Cannabinoids down-regulate PI3K/Akt and Erk signalling pathways and activate proapoptotic function of Bad protein

Cannabinoids were shown to induce apoptosis of glioma cells in vitro and tumor regression in vivo, but mechanisms of their antiproliferative action remain elusive. In the present studies, C6 cells were exposed to a synthetic cannabinoid, WIN 55,212-2, which produced down-regulation of the Akt and Erk signalling pathways prior to appearance of any sign of apoptosis. We hypothesized that cannabinoid-induced cell death may be mediated by a Bcl-2 family member--Bad, whose function is hampered by these kinases due to control of its phosphorylation state. Using Western blot analysis, we found that levels of phosphorylated Bad, but not total Bad protein, decreased under exposure to WIN 55,212-2. WIN 55,212-2 treatment further resulted in mitochondrial depolarization and activation of caspase cascade. Thus, we suggest that the increase of proapoptotic Bad activity is an important link between the inhibition of survival pathways and an onset of execution phase of cannabinoid-induced glioma cell death.     

VEGF-A engages at least three tyrosine kinases to activate PI3K/Akt

Comment on: Canettieri G, et al. Nat Cell Biol 2010; 12:132-42.     

Leptin regulates proliferation and apoptosis of colorectal carcinoma through PI3K/Akt/mTOR signalling pathway

Epidemiological studies have indicated that obesity is associated with colorectal cancer. The obesity hormone leptin is considered as a key mediator for cancer development and progression. The present study aims to investigate regulatory effects of leptin on colorectal carcinoma. The expression of leptin and its receptor Ob-R was examined by immunohistochemistry in 108 Chinese patients with colorectal carcinoma. The results showed that leptin/Ob-R expression was significantly associated with T stage, TNM stage, lymph node metastasis, distant metastasis, differentiation and expression of p-mTOR, p-70S6 kinase, and p-Akt. Furthermore, the effects of leptin on proliferation and apoptosis of HCT-116 colon carcinoma cells were determined. The results showed that leptin could stimulate the proliferation and inhibit the apoptosis of HCT-116 colon cells through the PI3K/Akt/mTOR pathway. Ly294002 (a PI3K inhibitor) and rapamycin (an mTOR inhibitor) could prevent the regulatory effects of leptin on the proliferation and apoptosis of HCT-116 cells via abrogating leptin-mediated PI3K/Akt/mTOR pathway. All these results indicated that leptin could regulate proliferation and apoptosis of colorectal carcinoma through the PI3K/Akt/mTOR signalling pathway.     

Pristimerin-induced uveal melanoma cell death via inhibiting PI3K/Akt/FoxO3a signalling pathway

Uveal melanoma (UM) is a highly invasive intraocular malignancy with high mortality. Presently, there is no FDA-approved standard for the treatment of metastatic UM. Pristimerin is a natural quinine methide triterpenoid compound with anti-angiogenic, anti-cancer and anti-inflammatory activities. However, Pristimerin potential cytotoxic effect on UM was poorly investigated. In the present study, we found the migration and invasion of UM-1 cells were inhibited by Pristimerin which also caused a rapid increase of ROS, decreased mitochondrial membrane potential, induced the accumulation of cells in G0/G1 phase, ending with apoptotic cell death. Pristimerin inhibited Akt and FoxO3a phosphorylation and induced nuclear accumulation of FoxO3a in UM-1 cells, increased the expression of pro-apoptotic proteins Bim、p27^Kip1, cleaved caspase-3, PARP and Bax, and decreased the expression of Cyclin D1 and Bcl-2. LY294002 or Akt-siRNA inhibited the PI3K/Akt/FoxO3a pathway and promoted the Pristimerin-induced apoptosis, while Pristimerin effects were partially abolished in FoxO3a knockdown UM-1 cell cultures. Taken together, present results showed that Pristimerin induced apoptotic cell death through inhibition of PI3K/Akt/FoxO3a pathway in UM-1 cells. These findings indicate that Pristimerin may be considered as a potential chemotherapeutic agent for patients with UM.     

CTGF facilitates cell‐cell communication in chondrocytes via PI3K/Akt signalling pathway

PurposesGap junction intercellular communication (GJIC) is essential for articular cartilage to respond appropriately to physical or biological stimuli and maintain homeostasis. Connective tissue growth factor (CTGF), identified as an endochondral ossification genetic factor, plays a vital role in cell proliferation, migration and adhesion. However, how CTGF regulates GJIC in chondrocytes is still unknown. This study aims to explore the effects of CTGF on GJIC in chondrocytes and its potential biomechanism.Materials and methodsqPCR was performed to determine the expression of gene profile in the CCN family in chondrocytes. After CTGF treatment, CCK‐8 assay and scratch assay were performed to explore cell proliferation and migration. A scrape loading/dye transfer assay was adopted to visualize GJIC in living chondrocytes. Western blot analysis was done to detect the expression of Cx43 and PI3K/Akt signalling. Immunofluorescence staining was used to show protein distribution. siRNA targeting CTGF was used to detect the influence on cell‐cell communication.ResultsThe CTGF (CCN2) was shown to be the highest expressed member of the CCN family in chondrocytes. CTGF facilitated functional gap junction intercellular communication in chondrocytes through up‐regulation of Cx43 expressions. CTGF activated PI3K/Akt signalling to promote Akt phosphorylation and translocation. Suppressing CTGF also reduced the expression of Cx43. The inhibition of PI3K/Akt signalling decreased the expressions of Cx43 and thus impaired gap junction intercellular communication enhanced by CTGF.ConclusionsFor the first time, we provide evidence to show CTGF facilitates cell communication in chondrocytes via PI3K/Akt signalling pathway.     

Dehydrocostus lactone inhibits cell proliferation and induces apoptosis by PI3K/Akt/Bad and ERS signalling pathway in human laryngeal carcinoma

The anti-cancer effect of dehydrocostus lactone (DHL) derived from Saussurea costus (Falc.) Lipech against laryngeal carcinoma was assessed. The cytotoxic activity of DHL against laryngeal carcinoma is still obscure. Therefore, our study investigated the role of DHL in the growth inhibition of laryngeal carcinoma in vitro and in vivo, and the molecular mechanism of DHL-induced apoptosis in cancer cells of the larynx. The results showed that DHL inhibits the viability, migration and proliferation of Hep-2 and TU212 cells with little toxic effects on human normal larynx epithelial HBE cell line. Flow cytometry analysis (FAC) analysis and staining assay (Hoechst 33258) indicated that DHL stimulated Hep-2 and TU212 cell apoptosis in a dose-dependent manner. Mechanistically, DHL is capable of inhibiting Hep-2 and TU212 cell viability via promoting p53 and P21 function, meanwhile DHL dose-dependently induces Hep-2 and TU212 cells apoptosis via activating mitochondrial apoptosis by inhibiting PI3K/Akt/Bad pathway and stimulating endoplasmic reticulum stress-mediated apoptosis pathway. In vivo, DHL inhibited the growth of the Hep-2 nude mouse xenograft model and observed no significant signs of toxicity in the organs of nude mice. In vivo experiments further confirmed the anti-cancer effect of DHL on laryngeal carcinoma cells in vitro, and DHL-treated nude mice can reduce the volume of tumours. Together, our study indicated that DHL has the potential to inhibit human laryngeal carcinoma via activating mitochondrial apoptosis pathway by inhibiting PI3K/Akt/Bad signalling pathway and stimulating endoplasmic reticulum stress-mediated apoptosis pathway, providing a strategy for the treatment of human laryngeal carcinoma.     

GHR is involved in gastric cell growth and apoptosis via PI3K/AKT signalling

Growth hormone receptor (GHR), the cognate receptor of growth hormone (GH), is a membrane bound receptor that belongs to the class I cytokine receptor superfamily. GH binding GHR induces cell differentiation and maturation, initiates the anabolism inside the cells and promotes cell proliferation. Recently, GHR has been reported to be associated with various types of cancer. However, the underlying mechanism of GHR in gastric cancer has not been defined. Our results showed that silence of GHR inhibited the growth of SGC-7901 and MGC-803 cells, and tumour development in mouse xenograft model. Flow cytometry showed that GHR knockout significantly stimulated gastric cancer cell apoptosis and caused G1 cell cycle arrest, which was also verified by Western blot that GHR deficiency induced the protein level of cleaved-PARP, a valuable marker of apoptosis. In addition, GHR deficiency inhibited the activation of PI3K/AKT signalling pathway. On the basis of the results, that GHR regulates gastric cancer cell growth and apoptosis through controlling G1 cell cycle progression via mediating PI3K/AKT signalling pathway. These findings provide a novel understanding for the role of GHR in gastric cancer.     

Low dose leflunomide activates PI3K/Akt signalling in erythroleukemia cells and reduces apoptosis induced by anticancer agents

Rheumatoid arthritis (RA) is characterized by persistent joint synovial tissue inflammation. Leflunomide is an immunomodulatory agent that has been approved for treatment of active RA. In the past few years, uses other than RA treatment have appeared. Leflunomide has been reported to show antitumor potential through inhibition of cancer cell proliferation. We thus tested the antiproliferative potential of leflunomide on HEL and K562 erythroleukemia cells. The findings summarized in this report demonstrate for the first time that low dose leflunomide prolonged survival and reduced apoptosis induced by several anticancer agents in erythroleukemia cells. We showed that in treated cells, leflunomide reduced the signalling pathways involved in promoting apoptosis by reducing p38 MAPK and JNK basal activity. On the other hand, leflunomide transiently activated the ERK signalling pathway and induced a sustained activation of Akt. We also showed that leflunomide reduced caspase-3 activity and DNA fragmentation induced by anticancer agents. By using an inhibitory strategy, we showed that inhibition of Akt activation but not ERK abolished the protective effect of leflunomide. Thus our findings suggested that leflunomide reduced apoptosis induced by anticancer agents through PI3K/Akt signalling activation.     

Quercetin-induced apoptosis of HL-60 cells by reducing PI3K/Akt

To explore the effect and mechanism of quercetin on proliferation and apoptosis of leukemia cells, and provide a theoretical basis for its clinical application. HL-60 leukemia cell lines was treated with different dose quercetin, the proliferation activity of leukemia cells was assessed by MTT method; the morphological changes of apoptosis of HL-60 cells, including nuclear condensation and DNA fragmentation, were observed by Hoechst 33258 fluorescence staining, the apoptosis rate and caspase 2,3 activation were assessed by flow cytometry, and the cell signal pathway including phosphatidylinositol 3-kinase (PI3K), phosphorylated protein kinase B (pAkt), Bcl-2, Bax were detected by western blotting. Quercetin could significantly decrease the proliferation activity of HL-60 cells through the blockade of G(0)/G(1) phase, and induce the apoptosis of HL-60 cells in a time- and dose-dependent manner. Quercetin caused leukemia cells apoptosis by decreasing the protein expression of PI3K and Bax, the inhibitory phosphorylation of Akt, the decreased levels of Bcl-2 protein and increased activations of caspase-2 and -3, and increased poly(ADP-ribose) polymerase cleavage. Our results indicate that the apoptotic processes caused by quercetin are mediated by the decrease of pAkt and Bcl-2 levels, the increase of Bax level, and the activation of caspase families in HL-60 cells.     

Nicorandil alleviates apoptosis in diabetic cardiomyopathy through PI3K/Akt pathway

Nicorandil exerts myocardial protection through its antihypoxia and antioxidant effects. Here, we investigated whether it plays an anti‐apoptotic role in diabetic cardiomyopathy. Sprague‐Dawley rats were fed with high‐fat diet; then single intraperitoneal injection of streptozotocin was performed. Rats with fasting blood glucose (FBG) higher than 11.1 mmol/L were selected as models. Eight weeks after the models were built, rats were treated with nicorandil (7.5 mg/kg day and 15 mg/kg day respectively) for 4 weeks. H9c2 cardiomyocytes were treated with nicorandil and then stimulated with high glucose (33.3 mmol/L). TUNEL assay and level of bcl‐2, bax and caspase‐3 were measured. 5‐HD was used to inhibit nicorandil. Also, PI3K inhibitor (Miltefosine) and mTOR inhibitor (rapamycin) were used to inhibit PI3K/Akt pathway. The results revealed that nicorandil (both 7.5 mg/kg day and 15mg/kg day) treatment can increase the level of NO in the serum and eNOS in the heart of diabetic rats compared with the untreated diabetic group. Nicorandil can also improve relieve cardiac dysfunction and reduce the level of apoptosis. In vitro experiments, nicorandil (100 µmol) can attenuate the level of apoptosis stimulated by high glucose significantly in H9C2 cardiomyocyte compared with the untreated group. The effect of nicorandil on apoptosis was blocked by 5‐HD, and it was accompanied with inhibition of the phosphorylation of PI3K, Akt, eNOS, and mTOR. After inhibition of PI3K/Akt pathway, the protective effect of nicorandil is restrained. These results verified that as a NO donor, nicorandil can also inhibit apoptosis in diabetic cardiomyopathy which is mediated by PI3K/Akt pathway.     

Regulation of IGF-1/PI3K/Akt signalling by the phosphoinositide phosphatase pharbin

Pharbin, a 5-phosphatase that induces arborization, is one of the phosphoinositide 5-phosphatases that is highly mutated in patients with Joubert syndrome. Pharbin can hydrolyse PI(4,5)P(2) and PI(3,4,5)P(3) and has the same substrate specificity as SHIP2 and SKIP, which negatively regulate PI3K signalling. Here, we investigated the role of pharbin in IGF-1/PI3K signalling. Ectopic expression of pharbin markedly suppressed the IGF-1-induced activation of Akt without affecting p42/44 MAP kinase phosphorylation. In contrast, pharbin silencing by RNA interference increased the IGF-1-induced phosphorylation of Akt, suggesting that pharbin negatively regulates PI3K/Akt signalling. Pharbin expression also inhibited the phosphorylation of p70 S6 kinase and 4E-BP1 as well as the subsequent protein synthesis in response to IGF-1 treatment. Taken together, these results indicate that pharbin is an important negative regulator of IGF-1/PI3K/Akt signalling and protein synthesis.     

Salvianolic acid B inhibits hydrogen peroxide-induced endothelial cell apoptosis through regulating PI3K/Akt signaling

Background

Salvianolic acid B (Sal B) is one of the most bioactive components of Salvia miltiorrhiza, a traditional Chinese herbal medicine that has been commonly used for prevention and treatment of cerebrovascular disorders. However, the mechanism responsible for such protective effects remains largely unknown. It has been considered that cerebral endothelium apoptosis caused by reactive oxygen species including hydrogen peroxide (H₂O₂) is implicated in the pathogenesis of cerebrovascular disorders.

Methodology and Principal Findings

By examining the effect of Sal B on H₂O₂-induced apoptosis in rat cerebral microvascular endothelial cells (rCMECs), we found that Sal B pretreatment significantly attenuated H₂O₂-induced apoptosis in rCMECs. We next examined the signaling cascade(s) involved in Sal B-mediated anti-apoptotic effects. We showed that H₂O₂ induces rCMECs apoptosis mainly through the PI3K/ERK pathway, since a PI3K inhibitor ({"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002) blocked ERK activation caused by H₂O₂ and a specific inhibitor of MEK (U0126) protected cells from apoptosis. On the other hand, blockage of the PI3K/Akt pathway abrogated the protective effect conferred by Sal B and potentated H₂O₂-induced apoptosis, suggesting that Sal B prevents H₂O₂-induced apoptosis predominantly through the PI3K/Akt (upstream of ERK) pathway.

Significance

Our findings provide the first evidence that H₂O₂ induces rCMECs apoptosis via the PI3K/MEK/ERK pathway and that Sal B protects rCMECs against H₂O₂-induced apoptosis through the PI3K/Akt/Raf/MEK/ERK pathway.     

Adherens junction-dependent PI3K/Akt activation induces resistance to genotoxin-induced cell death in differentiated intestinal epithelial cells

The crypt-villi axis of intestinal mucosa maintains homeostasis by renewal of epithelia, and also exhibits different properties from undifferentiated to terminally differentiated cells. We investigated differential susceptibility to genotoxin-induced cell death, based on the degree of differentiation of epithelial cells, and its mechanism. Differentiation was induced by post-confluence culture in Caco-2 cells. Methyl methanesulfonate (MMS), a direct-acting DNA alkylating agent, was used for genotoxin-induced cell death. Compared to subconfluent Caco-2 cells, 7 days post-confluent cells showed resistance to MMS-induced cell death. With increasing expression of adherens junction components of E-cadherin and β-catenin, E-cadherin and p-Akt expression increased in 7 days post-confluent Caco-2 cells, and in human intestinal tissue, expression of E-cadherin and p-Akt also increased in the upper portion of villi, compared to the crypt. Inhibition of cell-cell adhesion using EGTA decreased Akt phosphorylation, which was reversed by calcium restoration. Akt phosphorylation by calcium-mediated cell-cell adhesion was more prominent in differentiated cells. In addition, treatment of a PI3K inhibitor, LY294002, inhibited Akt phosphorylation by calcium-mediated cell-cell adhesion. Finally, the differential sensitivity to MMS-induced cell death between subconfluent and 7 days post-confluent Caco-2 cells was eliminated by inhibiting cell-cell adhesion or PI3K. Our data demonstrated that cell adhesion-mediated PI3K/Akt activation could be one of the important mechanisms of resistance to genotoxin-induced cell death in differentiated epithelial cells.     

gamma-Tocotrienol inhibits ErbB3-dependent PI3K/Akt mitogenic signalling in neoplastic mammary epithelial cells

The antiproliferative effects of gamma-tocotrienol are associated with suppression in epidermal growth factor (EGF)-dependent phosphatidylinositol-3-kinase (PI3K)/PI3K-dependent kinase-1 (PDK-1)/Akt mitogenic signalling in neoplastic mammary epithelial cells. Studies were conducted to investigate the direct effects of gamma-tocotrienol treatment on specific components within the PI3K/PDK-1/Akt mitogenic pathway. +SA cells were grown in culture and maintained in serum-free media containing 10 ng/ml EGF as a mitogen. Treatment with 0-8 microm gamma-tocotrienol resulted in a dose-responsive decrease in the +SA cell growth and a corresponding decrease in phospho-Akt (active) levels. However, gamma-tocotrienol treatment had no direct inhibitory effect on Akt or PI3K enzymatic activity, suggesting that the inhibitory effects of gamma-tocotrienol occur upstream of PI3K, possibly at the level of the EGF-receptor (ErbB1). Additional studies were conducted to determine the effects of gamma-tocotrienol on ErbB receptor activation. Results showed that gamma-tocotrienol treatment had little or no effect on ErbB1 or ErbB2 receptor tyrosine phosphorylation, a prerequisite for substrate interaction and signal transduction, but did cause a significant and progressive decrease in the ErbB3 tyrosine phosphorylation. Because ErbB1 or ErbB2 receptors form heterodimers with the ErbB3 receptor, and ErbB3 heterodimers have been shown to be the most potent activators of PI3K, these findings strongly suggest that the antiproliferative effects of gamma-tocotrienol in neoplastic +SA mouse mammary epithelial cells are mediated by a suppression in ErbB3-receptor tyrosine phosphorylation and subsequent reduction in PI3K/PDK-1/Akt mitogenic signalling.     

Duvelisib attenuates bleomycin-induced pulmonary fibrosis via inhibiting the PI3K/Akt/mTOR signalling pathway

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive interstitial lung disease that seriously threatens the health of patients. The pathogenesis of IPF is still unclear, and there is a lack of effective therapeutic drugs. Myofibroblasts are the main effector cells of IPF, leading to excessive deposition of extracellular matrix (ECM) and promoting the progression of fibrosis. Inhibiting the excessive activation and relieving autophagy blockage of myofibroblasts is the key to treat IPF. PI3K/Akt/mTOR pathway plays a key regulatory role in promoting fibroblast activation and autophagy inhibition in lung fibrosis. Duvelisib is a PI3K inhibitor that can simultaneously inhibit the activities of PI3K-δ and PI3K-γ, and is mainly used for the treatment of relapsed/refractory chronic lymphocytic leukaemia (CLL) and small lymphocytic lymphoma tumour (SLL). In this study, we aimed to examine the effects of Duvelisib on pulmonary fibrosis. We used a mouse model of bleomycin-induced pulmonary fibrosis to evaluate the effects of Duvelisib on pulmonary fibrosis in vivo and further explored the potential pharmacological mechanisms of Duvelisib in lung fibroblasts in vitro. The in vivo experiments showed that Duvelisib significantly alleviated bleomycin-induced collagen deposition and improved pulmonary function. In vitro and in vivo pharmacological experiments showed that Duvelisib dose-dependently suppressed lung fibroblast activation and improved autophagy inhibition by inhibiting the phosphorylation of PI3K, Akt and mTOR. Our results indicate that Duvelisib can alleviate the severity of pulmonary fibrosis and provide potential drugs for the treatment of pulmonary fibrosis.     

Structural basis and energy landscape of apigenin-induced cancer cell apoptosis mechanism in PI3K/Akt pathway

This study attempted to elucidate how apigenin (AGI) interferes with the PI3K/Akt pathway to fulfill its anti-tumour activity by anchoring on the ATP-binding pocket of PI3K and PDK1. The structural basis and energetic property of AGI and ATP binding to human PDK1 and PI3K isoforms α, β, γ and δ were investigated in detail with homology modelling and molecular docking. Free binding energy calculations and molecular dynamics simulations revealed that AGI can cause less conformational entropy loss than ATP upon the binding and possess the same level of binding stability with that of ATP. Combining ADMET prediction, AGI was evaluated as a strong ATP-competitive inhibitor with good pharmacokinetics profile.     

The PI3K/Akt pathway contributes to arenavirus budding

Several arenaviruses, chiefly Lassa virus (LASV), cause hemorrhagic fever (HF) disease in humans and pose a significant public health concern in regions where they are endemic. On the other hand, evidence indicates that the globally distributed prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) is a neglected human pathogen. The phosphatidylinositol 3-kinase (PI3K)/Akt pathway participates in many cellular processes, including cell survival and differentiation, and also has been shown to play important roles in different steps of the life cycles of a variety of viruses. Here we report that the inhibition of the PI3K/Akt pathway inhibited budding and to a lesser extent RNA synthesis, but not cell entry, of LCMV. Accordingly, BEZ-235, a PI3K inhibitor currently in cancer clinical trials, inhibited LCMV multiplication in cultured cells. These findings, together with those previously reported for Junin virus (JUNV), indicate that targeting the PI3K/Akt pathway could represent a novel antiviral strategy to combat human-pathogenic arenaviruses.     

Reciprocal regulation of Notch and PI3K/Akt signalling in T-ALL cells in vitro

Notch signalling plays an important role in hematopoiesis and in the pathogenesis of T-ALL. Notch is known to interact with Ras and PTEN/PI3K (phosphoinositide-3 kinase)/Akt pathways. We investigated the interaction of Notch with these pathways and the possible reciprocal regulation of these signalling systems in T-ALL cells in vitro. Our analyses indicate that the PI3K/Akt pathway is constitutively active in the four T-ALL cell lines tested. Akt phosphorylation was not altered by the sequestration of growth factors, that is, Akt activation seems to be less dependent on but not completely independent of growth factors, possibly being not subject to negative feedback regulation. PTEN expression was not detected in 3/4 cell lines tested, suggesting the loss of PTEN-mediated Akt activation. Inhibition of the PI3K/Akt pathway arrests growth and enhances apoptosis, but with no modulation of expression of Bax-alpha and Bcl-2 proteins. We analysed the relationship between Notch-1 and the PI3K/Akt signalling and show that inhibition of the Akt pathway changes Notch expression; Notch-1 protein decreased in all the cell lines upon treatment with the inhibitor. Our studies strongly suggest that Notch signalling interacts with PI3K/Akt signalling and further that this occurs in the absence of PTEN expression. The consequences of this to the signalling outcome are yet unclear, but we have uncovered a significant inverse relationship between Notch and PI3K/Akt pathway, which leads us to postulate the operation of a reciprocal regulatory loop between Notch and Ras-PI3K/Akt in the pathogenesis of T-ALL.