p38alpha blockade inhibits colorectal cancer growth in vivo by inducing a switch from HIF1alpha- to FoxO-dependent transcription

The Stress Kinase p38α as a Target for Cancer Therapy

p38α is a ubiquitous protein kinase strongly activated by stress signals, inflammatory cytokines, and many other stimuli, which has been implicated in the modulation of multiple cellular processes. There is good evidence in the literature that p38α plays an important tumor-suppressor role by interfering with malignant cell transformation. This is mainly based on the ability of the p38α pathway to regulate tissue homeostasis by integrating signals that balance cell proliferation and differentiation or induce apoptosis. However, recent reports have also illustrated protumorigenic functions for p38α. Thus, p38α signaling may facilitate the survival and proliferation of tumor cells contributing to the progression of some tumor types. In addition, p38α activation helps tumor cells to survive chemotherapeutic treatments. In all these cases, the inhibition of p38α has a potential therapeutic interest. Further elucidation of the context-dependent functions of p38α signaling in tumoral processes is of obvious importance for the use of inhibitors of this pathway in cancer therapy.

Coronin 2A (CRN5) expression is associated with colorectal adenoma-adenocarcinoma sequence and oncogenic signalling

BACKGROUND

Coronin proteins are known as regulators of actin-based cellular processes, and some of them are associated with the malignant progression of human cancer. Here, we show that expression of coronin 2A is up-regulated in human colon carcinoma.

METHODS

This study included 26 human colon tumour specimens and 9 normal controls. Expression and localisation of coronin 2A was studied by immunohistochemistry, immunofluorescence imaging, cell fractionation, and immunoblotting. Functional roles of coronin 2A were analysed by over-expression and knock-down of the protein. Protein interactions were studied by co-immunoprecipitation and pull-down experiments, mass spectrometry analyses, and in vitro kinase and methylation assays.

RESULTS

Histopathological investigation revealed that the expression of coronin 2A in colon tumour cells is up-regulated during the adenoma-adenocarcinoma progression. At the subcellular level, coronin 2A localised to multiple compartments, i.e. F-actin stress fibres, the front of lamellipodia, focal adhesions, and the nuclei. Over-expression of coronin 2A led to a reduction of F-actin stress fibres and elevated cell migration velocity. We identified two novel direct coronin 2A interaction partners. The interaction of coronin 2A with MAPK14 (mitogen activated protein kinase 14 or MAP kinase p38α) led to phosphorylation of coronin 2A and also to activation of the MAPK14 pathway. Moreover, coronin 2A interacted with PRMT5 (protein arginine N-methyltransferase 5), which modulates the sensitivity of tumour cells to TRAIL-induced cell death.

CONCLUSIONS

We show that increased expression of coronin 2A is associated with the malignant phenotype of human colon carcinoma. Moreover, we linked coronin 2A to MAPK14 and PRMT5 signalling pathways involved in tumour progression.

Butein sensitizes HeLa cells to cisplatin through the AKT and ERK/p38 MAPK pathways by targeting FoxO3a

Drug resistance remains a major challenge in cancer therapy. Butein, a polyphenolic compound, has been shown to exhibit anticancer activity through the inhibition of the activation of the protein kinase B (PKB/AKT) and mitogen-activated protein kinase (MAPK) pathways, which are two pathways known to be involved in resistance to cisplatin. Hence, we hypotheiszed that butein may be a chemosensitizer to cisplatin. In the present study, we demonstrated that butein synergistically enhanced the growth inhibitory and apoptosis-inducing effects of cisplatin on HeLa cells. Moreover, the combination of butein and cisplatin led to G1 phase arrest. We then aimed to explore the underlying mechanisms. We found that butein inhibited the activation of AKT, extracellular signal-regulated kinase (ERKs) and p38 kinases in the presence of cisplatin. The use of the AKT inhibitor, LY294002, in combination with cisplatin, induced an increase in apoptosis compared to treatment with cisplatin alone, although this effect was not as prominent as that exerted by butein in combination with cisplatin. Of note, the inhibition of ERK or p38 MAPK by U0126 or SB203580, respectively, decreased the apoptosis induced by cisplatin; however, enhanced apoptotic effects were observed with the use of ERK/p38 MAPK inhibitor in combination with butein. These data suggest that the AKT and ERK/p38 MAPK pathways are involved in the synergistic effects of butein and cisplatin. Furthermore, co-treatment with butein and cisplatin promoted the nuclear translocation and expression of forkhead box O3a (FoxO3 or FoxO3a). FoxO3a may be the key molecule on which these pathways converge and is thus implicated in the synergistic effects of butein and cisplatin. This was further confirmed by the RNAi-mediated suppression of FoxO3a. FoxO3a target genes involved in cell cycle progression and apoptosis were also investigated, and combined treatment with butein and cisplatin resulted in the downregulation of cyclin D1 and Bcl-2 and the upregulation of p27 and Bax. In addition, the combination of both agents markedly inhibited tumor growth and increased the expression of FoxO3a in mouse tumor xenograft models of cervical cancer. Taken together, to the best of our knowledge, our results reveal for the first time that butein sensitizes cervical cancer cells to cisplatin in vitro and in vivo, and these effects of butien may be related to the inhibition of the activation of the AKT and ERK/p38 MAPK pathways by targeting FoxO3a.

Curcumol Inhibits Growth and Induces Apoptosis of Colorectal Cancer LoVo Cell Line via IGF-1R and p38 MAPK Pathway

Curcumol, isolated from the traditional medical plant Rhizoma Curcumae, is the bioactive component of Zedoary oil, whose potential anti-tumor effect has attracted considerable attention in recent years. Though many researchers have reported curcumol and its bioactivity, the potential molecular mechanism for its anti-cancer effect in colorectal cancer LoVo cells still remains unclear. In the present study, we found that curcumol showed growth inhibition and induced apoptosis of LoVo cells in a dose- and time-dependent manner. The occurrence of its proliferation inhibition and apoptosis came with suppression of IGF-1R expression, and then increased the phosphorylation of p38 mitogen activated protein kinase (MAPK), which might result in a cascade response by inhibiting the CREB survival pathway and finally triggered Bax/Bcl-2 and poly(ADP-ribose) polymerase 1 (PARP-1) apoptosis signals. Moreover, curcumol inhibited colorectal cancer in xenograft models of nude mice. Immunohistochemical and Western blot analysis revealed that curcumol could decrease the expression of ki-67, Bcl-2 as well as CREB1, and increase the expression of Bax and the phosphorylation of p38, which were consistent with our in vitro study. Overall, our in vitro and in vivo data confirmed the anti-cancer activity of curcumol, which was related to a significant inhibition of IGF-1R and activation of p38 MAPKs, indicating that curcumol may be a potential anti-tumor agent for colorectal carcinoma therapy.

Ataxia-telangiectasia mutated (ATM) participates in the regulation of ionizing radiation-induced cell death via MAPK14 in lung cancer H1299 cells

OBJECTIVES

The role of Ataxia-telangiectasia mutated (ATM) in response to DNA damage has previously been studied, but its underlying mechanisms specific to ionizing radiation (IR) have remained to be elucidated. In this study, function of ATM on radiation-induced cell death in lung cancer H1299 cells was analysed.

MATERIALS AND METHODS

Human lung cancer cells, H1299, were used, and cell models with ATM(-/-) and MAPK14(-/-) were established by genetic engineering. Radiosensitivity was analysed using colony formation assays. Western blotting and co-immunoprecipitation were implemented to detect protein expression and interaction. MDC staining and GFP-LC3 relocalization were used to detect autophagy.

RESULTS

Autophagy as well as phosphorylation of ATM was activated by ionizing radiation. Both the inhibitor of ATM, KU55933 and ATM silencing reduced phosphorylation of ATM and MAPKAPK2 expression. Both ATM(-/-) and MAPK14(-/-) cells displayed hypersensitivity. IR increased autophagy level by more than 129% in DMSO-treated cells, while only by 47% and 27% in KU55933-treated and ATM(-/-) cells respectively. MAPK14 knock-down alone gave rise to the basal autophagy level, but decreased notably after IR. KU55933 and ATM knock-down inhibited IR-induced autophagy by activating mTOR pathways. Both Beclin1-PI3KIII and Beclin1-MAPKAPK2 interactions as were remarkably affected by silencing either ATM or MAPK14.

CONCLUSIONS

ATM promoted IR-induced autophagy via the MAPK14 pathway, mTOR pathway and Beclin1/PI3KIII complexes. MAPK14 contributed to radiosensitization of H1299 cells.

Macrophage migration inhibitory factor confers resistance to senescence through CD74-dependent AMPK-FOXO3a signaling in mesenchymal stem cells

Introduction

Mesenchymal stem cells (MSCs)-based therapies have had positive outcomes in animal models of cardiovascular diseases. However, the number and function of MSCs decline with age, reducing their ability to contribute to endogenous injury repair. The potential of stem cells to restore damaged tissue in older individuals can be improved by specific pretreatment aimed at delaying senescence and improving their regenerative properties. Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that modulates age-related signaling pathways, and hence is a good candidate for rejuvenative function.

Methods

Bone marrow-derived mesenchymal stem cells (BM-MSCs) were isolated from young (6-month-old) or aged (24-month-old) male donor rats. Cell proliferation was measured using the CCK8 cell proliferation assay; secretion of VEGF, bFGF, HGF, and IGF was assessed by RT-qPCR and ELISA. Apoptosis was induced by hypoxia and serum deprivation (hypoxia/SD) for up to 6 hr, and examined by flow cytometry. Expression levels of AMP-activated protein kinase (AMPK) and forkhead box class O 3a (FOXO3a) were detected by Western blotting. CD74 expression was assayed using RT-qPCR, Western blotting, and immunofluorescence.

Results

In this study, we found that MSCs isolated from the bone marrow of aged rats displayed reduced proliferative capacity, impaired ability to mediate paracrine signaling, and lower resistance to hypoxia/serum deprivation-induced apoptosis, when compared to younger MSCs. Interestingly, pretreatment of aged MSCs with MIF enhanced their growth, paracrine function and survival. We detected enhanced secretion of VEGF, bFGF, HGF, and IGF from MIF-treated MSCs using ELISA. Finally, we show that hypoxia/serum deprivation-induced apoptosis is inhibited in aged MSCs following MIF exposure. Next, we found that the mechanism underlying the rejuvenating function of MIF involves increased CD74-dependent phosphorylation of AMPK and FOXO3a. Furthermore, this effect was abolished when CD74, AMPK, or FOXO3a expression was silenced using small-interfering RNAs(siRNA).

Conclusions

MIF can rejuvenate MSCs from a state of age-induced senescence by interacting with CD74 and subsequently activating AMPK-FOXO3a signaling pathways. Pretreatment of MSCs with MIF may have important therapeutic implications in restoration or rejuvenation of endogenous bone marrow-MSCs in aged individuals.

Roles of p38α mitogen-activated protein kinase in mouse models of inflammatory diseases and cancer

The p38α mitogen‐activated protein kinase pathway not only regulates the production of inflammatory mediators, but also controls processes related to tissue homeostasis, such as cell proliferation, differentiation and survival, which are often disrupted during malignant transformation. The versatility of this signaling pathway allows for the regulation of many specific functions depending on the cell type and context. Here, we discuss mouse models that have been used to identify in vivo functions of p38α signaling in the pathogenesis of inflammatory diseases and cancer. Experiments using genetically modified mice and pharmacological inhibitors support that targeting the p38α pathway could be therapeutically useful for some inflammatory diseases and tumor types.

The problem of pyridinyl imidazole class inhibitors of MAPK14/p38α and MAPK11/p38β in autophagy research

In addition to its established role in inflammation, the stress-activated p38 MAP kinase pathway plays major roles in the regulation of cell cycle, senescence, and autophagy. Robust studies could establish mechanistic links between MAPK11-MAPK14/p38 signaling and macroautophagy converging at ATG9-trafficking and BECN1 phosphorylation. However, several reports seem to monitor MAPK11-MAPK14/p38-dependence of autophagy exclusively by the use of the SB203580/SB202190 class of MAPK14/MAPK11/p38α/β inhibitors. In this "Letter to the editor" we present data to support our claim that these inhibitors interfere with autophagic flux in a MAPK11-MAPK14/p38-independent manner and hence should no longer be used as pharmacological tools in the analysis of MAPK11-MAPK14/p38-dependence of autophagy. We propose a general guideline from Autophagy with regard to this issue to avoid such misinterpretations in the future.

Forkhead box protein O3 transcription factor negatively regulates autophagy in human cancer cells by inhibiting forkhead box protein O1 expression and cytosolic accumulation

FoxO proteins are important regulators in cellular metabolism and are recognized to be nodes in multiple signaling pathways, most notably those involving PI3K/AKT and mTOR. FoxO proteins primarily function as transcription factors, but recent study suggests that cytosolic FoxO1 participates in the regulation of autophagy. In the current study, we find that cytosolic FoxO1 indeed stimulates cellular autophagy in multiple cancer cell lines, and that it regulates not only basal autophagy but also that induced by rapamycin and that in response to nutrient deprivation. These findings illustrate the importance of FoxO1 in cell metabolism regulation independent of its transcription factor function. In contrast to FoxO1, we find the closely related FoxO3a is a negative regulator of autophagy in multiple cancer cell lines, a previously unrecognized function for this protein, different from its function in benign fibroblast and muscle cells. The induction of autophagy by the knockdown of FoxO3a was found not to be mediated through the suppression of mTORC1 signaling; rather, the regulatory role of FoxO3a on autophagy was determined to be through its ability to transcriptionally suppress FoxO1. This complicated interplay of FoxO1 and FoxO3a suggests a complex checks- and balances-relationship between FoxO3a and FoxO1 in regulating autophagy and cell metabolism.

Metformin reduces the Walker-256 tumor development in obese-MSG rats via AMPK and FOXO3a

AIMS

Studies have associated obesity with a wide variety of cancers. Metformin, an anti-diabetic drug, has recently received attention as a potentially useful therapeutic agent for treating cancer. Therefore, the objective of this study was to analyze the mechanisms involved in the increase in tumor development and the reduction of it by metformin in obesity using an experimental breast tumor model.

MATERIAL AND METHODS

Newborn male Wistar rats were subcutaneously injected with 400mg/kg monosodium glutamate (MSG) (obese) or saline (control) at 2, 3, 4, 5 and 6 days of age. After 16 weeks, 1 × 10(7) Walker-256 tumor cells were subcutaneously injected in the right flank of the rats and concomitantly the treatment with metformin 300 mg/kg/15 days, via gavage, started. The rats were divided into 4 groups: control tumor (CT), control tumor metformin (CTM), obese-MSG tumor (OT) and obese-MSG tumor metformin (OTM). On the 18th week the tumor development and metformin effect were analyzed.

KEY FINDINGS

Tumor development was higher in OT rats compared with CT rats. Activation of insulin-IR-ERK1/2 pathway and an anti-apoptotic effect might be the mechanisms involved in the higher development of tumor in obesity. The effect of metformin reducing the tumor development in obese rats might involve increased mRNA expression of pRb and p27, increased activity of AMPK and FOXO3a and decreased expression of p-ERK1/2 (Thr202/Tyr204) in Walker-256 tumor.

SIGNIFICANCE

Our data allow us to suggest that metformin, reducing the stimulatory effect of obesity on tumor development, has a potential role in the management of cancers.

The role of TLR8 signaling in acute myeloid leukemia differentiation

Acute myeloid leukemia (AML) is an aggressive disease with a poor 5-year survival of 21% that is characterized by a differentiation arrest of immature myeloid cells. For a rare subtype of AML (acute promyeloctyic leukemia, 5-10% of cases) all-trans retinoic acid therapy removes the differentiation block, yielding over a 90% cure rate. However, this treatment is not effective for the other 90-95% of AML patients, suggesting new differentiation strategies are needed. Interestingly, differentiation is induced in normal hematopoietic cells through Toll-like receptor (TLR) stimulation and TLRs are expressed on AML cells. We present evidence that the TLR8 activation promotes AML differentiation and growth inhibition in a TLR8/MyD88/p38 dependent manner. We also show that that TLR7/TLR8 agonist, R848, considerably impairs the growth of human AML cells in immunodeficient mice. Our data suggests TLR8 activation has direct anti-leukemic effects independent of its immunomodulating properties that are currently under investigation for cancer therapy. Taken together, our results suggest that treatment with TLR8 agonists may be a promising new therapeutic strategy for AML.

p38α MAPK pathway: A key factor in colorectal cancer therapy and chemoresistance

Colorectal cancer (CRC) remains one of the most common malignancies in the world. Although surgical resection combined with adjuvant therapy is effective at the early stages of the disease, resistance to conventional therapies is frequently observed in advanced stages, where treatments become ineffective. Resistance to cisplatin, irinotecan and 5-fluorouracil chemotherapy has been shown to involve mitogen-activated protein kinase (MAPK) signaling and recent studies identified p38α MAPK as a mediator of resistance to various agents in CRC patients. Studies published in the last decade showed a dual role for the p38α pathway in mammals. Its role as a negative regulator of proliferation has been reported in both normal (including cardiomyocytes, hepatocytes, fibroblasts, hematopoietic and lung cells) and cancer cells (colon, prostate, breast, lung tumor cells). This function is mediated by the negative regulation of cell cycle progression and the transduction of some apoptotic stimuli. However, despite its anti-proliferative and tumor suppressor activity in some tissues, the p38α pathway may also acquire an oncogenic role involving cancer related-processes such as cell metabolism, invasion, inflammation and angiogenesis. In this review, we summarize current knowledge about the predominant role of the p38α MAPK pathway in CRC development and chemoresistance. In our view, this might help establish the therapeutic potential of the targeted manipulation of this pathway in clinical settings.

Therapeutic targeting of autophagy in cancer. Part I: molecular pathways controlling autophagy

Autophagy is a process in which cells can generate energy and building materials, by degradation of redundant and/or damaged organelles and proteins. Especially during conditions of stress, autophagy helps to maintain homeostasis. In addition, autophagy has been shown to influence malignant transformation and cancer progression. The precise molecular events in autophagy are complex and the core autophagic machinery described to date consists of nearly thirty proteins. Apart from these factors that execute the process of autophagy, several signalling pathways are involved in converting internal and external stimuli into an autophagic response. In this review we provide an overview of the signalling pathways that influence autophagy, particularly in cancer cells. We will illustrate that interference with multiple of these signalling pathways can have significant effects on cancer cell survival.

Metformin induces apoptosis and cell cycle arrest mediated by oxidative stress, AMPK and FOXO3a in MCF-7 breast cancer cells

Recent studies have demonstrated that the anti-diabetic drug, metformin, can exhibit direct antitumoral effects, or can indirectly decrease tumor proliferation by improving insulin sensitivity. Despite these recent advances, the underlying molecular mechanisms involved in decreasing tumor formation are not well understood. In this study, we examined the antiproliferative role and mechanism of action of metformin in MCF-7 cancer cells treated with 10 mM of metformin for 24, 48, and 72 hours. Using BrdU and the MTT assay, it was found that metformin demonstrated an antiproliferative effect in MCF-7 cells that occurred in a time- and concentration- dependent manner. Flow cytometry was used to analyze markers of cell cycle, apoptosis, necrosis and oxidative stress. Exposure to metformin induced cell cycle arrest in G₀-G₁ phase and increased cell apoptosis and necrosis, which were associated with increased oxidative stress. Gene and protein expression were determined in MCF-7 cells by real time RT-PCR and western blotting, respectively. In MCF-7 cells metformin decreased the activation of IRβ, Akt and ERK1/2, increased p-AMPK, FOXO3a, p27, Bax and cleaved caspase-3, and decreased phosphorylation of p70S6K and Bcl-2 protein expression. Co-treatment with metformin and H₂O₂ increased oxidative stress which was associated with reduced cell number. In the presence of metformin, treating with SOD and catalase improved cell viability. Treatment with metformin resulted in an increase in p-p38 MAPK, catalase, MnSOD and Cu/Zn SOD protein expression. These results show that metformin has an antiproliferative effect associated with cell cycle arrest and apoptosis, which is mediated by oxidative stress, as well as AMPK and FOXO3a activation. Our study further reinforces the potential benefit of metformin in cancer treatment and provides novel mechanistic insight into its antiproliferative role.

Dual function of p38α MAPK in colon cancer: suppression of colitis-associated tumor initiation but requirement for cancer cell survival

Colorectal cancer is frequently associated with chronic inflammation, with the intestinal epithelial barrier playing an important protective role against the infections and injuries that cause colitis. The p38α pathway regulates inflammatory responses but can also suppress tumor initiation in epithelial cells. We have found that p38α signaling has a dual function in colorectal tumorigenesis. On one side, p38α protects intestinal epithelial cells against colitis-associated colon cancer by regulating intestinal epithelial barrier function. Accordingly, p38α downregulation results in enhanced colitis-induced epithelial damage and inflammation, which potentiates colon tumor formation. Surprisingly, inhibition of p38α in transformed colon epithelial cells reduces tumor burden. Thus, p38α suppresses inflammation-associated epithelial damage and tumorigenesis but contributes to the proliferation and survival of tumor cells.

Cell differentiation versus cell death: extracellular glucose is a key determinant of cell fate following oxidative stress exposure

Cells, particularly mechano-sensitive musculoskeletal cells such as tenocytes, routinely encounter oxidative stress. Oxidative stress can not only stimulate tissue repair, but also cause damage leading to tissue degeneration. As diabetes is associated with increased oxidative damage as well as increased risk of tendon degeneration, the aim of this study was to determine if extracellular glucose levels alter the response of tendon cells to oxidative stress. Primary human tenocytes were cultured in either high (17.5 mM) or low (5 mM) glucose and treated with 100 μM hydrogen peroxide. In low glucose, peroxide-treated cells remained fully viable and collagen synthesis was increased, suggesting an anabolic response. In high glucose, however, peroxide treatment led to increased bim-mediated apoptosis. The activities of both forkhead box O (FOXO1) and p53 were required for upregulation of bim RNA expression in high glucose. We found that both p53-mediated inhibition of the bim repressor micro RNA (miR17-92) and FOXO1-mediated upregulation of bim transcription were required to permit accumulation of bim RNA. High glucose coupled with oxidative stress resulted in upregulation of miR28-5p, which directly inhibited expression of the p53 deacetylase sirtuin 3, resulting in increased levels of acetylated p53. In peroxide-treated cells in both high and low glucose, protein levels of acetylated FOXO1 as well as HIF1α (hypoxia-inducible factor 1α) were increased. However, under low-glucose conditions, peroxide treatment resulted in activation of p38, which inhibited FOXO1-mediated but promoted HIF1α-mediated transcriptional activity. In low glucose, HIF1α upregulated expression of sox9 and scleraxis, two critical transcription factors involved in establishing the tenocyte phenotype, and increased collagen synthesis. The switch from FOXO1-mediated (proapoptosis) to HIF1α-mediated (prodifferentiation) transcription occurred at an extracellular glucose concentration of 7 mM, a concentration equivalent to the maximum normal blood glucose concentration. Extracellular glucose has a profound effect on the cellular response to oxidative stress. A level of oxidative stress normally anabolic may be pathological in high glucose.

p38 and JNK MAPK pathways control the balance of apoptosis and autophagy in response to chemotherapeutic agents

The Mitogen Activated Protein Kinase (MAPK) signaling plays a critical role in the outcome and the sensitivity to anticancer therapies. Activated MAPK can transmit extracellular signals to regulate cell growth, proliferation, differentiation, migration, apoptosis and so on. Apoptosis as well as macroautophagy (hereafter referred to as autophagy) can be induced by extracellular stimuli such the treatment of chemotherapeutic agents, resulting in different cell response to these drugs. However, the molecular mechanisms mediating these two cellular processes remain largely unknown. Recently, several studies provide new insights into p38 and JNK MAPK pathways function in the control of the balance of autophagy and apoptosis in response to genotoxic stress. Our increased understanding of the role of p38 and JNK MAPK pathways in regulating the balance of autophagy and apoptosis will hopefully provide prospective strategies for cancer therapy.

Targeted therapy against chemoresistant colorectal cancers: Inhibition of p38α modulates the effect of cisplatin in vitro and in vivo through the tumor suppressor FoxO3A

Chemoresistance is a major obstacle to effective therapy against colorectal cancer (CRC) and may lead to deadly consequences. The metabolism of CRC cells depends highly on the p38 MAPK pathway, whose involvement in maintaining a chemoresistant behavior is currently being investigated. Our previous studies revealed that p38α is the main p38 isoform in CRC cells. Here we show that p38α pharmacological inhibition combined with cisplatin administration decreases colony formation and viability of cancer cells and strongly increases Bax-dependent apoptotic cell death by activating the tumor suppressor protein FoxO3A. Our results indicate that FoxO3A activation up-regulates transcription of its target genes (p21, PTEN, Bim and GADD45), which forces both chemosensitive and chemoresistant CRC cells to undergo apoptosis. Additionally, we found that FoxO3A is required for apoptotic cell death induction, as confirmed by RNA interference experiments. In animal models xenografted with chemoresistant HT29 cells, we further confirmed that the p38-targeted dual therapy strategy produced an increase in apoptosis in cancer tissue leading to tumor regression. Our study uncovers a major role for the p38-FoxO3A axis in chemoresistance, thereby suggesting a new therapeutic approach for CRC treatment; moreover, our results indicate that Bax status may be used as a predictive biomarker.

Forkhead box class O transcription factors in liver function and disease

The forkhead box transcription factor class O (FOXO) family represents a group of transcription factors that is required for a number of stress-related transcriptional programs including antioxidant response, gluconeogenesis, cell cycle control, apoptosis, and autophagy. The liver utilizes several FOXO-dependent pathways to adapt to its routine cycles of feeding and fasting and to respond to the stresses induced by disease. FOXO1 is a direct transcriptional regulator of gluconeogenesis, reciprocally regulated by insulin, and has profound effects on hepatic lipid metabolism. FOXO3 is required for antioxidant responses and autophagy and is altered in hepatitis C infection and fatty liver. Emerging evidence suggests dysregulation of FOXO3 in some hepatocellular carcinomas. FOXOs are notable for the extensive number of functionally significant posttranslational modifications that they undergo. Recent advances in our understanding how FOXOs are regulated are providing a more detailed picture of how specific combinations of posttranslational modifications alter both nuclear translocation as well as transcriptional specificity under different conditions. This review summarizes emerging knowledge of FOXO function in the liver, FOXO changes in liver disease, and the posttranslational modifications responsible for these effects.

Interferon-β gene-modified human bone marrow mesenchymal stem cells attenuate hepatocellular carcinoma through inhibiting AKT/FOXO3a pathway

OBJECTIVE

This study aims to investigate the using of bone marrow mesenchymal stem cells (BMSCs) genetically engineered to produce interferon-β (IFN-β) as a gene delivery system to treat hepatocellular carcinoma (HCC) in vitro and in vivo.

METHODS

To measure the effects on tumour cell growth in vitro, IFN-β-producing BMSCs (BMSC/IFN-β) were co-cultured with the HCC cell line HepG2 and Huh7. Enzyme-linked immunosorbent assay (ELISA) was used to detect the IFN-β secretion in the BMSC culture condition medium (CM). The effect of BMSC/IFN-β on HCC cells proliferation was examined both in vitro and in vivo by using MTT, colony formation assay, BrdU staining, cell cycle analysis, and xenografted NOD/SCID mouse tumour model. To examine the impact of BMSC/IFN-β on the AKT/FOXO3a signalling, RT-PCR and western blotting were performed.

RESULTS

The BMSC/IFN-β cells can stably secrete high levels of IFN-β. Both MTT and colony forming assay showed that HCC cells had a lower growth rate when cultured in BMSC/IFN-β-CM as compared with that in BMSC/vector-CM or DMEM culture group. Co-culture with BMSC/IFN-β-CM dramatically decreased the percentages of cells with incorporated BrdUrd. In BMSC/IFN-β-CM-treated HCC cells, the proportion of G1-phase cells increased but it decreased in the S phase of the cell. The BMSC/IFN-β inhibited HCC growth in NOD/SCID mice and proved the survival period of these mice. Compared with the control group, p21 and p27 expression of hepatoma cells increased, whereas cyclin D1 and phosphorylation of Rb expression decreased when co-cultured with BMSC/IFN-β-CM. It was associated with suppression of Akt activity and enhanced transcriptional activity of FOXO3a.

CONCLUSION

The IFN-β gene-modified BMSCs can effectively inhibit the proliferation of HCC cells in vitro and in vivo through inhibiting AKT/FOXO3a pathway. These results indicate that BMSC/IFN-β are a powerful anticancer cytotherapeutic tool for HCC.

A novel AMPK-dependent FoxO3A-SIRT3 intramitochondrial complex sensing glucose levels

Reduction of nutrient intake without malnutrition positively influences lifespan and healthspan from yeast to mice and exerts some beneficial effects also in humans. The AMPK-FoxO axis is one of the evolutionarily conserved nutrient-sensing pathways, and the FOXO3A locus is associated with human longevity. Interestingly, FoxO3A has been reported to be also a mitochondrial protein in mammalian cells and tissues. Here we report that glucose restriction triggers FoxO3A accumulation into mitochondria of fibroblasts and skeletal myotubes in an AMPK-dependent manner. A low-glucose regimen induces the formation of a protein complex containing FoxO3A, SIRT3, and mitochondrial RNA polymerase (mtRNAPol) at mitochondrial DNA-regulatory regions causing activation of the mitochondrial genome and a subsequent increase in mitochondrial respiration. Consistently, mitochondrial transcription increases in skeletal muscle of fasted mice, with a mitochondrial DNA-bound FoxO3A/SIRT3/mtRNAPol complex detectable also in vivo. Our results unveil a mitochondrial arm of the AMPK-FoxO3A axis acting as a recovery mechanism to sustain energy metabolism upon nutrient restriction.

Resistance to hypoxia-induced necroptosis is conferred by glycolytic pyruvate scavenging of mitochondrial superoxide in colorectal cancer cells

Cancer cells may survive under oxygen and nutrient deprivation by metabolic reprogramming for high levels of anaerobic glycolysis, which contributes to tumor growth and drug resistance. Abnormally expressed glucose transporters (GLUTs) are colocalized with hypoxia (Hx) inducible factor (HIF)1α in peri-necrotic regions in human colorectal carcinoma. However, the underlying mechanisms of anti-necrotic resistance conferred by glucose metabolism in hypoxic cancer cells remain poorly understood. Our aim was to investigate signaling pathways of Hx-induced necroptosis and explore the role of glucose pyruvate metabolite in mechanisms of death resistance. Human colorectal carcinoma cells were Hx exposed with or without glucose, and cell necroptosis was examined by receptor-interacting protein (RIP)1/3 kinase immunoprecipitation and (32)P kinase assays. Our results showed increased RIP1/3 complex formation and phosphorylation in hypoxic, but not normoxic cells in glucose-free media. Blocking RIP1 signaling, by necrostatin-1 or gene silencing, decreased lactodehydrogenase (LDH) leakage and plasma membrane disintegration. Generation of mitochondrial superoxide was noted after hypoxic challenge; its reduction by antioxidants inhibited RIP signaling and cell necrosis. Supplementation of glucose diminished the RIP-dependent LDH leakage and morphological damage in hypoxic cells, whereas non-metabolizable sugar analogs did not. Hypoxic cells given glucose showed nuclear translocation of HIF1α associated with upregulation of GLUT-1 and GLUT-4 expression, as well as increase of intracellular ATP, pyruvate and lactate levels. The glucose-mediated death resistance was ablated by iodoacetate (an inhibitor to glyceraldehyde-3-phosphate dehydrogenase), but not by UK5099 (an inhibitor to mitochondrial pyruvate carrier), suggesting that glycolytic pathway was involved in anti-necrotic mechanism. Lastly, replacing glucose with cell-permeable pyruvate derivative also led to decrease of Hx-induced necroptosis by suppression of mitochondrial superoxide in an energy-independent manner. In conclusion, glycolytic metabolism confers resistance to RIP-dependent necroptosis in hypoxic cancer cells partly through pyruvate scavenging of mitochondrial free radicals.

Posttranslational modification and quality control

Protein quality control functions to minimize the level and toxicity of misfolded proteins in the cell. Protein quality control is performed by intricate collaboration among chaperones and target protein degradation. The latter is performed primarily by the ubiquitin-proteasome system and perhaps autophagy. Terminally misfolded proteins that are not timely removed tend to form aggregates. Their clearance requires macroautophagy. Macroautophagy serves in intracellular quality control also by selectively segregating defective organelles (eg, mitochondria) and targeting them for degradation by the lysosome. Inadequate protein quality control is observed in a large subset of failing human hearts with a variety of causes, and its pathogenic role has been experimentally demonstrated. Multiple posttranslational modifications can occur to substrate proteins and protein quality control machineries, promoting or hindering the removal of the misfolded proteins. This article highlights recent advances in posttranslational modification-mediated regulation of intracellular quality control mechanisms and its known involvement in cardiac pathology.

The FOX transcription factor Hcm1 regulates oxidative metabolism in response to early nutrient limitation in yeast. Role of Snf1 and Tor1/Sch9 kinases

Within Saccharomyces cerevisiae, Hcm1is a member of the forkhead transcription factor family with a role in chromosome organization. Our group recently described its involvement in mitochondrial biogenesis and stress resistance, and reports here that Hcm1 played a role in adaptation to respiratory metabolism when glucose or nitrogen was decreased. Regulation of Hcm1 activity occurs in at least three ways: i) protein quantity, ii) subcellular localization, and iii) transcriptional activity. Transcriptional activity was measured using a reporter gene fused to a promoter that contains a binding site for Hcm1. We also analyzed the levels of several genes whose expression is known to be regulated by Hcm1 levels and the role of the main kinases known to respond to nutrients. Lack of sucrose-nonfermenting (Snf1) kinase increases cytoplasmic localization of Hcm1, whereas Δtor1 cells showed a mild increase in nuclear Hcm1. In vitro experiments showed that Snf1 clearly phosphorylates Hcm1 while Sch9 exerts a milder phosphorylation. Although in vitroTor1 does not directly phosphorylate Hcm1, in vivo rapamycin treatment increases nuclear Hcm1. We conclude that Hcm1 participates in the adaptation of cells from fermentation to respiratory metabolism during nutrient scarcity. According to our hypothesis, when nutrient levels decrease, Snf1 phosphorylates Hcm1. This results in a shift from the cytoplasm to the nucleus and increased transcriptional activity of genes involved in respiration, use of alternative energy sources, NAD synthesis and oxidative stress resistance.

PTEN-regulated AKT/FoxO3a/Bim signaling contributes to reactive oxygen species-mediated apoptosis in selenite-treated colorectal cancer cells

Mounting evidence shows that selenium possesses chemotherapeutic potential against tumor cells, including leukemia, prostate cancer and colorectal cancer (CRC) cells. However, the detailed mechanism by which sodium selenite specifically kills tumor cells remains unclear. Herein, we demonstrated that supranutritional doses of selenite-induced apoptosis in CRC cells through reactive oxygen species (ROS)-dependent modulation of the PI3K/AKT/FoxO3a signaling pathway. First, we found that selenite treatment in HCT116 and SW480 CRC cells caused inhibition of AKT and the nuclear accumulation of FoxO3a by western blot and immunofluorescence analyses, respectively, thereby facilitating transcription of the target genes bim and PTEN. Modulation of the AKT/FoxO3a/Bim signaling pathway by chemical inhibitors or RNA interference revealed that these events were critical for selenite-induced apoptosis in CRC cells. Additionally, we discovered that FoxO3a-mediated upregulation of PTEN exerted a further inhibitory effect on the AKT survival pathway. We also corroborated our findings in vivo by performing immunohistochemistry experiments. In summary, our results show that selenite could induce ROS-dependent FoxO3a-mediated apoptosis in CRC cells and xenograft tumors through PTEN-mediated inhibition of the PI3K/AKT survival axis. These results help to elucidate the molecular mechanisms underlying selenite-induced cell death in tumor cells and provide a theoretical basis for translational applications of selenium.

Modulating autophagy: a strategy for cancer therapy

Autophagy is a process in which long-lived proteins, damaged cell organelles, and other cellular particles are sequestered and degraded. This process is important for maintaining the cellular microenvironment when the cell is under stress. Many studies have shown that autophagy plays a complex role in human diseases, especially in cancer, where it is known to have paradoxical effects. Namely, autophagy provides the energy for metabolism and tumor growth and leads to cell death that promotes tumor suppression. The link between autophagy and cancer is also evident in that some of the genes that regulate Carcinogenesis, oncogenes and tumor suppressor genes, participate in or impact the autophagy process. Therefore, modulating autophagy will be a valuable topic for cancer therapy. Many studies have shown that autophagy can inhibit the tumor growth when autophagy modulators are combined with radiotherapy and/or chemotherapy. These findings suggest that autophagy may be a potent target for cancer therapy.

The autophagy-related gene 14 (Atg14) is regulated by forkhead box O transcription factors and circadian rhythms and plays a critical role in hepatic autophagy and lipid metabolism

Autophagy plays a critical role in cell survival from prolonged starvation and recycling of aggregated proteins and damaged organelles. One of the essential genes involved in the autophagic initiation is autophagy-related 14 (Atg14), also called Barkor for Beclin 1-associated autophagy-related key regulator. Although its crucial role in the autophagic process has been reported, the gene regulation of Atg14 and its metabolic functions remain unclear. In this work we have identified that the Atg14 gene is regulated by forkhead box O (FoxO) transcription factors and circadian rhythms in the mouse liver. Luciferase reporter analyses and chromatin immunoprecipitation assays have revealed well conserved cis-elements for FoxOs and Clock/Bmal1 in the proximal promoter of the Atg14 gene. To examine the functions of hepatic Atg14, we have performed the gene knockdown and overexpression in the mouse livers. Remarkably, knockdown of Atg14 leads to elevated levels of triglycerides in the liver and serum as well. Conversely, overexpression of Atg14 improves hypertriglyceridemia in both high fat diet-treated wild-type mice and FoxO1/3/4 liver-specific knock-out mice. In summary, our data suggest that Atg14 is a new target gene of FoxOs and the core clock machinery, and this gene plays an important role in hepatic lipid metabolism.

Sorafenib inhibits p38α activity in colorectal cancer cells and synergizes with the DFG-in inhibitor SB202190 to increase apoptotic response

In the search for new strategies to efficiently fight colorectal cancer, efforts are being increasingly focused on targeting regulatory signaling pathways involved in cancer-specific features. As a result, several studies have recently addressed the therapeutic potential of molecularly-targeted drugs capable of inhibiting the activity of protein kinases involved in relevant signaling cascades. Here we show that simultaneous inhibition of the DFG-in and DFG-out conformations of p38α by means of type-I and type-II inhibitors is beneficial to impair more efficiently its kinase activity. Moreover, we found that SB202190 (type-I) and sorafenib (type-II) synergize at the molecular and biological level, as co-treatment with these compounds enhances tumor growth inhibition and induction of apoptosis both in colorectal cancer cell lines and animal models. These results support the need to reconsider sorafenib as a therapeutic agent against colorectal cancer and provide new insights that underline the importance to elucidate the activity of protein kinase inhibitors for the treatment of colorectal carcinoma.

Updates from the Intestinal Front Line: Autophagic Weapons against Inflammation and Cancer

The intestine lies at the interface between the organism and its environment and responds to infection/inflammation in a multi-leveled manner, potentially leading to chronic inflammatory pathologies and cancer formation. Indeed, the immune response at the intestinal epithelium has been found to be involved in the origin and development of colorectal cancer, which is the third most commonly diagnosed neoplastic disease. Among the mechanisms induced upon inflammation, autophagy appears as a defensive strategy for the clearance of invading microbes and intracellular waste components. Autophagy has also been found to play an important role in colorectal cancer, where it seems to have a pro-survival or pro-death function depending on the stage of the neoplastic process. In this paper we discuss the dual role of autophagy in colorectal cancer and review evidence showing that modulation of autophagy affects the immune response and cancer biology. The study of key players involved in autophagy might contribute to the design of new approaches for colorectal cancer, consisting in combined therapies capable of modifying cancer-specific metabolism rather than simply evoking a generic apoptotic and/or autophagic response, thus enhancing the efficacy of currently used drugs and treatments.

FoxOs in neural stem cell fate decision

Neural stem cells (NSCs) persist over the lifespan of mammals to give rise to committed progenitors and their differentiated cells in order to maintain the brain homeostasis. To this end, NSCs must be able to self-renew and otherwise maintain their quiescence. Suppression of aberrant proliferation or undesired differentiation is crucial to preclude either malignant growth or precocious depletion of NSCs. The PI3K-Akt-FoxO signaling pathway plays a central role in the regulation of multiple stem cells including one in the mammalian brain. In particular, members of FoxO family transcription factors are highly expressed in these stem cells. As an important downstream effector of growth, differentiation, and stress stimuli, mammalian FoxO transcription factor family controls cellular proliferation, oxidative stress response, homeostasis, and eventual maintenance of long-term repopulating potential. The review will focus on the current understanding of FoxO function in NSCs as well as discuss their biological activities that contribute to determining neural stem cell fate.

Survival by self-destruction: a role for autophagy in the placenta?

Autophagy is a burgeoning area of research from yeast to humans. Although previously described as a death pathway, autophagy is now considered an important survival phenomenon in response to environmental stressors to which most organs are exposed. Despite an ever expanding literature in non-placental cells, studies of autophagy in the placenta are lagging. We review the regulation of autophagy, summarize available placental studies of autophagy, and highlight potential areas for future research. We believe that such studies will yield novel insights into how placentas protect the survival of the species by "self-eating".

Blocking p38/ERK crosstalk affects colorectal cancer growth by inducing apoptosis in vitro and in preclinical mouse models

We recently demonstrated that p38α is required to maintain colorectal cancer (CRC) metabolism, as its inhibition leads to FoxO3A activation, autophagy, cell death, and tumor growth reduction both in vitro and in vivo. Here we show that inhibition of p38α is followed by TRAIL-mediated activation of caspase-8 and FoxO3A-dependent HER3 upregulation with consequent overactivation of the MEK-ERK1/2 survival pathway. p38α and MEK combined inhibition specifically induces apoptosis by enabling TRAIL signaling propagation through t-Bid and caspase-3, and fosters cell death in CRC cells and preclinical mouse models. Current MEK1-directed pharmacological strategies could thus be exploited, in combination with p38α inhibition, to develop new approaches for CRC treatment.

AMP-activated protein kinase (AMPK) controls the aging process via an integrated signaling network

Efficient control of energy metabolic homeostasis, enhanced stress resistance, and qualified cellular housekeeping are the hallmarks of improved healthspan and extended lifespan. AMPK signaling is involved in the regulation of all these characteristics via an integrated signaling network. Many studies with lower organisms have revealed that increased AMPK activity can extend the lifespan. Experiments in mammals have demonstrated that AMPK controls autophagy through mTOR and ULK1 signaling which augment the quality of cellular housekeeping. Moreover, AMPK-induced stimulation of FoxO/DAF-16, Nrf2/SKN-1, and SIRT1 signaling pathways improves cellular stress resistance. Furthermore, inhibition of NF-κB signaling by AMPK suppresses inflammatory responses. Emerging studies indicate that the responsiveness of AMPK signaling clearly declines with aging. The loss of sensitivity of AMPK activation to cellular stress impairs metabolic regulation, increases oxidative stress and reduces autophagic clearance. These age-related changes activate innate immunity defence, triggering a low-grade inflammation and metabolic disorders. We will review in detail the signaling pathways of this integrated network through which AMPK controls energy metabolism, autophagic degradation and stress resistance and ultimately the aging process.

Guidelines for the use and interpretation of assays for monitoring autophagy

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.

Special Agents Hunting Down Women Silent Killer: The Emerging Role of the p38α Kinase

Ovarian cancer is sensitive to chemotherapy with platinum compounds; however, the therapy success rate is significantly lowered by a high incidence of recurrence and by the acquisition of drug resistance. These negative outcomes mainly depend on altered apoptotic and drug resistance pathways, determining the need for the design of new therapeutic strategies to improve patient survival. This challenge has become even more critical because it has been recognized that hindering uncontrolled cell growth is not sufficient as the only curative approach. In fact, while current therapies are mostly conceived to impair survival of highly proliferating cells, several lines of research are now focusing on cancer-specific features to specifically target malignant cells with the aim of avoiding drug resistance and reducing adverse effects. Recently, great interest has been generated by the identification of metabolic reprogramming mechanisms occurring in cancer cells, such as the increase in glycolysis levels. In this light, pharmacologic manipulation of relevant pathways involved in cancer-specific metabolism and drug resistance could prove an effective approach to treat ovarian cancer patients.

Role and Therapeutic Potential of the Pro-Longevity Factor FOXO and Its Regulators in Neurodegenerative Disease

Studies in simple model organisms have yielded crucial insights into the genetic and molecular aspects of longevity. FOXO, which is most notable for its association with longevity, and its upstream regulators such as sirtuins have received particular attention in translational research because these genes modulate cell survival in several models of neurodegenerative diseases. There is a large amount of knowledge on the pathways that regulate FOXO activity and genes that may be regulated by FOXO. However, for the same reason that the FOXO network is a complex stress response system, its therapeutic potential to develop disease-modifying strategies requires further examination. Although the FOXO network contains druggable genes such as sirtuins and AMPK, whether they should be activated or inhibited and whether protection against the early or late phases of neuronal cell decline might require opposite therapeutic strategies remains unclear. Additionally, the mode of action of small compound molecules believed to act on FOXO network targets was questioned. This review recapitulates essential facts and questions about the promises of FOXO and its interactors in neurodegenerative disease.

Identification of HSP90 as a new GABARAPL1 (GEC1)-interacting protein

GABARAPL1 belongs to the small family of GABARAP proteins (including GABARAP, GABARAPL1 and GABARAPL2/GATE-16), one of the two subfamilies of the yeast Atg8 orthologue. GABARAPL1 is involved in the intracellular transport of receptors, via an interaction with tubulin and GABA(A) or kappa opioid receptors, and also participates in autophagy and cell proliferation. In the present study, we identify the HSP90 protein as a novel interaction partner for GABARAPL1 using GST pull-down, mass spectrometry and coimmunoprecipitation experiments. GABARAPL1 and HSP90 partially colocalize in MCF-7 breast cancer cells overexpressed Dsred-GABARAPL1 and in rat brain. Moreover, treatment of MCF-7 cells overexpressed FLAG-GABARAPL1-6HIS with the HSP90 inhibitor 17-AAG promotes the GABARAPL1 degradation, a process that is blocked by proteasome inhibitors such as MG132, bortezomib and lactacystin. Accordingly, we demonstrate that HSP90 interacts and protects GABARAPL1 from its degradation by the proteasome.

Oncogenic stress induced by acute hyper-activation of Bcr-Abl leads to cell death upon induction of excessive aerobic glycolysis

In response to deregulated oncogene activation, mammalian cells activate disposal programs such as programmed cell death. To investigate the mechanisms behind this oncogenic stress response we used Bcr-Abl over-expressing cells cultivated in presence of imatinib. Imatinib deprivation led to rapid induction of Bcr-Abl activity and over-stimulation of PI3K/Akt-, Ras/MAPK-, and JAK/STAT pathways. This resulted in a delayed necrosis-like cell death starting not before 48 hours after imatinib withdrawal. Cell death was preceded by enhanced glycolysis, glutaminolysis, and amino acid metabolism leading to elevated ATP and protein levels. This enhanced metabolism could be linked to induction of cell death as inhibition of glycolysis or glutaminolysis was sufficient to sustain cell viability. Therefore, these data provide first evidence that metabolic changes induced by Bcr-Abl hyper-activation are important mediators of oncogenic stress-induced cell death.

During the first 30 hours after imatinib deprivation, Bcr-Abl hyper-activation did not affect proliferation but resulted in cellular swelling, vacuolization, and induction of eIF2α phosphorylation, CHOP expression, as well as alternative splicing of XPB, indicating endoplasmic reticulum stress response. Cell death was dependent on p38 and RIP1 signaling, whereas classical death effectors of ER stress, namely CHOP-BIM were antagonized by concomitant up-regulation of Bcl-xL.

Screening of 1,120 compounds for their potential effects on oncogenic stress-induced cell death uncovered that corticosteroids antagonize cell death upon Bcr-Abl hyper-activation by normalizing cellular metabolism. This protective effect is further demonstrated by the finding that corticosteroids rendered lymphocytes permissive to the transforming activity of Bcr-Abl. As corticosteroids are used together with imatinib for treatment of Bcr-Abl positive acute lymphoblastic leukemia these data could have important implications for the design of combination therapy protocols.

In conclusion, excessive induction of Warburg type metabolic alterations can cause cell death. Our data indicate that these metabolic changes are major mediators of oncogenic stress induced by Bcr-Abl.