PIKE-A is amplified in human cancers and prevents apoptosis by up-regulating Akt

Functional Role of AGAP2/PIKE-A in Fcγ Receptor-Mediated Phagocytosis

In phagocytes, cytoskeletal and membrane remodeling is finely regulated at the phagocytic cup. Various smaFll G proteins, including those of the Arf family, control these dynamic processes. Human neutrophils express AGAP2, an Arf GTPase activating protein (ArfGAP) that regulates endosomal trafficking and focal adhesion remodeling. We first examined the impact of AGAP2 on phagocytosis in CHO cells stably expressing the FcγRIIA receptor (CHO-IIA). In unstimulated CHO-IIA cells, AGAP2 only partially co-localized with cytoskeletal elements and intracellular compartments. In CHO-IIA cells, AGAP2 transiently accumulated at actin-rich phagocytic cups and increased Fcγ receptor-mediated phagocytosis. Enhanced phagocytosis was not dependent on the N-terminal GTP-binding protein-like (GLD) domain of AGAP2. AGAP2 deleted of its GTPase-activating protein (GAP) domain was not recruited to phagocytic cups and did not enhance the engulfment of IgG-opsonized beads. However, the GAP-deficient [R618K]AGAP2 transiently localized at the phagocytic cups and enhanced phagocytosis. In PLB-985 cells differentiated towards a neutrophil-like phenotype, silencing of AGAP2 reduced phagocytosis of opsonized zymosan. In human neutrophils, opsonized zymosan or monosodium urate crystals induced AGAP2 phosphorylation. The data indicate that particulate agonists induce AGAP2 phosphorylation in neutrophils. This study highlights the role of AGAP2 and its GAP domain but not GAP activity in FcγR-dependent uptake of opsonized particles.

PIKE-A Modulates Mitochondrial Metabolism through Increasing SDHA Expression Mediated by STAT3/FTO Axis

Previous studies have shown that phosphoinositide 3-kinase enhancer-activating Akt (PIKE-A) is involved in the regulation of several biological processes in cancer. In our previous study, we demonstrated a crucial function of PIKE-A in cancer energy metabolism by regulating pentose phosphate pathway (PPP) flux. However, whether PIKE-A regulates energy metabolism through affecting mitochondrial changes are poorly understood. In the present study, we show that PIKE-A promotes mitochondrial membrane potential, leading to increasing proliferation of glioblastoma cell. Mechanistically, PIKE-A affects the expression of respiratory chain complex Ⅱ succinate dehydrogenase A (SDHA), mediated by regulating the axis of STAT3/FTO. Taken together, these results revealed that inhibition of PIKE-A reduced STAT3/FTO/SDHA expression, leading to the suppression of mitochondrial function. Thus, our findings suggest the PIKE-A/STAT3/FTO/SDHA axis as promising anti-cancer treatment targets.

Induction of PLXNA4 Gene during Neural Differentiation in Human Umbilical-Cord-Derived Mesenchymal Stem Cells by Low-Intensity Sub-Sonic Vibration

Human umbilical-cord-derived mesenchymal stem cells (hUC-MSC) are a type of mesenchymal stem cells and are more primitive than other MSCs. In this study, we identify novel genes and signal-activating proteins involved in the neural differentiation of hUC-MSCs induced by Low-Intensity Sub-Sonic Vibration (LISSV). RNA sequencing was used to find genes involved in the differentiation process by LISSV. The changes in hUC-MSCs caused by LISSV were confirmed by PLXNA4 overexpression and gene knockdown through small interfering RNA experiments. The six genes were increased among genes related to neurons and the nervous system. One of them, the PLXNA4 gene, is known to play a role as a guide for axons in the development of the nervous system. When the PLXNA4 recombinant protein was added, neuron-related genes were increased. In the PLXNA4 gene knockdown experiment, the expression of neuron-related genes was not changed by LISSV exposure. The PLXNA4 gene is activated by sema family ligands. The expression of SEMA3A was increased by LISSV, and its downstream signaling molecule, FYN, was also activated. We suggest that the PLXNA4 gene plays an important role in hUC-MSC neuronal differentiation through exposure to LISSV. The differentiation process depends on SEMA3A-PLXNA4-dependent FYN activation in hUC-MSCs.

SOCS3 is Related to Cell Proliferation in Neuronal Tissue: An Integrated Analysis of Bioinformatics and Experiments

Glioma is the most common primary malignant tumor that occurs in the central nervous system. Gliomas are subdivided according to a combination of microscopic morphological, molecular, and genetic factors. Glioblastoma (GBM) is the most aggressive malignant tumor; however, efficient therapies or specific target molecules for GBM have not been developed. We accessed RNA-seq and clinical data from The Cancer Genome Atlas, the Chinese Glioma Genome Atlas, and the GSE16011 dataset, and identified differentially expressed genes (DEGs) that were common to both GBM and lower-grade glioma (LGG) in three independent cohorts. The biological functions of common DEGs were examined using NetworkAnalyst. To evaluate the prognostic performance of common DEGs, we performed Kaplan-Meier and Cox regression analyses. We investigated the function of SOCS3 in the central nervous system using three GBM cell lines as well as zebrafish embryos. There were 168 upregulated genes and 50 downregulated genes that were commom to both GBM and LGG. Through survival analyses, we found that SOCS3 was the only prognostic gene in all cohorts. Inhibition of SOCS3 using siRNA decreased the proliferation of GBM cell lines. We also found that the zebrafish ortholog, socs3b, was associated with brain development through the regulation of cell proliferation in neuronal tissue. While additional mechanistic studies are necessary, our results suggest that SOCS3 is an important biomarker for glioma and that SOCS3 is related to the proliferation of neuronal tissue.

PIKE-A promotes glioblastoma growth by driving PPP flux through increasing G6PD expression mediated by phosphorylation of STAT3

Reprogramming of energy metabolism is a hallmarkofcancer, and the pentose phosphate pathway (PPP) is a major glucose metabolic pathway important for meeting the cellular demands of biosynthesis and anti-oxidant defense. Our previous study showed that phosphoinositide 3-kinase enhancer-activating Akt (PIKE-A) plays an important role in glioblastoma cell survival and growth under cellular energy stress condition. However, the crucial functions of PIKE-A in cancer energy metabolism are poorly understood.In the present study, we show that PIKE-A promotes DNA biosynthesis, NADPH production and inhibits reactive oxygen species (ROS) production, leading to increasing proliferation and growth of glioblastoma cell and suppressing cellular senescence. Mechanistically, PIKE-A binds to STAT3 and stimulates its phosphorylation mediated by tyrosine kinase Fyn, which enhances transcription of the rate-limitting enzyme glucose-6-phosphate dehydrogenase (G6PD) in the PPP. Finally, targeting PIKE-A-G6PD axis sensitizes glioblastoma to temozolomide (TMZ)treatment. This study reveals that STAT3 is a novel binding partner of PIKE-A which recruits Fyn to phosphorylate STAT3, contributing to the expression of G6PD, leading to promoting tumor growth and suppressing cellular senescence. Thus, the PIKE-A/STAT3/G6PD axis strongly links the PPP to carcinogenesis and may become a promising cancer therapeutic target.

The pseudoGTPase group of pseudoenzymes

Pseudoenzymes are emerging as significant mediators and regulators of signal transduction. These proteins maintain enzyme folds and topologies, but are disrupted in the conserved motifs required for enzymatic activity. Among the pseudoenzymes, the pseudoGTPase group of atypical GTPases has recently expanded and includes the Rnd and RGK groups, RhoH and the RhoBTB proteins, mitochondrial RhoGTPase and centaurin-γ groups, CENP-M, dynein LIC, Entamoeba histolytica RabX3, leucine-rich repeat kinase 2, and the p190RhoGAP proteins. The wide range of cellular functions associated with pseudoGTPases includes cell migration and adhesion, membrane trafficking and cargo transport, mitosis, mitochondrial activity, transcriptional control, and autophagy, placing the group in an expanding portfolio of signaling pathways. In this review, we examine how the pseudoGTPases differ from canonical GTPases and consider their mechanistic and functional roles in signal transduction. We review the amino acid differences between the pseudoGTPases and discuss how these proteins can be classified based on their ability to bind nucleotide and their enzymatic activity. We discuss the molecular and structural consequences of amino acid divergence from canonical GTPases and use comparison with the well-studied pseudokinases to illustrate the classifications. PseudoGTPases are fast becoming recognized as important mechanistic components in a range of cellular roles, and we provide a concise discussion of the currently identified members of this group. ENZYMES: small GTPases; EC number: EC 3.6.5.2.

The Antisense long noncoding RNA AGAP2-AS1 regulates cell proliferation and metastasis in Epithelial Ovarian Cancer

Antisense long noncoding RNAs serve as important regulators of protein-coding genes and contribute to tumorigenesis and metastasis. AGAP2-AS1, an antisense lncRNA transcribed from AGAP2, is involved in various cancer types. However, the clinical significance, biological roles and regulatory mechanisms of AGAP2-AS1 in epithelial ovarian cancer (EOC) have not been thoroughly elucidated to date. In this study, we demonstrated the expression pattern and biological roles of AGAP2-AS1 in EOC. Clinically, AGAP2-AS1 expression was decreased in EOC tissues compared to that in the controls. Low expression of AGAP2-AS1 was associated with advanced FIGO stage, high histological grade, serous subtype and lymph node metastasis in patients with EOC. AGAP2-AS1 inhibited cell migration, invasion and proliferation in vitro. AGAP2-AS1 suppressed tumor growth in vivo. Mechanistically, AGAP2-AS1 inhibited cell metastasis and proliferation by downregulating KRAS, FGFR4, and CTSK and suppressing epithelial-mesenchymal transition. In conclusion, we provide the first evidence for the tumor-suppressing effect of AGAP2-AS1 in EOC and demonstrate that AGAP2-AS1 may represent a promising therapeutic target for EOC patients.

SP1 and RARα regulate AGAP2 expression in cancer

AGAP2 (Arf GAP with GTP-binding protein-like domain, Ankyrin repeat and PH domain 2) isoform 2 is considered a proto-oncogene, but not much is known about AGAP2 gene expression regulation. To get some insight into this process, AGAP2 proximal promoter was cloned and characterised using reporter assays. We have identified SP1 as a transcription factor bound to AGAP2 promoter and required for AGAP2 expression in two different types of cancer cells (KU812, a chronic myeloid leukaemia cell line; and DU145, a prostate cancer cell line): silencing SP1 decreased AGAP2 protein levels. We have also found that all-trans retinoic acid (ATRA) treatment increased AGAP2 protein levels in both cell lines whilst curcumin treatment reduced ATRA-mediated AGAP2 increase. Furthermore, chromatin immunoprecipitation studies revealed the presence of RARα, RXRα and the lysine acetyl transferase PCAF in AGAP2 promoter. Our results provide a novel understanding of AGAP2 expression regulation that could be beneficial to those patients with cancers where AGAP2 is overexpressed.

Role of AGAP2 in the profibrogenic effects induced by TGFβ in LX-2 hepatic stellate cells

Liver damage induces hepatic stellate cells (HSC) activation, characterised by a fibrogenic, proliferative and migratory phenotype. Activated HSC are mainly regulated by transforming growth factor β 1 (TGFβ1), which increases the production of extracellular matrix proteins (e.g. collagen-I) promoting the progression of hepatic fibrosis. AGAP2 (ArfGAP with GTPase domain, ankyrin repeat and PH domain 2) is a GTPase/GTP-activating protein involved in the actin remodelling system and receptor recycling. In the present work the role of AGAP2 in human HSC in response to TGFβ1 was investigated. LX-2 HSC were transfected with AGAP2 siRNA and treated with TGFβ1. AGAP2 knockdown prevented to some extent the proliferative and migratory TGFβ1-induced capacities of LX-2 cells. An array focused on human fibrosis revealed that AGAP2 knockdown partially prevented TGFβ1-mediated gene expression of the fibrogenic genes ACTA2, COL1A2, EDN1, INHBE, LOX, PDGFB, TGFΒ12, while favored the expression of CXCR4, IL1A, MMP1, MMP3 and MMP9 genes. Furthermore, TGFβ1 induced AGAP2 promoter activation and its protein expression in LX-2. Moreover, AGAP2 protein levels were significantly increased in liver samples from rats with thioacetamide-induced fibrosis. In addition, AGAP2 silencing affected TGFβ1-receptor 2 (TGFR2) trafficking in U2OS cells, blocking its effective recycling to the membrane. AGAP2 silencing in LX-2 cells prevented the TGFβ1-induced increase of collagen-I protein levels, while its overexpression enhanced collagen-I protein expression in the presence or absence of the cytokine. AGAP2 overexpression also increased focal adhesion kinase (FAK) phosphorylated levels in LX-2 cells. FAK and MEK1 inhibitors prevented the increase of collagen-I expression caused by TGFβ1 in LX-2 overexpressing AGAP2. In summary, the present work shows for the first time, that AGAP2 is a potential new target involved in TGFβ1 signalling, contributing to the progression of hepatic fibrosis.

G-protein-coupled receptor 81 promotes a malignant phenotype in breast cancer through angiogenic factor secretion

G-protein-coupled receptor 81 (GPR81) functions as a receptor for lactate and plays an important role in the regulation of anti-lipolytic effects in adipocytes. However, to data, a role for GPR81 in the tumor microenvironment has not been clearly defined. Here, GPR81 expression in breast cancer patients and several breast cancer cell lines was significantly increased compared with normal mammary tissues and cells. GPR81 knockdown resulted in impaired breast cancer growth and led to apoptosis both in vitro and in vivo. Furthermore, the inhibition of GPR81 signaling suppressed angiogenesis through a phosphoinositide 3-OH kinase (PI3K)/Akt-cAMP response element binding protein (CREB) pathway, which led to decreased production of the pro-angiogenic mediator amphiregulin (AREG). Overall, these findings identify GPR81 as a tumor-promoting receptor in breast cancer progression and suggest a novel mechanism that regulates GPR81-dependent activation of the PI3K/Akt signaling axis in tumor microenvironment.

Co-amplification of phosphoinositide 3-kinase enhancer A and cyclin-dependent kinase 4 triggers glioblastoma progression

Glioblastoma (GBM) is the most common primary brain tumor and has a dismal prognosis. Amplification of chromosome 12q13-q15 (Cyclin-dependent kinase 4 (CDK4) amplicon) is frequently observed in numerous human cancers including GBM. Phosphoinositide 3-kinase enhancer (PIKE) is a group of GTP-binding proteins that belong to the subgroup of centaurin GTPase family, encoded by CENTG1 located in CDK4 amplicon. However, the pathological significance of CDK4 amplicon in GBM formation remains incompletely understood. In the current study, we show that co-expression of PIKE-A and CDK4 in TP53/PTEN double knockout GBM mouse model additively shortens the latency of glioma onset and survival compared to overexpression of these genes alone. Consequently, p-mTOR, p-Akt and p-ERK pathways are highly upregulated in the brain tumors, in alignment with their oncogenic activities by CDK4 and PIKE-A stably transfected in GBM cell lines. Hence, our findings support that PIKE amplification or overexpression coordinately acts with CDK4 to drive GBM tumorigenesis.

Tumor Necrosis Factor-α Promotes Phosphoinositide 3-Kinase Enhancer A and AMP-Activated Protein Kinase Interaction to Suppress Lipid Oxidation in Skeletal Muscle

Tumor necrosis factor-α (TNF-α) is an inflammatory cytokine that plays a central role in obesity-induced insulin resistance. It also controls cellular lipid metabolism, but the underlining mechanism is poorly understood. We report in this study that phosphoinositide 3-kinase enhancer A (PIKE-A) is a novel effector of TNF-α to facilitate its metabolic modulation in the skeletal muscle. Depletion of PIKE-A in C2C12 myotubes diminished the inhibitory activities of TNF-α on mitochondrial respiration and lipid oxidation, whereas PIKE-A overexpression exacerbated these cellular responses. We also found that TNF-α promoted the interaction between PIKE-A and AMP-activated protein kinase (AMPK) to suppress its kinase activity in vitro and in vivo. As a result, animals with PIKE ablation in the skeletal muscle per se display an upregulation of AMPK phosphorylation and a higher preference to use lipid as the energy production substrate under high-fat diet feeding, which mitigates the development of diet-induced hyperlipidemia, ectopic lipid accumulation, and muscle insulin resistance. Hence, our data reveal PIKE-A as a new signaling factor that is important for TNF-α-initiated metabolic changes in skeletal muscle.

Antiglioma effects of cytarabine on leptomeningeal metastasis of high-grade glioma by targeting the PI3K/Akt/mTOR pathway

Leptomeningeal metastasis (LM) of high-grade glioma is a highly lethal disease requiring new effective therapeutic measures. For both de novo or relapsed glioma with LM, intrathecal cytarabine chemotherapy is not frequently used for first-line and relapse protocols. We encountered a clinical case demonstrating effective application of cytarabine in high-grade glioma with LM, prompting us to explore the effects of cytarabine on malignant glioma and molecular mechanisms of such effects through in vivo and in vitro experiments. The U87 cell line was selected to represent human glioma for studies. Cell viability was measured by MTT assay, plate colony formation assay, and trypan-blue dye exclusion test. Apoptosis was assessed by flow cytometry. Protein expression levels were detected by Western blot assay and immunohistochemistry. mRNA expression was examined by quantitative real-time reverse transcription polymerase chain reaction. Cytarabine inhibited tumor growth during the in vivo experiment. The present study confirmed that cytarabine inhibits proliferation and promotes apoptosis of U87 cells, and molecular analysis of this effect showed that cytarabine significantly reduces expression of phosphatidylinositol 3-kinase/serine/threonine kinase also known as the protein kinase B/mechanistic target of rapamycin (PI3K/Akt/mTOR) pathway, Ki-67, BCL2, and 4-1BB, and upregulates Bax and cleaved caspase-3. Our findings indicated that intrathecal administration of cytarabine manifests potential in prophylaxis and treatment of malignant glioma with LM. Effective medications for high-grade glioma with LM should contain cytarabine.

Arf GAPs and molecular motors

Arf GTPase-activating proteins (Arf GAPs) were first identified as regulators of the small GTP-binding proteins ADP-ribosylation factors (Arfs). The Arf GAPs are a large family of proteins in metazoans, outnumbering the Arfs that they regulate. The members of the Arf GAP family have complex domain structures and some have been implicated in particular cellular functions, such as cell migration, or with particular pathologies, such as tumor invasion and metastasis. The specific effects of Arfs sometimes depend on the Arf GAP involved in their regulation. These observations have led to speculation that the Arf GAPs themselves may affect cellular activities in capacities beyond the regulation of Arfs. Recently, 2 Arf GAPs, ASAP1 and AGAP1, have been found to bind directly to and influence the activity of myosins and kinesins, motor proteins associated with filamentous actin and microtubules, respectively. The Arf GAP-motor protein interaction is critical for cellular behaviors involving the actin cytoskeleton and microtubules, such as cell migration and other cell movements. Arfs, then, may function with molecular motors through Arf GAPs to regulate microtubule and actin remodeling.

α-Synuclein binds and sequesters PIKE-L into Lewy bodies, triggering dopaminergic cell death via AMPK hyperactivation

The abnormal aggregation of fibrillar α-synuclein in Lewy bodies plays a critical role in the pathogenesis of Parkinson's disease. However, the molecular mechanisms regulating α-synuclein pathological effects are incompletely understood. Here we show that α-synuclein binds phosphoinositide-3 kinase enhancer L (PIKE-L) in a phosphorylation-dependent manner and sequesters it in Lewy bodies, leading to dopaminergic cell death via AMP-activated protein kinase (AMPK) hyperactivation. α-Synuclein interacts with PIKE-L, an AMPK inhibitory binding partner, and this action is increased by S129 phosphorylation through AMPK and is decreased by Y125 phosphorylation via Src family kinase Fyn. A pleckstrin homology (PH) domain in PIKE-L directly binds α-synuclein and antagonizes its aggregation. Accordingly, PIKE-L overexpression decreases dopaminergic cell death elicited by 1-methyl-4-phenylpyridinium (MPP⁺), whereas PIKE-L knockdown elevates α-synuclein oligomerization and cell death. The overexpression of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or α-synuclein induces greater dopaminergic cell loss and more severe motor defects in PIKE-KO and Fyn-KO mice than in wild-type mice, and these effects are attenuated by the expression of dominant-negative AMPK. Hence, our findings demonstrate that α-synuclein neutralizes PIKE-L's neuroprotective actions in synucleinopathies, triggering dopaminergic neuronal death by hyperactivating AMPK.

Arf proteins in cancer cell migration

Members of the ADP-ribosylation factor (Arf) family of small GTP-binding (G) proteins regulate several aspects of membrane trafficking, such as vesicle budding, tethering and cytoskeleton organization. Arf family members, including Arf-like (Arl) proteins have been implicated in several essential cellular functions, like cell spreading and migration. These functions are used by cancer cells to disseminate and invade the tissues surrounding the primary tumor, leading to the formation of metastases. Indeed, Arf and Arl proteins, as well as their guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) have been found to be abnormally expressed in different cancer cell types and human cancers. Here, we review the current evidence supporting the involvement of Arf family proteins and their GEFs and GAPs in cancer progression, focusing on 3 different mechanisms: cell-cell adhesion, integrin internalization and recycling, and actin cytoskeleton remodeling.

Akt attenuates apoptotic death through phosphorylation of H2A under hydrogen peroxide-induced oxidative stress in PC12 cells and hippocampal neurons

Although the essential role of protein kinase B (PKB)/Akt in cell survival signaling has been clearly established, the mechanism by which Akt mediates the cellular response to hydrogen peroxide (H₂O₂)-induced oxidative stress remains unclear. We demonstrated that Akt attenuated neuronal apoptosis through direct association with histone 2A (H2A) and phosphorylation of H2A at threonine 17. At early time points during H₂O₂ exposure of PC12 cells and primary hippocampal neurons, when the cells can tolerate the level of DNA damage, Akt was activated and phosphorylated H2A, leading to inhibition of apoptotic death. At later time points, Akt delivered the NAD⁺-dependent protein deacetylase Sirtuin 2 (Sirt 2) to the vicinity of phosphorylated H2A in response to irreversible DNA damage, thereby inducing H2A deacetylation and subsequently leading to apoptotic death. Ectopically expressed T17A-substituted H2A minimally interacted with Akt and failed to prevent apoptosis under oxidative stress. Thus Akt-mediated H2A phosphorylation has an anti-apoptotic function in conditions of H₂O₂-induced oxidative stress in neurons and PC12 cells.

Fyn-phosphorylated PIKE-A binds and inhibits AMPK signaling, blocking its tumor suppressive activity

The AMP-activated protein kinase, a key regulator of energy homeostasis, has a critical role in metabolic disorders and cancers. AMPK is mainly regulated by cellular AMP and phosphorylation by upstream kinases. Here, we show that PIKE-A binds to AMPK and blocks its tumor suppressive actions, which are mediated by tyrosine kinase Fyn. PIKE-A directly interacts with AMPK catalytic alpha subunit and impairs T172 phosphorylation, leading to repression of its kinase activity on the downstream targets. Mutation of Fyn phosphorylation sites on PIKE-A, depletion of Fyn, or pharmacological inhibition of Fyn blunts the association between PIKE-A and AMPK, resulting in loss of its inhibitory effect on AMPK. Cell proliferation and oncogenic assays demonstrate that PIKE-A antagonizes tumor suppressive actions of AMPK. In human glioblastoma samples, PIKE-A expression inversely correlates with the p-AMPK levels, supporting that PIKE-A negatively regulates AMPK activity in cancers. Thus, our findings provide additional layer of molecular regulation of the AMPK signaling pathway in cancer progression.

Novel candidate key drivers in the integrative network of genes, microRNAs, methylations, and copy number variations in squamous cell lung carcinoma

The mechanisms of lung cancer are highly complex. Not only mRNA gene expression but also microRNAs, DNA methylation, and copy number variation (CNV) play roles in tumorigenesis. It is difficult to incorporate so much information into a single model that can comprehensively reflect all these lung cancer mechanisms. In this study, we analyzed the 129 TCGA (The Cancer Genome Atlas) squamous cell lung carcinoma samples with gene expression, microRNA expression, DNA methylation, and CNV data. First, we used variance inflation factor (VIF) regression to build the whole genome integrative network. Then, we isolated the lung cancer subnetwork by identifying the known lung cancer genes and their direct regulators. This subnetwork was refined by the Bayesian method, and the directed regulations among mRNA genes, microRNAs, methylations, and CNVs were obtained. The novel candidate key drivers in this refined subnetwork, such as the methylation of ARHGDIB and HOXD3, microRNA let-7a and miR-31, and the CNV of AGAP2, were identified and analyzed. On three large public available lung cancer datasets, the key drivers ARHGDIB and HOXD3 demonstrated significant associations with the overall survival of lung cancer patients. Our results provide new insights into lung cancer mechanisms.

Molecular heterogeneity of glioblastoma and its clinical relevance

Glioblastoma is the most common intracranial malignancy and constitutes about 50 % of all gliomas. Both inter-tumor and intra-tumor histological heterogeneity had been recognized by the early 1980-ies. Recent works using novel molecular platforms provided molecular definitions of these tumors. Based on comprehensive genomic sequence analyses, The Cancer Genome Atlas Research Network (TCGA) cataloged somatic mutations and recurrent copy number alterations in glioblastoma. Robust transcriptome and epigenome studies also revealed inter-tumor heterogeneity. Integration and cluster analyses of multi-dimensional genomic data lead to a new classification of glioblastoma tumors into subtypes with distinct biological features and clinical correlates. However, multiple observations also revealed tumor area-specific patterns of genomic imbalance. In addition, genetic alterations have been identified that were common to all areas analyzed and other alterations that were area specific. Analyses of intra-tumor transcriptome variations revealed that in more than half of the examined cases, fragments from the same tumor mass could be classified into at least two different glioblastoma molecular subgroups. Intra-tumor heterogeneity of molecular genetic profiles in glioblastoma may explain the difficulties encountered in the validation of oncologic biomarkers, and contribute to a biased selection of patients for single target therapies, treatment failure or drug resistance. In this paper, we summarize the currently available literature concerning inter- and intra-tumor molecular heterogeneity of glioblastomas, and call attention to the importance of this topic in relation to the growing efforts in routine molecular diagnostics and personalized therapy.

The roles of PIKE in tumorigenesis

Tumorigenesis is the process by which normal cells evolve the capacity to evade and overcome the constraints usually placed upon their growth and survival. To ensure the integrity of organs and tissues, the balance of cell proliferation and cell death is tightly maintained. The proteins controlling this balance are either considered oncogenes, which promote tumorigenesis, or tumor suppressors, which prevent tumorigenesis. Phosphoinositide 3-kinase enhancer (PIKE) is a family of GTP-binding proteins that possess anti-apoptotic functions and play an important role in the central nervous system. Notably, accumulating evidence suggests that PIKE is a proto-oncogene involved in tumor progression. The PIKE gene (CENTG1) is amplified in a variety of human cancers, leading to the resistance against apoptosis and the enhancement of invasion. In this review, we will summarize the functions of PIKE proteins in tumorigenesis and discuss their potential implications in cancer therapy.

Fyn regulates adipogenesis by promoting PIKE-A/STAT5a interaction

Fyn is a tyrosine kinase with multiple roles in a variety of cellular processes. Here we report that Fyn is a new kinase involved in adipocyte differentiation. Elevated Fyn protein is detected specifically in the adipocytes of obese mice. Moreover, Fyn expression increases progressively in 3T3-L1 cells during in vitro adipogenesis, which correlates with its kinase activity. Inhibition of Fyn by either genetic or pharmacological manipulation restrains the 3T3-L1 preadipocytes from fully differentiating into mature adipocytes. Mechanistically, Fyn regulates the activity of the adipogenic transcription factor signal transducer and activator of transcription 5a (STAT5a) through enhancing its interaction with the GTPase phosphoinositide 3-kinase enhancer A (PIKE-A). The STAT5a activity is therefore reduced in Fyn- or PIKE-ablated adipose tissues, leading to diminished expression of adipogenic markers and adipocyte differentiation. Our data thus demonstrate a novel functional interaction between Fyn, PIKE-A, and STAT5a in mediating adipogenesis.

Disrupting the PIKE-A/Akt interaction inhibits glioblastoma cell survival, migration, invasion and colony formation

The cyclin-dependent kinase 4 (CDK4) amplicon is frequently amplified in numerous human cancers including gliomas. PIKE-A, a proto-oncogene that is one of the important components of the CDK4 amplicon, binds to and enhances the kinase activity of Akt, thereby promoting cancer progression. To define the roles of the PIKE-A/Akt interaction in glioblastoma multiform (GBM) progression, we used biochemical protein/protein interaction (PPI) assays and live cell fluorescence-based protein complementation assays to search for small peptide antagonist from these proteins that were able to block their interaction. Here, we show that disruption of the interaction between PIKE-A and Akt by the small peptides significantly reduces glioblastoma cell proliferation, colony formation, migration and invasion. Disruption of PIKE-A/Akt association potently suppressed GBM cell proliferation and sensitized the cells to two clinical drugs that are currently used to treat GBM. Interestingly, GBM cells containing the CDK4 amplicon were more responsive to the inhibition of the PIKE-A/Akt interaction than GBM cells lacking this amplicon. Taken together, our findings provide proof-of-principle that blocking a PPI that is essential for cancer progression provides a valuable strategy for therapeutic discovery.

PIKE mediates EGFR proliferative signaling in squamous cell carcinoma cells

One of the key drivers for squamous cell carcinoma (SCC) proliferation is activation of the epidermal growth factor receptor (EGFR), a known proto-oncogene. However, the mechanism of EGFR-dependent SCC proliferation remains unclear. Our previous studies indicate that epidermal growth factor (EGF)-induced SCC cell proliferation requires the SH3 domain of phospholipase C-γ1 (PLC-γ1), but not its catalytic activity. The SH3 domain of PLC-γ1 is known to activate the short form of nuclear phosphatidylinositol 3-kinase enhancer (PIKE) that enhances the activity of nuclear class Ia phosphatidylinositol 3-kinase (PI3K) required for proliferation. However, PIKE has been described for more than a decade to be present exclusively in neuronal cells. In the present study, we found that PIKE was highly expressed in malignant human keratinocytes (SCC4 and SCC12B2) but had low expression in normal human keratinocytes. Immunohistochemical analysis showed strong nuclear staining of PIKE in human epidermal and tongue SCC specimens but little staining in the adjacent non-cancerous epithelium. Treatment of SCC4 cells with EGF-induced translocation of PLC-γ1 to the nucleus and binding of PLC-γ1 to the nuclear PIKE. Knockdown of PLC-γ1 or PIKE blocked EGF-induced activation of class Ia PI3K and protein kinase C-ζ and phosphorylation of nucleolin in the nucleus as well as EGF-induced SCC cell proliferation. However, inhibition of the catalytic activity of PLC-γ1 had little effect. These data suggest that PIKE has a critical role in EGF-induced SCC cell proliferation and may function as a proto-oncogene in SCC.

The role of semaphorins and their receptors in gliomas

Gliomas are the most common tumor in the central nervous system. High-grade glioblastomas are characterized by their high invasiveness and resistance to radiotherapy, leading to high recurrence rate and short median survival despite radical surgical resection. Characterizations of gliomas at molecular level have revealed aberrations of various growth factor receptors, receptor tyrosine kinases, and tumor suppressor genes that lead to deregulation of multiple signaling pathways, thereby contributing to abnormal proliferation, invasion, and resistance to apoptosis in cancer cells. Recently, accumulating evidence points to the emerging role of axon guidance molecules in glioma progression. Notably, many signaling events harnessed by guidance molecules to regulate cell migration and axon navigation during development are also found to be involved in the modulation of deregulated pathways in gliomas. This paper focused on the signalings triggered by the guidance molecule semaphorins and their receptors plexins and neuropilins, and how their crosstalk with oncogenic pathways in gliomas might modulate cancer progression. The emerging role of semaphorins and plexins as tumor suppressors or oncogenes is also discussed.

Phosphoinositide 3-kinase enhancer (PIKE) in the brain: is it simply a phosphoinositide 3-kinase/Akt enhancer?

Since its discovery in 2000, phosphoinositide 3-kinase enhancer (PIKE) has been recognized as a class of GTPase that controls the enzymatic activities of phosphoinositide 3-kinase (PI3K) and Akt in the central nervous system (CNS). However, recent studies suggest that PIKEs are not only enhancers to PI3K/Akt but also modulators to other kinases including insulin receptor tyrosine kinase and focal adhesion kinases. Moreover, they regulate transcription factors such as signal transducer and activator of transcription and nuclear factor κB. Indeed, PIKE proteins participate in multiple cellular processes including control of cell survival, brain development, memory formation, gene transcription, and metabolism. In this review, we have summarized the functions of PIKE proteins in CNS and discussed their potential implications in various neurological disorders.

Inhibitors of Glioma Growth that Reveal the Tumour to the Immune System

Treated glioblastoma patients survive from 6 to 14 months. In the first part of this review, we describe glioma origins, cancer stem cells and the genomic alterations that generate dysregulated cell division, with enhanced proliferation and diverse response to radiation and chemotherapy. We review the pathways that mediate tumour cell proliferation, neo-angiogenesis, tumor cell invasion, as well as necrotic and apoptotic cell death. Then, we examine the ability of gliomas to evade and suppress the host immune system, exhibited at the levels of antigen recognition and immune activation, limiting the effective signaling between glioma and host immune cells.The second part of the review presents current therapies and their drawbacks. This is followed by a summary of the work of our laboratory during the past 20 years, on oligosaccharide and glycosphingolipid inhibitors of astroblast and astrocytoma division. Neurostatins, the O-acetylated forms of gangliosides GD1b and GT1b naturally present in mammalian brain, are cytostatic for normal astroblasts, but cytotoxic for rat C6 glioma cells and human astrocytoma grades III and IV, with ID50 values ranging from 200 to 450 nM. The inhibitors do not affect neurons or fibroblasts up to concentrations of 4 μM or higher.At least four different neurostatin-activated, cell-mediated antitumoral processes, lead to tumor destruction: (i) inhibition of tumor neovascularization; (ii) activation of microglia; (iii) activation of natural killer (NK) cells; (iv) activation of cytotoxic lymphocytes (CTL). The enhanced antigenicity of neurostatin-treated glioma cells, could be related to their increased expression of connexin 43. Because neurostatins and their analogues show specific activity and no toxicity for normal cells, a clinical trial would be the logical next step.

Phosphoinositide 3-kinase enhancer regulates neuronal dendritogenesis and survival in neocortex

Phosphoinositide 3-kinase enhancer (PIKE) binds and enhances phosphatidylinositol 3-kinase (PI3K)/Akt activities. However, its physiological functions in brain have never been explored. Here we show that PIKE is important in regulating the neuronal survival and development of neocortex. During development, enhanced apoptosis is observed in the ventricular zone of PIKE knock-out (PIKE(-/-)) cortex. Moreover, PIKE(-/-) neurons show reduced dendritic complexity, dendritic branch length, and soma size. These defects are due to the reduced PI3K/Akt activities in PIKE(-/-) neurons, as the impaired dendritic arborization can be rescued when PI3K/Akt cascade is augmented in vitro or in PIKE(-/-)PTEN(-/-) double-knock-out mice. Interestingly, PIKE(-/-) mice display behavioral abnormality in locomotion and spatial navigation. Because of the diminished PI3K/Akt activities, PIKE(-/-) neurons are more vulnerable to glutamate- or stroke-induced neuronal cell death. Together, our data established the critical role of PIKE in regulating neuronal survival and development by substantiating the PI3K/Akt pathway.

What we have learnt about PIKE from the knockout mice

Phosphoinositide 3-kinase enhancer (PIKE) is a group of GTPase that belongs to the centaurin superfamily. These proteins have been discovered for more than a decade but our understandings on their functions are still limited. Studies from our research group and others have revealed some of their functions in a cellular context but their roles in organ development or systemic homeostasis just begin to unveil. The generation of PIKE knockout mice thus provides the valuable model to delineate the physiological roles of PIKE. In addition to being a PI3K/Akt enhancer, phenotypic characterization of the PIKE knockout mice demonstrates that the proteins are involved in multiple signaling cascades including Janus kinase (JAK)/ Signal Transducer and Activator of Transcription (STAT), AMP-activated protein kinase (AMPK)/Acetyl-CoA carboxylase (ACC) and insulin receptor (IR)/Akt. In this article, we will review the current findings from the PIKE knockout mice studies and will discuss how these in vivo observations lead to the identifications of novel signaling cascades regulated by PIKE.

Akt-phosphorylated PIKE-A inhibits UNC5B-induced apoptosis in cancer cell lines in a p53-dependent manner

UNC5B acts as a tumor suppressor, and it induces apoptosis in the absence of its cognate ligand netrins. UNC5B is a direct transcriptional target of p53 upon UV stimulation. Here we show that Akt phosphorylates PIKE-A and regulates its association with UNC5B and inhibits UNC5B-provoked apoptosis in a p53-dependent manner. PIKE-A GTPase binds active Akt and stimulates its kinase activity in a guanine-nucleotide-dependent way. Akt feeds back and phosphorylates PIKE-A on Ser-472 and subsequently enhances its stimulatory effect on Akt kinase activity. Akt activity is significantly reduced in PIKE -/- Mouse Embryonic Fibroblast (MEF) cells as compared to wild-type cells. PIKE-A directly interacts with UNC5B, which is regulated by netrin-1-activated Akt. Overexpression of PIKE-A diminishes UNC5B expression through down-regulation of p53. Knocking down PIKE-A stabilizes p53, increases UNC5B, and escalates UV-triggered apoptosis. Depletion of Akt abrogates PIKE-A's inhibitory effect on both p53 and UNC5B. Hence our findings support the notion that Akt--phosphorylated PIKE-A inhibits UNC5B-elicited apoptosis and reduces its expression level through inactivation of p53.

Ras superfamily GEFs and GAPs: validated and tractable targets for cancer therapy?

There is now considerable and increasing evidence for a causal role for aberrant activity of the Ras superfamily of small GTPases in human cancers. These GTPases function as GDP-GTP-regulated binary switches that control many fundamental cellular processes. A common mechanism of GTPase deregulation in cancer is the deregulated expression and/or activity of their regulatory proteins, guanine nucleotide exchange factors (GEFs) that promote formation of the active GTP-bound state and GTPase-activating proteins (GAPs) that return the GTPase to its GDP-bound inactive state. In this Review, we assess the association of GEFs and GAPs with cancer and their druggability for cancer therapeutics.

Deficiency of phosphoinositide 3-kinase enhancer protects mice from diet-induced obesity and insulin resistance

OBJECTIVE

Phosphoinositide 3-kinase enhancer A (PIKE-A) is a proto-oncogene that promotes tumor growth and transformation by enhancing Akt activity. However, the physiological functions of PIKE-A in peripheral tissues are unknown. Here, we describe the effect of PIKE deletion in mice and explore the role of PIKE-A in obesity development.

RESEARCH DESIGN AND METHODS

Whole-body PIKE knockout mice were generated and subjected to high-fat-diet feeding for 20 weeks. The glucose tolerance, tissue-specific insulin sensitivity, adipocyte differentiation, and lipid oxidation status were determined. The molecular mechanism of PIKE in the insulin signaling pathway was also studied.

RESULTS

We show that PIKE-A regulates obesity development by modulating AMP-activated protein kinase (AMPK) phosphorylation. PIKE-A is important for insulin to suppress AMPK phosphorylation. The expression of PIKE-A is markedly increased in adipose tissue of obese mice, whereas depletion of PIKE-A inhibits adipocyte differentiation. PIKE knockout mice exhibit a prominent phenotype of lipoatrophy and are resistant to high-fat diet-induced obesity, liver steatosis, and diabetes. PIKE knockout mice also have augmented lipid oxidation, which is accompanied by enhanced AMPK phosphorylation in both muscle and adipose tissue. Moreover, insulin sensitivity is improved in PIKE-A-deficient muscle and fat, thus protecting the animals from diet-induced diabetes.

CONCLUSIONS

Our results suggest that PIKE-A is implicated in obesity and associated diabetes development by negatively regulating AMPK activity.

Automated network analysis identifies core pathways in glioblastoma

Background

Glioblastoma multiforme (GBM) is the most common and aggressive type of brain tumor in humans and the first cancer with comprehensive genomic profiles mapped by The Cancer Genome Atlas (TCGA) project. A central challenge in large-scale genome projects, such as the TCGA GBM project, is the ability to distinguish cancer-causing “driver” mutations from passively selected “passenger” mutations.

Principal Findings

In contrast to a purely frequency based approach to identifying driver mutations in cancer, we propose an automated network-based approach for identifying candidate oncogenic processes and driver genes. The approach is based on the hypothesis that cellular networks contain functional modules, and that tumors target specific modules critical to their growth. Key elements in the approach include combined analysis of sequence mutations and DNA copy number alterations; use of a unified molecular interaction network consisting of both protein-protein interactions and signaling pathways; and identification and statistical assessment of network modules, i.e. cohesive groups of genes of interest with a higher density of interactions within groups than between groups.

Conclusions

We confirm and extend the observation that GBM alterations tend to occur within specific functional modules, in spite of considerable patient-to-patient variation, and that two of the largest modules involve signaling via p53, Rb, PI3K and receptor protein kinases. We also identify new candidate drivers in GBM, including AGAP2/CENTG1, a putative oncogene and an activator of the PI3K pathway; and, three additional significantly altered modules, including one involved in microtubule organization. To facilitate the application of our network-based approach to additional cancer types, we make the method freely available as part of a software tool called NetBox.

PIKE-A is required for prolactin-mediated STAT5a activation in mammary gland development

PI 3-kinase enhancer A (PIKE-A) is critical for the activation of Akt signalling, and has an essential function in promoting cancer cell survival. However, its physiological functions are poorly understood. Here, we show that PIKE-A directly associates with both signal transducer and activator of transcription 5a (STAT5a) and prolactin (PRL) receptor, which is essential for PRL-provoked STAT5a activation and the subsequent gene transcription. Depletion of PIKE-A in HC11 epithelial cells diminished PRL-induced STAT5 activation and cyclin D1 expression, resulting in profoundly impaired cell proliferation in vitro. To confirm the function of PIKE-A in PRL signalling in vivo, we generated PIKE knockout (PIKE-/-) mice. PIKE-/- mice displayed a severe lactation defect that was characterized by enhanced apoptosis and impaired proliferation of mammary epithelial cells. At parturition, STAT5 activation and cyclin D1 expression were substantially reduced in the mammary epithelium of PIKE-/- mice. The defective mammary gland development in PIKE-/- mice was rescued by overexpression of a mammary-specific cyclin D1 transgene. These data establish a critical function for PIKE-A in mediating PRL functions.

Integrative genome analysis reveals an oncomir/oncogene cluster regulating glioblastoma survivorship

Using a multidimensional genomic data set on glioblastoma from The Cancer Genome Atlas, we identified hsa-miR-26a as a cooperating component of a frequently occurring amplicon that also contains CDK4 and CENTG1, two oncogenes that regulate the RB1 and PI3 kinase/AKT pathways, respectively. By integrating DNA copy number, mRNA, microRNA, and DNA methylation data, we identified functionally relevant targets of miR-26a in glioblastoma, including PTEN, RB1, and MAP3K2/MEKK2. We demonstrate that miR-26a alone can transform cells and it promotes glioblastoma cell growth in vitro and in the mouse brain by decreasing PTEN, RB1, and MAP3K2/MEKK2 protein expression, thereby increasing AKT activation, promoting proliferation, and decreasing c-JUN N-terminal kinase-dependent apoptosis. Overexpression of miR-26a in PTEN-competent and PTEN-deficient glioblastoma cells promoted tumor growth in vivo, and it further increased growth in cells overexpressing CDK4 or CENTG1. Importantly, glioblastoma patients harboring this amplification displayed markedly decreased survival. Thus, hsa-miR-26a, CDK4, and CENTG1 comprise a functionally integrated oncomir/oncogene DNA cluster that promotes aggressiveness in human cancers by cooperatively targeting the RB1, PI3K/AKT, and JNK pathways.

Akt2 and Akt3 play a pivotal role in malignant gliomas

Akt, one of the major downstream effectors of phosphatidylinositol 3-kinase, is hyper-expressed and activated in a variety of cancers including glioblastoma. However, the expression profiles of the Akt isoforms Akt1/PKBalpha, Akt2/PKBbeta, and Akt3/PKBgamma and their functional roles in malignant glioma are not well understood. Therefore, we examined the protein and mRNA expression patterns of Akt isoforms in tissues from human astrocytomas, glioblastomas, and non-neoplastic regions. We also explored the biological role of each Akt isoform in malignant glioma cells using RNA interference-mediated knock-down and the over-expression of plasmid DNA of each isoform. The expression of Akt1 protein and mRNA was similar in glioma and normal control tissues. Although the protein and mRNA level of Akt2 increased with the pathological grade of malignancy, the expression of Akt3 mRNA and protein decreased as the malignancy grade increased. In U87MG, T98G, and TGB cells, the down-regulation of Akt2 or Akt3 by RNA interference reduced the expression of the phosphorylated form of Bad, resulting in the induction of caspase-dependent apoptosis. Akt1 knock-down did not affect cell growth or survival. We first demonstrate that the over-expression of Akt2 or Akt3 down-regulated the expression of the other protein and that endogenous Akt3 protein showed high kinase activity in U87MG cells. Our data suggest that Akt2 and Akt3 play an important role in the viability of human malignant glioma cells. Targeting Akt2 and Akt3 may hold promise for the treatment of patients with gliomas.

Arf GTPase-activating protein AGAP2 regulates focal adhesion kinase activity and focal adhesion remodeling

Focal adhesions are specialized sites of cell attachment to the extracellular matrix where integrin receptors link extracellular matrix to the actin cytoskeleton, and they are constantly remodeled during cell migration. Focal adhesion kinase (FAK) is an important regulator of focal adhesion remodeling. AGAP2 is an Arf GTPase-activating protein that regulates endosomal trafficking and is overexpressed in different human cancers. Here we examined the regulation of the FAK activity and the focal adhesion remodeling by AGAP2. Our results show that FAK binds the pleckstrin homology domain of AGAP2, and the binding is independent of FAK activation following epidermal growth factor receptor stimulation. Overexpression of AGAP2 augments the activity of FAK, and concordantly, the knockdown of AGAP2 expression with RNA interference attenuates the FAK activity stimulated by epidermal growth factor or platelet-derived growth factor receptors. AGAP2 is localized to the focal adhesions, and its overexpression results in dissolution of the focal adhesions, whereas knockdown of its expression stabilizes them. The AGAP2-induced dissolution of the focal adhesions is independent of its GTPase-activating protein activity but may involve its N-terminal G protein-like domain. Our results indicate that AGAP2 regulates the FAK activity and the focal adhesion disassembly during cell migration.

GGAP2/PIKE-a directly activates both the Akt and nuclear factor-kappaB pathways and promotes prostate cancer progression

GGAP2/PIKE-A is a GTP-binding protein that can enhance Akt activity. Increased activation of the AKT and nuclear factor-kappaB (NF-kappaB) pathways have been identified as critical steps in cancer initiation and progression in a variety of human cancers. We have found significantly increased expression GGAP2 in the majority of human prostate cancers and GGAP2 expression increases Akt activation in prostate cancer cells. Thus, increased GGAP2 expression is a common mechanism for enhancing the activity of the Akt pathway in prostate cancers. In addition, we have found that activated Akt can bind and phosphorylate GGAP2 at serine 629, which enhances GTP binding by GGAP2. Phosphorylated GGAP2 can bind the p50 subunit of NF-kappaB and enhances NF-kappaB transcriptional activity. When expressed in prostate cancer cells, GGAP2 enhances proliferation, foci formation, and tumor progression in vivo. Thus, increased GGAP2 expression, which is present in three quarters of human prostate cancers, can activate two critical pathways that have been linked to prostate cancer initiation and progression.

TMZ-BioShuttle--a reformulated temozolomide

There is a large number of effective cytotoxic drugs whose side effect profile, efficacy, and long-term use in man are well understood and documented over decades of use in clinical routine e.g. in the treatment of recurrent glioblastoma multiforme (GBM) and the hormone-refractory prostate cancer (HRPC). Both cancers are insensitive against most chemotherapeutic interventions; they have low response rates and poor prognoses. Some cytotoxic agents can be significantly improved by using modern technology of drug delivery or formulation. We succeeded to enhance the pharmacologic potency with simultaneous reduction of unwanted adverse reactions of the highly efficient chemotherapeutic temozolomide (TMZ) as an example. The TMZ connection to transporter molecules (TMZ-BioShuttle) resulted in a much higher pharmacological effect in glioma cell lines while using reduced doses. This permits the conclusion that a suitable chemistry could realize the ligation of pharmacologically active, but sensitive and highly unstable pharmaceutical ingredients without functional deprivation. The re-formulation of TMZ to TMZ-BioShuttle achieved a nearly 10-fold potential of the established pharmaceutic TMZ far beyond the treatment of brain tumors cells and results in an attractive reformulated drug with enhanced therapeutic index.

Cdk5-mediated regulation of the PIKE-A-Akt pathway and glioblastoma cell invasion

Isoform A of phosphatidylinositol 3-kinase enhancer (PIKE-A) is a newly identified prooncogenic factor that has been implicated in cancer cell growth. How PIKE-A activity is regulated in response to growth signal is poorly understood. Here, we demonstrate that cyclin dependent kinase 5 (Cdk5), a protein known to function mainly in postmitotic neurons, directly phosphorylates PIKE-A at Ser-279 in its GTPase domain in glioblastoma cells. This phosphorylation event stimulates PIKE-A GTPase activity and the activity of its downstream effector Akt. Growth signal activates Cdk5 and results in a Cdk5-dependent accumulation of phosphorylated PIKE-A and activation of Akt in the nucleus. Furthermore, PIKE-A phosphorylation and Cdk5 are increased in human glioblastoma specimens. Phosphorylation of PIKE-A by Cdk5 mediates growth factor-induced migration and invasion of human glioblastoma cells. Together, these findings identify PIKE as the first Cdk5 target in cancer cells, revealing a previously undescribed regulatory mechanism that mediates growth signal-induced activation of PIKE-A/Akt and tumor invasion.

Neuroprotective actions of PIKE-L by inhibition of SET proteolytic degradation by asparagine endopeptidase

Ischemia and seizure cause excessive neuronal excitation that is associated with brain acidosis and neuronal cell death. However, the molecular mechanism of acidification-triggered neuronal injury is incompletely understood. Here, we show that asparagine endopeptidase (AEP) is activated under acidic condition, cuts SET, an inhibitor of DNase, and triggers DNA damage in brain, which is inhibited by PIKE-L. SET, a substrate of caspases, was cleaved by acidic cytosolic extract independent of caspase activation. Fractionation of the acidic cellular extract yielded AEP that is required for SET cleavage. We found that kainate provoked AEP activation and SET cleavage at N175, triggering DNA nicking in wild-type, but not AEP null, mice. PIKE-L strongly bound SET and prevented its degradation by AEP, leading to resistance of neuronal cell death. Moreover, AEP also mediated stroke-provoked SET cleavage and cell death in brain. Thus, AEP might be one of the proteinases activated by acidosis triggering neuronal injury during neuroexcitotoxicity or ischemia.

Split pleckstrin homology domain-mediated cytoplasmic-nuclear localization of PI3-kinase enhancer GTPase

Cytoplasm-nucleus shuttling of phosphoinositol 3-kinase enhancer (PIKE) is known to correlate directly with its cellular functions. However, the molecular mechanism governing this shuttling is not known. In this work, we demonstrate that PIKE is a new member of split pleckstrin homology (PH) domain-containing proteins. The structure solved in this work reveals that the PIKE PH domain is split into halves by a positively charged nuclear localization sequence. The PIKE PH domain binds to the head groups of di- and triphosphoinositides with similar affinities. Lipid membrane binding of the PIKE PH domain is further enhanced by the positively charged nuclear localization sequence, which is juxtaposed to the phosphoinositide head group-binding pocket of the domain. We demonstrate that the cytoplasmic-nuclear shuttling of PIKE is dynamically regulated by the balancing actions of the lipid-binding property of both the split PH domain and the nuclear targeting function of its nuclear localization sequence.

Malignant astrocytic glioma: genetics, biology, and paths to treatment

Malignant astrocytic gliomas such as glioblastoma are the most common and lethal intracranial tumors. These cancers exhibit a relentless malignant progression characterized by widespread invasion throughout the brain, resistance to traditional and newer targeted therapeutic approaches, destruction of normal brain tissue, and certain death. The recent confluence of advances in stem cell biology, cell signaling, genome and computational science and genetic model systems have revolutionized our understanding of the mechanisms underlying the genetics, biology and clinical behavior of glioblastoma. This progress is fueling new opportunities for understanding the fundamental basis for development of this devastating disease and also novel therapies that, for the first time, portend meaningful clinical responses.

Contribution of AZAP-Type Arf GAPs to cancer cell migration and invasion

Arf GAPs are a family of proteins with a common catalytic domain that induces hydrolysis of GTP bound to the small GTP-binding protein Arf. The proteins are otherwise structurally diverse. Several subtypes of Arf GAPs have been found to be targets of oncogenes and to control cell proliferation and cell migration. The latter effects are thought to be mediated by coordinating changes in actin remodeling and membrane traffic. In this chapter, we discuss Arf GAPs that have been linked to oncogenesis and the molecular mechanisms underlying the effects of these proteins in cancer cells. We also discuss the enzymology of the Arf GAPs related to possible targeted inhibition of specific subtypes of Arf GAPs.

Candidate glioblastoma development gene identification using concordance between copy number abnormalities and gene expression level changes

Copy number abnormalities (CNAs) in tumor cells are presumed to affect expression levels of genes located in region of abnormality. To investigate this relationship we have surveyed the losses, gains and amplifications in 30 glioblastomas using array comparative genome hybridization and compared these data with gene expression changes in the same tumors using the Affymetrix U133Plus2.0 oligonucleotide arrays. The two datasets were overlaid using our in-house overlay tool which highlights concordance between CNAs and expression level changes for the same tumors. In this survey we have highlighted genes frequently overexpressed in amplified regions on chromosomes 1, 4, 11, and 12 and have identified novel amplicons on these chromosomes. Deletions of specific regions on chromosomes 9, 10, 11, 14, and 15 have also been correlated with reduced gene expression in the regions of minimal overlap. In addition we describe a novel approach for comparing gene expression levels between tumors based on the presence or absence of chromosome CNAs. This genome wide screen provides an efficient and comprehensive survey of genes which potentially serve as the drivers for the CNAs in GBM.

The physiology of phosphoinositides

Phosphoinositides are a family of phosphorylated derivatives of the membrane lipid phosphatidylinositol. These lipids are highly concentrated in distinct pools located in a cell's plasma membrane, endosomes or nucleus, where they function as ligands for phosphoinositide-binding proteins. Protein domains that bind phosphoinositides include the pleckstrin homology (PH) domain, the phox homology (PX) domain and the Fab1p-YOPB-Vps27p-EEA1 (FYVE) domain. These domains are found in many proteins involved in intracellular signaling, membrane trafficking and cytoskeletal rearrangement. Recent studies have identified potential links between alterations to various signaling pathways involving phosphoinositides and the etiology of many human diseases.

The role of cell signaling in poxvirus tropism: the case of the M-T5 host range protein of myxoma virus

Poxviruses demonstrate strict species specificity in vivo that range from narrow to broad, however the fundamental factors that mediate the basis of poxvirus tropism remain poorly understood. It is generally believed that most, if not all, poxviruses can efficiently bind and enter a wide range of mammalian cells and all of the known host anti-viral pathways that block viral replication in nonpremissive cells operate downstream of virus entry. A productive poxvirus infection is heavily dependent upon the production of a vast array of host modulatory products that specifically target and manipulate both extracellular immune response pathways of the host, as well as intracellular signal transduction pathways of the individually infected cells. The unique pathogenesis and host tropism of specific poxviruses can be attributed to the broad diversity of host modulatory proteins they express. Myxoma virus (MV) is a rabbit-specific poxviruses that encodes multiple host range factors, including an ankyrin-repeat protein M-T5, which functions to regulate tropism of MV for rabbit lymphocytes and some human cancer cells. At the molecular level, M-T5 binds and alters at least two distinct cellular proteins: Akt and cullin-1. The direct interaction between M-T5 and Akt was shown to be a key restriction determinant for MV tropism in a spectrum of human cancer cells making MV an excellent oncolytic candidate. Thus, the intricate relationship between viral encoded proteins and components of the host cell signaling networks can have profound impact on poxvirus tropism. The lessons we continue to learn from poxvirus host range factors like M-T5 will provide further insights into the factors that regulate poxvirus tropism and the mechanisms by which poxviruses micromanipulate the signaling pathways of the infected cell.

PIKE-A is a proto-oncogene promoting cell growth, transformation and invasion

PIKE-A (phosphoinositide 3-kinases (PI 3)-kinase enhancer) is a ubiquitously expressed GTPase, which binds to and enhances protein kinase B (Akt) kinase activity in a guanine nucleotide-dependent manner. PIKE-A is one of the components of the CDK4 amplicon that is amplified in numerous human cancers. However, whether PIKE-A itself can mediate cell transformation, proliferation and migration remains unknown. Here, we show that PIKE-A is overexpressed in various human cancer samples, escalates U87MG glioblastoma invasion and provokes NIH3T3 cell transformation. Overexpression of wild-type (WT) PIKE-A enhances NIH3T3 and U87MG cell growth, which is further increased by cancer cell-derived PIKE-A active mutants. In contrast, both the dominant-negative mutant and the phosphoinositide lipids interaction-defective mutant antagonize cell proliferation. Moreover, PIKE-A and its active and inactive mutants similarly enhance or antagonize U87MG cell survival and invasion, and their ability to do so is coupled with the catalytic effect they have on Akt activation. Furthermore, PIKE-A WT and its active mutants significantly elicit NIH3T3 cell transformation. Thus, our findings support the concept that PIKE-A acts as a proto-oncogene, promoting cell transformation through Akt activation.

The centaurin gamma-1 GTPase-like domain functions as an NTPase

Centaurins are a family of proteins that contain GTPase-activating protein domains, with the gamma family members containing in addition a GTPase-like domain. Centaurins reside mainly in the nucleus and are known to activate phosphoinositide 3-kinase, a key regulator of cell proliferation, motility and vesicular trafficking. In the present study, using X-ray structural analysis, enzymatic assays and nucleotide-binding studies, we show that, for CENTG1 (centaurin gamma-1) the GTPase-like domain has broader trinucleotide specificity. Alterations within the G4 motif of CENTG1 from the highly conserved NKXD found in typical GTPases to TQDR result in the loss of specificity, a lower affinity for the nucleotides and higher turnover rates. These results indicate that the centaurins could be more accurately classified as NTPases and point to alternative mechanisms of cell signalling control.