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At least 469 records · Page 26Linked to original sources
PubMed2004

Cellular targets of the SV40 small-t antigen in human cell transformation.

SV40 LT and ST antigens cooperate to induce the proliferation and eventual transformation of several human cell types. In natural virus infections, ST often enhances the function of LT when both proteins are present, and it can be difficult to completely separate the roles of the individual proteins. By studying ST in the absence of LT or by replacing ST function with combinations of cellular proteins, several themes have emerged which help define the requirement for ST in human cell transformation. These include the activation of transcription of two cyclins, D and A, along with downregulation of the cyclin kinase inhibitor p27. Modification of these key cell cycle regulators may be influenced by the activation of key downstream targets in the PI3K pathway.

Animals↗
PubMed2004

Polo-like kinase 1 inactivation following mitotic DNA damaging treatments is independent of ataxia telangiectasia mutated kinase.

Polo-like kinase 1 (Plk1) is an important regulator of several events during mitosis. Recent reports show that Plk1 is involved in both G2 and mitotic DNA damage checkpoints. Ataxia telangiectasia mutated kinase (ATM) is an important enzyme involved in G2 phase cell cycle arrest following interphase DNA damage, and inhibition of Plk1 by DNA damage during G2 occurs in an ATM-/ATM-Rad3-related kinase (ATR)-dependent fashion. However, it is unclear how Plk1 is regulated in response to M phase DNA damage. We found that treatment of mitotic cells with DNA damaging agents inhibits Plk1 activity primarily through dephosphorylation of Plk1, which occurred in both p53 wild-type and mutant cells. Inhibition of Plk1 is not prevented by caffeine pretreatment that inhibits ATM activity and also occurs in ATM mutant cell lines. Furthermore, ATM mutant cell lines, unlike wild-type cells, fail to arrest after mitotic DNA damaging treatments. The phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, reduces Plk1 dephosphorylation following mitotic DNA damaging treatments, suggesting that the PI3K pathway may be involved in regulating Plk1 activity. Earlier studies showed that inhibition of Plk1 by G2 DNA damage occurs in an ATM-dependent fashion. Our results extend the previous studies by showing that ATM is not required for dephosphorylation and inhibition of Plk1 activity following mitotic DNA damage, and also suggest that Plk1 is not a principal regulator or mediator of the mitotic DNA damage response.

Ataxia Telangiectasia Mutated Proteins↗
PubMed2006

Extracellular acidosis elevates carbonic anhydrase IX in human glioblastoma cells via transcriptional modulation that does not depend on hypoxia.

Most solid tumors display extracellular acidosis, which only partially overlaps with hypoxia and induces distinct adaptive changes leading to aggressive phenotype. Although acidosis is mainly attributable to excessive production of lactic acid, it also involves carbonic anhydrase (CA) IX-mediated conversion of CO(2) to an extracellular proton and a bicarbonate ion transported to cytoplasm. CA IX is pre-dominantly expressed in tumors with poor prognosis and its transcription and activity are induced by hypoxia. Here we investigated whether low extracellular pH in absence of hypoxia can influence CA IX expression in cell lines derived from glioblastoma, a tumor type particularly linked with acidosis. Our data show that extracellular acidosis increased the level of CA IX protein, mRNA and the activity of minimal CA9 promoter that contains binding sites for HIF-1 and SP-1 transcription factors. Mutation within each of these two biding sites reduced the promoter activity, but did not eliminate the increase by acidosis. Transfection of HIF-1alpha cDNA produced additive inducing effect with acidosis. Normoxic acidosis was accompanied by HIF-1alpha protein accumulation and transiently increased phosphorylation of ERK1/2. Expression of a dominant-negative mutant of ERK2 reduced the CA9 promoter activity in both standard and acidic conditions. Similar result was obtained by inhibitors of MAPK and PI3K pathways, whose combination completely suppressed CA IX expression and abolished induction by acidosis. Altogether, our results suggest that acidosis increases the CA IX expression via a hypoxia-independent mechanism that operates through modulation of the basic CA9 transcriptional machinery.

Acidosis↗
PubMed2005

Platelet-activating factor induces matrix metalloproteinase-9 expression through Ca(2+)- or PI3K-dependent signaling pathway in a human vascular endothelial cell line.

Platelet-activating factor (PAF) augments angiogenesis by promoting the synthesis of a variety of angiogenic factors, via the nuclear factor (NF)-kappaB activation. Recently, we reported that PAF upregulates MMP-9 expression in a NF-kappaB-dependent manner. In this study, we investigated the signaling pathway involved in PAF-induced MMP-9 expression in ECV304 cells. Our current data indicate that the Ca(2+)- or phosphatidylinositol 3-kinase (PI3K)-dependent signaling pathway is necessary for PAF-induced MMP-9 expression. Furthermore, PAF-induced NF-kappaB activation was blocked by selective inhibitors of Ca(2+), PI3K, or extracellular signal-regulated kinase (ERK). Our results suggest that PAF-induced MMP-9 expression, in a NF-kappaB-dependent manner, is regulated by Ca(2+), PI3K and ERK signaling pathways.

Calcium↗
PubMed2006

FcgammaR-induced production of superoxide and inflammatory cytokines is differentially regulated by SHIP through its influence on PI3K and/or Ras/Erk pathways.

Phagocytosis of IgG-coated particles via FcgammaR is accompanied by the generation of superoxide and inflammatory cytokines, which can cause collateral tissue damage in the absence of regulation. Molecular mechanisms regulating these phagocytosis-associated events are not known. SHIP is an inositol phosphatase that downregulates PI3K-mediated activation events. Here, we have examined the role of SHIP in FcgammaR-induced production of superoxide and inflammatory cytokines. We report that primary SHIP-deficient bone marrow macrophages produce elevated levels of superoxide upon FcgammaR clustering. Analysis of the molecular mechanism revealed that SHIP regulates upstream Rac-GTP binding, an obligatory event for superoxide production. Likewise, SHIP-deficient macrophages displayed enhanced IL-1beta and IL-6 production in response to FcgammaR clustering. Interestingly, whereas IL-6 production required activation of both PI3K and Ras/Erk pathways, IL-1beta production was dependent only on Ras/Erk activation, suggesting that SHIP may also regulate the Ras/Erk pathway in macrophages. Consistently, SHIP-deficient macrophages displayed enhanced activation of Erk upon FcgammaR clustering. Inhibition of Ras/Erk or PI3K suppressed the enhanced production of IL-6 in SHIP-deficient macrophages. In contrast, inhibition of Ras/Erk, but not PI3K, suppressed IL-1beta production in these cells. Together, these data demonstrate that SHIP regulates phagocytosis-associated events through the inhibition of PI3K and Ras/Erk pathways.

Animals↗
PubMed2002

Topotecan inhibits VEGF- and bFGF-induced vascular endothelial cell migration via downregulation of the PI3K-Akt signaling pathway.

Angiogenesis plays a crucial role in tumor growth and metastases. The extent of angiogenesis correlates with the increased invasion and metastasis in a variety of human neoplasms. Vascular endothelial cell proliferation and migration are critical steps in angiogenesis and are regulated by various growth factors, such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). The topoisomerase I inhibitor topotecan (10-hydroxy-9-dimethylaminomethyl-(S)-camptothecin) is a water-soluble camptothecin analogue and possesses an indirect in vivo antitumor effect mediated through the inhibition of angiogenesis. We found that topotecan inhibited VEGF- and bFGF-induced migration of human umbilical vein endothelial cells (HUVECs) in vitro. The migration of HUVECs was also inhibited by a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002. Thus, we investigated the possibility that topotecan's antiangiogenic property might be mediated by its inhibitory effect on VEGF- and bFGF-induced activation of the PI3K-Akt signaling pathway. We found that topotecan treatment decreased the amount of the phosphorylated (activated) form of Akt, but not the amount of Akt protein, in HUVECs. Moreover, transient transfection of constitutive active akt cDNA into HUVECs reversed the topotecan-mediated decrease in HUVEC migration. These results suggest that the antiangiogenic activity of topotecan is mediated in part by downregulating the PI3K-Akt signaling pathway.

Antineoplastic Agents↗
PubMed2006

Ultrasensitive and absolute quantification of the phosphoinositide 3-kinase/Akt signal transduction pathway by mass spectrometry.

The phosphoinositide 3-kinase (PI3K)/Akt pathway controls a vast array of normal physiological processes and is frequently aberrantly activated in cancer, thus identifying PI3K/Akt-signaling components as promising drug targets in oncology. However, implementation of rational cancer therapies for this pathway needs robust and simple tools to stratify patients according to PI3K pathway activation and to validate and measure the impact of targeted inhibition on primary cancer tissues. Herein we present a technique for the quantification of the PI3K/Akt-signaling pathway based on the mass spectrometric measurement of PI3K-dependent protein kinase activity in cell lysates. The concept of this application of MS is to exploit enzymatic activity to amplify the signal of the enzyme under study analogous to the PCR used to amplify nucleic acid sequences. We show that this approach allows quantitative analysis of a cell-signaling pathway with high sensitivity, precision of quantification, and specificity. Due to its special analytical capabilities and potential for multiplexing, this approach could contribute significantly to cell-signaling studies and to the development and implementation of personalized cancer therapies.

Animals↗
PubMedDate not supplied

The antiproliferative effect of Quercetin in cancer cells is mediated via inhibition of the PI3K-Akt/PKB pathway.

BACKGROUND: The tumor suppressor gene PTEN, mutated in 40-50% of patients with brain tumors, especially those with glioblastomas, maps to chromosome 10q23.3 and encodes a dual-specificity phosphatase. PTEN exerts its effects partly via inhibition of protein tyrosine kinase B (Akt/Protein Kinase B), which is involved in the phosphatidylinositol (PtdIns) 3-kinase (PI3K)-mediated cell-survival pathway. The naturally occurring bioflavonoid Quercetin (Qu) shares structural homology with the commercially available selective PI3K inhibitor, LY 294002 (LY). Here, the effects of Qu on the Akt/PKB pathway were evaluated. MATERIALS AND METHODS: The human breast carcinoma cell lines, HCC1937, with homozygous deletion of the PTEN gene, and T47D, with intact PTEN, were time-treated with Qu or LY and analyzed for activated levels of Akt by measuring phospho-Akt (p-Akt) levels using immunoblotting analysis. To detect p-Akt, the T47D cells were treated with EGF prior to treatment with or without Qu or LY Cell proliferation after 24-h treatment with Qu or LY was quantified by the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. RESULTS: Treatment with Qu (25 microM) for 0.5, 1 and 3 h completely suppressed constitutively activated Akt/PKB phosphorylation at Ser-473 in HCC1937 cells. Pre-exposing T47D cells to Qu (25 microM) or LY (10 microM) abrogated EGF-induced Akt/PKB phosphorylation at Ser-473. Both Qu (100 microM) and LY (50 microM) treatments for 24 h significantly decreased cell proliferation, as shown by the MTT assay. CONCLUSION: Pharmacologically safe doses of the naturally occurring bioflavonoid Qu inhibit the PI3K-Akt/PKB pathway, in a manner similar to that of the commercially available LY. Overall, our results indicated that Qu inhibited the constitutively activated-Akt/PKB pathway in PTEN-null cancer cells, and suggest that this compound may have therapeutic benefit against tumorigenesis and cancer progression.

Antineoplastic Agents↗
PubMed2006

Time-dependent sensitivity analysis of biological networks: coupled MAPK and PI3K signal transduction pathways.

Sensitivity analysis has been widely used in the studies of complicated chemical reaction and biological networks, for example, in combustion studies and metabolic control analysis of pathways. In the latter cases, the responses of system properties at steady states with respect to changes of parameters, such as initial concentrations and rate constants, are often expressed as sensitivities. Besides steady-state sensitivities, time-dependent sensitivities should be useful; however, the explicit use of them in analyzing complicated biological systems has so far been limited. Using the coupled mitogen activated protein kinase (MAPK)-phophatidylinoisitol 3'-kinase (PI3K) system of the Ras pathways, known to be involved in about 30% of human cancers, as an example, we show that time-dependent sensitivities are useful for the studies of complex biological systems. They provide, for example, the following information: (a) multiple time scales existing in a complex system involving cross-talks and feedback loops; (b) the signs and strengths of responses to perturbations (as system complication increases, the signs of global responses are not always easily determined; for example, response may change sign more than once as time evolves); (c) beyond concentration dynamics, sensitivities revealing further details about the intricate dynamics and the effects of the cross-talks; (d) ranking of vulnerability of nodes of a biological network using integrated sensitivity-a first step toward the identification of drug targets; (e) reduced sensitivity serving as a measure of the stability or robustness of pathways. Our results indicate that the role of the PI3K branch in the coupled pathways is to enhance the robustness of the MAPK pathway. More importantly, they demonstrate that time-dependent sensitivity analysis can be a valuable tool in system biology.

Mitogen-Activated Protein Kinases↗
PubMed2007

Hormonal induction of adipogenesis induces Skp2 expression through PI3K and MAPK pathways.

We have previously shown that the F-box protein, S-phase kinase-associated protein (Skp2) plays a mechanistic role in targeting the cell-cycle inhibitor, p27 for degradation by the 26S proteasome during early stages of 3T3-L1 adipocyte differentiation. Here, we demonstrate that protein levels of Skp2 and its accessory protein, Cks1 increased as density-arrested preadipocytes re-entered the cell cycle during clonal expansion, decreased with differentiation-induced growth arrest, and became refractory to hormonal stimulation following the onset of terminal adipocyte differentiation. Component analysis revealed that while maximal Skp2/Cks1 protein accumulation required the complete differentiation cocktail, that insulin was principally involved. Skp2 mRNA accumulation was found to precede the increase in Skp2 protein and succeed the activation of Akt and Erk1/2, mediators of phosphatidylinositol-3 kinase (PI3K) and mitogen-activated protein kinase (MAPK) signal transduction pathways, respectively. Using specific inhibitors, we found that while activation of both pathways was required for maximal expression, PI3K signaling was primarily responsible for the increase in Skp2/Cks1 accumulation. The increase in Skp2 mRNA was notable 4 h following hormonal stimulation, plateaued by 12 h during mid-G1 phase progression, and occurred without change to mRNA stability. We further demonstrate that luciferase activity, originating from a pGL3 vector containing 2.4 kb of the Skp2 promoter, increased 2.5-fold with hormonal stimulation. This increase in promoter activity was markedly suppressed following PI3K and MAPK blockade. Deletion studies indicate that responsive elements were located within the proximal Skp2 promoter. These data demonstrate that Skp2 is transcriptionally regulated by PI3K and MAPK pathways as 3T3-L1 preadipocytes transition from quiescence to proliferation during adipocyte hyperplasia.

1-Methyl-3-isobutylxanthine↗
PubMed2004

Participation of PI3K and ERK1/2 pathways are required for human brain vascular smooth muscle cell migration.

Human brain vascular smooth muscle cell (HBVSMC) migration contributes to angiogenesis and several pathological processes in the brain. However, the molecular mechanism of angiogenesis, in which smooth muscle cell contributes, remains unclear. Our study investigates the role of vascular endothelial growth factor (VEGF) in the HBVSMC migration and elucidates the chemotactic signaling pathway mediating this action. We used the in vitro 'scratch' wound method to detect the HBVSMC migration. VEGF(165) (1-40ng/ml) induced the HBVSMC migration in a dose-dependent manner (P<0.05). VEGF(165) does not induce HBVSMC proliferation. Wortmannin, a specific phosphatidylinositol 3-kinase (PI3K) inhibitor, significantly inhibited serine/threonine kinase Akt/protein kinase B (PKB) phosphorylation and reduced HBVSMC migration into the wound edge following VEGF(165) stimulation (P<0.05). PD98059, an extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor, also significantly inhibited ERK1/2 phosphorylation and reduced the numbers of SMC migration. Parallel distance measurement showed that VEGF(165) induced HBVSMC migration significantly reduced due to inhibition of PI3K or ERK1/2 phosphorylation (P<0.05). Our results demonstrate that VEGF(165) could induce HBVSMC migration but not proliferation in vitro. Inhibiting Akt/PKB or ERK1/2 phosphorylation could reduce VEGF(165) induced HBVSMC migration. We provide the first evidence that activation of PI3K or ERK1/2 pathways are a crucial event in VEGF(165) mediated signal transduction leading to HBVSMC migration.

Androstadienes↗
PubMed2006

Inhibition of the phosphatidylinositol 3'-kinase pathway promotes autocrine Fas-induced death of phosphatase and tensin homologue-deficient prostate cancer cells.

Rationally designed therapeutics that target the phosphatidylinositol 3'-kinase (PI3K) cell survival pathway are currently in preclinical and clinical development for cancer therapy. Drugs targeting the PI3K pathway aim to inhibit proliferation, promote apoptosis, and enhance chemosensitivity and radiosensitivity of cancer cells. The phosphatase and tensin homologue (PTEN) phosphatidylinositol 3'-phosphatase is a key negative regulator of the PI3K pathway. Inactivation of the PTEN tumor suppressor results in constitutive activation of the PI3K pathway and is found in approximately 50% of advanced prostate cancers, which correlates with a high Gleason score and poor prognosis. Inhibition of the PI3K pathway leads to apoptosis of prostate cancer cells; however, the precise mechanism by which this occurs is unknown. Here we report that apoptotic cell death of PTEN-deficient LNCaP and PC3 prostate cancer cells induced by the PI3K inhibitor LY294002 can be abrogated by disrupting Fas/Fas ligand (FasL) interactions with recombinant Fas:Fc fusion protein or FasL neutralizing antibody (Nok-1), or by expressing dominant-negative Fas-associated death domain. Furthermore, we find that apoptosis induced by expression of wild-type PTEN, driven by a tetracycline-inducible expression system in LNCaP cells, can be inhibited by blocking Fas/FasL interaction using Fas:Fc or Nok-1. These data show that apoptosis induced by blockade of the PI3K pathway in prostate tumor cells is mediated by an autocrine Fas/FasL apoptotic mechanism and the Fas apoptotic pathway is both necessary and sufficient to mediate apoptosis by PI3K inhibition.

Adaptor Proteins, Signal Transducing↗
PubMed2005

KGF induces lipogenic genes through a PI3K and JNK/SREBP-1 pathway in H292 cells.

Lipid synthesis is required for cell growth and is subject to pharmacologic regulation. Keratinocyte growth factor (KGF) stimulates proliferation and lipogenesis in H292 cells, a pulmonary epithelial cancer cell line, but the signaling pathways are not known. KGF stimulated the expression of the transcription factors sterol-regulatory element binding protein-1 (SREBP-1), CCAAT/enhancer binding protein alpha (C/EBPalpha), and C/EBPdelta and two key enzymes involved in lipogenesis, FAS and stearoyl coenzyme A desaturase-1 (SCD-1). We found that KGF induced rapid activation of Akt, p70 S6K, JNK, and extracellular signal-regulated (ERK). Induction of SREBP-1, SCD-1, and FAS by KGF was inhibited by the JNK inhibitor SP600125 and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 but not by the ERK inhibitor PD98059. Using FAS and SCD-1-luciferase promoter constructs, we observed that KGF stimulated the transcription of these promoters and that exogenous cholesterol inhibited the induction. Mutation of the SREBP-1 binding site in the SCD-1 promoter abolished the effect of KGF on SCD-1 transcription. In addition, overexpression of active SREBP-1 directly stimulated SCD-1 and FAS. Conversely, adenovirus-mediated overexpression of a dominant negative form of SREBP-1 inhibited the KGF effect on FAS and SCD-1 expression. In summary, we conclude that KGF requires both PI3K and JNK signaling pathways to induce SREBP-1, which in turn induces SCD-1 and FAS expression in H292 cells.

Adenoviridae↗
PubMed2004

Phosphatidylinositol 3-kinase inhibition down-regulates survivin and facilitates TRAIL-mediated apoptosis in neuroblastomas.

BACKGROUND/PURPOSE: Recent findings have correlated neuroblastoma development with aberration of apoptosis. In particular, increased levels of survivin, a member of the inhibitor of apoptosis protein (IAP) family, have been associated with increased resistance to apoptosis in neuroblastomas. The purpose of this study was to determine whether the phosphatidylinositol 3-kinase (PI3K)/Akt pathway can alter the expression of survivin and facilitate tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis in neuroblastoma cells. METHODS: Human neuroblastoma cells (SK-N-SH, BE[2]C, LAN-1 and IMR-32) were treated with LY294002 or wortmannin, inhibitors of PI3K, for 24 hours. Transient transfection of a dominant negative PI3K expression plasmid, pCGNN-Deltap85, was performed to inhibit PI3K activation. Cells were treated with TRAIL, caspase-3, or pan-caspase inhibitors. RNase protection assay was performed to assess mRNA changes in IAP family members, including survivin. Western blot analysis was performed to measure changes in the levels of procaspases and survivin. Apoptosis was assessed by a DNA fragmentation ELISA assay. RESULTS: The authors found that survivin and cIAP1 mRNA as well as protein expression were decreased after PI3K inhibition. Combination treatment with LY294002 and TRAIL increased apoptosis of SK-N-SH cells compared with TRAIL alone; these results were further corroborated by complete inhibition of apoptosis by caspase-3 or pan-caspase inhibitor. CONCLUSIONS: The authors report that PI3K pathway inhibition down-regulates survivin expression and enhances TRAIL-mediated apoptosis in neuroblastomas. PI3K pathway may play a crucial role in neuroblastoma cell survival; therefore, treatment with inhibitors of PI3K may provide potential novel therapeutic options.

Androstadienes↗
PubMed2006

IL-17 enhances IL-1beta-mediated CXCL-8 release from human airway smooth muscle cells.

Recent studies into the pathogenesis of airway disorders such as asthma have revealed a dynamic role for airway smooth muscle cells in the perpetuation of airway inflammation via secretion of cytokines and chemokines. In this study, we evaluated whether IL-17 could enhance IL-1beta-mediated CXCL-8 release from human airway smooth muscle cells (HASMC) and investigated the upstream and downstream signaling events regulating the induction of CXCL-8. CXCL-8 mRNA and protein induction were assessed by real-time RT-PCR and ELISA from primary HASMC cultures. HASMC transfected with site-mutated activator protein (AP)-1/NF-kappaB CXCL-8 promoter constructs were treated with selective p38, MEK1/2, and phosphatidylinositol 3-kinase (PI3K) inhibitors to determine the importance of MAPK and PI3K signaling pathways as well as AP-1 and NF-kappaB promoter binding sites. We demonstrate IL-17 induced and synergized with IL-1beta to upregulate CXCL-8 mRNA and protein levels. Erk1/2 and p38 modulated IL-17 and IL-1beta CXCL-8 promoter activity; however, IL-1beta also activated the PI3K pathway. The synergistic response mediating CXCL-8 promoter activity was dependent on both MAPK and PI3K signal transduction pathways and required the cooperation of AP-1 and NF-kappaB cis-acting elements upstream of the CXCL-8 gene. Collectively, our observations indicate MAPK and PI3K pathways regulate the synergy of IL-17 and IL-1beta to enhance CXCL-8 promoter activity, mRNA induction, and protein synthesis in HASMC via the cooperative activation of AP-1 and NF-kappaB trans-acting elements.

Humans↗
PubMed2005

Inhibition of phosphatidylinositol-3-kinase synergizes with gemcitabine in low-passage tumor cell lines correlating with Bax translocation to the mitochondria.

Apoptotic pathways, including the phosphatidylinositol-3-kinase (PI3K)/AKT survival pathway, are altered in most cancer cells in relation to their normal counterparts and these differences may present an excellent therapeutic window. To gain insight into the relevance of the PI3K pathway as a target for drug discovery we generated tumor cell lines from different tumor samples that we maintained at low passage. The characterization of these cell lines indicates that all of them have constitutively activated the PI3K pathway through different mechanisms. All cell lines were differentially sensitive to the PI3K inhibitor LY294002. Our data also support previous work indicating that PI3K inhibition might help classical chemotherapeutic treatments such as gemcitabine and strengthen suboptimal doses that might be effective for these purposes in decreasing the risk of side-effects. Finally, the analysis of the molecular markers that might be implicated in the synergism between LY294002 and gemcitabine suggests that PI3K inhibition might aid chemotherapeutic treatment, leading to changes in the balance between anti- and pro-apoptotic molecules of the Bcl-2 family, Bcl-XL and Bax. These results facilitate the exploration of potential synergism between chemotherapeutic treatment and the search for others that can account for similar molecular mechanisms of cooperation.

Carcinoma↗
PubMed2002

HIV-1 Nef downregulates MHC-I by a PACS-1- and PI3K-regulated ARF6 endocytic pathway.

The HIV-1 Nef-mediated downregulation of cell surface MHC-I molecules to the trans-Golgi network (TGN) enables HIV-1 to escape immune surveillance. However, the cellular pathway used by Nef to downregulate MHC-I is unknown. Here, we show that Nef and PACS-1 combine to usurp the ARF6 endocytic pathway by a PI3K-dependent process and downregulate cell surface MHC-I to the TGN. This mechanism requires the hierarchical actions of three Nef motifs-the acidic cluster 62EEEE(65), the SH3 domain binding site 72PXXP(75), and M(20)-in controlling PACS-1-dependent sorting to the TGN, ARF6 activation, and sequestering internalized MHC-I to the TGN, respectively. These data provide new insights into the cellular basis of HIV-1 immunoevasion.

ADP-Ribosylation Factor 6↗
PubMed2003

Role of the phosphatidylinositol 3 kinase-Akt pathway in the regulation of IL-10 and IL-12 by Porphyromonas gingivalis lipopolysaccharide.

Stimulation of the APC by Porphyromonas gingivalis LPS has been shown to result in the production of certain pro- and anti-inflammatory cytokines. However, the signaling pathways that regulate these processes are currently unknown. In the present study, the role of the phosphatidylinositol 3 kinase (PI3K)-Akt pathway in regulating P. gingivalis LPS-induced production of IL-10, IL-12 p40, and IL-12 p70 by human monocytes was investigated. P. gingivalis LPS selectively activates the PI3K-Akt pathway via Toll-like receptor 2, and inhibition of this pathway results in an abrogation of extracellular signal-regulated kinase 1/2 phosphorylation, whereas the activation of p38 and c-Jun N-terminal kinase 1/2 kinases were unaffected. Analysis of cytokine production following stimulation of monocytes with P. gingivalis LPS revealed that inhibition of the PI3K pathway differentially regulated IL-10 and IL-12 synthesis. IL-10 production was suppressed, whereas IL-12 levels were enhanced. Inhibition of P. gingivalis LPS-mediated activation of the PI3K-Akt pathway resulted in a pronounced augmentation of NF-kappaB p65 that was independent of IkappaB-alpha degradation. Furthermore, the ability of the PI3K-Akt pathway to modulate IL-10 and IL-12 production appears to be mediated by the selective suppression of extracellular signal-regulated kinase 1/2 activity, as the MEK1 inhibitor PD98059 closely mimicked the effects of wortmannin and LY294002 to differentially regulate IL-10 and IL-12 production by P. gingivalis LPS-stimulated monocytes. These studies provide new insight into how engagement of the PI3K-Akt pathway by P. gingivalis LPS affects the induction of key immunoregulatory cytokines that control both qualitative and quantitative aspects of innate and adaptive immunity.

Cells, Cultured↗