p130Cas regulates the activity of AND-34, a novel Ral, Rap1, and R-Ras guanine nucleotide exchange factor

We previously identified a novel murine protein, AND-34, with a carboxyl-terminal domain homologous to Ras family guanine nucleotide exchange factors (GEFs), which bound to the focal adhesion docking protein p130(Cas). Work by others has implicated both the human homologue of AND-34, BCAR3, and human p130(Cas), BCAR1, in the resistance of breast cancer cells to the anti-estrogen tamoxifen. Here we report that AND-34 displays GEF activity on RalA, Rap1A, and R-Ras but not Ha-Ras GTPases in cells. In contrast to several other Ral-GEFs, the Ral GEF activity of AND-34 is not augmented by constitutively active Ha-Ras(Val-12), consistent with the absence of a detectable Ras-binding domain. Efficient binding to AND-34 required both the Src-binding domain and a flanking carboxyl-terminal region of p130(Cas). The p130(Cas)-binding site mapped to a carboxyl-terminal sequence within the AND-34 GEF domain. Overexpression of p130(Cas), but not an AND-34-binding mutant of p130(Cas), inhibited the Ral GEF activity of co-transfected AND-34. This work identifies a new potential function for p130(Cas) and a new regulatory pathway involved in the control of Ral, Rap, and R-Ras GTPases that may participate in the progression of breast cancer cells to tamoxifen resistance.     

17 beta-estradiol activates PI3K/Akt signaling pathway by estrogen receptor (ER)-dependent and ER-independent mechanisms in endometrial cancer cells

Cellular response to estrogen is mediated both by estrogen receptor (ER) binding to estrogen response element (ERE) and by non-nuclear actions like activation of signal transducing pathways. The main aims are to study if PI3K/Akt signaling pathway can be activated by 17beta-estradiol (E2) via non-nuclear action and to investigate the relationship of the action of E2 and ER in endometrial cancer cells expressing with different status of ER. The levels of phosphorylated Akt (Ser473) (P-Akt) and total Akt were examined by western blot and Akt kinase activity was measured in cells after stimulation with 1 microM E2 at different time points. Inhibitory role of LY294002 on activation of Akt induced by E2 and its estrogen antagonist, ICI182780 were also tested. P-Akt/Akt was used as a measure of activation of Akt. We found that maximum P-Akt/Akt and Akt kinase activity took place at 30 min in Ishikawa cells and 15 min in HEC-1A cells and the activation persisted for at least 2 h after stimulation with 1 microM E2. The activation of Akt elicited gradually with increasing doses of E2. PI3K inhibitor, LY294002, stopped the activating Akt in a dose-dependent manner and 50 microM LY294002 completely blocked the activation of Akt induced by E2. ICI182780 could block the activation of PI3K/Akt in ER-positive Ishikawa cells but not in HEC-1A cells with poor-expressed ER. This study demonstrated that E2 is able to promptly activate PI3K/Akt signal pathway in Ishikawa cells in an ER-dependent manner and ER-independent in HEC-1A cells. Blockage of PI3K/Akt cascade may become a potential and effective way to control endometrial carcinoma, especially in ER-negative cancers, which show no response to endocrinal therapy.     

Thrombin induces NF-kappaB activation and IL-8/CXCL8 expression in lung epithelial cells by a Rac1-dependent PI3K/Akt pathway

We previously showed that thrombin induces interleukin (IL)-8/CXCL8 expression via the protein kinase C (PKC)α/c-Src-dependent IκB kinase α/β (IKKα/β)/NF-κB signaling pathway in human lung epithelial cells. In this study, we further investigated the roles of Rac1, phosphoinositide 3-kinase (PI3K), and Akt in thrombin-induced NF-κB activation and IL-8/CXCL8 expression. Thrombin-induced IL-8/CXCL8 release and IL-8/CXCL8-luciferase activity were attenuated by a PI3K inhibitor (LY294002), an Akt inhibitor (1-L-6-hydroxymethyl-chiro-inositol-2-((R)-2-O-methyl-3-O-octadecylcarbonate)), and the dominant negative mutants of Rac1 (RacN17) and Akt (AktDN). Treatment of cells with thrombin caused activation of Rac and Akt. The thrombin-induced increase in Akt activation was inhibited by RacN17 and LY294002. Stimulation of cells with thrombin resulted in increases in IKKα/β activation and κB-luciferase activity; these effects were inhibited by RacN17, LY294002, an Akt inhibitor, and AktDN. Treatment of cells with thrombin induced Gβγ, p85α, and Rac1 complex formation in a time-dependent manner. These results imply that thrombin activates the Rac1/PI3K/Akt pathway through formation of the Gβγ, Rac1, and p85α complex to induce IKKα/β activation, NF-κB transactivation, and IL-8/CXCL8 expression in human lung epithelial cells.     

Transmigration characteristics of breast cancer and melanoma cells through the brain endothelium: Role of Rac and PI3K

Brain metastases are common and devastating complications of both breast cancer and melanoma. Although mammary carcinoma brain metastases are more frequent than those originating from melanoma, this latter has the highest tropism to the brain. Using static and dynamic in vitro approaches, here we show that melanoma cells have increased adhesion to the brain endothelium in comparison to breast cancer cells. Moreover, melanoma cells can transmigrate more rapidly and in a higher number through brain endothelial monolayers than breast cancer cells. In addition, melanoma cells have increased ability to impair tight junctions of cerebral endothelial cells. We also show that inhibition of Rac or PI3K impedes adhesion of breast cancer cells and melanoma cells to the brain endothelium. In addition, inhibition of Rac or PI3K inhibits the late phase of transmigration of breast cancer cells and the early phase of transmigration of melanoma cells. On the other hand, the Rac inhibitor EHT1864 impairs the junctional integrity of the brain endothelium, while the PI3K inhibitor LY294002 has no damaging effect on interendothelial junctions. We suggest that targeting the PI3K/Akt pathway may represent a novel opportunity in preventing the formation of brain metastases of melanoma and breast cancer.     

Inhibition of MLK3-MKK4/7-JNK1/2 pathway by Akt1 in exogenous estrogen-induced neuroprotection against transient global cerebral ischemia by a non-genomic mechanism in male rats

Numerous studies have demonstrated the neuroprotective effects of estrogen in experimental cerebral ischemia. To investigate molecular mechanisms of estrogen neuroprotection in global ischemia, immunoblotting, immunohistochemistry and Nissel-staining analysis were used. Our results showed that chronic pretreatment with beta-estradiol 3-benzoate (E2) enhanced Akt1 activation and reduced the activation of mixed-lineage kinase 3 (MLK3), mitogen-activated protein kinase kinase 4/7 (MKK4/7), and c-Jun N-terminal kinase 1/2 (JNK1/2) in the hippocampal CA1 subfield during reperfusion after 15 min of global ischemia. In addition, E2 reduced downstream JNK nuclear and non-nuclear components, c-Jun and Bcl-2 phosphorylation and Fas ligand protein expression induced by ischemia/reperfusion. Administration of phosphoinositide 3-kinase (PI3K) inhibitor LY 294,002 prevented both activation of Akt1 and inhibition of MLK3, MKK4/7 and JNK1/2. The interaction between ERalpha and the p85 subunit of PI3K was also examined. E2 and antiestrogen ICI 182,780 promoted and prevented this interaction, respectively. Furthermore, ICI 182,780 blocked both the activation of Akt1 and the inhibition of MLK3, MKK4/7 and JNK1/2. Photomicrographs of cresyl violet-stained brain sections showed that E2 reduced CA1 neuron loss after 5 days of reperfusion, which was abolished by ICI 182,780 and LY 294,002. Our data indicate that in response to estrogen, ERalpha interacts with PI3K to activate Akt1, which may inhibit the MLK3-MKK4/7-JNK1/2 pathway to protect hippocampal CA1 neurons against global cerebral ischemia in male rats.     

PI3K and ERK-induced Rac1 activation mediates hypoxia-induced HIF-1α expression in MCF-7 breast cancer cells

Background

Hypoxia-inducible factor 1 (HIF-1α) expression induced by hypoxia plays a critical role in promoting tumor angiogenesis and metastasis. However, the molecular mechanisms underlying the induction of HIF-1α in tumor cells remain unknown.

Methodology/Principal Findings

In this study, we reported that hypoxia could induce HIF-1α and VEGF expression accompanied by Rac1 activation in MCF-7 breast cancer cells. Blockade of Rac1 activation with ectopic expression of an inactive mutant form of Rac1 (T17N) or Rac1 siRNA downregulated hypoxia-induced HIF-1α and VEGF expression. Furthermore, Hypoxia increased PI3K and ERK signaling activity. Both PI3K inhibitor {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 and ERK inhibitor U0126 suppressed hypoxia-induced Rac1 activation as well as HIF-1α expression. Moreover, hypoxia treatment resulted in a remarkable production of reactive oxygen species (ROS). N-acetyl-L-cysteine, a scavenger of ROS, inhibited hypoxia-induced ROS generation, PI3K, ERK and Rac1 activation as well as HIF-1α expression.

Conclusions/Significance

Taken together, our study demonstrated that hypoxia-induced HIF-1α expression involves a cascade of signaling events including ROS generation, activation of PI3K and ERK signaling, and subsequent activation of Rac1.     

Suppression of epidermal growth factor receptor‐mediated β‐catenin nuclear accumulation enhances the anti‐tumor activity of phosphoinositide 3‐kinase inhibitor in breast cancer

Phosphoinositide 3‐kinase (PI3K) signaling is frequently deregulated in breast cancer and plays a critical role in tumor progression. However, resistance to PI3K inhibitors in breast cancer has emerged, which is due to the enhanced β‐catenin nuclear accumulation. Until now, the mechanisms underlying PI3K inhibition‐induced β‐catenin nuclear accumulation remains largely unknown. In the present study, we found inhibition of PI3K with LY294002 promoted β‐catenin nuclear accumulation in MCF‐7 and MDA‐MB‐231 breast cancer cells. Combining PI3K inhibitor LY294002 with XAV‐939, an inhibitor against β‐catenin nuclear accumulation, produced an additive anti‐proliferation effect against breast cancer cells. Subsequent experiments suggested β‐catenin nuclear accumulation induced by PI3K inhibition depended on the feedback activation of epidermal growth factor receptor (EGFR) signaling pathway in breast cancer cells. Inhibition of EGFR phosphorylation with Gefitinib enhanced anti‐proliferation effect of PI3K inhibitor LY294002 in MCF‐7 and MDA‐MB‐231 cells. Taken together, our findings may elucidate a possible mechanism explaining the poor outcome of PI3K inhibitors in breast cancer treatment.     

PAK4 confers cisplatin resistance in gastric cancer cells via PI3K/Akt- and MEK/ERK-dependent pathways

CDDP [cisplatin or cis-diamminedichloroplatinum(II)] and CDDP-based combination chemotherapy have been confirmed effective against gastric cancer. However, CDDP efficiency is limited because of development of drug resistance. In this study, we found that PAK4 (p21-activated kinase 4) expression and activity were elevated in gastric cancer cells with acquired CDDP resistance (AGS/CDDP and MKN-45/CDDP) compared with their parental cells. Inhibition of PAK4 or knockdown of PAK4 expression by specific siRNA (small interfering RNA)-sensitized CDDP-resistant cells to CDDP and overcome CDDP resistance. Combination treatment of {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 [the inhibitor of PI3K (phosphoinositide 3-kinase)/Akt (protein kinase B or PKB) pathway] or PD98509 {the inhibitor of MEK [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase] pathway} with PF-3758309 (the PAK4 inhibitor) resulted in increased CDDP efficacy compared with {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 or PD98509 alone. However, after the concomitant treatment of {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 and PD98509, PF-3758309 administration exerted no additional enhancement of CDDP cytotoxicity in CDDP-resistant cells. Inhibition of PAK4 by PF-3758309 could significantly suppress MEK/ERK and PI3K/Akt signalling in CDDP-resistant cells. Furthermore, inhibition of PI3K/Akt pathway while not MEK/ERK pathway could inhibit PAK4 activity in these cells. The in vivo results were similar with those of in vitro. In conclusion, these results indicate that PAK4 confers CDDP resistance via the activation of MEK/ERK and PI3K/Akt pathways. PAK4 and PI3K/Akt pathways can reciprocally activate each other. Therefore, PAK4 may be a potential target for overcoming CDDP resistance in gastric cancer.     

Phosphatidylinositol 3-kinase activation and interaction with focal adhesion kinase in Escherichia coli K1 invasion of human brain microvascular endothelial cells

Invasion of brain microvascular endothelial cells (BMEC) is a prerequisite for successful crossing of the blood-brain barrier by Escherichia coli K1. We have previously demonstrated the requirement of cytoskeletal rearrangements and activation of focal adhesion kinase (FAK) in E. coli K1 invasion of human BMEC (HBMEC). The current study investigated the role of phosphatidylinositol 3-kinase (PI3K) activation and PI3K interaction with FAK in E. coli invasion of HBMEC. PI3K inhibitor LY294002 blocked E. coli K1 invasion of HBMEC in a dose-dependent manner, whereas an inactive analogue LY303511 had no such effect. In HBMEC, E. coli K1 increased phosphorylation of Akt, a downstream effector of PI3K, which was completely blocked by LY294002. In contrast, non-invasive E. coli failed to activate PI3K. Overexpression of PI3K mutants Deltap85 and catalytically inactive p110 in HBMEC significantly inhibited both PI3K/Akt activation and E. coli K1 invasion of HBMEC. Stimulation of HBMEC with E. coli K1 increased PI3K association with FAK. Furthermore, PI3K/Akt activation was blocked in HBMEC-overexpressing FAK dominant-negative mutants (FRNK and Phe397FAK). These results demonstrated the involvement of PI3K signaling in E. coli K1 invasion of HBMEC and identified a novel role for PI3K interaction with FAK in the pathogenesis of E. coli meningitis.     

Bcl-xL mediates a survival mechanism independent of the phosphoinositide 3-kinase/Akt pathway in prostate cancer cells

Among various molecular strategies by which prostate cancer cells evade apoptosis, phosphoinositide 3-kinase (PI3K)/Akt signaling represents a dominant survival pathway. However, different prostate cancer cell lines such as LNCaP and PC-3 display differential sensitivity to the apoptotic effect of PI3K inhibition in serum-free media, reflecting the heterogeneous nature of prostate cancer in apoptosis regulation. Whereas both cell lines are equally susceptible to LY294002-mediated Akt dephosphorylation, only LNCaP cells default to apoptosis, as evidenced by DNA fragmentation and cytochrome c release. In PC-3 cells, Akt deactivation does not lead to cytochrome c release, suggesting that the intermediary signaling pathway is short-circuited by an antiapoptotic factor. This study presents evidence that Bcl-xL overexpression provides a distinct survival mechanism that protects PC-3 cells from apoptotic signals emanating from PI3K inhibition. First, the Bcl-xL/BAD ratio in PC-3 cells is at least an order of magnitude greater than that of LNCaP cells. Second, ectopic expression of Bcl-xL protects LNCaP cells against LY294002-induced apoptosis. Third, antisense down-regulation of Bcl-xL sensitizes PC-3 cells to the apoptotic effect of LY294002. The physiological relevance of this Bcl-xL-mediated survival mechanism is further underscored by the protective effect of serum on LY294002-induced cell death in LNCaP cells, which is correlated with a multifold increase in Bcl-xL expression. In contrast to Bcl-xL, Bcl-2 expression levels are similar in both cells lines, and do not respond to serum stimulation, suggesting that Bcl-2 may not play a physiological role in antagonizing apoptosis signals pertinent to BAD activation in prostate cancer cells.     

The T-cell receptor regulates Akt (protein kinase B) via a pathway involving Rac1 and phosphatidylinositide 3-kinase

The serine/threonine kinase Akt (also known as protein kinase B) (Akt/PKB) is activated upon T-cell antigen receptor (TCR) engagement or upon expression of an active form of phosphatidylinositide (PI) 3-kinase in T lymphocytes. Here we report that the small GTPase Rac1 is implicated in this pathway, connecting the receptor with the lipid kinase. We show that in Jurkat cells, activated forms of Rac1 or Cdc42, but not Rho, stimulate an increase in Akt/PKB activity. TCR-induced Akt/PKB activation is inhibited either by PI 3-kinase inhibitors (LY294002 and wortmannin) or by overexpression of a dominant negative mutant of Rac1 but not Cdc42. Accordingly, triggering of the TCR rapidly stimulates a transient increase in GTP-Rac content in these cells. Similar to TCR stimulation, L61Rac-induced Akt/PKB kinase activity is also LY294002 and wortmannin sensitive. However, induction of Akt/PKB activity by constitutive active PI 3-kinase is unaffected when dominant negative Rac1 is coexpressed, placing Rac1 upstream of PI 3-kinase in the signaling pathway. When analyzing the signaling hierarchy in the pathway leading to cytoskeleton rearrangements, we found that Rac1 acts downstream of PI 3-kinase, a finding that is in accordance with numerous studies in fibroblasts. Our results reveal a previously unrecognized role of the GTPase Rac1, acting upstream of PI 3-kinase in linking the TCR to Akt/PKB. This is the first report of a membrane receptor employing Rac1 as a downstream transducer for Akt/PKB activation.     

Involvement of phospholipase D in sphingosine 1-phosphate-induced activation of phosphatidylinositol 3-kinase and Akt in Chinese hamster ovary cells overexpressing EDG3

Phospholipase D (PLD), phosphatidylinositol 3-kinase (PI3K), and Akt are known to be involved in cellular signaling related to proliferation and cell survival. In this report, we provide evidence that PLD links sphingosine 1-phosphate (S1P)-induced activation of the G protein-coupled EDG3 receptor to stimulation of PI3K and its downstream effector Akt in Chinese hamster ovary (CHO) cells. S1P stimulation of EDG3-overexpressing CHO cells but not vector-transfected cells induced activation of PLD, PI3K, and Akt in a time- and dose-dependent manner. Akt phosphorylation was prevented by the PI3K inhibitors wortmannin and LY294002 (2-(4-monrpholinyl)-8-phenyl-4H-1-benzopyran-4-one), indicating that Akt activation was dependent on PI3K. S1P-induced activation of PI3K and Akt was abrogated by 1-butanol, which inhibited S1P-induced accumulation of phosphatidic acid by serving as a phosphatidyl group acceptor in the transphosphatidylation reaction catalyzed by PLD, whereas both PI3K and Akt activation were not inhibited by 2-butanol without such reaction. Co-expression of wild-type PLD2 with myc-Akt resulted in increased Akt activation in response to S1P. In contrast, co-expression of a catalytically inactive mutant of PLD2 eliminated the S1P-induced Akt activation. The treatment of EDG3-expressing CHO cells with exogenous Streptomyces chromofuscus PLD, which caused an accumulation of phosphatidic acid, resulted in increases in PI3K activity and the phosphorylation of Akt, the latter of which was completely abolished by LY294002. Furthermore, S1P-induced membrane ruffling, which was dependent on PI3K and Rac, was inhibited by 1-butanol, but not by 2-butanol. These results demonstrate that PLD participates in the activation of PI3K and Akt stimulation of EDG3 receptor.     

PI3K induced actin filament remodeling through Akt and p70S6K1: implication of essential role in cell migration

This study was designed to identify the molecular mechanisms of phosphatidylinositol 3-kinase (PI3K)-induced actin filament remodeling and cell migration. Expression of active forms of PI3K, v-P3k or Myr-P3k, was sufficient to induce actin filament remodeling to lead to an increase in cell migration, as well as the activation of Akt in chicken embryo fibroblast (CEF) cells. Either the inhibition of PI3K activity using a PI3K-specific inhibitor, LY-294002, or the disruption of Akt activity restored the integrity of actin filaments in CEF cells and inhibited PI3K-induced cell migration. We also found that expression of an activated form of Akt (Myr-Akt) was sufficient to remodel actin filaments to lead to an increase in cell migration, which was unable to be inhibited by the presence of LY-294002. Furthermore, we found that p70S6K1 kinase was a downstream molecule that can mediate the effects of both PI3K and Akt on actin filaments and cell migration. Overexpression of an active form of p70S6K1 was sufficient to induce actin filament remodeling and cell migration in CEF cells, which requires Rac activity. These results demonstrate that activation of PI3K activity alone is sufficient to remodel actin filaments to increase cell migration through the activation of Akt and p70S6K1 in CEF cells. phosphatidylinositol 3-kinase; Rac; actin filaments     

Rac is activated by tumor necrosis factor alpha and is involved in activation of Erk.

Tumor necrosis factor alpha (TNFalpha) activates various signal transduction pathways including those involving phosphatidylinositol 3-kinase (PI3K), extracellular signal-regulated kinases (Erk), c-Jun N-terminal protein kinases (JNK), and p38 kinases. Using the Rac binding domain of PAK (PAK-RBD) as an activation-specific probe, here we demonstrate that TNFalpha very rapidly and transiently activates the Rho family GTPase Rac in L929 cells. The PI3K inhibitor LY294002 significantly inhibited TNFalpha activation of Rac as well as Erk and abolished that of the PI3K target Akt, without showing any inhibitory effects on JNK and p38 activation. Furthermore, TNFalpha activation of Erk was abolished by a dominant negative Rac mutant, Rac17N, or by an activated Rac mutant, Rac12V. These findings suggest that Rac is activated by a mechanism that is at least partly dependent on PI3K in TNFalpha stimulated cells and plays a critical role in activation of the Erk signaling pathway.     

Odorant Stimulation Promotes Survival of Rodent Olfactory Receptor Neurons via PI3K/Akt Activation and Bcl-2 Expression

Olfactory stimulation activates multiple signaling cascades in order to mediate activity-driven changes in gene expression that promote neuronal survival. To date, the mechanisms involved in activity-dependent olfactory neuronal survival have yet to be fully elucidated. In the current study, we observed that olfactory sensory stimulation, which caused neuronal activation, promoted activation of the phosphatidylinositol 3′-kinase (PI3K)/Akt pathway and the expression of Bcl-2, which were responsible for olfactory receptor neuron (ORN) survival. We demonstrated that Bcl-2 expression increased after odorant stimulation both in vivo and in vitro. We also showed that odorant stimulation activated Akt, and that Akt activation was completely blocked by incubation with both a PI3K inhibitor ({"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002) and Akt1 small interfering RNA. Moreover, blocking the PI3K/Akt pathway diminished the odorant-induced Bcl-2 expression, as well as the effects on odorant-induced ORN survival. A temporal difference was noted between the activation of Akt1 and the expression of Bcl-2 following odorant stimulation. Blocking the PI3K/Akt pathway did not affect ORN survival in the time range prior to the increase in Bcl-2 expression, implying that these two events, activation of the PI3K pathway and Bcl-2 induction, were tightly connected to promote post-translational ORN survival. Collectively, our results indicated that olfactory activity activated PI3K/Akt, induced Bcl-2, and promoted long term ORN survival as a result.     

Activation of the Akt Survival Pathway Contributes to TRAIL Resistance in Cancer Cells

The mechanism of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) resistance in cancer cells is not fully understood. Here, we show that the Akt survival pathway plays an important role in TRAIL resistance in human cancer cells. Specifically, we found that TRAIL treatment activates the Akt survival pathway and that inhibition of this pathway by the PI3K inhibitor {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 or knockdown of Akt sensitizes resistant cancer cells to TRAIL. Since Akt is negatively regulated by the tumor suppressor PTEN, we examined the TRAIL sensitivity in PTEN knockdown mouse prostate epithelial cells and found that PTEN^−/− cells are more resistant than PTEN^+/+ cells while the sensitivity of PTEN^+/− cells fell in between. Further, we showed that overexpression of a mutant PTEN confers TRAIL resistance in PTEN^+/+ cells, supporting a role of PTEN in TRAIL sensitivity. In TRAIL resistant breast T47D cells, overexpression of the mutant PTEN further increased their resistance to TRAIL. Taken together, our data indicate that inactivation of functional PTEN and the consequent activation of the Akt pathway prevents TRAIL-induced apoptosis, leading to TRAIL resistance. Therefore, our results suggest that TRAIL resistance can be overcome by targeting PTEN or the Akt survival pathway in cancer cells.