Control of dendritic arborization by the phosphoinositide-3'-kinase-Akt-mammalian target of rapamycin pathway

The molecular mechanisms that determine the size and complexity of the neuronal dendritic tree are unclear. Here, we show that the phosphoinositide-3' kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) signaling pathway promotes the growth and branching of dendrites in cultured hippocampal neurons. Constitutively active mutants of Ras, PI3K, and Akt, or RNA interference (RNAi) knockdown of lipid phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome Ten), induced growth and elaboration of dendrites that was blocked by mTOR inhibitor rapamycin and/or by overexpression of eIF-4E binding protein 1 (4E-BP1), which inhibits translation of 5' capped mRNAs. The effect of PI3K on dendrites was lost in more mature neurons (>14 d in vitro). Dendritic complexity was reduced by inhibition of PI3K and by RNAi knockdown of mTOR or p70 ribosomal S6 kinase (p70S6K, an effector of mTOR). A rapamycin-resistant mutant of mTOR "rescued" the morphogenetic effects of PI3K in the presence of rapamycin. By regulating global and/or local protein translation, and as a convergence point for multiple signaling pathways, mTOR could play a central role in the control of dendrite growth and branching during development and in response to activity.

Identification of arctigenin as an antitumor agent having the ability to eliminate the tolerance of cancer cells to nutrient starvation

Tumor cells generally proliferate rapidly and the demand for essential nutrients as well as oxygen always exceeds the supply due to the unregulated growth and the insufficient and inappropriate vascular supply. However, cancer cells show an inherent ability to tolerate extreme conditions, such as that characterized by low nutrient and oxygen supply, by modulating their energy metabolism. Thus, targeting nutrient-deprived cancer cells may be a novel strategy in anticancer drug development. Based on that, we established a novel screening method to discover anticancer agents that preferentially inhibit cancer cell viability under the nutrient-deprived condition. After screening 500 medicinal plant extracts used in Japanese Kampo medicine, we found that a CH(2)Cl(2)-soluble extract of Arctium lappa exhibited 100% preferential cytotoxicity under the nutrient-deprived condition at a concentration of 50 microg/mL with virtually no cytotoxicity under nutrient-rich condition. Further bioassay-guided fractionation and isolation led to the isolation of arctigenin as the primary compound responsible for such preferential cytotoxicity; the compound exhibited 100% preferential cytotoxicity against nutrient-deprived cells at a concentration of 0.01 microg/mL. Furthermore, arctigenin was also found to strongly suppress the PANC-1 tumor growth in nude mice, as well as the growth of several of the tested pancreatic cancer cell lines, suggesting the feasibility of this novel antiausterity approach in cancer therapy. Further investigation of the mechanism of action of arctigenin revealed that the compound blocked the activation of Akt induced by glucose starvation, which is a key process in the tolerance exhibited by cancer cells to glucose starvation.

Spectrum of activity and molecular correlates of response to phosphatidylinositol ether lipid analogues, novel lipid-based inhibitors of Akt

The serine/threonine kinase Akt is a promising target in cancer. We previously identified five phosphatidylinositol ether lipid analogues (PIA) that inhibited Akt activation and selectively killed lung and breast cancer cells with high levels of Akt activity. To assess the spectrum of activity in other cell types and to compare PIAs with other inhibitors of the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway, we compared growth inhibition by PIAs against the PI3K inhibitors LY294002 and wortmannin and the mTOR inhibitor rapamycin in the NCI60 cell line panel. Although each of these compounds inhibited the growth of all the cell lines, distinct patterns were observed. The PIAs were the least potent but the most cytotoxic. The broad spectrum of activity of PIAs was confirmed in vivo in hollow fiber assays. The response to PIAs was significantly correlated with levels of active but not total Akt in the NCI60, as assessed using COMPARE analysis. However, a number of molecular targets were identified whose expression was more highly correlated with sensitivity to PIAs than active Akt. Expression of these molecular targets did not overlap with those that correlated with sensitivity to LY294002, wortmannin, or rapamycin. A COMPARE analysis of the National Cancer Institute chemical screening database revealed that the patterns of activity of PIAs correlated best with patterns of activity of other lipid-based compounds. These studies show that although PIAs are widely active in cancer cells, which correlates with the presence of its intended target, active Akt, PIAs are biologically distinct from other known inhibitors of the PI3K/Akt/mTOR pathway.

Ultrasound Stimulates Cyclooxygenase-2 Expression and Increases Bone Formation through Integrin, Focal Adhesion Kinase, Phosphatidylinositol 3-Kinase, and Akt Pathway in Osteoblasts

It has been shown that ultrasound (US) stimulation accelerates fracture healing in animal models and in clinical studies. Here we found that US stimulation transiently increased the surface expression of alpha2, alpha5, beta1, and beta3 integrins in cultured osteoblasts, as shown by flow cytometric analysis and immunofluorescence staining. US stimulation increased prostaglandin E(2) formation and the protein and mRNA levels of cyclooxygenase-2 (COX-2). At the mechanistic level, anti-integrin alpha5beta1 and alphavbeta3 antibodies or rhodostomin, a snake venom disintegrin, attenuated the US-induced COX-2 expression. Phosphatidylinositol 3-kinase (PI3K) inhibitors 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002) and wortmannin also inhibited the potentiating action of US. US stimulation increased the phosphorylation of focal adhesion kinase (FAK), extracellular signal-regulated kinases (ERK), p85 subunit of PI3K, and serine 473 of Akt. COX-2 promoter activity was enhanced by US stimulation in cells transfected with pCOX2-Luc. Cotransfection with dominant-negative mutant of FAK(Y397F), p85(Deltap85), Akt(K179A), or ERK2(K52R) inhibited the potentiating action of US on COX-2 promoter activity. Expression of mineralized nodule was lower in dominant-negative mutants of FAK, p85, and Akt-transfected clones than in vector-transfected control cells. Taken together, our results provide evidence that US stimulation increases COX-2 expression and promotes bone formation in osteoblasts via the integrin/FAK/PI3K/Akt and ERK signaling pathway.

Infection of human cancer cells with myxoma virus requires Akt activation via interaction with a viral ankyrin-repeat host range factor

We demonstrate that the susceptibility of human cancer cells to be infected and killed by an oncolytic poxvirus, myxoma virus (MV), is related to the basal level of endogenous phosphorylated Akt. We further demonstrate that nonpermissive tumor cells will switch from resistant to susceptible for MV infection after expression of ectopically active Akt (Myr-Akt) and that permissive cancer cells can be rendered nonpermissive by blocking Akt activation with a dominant-negative inhibitor of Akt. Finally, the activation of Akt by MV involves the formation of a complex between the viral host range ankyrin-repeat protein, M-T5, and Akt. We conclude that the Akt pathway is a key restriction determinant for permissiveness of human cancer cells by MV.

Glycine-extended gastrin inhibits apoptosis in colon cancer cells via separate activation of Akt and JNK pathways

Glycine-extended gastrin (G-Gly) is produced by colon cancers and has growth promoting and anti-apoptotic effects in the colonic epithelium. We have examined the anti-apoptotic effects of G-Gly and the signal transduction pathways involved. G-Gly stimulated HT-29 cell proliferation in a concentration dependent manner and inhibited serum-starvation and celecoxib-induced apoptosis. Inhibition of signalling via c-Jun NH2-terminal kinase (JNK) with SP600125 or PI3-kinase/Akt with LY294002 abolished the effects of G-Gly. G-Gly significantly increased phosphorylation of both JNK and Akt. The JAK2 inhibitor AG490 abolished the anti-apoptotic effect of G-Gly and inhibited phosphorylation of Akt but not of JNK. G-Gly stimulated tyrosine phosphorylation of JAK2. G-Gly-increased activation of AP-1 was JNK-dependant and activation of STAT3 was JAK2-dependant. We conclude that G-Gly promotes growth and inhibits apoptosis in colon cancer cells. These effects are mediated via the JAK2, PI3-kinase/Akt and JNK pathways. Activation of JAK2 is upstream of Akt but not of JNK.

Inhibition of the phosphatidylinositol-3 kinase/Akt promotes G1 cell cycle arrest and apoptosis in Hodgkin lymphoma

Activation of the phosphatidylinositol 3-kinase (PI(3)K) pathway has been linked with tumour cell growth, survival and resistance to therapy in several cancer types. The active, phosphorylated form of Akt (pAkt) was found to be aberrantly expressed in Hodgkin lymphoma (HL)-derived cell lines and in Hodgkin-Reed-Sternberg (HRS) cells in 27 of 42 (64.3%) of primary lymph node sections of HL, indicative of PI(3)K activity. Akt phosphorylation was not associated with loss of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) expression, but with its phosphorylation in HL-cell lines, suggesting that its biological function is impaired. Akt phosphorylation was further induced by CD30 ligand (CD30L), CD40L and receptor activator of nuclear factor kappa B (RANK) ligand. The PI(3)K inhibitor LY294002 demonstrated antiproliferative effects in a dose- and time-dependent manner, which was associated with Akt dephosphorylation on Thr308 and Ser473 sites and dephosphorylation of the downstream ribosomal protein S6. LY209002 induced cell cycle arrest in the G0/G1 phase and apoptosis, which were associated with upregulation of MDM2, downregulation of cyclin D1, activation of caspase 9 and poly-ADP-ribose polymerase cleavage. The Akt inhibitor QLT394 also demonstrated antiproliferative effects in a dose- and time-dependent manner, dephosphorylated ribosomal S6 and cleaved caspase 9. Collectively, these data suggest that the aberrant activation of the PI(3)K/Akt survival pathway in HRS cells is not because of loss of PTEN expression. Our data suggest that PTEN phosphorylation and activation of CD30, CD40 and RANK may play a role in activating Akt in HRS cells.

AKT1 provides an essential survival signal required for differentiation and stratification of primary human keratinocytes

Keratinocyte differentiation and stratification are complex processes involving multiple signaling pathways, which convert a basal proliferative cell into an inviable rigid squame. Loss of attachment to the basement membrane triggers keratinocyte differentiation, while in other epithelial cells, detachment from the extracellular matrix leads to rapid programmed cell death or anoikis. The potential role of AKT in providing a survival signal necessary for stratification and differentiation of primary human keratinocytes was investigated. AKT activity increased during keratinocyte differentiation and was attributed to the specific activation of AKT1 and AKT2. Targeted reduction of AKT1 expression, but not AKT2, by RNA interference resulted in an abnormal epidermis in organotypic skin cultures with a thin parabasal region and a pronounced but disorganized cornified layer. This abnormal stratification was due to significant cell death in the suprabasal layers and was alleviated by caspase inhibition. Normal expression patterns of both early and late markers of keratinocyte differentiation were also disrupted, producing a poorly developed stratum corneum.

Modulation of bradykinin signaling by EP24.15 and EP24.16 in cultured trigeminal ganglia

Metalloendopeptidases expressed in neural tissue are characterized in terms of their neuropeptide substrates. One such neuropeptide, bradykinin (BK), is an important inflammatory mediator that activates the type-2 BK receptor (B2R) on the terminal endings of specialized pain-sensing neurons known as nociceptors. Among several metalloendopeptidases that metabolize and inactivate BK, EP24.15 and EP24.16 are known to associate with the plasma membrane in several immortalized cell lines. Potentially, the colocalization of EP24.15/16 and B2R at plasma membrane microdomains known as lipid rafts in a physiologically relevant nociceptive system would allow for discrete, peptidase regulation of BK signaling. Western blot analysis of crude subcellular fractions and lipid raft preparations of cultured rat trigeminal ganglia demonstrate similar expression profiles between EP24.15/16 and B2R on a subcellular level. Furthermore, the treatment of primary cultures of trigeminal ganglia with inhibitors of EP24.15/16 led to the potentiation of several bradykinin-induced events that occur downstream of B2R activation. EP24.15/16 inhibition by N-[1(R,S)-carboxy-3-phenylpropyl]-Ala-AlalTyr-p-aminobenzoate (cFP) resulted in a 1000-fold increase in B2R sensitivity to BK as measured by inositol phosphate accumulation. In addition, cFP treatment resulted in a 31.1+/-5.0% potentiation of the ability of BK to inhibit protein kinase B (Akt) activity. Taken together, these data demonstrate that EP24.15/16 modulate intracellular, peptidergic signaling cascades through B2R in a physiologically relevant nociceptive system.

Suppression of pro-metastasis phenotypes expression in malignant pleural mesothelioma by the PI3K inhibitor LY294002 or the MEK inhibitor UO126

BACKGROUND

This study aimed to evaluate the impact of selective abrogation of either the MEK/ERK1/2 (UO126 or PD98059) or the PI3K/AKT (LY294002) signaling cascade on cell proliferation, motility and invasion and production of VEGF (collectively termed pro-metastasis phenotypes) in cultured malignant pleural mesothelioma (MPM) cells.

MATERIALS AND METHODS

Treatment-induced cytotoxicity was evaluated by MTT or Annexin V assays. Cell motility was assessed by wound healing and Matrigel invasion assays. VEGF in conditioned media of cancer cells was measured by ELISA.

RESULTS

LY294002 and UO126 significantly inhibited cell proliferation and clonogenicity of MPM cells in vitro. A substantial reduction of cell motility, Matrigel invasion as well as inhibition of basal or EGF-induced VEGF production were observed in drug-treated cells.

CONCLUSION

The selective MEK or PI3K kinase inhibitors are equally effective in down-regulating the expression of pro-metastasis phenotypes, suggesting that MEK or PI3K are appropriate targets for the development of molecular therapeutics for malignant pleural mesothelioma.

Inhibitory effect of luteolin on hepatocyte growth factor/scatter factor-induced HepG2 cell invasion involving both MAPK/ERKs and PI3K–Akt pathways

Hepatocyte growth factor (HGF), also known as scatter factor (SF), and its receptor, the c-Met tyrosine kinase, play roles in cancer invasion and metastasis in a wide variety of tumor cells. Clinical observations suggest that HGF can promote metastasis of hepatoma cells while stimulating tumor invasiveness. We use HGF as an invasive inducer of human hepatoma HepG2 cells to investigate the effect of flavonoids on anti-invasion. In our preliminary study, we investigated the effect of flavonoids including luteolin, quercetin, baicalein, genistein, taxifolin and catechin on HGF-mediated migration and invasion of HepG2 cells. We found that luteolin presented the most potent potential on anti-migration and anti-invasion by Boyden chamber assay. Furthermore, luteolin inhibited HGF-induced cell scattering and cytoskeleton change such as filopodia and lamellipodia was determined by both phase-contrast and fluorescence microscopy studies. In addition, Western blotting and immunoprecipitation were performed to confirm luteolin suppressed the phosphorylation of c-Met, the membrane receptor of HGF, as well as ERK1/2 and Akt, but not JNK1/2, which is activated by HGF. Our investigation demonstrated that luteolin similar to PD98059, which acts as a specific inhibitor of MEK, an up stream kinase regulating ERK1/2, and wortmannin, a PI3K inhibitor, inhibited the invasiveness induced by HGF. In conclusion, the luteolin inhibited HGF-induced HepG2 cell invasion involving both MAPK/ERKs and PI3K-Akt pathways.

G-CSF induced reactive oxygen species involves Lyn-PI3-kinase-Akt and contributes to myeloid cell growth

Granulocyte colony-stimulating factor (G-CSF) drives the production, survival, differentiation, and inflammatory functions of granulocytes. Reactive oxygen species (ROSs) provide a major thrust of the inflammatory response, though excessive ROSs may be deleterious. G-CSF stimulation showed a time- and dose-dependent increase in ROS production, correlating with activation of Lyn and Akt. Inhibition of Lyn, PI3-kinase, and Akt abrogated G-CSF-induced ROS production. This was also blocked by DPI, a specific inhibitor of NADPH oxidase. Following G-CSF stimulation, neutrophils from Lyn-/- mice produced less ROSs than wild-type littermates. G-CSF induced both serine phosphorylation and membrane translocation of p47phox, a subunit of NADPH oxidase. Because patients with a truncated G-CSF receptor have a high risk of developing acute myeloid leukemia (AML), we hypothesized that dysregulation of ROSs contributes to leukemogenesis. Cells expressing the truncated G-CSF receptor produced more ROSs than those with the full-length receptor. G-CSF-induced ROS production was enhanced in bone marrow-derived neutrophils expressing G-CSFRdelta715, a truncated receptor. The antioxidant N-acetyl-L-cysteine diminished G-CSF-induced ROS production and cell proliferation by inhibiting Akt activation. These data suggest that the G-CSF-induced Lyn-PI3K-Akt pathway drives ROS production. One beneficial effect of therapeutic targeting of Lyn-PI3K-kinase-Akt cascade is abrogating ROS production.

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.

Functional diversity of flavonoids in the inhibition of the proinflammatory NF-kappaB, IRF, and Akt signaling pathways in murine intestinal epithelial cells

The molecular understanding of nutritional factors in the process of host factor-mediated activation of the intestinal epithelium may play an important role in the assessment of adjunct nutritional therapy for chronic intestinal inflammation. We characterized the molecular mechanisms of flavonoids including apigenin, luteolin, genistein, 3'-hydroxy-flavone, and flavone in inhibiting tumor necrosis factor-alpha (TNF)-induced interferon-induced protein (IP)-10 gene expression in the murine intestinal epithelial cell (IEC) line Mode-K. We demonstrated that 3'-hydroxy-flavone but not the chemical core structure flavone blocked TNF-alpha-induced nuclear factor (NF)-kappaB transcriptional activity and IP-10 expression at the level of NF-kappaB/IkappaBalpha phosphorylation/degradation by inhibiting IkappaB kinase activity. Although 3'-hydroxy-flavone effectively triggered p38 mitogen-activated protein kinase signaling and late caspase-3 cleavage, the induction of apoptotic cell death in TNF-activated IEC was not the primary mechanism inhibiting NF-kappaB transcriptional activity and IP-10 expression. In addition to the compound-specific inhibition of TNF-induced NF-kappaB DNA binding and NF-kappaB transcriptional activity, apigenin and luteolin selectively blocked Akt phosphorylation/activity. The ability of these polyphenolic compounds to target various signal transduction pathways was further supported by the observation that luteolin and 3'-hydroxy-flavone selectively induced interferon regulatory factor (IRF)-1 degradation. Finally, we showed that genistein blocked IP-10 but not IL-6 expression through NF-kappaB, IRF, and Akt independent mechanisms, demonstrating the functional diversity of flavonoids in inhibiting proinflammatory processes in IEC. In conclusion, we provide molecular evidence for the presence of characteristic inhibition patterns of these polyphenolic compounds to inhibit proinflammatory gene expression in IEC through the specific modulation of the NF-kappaB, IRF and Akt signaling pathways.

Essential role for Rac in heregulin beta1 mitogenic signaling: a mechanism that involves epidermal growth factor receptor and is independent of ErbB4

Heregulins are a family of ligands for the ErbB3/ErbB4 receptors that play important roles in breast cancer cell proliferation and tumorigenesis. Limited information is available on the contribution of Rho GTPases to heregulin-mediated signaling. In breast cancer cells, heregulin beta1 (HRG) causes a strong activation of Rac; however, it does so with striking differences in kinetics compared to epidermal growth factor, which signals through ErbB1 (epidermal growth factor receptor [EGFR]). Using specific ErbB receptor inhibitors and depletion of receptors by RNA interference (RNAi), we established that, surprisingly, activation of Rac by HRG is mediated not only by ErbB3 and ErbB2 but also by transactivation of EGFR, and it is independent of ErbB4. Similar receptor requirements are observed for HRG-induced actin cytoskeleton reorganization and mitogenic activity via extracellular signal-regulated kinase (ERK). HRG-induced Rac activation was phosphatidylinositol 3-kinase dependent and Src independent. Furthermore, inactivation of Rac by expression of the Rac GTPase-activating protein beta2-chimerin inhibited HRG-induced ERK activation, mitogenicity, and migration in breast cancer cells. HRG mitogenic activity was also impaired by depletion of Rac1 using RNAi. Our studies established that Rac is a critical mediator of HRG mitogenic signaling in breast cancer cells and highlight additional levels of complexity for ErbB receptor coupling to downstream effectors that control aberrant proliferation and transformation.

Paclitaxel-induced nuclear translocation of FOXO3a in breast cancer cells is mediated by c-Jun NH2-terminal kinase and Akt

The microtubule-targeting compound paclitaxel is often used in the treatment of endocrine-resistant or metastatic breast cancer. We have previously shown that apoptosis of breast cancer cells in response to paclitaxel is mediated by induction of FOXO3a expression, a transcription factor downstream of the phosphatidylinositol-3-kinase/Akt signaling pathway. To further investigate its mechanism of action, we treated MCF-7 cells with paclitaxel and showed a dose-dependent increase in nuclear localization of FOXO3a, which coincided with decreased Akt signaling but increased c-Jun NH2-terminal kinase 1/2 (JNK1/2), p38, and extracellular signal-regulated kinase 1/2 (ERK1/2) activity. Flow cytometry revealed that paclitaxel-induced apoptosis of MCF-7 cells and of other paclitaxel-sensitive breast cancer cell lines was maintained in the presence of inhibitors of p38 (SB203580) or mitogen-activated protein/ERK kinase 1 signaling (PD98059) but abrogated when cells were treated with the JNK1/2 inhibitor SP600125. SP600125 reversed Akt inhibition and abolished FOXO3a nuclear accumulation in response to paclitaxel. Moreover, conditional activation of JNK mimicked paclitaxel activity and led to dephosphorylation of Akt and FOXO3a. Furthermore, mouse embryonic fibroblasts (MEF) derived from JNK1/2 knockout mice displayed very high levels of active Akt, and in contrast to wild-type MEFs, paclitaxel treatment did not alter Akt activity or elicit FOXO3a nuclear translocation. Taken together, the data show that cell death of breast cancer cells in response to paclitaxel is dependent upon JNK activation, resulting in Akt inhibition and increased FOXO3a activity.

Loss of phosphatase and tensin homologue increases transforming growth factor beta-mediated invasion with enhanced SMAD3 transcriptional activity

In normal epithelial tissues, the multifunctional cytokine transforming growth factor-beta (TGF-beta) acts as a tumor suppressor through growth inhibition and induction of differentiation whereas in advanced cancers, TGF-beta promotes tumor progression through induction of tumor invasion, neoangiogenesis, and immunosuppression. The molecular mechanisms through which TGF-beta shifts from a tumor suppressor to a tumor enhancer are poorly understood. We now show a role for the tumor suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) in repressing the protumorigenic effects of TGF-beta. The TGF-beta effector SMAD3 inducibly interacts with PTEN on TGF-beta treatment under endogenous conditions. RNA interference (RNAi) suppression of PTEN expression enhances SMAD3 transcriptional activity and TGF-beta-mediated induction of SMAD3 target genes whereas reconstitution of PTEN in a null cancer cell line represses the expression of TGF-beta-regulated target genes. Targeting PTEN expression through RNAi in a PTEN wild-type cell line increases TGF-beta-mediated invasion but does not affect TGF-beta-mediated growth inhibition. Reconstitution of PTEN expression in a PTEN-null cell line blocks TGF-beta-induced invasion but does not modulate TGF-beta-mediated growth regulation. These effects are distinct from Akt and Forkhead family members that also interact with SMAD3 to regulate apoptosis or proliferation, respectively. Pharmacologic inhibitors targeting TGF-beta receptors and phosphatidylinositol 3-kinase signaling downstream from PTEN cooperate to block TGF-beta-mediated invasion. Thus, the loss of PTEN expression in human cancers may contribute to a role for TGF-beta as a tumor enhancer with specific effects on cellular motility and invasion.

Retroinfusion of embryonic endothelial progenitor cells attenuates ischemia-reperfusion injury in pigs: role of phosphatidylinositol 3-kinase/AKT kinase

BACKGROUND

Adult endothelial progenitor cells (EPCs) reduce myocardial infarct size and improve postischemic myocardial function. We have recently shown that clonal embryonic EPCs (eEPCs), derived from 7.5-day-old mice, home specifically to hypoxic areas in tumor metastasis mouse models but spare normal organs and do not form carcinomas. Here, we assessed the potential of eEPCs to limit organ dysfunction after ischemia and reperfusion in a preclinical pig model.

METHODS AND RESULTS

Pigs were subjected to ischemia (60-minute left anterior descending [LAD] artery occlusion) and reperfusion (7 days). At the end of ischemia, we applied medium with or without 5 x 10(6) eEPCs by either pressure-regulated retroinfusion or intravenous transfusion. One hour after reperfusion, 99Tc-labeled eEPCs engrafted to a 6-fold higher extent in the ischemic myocardium after retroinfusion than after intravenous application. Regional myocardial function (subendocardial segment shortening [SES] at 150/min, given in percent of nonischemic circumflex region) and infarct size (TTC viability and Methylene-blue exclusion) were determined 24 hours and 7 days later. Compared with medium-treated animals, retroinfusion of eEPCs decreased infarct size (35+/-4% versus 51+/-6%) and improved regional myocardial reserve of the apical LAD region (SES 31+/-4% versus 6+/-8%), whereas intravenous application displayed a less pronounced effect (infarct size 44+/-4%; SES 12+/-3%). Retroinfusion of an equal amount of neonatal coronary endothelial cells (rat) did not affect infarct size (49+/-5%) nor regional myocardial reserve (16+/-7%). The eEPC-dependent effect was detected at 24 hours of reperfusion (infarct size 34+/-7% versus 58+/-6%) and was sensitive to Wortmannin coapplication (50+/-5%).

CONCLUSIONS

Our findings show that eEPCs reduce ischemia-reperfusion injury in a preclinical pig model. The rapid effect (as early as 24 hours) indicates a role for enzyme-mediated cardioprotection, which involves, at least in part, the phosphatidylinositol 3-kinase/AKT pathway.

Genistein Represses Telomerase Activity via Both Transcriptional and Posttranslational Mechanisms in Human Prostate Cancer Cells

Genistein, the most abundant isoflavone present in soybean has antiproliferative effects on a variety of cancer cells, including prostate cancer. However, the molecular mechanism of antiproliferative effects of genistein is not entirely understood. Because the activation of telomerase is crucial for cells to gain immortality and proliferation ability, we examined the role of genistein in the regulation of telomerase activity in prostate cancer cells. Here, we show that genistein-induced inhibition in cell proliferation is associated with a reduction in telomerase activity. Using reverse transcriptase-PCR and hTERT promoter activity assays, we showed that genistein decreased hTERT expression and transcriptional activity dose-dependently. Using various deleted hTERT promoter constructs, we defined that the hTERT core promoter is enough to observe the genistein-induced repression of hTERT transcriptional activity. Because c-Myc is involved in transcriptional regulation of hTERT, c-Myc expression was examined. A dose-dependent decrease in c-Myc message and proteins was observed with genistein treatment. These results indicate that genistein represses hTERT transcriptional activity via the down-regulation of c-Myc expression. However, genistein-induced repression of hTERT transcriptional activity was not blocked by the mutation of c-Myc at the hTERT promoter, suggesting that additional factors are involved in genistein-dependent repression of telomerase activity. Interestingly, we observed that genistein down-regulates the activation of Akt thereby phosphorylation of hTERT and inhibits its translocation to the nucleus. These results show for the first time that genistein represses telomerase activity in prostate cancer cells not only by repressing hTERT transcriptional activity via c-Myc but also by posttranslational modification of hTERT via Akt.

The skin and hair as surrogate tissues for measuring the target effect of inhibitors of phosphoinositide-3-kinase signaling

BACKGROUND

The purpose of the study was to evaluate the use of phospho-Akt in mouse and human skin as a surrogate target for tumor phospho-Akt to measure the effect of antitumor inhibitors of phosphatidylinositol-3-kinase (PI-3-K)/Akt (protein kinase B) signaling.

METHOD

The expression of phosphoSer473-Akt was quantitatively assessed by Western blotting in human HT-29 colon, MCF-7 breast, A-549 non small cell lung tumor xenografts in mice, and by immunohistochemistry in mouse skin and human hair.

RESULTS

The pattern of PI-3-K isoforms in human hair keratinocytes was similar to that in tumor but mouse hair keratinocytes showed a different pattern. A high level of phospho-Akt staining was present in keratinocytes of the external root sheath of the hair and was inhibited by the PI-3-K inhibitor PX-866 administered to mice, and in human hair exposed to PX-866 in culture. The inhibition of phospho-Akt by PX-866 in mouse hair keratinocytes was greater than inhibition of phospho-Akt in HT-29 and A-549 xenografts in the same mice. Phospho-Akt in mouse hair keratinocytes was inhibited by the Akt inhibitor PX-316 to a lesser degree than in MCF-7 tumor xenografts.

CONCLUSIONS

Hair offers a way of measuring the effects of PI-3-K signaling inhibitors and, in cancer patients, may provide a readily obtainable surrogate tissue for assessing PI-3-K and phospho-Akt inhibition in tumor.

Protein Kinase B/Akt-Dependent Phosphorylation of Glycogen Synthase Kinase-3β in Irradiated Vascular Endothelium

The vascular endothelium plays a critical role in the response of cancer to ionizing radiation. Activation of the phosphoinositide-3-kinase/Akt pathway is one initial signaling event in irradiated endothelial cells. Specifically, a low dose of ionizing radiation (3 Gy) induces phosphorylation of Akt at Ser473 in the vascular endothelium within minutes of irradiation. However, signaling events that are downstream of Akt have not been well defined. Here, we show that phosphorylation of the Akt downstream target glycogen synthase kinase-3beta (GSK-3beta) at Ser9 also occurred within minutes of exposure to ionizing radiation. In addition, ionizing radiation caused the dissociation of GSK-3beta from the cell membrane, consistent with the inactivation of GSK-3beta enzyme activity. Overexpression of the dominant negative mutant Akt attenuated GSK-3beta phosphorylation at Ser9 and enhanced radiation-induced apoptosis. X-irradiated endothelial cells formed capillaries in both in vitro and in vivo models, whereas overexpression of the dominant negative mutant Akt inhibited capillary tubule formation. Studies using GSK-3beta antagonists showed that GSK-3beta activity was required for apoptosis in endothelial cells treated simultaneously with Akt antagonists and radiation. In mouse vascular models, radiation-induced microvascular destruction in response to Akt antagonists also required GSK-3beta function. These data indicate that on exposure of vascular endothelium to ionizing radiation, activation of Akt signaling contributes to GSK-3beta inhibition, which in turn promotes endothelial cell survival and capillary formation. Thus, pharmacologic regulation of Akt/GSK-3beta signaling may present a new approach to the radiation response in the tumor microvasculature.

Synergistic roles of platelet-derived growth factor-BB and interleukin-1beta in phenotypic modulation of human aortic smooth muscle cells

The phenotype of smooth muscle cells (SMCs) plays an important role in vascular function in health and disease. We investigated the mechanism of modulation of SMC phenotype (from contractile to synthetic) induced by the synergistic action of a growth factor (platelet-derived growth factor, PDGF-BB) and a cytokine (interleukin, IL-1beta). Human aortic SMCs grown on polymerized collagen showed high expression levels of contractile markers (smooth muscle alpha-actin, myosin heavy chain, and calponin). These levels were not significantly affected by PDGF-BB and IL-1beta individually, but decreased markedly after the combined usage of PDGF-BB and IL-1beta. PDGF/IL-1beta costimulation also induced a sustained phosphorylation of Akt and p70 ribosomal S6 kinase (p70S6K). The effects of PDGF/IL-1beta costimulation on contractile marker expression and Akt and p70S6K phosphorylation were blocked by the phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002 and by adenovirus expressing a dominant-negative Akt, and they were mimicked by constitutively active Akt. PDGF-BB/IL-1beta induced a sustained phosphorylation of PDGF receptor (PDGFR)-beta and its association with IL-1 receptor (IL-1R1). Such activation and association of receptors were blocked by a PDGFR-beta neutralizing antibody (AF385), an IL-1R1 antagonist (IL-1ra), as well as a specific inhibitor of PDGFR-beta phosphorylation (AG1295); these agents also eliminated the PDGF-BB/IL-1beta-induced signaling and phenotypic modulation. PDGF-BB/IL-1beta inhibited the polymerized collagen-induced serum response factor DNA binding activity in the nucleus, and this effect was mediated by the PDGFR-beta/IL-1R1 association and phosphatidylinositol 3-kinase/Akt/p70S6K pathway. Our findings provide insights into the mechanism of SMC phenotypic modulation from contractile to synthetic, e.g., in atherosclerosis.

Regulation of vascular endothelial growth factor expression and vascularization in the myocardium by insulin receptor and PI3K/Akt pathways in insulin resistance and ischemia

OBJECTIVE

This study characterized the role of insulin receptors and resistance on vascular endothelial growth factor (VEGF) expression and myocardial vascularization in physiological conditions and after ischemia.

METHODS AND RESULTS

Cardiac microvascular density was reduced by 30% in insulin-resistant Zucker fatty rats versus lean controls. This was associated with a parallel 40% inhibition of insulin-stimulated activation of both Akt and VEGF expression in the myocardium and cardiomyocytes. In contrast, the activation of Erk1/2 by insulin remained unchanged. In cultured cardiomyocytes, insulin or insulin-like growth factor (IGF)-1 increased VEGF mRNA and protein expression by 2-fold. Inhibition of PI3K/Akt, especially Akt2-mediated cascades but not the Ras/MEK/Erk pathway, using chemical inhibitors, dominant negative adenoviral constructs, or siRNA approaches suppressed VEGF mRNA expression by insulin. Ventricular tissues from muscle insulin receptor knockout (MIRKO) mice, which lack insulin receptors in the myocardium, have significant reductions in insulin but not IGF-1 signaling, VEGF expression, and vascular density before and after ischemia versus controls.

CONCLUSIONS

Insulin regulates VEGF gene expression and vascularization in the myocardium specifically via insulin receptors and the activation of PI3K/Akt pathway. Selective inhibition of this pathway may lead to the decreases in VEGF expression and capillary density in the myocardium of patients with insulin resistance.

Inhibition of PI3K/Akt signaling: an emerging paradigm for targeted cancer therapy

The phosphatidylinositol 3-kinase (PI3K)/Akt (protein kinase B, PKB) signaling pathway plays a critical role in cell growth and survival. Dysregulation of this pathway has been found in a variety of cancer cells. Recently, constitutively active PI3K/Akt signaling has been firmly established as a major determinant for cell growth and survival in an array of cancers. Blocking the constitutively active PI3K/AKT signaling pathway provides a new strategy for targeted cancer therapy. Thus, inhibitors of this signaling pathway would be potential anticancer agents, particularly for cancer cells whose survival and growth are dominated by constitutively active PI3K/Akt signaling. This review describes the current understanding of small molecule drugs targeting this pathway both in vitro and in vivo. Inhibitors and functions of the upstream and downstream molecular targets of the PI3K/Akt pathway are discussed in the context of using the inhibitors to block this pathway for targeted cancer therapy. Special emphasis is placed on the following targets: receptor tyrosine kinases, PI3K, Akt, and the mammalian target of rapamycin. While the molecular therapeutic strategy holds great promise for the treatment of a variety of cancers, few small molecule inhibitors with potential high therapeutic indexes are available. Thus, new inhibitors with high selectivity, bioavailability, and potency are greatly needed. Novel approaches toward the development of PI3K/Akt pathway inhibitors as anticancer therapeutics are discussed in detail, with emphasis on chemical genetics-based and structure-based drug design.

Inhibition of the PI3 kinase/Akt pathway enhances doxorubicin-induced apoptotic cell death in tumor cells in a p53-dependent manner

Constitutive activation of the PI3 kinase/Akt pathway is associated with the neoplastic phenotype of a large number of human tumor cells. As the anti-apoptotic role of the PI3 kinase/Akt pathway has been established, we have examined whether specific blockade of this pathway sensitizes tumor cells to DNA-damaging agent-induced cytotoxicity by enhancing apoptotic cell death. Although a PI3 kinase inhibitor, LY294002, by itself does not induce apoptotic cell death, LY294002 selectively and markedly enhances the apoptosis-inducing efficacy of doxorubicin: such an enhanced cell death is only detected in tumor cells in which the PI3 kinase/Akt pathway is constitutively activated, and it is totally dependent on the functional p53 pathway. These results suggest that the combination of a PI3 kinase/Akt pathway inhibitor and doxorubicin provides an efficient chemotherapeutic strategy for the treatment of tumor cells in which the PI3 kinase/Akt pathway is constitutively activated and the p53 pathway is functional.

A small molecule compound inhibits AKT pathway in ovarian cancer cell lines

BACKGROUND AND OBJECTIVE

Overactivation of AKT1 and gene amplification of AKT2 are frequently detected in ovarian cancer. Activated AKT kinases provide a cell survival signal that may confer resistance to apoptosis induced by conventional therapies in cancer cells. Therefore, development of potent inhibitors that block AKT pathway is an attractive therapeutic strategy for treating ovarian carcinoma.

METHODS

Ovarian cancer cell lines, A2780, MDAH2774, OVCAR-8, Caov-3, and normal murine fibroblasts (NIH3T3) were used. Cells were treated with different doses of a non-peptide small molecule compound, 9-methoxy-2-methylellipticinium acetate (termed API-59-OME) that potentially inhibit AKT pathway. Kinase assays and the phosphorylation of AKT, GSK-3alpha/beta, PDK1, ERK1/2, SGK, p38, FAK, EGFR, JAK2, PKC isoforms, and the cleavage of poly (ADP-ribose) polymerase (PARP) were examined in treated and untreated cell lines. Further, cells treated with API-59-OME were analyzed for induction of apoptosis using sub-G1 profile with propidium iodide staining.

RESULTS

API-59-OME inhibited AKT kinase activity but did not inhibit ERK or JNK kinase activities in A2780, MDAH2774, and OVCAR-8 cell lines. API-59-OME did not reduce phosphorylation of other protein kinases in these cell lines. API-59-OME induced apoptosis and the cleavage of PARP in A2780, MDAH2774, and OVCAR-8 ovarian cancer cell lines that express elevated levels of phosphorylated AKT. In contrast, in Caov-3 and NIH3T3 cell lines, which lack constitutive AKT activity, API-59-OME only had minimal effect to induce apoptosis.

CONCLUSION

These data suggest that API-59-OME may be a potent agent to target constitutively activated AKT pathway in ovarian cancer cells.

3,3′-Diindolylmethane downregulates pro-survival pathway in hormone independent prostate cancer

Epidemiological evidences suggest that the progression and promotion of prostate cancer (CaP) can be modulated by diet. Since all men die with prostate cancer rather than of the disease, it is of particular interest to prevent or delay the progression of the disease by chemopreventive strategies. We have been studying the anticancer properties of compounds present in cruciferous vegetables such as indole-3-carbinol (I3C). Diindolylmethane (DIM) is a dimer of I3C that is formed under acidic conditions and unlike I3C is more stable with higher anti-cancer effects. In the present report, we demonstrate that DIM is a potent anti-proliferative agent compared to I3C in the hormone independent DU 145 CaP cells. The anti-prostate cancer effect is mediated by the inhibition of the Akt signal transduction pathway as DIM, in sharp contrast to I3C, induces the downregulation of Akt, p-Akt, and PI3 kinase. DIM also induced a G1 arrest in DU 145 cells by flow cytometry and downstream concurrent inhibition of cell cycle parameters such as cyclin D1, cdk4, and cdk6. Our data suggest a need for further development of DIM, as a chemopreventive agent for CaP, which justifies epidemiological evidences and molecular targets that are determinants for CaP dissemination/progression. The ingestion of DIM may benefit CaP patients and reduce disease recurrence by eliminating micro-metastases that may be present in patients who undergo radical prostatectomy.

A structurally optimized celecoxib derivative inhibits human pancreatic cancer cell growth

Deregulation of the phosphatidylinositol 3-kinase (PI-3K)/PDK-l/Akt signaling cascade is associated with pancreatic cancer tumor invasion, angiogenesis, and tumor progression. As such, it has been postulated that PDK-1/Akt signaling inhibitors may hold promise as novel therapeutic agents for pancreatic cancer. Disadvantages of currently available Akt inhibitors include tumor resistance, poor specificity, potential toxicity, and poor bioavailability. Previous studies have demonstrated that OSU-03012, a celecoxib derivative, specifically inhibits PDK-1 mediated phosphorylation of Akt with IC(50) values in the low muM range. Human pancreatic cancer cell lines AsPC-1, BxPC-3, Mia-PaCa 2, and PANC-1 were cultured in media containing varying concentrations of OSU-03012, 5-fluorouracil (5-FU), and gemcitabine, and changes in Akt phosphorylation and cell viability were evaluated using western blotting and a 3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide (MTT) assay, respectively. Treatment with OSU-03012 resulted in decreased PDK-1-mediated Akt phosphorylation and cell growth inhibition for all cell lines with IC(50) values ranging between 1.0 and 2.5 muM. Resistance to 5-FU and gemcitabine was observed in cell lines AsPC-1 and BxPC-3. Further analyses indicate that OSU-03012 induces both proapoptotic and antiproliferative effects in these cells. Taken together, these data suggest that OSU-03012 has potential value as a novel therapy for pancreatic cancer.

Inhibition of either phosphatidylinositol 3-kinase/Akt or the mitogen/extracellular-regulated kinase, MEK/ERK, signaling pathways suppress growth of breast cancer cell lines, but MEK/ERK signaling is critical for cell survival

The phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen/extracellular signal-regulated kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways are important integrators of growth and survival signals originating from extracellular stimuli. We assessed the importance of these signaling pathways in the growth and survival of 8 breast cell lines (MCF10A, an immortalized line; and 7 cancer cell lines). The cell lines expressed variable levels of both phosphorylated ERK and phosphorylated Akt, but these were unchanged by incubation in serum-free medium. Despite continued activity of these pathways, the cells arrested growth in the absence of serum demonstrating that additional pathways are required for growth. Incubation with the PI3K inhibitor LY294002 suppressed growth of all cell lines, but most remained viable for at least 7-14 days. This long-term survival may be attributable to recovery of phospho-Akt by 24-48 h despite the continued presence of active LY294002, suggesting that alternate pathways may be activating Akt. In contrast, incubation with the MEK inhibitor U0126 not only arrested growth, but also killed all the cell lines within 2-4 days in the absence of serum; the presence of serum only slighted extended viability, except in MCF10A and MDA-MB-468 cells, in which serum provided significantly greater protection. It is likely that these signaling pathways control the level of pro-and anti-apoptotic proteins, yet assessment of Bcl-2 and Bcl-X showed dramatic reduction in level only when large numbers of cells were dead suggesting this may be a consequence rather than cause of death. Overall, the results demonstrate that the MEK/ERK pathway represents the more critical pathway for cell survival of these breast cancer cell lines, and suggest this pathways represents the better target for cancer therapy.

Optimal classes of chemotherapeutic agents sensitized by specific small-molecule inhibitors of akt in vitro and in vivo

Akt is a serine/threonine kinase that transduces survival signals from survival/growth factors. Deregulation and signal imbalance in cancer cells make them prone to apoptosis. Upregulation or activation of Akt to aid the survival of cancer cells is a common theme in human malignancies. We have developed small-molecule Akt inhibitors that are potent and specific. These Akt inhibitors can inhibit Akt activity and block phosphorylation by Akt on multiple downstream targets in cells. Synergy in apoptosis induction was observed when Akt inhibitors were combined with doxorubicin or camptothecin. Akt inhibitor-induced enhancement of topoisomerase inhibitor cytotoxicity was also evident in long-term cell survival assay. Synergy with paclitaxel in apoptosis induction was evident in cells pretreated with paclitaxel, and enhancement of tumor delay by paclitaxel was demonstrated through cotreatment with Akt inhibitor Compound A (A-443654). Combination with other classes of chemotherapeutic agents did not yield any enhancement of cytotoxicity. These findings provide important guidance in selecting appropriate classes of chemotherapeutic agents for combination with Akt inhibitors in cancer treatment.

Isoflurane postconditioning prevents opening of the mitochondrial permeability transition pore through inhibition of glycogen synthase kinase 3beta

BACKGROUND

Postischemic administration of volatile anesthetics activates reperfusion injury salvage kinases and decreases myocardial damage. However, the mechanisms underlying anesthetic postconditioning are unclear.

METHODS

Isolated perfused rat hearts were exposed to 40 min of ischemia followed by 1 h of reperfusion. Anesthetic postconditioning was induced by 15 min of 2.1 vol% isoflurane (1.5 minimum alveolar concentration) administered at the onset of reperfusion. In some experiments, atractyloside (10 microm), a mitochondrial permeability transition pore (mPTP) opener, and LY294002 (15 microm), a phosphatidylinositol 3-kinase inhibitor, were coadministered with isoflurane. Western blot analysis was used to determine phosphorylation of protein kinase B/Akt and its downstream target glycogen synthase kinase 3beta after 15 min of reperfusion. Myocardial tissue content of nicotinamide adenine dinucleotide served as a marker for mPTP opening. Accumulation of MitoTracker Red 580 (Molecular Probes, Invitrogen, Basel, Switzerland) was used to visualize mitochondrial function.

RESULTS

Anesthetic postconditioning significantly improved functional recovery and decreased infarct size (36 +/- 1% in unprotected hearts vs. 3 +/- 2% in anesthetic postconditioning; P < 0.05). Isoflurane-mediated protection was abolished by atractyloside and LY294002. LY294002 inhibited isoflurane-induced phosphorylation of protein kinase B/Akt and glycogen synthase kinase 3beta and opened mPTP as determined by nicotinamide adenine dinucleotide measurements. Atractyloside, a direct opener of the mPTP, did not inhibit phosphorylation of protein kinase B/Akt and glycogen synthase kinase 3beta by isoflurane but reversed isoflurane-mediated cytoprotection. Microscopy showed accumulation of the mitochondrial tracker in isoflurane-protected functional mitochondria but no staining in mitochondria of unprotected hearts.

CONCLUSIONS

Anesthetic postconditioning by isoflurane effectively protects against reperfusion damage by preventing opening of the mPTP through inhibition of glycogen synthase kinase 3beta.

Nucleolin links to arsenic-induced stabilization of GADD45alpha mRNA

The present study shows that arsenic induces GADD45alpha (growth arrest and DNA damage inducible gene 45alpha) mainly through post-transcriptional mechanism. Treatment of the human bronchial epithelial cell line, BEAS-2B, with arsenic(III) chloride (As3+) resulted in a significant increase in GADD45alpha protein and mRNA. However, As3+ only exhibited a marginal effect on the transcription of the GADD45alpha gene. The accumulation of GADD45alpha mRNA is largely achieved by the stabilization of GADD45alpha mRNA in the cellular response to As3+. As3+ is able to induce binding of mRNA stabilizing proteins, nucleolin and less potently, HuR, to the GADD45alpha mRNA. Although As3+ was unable to affect the expression of nucleolin, treatment of the cells with As3+ resulted in re-distribution of nucleolin from nucleoli to nucleoplasm. Silencing of the nucleolin mRNA by RNA interference reversed As3+-induced stabilization of the GADD45alpha mRNA and accumulation of the GADD45alpha protein. Stabilization of GADD45alpha mRNA, thus, represents a novel mechanism contributing to the production of GADD45alpha and cell cycle arrest in response to As3+.

Synthesis and structure-activity relationship of 3,4'-bispyridinylethylenes: discovery of a potent 3-isoquinolinylpyridine inhibitor of protein kinase B (PKB/Akt) for the treatment of cancer

Structure-based design and synthesis of the 3,4'-bispyridinylethylene series led to the discovery of 3-isoquinolinylpyridine 13a as a potent PKB/Akt inhibitor with an IC(50) of 1.3nM against Akt1. Compound 13a shows excellent selectivity against distinct families of kinases such as tyrosine kinases and CAMK, and displays poor to marginal selectivity against closely related kinases in the AGC and CMGC families. Moreover, 13a demonstrates potent cellular activity comparable to staurosporine, with IC(50) values of 0.42 and 0.59microM against MiaPaCa-2 and the Akt1 overexpressing FL5.12-Akt1, respectively. Inhibition of phosphorylation of the Akt downstream target GSK3 was also observed in FL5.12-Akt1 cells with an EC(50) of 1.5microM. The X-ray structures of 12 and 13a in complex with PKA in the ATP-binding site were determined.

Resveratrol inhibits hypoxia-induced accumulation of hypoxia-inducible factor-1alpha and VEGF expression in human tongue squamous cell carcinoma and hepatoma cells

Hypoxia-inducible factor-1alpha (HIF-1alpha) is overexpressed in many human tumors and their metastases, and is closely associated with a more aggressive tumor phenotype. In this study, we investigated the effect of resveratrol, a natural product commonly found in grapes and various other fruits, on hypoxia-induced HIF-1alpha protein accumulation and vascular endothelial growth factor (VEGF) expression in human tongue squamous cell carcinomas and hepatoma cells. Our results showed that resveratrol significantly inhibited both basal level and hypoxia-induced HIF-1alpha protein accumulation in cancer cells, but did not affect HIF-1alpha mRNA levels. Pretreatment of cells with resveratrol significantly reduced hypoxia-induced VEGF promoter activities and VEGF expression at both mRNA and protein levels. The mechanism of resveratrol inhibition of hypoxia-induced HIF-1alpha accumulation seems to involve a gradually shortened half-life of HIF-1alpha protein caused by an enhanced protein degradation through the 26S proteasome system. In addition, resveratrol remarkably inhibited hypoxia-mediated activation of extracellular signal-regulated kinase 1/2 and Akt, leading to a marked decrease in hypoxia-induced HIF-1alpha protein accumulation and VEGF transcriptional activation. Functionally, we observed that resveratrol also significantly inhibited the hypoxia-stimulated invasiveness of cancer cells. These data suggested that HIF-1alpha/VEGF could be a promising drug target for resveratrol in the development of an effective chemopreventive and anticancer therapy in human cancers.

Leptosins isolated from marine fungus Leptoshaeria species inhibit DNA topoisomerases I and/or II and induce apoptosis by inactivation of Akt/protein kinase B

DNA topoisomerases (topo) I and II are molecular targets of several potent anticancer agents. Thus, inhibitors of these enzymes are potential candidates or model compounds for anticancer drugs. Leptosins (Leps) F and C, indole derivatives, were isolated from a marine fungus, Leptoshaeria sp. as cytotoxic substances. In vitro cytotoxic effects of Lep were measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide-based viability assay. Lep F inhibited the activity of topos I and II, whereas Lep C inhibited topo I in vitro. Interestingly both of the compounds were found to be catalytic inhibitors of topo I, as evidenced by the lack of stabilization of reaction intermediate cleavable complex (CC), as camptothecin (CPT) does stabilize. Furthermore, Lep C inhibited the CC stabilization induced by CPT in vitro. In vivo band depletion analysis demonstrated that Lep C likewise appeared not to stabilize CC, and inhibited CC formation by CPT, indicating that Lep C is also a catalytic inhibitor of topo I in vivo. Cell cycle analysis of Lep C-treated cells showed that Lep C appeared to inhibit the progress of cells from G(1) to S phase. Lep C induced apoptosis in RPMI8402 cells, as revealed by the accumulation of cells in sub-G(1) phase, activation of caspase-3 and the nucleosomal degradation of chromosomal DNA. Furthermore, Leps F and C inhibited the Akt pathway, as demonstrated by dose-dependent and time-dependent dephosphorylation of Akt (Ser473). Our study shows that Leps are a group of anticancer chemotherapeutic agents with single or dual catalytic inhibitory activities against topos I and II.

Discovery of trans-3,4'-bispyridinylethylenes as potent and novel inhibitors of protein kinase B (PKB/Akt) for the treatment of cancer: Synthesis and biological evaluation

A novel series of Akt/PKB inhibitors derived from a screening lead (1) has been prepared. The novel trans-3,4'-bispyridinylethylenes described herein are potent inhibitors of Akt/PKB with IC(50) values in the low double-digit nanomolar range against Akt1. Compound 2q shows excellent selectivity against distinct families of kinases such as tyrosine kinases and CAMK, and displays poor to modest selectivity against closely related kinases in the AGC and CMGC families. The cellular activities including inhibition of cell growth and phosphorylation of downstream target GSK3 are also described. The X-ray structure of compound 2q complexed with PKA in the ATP binding site was determined.

In vitro and In vivo Antitumor Effects of the Dual Insulin-Like Growth Factor-I/Insulin Receptor Inhibitor, BMS-554417

The insulin-like growth factor receptor (IGF-IR) and insulin receptor are either overactivated and/or overexpressed in a wide range of tumor types and contribute to tumorigenicity, proliferation, metastasis, and drug resistance. Here, we show that BMS-554417, a novel small molecule developed as an inhibitor of IGF-IR, inhibits IGF-IR and insulin receptor kinase activity and proliferation in vitro, and reduces tumor xenograft size in vivo. In a series of carcinoma cell lines, the IC50 for proliferation ranged from 120 nmol/L (Colo205) to >8.5 micromol/L (OV202). The addition of stimulatory ligands was unnecessary for the antiproliferative effect in MCF-7 and OV202 cells. BMS-554417 treatment inhibited IGF-IR and insulin receptor signaling through extracellular signal-related kinase as well as the phosphoinositide 3-kinase/Akt pathway, as evidenced by decreased Akt phosphorylation at Ser473. At doses that inhibited proliferation, the compound also caused a G0-G1 arrest and prevented nuclear accumulation of cyclin D1 in response to LR3 IGF-I. In Jurkat T-cell leukemia cells, this agent triggered apoptotic cell death via the mitochondrial pathway. BMS-554417 was orally bioavailable and significantly inhibited the growth of IGF1R-Sal tumor xenografts in vivo. BMS-554417 is a member of a novel class of IGF-IR/insulin receptor inhibitors that have potential clinical applications because of their antiproliferative and proapoptotic activity in vitro and in vivo.

Phosphatidylinositol 3-kinase/Akt plays a role in sphingosine 1-phosphate-stimulated HSP27 induction in osteoblasts

We previously reported that p38 mitogen-activated protein (MAP) kinase plays a part in sphingosine 1-phosphate-stimulated heat shock protein 27 (HSP27) induction in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) is involved in the induction of HSP27 in these cells. Sphingosine 1-phosphate time dependently induced the phosphorylation of Akt. Akt inhibitor, 1L-6-hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate, reduced the HSP27 induction stimulated by sphingosine 1-phosphate. The sphingosine 1-phosphate-induced phosphorylation of GSK-3beta was suppressed by Akt inhibitor. The sphingosine 1-phosphate-induced HSP27 levels were attenuated by LY294002 or wortmannin, PI3K inhibitors. Furthermore, LY294002 or Akt inhibitor did not affect the sphingosine 1-phosphate-induced phosphorylation of p38 MAP kinase and SB203580, a p38 MAP kinase inhibitor, had little effect on the phosphorylation of Akt. These results suggest that PI3K/Akt plays a part in the sphingosine 1-phosphate-stimulated induction of HSP27, maybe independently of p38 MAP kinase, in osteoblasts.

Sphinganine causes early activation of JNK and p38 MAPK and inhibition of AKT activation in HT-29 human colon cancer cells

The sphingoid base sphinganine induces apoptosis in HT-29 human colon cancer cells more potently than other bioactive sphingolipid metabolites sphingosine and C2-ceramide tested in our previous study. The objective of this study was to investigate the effect of sphinganine, at a concentration that induces apoptosis, on the mitogen activated protein kinases (MAPKs) including ERK1/ERK2, JNK2/JNK1, and p38 MAPK and AKT (protein kinase B), which regulate cell proliferation and apoptosis. HT-29 cells were cultured with sphinganine at 35 microM and the protein expression and phosphorylation status of ERK1/ERK2 (p44/p42), JNK2/JNK1 (p54/p46), p38 MAPK, and AKT were determined using Western blot analysis. Sphinganine clearly increased the active phosphorylated forms of JNK2/JNK1 and p38 MAPK after 15, 30, and 60 min treatment, with minimal effects on activation of ERK1/ERK2. Sphinganine weakly inhibited the phosphorylation of AKT at ser473 after 30 and 60 min. Sphinganine had little or no effect on the protein expression level of any of the kinases. The findings are consistent with a mechanism by which sphinganine induces apoptosis in HT-29 cells via early and strong activation of JNK and p38 MAPK and weak inhibition of AKT activation.

Ascorbyl stearate inhibits cell proliferation and tumor growth in human ovarian carcinoma cells by targeting the PI3K/AKT pathway

Ascorbyl stearate is a lipophilic, vitamin C derivative with antitumorigenic properties. The molecular mechanism(s) underlying the anticarcinogenic effect of this compound have not been well documented. The effect of ascorbyl stearate was studied in a panel of human ovarian epithelial cancer cells. Treatment with ascorbyl stearate caused a dose-dependent inhibition of the cell proliferation. The antiproliferative effect was due to the arrest of cells in the S/G2-M-phase of the cell cycle. Treatment of OVCAR-3 cells with ascorbyl stearate also inhibited PI3K/AKT activity. The presence of a constitutively active AKT protected OVCAR-3 cells from the effects of ascorbyl stearate, suggesting that this nutraceutical targets the PI3K/AKT pathway. The administration of ascorbyl stearate by gavage induced involution of human ovarian carcinoma xenografts in nude mice. These studies indicate that the antiproliferative effect of ascorbyl stearate on ovarian epithelial cancer cells is associated with decreased PI3K/AKT activity, and point toward the PI3K/AKT signaling pathway as a target for this drug.

Inhibition of Akt/PKB by a COX-2 inhibitor induces apoptosis in gastric cancer cells

BACKGROUND/AIM

Inhibition of cyclooxygenase-2 has been proposed to be a potential mechanism for the chemoprevention of gastrointestinal tumors by nonsteroidal anti-inflammatory drugs. This study investigates the mechanisms by which the cyclooxygenase-2 inhibitor SC236 induces apoptosis of gastric cancer cell lines and its downstream signaling pathway.

METHODS

Two gastric cancer cell lines, AGS and MKN28, were treated with SC236 and assessed for cell growth and apoptosis. The involvement of mitogen-activated protein kinase and Akt kinase/protein kinase B (Akt/PKB) pathways and their downstream signalings were studied in the AGS cell line.

RESULTS

SC236 treatment induced apoptosis in gastric cancer cells and caused activation of p38 and stress-activated protein kinase/jun kinase, but down-regulated Akt/PKB. The specific p38 inhibitor SB203580 and the dominant-negative stress-activated protein kinase/jun kinase both failed, while the constitutively active form of Akt/PKB was able to block SC236-induced apoptosis. SC236-induced apoptosis was coupled with release of cytochrome c and activation of caspases.

CONCLUSION

One of the pathways involved in SC-236-induced apoptosis in gastric cancer cells is through downregulation of Akt and then release of cytochrome c.

Cotreatment with a novel phosphoinositide analogue inhibitor and carmustine enhances chemotherapeutic efficacy by attenuating AKT activity in gliomas

BACKGROUND

Heightened activity of the AKT signaling pathway is prominent in malignant gliomas and has been suggested to play a role in treatment resistance. Selective targeting of AKT, therefore, may increase chemosensitivity. Recently, a novel class of AKT-selective inhibitors has been described, including SH-6, a phosphatidylinositol analogue.

METHODS

The effects of SH-6 on AKT signaling were tested in glioma cells, and the putative role of AKT signaling in chemoresistance was tested by attenuating AKT signaling pharmacologically and genetically. The initial characterization of SH-6 included treatment of glioma cells with increasing doses of SH-6 (0.30-30 microM) and examining the effects on AKT signaling proteins by Western blot analyses and in kinase assays with immunoprecipitated AKT1. Dose-response studies with SH-6 administered to glioma cell lines were performed using a luminescent cell-viability assay (0.1-30 microM). Studies examining the effect of carmustine, either alone or in combination with either the phosphatidylinositol 3-kinase inhibitor LY294002 or SH-6, were performed by cell viability assays and clonogenic survival assays. The effect of carmustine on AKT activity as a response to treatment also was examined. Caspase assays were used to examine the potential role of apoptosis in SH-6/ carmustine -elicited cell death. Finally, the induction of a dominant-negative AKT1 transgene was used in combination with carmustine to demonstrate the role of AKT1 in carmustine chemoresistance.

RESULTS

Serum-stimulated phosphorylation of AKT1 was inhibited by SH-6 at doses > or =10 microM (>70% decrease in Threonine 308 and Serine 473 phosphorylation of AKT1). In adenosine triphosphate assays, 72 hours of treatment with SH-6 led to 50% lethal doses near 10 microM for 2 cell lines tested. SH-6 enhancement of carmustine-mediated cell death led to synergistic increases in Caspase 3/Capsase 7 activity, implicating apoptosis as the cell death mechanism. In clonogenic assays, SH-6 cotreatment with carmustine significantly decreased the number of colonies at 10 microM (P < .05) compared with carmustine alone. No decrease was observed in cells that were treated with SH-6 alone (10 microM). LY294002 (10 microM) was also able to enhance the effects of carmustine significantly in both cell lines.

CONCLUSIONS

In the current study, the authors characterized the efficacy of a new class of adjuvant chemotherapeutics that show promise in enhancing the efficacy of standard chemotherapy regimens in gliomas.

[PI3K-AKT-mTOR pathway inhibitors]

Molecular targeted agents have enlarged the armamentarium of anti-cancer therapies. Along with the success of some anti-growth factor receptors, signal transduction inhibitors represent a promising anti-cancer strategy. The PI3K-AKT-mTOR pathway is a key pathway frequently altered in cancer cells. This manuscript provides an overview of the PI3K-AKT-mTOR pathway and its targeting in human malignancies. A focus is delivered for mTOR inhibitors.

ErbB4 Activation Inhibits MPP+-Induced Cell Death In PC12-ErbB4 Cells: Involvement of PI3K and Erk Signaling

The neuroprotective effects of neuregulin (NRG), a polypeptide growth factor, on 1-methyl-4-phenylpyridinium ion (MPP+)-induced cell death and oxidative stress in PC12-ErbB4 cells were investigated. Treatment of PC12-ErbB4 cells with MPP+ induced cell death that was markedly attenuated by NRG. The PI3K/PKB/Akt and Ras/MapK signaling pathways probably mediate the survival effect of NRG. NRG induces prolonged activation of PKB/Akt and Erk. Moreover, inhibition of the PI3K and MEK activities prevented the NRG-induced survival effect. Overexpression of constitutively active PI3K or H-Ras (12V) inhibited MPP+-mediated cell death. In addition, MPP+- mediated reactive oxygen species (ROS) elevation was also inhibited by NRG. The effect of NRG on ROS levels was blocked by PI3K and MEK inhibitors, indicating that both signaling pathways can regulate the toxic ROS levels induced by MPP+. Taken together, these results indicate that in PC12-ErbB4 cells, the NRG-induced neuroprotective effect from MPP+ treatment, requires PI3K/PKB/Akt and Ras/MapK signaling networks.

Involvement of protein kinase C and E2F-5 in euxanthone-induced neurite differentiation of neuroblastoma

Euxanthone, a neuritogenic agent isolated from the medicinal herb Polygala caudata, has been shown to induce morphological differentiation and neurite outgrowth in murine neuroblastoma Neuro 2a cells (BU-1 subclone). In order to elucidate the underlying mechanisms of euxanthone-induced neurite outgrowth, a proteomic approach was employed. In the present study, two dimensional (2-D) gel electrophoresis and matrix-assisted laser desorption/ionization-time of flight (MALDI-ToF) mass spectrometry were performed to investigate the alterations in protein expression profile of euxanthone-treated BU-1 cells. Fourteen identified proteins were changed in expression levels after induction of neurite growth. These proteins included participants in transcription and cell cycle regulation, calcium influx and calcium signaling, fatty acid metabolism, cytoskeleton reorganization, casein kinase signal transduction, putative transbilayer amphipath transport and protein biosynthesis. Among the 14 identified proteins, E2F transcription factor 5 (E2F-5) was significantly up-regulated after euxanthone treatment. Go6976, a protein kinase C (PKC) alpha/betaI inhibitor, was found to inhibit neuritogenesis and expression of E2F-5 in the euxanthone-treated BU-1 cells, while SH-6, the Akt/PKB inhibitor, had no inhibitory effect. The gene silencing of E2F-5 by small interfering RNA (siRNA) was found to abolish the euxanthone-induced neurite outgrowth. In conclusion, these results indicated that the transcription factor E2F-5 was actively involved in the regulation of euxanthone-induced neurite outgrowth via PKC pathway.

Vasculoprotective effect of insulin in the ischemic/reperfused canine heart: Role of Akt-stimulated NO production

OBJECTIVES

The objectives of this study were to investigate the vasculoprotective effects of glucose-insulin-potassium (GIK) on ischemia/reperfusion-induced coronary endothelial functional injury and to elucidate the mechanism involved.

METHODS

Dogs were subjected to 50 min of coronary occlusion and 4 h of reperfusion. Vehicle, GIK, or GK were intravenously infused 5 min before reperfusion, and the coronary vascular dysfunction and endothelial apoptosis were determined. In a separate study, cultured endothelial cells were subjected to simulated ischemia/reperfusion, and the signaling pathway involved in insulin's anti-apoptotic effect was investigated.

RESULTS

In vivo ischemia/reperfusion caused significant coronary vascular endothelial dysfunction as evidenced by reduced endothelium-dependent vasorelaxation, decreased nitric oxide (NO) production, and endothelial cell apoptosis as determined by caspase 3 activation and TUNEL staining. Treatment with GIK, but not GK, markedly improved the endothelium-dependent coronary vasorelaxation (P<0.01 versus vehicle), increased total NO production (P<0.01), and attenuated endothelial apoptosis. In cultured endothelial cells, treatment with insulin also markedly increased NO production and reduced simulated ischemia/reperfusion-induced apoptosis. Moreover, pre-treatment with either Akt inhibitor or NO synthase inhibitor almost abolished the anti-apoptotic effect exerted by insulin but not by SNAP, an NO donor.

CONCLUSION

These results demonstrate that in vivo treatment with GIK at reperfusion attenuates ischemia/reperfusion-induced coronary endothelial dysfunction and endothelial apoptosis in an Akt-dependent and NO-mediated fashion. The coronary vasculoprotective effect elicited by insulin may contribute to the previously observed cardiac protective effect of GIK.

TNF blockade: an inflammatory issue

Tumor necrosis factor (TNF), initially discovered as a result of its antitumor activity, has now been shown to mediate tumor initiation, promotion, and metastasis. In addition, dysregulation of TNF has been implicated in a wide variety of inflammatory diseases including rheumatoid arthritis, Crohn's disease, multiple sclerosis, psoriasis, scleroderma, atopic dermatitis, systemic lupus erythematosus, type II diabetes, atherosclerosis, myocardial infarction, osteoporosis, and autoimmune deficiency disease. TNF, however, is a critical component of effective immune surveillance and is required for proper proliferation and function of NK cells, T cells, B cells, macrophages, and dendritic cells. TNF activity can be blocked, either by using antibodies (Remicade and Humira) or soluble TNF receptor (Enbrel), for the symptoms of arthritis and Crohn's disease to be alleviated, but at the same time, such treatment increases the risk of infections, certain type of cancers, and cardiotoxicity. Thus blockers of TNF that are safe and yet efficacious are urgently needed. Some evidence suggests that while the transmembrane form of TNF has beneficial effects, soluble TNF mediates toxicity. In most cells, TNF mediates its effects through activation of caspases, NF-kappaB, AP-1, c-jun N-terminal kinase, p38 MAPK, and p44/p42 MAPK. Agents that can differentially regulate TNF expression or TNF signaling can be pharmacologically safe and effective therapeutics. Our laboratory has identified numerous such agents from natural sources. These are discussed further in detail.

Mechanisms of the antiangiogenic activity by the hop flavonoid xanthohumol: NF‐κB and Akt as targets

Xanthohumol (XN), the principal flavonoid of the hop plant (Humulus lupulus L.) and a constituent of beer, has been suggested to have potential cancer chemopreventive activities. We have observed that most cancer chemopreventive agents show antiangiogenic properties in vitro and in vivo, a concept we termed "angioprevention." Here we show for the first time that XN can inhibit growth of a vascular tumor in vivo. Histopathology and in vivo angiogenesis assays indicated that tumor angiogenesis inhibition was involved. Further, we show the mechanisms for its inhibition of angiogenesis in vivo and related endothelial cell activities in vitro. XN repressed both the NF-kappaB and Akt pathways in endothelial cells, indicating that components of these pathways are major targets in the molecular mechanism of XN. Moreover, using in vitro analyses, we show that XN interferes with several points in the angiogenic process, including inhibition of endothelial cell invasion and migration, growth, and formation of a network of tubular-like structures. Our results suggest that XN can be added to the expanding list of antiangiogenic chemopreventive drugs whose potential in cancer prevention and therapy should be evaluated.