Class II phosphoinositide 3-kinases are downstream targets of activated polypeptide growth factor receptors

Inhibition of class II phosphoinositide 3-kinase gamma expression by p185(Bcr-Abl) contributes to impaired chemotaxis and aberrant homing of leukemic cells

The expression of p185(Bcr-Abl) in Ba/F3 cells inhibits the chemotactic response of these cells to SDF1alpha. A mutant p185(Bcr-Abl) with deletion of amino acids from 176 to 426 (p185(Delta176-426)) is deficient in suppressing SDF1alpha-stimulated chemotaxis. Comparison of the gene expression profiles among parental Ba/F3 cells and cells transformed by p185(Bcr-Abl) and p185(Delta176-426) reveals that class II phosphoinositide 3-kinase gamma (PI3KC2gamma) expression is markedly down-regulated by p185(Bcr-Abl) but not p185(Delta176-426). Furthermore, knockdown of PI3KC2gamma expression in p185(Delta176-426) cells is sufficient to suppress SDF1alpha-stimulated chemotaxis and to promote infiltration of these cells into the liver. Together, these studies suggest that inhibition of PI3KC2gamma expression may represent a mechanism by which Bcr-Abl suppresses SDF1alpha-induced chemotaxis and induces abnormal homing of leukemic cells.

Quantitative analysis of HGF and EGF-dependent phosphotyrosine signaling networks

We have used stable isotope labeling by amino acids in cell culture (SILAC), in combination with high-resolution mass spectrometry, to identify common and discrete components of the respective receptor tyrosine kinase-dependent phosphotyrosine-associated networks induced by acute stimulation of A549 lung adenocarcinoma cells with EGF or HGF. In total, we obtained quantitative information for 274 proteins, which respond to either or both stimuli by >1.5 fold changes in enrichment, following immuno-precipitation with antiphosphotyrosine antibodies. The data reveal a high degree of overlap between the respective signaling networks but also clear points of departure. A small number of HGF specific effectors were identified including myosin-X, galectin-1, ELMO2 and EphrinB1, while a larger set of EGF specific effectors (39 proteins) includes both novel (e.g., MAP4K3) and established components of receptor tyrosine kinase receptor signaling pathways. Using available protein-interaction data the identified proteins have been assembled into a highly connected network that can be visualized using the Cytoscape tool.

The emerging mechanisms of isoform-specific PI3K signalling

Phosphoinositide 3-kinases (PI3Ks) function early in intracellular signal transduction pathways and affect many biological functions. A further level of complexity derives from the existence of eight PI3K isoforms, which are divided into class I, class II and class III PI3Ks. PI3K signalling has been implicated in metabolic control, immunity, angiogenesis and cardiovascular homeostasis, and is one of the most frequently deregulated pathways in cancer. PI3K inhibitors have recently entered clinical trials in oncology. A better understanding of how the different PI3K isoforms are regulated and control signalling could uncover their roles in pathology and reveal in which disease contexts their blockade could be most beneficial.

Insulin-feedback via PI3K-C2alpha activated PKBalpha/Akt1 is required for glucose-stimulated insulin secretion

Phosphatidylinositide 3-kinases (PI3Ks) play central roles in insulin signal transduction. While the contribution of class Ia PI3K members has been extensively studied, the role of class II members remains poorly understood. The diverse actions of class II PI3K-C2alpha have been attributed to its lipid product PI(3)P. By applying pharmacological inhibitors, transient overexpression and small-interfering RNA-based knockdown of PI3K and PKB/Akt isoforms, together with PI-lipid profiling and live-cell confocal and total internal reflection fluorescence microscopy, we now demonstrate that in response to insulin, PI3K-C2alpha generates PI(3,4)P(2), which allows the selective activation of PKBalpha/Akt1. Knockdown of PI3K-C2alpha expression and subsequent reduction of PKBalpha/Akt1 activity in the pancreatic beta-cell impaired glucose-stimulated insulin release, at least in part, due to reduced glucokinase expression and increased AS160 activity. Hence, our results identify signal transduction via PI3K-C2alpha as a novel pathway whereby insulin activates PKB/Akt and thus discloses PI3K-C2alpha as a potential drugable target in type 2 diabetes. The high degree of codistribution of PI3K-C2alpha and PKBalpha/Akt1 with insulin receptor B type, but not A type, in the same plasma membrane microdomains lends further support to the concept that selectivity in insulin signaling is achieved by the spatial segregation of signaling events.

KRAS mutation testing in human cancers: The pathologist's role in the era of personalized medicine

A number of studies have shown that although antiepidermal growth factor receptor (EGFR) monoclonal antibodies are effective treatments for metastatic colorectal cancer (mCRC), only patients with wild-type KRAS tumors derive clinical benefit from these therapies. The anti-EGFR monoclonal antibodies panitumumab and cetuximab are approved in the United States for treatment of mCRC refractory to chemotherapy but are not recommended for use in patients with mutations in KRAS codons 12 or 13. Similarly, panitumumab is approved for the treatment of mCRC only in patients with wild-type KRAS in Europe and Canada. It is clear that KRAS mutational analysis will become an important aspect of disease management in patients with mCRC. Consequently, it will be important for pathologists and oncologists to develop and agree on standardized KRAS testing and reporting procedures to ensure optimum patient care. Pathologists will be central to this process because of their crucial role in selecting appropriate tumor specimens for testing, choosing the molecular diagnostic laboratory to be used, assisting in the selection of a suitable KRAS test, and interpreting the results of KRAS mutational analysis. Guidelines for KRAS testing that address these and other important points of consideration have recently been proposed in the United States and the European Union.

Epidermal growth factor stimulates translocation of the class II phosphoinositide 3-kinase PI3K-C2beta to the nucleus

Although the class II phosphoinositide 3-kinase enzymes PI3K-C2alpha and PI3K-C2beta act acutely downstream of cell surface receptors they have also been localized to nuclei in mammalian cells. As with the class I PI3K enzymes, the relationship between the pools of enzyme present in cytoplasm and nuclei remains poorly understood. In this study we test the hypothesis that PI3K-C2beta translocates to nuclei in response to growth factor stimulation. Fractionating homogenates of quiescent cells revealed that less than 5% of total PI3K-C2beta resides in nuclei. Stimulation with epidermal growth factor sequentially increased levels of this enzyme, firstly in the cytosol and secondly in the nuclei. Using detergent-treated nuclei, we showed that PI3K-C2beta co-localized with lamin A/C in the nuclear matrix. This was confirmed biochemically, and a phosphoinositide kinase assay showed a statistically significant increase in nuclear PI3K-C2beta levels and lipid kinase activity following epidermal growth factor stimulation. C-terminal deletion and point mutations of PI3K-C2beta demonstrated that epidermal growth factor-driven translocation to the nucleus is dependent on a sequence of basic amino acid residues (KxKxK) that form a nuclear localization motif within the C-terminal C2 domain. Furthermore, when this sequence was expressed as an EGFP (enhanced green fluorescent protein) fusion protein, it translocated fluorescence into nuclei with an efficiency dependent upon copy number. These data demonstrate that epidermal growth factor stimulates the appearance of PI3K-C2beta in nuclei. Further, this effect is dependent on a nuclear localization signal present within the C-terminal C2 domain, indicating its bimodal function regulating phospholipid binding and shuttling PI3K-C2beta into the nucleus.

Ablation of phosphoinositide-3-kinase class II alpha suppresses hepatoma cell proliferation

Cancer such as hepatocellular carcinoma (HCC) is characterized by complex perturbations in multiple signaling pathways, including the phosphoinositide-3-kinase (PI3K/AKT) pathways. Herein we investigated the role of PI3K catalytic isoforms, particularly class II isoforms in HCC proliferation. Among the siRNAs tested against the eight known catalytic PI3K isoforms, specific ablation of class II PI3K alpha (PIK3C2alpha) was the most effective in impairing cell growth and this was accompanied by concomitant decrease in PIK3C2alpha mRNA and protein levels. Colony formation ability of cells deficient for PIK3C2alpha was markedly reduced and growth arrest was associated with increased caspase 3 levels. A small but significant difference in gene dosage and expression levels was detected between tumor and non-tumor tissues in a cohort of 19 HCC patients. Taken together, these data suggest for the first time that in addition to class I PI3Ks in cancer, class II PIK3C2alpha can modulate HCC cell growth.

The class II phosphatidylinositol 3 kinase C2beta is required for the activation of the K+ channel KCa3.1 and CD4 T-cells

The Ca(2+)-activated K(+) channel KCa3.1 is required for Ca(2+) influx and the subsequent activation of T-cells. We previously showed that nucleoside diphosphate kinase beta (NDPK-B), a mammalian histidine kinase, directly phosphorylates and activates KCa3.1 and is required for the activation of human CD4 T lymphocytes. We now show that the class II phosphatidylinositol 3 kinase C2beta (PI3K-C2beta) is activated by the T-cell receptor (TCR) and functions upstream of NDPK-B to activate KCa3.1 channel activity. Decreased expression of PI3K-C2beta by siRNA in human CD4 T-cells resulted in inhibition of KCa3.1 channel activity. The inhibition was due to decreased phosphatidylinositol 3-phosphate [PI(3)P] because dialyzing PI3K-C2beta siRNA-treated T-cells with PI(3)P rescued KCa3.1 channel activity. Moreover, overexpression of PI3K-C2beta in KCa3.1-transfected Jurkat T-cells led to increased TCR-stimulated activation of KCa3.1 and Ca(2+) influx, whereas silencing of PI3K-C2beta inhibited both responses. Using total internal reflection fluorescence microscopy and planar lipid bilayers, we found that PI3K-C2beta colocalized with Zap70 and the TCR in peripheral microclusters in the immunological synapse. This is the first demonstration that a class II PI3K plays a critical role in T-cell activation.

Mammalian phosphoinositide kinases and phosphatases

Phosphoinositides are lipids that are present in the cytoplasmic leaflet of a cell's plasma and internal membranes and play pivotal roles in the regulation of a wide variety of cellular processes. Phosphoinositides are molecularly diverse due to variable phosphorylation of the hydroxyl groups of their inositol rings. The rapid and reversible configuration of the seven known phosphoinositide species is controlled by a battery of phosphoinositide kinases and phosphoinositide phosphatases, which are thus critical for phosphoinositide isomer-specific localization and functions. Significantly, a given phosphoinositide generated by different isozymes of these phosphoinositide kinases and phosphatases can have different biological effects. In mammals, close to 50 genes encode the phosphoinositide kinases and phosphoinositide phosphatases that regulate phosphoinositide metabolism and thus allow cells to respond rapidly and effectively to ever-changing environmental cues. Understanding the distinct and overlapping functions of these phosphoinositide-metabolizing enzymes is important for our knowledge of both normal human physiology and the growing list of human diseases whose etiologies involve these proteins. This review summarizes the structural and biological properties of all the known mammalian phosphoinositide kinases and phosphoinositide phosphatases, as well as their associations with human disorders.

PI3K signaling: a crossroads of metabolic regulation

Insulin exerts a fundamental role in glucose metabolism. Several lines of evidence have established PI3Ks as crucial signaling crossroads of metabolic regulation. These kinases play a key role in glucose homeostasis through the generation of lipid secondary messengers upon membrane receptor activation, thus regulating liver gluconeogenesis and glycogen synthesis. While class IA Pl3Kα historically appeared as the major PI3K isoform involved in insulin-mediated glucose metabolism, emerging evidence has demonstrated the contribution of other PI3K isoforms. In this review, we focus on the prototypical insulin receptor-PI3K pathway and on the effects of its impairment on metabolism, insulin sensitivity and the molecular pathophysiology of diabetes mellitus.

Akt demoted in glioblastoma

In glioblastomas, an Akt-independent, PTEN (phosphatase and tensin homolog deleted on chromosome ten)-regulated signaling pathway links EGFR (epidermal growth factor receptor) to the phosphorylation of TOR (target of rapamycin) and of the ribosomal protein S6 and to the control of cell replication. Although PKCalpha (protein kinase Calpha) has been identified as an essential component, the detailed wiring of this previously unexplored noncanonical pathway remains to be worked out.

Great expectations for PIP: phosphoinositides as regulators of signaling during development and disease

Phosphoinositides function as signaling precursors as well as regulators and scaffolds of signaling molecules required for important cellular processes such as membrane trafficking. Although a picture of the biochemical and cell biological functions of phosphoinositides is emerging, less is known about how these functions impact signaling on a broader scale during development. This review summarizes recent work on the role of phosphoinositides in developmental signaling and in a number of diseases and developmental disorders.

Vascular endothelial growth factor acts through novel, pregnancy-enhanced receptor signalling pathways to stimulate endothelial nitric oxide synthase activity in uterine artery endothelial cells

During pregnancy, VEGF (vascular endothelial growth factor) regulates in part endothelial angiogenesis and vasodilation. In the present study we examine the relative roles of VEGFRs (VEGF receptors) and associated signalling pathways mediating the effects of VEGF(165) on eNOS (endothelial nitric oxide synthase) activation. Despite equal expression levels of VEGFR-1 and VEGFR-2 in UAECs (uterine artery endothelial cells) from NP (non-pregnant) and P (pregnant) sheep, VEGF(165) activates eNOS at a greater level in P- compared with NP-UAEC, independently of Akt activation. The selective VEGFR-1 agonist PlGF (placental growth factor)-1 elicits only a modest activation of eNOS in P-UAECs compared with VEGF(165), whereas the VEGFR-2 kinase inhibitor blocks VEGF(165)-stimulated eNOS activation, suggesting VEGF(165) predominantly activates eNOS via VEGFR-2. Although VEGF(165) also activates ERK (extracellular-signal-regulated kinase)-1/2, this is not necessary for eNOS activation since U0126 blocks ERK-1/2 phosphorylation, but not eNOS activation, and the VEGFR-2 kinase inhibitor inhibits eNOS activation, but not ERK-1/2 phosphorylation. Furthermore, the inability of PlGF to activate ERK-1/2 and the ability of the VEGFR-2 selective agonist VEGF-E to activate ERK-1/2 and eNOS suggests again that both eNOS and ERK-1/2 activation occur predominantly via VEGFR-2. The lack of VEGF(165)-stimulated Akt phosphorylation is consistent with a lack of robust phosphorylation of Ser(1179)-eNOS. Although VEGF(165)-stimulated eNOS phosphorylation is observed at Ser(617) and Ser(635), pregnancy does not significantly alter this response. Our finding that VEGF(165) activation of eNOS is completely inhibited by wortmannin but not LY294002 implies a downstream kinase, possibly a wortmannin-selective PI3K (phosphoinositide 3-kinase), is acting between the VEGFR-2 and eNOS independently of Akt.

PI3K/PTEN signaling in angiogenesis and tumorigenesis

Phosphatidylinositol 3-kinase (PI3K) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) signaling pathway play an important role in multiple cellular functions such as cell metabolism, proliferation, cell-cycle progression, and survival. PI3K is activated by growth factors and angiogenesis inducers such as vascular endothelial growth factor (VEGF) and angiopoietins. The amplification and mutations of PI3K and the loss of the tumor suppressor PTEN are common in various kinds of human solid tumors. The genetic alterations of upstream and downstream of PI3K signaling molecules such as receptor tyrosine kinases and AKT, respectively, are also frequently altered in human cancer. PI3K signaling regulates tumor growth and angiogenesis by activating AKT and other targets, and by inducing HIF-1 and VEGF expression. Angiogenesis is required for tumor growth and metastasis. In this review, we highlight the recent studies on the roles and mechanisms of PI3K and PTEN in regulating tumorigenesis and angiogenesis, and the roles of the downstream targets of PI3K for transmitting the signals. We also discuss the crosstalk of these signaling molecules and cellular events during tumor growth, metastasis, and tumor angiogenesis. Finally, we summarize the potential applications of PI3K, AKT, and mTOR inhibitors and their outcome in clinical trials for cancer treatment.

Ca2+-regulated pool of phosphatidylinositol-3-phosphate produced by phosphatidylinositol 3-kinase C2alpha on neurosecretory vesicles

Phosphatidylinositol-3-phosphate [PtdIns(3)P] is a key player in early endosomal trafficking and is mainly produced by class III phosphatidylinositol 3-kinase (PI3K). In neurosecretory cells, class II PI3K-C2alpha and its lipid product PtdIns(3)P have recently been shown to play a critical role during neuroexocytosis, suggesting that two distinct pools of PtdIns(3)P might coexist in these cells. However, the precise characterization of this additional pool of PtdIns(3)P remains to be established. Using a selective PtdIns(3)P probe, we have identified a novel PtdIns(3)P-positive pool localized on secretory vesicles, sensitive to PI3K-C2alpha knockdown and relatively resistant to wortmannin treatment. In neurosecretory cells, stimulation of exocytosis promoted a transient albeit large increase in PtdIns(3)P production localized on secretory vesicles sensitive to PI3K-C2alpha knockdown and expression of PI3K-C2alpha catalytically inactive mutant. Using purified chromaffin granules, we found that PtdIns(3)P production is controlled by Ca(2+). We confirmed that PtdIns(3)P production from recombinantly expressed PI3K-C2alpha is indeed regulated by Ca(2+). We provide evidence that a dynamic pool of PtdIns(3)P synthesized by PI3K-C2alpha occurs on secretory vesicles in neurosecretory cells, demonstrating that the activity of a member of the PI3K family is regulated by Ca(2+) in vitro and in living neurosecretory cells.

Down-regulation of class II phosphoinositide 3-kinase alpha expression below a critical threshold induces apoptotic cell death

Members of the phosphoinositide 3-kinase (PI3K) family collectively control multiple cellular responses, including proliferation, growth, chemotaxis, and survival. These diverse effects can partly be attributed to the broad range of downstream effectors being regulated by the products of these lipid kinases, the 3'-phosphoinositides. However, an additional layer of complexity is introduced by the existence of multiple PI3K enzyme isoforms. Much has been learned over the last years on the roles of the classes I and III PI3K members in cellular signaling, but little is known about the isoform-specific tasks done by the class II PI3Ks (C2alpha, beta, and gamma). In this study, we used quantitative reverse transcription-PCR and RNA interference in mammalian cells to gain further insight into the function of these lesser studied PI3K enzymes. We find that PI3K-C2alpha, but not PI3K-C2beta, has an important role in controlling cell survival and by using a panel of RNA interference reagents, we were able to determine a critical threshold of PI3K-C2alpha mRNA levels, below which the apoptotic program is switched on, via the intrinsic cell death pathway. In addition, knockdown of PI3K-C2alpha to levels that by themselves do not induce apoptosis sensitize cells to the anticancer agent Taxol (paclitaxel). Lastly, we report that lowering the levels of PI3K-C2alpha in a number of cancer cell lines reduces their proliferation and cell viability, arguing that PI3K inhibitors targeting not only the class Ialpha isoform but also class IIalpha may contribute to an effective anticancer strategy.

Crystal structures of PI3K-C2alpha PX domain indicate conformational change associated with ligand binding

BACKGROUND

PX domains have specialized protein structures involved in binding of phosphoinositides (PIs). Through binding to the various PIs PX domains provide site-specific membrane signals to modulate the intracellular localisation and biological activity of effector proteins. Several crystal structures of these domains are now available from a variety of proteins. All PX domains contain a canonical core structure with main differences exhibited within the loop regions forming the phosphoinositide binding pockets. It is within these areas that the molecular basis for ligand specificity originates.

RESULTS

We now report two new structures of PI3K-C2alpha PX domain that crystallised in a P3121 space group. The two structures, refined to 2.1 A and 2.5 A, exhibit significantly different conformations of the phosphoinositide-binding loops. Unexpectedly, in one of the structures, we have detected a putative-ligand trapped in the binding site during the process of protein purification and crystallisation.

CONCLUSION

The two structures reported here provide a more complete description of the phosphoinositide binding region compared to the previously reported 2.6 A crystal structure of human PI3K-C2alpha PX where this region was highly disordered. The structures enabled us to further analyse PI specificity and to postulate that the observed conformational change could be related to ligand-binding.

Characterization of Rab21-positive tubular endosomes induced by PI3K inhibitors

We found that wortmannin, a potent phosphoinositide 3-kinase (PI3K) inhibitor, markedly induced the formation of Rab21-positive tubular compartments in A431 cells. By time-lapse fluorescence microscopy of live cells co-expressing fluorescent protein-fused Rab21 and other marker proteins, it was shown that the Rab21-positive tubules in wortmannin-treated cells were derived from Rab5-positive early endosomes, but not from late endosomes, recycling endosomes, lysosomes or the trans-Golgi network. The formation of Rab21-positive tubules was very dynamic and required microtubules. Rab21-positive tubules were also formed by the treatment of cells with 3-methyladenine (3-MA), which inhibits class III PI3K rather than class I PI3K. Furthermore, the loss of PI(3)P correlated with the tubulation of Rab21-positive endosomes in cells co-expressing fluorescent protein-fused Rab21 and a tandem FYVE domain. These results suggest that the lowering of PI(3)P as a result of class III PI3K inhibition may be an important cue for the morphological change of Rab21-positive early endosomes from vesicular to tubular form.

Regulation of neuron survival through an intersectin-phosphoinositide 3'-kinase C2beta-AKT pathway

While endocytosis attenuates signals from plasma membrane receptors, recent studies suggest that endocytosis also serves as a platform for the compartmentalized activation of cellular signaling pathways. Intersectin (ITSN) is a multidomain scaffolding protein that regulates endocytosis and has the potential to regulate various biochemical pathways through its multiple, modular domains. To address the biological importance of ITSN in regulating cellular signaling pathways versus in endocytosis, we have stably silenced ITSN expression in neuronal cells by using short hairpin RNAs. Decreasing ITSN expression dramatically increased apoptosis in both neuroblastoma cells and primary cortical neurons. Surprisingly, the loss of ITSN did not lead to major defects in the endocytic pathway. Yeast two-hybrid analysis identified class II phosphoinositide 3'-kinase C2beta (PI3K-C2beta) as an ITSN binding protein, suggesting that ITSN may regulate a PI3K-C2beta-AKT survival pathway. ITSN associated with PI3K-C2beta on a subset of endomembrane vesicles and enhanced both basal and growth factor-stimulated PI3K-C2beta activity, resulting in AKT activation. The use of pharmacological inhibitors, dominant negatives, and rescue experiments revealed that PI3K-C2beta and AKT were epistatic to ITSN. This study represents the first demonstration that ITSN, independent of its role in endocytosis, regulates a critical cellular signaling pathway necessary for cell survival.

Beclin 1-independent pathway of damage-induced mitophagy and autophagic stress: implications for neurodegeneration and cell death

Growing evidence supports an active role for dysregulated macroautophagy (autophagic stress) in neuronal cell death and neurodegeneration. Alterations in mitochondrial function and dynamics are also strongly implicated in neurodegenerative diseases. Interestingly, whereas the core autophagy machinery is evolutionarily conserved and shared among constitutive and induced or selective autophagy, recent studies implicate distinct mechanisms regulating mitochondrial autophagy (mitophagy) in response to general autophagic stimuli. Little is known about pathways regulating selective, damage-induced mitophagy. We found that the parkinsonian neurotoxin MPP(+) induces autophagy and mitochondrial degradation that is inhibited by siRNA knockdown of autophagy proteins Atg5, Atg7 and Atg8, but occurs independently of Beclin 1, a component of the class III (PIK3C3/Vps34) phosphoinositide 3-kinase (PI3K) complex. Instead, MPP(+)-induced mitophagy is dependent upon MAPK signaling. Interestingly, all treatments that inhibited autophagy also conferred protection from MPP(+)-induced cell death. A prior human tissue study further supports a role for ERK/MAPK-regulated autophagy in Parkinson's and Lewy body diseases. As competition for limiting amounts of Beclin 1 may serve to prevent harmful overactivation of autophagy, understanding mechanisms that bypass or complement a requirement for PI3K-Beclin 1 activity could lead to strategies to modulate autophagic stress in injured or degenerating neurons.

Phase I trial of sirolimus combined with radiation and cisplatin in non-small cell lung cancer

PURPOSE

The safety and tolerability of sirolimus combined with thoracic radiation and cisplatin was evaluated in patients with lung cancer. In parallel, the effects of sirolimus were studied in a murine model of radiation pneumonitis.

MATERIALS AND METHODS

The phase I trial evaluated standard three-dimensional conformal thoracic radiation therapy (60 Gy) and weekly cisplatin (25 mg/m2 i.v.) in combination with escalating doses of oral sirolimus. Sirolimus drug levels and inhibition of mTOR signaling to ribosomal S6 protein were assessed in blood. The effects of sirolimus administered during and after whole thoracic radiation of C57BL6/J mice were evaluated by monitoring mouse breathing rates and survival.

RESULTS

Seven patients with stage III lung cancer were accrued to the clinical study. None of the four patients treated with 2 mg/day sirolimus developed dose-limiting toxicities. Three patients were treated with 5 mg/day sirolimus, and one patient at this dose level had dose-limiting toxicity of grade 3 dysphagia. However, the maximally tolerated dose of sirolimus in this regimen was not defined because the study was terminated prematurely because of loss of funding. In the mouse experiments, concomitant sirolimus treatment was not associated with an increase in radiation-associated morbidity or mortality.

CONCLUSIONS

Combination therapy with sirolimus, radiation, and cisplatin was well tolerated in patients.

Role of class II phosphoinositide 3-kinase in cell signalling

Although it is now well established that PI3K (phosphoinositide 3-kinase) is a key enzyme in several intracellular processes, there are still relatively few reports that precisely identify the specific isoforms of PI3K actually involved in such events. The lack of specific inhibitors has made it particularly difficult to address the physiological roles of some isoforms, such as the members of class II. As a consequence, there is still relatively little understanding of the role of these enzymes and the question about the intracellular role of these isoforms still waits for more answers.

Inhibition of the leucine-rich repeat protein LINGO-1 enhances survival, structure, and function of dopaminergic neurons in Parkinson's disease models

The nervous system-specific leucine-rich repeat Ig-containing protein LINGO-1 is associated with the Nogo-66 receptor complex and is endowed with a canonical EGF receptor (EGFR)-like tyrosine phosphorylation site. Our studies indicate that LINGO-1 expression is elevated in the substantia nigra of Parkinson's disease (PD) patients compared with age-matched controls and in animal models of PD after neurotoxic lesions. LINGO-1 expression is present in midbrain dopaminergic (DA) neurons in the human and rodent brain. Therefore, the role of LINGO-1 in cell damage responses of DA neurons was examined in vitro and in experimental models of PD induced by either oxidative (6-hydroxydopamine) or mitochondrial (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) toxicity. In LINGO-1 knockout mice, DA neuron survival was increased and behavioral abnormalities were reduced compared with WT. This neuroprotection was accompanied by increased Akt phosphorylation (p-Akt). Similar neuroprotective in vivo effects on midbrain DA neurons were obtained in WT mice by blocking LINGO-1 activity using LINGO-1-Fc protein. Neuroprotection and enhanced neurite growth were also demonstrated for midbrain DA neurons in vitro. LINGO-1 antagonists (LINGO-1-Fc, dominant negative LINGO-1, and anti-LINGO-1 antibody) improved DA neuron survival in response to MPP+ in part by mechanisms that involve activation of the EGFR/Akt signaling pathway through a direct inhibition of LINGO-1's binding to EGFR. These results show that inhibitory agents of LINGO-1 activity can protect DA neurons against degeneration and indicate a role for the leucine-rich repeat protein LINGO-1 and related classes of proteins in the pathophysiological responses of midbrain DA neurons in PD.

Regulation of class III (Vps34) PI3Ks

The class III PI3K (phosphoinositide 3-kinase), Vps34 (vacuolar protein sorting 34), was first identified as a regulator of vacuolar hydrolase sorting in yeast. Unlike other PI3Ks, the Vps34 lipid kinase specifically utilizes phosphatidylinositol as a substrate, producing the single lipid product PtdIns3P. While Vps34 has been studied for some time in the context of endocytosis and vesicular trafficking, it has more recently been implicated as an important regulator of autophagy, trimeric G-protein signalling, and the mTOR (mammalian target of rapamycin) nutrient-sensing pathway. The present paper will focus on studies that describe the regulation of hVps34 (human Vps34) intracellular targeting and enzymatic activity in yeast and mammalian cells.

Essential role for class II phosphoinositide 3-kinase alpha-isoform in Ca2+-induced, Rho- and Rho kinase-dependent regulation of myosin phosphatase and contraction in isolated vascular smooth muscle cells

The laser confocal fluorescent microscope-based observation of contractile responses in green fluorescent protein-expressing differentiated vascular smooth muscle cells, combined with the RNA interference-mediated gene-silencing technique, allowed us to determine the role of phosphoinositide 3-kinase (PI3K) class II alpha-isoform (PI3K-C2alpha) as a novel, Ca2+-dependent regulator of myosin light-chain phosphatase (MLCP) and contraction. The Ca2+-ionophore ionomycin induced a robust contractile response with an increase in the intracellular free Ca2+ concentration ([Ca2+]i). The PI3K-C2alpha-specific short interfering RNA (siRNA) induced a selective and marked reduction in PI3K-C2alpha protein expression. The siRNA-mediated knockdown of PI3K-C2alpha, but not class I PI3K p110alpha, suppressed ionomycin-induced contraction without altering Ca2+-mobilization. PI3K-C2alpha is uniquely less sensitive to the PI3K inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) than the other PI3K members, including p110alpha. Ionomycin-induced contraction was inhibited only by a relatively high concentration of LY294002. Consistent with our previous observations showing that ionomycin and membrane depolarization induced Rho activation in vascular smooth muscle tissues in a Ca2+-dependent manner, ionomycin-induced contraction was dependent on Rho and Rho-kinase. Ionomycin induced phosphorylation of the MLCP-regulatory subunit myosin targeting protein 1(MYPT1) at Thr850 and the 20-kDa myosin light chain (MLC) in a Rho kinase-dependent manner. Knockdown of PI3K-C2alpha suppressed phosphorylation of both MYPT1 and MLC. The receptor agonist noradrenaline, which induced a rapid increase in the [Ca2+]i and Ca2+-dependent contraction, stimulated phosphorylation of MYPT1 and MLC, which was also dependent on Ca2+, PI3K-C2alpha, and Rho-kinase. These observations indicate that PI3K-C2alpha is necessary for Ca2+-induced Rho- and Rho kinase-dependent negative regulation of MLCP and consequently MLC phosphorylation and contraction.

Ca2+-independent, inhibitory effects of cyclic adenosine 5'-monophosphate on Ca2+ regulation of phosphoinositide 3-kinase C2alpha, Rho, and myosin phosphatase in vascular smooth muscle

We have recently demonstrated in vascular smooth muscle (VSM) that membrane depolarization by high KCl induces Ca(2+)-dependent Rho activation and myosin phosphatase (MLCP) inhibition (Ca(2+)-induced Ca(2+)-sensitization) through the mechanisms involving phosphorylation of myosin-targeting protein 1 (MYPT1) and 17-kDa protein kinase C (PKC)-potentiated inhibitory protein of PP1 (CPI-17). In the present study, we investigated whether and how cAMP affected Ca(2+)-dependent MLCP inhibition by examining the effects of forskolin, cell-permeable dibutyryl cAMP (dbcAMP), and isoproterenol. Forskolin, but not its inactive analog 1,9-dideoxyforskolin, inhibited KCl-induced contraction and the 20-kDa myosin light chain (MLC) phosphorylation without inhibiting Ca(2+) mobilization in rabbit aortic VSM. dbcAMP mimicked these forskolin effects. We recently suggested that Ca(2+)-mediated Rho activation is dependent on class II alpha-isoform of phosphoinositide 3-kinase (PI3K-C2alpha). Forskolin inhibited KCl-induced stimulation of PI3K-C2alpha activity. KCl-induced membrane depolarization stimulated Rho in a manner dependent on a PI3K but not PKC and stimulated phosphorylation of MYPT1 at Thr(850) and CPI-17 at Thr(38) in manners dependent on both PI3K and Rho kinase, but not PKC. Forskolin, dbcAMP, and isoproterenol inhibited KCl-induced Rho activation and phosphorylation of MYPT1 and CPI-17. Consistent with these data, forskolin, isoproterenol, a PI3K inhibitor, or a Rho kinase inhibitor, but not a PKC inhibitor, abolished KCl-induced diphosphorylation of MLC. These observations indicate that cAMP inhibits Ca(2+)-mediated activation of the MLCP-regulating signaling pathway comprising PI3K-C2alpha, Rho, and Rho kinase in a manner independent of Ca(2+) and point to the novel mechanism of the cAMP actions in the regulation of vascular smooth muscle contraction.

Emerging roles of phosphatidylinositol 3-monophosphate as a dynamic lipid second messenger

The lipid products of phosphoinositide 3-kinase (PI3K) are involved in many cellular responses such as proliferation, migration and survival. Disregulation of PI3K-activated pathways is implicated in different disease including diabetes and cancer. Among the different products of PI3Ks, phosphatidylinositol-3,4,5-trisphosphate (PtdIns-3,4,5-P3) has a well established role in signal transduction whereas the monophosphate phosphatidylinositol-3-phosphate (PtdIns-3-P) has been considered for a long time just a cellular component confined in endosomal structures. Only recently several evidence have indicated that PtdIns-3-P can also act as a dynamic intracellular second messenger. The role of PtdIns-3-P as mediator of crucial intracellular signals is therefore just beginning to be appreciated. Here we review some of the latest evidence showing that pools of PtdIns-3-P can be generated upon cellular stimulation in compartments different from the "classical" endosomal region. We describe several proteins that can be targets in mediating signals deriving from such stimulated PtdIns-3-P pools. In addition we describe the potential mechanism of switching on and off such signals. Taken together all this evidence suggest a novel, key role for PtdIns-3-P in signal transduction.

Class II phosphoinositide 3-kinase alpha-isoform regulates Rho, myosin phosphatase and contraction in vascular smooth muscle

We demonstrated previously that membrane depolarization and excitatory receptor agonists such as noradrenaline induce Ca2+-dependent Rho activation in VSM (vascular smooth muscle), resulting in MP (myosin phosphatase) inhibition through the mechanisms involving Rho kinase-mediated phosphorylation of its regulatory subunit MYPT1. In the present study, we show in de-endothelialized VSM strips that the PI3K (phosphoinositide 3-kinase) inhibitors LY294002 and wortmannin inhibited KCl membrane depolarization- and noradrenaline-induced Rho activation and MYPT1 phosphorylation, with concomitant inhibition of MLC (20-kDa myosin light chain) phosphorylation and contraction. LY294002 also augmented de-phosphorylation of MLC and resultantly relaxation in KCl-contracted VSM, whereas LY294002 was much less effective or ineffective under the conditions in which MP was inhibited by either a phosphatase inhibitor or a phorbol ester in Rho-independent manners. VSM express at least four PI3K isoforms, including the class I enzymes p110alpha and p110beta and the class II enzymes PI3K-C2alpha and -C2beta. The dose-response relationships of PI3K-inhibitor-induced inhibition of Rho, MLC phosphorylation and contraction were similar to that of PI3K-C2alpha inhibition, but not to that of the class I PI3K inhibition. Moreover, KCl and noradrenaline induced stimulation of PI3K-C2alpha in a Ca2+-dependent manner, but not of p110alpha or p110beta. Down-regulation of PI3K-C2alpha expression by siRNA (small interfering RNA) inhibited contraction and phosphorylation of MYPT1 and MLC in VSM cells. Finally, intravenous wortmannin infusion induced sustained hypotension in rats, with inhibition of PI3K-C2alpha activity, GTP-loading of Rho and MYPT1 phosphorylation in the artery. These results indicate the novel role of PI3K-C2alpha in Ca2+-dependent Rho-mediated negative control of MP and thus VSM contraction.

Activation of phosphoinositide 3-kinase C2 beta in the nuclear matrix during compensatory liver growth

In the nuclear matrix harvested 20 h after partial hepatectomy, an increase in immunoprecipitable PI3K-C2beta activity is observed, which is sensitive to wortmannin (10 Mm) and shows strong preference for PtdIns over PtdIns(4)P as a substrate. On western blots PI3K-C2beta revealed a single immunoreactive band of 180 kD, whereas 20 h after partial hepatectomy gel shift of 18kDa was noticed in the nuclear matrix, suggesting that observed activation of enzyme is achieved by proteolysis. As it is know that PI3K-C2alpha is associated with nuclear speckles [Didichenko SA, Thelen M. Phosphatidylinositol 3-kinase C2alpha contains a nuclear localization sequence and associates with nuclear speckles. J Biol Chem 2001;276:48135-42.], the data presented in this report show that in the nuclear matrix PI3K-C2beta is activated during the compensatory liver growth, which clearly demonstrates that different class II PI3K enzymes have different subnuclear localization and therefore might have different intranuclear functions.

Phosphoinositide 3-Kinase C2beta regulates cytoskeletal organization and cell migration via Rac-dependent mechanisms

Receptor-linked class I phosphoinositide 3-kinases (PI3Ks) induce assembly of signal transduction complexes through protein-protein and protein-lipid interactions that mediate cell proliferation, survival, and migration. Although class II PI3Ks have the potential to make the same phosphoinositides as class I PI3Ks, their precise cellular role is currently unclear. In this report, we demonstrate that class II phosphoinositide 3-kinase C2beta (PI3KC2beta) associates with the Eps8/Abi1/Sos1 complex and is recruited to the EGF receptor as part of a multiprotein signaling complex also involving Shc and Grb2. Increased expression of PI3KC2beta stimulated Rac activity in A-431 epidermoid carcinoma cells, resulting in enhanced membrane ruffling and migration speed of the cells. Conversely, expression of dominant negative PI3KC2beta reduced Rac activity, membrane ruffling, and cell migration. Moreover, PI3KC2beta-overexpressing cells were protected from anoikis and displayed enhanced proliferation, independently of Rac function. Taken together, these findings suggest that PI3KC2beta regulates the migration and survival of human tumor cells by distinct molecular mechanisms.

The N-terminus of phosphoinositide 3-kinase-C2beta regulates lipid kinase activity and binding to clathrin

The class II phosphoinositide 3-kinase (PI3K)-C2beta is recruited to polypeptide growth factor receptors following ligand stimulation. In contrast to the class I A p85/p110 heterodimers, this interaction is dependent upon proline residues present within the N-terminal sequence of the 3-phosphoinositide kinase. However, the mechanism by which PI3K-C2beta catalytic activity is regulated currently remains unknown. In many tumours, increased expression of ErbB receptors confers a poor prognosis. We demonstrate that increased expression of EGFR enhanced its association with PI3K-C2beta following stimulation with EGF. Deletion of the first proline rich region within the N-terminus precluded recruitment of PI3K-C2beta to activated EGFR. Although deletion of the first proline rich motif also rendered the enzyme catalytically inactive, further deletions (residues 1-148 and 1-261) that removed the second and third proline rich motifs increased kinase activity. These data confirm a regulatory role for the N-terminus of class II PI3K enzymes suggesting that catalytic activity is regulated by factors that associate with this region during recruitment to activated growth factor receptors. Using an N-terminal PI3K-C2beta-GST fusion protein, clathrin heavy chain was affinity purified from A431 cell lysates. Association of PI3K-C2beta with clathrin was confirmed by co-immunoprecipitation from cell lysates while intracellular co-localisation of PI3K-C2beta and clathrin was confirmed by confocal microscopy. Our findings demonstrate for the first time that the PI3K-C2beta isoform associates with clathrin and thus provides a link between receptor mediated intracellular signalling and clathrin coated vesicle transport.

The class II phosphoinositide 3-kinase C2beta is not essential for epidermal differentiation

Phosphoinositide 3-kinases (PI3Ks) regulate an array of cellular processes and are comprised of three classes. Class I PI3Ks include the well-studied agonist-sensitive p110 isoforms; however, the functions of class II and III PI3Ks are less well characterized. Of the three class II PI3Ks, C2alpha and C2beta are widely expressed in many tissues, including the epidermis, while C2gamma is confined to the liver. In contrast to the class I PI3K p110alpha, which is expressed throughout the epidermis, C2beta was found to be localized in suprabasal cells, suggesting a potential role for C2beta in epidermal differentiation. Overexpressing C2beta in epidermal cells in vitro induced differentiation markers. To study a role for C2beta in tissue, we generated transgenic mice overexpressing C2beta in both suprabasal and basal epidermal layers. These mice lacked epidermal abnormalities. Mice deficient in C2beta were then generated by targeted gene deletion. C2beta knockout mice were viable and fertile and displayed normal epidermal growth, differentiation, barrier function, and wound healing. To exclude compensation by C2alpha, RNA interference was then used to knock down both C2alpha and C2beta in epidermal cells simultaneously. Induction of differentiation markers was unaffected in the absence of C2alpha and C2beta. These findings indicate that class II PI3Ks are not essential for epidermal differentiation.

The class II phosphoinositide 3-kinase PI3K-C2beta regulates cell migration by a PtdIns3P dependent mechanism

The biological and pathophysiological significance of class II phosphoinositide 3-kinase enzyme expression currently remains unclear. Using an in vitro scrape wound assay and time-lapse video microscopy, we demonstrate that cell motility is increased in cultures expressing recombinant PI3K-C2beta enzyme. In addition, overexpression of PI3K-C2beta transiently decreased cell adhesion, stimulated the formation of cytoplasmic processes, and decreased the rate of cell proliferation. Consistent with these observations, expression of PI3K-C2beta also decreased expression of alpha4 beta1 integrin subunits. Using asynchronous cultures, we show that endogenous PI3K-C2beta is present in lamellipodia of motile cells. When cells expressing recombinant PI3K-C2beta were plated onto fibronectin, cortical actin staining increased markedly and actin rich lamellipodia and filopodia became evident. Overexpression of a 2xFYVE(Hrs) domain fusion protein abolished this response demonstrating that the effect of PI3K-C2beta on the reorganization of actin filaments is dependent upon PtdIns3P. Finally, overexpression of PI3K-C2beta increased GTP loading of Cdc42. Our data demonstrates for the first time, that PI3K-C2beta plays a regulatory role in cell motility and that the mechanism by which it reorganizes the actin cytoskeleton is dependent upon PtdIns3P production.

Individual Phosphoinositide 3-Kinase C2α Domain Activities Independently Regulate Clathrin Function

Phosphoinositide 3-kinase C2alpha (PI3K-C2alpha) is a member of the class II PI-3 kinases, defined by the presence of a second C2 domain at their C termini. The cellular functions of the class II enzymes are incompletely understood, though they have been implicated in receptor activation pathways initiated by epidermal growth factor, insulin, and chemokines. PI3K-C2alpha was recently found to be localized to clathrin-coated membranes in the trans-Golgi network and at endocytic sites on the plasma membrane. Further, a specific binding site was identified for clathrin on the N terminus of PI3K-C2alpha, whose occupancy resulted in lipid kinase activation. Expression of PI3K-C2alpha in cells dramatically affected clathrin distribution and function in cells, leading to accumulation of intracellular clathrin-coated structures, which are visualized here at the ultrastructural level, and inhibition of clathrin-mediated transport from both the plasma membrane and the trans-Golgi network. In this study we have demonstrated that the isolated clathrin binding domain of PI3K-C2alpha can drive clathrin lattice assembly and that both it and the lipid kinase activity of the protein can independently modulate clathrin distribution and function when expressed in cells. Together, these results suggest that PI3K-C2alpha employs both protein-protein interaction and localized production of 3-phosphoinositides to affect clathrin dynamics at sites of membrane budding and targeting.

Antigen-induced Ca2+ mobilization in RBL-2H3 cells: Role of I(1,4,5)P3 and S1P and necessity of I(1,4,5)P3 production

Inositol 1,4,5-trisphosphate (IP3) has long been recognized as a second messenger for intracellular Ca2+ mobilization. Recently, sphingosine 1-phosphate (S1P) has been shown to be involved in Ca2+ release from the endoplasmic reticulum (ER). Here, we investigated the role of S1P and IP3 in antigen (Ag)-induced intracellular Ca2+ mobilization in RBL-2H3 mast cells. Antigen-induced intracellular Ca2+ mobilization was only partially inhibited by the sphingosine kinase inhibitor dl-threo-dihydrosphingosine (DHS) or the IP3 receptor inhibitor 2-aminoethoxydiphenyl borate (2-APB), whereas preincubation with both inhibitors led to complete inhibition. In contrast, stimulation of A3 adenosine receptors with N5-ethylcarboxamidoadenosine (NECA) caused intracellular Ca2+ mobilization that was completely abolished by 2-APB but not by DHS, suggesting that NECA required only the IP3 pathway, while antigen used both the IP3 and S1P pathways. Interestingly, however, inhibition of IP3 production with the phospholipase C inhibitor U73122 completely abolished Ca2+ release from the ER induced by either stimulant. This suggested that S1P alone, without concomitant production of IP3, would not cause intracellular Ca2+ mobilization. This was further demonstrated in some clones of RBL-2H3 cells excessively overexpressing a beta isoform of Class II phosphatidylinositol 3-kinase (PI3KC2beta). In such clones including clone 5A4C, PI3KC2beta was overexpressed throughout the cell, although endogenous PI3KC2beta was normally expressed only in the ER. Overexpression of PI3KC2beta in the cytosol and the PM led to depletion of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), resulting in a marked reduction in IP3 production. This could explain the abolishment of intracellular Ca2+ mobilization in clone 5A4C. Supporting this hypothesis, the Ca2+ mobilization was reconstituted by the addition of exogenous PI(4,5)P2 in these cells. Our results suggest that both IP3 and S1P contribute to FcvarepsilonRI-induced Ca2+ release from the ER and production of IP3 is necessary for S1P to cause Ca2+ mobilization from the ER.

Phosphatidylinositol 3-kinase C2alpha is essential for ATP-dependent priming of neurosecretory granule exocytosis

Neurotransmitter release and hormonal secretion are highly regulated processes culminating in the calcium-dependent fusion of secretory vesicles with the plasma membrane. Here, we have identified a role for phosphatidylinositol 3-kinase C2alpha (PI3K-C2alpha) and its main catalytic product, PtdIns3P, in regulated exocytosis. In neuroendocrine cells, PI3K-C2alpha is present on a subpopulation of mature secretory granules. Impairment of PI3K-C2alpha function specifically inhibits the ATP-dependent priming phase of exocytosis. Overexpression of wild-type PI3K-C2alpha enhanced secretion, whereas transfection of PC12 cells with a catalytically inactive PI3K-C2alpha mutant or a 2xFYVE domain sequestering PtdIns3P abolished secretion. Based on these results, we propose that production of PtdIns3P by PI3K-C2alpha is required for acquisition of fusion competence in neurosecretion.

Class II phosphoinositide 3-kinase defines a novel signaling pathway in cell migration

The lipid products of phosphoinositide 3-kinase (PI3K) are involved in many cellular responses such as proliferation, migration, and survival. Disregulation of PI3K-activated pathways is implicated in different diseases including cancer and diabetes. Among the three classes of PI3Ks, class I is the best characterized, whereas class II has received increasing attention only recently and the precise role of these isoforms is unclear. Similarly, the role of phosphatidylinositol-3-phosphate (PtdIns-3-P) as an intracellular second messenger is only just beginning to be appreciated. Here, we show that lysophosphatidic acid (LPA) stimulates the production of PtdIns-3-P through activation of a class II PI3K (PI3K-C2β). Both PtdIns-3-P and PI3K-C2β are involved in LPA-mediated cell migration. This study is the first identification of PtdIns-3-P and PI3K-C2β as downstream effectors in LPA signaling and demonstration of an intracellular role for a class II PI3K. Defining this novel PI3K-C2β–PtdIns-3-P signaling pathway may help clarify the process of cell migration and may shed new light on PI3K-mediated intracellular events.

Suppression of the alpha-isoform of class II phosphoinositide 3-kinase gene expression leads to apoptotic cell death

Phosphoinositide 3-kinases (PI3Ks) have known to be key enzymes activating intracellular signaling molecules when a number of growth factors bind to their cell surface receptors. PI3Ks are divided into three classes (I, II, and III) and enzymes of each class have different tissue-specificities and physiological functions. Class II PI3Ks consist of three isoforms (alpha,beta,gamma). Although the alpha-isoform (PI3K-C2alpha) is considered ubiquitous and preferentially activated by insulin rather than the beta-isoform, the physiological significance of PI3K-C2alpha is poorly understood. The present study aimed to determine whether PI3K-C2alpha is associated with the suppression of apoptotic cell death. Different sense- and antisense oligonucleotides (ODNs) were synthesized based on the sequence of C2 domain of PI3K-C2alpha gene. Transfection of CHO-IR cells with two different antisense ODNs clearly reduced the protein content as well as mRNA levels of PI3K-C2alpha whereas neither the nonspecific mock- nor sense ODNs affected. The decrease of PI3K-C2alpha gene expression was paralleled by cellular changes indicating apoptotic cell death such as nuclear condensation, formation of apoptotic bodies, and DNA fragmentation. PI3K-C2alpha mRNA levels were also reduced when cells were incubated in growth factor-deficient medium. Supplementing growth factors (serum or insulin) into medium lead to an increase of PI3K-C2alpha mRNA levels. This finding strongly suggests that PI3K-C2alpha is a crucial survival factor.

Catalase induces the expression of inducible nitric oxide synthase through activation of NF-κB and PI3K signaling pathway in Raw 264.7 cells

It has been reported that macrophages produce substantial amounts of nitrite and nitrate after addition of catalase, but the mechanism associated remains unclear. In present study, we investigated whether catalase modulates the expression of inducible nitric oxide synthase (iNOS), an enzyme that produces nitric oxide. Exposure of Raw 264.7 macrophages (Raw cells) to catalase induced high expression of iNOS mRNA as well as protein with enzymatic activity. Data of mechanical analyses, such as iNOS promoter-driven luciferase assay and actinomycin D chase experiments demonstrated that the induction was due to increased iNOS transcription and post-transcriptional iNOS mRNA stability. Of interest, catalase-induced iNOS protein expression was abrogated through inactivation of NF-kappaB pathway by MG132 or BAY 11-7085 and PI3K pathway by LY294002 or wortmannin, respectively. In particular, blockage of PI3K pathway by LY294002 down-regulated iNOS transcription and steady-state iNOS mRNA levels as well as iNOS mRNA stability induced by catalase, suggesting regulation of PI3K pathway in catalase-induced iNOS expression at the levels of iNOS transcription, steady-state mRNA status, and mRNA stability. Additional cell culture works in different types of cells indicated that iNOS expression by catalase might be cell type-specific, based on the facts that catalase induced iNOS expression in BV2 microglial macrophage-like cells, but not in HT-29 or A549, human colon or lung cancer epithelial-like cells. Together, these results demonstrate for the first time that catalase induces iNOS expression in Raw cells, which seems to be associated with the increase of iNOS transcription and mRNA stability as well as the activation of NF-kappaB and PI3K signaling pathways.

Phosphorylation of both EGFR and ErbB2 is a reliable predictor of prostate cancer cell proliferation in response to EGF

Despite multiple reports of overexpression in prostate cancer (PC), the reliance of PC cells on activated epidermal growth factor receptor (EGFR) and its downstream signaling to phosphoinositide 3'-kinase/Akt (PI3K/Akt/PTEN) and/or mitogen-activated protein kinase (MAPK/ERK) pathways has not been fully elucidated. In this study, we compared the role of EGF-mediated signaling in nonmalignant (BPH-1, PNT1A, and PNT1B) and PC cell lines (DU145, PC3, LNCaP, and CWR22Rv1). EGF-induced proliferation was observed in all EGFR-expressing PC cells except PC3, indicating that EGFR expression does not unequivocally trigger proliferation following EGF stimulation. ErbB2 recruitment potentiated EGF-induced signals and was associated with the most pronounced effects of EGF despite low EGFR expression. In this way, the sum of EGFR and ErbB2 receptor phosphorylation proved to be a more sensitive indicator of EGF-induced proliferation than quantification of the expression of either receptor alone. Both Akt and ERK were rapidly phosphorylated in response to EGF, with ERK phosphorylation being the weakest in PC3 cells. Extrapolation of these findings to clinical PC suggests that assessment of phosphorylated EGFR + ErbB2 together could serve as a marker for sensitivity to anti-EGFR-targeted therapies.

In silico analysis of gene expression profiles in the olfactory mucosae of aging senescence-accelerated mice

We utilized high-density Affymetrix oligonucleotide arrays to investigate gene expression in the olfactory mucosae of near age-matched aging senescence-accelerated mice (SAM). The senescence-prone (SAMP) strain has a significantly shorter lifespan than does the senescence-resistant (SAMR) strain. To analyze our data, we applied biostatistical methods that included a correlation analysis to evaluate sources of methodologic and biological variability; a two-sided t-test to identify a subpopulation of Present genes with a biologically relevant P-value <0.05; and a false discovery rate (FDR) analysis adjusted to a stringent 5% level that yielded 127 genes with a P-value of <0.001 that were differentially regulated in near age-matched SAMPs (SAMP-Os; 13.75 months) compared to SAMRs (SAMR-Os, 12.5 months). Volcano plots related the variability in the mean hybridization signals as determined by the two-sided t-test to fold changes in gene expression. The genes were categorized into the six functional groups used previously in gene profiling experiments to identify candidate genes that may be relevant for senescence at the genomic and cellular levels in the aging mouse brain (Lee et al. [2000] Nat Genet 25:294-297) and in the olfactory mucosa (Getchell et al. [2003] Ageing Res Rev 2:211-243), which serves several functions that include chemosensory detection, immune barrier function, xenobiotic metabolism, and neurogenesis. Because SAMR-Os and SAMP-Os have substantially different median lifespans, we related the rate constant alpha in the Gompertz equation on aging to intrinsic as opposed to environmental mechanisms of senescence based on our analysis of genes modulated during aging in the olfactory mucosa.

Induction of cyclooxygenase-2 in macrophages by catalase: role of NF-kappaB and PI3K signaling pathways

Induction of COX-2 by catalase in smooth muscle cells, endothelial cells, and neuronal cells has been previously reported. However, the mechanism by which catalase up-regulates COX-2 remains poorly understood. In this study, we investigated the effect of catalase on induction of COX-2 in macrophages. The addition of catalase into Raw 264.7 macrophages induced COX-2 expression that was correlated with increased COX-2 transcription and mRNA stability. Catalase also induced activation of NF-kappaB, PI3K, ERKs, p38s, or JNKs. Catalase-induced COX-2 expression was abrogated by treatment of MG-132 (a NF-kappaB inhibitor) or LY294002 (a PI3K inhibitor), but not by treatment of PD98059 (an ERK inhibitor), SB203580 (a p38 inhibitor), or SP600125 (a JNK inhibitor). Moreover, inhibition of PI3K by LY294002 caused partial decrease of catalase-induced COX-2 transcription and steady-state COX-2 transcript levels, but not COX-2 mRNA stability. Together, these results suggest that catalase induces the expression of COX-2 in Raw 264.7 macrophages, and the induction is related with activation of NF-kappaB transcription factor and PI3K signaling pathway.

Targeted expression of the class II phosphoinositide 3-kinase in Drosophila melanogaster reveals lipid kinase-dependent effects on patterning and interactions with receptor signaling pathways

Phosphoinositide 3-kinases (PI3Ks) can be divided into three distinct classes (I, II, and III) on the basis of their domain structures and the lipid signals that they generate. Functions have been assigned to the class I and class III enzymes but have not been established for the class II PI3Ks. We have obtained the first evidence for a biological function for a class II PI3K by expressing this enzyme during Drosophila melanogaster development and by using deficiencies that remove the endogenous gene. Wild-type and catalytically inactive PI3K_68D transgenes have opposite effects on the number of sensory bristles and on wing venation phenotypes induced by modified epidermal growth factor (EGF) receptor signaling. These results indicate that the endogenous PI3K_68D may act antagonistically to the EGF receptor-stimulated Ras-mitogen-activated protein kinase pathway and downstream of, or parallel to, the Notch receptor. A class II polyproline motif in PI3K_68D can bind the Drk adaptor protein in vitro, primarily via the N-terminal SH3 domain of Drk. Drk may thus be important for the localization of PI3K_68D, allowing it to modify signaling pathways downstream of cell surface receptors. The phenotypes obtained are markedly distinct from those generated by expression of the Drosophila class I PI3K, which affects growth but not pattern formation.

Phosphoinositide 3-kinase regulates excitation-contraction coupling in neonatal cardiomyocytes

The phosphoinositide 3-kinase (PI3K) inhibitor LY-294002 decreased steady-state contraction in neonatal rat ventricular myocytes (NRVM). To determine whether the effect on steady-state contraction could be due to decreased intracellular Ca2+content, Ca2+content was assessed with fluorescent plate reader analysis by using the caffeine-releasable Ca2+stores as an index of sarcoplasmic reticulum (SR) Ca2+content. Caffeine-releasable Ca2+content was diminished in a dose-dependent manner with LY-294002, suggesting that the decrease in steady-state contraction was due to diminished intracellular Ca2+content. Activation of the L-type Ca2+channel by BAY K 8644 was attenuated by LY-294002, suggesting the effect of LY-294002 is to reduce Ca2+influx at this channel. To investigate whether additional proteins involved in excitation-contraction (EC) coupling are likewise regulated by PI3K activity, the effects of compounds acting at sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2a), the ryanodine receptor, and the Na/Ca exchanger (NCX) were compared with LY-294002. Inhibition of SERCA2a by thapsigargin increased basal Ca2+levels in contrast to LY-294002, indicating that SERCA2a activity is sustained in the presence of LY-294002. Ryanodine decreased SR Ca2+content. The additive effect with coadministration of LY-294002 could be attributed to a decrease in Ca2+influx at the L-type Ca2+channel. The NCX inhibitor Ni2+was used to investigate whether the decrease in intracellular Ca2+content with LY-294002 could be due to inhibition of the NCX reverse-mode activity. The minimal effect of LY-294002 with Ni2+suggests that the primary effect of LY-294002 on EC coupling occurs through inhibition of PI3K-mediated L-type Ca2+channel activity.

Topographical expression of class IA and class II phosphoinositide 3-kinase enzymes in normal human tissues is consistent with a role in differentiation

Background

Growth factor, cytokine and chemokine-induced activation of PI3K enzymes constitutes the start of a complex signalling cascade, which ultimately mediates cellular activities such as proliferation, differentiation, chemotaxis, survival, trafficking, and glucose homeostasis. The PI3K enzyme family is divided into 3 classes; class I (subdivided into IA and IB), class II (PI3K-C2α, PI3K-C2β and PI3K-C2γ) and class III PI3K. Expression of these enzymes in human tissue has not been clearly defined.

Methods

In this study, we analysed the immunohistochemical topographical expression profile of class IA (anti-p85 adaptor) and class II PI3K (PI3K-C2α and PI3K-C2β) enzymes in 104 formalin-fixed, paraffin embedded normal adult human (age 33–71 years, median 44 years) tissue specimens including those from the gastrointestinal, genitourinary, hepatobiliary, endocrine, integument and lymphoid systems. Antibody specificity was verified by Western blotting of cell lysates and peptide blocking studies. Immunohistochemistry intensity was scored from undetectable to strong.

Results

PI3K enzymes were expressed in selected cell populations of epithelial or mesenchymal origin. Columnar epithelium and transitional epithelia were reactive but mucous secreting and stratified squamous epithelia were not. Mesenchymal elements (smooth muscle and endothelial cells) and glomerular epithelium were only expressed PI3K-C2α while ganglion cells expressed p85 and PI3K-C2β. All three enzymes were detected in macrophages, which served as an internal positive control. None of the three PI3K isozymes was detected in the stem cell/progenitor compartments or in B lymphocyte aggregates.

Conclusions

Taken together, these data suggest that PI3K enzyme distribution is not ubiquitous but expressed selectively in fully differentiated, non-proliferating cells. Identification of the normal in vivo expression pattern of class IA and class II PI3K paves the way for further analyses which will clarify the role played by these enzymes in inflammatory, neoplastic and other human disease conditions.

Role of phosphoinositide 3-kinase signaling in mast cells: new insights from knockout mouse studies

Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases essential for diverse physiological reactions. In recent years a series of gene-targeted mice lacking different types of PI3Ks and related molecules have been generated which enable us to understand the role of PI3K pathways, particularly class I members, in vivo. Analyses of such gene-targeted mice have led to major discoveries in the physiological roles of PI3K signaling in mast cell biology. In particular the role of PI3Ks has been extensively studied in signaling through the high-affinity IgE receptor (FcepsilonRI), since mast cells are the main effector cells in type I allergic reaction associated with IgE-dependent mechanisms. Furthermore, the knockout mice have provided significant information concerning the role of PI3K signals in mast cell differentiation. This review presents several new insights into mast cell biology, which have been elucidated by the analyses of these knockout mice.

Selective abrogation of the proinvasive activity of the trefoil peptides pS2 and spasmolytic polypeptide by disruption of the EGF receptor signaling pathways in kidney and colonic cancer cells

Trefoil peptides (TFFs) are now considered as scatter factors, proinvasive and angiogenic agents acting through cyclooxygenase-2 (COX-2)- and thromboxane A2 receptor (TXA2-R)-dependent signaling pathways. As expression and activation levels of the epidermal growth factor receptor (EGFR) predict the metastatic potential of human colorectal cancers, the purpose of this study was to establish whether the EGF receptor tyrosine kinase (EGFR-TK) contributes to cellular invasion induced by TFFs in kidney and colonic cancer cells. Both the dominant negative form of the EGFR (HER-CD533) and the EGFR-TK inhibitor ZD1839 (Iressa) abrogated cellular invasion induced by pS2, spasmolytic polypeptide (SP) and the src oncogene, but not by ITF and the TXA2-R. Similarly, EGFR-TK inhibition by ZD1839 reversed the invasive phenotype promoted by the constitutively activated form of the EGFR (EGFRvIII) and the EGFR agonists transforming growth factor alpha (TGFalpha), amphiregulin and EGF. We also provide evidence that TFFs, EGFRvIII, and TGFalpha trigger common proinvasive pathways using the PI3'-kinase and Rho/Rho- kinase cascades. These findings identify the EGFR-TK as a key signaling element for pS2- and SP-mediated cellular invasion. It is concluded that although pS2, SP and ITF belong to the same family of inflammation- and cancer-associated regulatory peptides, they do not control identical signaling networks.

Mitotic and stress-induced phosphorylation of HsPI3K-C2alpha targets the protein for degradation

Activation of the phosphoinositide 3-kinases (PI 3-kinases) has been implicated in multiple cellular responses such as proliferation and survival, membrane and cytoskeletal reorganization, and intracellular vesicular trafficking. The activities and subcellular localization of PI 3-kinases were shown to be regulated by phosphorylation. Previously we demonstrated that class II HsPIK3-C2alpha becomes phosphorylated upon inhibition of RNA pol II-dependent transcription (Didichenko, S. A., and Thelen, M. (2001) J. Biol. Chem. 276, 48135-48142). In this study we investigated cell cycle-dependent and genotoxic stress-induced phosphorylation of HsPIK3-C2alpha. We find that the kinase becomes phosphorylated upon exposure of cells to UV irradiation and in proliferating cells at the G2/M transition of the cell cycle. Stress-dependent and mitotic phosphorylation of HsPIK3-C2alpha occurs on the same serine residue (Ser259) within a recognition motif for proline-directed kinases. Mitotic phosphorylation of HsPIK3-C2alpha can be attributed to Cdc2 activity, and stress-induced phosphorylation of HsPIK3-C2alpha is mediated by JNK/SAPK. The protein level of HsPIK3-C2alpha is regulated by proteolysis in a cell cycle-dependent manner and in response of cells to stress. Phosphorylation appears to be a prerequisite for proteasome-dependent degradation of HsPIK3-C2alpha and may therefore contribute indirectly to the regulation of the activity of the kinase.