in a p53 dispensable manner. In conclusion, we propose USP7 as a new druggable target in CLL.

A protocol for custom CRISPR Cas9 donor vector construction to truncate genes in mammalian cells using pcDNA3 backbone

BACKGROUND

Clustered regularly interspaced short palindromic repeat (CRISPR) RNA-guided adaptive immune systems are found in prokaryotes to defend cells from foreign DNA. CRISPR Cas9 systems have been modified and employed as genome editing tools in wide ranging organisms. Here, we provide a detailed protocol to truncate genes in mammalian cells using CRISPR Cas9 editing. We describe custom donor vector construction using Gibson assembly with the commonly utilized pcDNA3 vector as the backbone.

RESULTS

We describe a step-by-step method to truncate genes of interest in mammalian cell lines using custom-made donor vectors. Our method employs 2 guide RNAs, mutant Cas9D10A nickase (Cas9 = CRISPR associated sequence 9), and a custom-made donor vector for homologous recombination to precisely truncate a gene of interest with a selectable neomycin resistance cassette (NPTII: Neomycin Phosphotransferase II). We provide a detailed protocol on how to design and construct a custom donor vector using Gibson assembly (and the commonly utilized pcDNA3 vector as the backbone) allowing researchers to obtain specific gene modifications of interest (gene truncation, gene deletion, epitope tagging or knock-in mutation). Selection of mutants in mammalian cell lines with G418 (Geneticin) combined with several screening methods: western blot analysis, polymerase chain reaction, and Sanger sequencing resulted in streamlined mutant isolation. Proof of principle experiments were done in several mammalian cell lines.

CONCLUSIONS

Here we describe a detailed protocol to employ CRISPR Cas9 genome editing to truncate genes of interest using the commonly employed expression vector pcDNA3 as the backbone for the donor vector. Providing a detailed protocol for custom donor vector design and construction will enable researchers to develop unique genome editing tools. To date, detailed protocols for CRISPR Cas9 custom donor vector construction are limited (Lee et al. in Sci Rep 5:8572, 2015; Ma et al. in Sci Rep 4:4489, 2014). Custom donor vectors are commercially available, but can be expensive. Our goal is to share this protocol to aid researchers in performing genetic investigations that require custom donor vectors for specialized applications (specific gene truncations, knock-in mutations, and epitope tagging applications).

Loss of PTEN-assisted G2/M checkpoint impedes homologous recombination repair and enhances radio-curability and PARP inhibitor treatment response in prostate cancer

Here we report that PTEN contributes to DNA double-strand break (DSB) repair via homologous recombination (HR), as evidenced by (i) inhibition of HR in a reporter plasmid assay, (ii) enhanced sensitivity to mitomycin-C or olaparib and (iii) reduced RAD51 loading at IR-induced DSBs upon PTEN knockdown. No association was observed between PTEN-status and RAD51 expression either in-vitro or in-vivo in a tissue microarray of 1500 PTEN-deficient prostate cancer (PC) samples. PTEN depletion and sustained activation of AKT sequestered CHK1 in the cytoplasm, thus impairing the G2/M-checkpoint after irradiation. Consistently, AKT inhibition recovered the G2/M-checkpoint and restored HR efficiency in PTEN-depleted cells. We show that, although PTEN loss correlates with a worse prognosis, it may predict for improved response of PC patients to radiotherapy. Further, we provide evidence for the use of PTEN as a biomarker for predicting the response to PARP inhibitors as radiosensitizing agents in prostate cancer. Collectively, these data implicate PTEN in maintaining genomic stability by delaying G2/M-phase progression of damaged cells, thus allowing time for DSB repair by HR. Furthermore, we identify PTEN-status in PC as a putative predictor of (i) radiotherapy response and (ii) response to treatment with PARP inhibitor alone or combined with radiotherapy.

Loss of PTEN-assisted G2/M checkpoint impedes homologous recombination repair and enhances radio-curability and PARP inhibitor treatment response in prostate cancer

Here we report that PTEN contributes to DNA double-strand break (DSB) repair via homologous recombination (HR), as evidenced by (i) inhibition of HR in a reporter plasmid assay, (ii) enhanced sensitivity to mitomycin-C or olaparib and (iii) reduced RAD51 loading at IR-induced DSBs upon PTEN knockdown. No association was observed between PTEN-status and RAD51 expression either in-vitro or in-vivo in a tissue microarray of 1500 PTEN-deficient prostate cancer (PC) samples. PTEN depletion and sustained activation of AKT sequestered CHK1 in the cytoplasm, thus impairing the G2/M-checkpoint after irradiation. Consistently, AKT inhibition recovered the G2/M-checkpoint and restored HR efficiency in PTEN-depleted cells. We show that, although PTEN loss correlates with a worse prognosis, it may predict for improved response of PC patients to radiotherapy. Further, we provide evidence for the use of PTEN as a biomarker for predicting the response to PARP inhibitors as radiosensitizing agents in prostate cancer. Collectively, these data implicate PTEN in maintaining genomic stability by delaying G2/M-phase progression of damaged cells, thus allowing time for DSB repair by HR. Furthermore, we identify PTEN-status in PC as a putative predictor of (i) radiotherapy response and (ii) response to treatment with PARP inhibitor alone or combined with radiotherapy.

RSUME is implicated in tumorigenesis and metastasis of pancreatic neuroendocrine tumors

The factors triggering pancreatic neuroendocrine tumor (PanNET) progression are largely unknown. Here we investigated the role and mechanisms of the sumoylation enhancing protein RSUME in PanNET tumorigenesis. Immunohistochemical studies showed that RSUME is strongly expressed in normal human pancreas, in particular in β-cells. RSUME expression is reduced in insulinomas and is nearly absent in other types of PanNETs suggesting a role in PanNET tumorigenesis. In human pancreatic neuroendocrine BON1 cells, RSUME stimulates hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor-A (VEGF-A), which are key components of tumor neovascularisation. In contrast, RSUME suppresses nuclear factor-κB (NF-κB) and its target interleukin-8 (IL-8). Correspondingly, PanNET cells with RSUME knockdown showed decreased HIF-1α activity and increased NF-κB and IL-8 production leading to a moderate reduction of VEGF-A release as reduced HIF-1α/VEGF-A production is partly compensated by NF-κB/IL-8-induced VEGF-A. Notably, RSUME stabilizes the tumor suppressor PTEN, which is frequently lost in PanNETs and whose absence is associated with metastasis formation. In vivo orthotopic transplantation of PanNET cells with or without RSUME expression into nude mice showed that PanNETs without RSUME have reduced PTEN expression, grow faster and form multiple liver metastases. In sum, RSUME differentially regulates key components of PanNET formation suggesting that the observed loss of RSUME in advanced PanNETs is critically involved in PanNET tumorigenesis, particularly in metastasis formation.

Clinical implications of PTEN loss in prostate cancer

Genomic aberrations of the PTEN tumour suppressor gene are among the most common in prostate cancer. Inactivation of PTEN by deletion or mutation is identified in ∼20% of primary prostate tumour samples at radical prostatectomy and in as many as 50% of castration-resistant tumours. Loss of phosphatase and tensin homologue (PTEN) function leads to activation of the PI3K-AKT (phosphoinositide 3-kinase-RAC-alpha serine/threonine-protein kinase) pathway and is strongly associated with adverse oncological outcomes, making PTEN a potentially useful genomic marker to distinguish indolent from aggressive disease in patients with clinically localized tumours. At the other end of the disease spectrum, therapeutic compounds targeting nodes in the PI3K-AKT-mTOR (mechanistic target of rapamycin) signalling pathway are being tested in clinical trials for patients with metastatic castration-resistant prostate cancer. Knowledge of PTEN status might be helpful to identify patients who are more likely to benefit from these therapies. To enable the use of PTEN status as a prognostic and predictive biomarker, analytically validated assays have been developed for reliable and reproducible detection of PTEN loss in tumour tissue and in blood liquid biopsies. The use of clinical-grade assays in tumour tissue has shown a robust correlation between loss of PTEN and its protein as well as a strong association between PTEN loss and adverse pathological features and oncological outcomes. In advanced disease, assessing PTEN status in liquid biopsies shows promise in predicting response to targeted therapy. Finally, studies have shown that PTEN might have additional functions that are independent of the PI3K-AKT pathway, including those affecting tumour growth through modulation of the immune response and tumour microenvironment.

PTEN/PTENP1: 'Regulating the regulator of RTK-dependent PI3K/Akt signalling', new targets for cancer therapy

Regulation of the PI-3 kinase (PI3K)/Akt signalling pathway is essential for maintaining the integrity of fundamental cellular processes, cell growth, survival, death and metabolism, and dysregulation of this pathway is implicated in the development and progression of cancers. Receptor tyrosine kinases (RTKs) are major upstream regulators of PI3K/Akt signalling. The phosphatase and tensin homologue (PTEN), a well characterised tumour suppressor, is a prime antagonist of PI3K and therefore a negative regulator of this pathway. Loss or inactivation of PTEN, which occurs in many tumour types, leads to overactivation of RTK/PI3K/Akt signalling driving tumourigenesis. Cellular PTEN levels are tightly regulated by a number of transcriptional, post-transcriptional and post-translational regulatory mechanisms. Of particular interest, transcription of the PTEN pseudogene, PTENP1, produces sense and antisense transcripts that exhibit post-transcriptional and transcriptional modulation of PTEN expression respectively. These additional levels of regulatory complexity governing PTEN expression add to the overall intricacies of the regulation of RTK/PI-3 K/Akt signalling. This review will discuss the regulation of oncogenic PI3K signalling by PTEN (the regulator) with a focus on the modulatory effects of the sense and antisense transcripts of PTENP1 on PTEN expression, and will further explore the potential for new therapeutic opportunities in cancer treatment.

Targeting ataxia telangiectasia-mutated- and Rad3-related kinase (ATR) in PTEN-deficient breast cancers for personalized therapy

Purpose

Phosphate and tensin homolog (PTEN), a negative regulator of PI3K signaling, is involved in DNA repair. ATR is a key sensor of DNA damage and replication stress. We evaluated whether ATR signaling has clinical significance and could be targeted by synthetic lethality in PTEN-deficient triple-negative breast cancer (TNBC).

Methods

PTEN, ATR and pCHK1^Ser345 protein level was evaluated in 1650 human breast cancers. ATR blockade by VE-821 was investigated in PTEN-proficient- (MDA-MB-231) and PTEN-deficient (BT-549, MDA-MB-468) TNBC cell lines. Functional studies included DNA repair expression profiling, MTS cell-proliferation assay, FACS (cell cycle progression & γH2AX accumulation) and FITC-annexin V flow cytometry analysis.

Results

Low nuclear PTEN was associated with higher grade, pleomorphism, de-differentiation, higher mitotic index, larger tumour size, ER negativity, and shorter survival (p values < 0.05). In tumours with low nuclear PTEN, high ATR and/or high pCHK1^ser345 level was also linked to higher grade, larger tumour size and poor survival (all p values < 0.05). VE-821 was selectively toxic in PTEN-deficient TNBC cells and resulted in accumulation of double-strand DNA breaks, cell cycle arrest, and increased apoptosis.

Conclusion

ATR signalling adversely impact survival in PTEN-deficient breast cancers. ATR inhibition is synthetically lethal in PTEN-deficient TNBC cells.

Electronic supplementary material

The online version of this article (10.1007/s10549-018-4683-4) contains supplementary material, which is available to authorized users.

Integrative genomic and transcriptomic analysis of leiomyosarcoma

Leiomyosarcoma (LMS) is an aggressive mesenchymal malignancy with few therapeutic options. The mechanisms underlying LMS development, including clinically actionable genetic vulnerabilities, are largely unknown. Here we show, using whole-exome and transcriptome sequencing, that LMS tumors are characterized by substantial mutational heterogeneity, near-universal inactivation of TP53 and RB1, widespread DNA copy number alterations including chromothripsis, and frequent whole-genome duplication. Furthermore, we detect alternative telomere lengthening in 78% of cases and identify recurrent alterations in telomere maintenance genes such as ATRX, RBL2, and SP100, providing insight into the genetic basis of this mechanism. Finally, most tumors display hallmarks of "BRCAness", including alterations in homologous recombination DNA repair genes, multiple structural rearrangements, and enrichment of specific mutational signatures, and cultured LMS cells are sensitive towards olaparib and cisplatin. This comprehensive study of LMS genomics has uncovered key biological features that may inform future experimental research and enable the design of novel therapies.

Distinct subtypes of genomic PTEN deletion size influence the landscape of aneuploidy and outcome in prostate cancer

Background

Inactivation of the PTEN tumor suppressor gene by deletion occurs in 20-30% of prostate cancer tumors and loss strongly correlates with a worse outcome. PTEN loss of function not only leads to activation of the PI3K/AKT pathway, but is also thought to affect genome stability and increase levels of tumor aneuploidy. We performed an in silico integrative genomic and transcriptomic analysis of 491 TCGA prostate cancer tumors. These data were used to map the genomic sizes of PTEN gene deletions and to characterize levels of instability and patterns of aneuploidy acquisition.

Results

PTEN homozygous deletions had a significant increase in aneuploidy compared to PTEN tumors without an apparent deletion, and hemizygous deletions showed an intermediate aneuploidy profile. A supervised clustering of somatic copy number alterations (SCNA) demonstrated that the size of PTEN deletions was not random, but comprised five distinct subtypes: (1) "Small Interstitial" (70 bp-789Kb); (2) "Large Interstitial" (1-7 MB); (3) "Large Proximal" (3-65 MB); (4) "Large Terminal" (8-64 MB), and (5) "Extensive" (71-132 MB). Many of the deleted fragments in each subtype were flanked by low copy repetitive (LCR) sequences. SCNAs such as gain at 3q21.1-3q29 and deletions at 8p, RB1, TP53 and TMPRSS2-ERG were variably present in all subtypes. Other SCNAs appeared to be recurrent in some deletion subtypes, but absent from others. To determine how the aneuploidy influenced global levels of gene expression, we performed a comparative transcriptome analysis. One deletion subtype (Large Interstitial) was characterized by gene expression changes associated with angiogenesis and cell adhesion, structure, and metabolism. Logistic regression demonstrated that this deletion subtype was associated with a high Gleason score (HR = 2.386; 95% C.I. 1.245-4.572), extraprostatic extension (HR = 2.423, 95% C.I. 1.157-5.075), and metastasis (HR = 7.135; 95% C.I. 1.540-33.044). Univariate and multivariate Cox Regression showed that presence of this deletion subtype was also strongly predictive of disease recurrence.

Conclusions

Our findings indicate that genomic deletions of PTEN fall into five different size distributions, with breakpoints that often occur close LCR regions, and that each subtype is associated with a characteristic aneuploidy signature. The Large Interstitial deletion had a distinct gene expression signature that was related to cancer progression and was also predictive of a worse prognosis.

PTEN: Tumor Suppressor and Metabolic Regulator

Phosphatase and Tensin Homolog deleted on Chromosome 10 (PTEN) is a dual phosphatase with both protein and lipid phosphatase activities. PTEN was first discovered as a tumor suppressor with growth and survival regulatory functions. In recent years, the function of PTEN as a metabolic regulator has attracted significant attention. As the lipid phosphatase that dephosphorylates phosphatidylinositol-3, 4, 5-phosphate (PIP₃), PTEN reduces the level of PIP₃, a critical 2nd messenger mediating the signal of not only growth factors but also insulin. In this review, we introduced the discovery of PTEN, the PTEN-regulated canonical and nuclear signals, and PTEN regulation. We then focused on the role of PTEN and PTEN-regulated signals in metabolic regulation. This included the role of PTEN in glycolysis, gluconeogenesis, glycogen synthesis, lipid metabolism as well as mitochondrial metabolism. We also included how PTEN and PTEN regulated metabolic functions may act paradoxically toward insulin sensitivity and tumor metabolism and growth. Further understanding of how PTEN regulates metabolism and how such regulations lead to different biological outcomes is necessary for interventions targeting at the PTEN-regulated signals in either cancer or diabetes treatment.

A cell-penetrating antibody inhibits human RAD51 via direct binding

RAD51, a key factor in homology-directed repair (HDR), has long been considered an attractive target for cancer therapy, but few specific inhibitors have been found. A cell-penetrating, anti-DNA, lupus autoantibody, 3E10, was previously shown to inhibit HDR, sensitize tumors to radiation, and mediate synthetic lethal killing of BRCA2-deficient cancer cells, effects that were initially attributed to its affinity for DNA. However, as the molecular basis for its ability to inhibit DNA repair, we report that 3E10 directly binds to the N-terminus of RAD51, sequesters RAD51 in the cytoplasm, and impedes RAD51 binding to DNA. Further, we generate separation-of-function mutations in the complementarity-determining regions of 3E10 revealing that inhibition of HDR tracks with binding to RAD51 but not to DNA, whereas cell penetration is linked to DNA binding. The consequences of these mutations on putative 3E10 interactions with RAD51 and DNA are correlated with in silico molecular modeling. Taken together, the results identify 3E10 as a novel inhibitor of RAD51 by direct binding, accounting for its ability to suppress HDR and providing the molecular basis to guide pre-clinical development of 3E10 as an anti-cancer agent.

A phase 1b dose expansion study of the pan-class I PI3K inhibitor buparlisib (BKM120) plus carboplatin and paclitaxel in PTEN deficient tumors and with dose intensified carboplatin and paclitaxel

Purpose We previously reported the phase I dose escalation study of buparlisib, a pan-class 1A PI3K inhibitor, combined with platinum/taxane-based chemotherapy in patients with advanced solid tumors. The combination was well tolerated and promising preliminary efficacy was observed in PTEN deficient tumors. This phase I dose expansion study now evaluates buparlisib plus high dose carboplatin and paclitaxel in unselected patients with advanced solid tumors and buparlisib plus standard dose carboplatin and paclitaxel in patients with PTEN deficient tumors (ClinicalTrials.gov, NCT01297452). Methods There were two expansion cohorts: Cohort A received continuous buparlisib (100 mg/daily) orally plus high dose carboplatin AUC 6 and paclitaxel 200 mg/m2; Cohort B treated patients with PTEN deficient tumors only and they received the recommended phase II dose (RP2D) of continuous buparlisib (100 mg/daily) orally plus standard dose carboplatin AUC 5 and paclitaxel 175 mg/m2. Both cohorts received chemotherapy intravenously on day 1 of the 21-day cycle with pegfilgrastim support. Primary endpoint in Cohort A was to evaluate the safety and tolerability of chemotherapy dose intensification with buparlisib and in Cohort B was to describe preliminary efficacy of the combination among patients with tumors harboring a PTEN mutation or homozygous deletion. Results 14 subjects were enrolled, 7 in Cohort A and 7 in Cohort B. Dose reductions were required in 5 (71%) and 3 (43%) patients, in cohort A and B respectively. Grade 3 adverse events in Cohort A included lymphopenia (n = 5 [71%]), hyperglycemia (n = 2, [29%]), diarrhea (n = 2, [29%]) and rash (n = 2, [29%]) and in cohort B included lymphopenia (n = 5 [71%]), hyperglycemia (n = 4 [57%]) and neutropenia (n = 2 [29%]. The mean number of cycles on protocol was 6. The overall objective response rate was 14% (2 /14). No objective responses were observed in the PTEN deficient cohort. Four out of 6 patients with stable disease (SD) had SD or better for ≥6 cycles, 2 of which had PTEN deficient tumors. Conclusion The addition of buparlisib to high dose carboplatin and paclitaxel was not tolerable. The combination did not reveal significant clinical activity amongst a small and heterogenous group of PTEN deficient tumors.

Engineering PTEN-L for Cell-Mediated Delivery

The tumor suppressor PTEN is frequently inactivated in glioblastoma. PTEN-L is a long form of PTEN produced by translation from an alternate upstream start codon. Unlike PTEN, PTEN-L has a signal sequence and a tract of six arginine residues that allow PTEN-L to be secreted from cells and be taken up by neighboring cells. This suggests that PTEN-L could be used as a therapeutic to restore PTEN activity. However, effective delivery of therapeutic proteins to treat CNS cancers such as glioblastoma is challenging. One method under evaluation is cell-mediated therapy, where cells with tumor-homing abilities such as neural stem cells are genetically modified to express a therapeutic protein. Here, we have developed a version of PTEN-L that is engineered for enhanced cell-mediated delivery. This was accomplished by replacement of the native leader sequence of PTEN-L with a leader sequence from human light-chain immunoglobulin G (IgG). This version of PTEN-L showed increased secretion and an increased ability to transfer to neighboring cells. Neural stem cells derived from human fibroblasts could be modified to express this version of PTEN-L and were able to deliver catalytically active light-chain leader PTEN-L (lclPTEN-L) to neighboring glioblastoma cells.

PTEN regulates spindle assembly checkpoint timing through MAD1 in interphase

The spindle assembly checkpoint (SAC) restrains anaphase progression to ensure all chromosomes attach properly to the spindle. Although SAC timing has been extensively investigated in mitosis, its mechanism of regulation in interphase is unclear. We report that PTEN functions as a crucial activator of SAC timing and protects chromosome segregation under both spindle poison treated and untreated conditions. We show that PTEN physically interacts with MAD1 and promotes its dimerization and localization in the nuclear pore. Consequently, PTEN is important for the formation of the mitotic checkpoint complex (MCC) in interphase. We propose PTEN/MAD1 signaling is essential for maintenance of SAC timing and chromosome integrity.

Curcumin sensitizes lymphoma cells to DNA damage agents through regulating Rad51-dependent homologous recombination

Curcumin is a natural compound isolated from the rhizome of Curcuma longa. It possesses anti-tumor activity through arresting cell cycles and promoting cell apoptosis. However, the effect of curcumin on DNA damage is not well defined. In this study, we investigated the effect of curcumin on inducing DNA damage and on sensitizing lymphoma cells to anti-tumoral DNA damage drugs. Western blot showed curcumin induced γ-H2AX foci in CH12F3 lymphoma cells, which suggests curcumin induces DNA breaks. In addition, curcumin decreased the expression of Rad51, which suggests curcumin induces DNA damage through regulating Rad51-dependant homologous recombination. Rad51-dependant homologous recombination is a vital DNA repair pathway for cancer cells to resist anti-tumoral DNA damage drugs, therefore, we studied the effect of curcumin on the sensitizing lymphoma cells to various chemotherapeutic drugs. We found low level of curcumin (5μM) sensitized lymphoma cells to anti-tumoral DNA damage agents including cisplatin, methyl methanesulfonate, hydroxyurea and camptothecin. We also found curcumin sensitized CH12F3 lymphoma cells to DNA-PK and PARP inhibitors. Flow cytometry analysis showed curcumin promoted apoptosis and western blot analysis confirmed curcumin activated caspase3-dependent apoptosis. Taken together, these results demonstrate that curcumin induces DNA damage through regulating Rad51-dependant homologous recombination and triggers caspase3-dependent apoptosis, more importantly, curcumin sensitizes lymphoma cells to various DNA damage drugs. Consequently, curcumin would be a potent agent for sensitizing lymphoma cells to anti-tumoral chemotherapeutic agents.

SUMO proteins: Guardians of immune system

Small ubiquitin-like modifier (SUMO) proteins belong to the ubiquitin-like family and act to change the function of target proteins through post-translational modifications. Through their interactions with innate immune pathways, SUMOs promote an efficient immune response to pathogenic challenge avoiding, at the same time, an excess of immune response that could lead to the development of autoimmune diseases. This report discusses the general functions of SUMO proteins; highlights SUMO involvement in the innate immune response through their role in NF-κB and interferon pathways; the involvement of SUMO proteins in autoimmune diseases; and reviews bacterial, viral, and parasitic interactions with SUMO pathways. In conclusion, we speculate that targeting SUMOs could represent a new therapeutic strategy against infections and autoimmunity.

The Mechanism of Action of (-)-Lomaiviticin A

(-)-Lomaiviticin A (4) is a complex C2-symmetric bacterial metabolite that contains two diazofluorene functional groups. The diazofluorene consists of naphthoquinone, cyclopentadiene, and diazo substituents fused through a σ- and π-bonding network. Additionally, (-)-lomaiviticin A (4) is a potent cytotoxin, with half-maximal inhibitory potency (IC50) values in the low nanomolar range against many cancer cell lines. Because of limitations in supply, its mechanism of action had remained a "black box" since its isolation in the early 2000s. In this Account, I describe how studies directed toward the total synthesis of (-)-lomaiviticin A (4) provided a platform to elucidate the emergent properties of this metabolite and thereby connect chemical reactivity with cellular phenotype. We first developed a convergent strategy to prepare the diazofluorene (9 + 10 → 13). We then adapted this chemistry to the synthesis of lomaiviticin aglycon (21/22) and the natural monomeric diazofluorene (-)-kinamycin F (3). The key step in the lomaiviticin aglycon (21/22) synthesis involved the stereoselective oxidative coupling of two monomeric diazofluorenes (2 × 18 → 20) to establish the cojoining carbon-carbon bond of the target. As the absolute stereochemistry of the aglycon and carbohydrate residues of (-)-lomaiviticin A (4) were unknown, we developed a semisynthetic route to the metabolite that proceeds in one step and 42% yield by diazo transfer to the more abundant isolate (-)-lomaiviticin C (6). This allowed us to complete the stereochemical assignment of (-)-lomaiviticin A (4) and provided a renewable source of material. Using this material, we established that the remarkable cytotoxic effects of (-)-lomaiviticin A (4) derive from the induction of highly toxic double-strand breaks (DSBs) in DNA. At the molecular level, 1,7-nucleophilic additions to each electrophilic diazofluorene trigger homolytic decomposition pathways that produce sp2 radicals at the carbon atoms of each diazo group. These radicals abstract hydrogen atoms from the deoxyribose of DNA, a process known to initiate strand cleavage. NMR spectroscopy and molecular mechanics simulations were used to elucidate the mode of DNA binding. These studies showed that both diazofluorenes of (-)-lomaiviticin A (4) penetrate into the duplex. This mode of non-covalent binding places each diazo carbon atom in close proximity to each DNA strand. Throughout these studies, isolates containing one diazofluorene, such as (-)-lomaiviticin C (6) and (-)-kinamycin C (2), were used as controls. Consistent with our mechanistic model, these compounds do not induce DSBs in DNA and are several orders of magnitude less potent. Reactivity studies suggest that (-)-lomaiviticin A (4) is more electrophilic than simple monomeric diazofluorenes. We attribute this to through-space delocalization of the developing negative charge in the transition state for 1,7-addition. Consistent with this mechanism of action, (-)-lomaiviticin A (4) displays selective low-picomolar potencies toward DNA DSB repair-deficient cell types. The emergent properties of (-)-lomaiviticin A (4) derive from the specific arrangement of diazo, naphthoquinone, cyclopentadiene, and ketone functional groups. These functional groups work together to yield, essentially, a masked vinyl radical that can be exposed under biological conditions. Furthermore, the rotational symmetry of the metabolite, deriving from dimerization, allows it to interact with the antiparallel symmetry of DNA and affect cleavage of the duplex.

SUMOylation regulates nuclear accumulation and signaling activity of the soluble intracellular domain of the ErbB4 receptor tyrosine kinase

Erb-B2 receptor tyrosine kinase 4 (ErbB4) is a kinase that can signal via a proteolytically released intracellular domain (ICD) in addition to classical receptor tyrosine kinase-activated signaling cascades. Previously, we have demonstrated that ErbB4 ICD is posttranslationally modified by the small ubiquitin-like modifier (SUMO) and functionally interacts with the PIAS3 SUMO E3 ligase. However, direct evidence of SUMO modification in ErbB4 signaling has remained elusive. Here, we report that the conserved lysine residue 714 in the ErbB4 ICD undergoes SUMO modification, which was reversed by sentrin-specific proteases (SENPs) 1, 2, and 5. Although ErbB4 kinase activity was not necessary for the SUMOylation, the SUMOylated ErbB4 ICD was tyrosine phosphorylated to a higher extent than unmodified ErbB4 ICD. Mutation of the SUMOylation site compromised neither ErbB4-induced phosphorylation of the canonical signaling pathway effectors Erk1/2, Akt, or STAT5 nor ErbB4 stability. In contrast, SUMOylation was required for nuclear accumulation of the ErbB4 ICD. We also found that Lys-714 was located within a leucine-rich stretch, which resembles a nuclear export signal, and could be inactivated by site-directed mutagenesis. Furthermore, SUMOylation modulated the interaction of ErbB4 with chromosomal region maintenance 1 (CRM1), the major nuclear export receptor for proteins. Finally, the SUMO acceptor lysine was functionally required for ErbB4 ICD-mediated inhibition of mammary epithelial cell differentiation in a three-dimensional cell culture model. Our findings indicate that a SUMOylation-mediated mechanism regulates nuclear localization and function of the ICD of ErbB4 receptor tyrosine kinase.

Regulation of the tumor suppressor PTEN by natural anticancer compounds

The tumor suppressor phosphatase and tensin homologue (PTEN) has phosphatase activity, with phosphatidylinositol (3,4,5)-trisphosphate (PIP3), a product of phosphatidylinositol 3-kinase (PI3K), as one of the principal substrates. PTEN is a negative regulator of the Akt pathway, which plays a fundamental role in controlling cell growth, survival, and proliferation. Loss of PTEN function has been observed in many different types of cancer. Functional inactivation of PTEN as a consequence of germ-line mutations or promoter hypermethylation predisposes individuals to malignancies. PTEN undergoes posttranslational modifications, such as oxidation, acetylation, phosphorylation, SUMOylation, and ubiquitination, which influence its catalytic activity, interactions with other proteins, and subcellular localization. Cellular redox status is crucial for posttranslational modification of PTEN and its functional consequences. Oxidative stress and inflammation are major causes of loss of PTEN function. Pharmacologic or nutritional restoration of PTEN function is considered a reliable strategy in the management of PTEN-defective cancer. In this review, we highlight natural compounds, such as curcumin, indol-3 carbinol, and omega-3 fatty acids, that have the potential to restore or potentiate PTEN expression/activity, thereby suppressing cancer cell proliferation, survival, and resistance to chemotherapeutic agents.