Involvement of FKHR-dependent TRADD expression in chemotherapeutic drug-induced apoptosis

Sertaconazole provokes proapoptotic autophagy via stabilizing TRADD in nonsmall cell lung cancer cells

Nonsmall cell lung cancer (NSCLC) is one of the most commonly diagnosed and lethal cancers characterized by relatively low overall cure and poor survival rates with great challenge for consistent effective clinical treatment. Here we demonstrated that the antifungal sertaconazole displays potent anti-NSCLC effect by promoting apoptosis in vitro and in vivo. Further studies found that sertaconazole induces complete autophagic flux, which contributes to sertaconazole-induced apoptosis and subsequent growth suppression in NSCLC cells. Further studies demonstrated that sertaconazole provokes TNF receptor type 1 associated death domain protein (TRADD) expression via stabilizing it from ubiquitination-mediated degradation, which results in Akt dephosphorylation and thereby triggers proapoptotic autophagy in NSCLC cells. Moreover, we found that TRADD suppression reverses sertaconazole-induced proapoptotic autophagy and relieves growth suppression, indicating the vital role of TRADD-regulated proapoptotic autophagy in the anti-NSCLC activity of sertaconazole. In summary, our findings suggest that sertaconazole could be a highly promising anti-NSCLC drug by triggering proapoptotic autophagy via stabilizing TRADD, which may provide a new potential therapeutic option for patients with NSCLC.

Signaling Pathways That Control Apoptosis in Prostate Cancer

Prostate cancer is the second most common malignancy and the fifth leading cancer-caused death in men worldwide. Therapies that target the androgen receptor axis induce apoptosis in normal prostates and provide temporary relief for advanced disease, yet prostate cancer that acquired androgen independence (so called castration-resistant prostate cancer, CRPC) invariably progresses to lethal disease. There is accumulating evidence that androgen receptor signaling do not regulate apoptosis and proliferation in prostate epithelial cells in a cell-autonomous fashion. Instead, androgen receptor activation in stroma compartments induces expression of unknown paracrine factors that maintain homeostasis of the prostate epithelium. This paradigm calls for new studies to identify paracrine factors and signaling pathways that control the survival of normal epithelial cells and to determine which apoptosis regulatory molecules are targeted by these pathways. This review summarizes the recent progress in understanding the mechanism of apoptosis induced by androgen ablation in prostate epithelial cells with emphasis on the roles of BCL-2 family proteins and "druggable" signaling pathways that control these proteins. A summary of the clinical trials of inhibitors of anti-apoptotic signaling pathways is also provided. Evidently, better knowledge of the apoptosis regulation in prostate epithelial cells is needed to understand mechanisms of androgen-independence and implement life-extending therapies for CRPC.

Chasing the FOXO3: Insights into Its New Mitochondrial Lair in Colorectal Cancer Landscape

Colorectal cancer (CRC) poses a formidable challenge in terms of molecular heterogeneity, as it involves a variety of cancer-related pathways and molecular changes unique to an individual’s tumor. On the other hand, recent advances in DNA sequencing technologies provide an unprecedented capacity to comprehensively identify the genetic alterations resulting in tumorigenesis, raising the hope that new therapeutic approaches based on molecularly targeted drugs may prevent the occurrence of chemoresistance. Regulation of the transcription factor FOXO3a in response to extracellular cues plays a fundamental role in cellular homeostasis, being part of the molecular machinery that drives cells towards survival or death. Indeed, FOXO3a is controlled by a range of external stimuli, which not only influence its transcriptional activity, but also affect its subcellular localization. These regulation mechanisms are mediated by cancer-related signaling pathways that eventually drive changes in FOXO3a post-translational modifications (e.g., phosphorylation). Recent results showed that FOXO3a is imported into the mitochondria in tumor cells and tissues subjected to metabolic stress and cancer therapeutics, where it induces expression of the mitochondrial genome to support mitochondrial metabolism and cell survival. The current review discusses the potential clinical relevance of multidrug therapies that drive cancer cell fate by regulating critical pathways converging on FOXO3a.

FoxO transcription factors in cancer metabolism

FoxO transcription factors serve as the central regulator of cellular homeostasis and are tumor suppressors in human cancers. Recent studies have revealed that, besides their classic functions in promoting cell death and inducing cell cycle arrest, FoxOs also regulate cancer metabolism, an emerging hallmark of cancer. In this review, we summarize the regulatory mechanisms employed to control FoxO activities in the context of cancer biology, and discuss FoxO function in metabolism reprogramming in cancer and interaction with other key cancer metabolism pathways. A deeper understanding of FoxOs in cancer metabolism may reveal novel therapeutic opportunities in cancer treatment.

Macrovipecetin, a C-type lectin from Macrovipera lebetina venom, inhibits proliferation migration and invasion of SK-MEL-28 human melanoma cells and enhances their sensitivity to cisplatin

BACKGROUND

The resistance of melanoma cells to cisplatin restricts its clinical use. Therefore, the search for novel tumor inhibitors and effective combination treatments that sensitize tumor cells to this drug are still needed. We purified macrovipecetin, a novel heterodimeric C-type lectin, from Macrovipera lebetina snake venom and investigated its anti-tumoral effect on its own or combined with cisplatin, in human melanoma cells.

METHODS

Biochemical characterization, in vitro cells assays such as viability, apoptosis, adhesion, migration, invasion, Western blotting and in silico analysis were used in this study.

RESULTS

Macrovipecetin decreased melanoma cell viability 100 times more than cisplatin. Interestingly, when combined with the drug, macrovipecetin enhanced the sensitivity of SK-MEL-28 cells by augmenting their apoptosis through increased expression of the apoptosis inducing factor (AIF) and activation of ERK_1/2, p38, AKT and NF-κB. Moreover, macrovipecetin alone or combined with cisplatin induced the expression of TRADD, p53, Bax, Bim and Bad and down-regulated the Bcl-2 expression and ROS levels in SK-MEL-28 cells. Interestingly, these treatments impaired SK-MEL-28 cell adhesion, migration and invasion through modulating the function and expression of αvβ3 integrin along with regulating E-cadherin, vimentin, β-catenin, c-Src and RhoA expression. In silico study suggested that only the α chain of macrovipecetin interacts with a region overlapping the RGD motif binding site on this integrin.

CONCLUSIONS

We validated the antitumor effect of macrovipecetin when combined, or not, with cisplatin on SK-MEL-28 cells.

GENERAL SIGNIFICANCE

The presented work proposes the potential use of macrovipecetin and cisplatin in combination as an effective anti-melanoma treatment.

FOXO transcription factors at the interface of metabolism and cancer

Diabetes refers to a group of metabolic diseases characterized by impaired insulin signalling and high blood glucose. A growing body of epidemiological evidence links diabetes to several types of cancer but the underlying molecular mechanisms are poorly understood. The signalling cascade connecting insulin and FOXO proteins provides a compelling example for a conserved pathway at the interface between insulin signalling and cancer. FOXOs are transcription factors that orchestrate programs of gene expression known to control a variety of processes in response to cellular stress. Genes regulated by this family of proteins are involved in the regulation of cellular energy production, oxidative stress resistance and cell viability and proliferation. Accordingly, FOXO factors have been shown to play an important role in the suppression of tumour growth and in the regulation of metabolic homeostasis. There is emerging evidence that deregulation of FOXO factors might account for the association between insulin resistance-related metabolic disorders and cancer.

Sublytic C5b-9 Induces Glomerular Mesangial Cell Apoptosis through the Cascade Pathway of MEKK2-p38 MAPK-IRF-1-TRADD-Caspase 8 in Rat Thy-1 Nephritis

The apoptosis of glomerular mesangial cells (GMCs) in the early phase of rat Thy-1 nephritis (Thy-1N), a model of human mesangioproliferative glomerulonephritis (MsPGN), is primarily triggered by sublytic C5b-9. However, the mechanism of GMC apoptosis induced by sublytic C5b-9 remains unclear. In this study, we demonstrate that expressions of TNFR1-associated death domain-containing protein (TRADD) and IFN regulatory factor-1 (IRF-1) were simultaneously upregulated in the renal tissue of Thy-1N rats (in vivo) and in GMCs under sublytic C5b-9 stimulation (in vitro). In vitro, TRADD was confirmed to be a downstream gene of IRF-1, because IRF-1 could bind to TRADD gene promoter to promote its transcription, leading to caspase 8 activation and GMC apoptosis. Increased phosphorylation of p38 MAPK was verified to contribute to IRF-1 and TRADD production and caspase 8 activation, as well as to GMC apoptosis induced by sublytic C5b-9. Furthermore, phosphorylation of MEK kinase 2 (MEKK2) mediated p38 MAPK activation. More importantly, three sites (Ser^153/164/239) of MEKK2 phosphorylation were identified and demonstrated to be necessary for p38 MAPK activation. In addition, silencing of renal MEKK2, IRF-1, and TRADD genes or inhibition of p38 MAPK activation in vivo had obvious inhibitory effects on GMC apoptosis, secondary proliferation, and urinary protein secretion in rats with Thy-1N. Collectively, these findings indicate that the cascade axis of MEKK2-p38 MAPK-IRF-1-TRADD-caspase 8 may play an important role in GMC apoptosis following exposure to sublytic C5b-9 in rat Thy-1N.

Advances in revealing the molecular targets downstream of oxidative stress-induced proapoptotic kinase signaling in diabetic embryopathy

Preexisting maternal diabetes is a high-risk factor of diabetic embryopathy, such as neural tube defects and congenital heart defects. Maternal diabetes significantly increases the production of reactive oxygen species, resulting in oxidative stress and diabetic embryopathy. Multiple cellular and metabolic factors contribute to these processes. Forkhead box O (FoxO)-3a has been demonstrated as a key transcription factor in the signaling transduction pathways responsible for maternal diabetes-induced birth defects. Apoptosis signal-regulating kinase 1 (ASK1) activated by oxidative stress stimulates nuclear translocation of FoxO3a, resulting in the overexpression of tumor necrosis factor receptor 1-associated death domain protein, which, in turn, leads to caspase-8 activation and apoptosis. Maternal diabetes-activated c-Jun N-terminal kinase (JNK)-1/2, downstream effectors of ASK1, can be blocked by superoxide dismutase-1 overexpression, suggesting that oxidative stress is responsible for JNK1/2 signaling activation. Deletion of JNK1/2 significantly suppressed the activity of FoxO3a. These observations indicate that maternal diabetes-induced oxidative stress stimulates the activation of ASK1, JNK1/2, FoxO3a, tumor necrosis factor receptor 1-associated death domain protein, caspase-8 cleavage, and finally, apoptosis and diabetic embryopathy.

Bithionol inhibits ovarian cancer cell growth in vitro - studies on mechanism(s) of action

Background

Drug resistance is a cause of ovarian cancer recurrence and low overall survival rates. There is a need for more effective treatment approaches because the development of new drug is expensive and time consuming. Alternatively, the concept of ‘drug repurposing’ is promising. We focused on Bithionol (BT), a clinically approved anti-parasitic drug as an anti-ovarian cancer drug. BT has previously been shown to inhibit solid tumor growth in several preclinical cancer models. A better understanding of the anti-tumor effects and mechanism(s) of action of BT in ovarian cancer cells is essential for further exploring its therapeutic potential against ovarian cancer.

Methods

The cytotoxic effects of BT against a panel of ovarian cancer cell lines were determined by Presto Blue cell viability assay. Markers of apoptosis such as caspases 3/7, cPARP induction, nuclear condensation and mitochondrial transmembrane depolarization were assessed using microscopic, FACS and immunoblotting methods. Mechanism(s) of action of BT such as cell cycle arrest, reactive oxygen species (ROS) generation, autotaxin (ATX) inhibition and effects on MAPK and NF-kB signalling were determined by FACS analysis, immunoblotting and colorimetric methods.

Results

BT caused dose dependent cytotoxicity against all ovarian cancer cell lines tested with IC₅₀ values ranging from 19 μM – 60 μM. Cisplatin-resistant variants of A2780 and IGROV-1 have shown almost similar IC₅₀ values compared to their sensitive counterparts. Apoptotic cell death was shown by expression of caspases 3/7, cPARP, loss of mitochondrial potential, nuclear condensation, and up-regulation of p38 and reduced expression of pAkt, pNF-κB, pIκBα, XIAP, bcl-2 and bcl-xl. BT treatment resulted in cell cycle arrest at G1/M phase and increased ROS generation. Treatment with ascorbic acid resulted in partial restoration of cell viability. In addition, dose and time dependent inhibition of ATX was observed.

Conclusions

BT exhibits cytotoxic effects on various ovarian cancer cell lines regardless of their sensitivities to cisplatin. Cell death appears to be via caspases mediated apoptosis. The mechanisms of action appear to be partly via cell cycle arrest, ROS generation and inhibition of ATX. The present study provides preclinical data suggesting a potential therapeutic role for BT against recurrent ovarian cancer.

Critical physiological and pathological functions of Forkhead Box O tumor suppressors

The Forkhead box, subclass O (FOXO) proteins are critical transcription factors, ubiquitously expressed in the human body. These proteins are characterized by a remarkable functional diversity, being involved in cell cycle arrest, apoptosis, oxidative detoxification, DNA damage repair, stem cell maintenance, cell differentiation, cell metabolism, angiogenesis, cardiac development, aging and others. In addition, FOXO have critical implications in both normal and cancer stem cell biology. New strategies to modulate FOXO expression and activity may now be developed since the discovery of novel FOXO regulators and non-coding RNAs (such as microRNAs) targeting FOXO transcription factors. This review focuses on physiological and pathological functions of FOXO proteins and on their action as fine regulators of cell fate and context-dependent cell decisions. A better understanding of the structure and critical functions of FOXO transcription factors and tumor suppressors may contribute to the development of novel therapies for cancer and other diseases.

Maternal hyperglycemia activates an ASK1-FoxO3a-caspase 8 pathway that leads to embryonic neural tube defects

Neural tube defects result from failure to completely close neural tubes during development. Maternal diabetes is a substantial risk factor for neural tube defects, and available evidence suggests that the mechanism that links hyperglycemia to neural tube defects involves oxidative stress and apoptosis. We demonstrated that maternal hyperglycemia correlated with activation of the apoptosis signal-regulating kinase 1 (ASK1) in the developing neural tube, and Ask1 gene deletion was associated with reduced neuroepithelial cell apoptosis and development of neural tube defects. ASK1 activation stimulated the activity of the transcription factor FoxO3a, which increased the abundance of the apoptosis-promoting adaptor protein TRADD, leading to activation of caspase 8. Hyperglycemia-induced apoptosis and the development of neural tube defects were reduced with genetic ablation of either FoxO3a or Casp8 or inhibition of ASK1 by thioredoxin. Examination of human neural tissues affected by neural tube defects revealed increased activation or abundance of ASK1, FoxO3a, TRADD, and caspase 8. Thus, activation of an ASK1-FoxO3a-TRADD-caspase 8 pathway participates in the development of neural tube defects, which could be prevented by inhibiting intermediates in this cascade.

MOZ increases p53 acetylation and premature senescence through its complex formation with PML

Monocytic leukemia zinc finger (MOZ)/KAT6A is a MOZ, Ybf2/Sas3, Sas2, Tip60 (MYST)-type histone acetyltransferase that functions as a coactivator for acute myeloid leukemia 1 protein (AML1)- and Ets family transcription factor PU.1-dependent transcription. We previously reported that MOZ directly interacts with p53 and is essential for p53-dependent selective regulation of p21 expression. We show here that MOZ is an acetyltransferase of p53 at K120 and K382 and colocalizes with p53 in promyelocytic leukemia (PML) nuclear bodies following cellular stress. The MOZ-PML-p53 interaction enhances MOZ-mediated acetylation of p53, and this ternary complex enhances p53-dependent p21 expression. Moreover, we identified an Akt/protein kinase B recognition sequence in the PML-binding domain of MOZ protein. Akt-mediated phosphorylation of MOZ at T369 has a negative effect on complex formation between PML and MOZ. As a result of PML-mediated suppression of Akt, the increased PML-MOZ interaction enhances p21 expression and induces p53-dependent premature senescence upon forced PML expression. Our research demonstrates that MOZ controls p53 acetylation and transcriptional activity via association with PML.

Targeting tumor necrosis factor alpha (TNF-α) in diabetic rats could approve avenues for an efficient strategy for diabetic therapy

BACKGROUND

Several studies held belief that downregulation of TNF-α may be effective for preventing diabetes and it's complications. However, it is not known whether TNF-α downregulation in long-term can generate any biological adverse.

AIM

The aim of the present study was to clarify what the impact is for such treatment with specific antibody for TNF-α on the other biological activities after 4weeks.

METHODS

Using western blot, IHC, Elisa, biochemical assays and scanning electron microscope.

RESULTS

Results show that TNF-α, FOXO-1, IL-6 and MPO, when expressed in diabetic rats, collectively induce dramatic changes in diabetic rats. Since, TNF-α is involved in activation of transcription factor FOXO1 along with oxidative stress mediated by neutrophils. On one hand, IL-6 mediates neutrophils activation leading to an augmentation in stress mediators. And FOXO1 is activated in order to eliminate these oxidative mediators, on the other hand. Data show also that the prominent defect in mucosal IgA and IL-2 secretions may be the leading reasons for digestive atrophy. Finally, Akt-1 inhibits the cleavage of caspase 3, so, it could prevent the incidence of apoptosis.

CONCLUSION

Findings of this study reveal how TNF-α can be mechanistically coupled to greater diabetic complications potential.

Enhanced antiproliferative and apoptotic response of HT-29 adenocarcinoma cells to combination of photoactivated hypericin and farnesyltransferase inhibitor manumycin A

Several photodynamically-active substances and farnesyltransferase inhibitors are currently being investigated as promising anticancer drugs. In this study, the combined effect of hypericin (the photodynamically-active pigment from Hypericum perforatum) and selective farnesyltransferase inhibitor manumycin (manumycin A; the selective farnesyltransferase inhibitor from Streptomyces parvulus) on HT-29 adenocarcinoma cells was examined. We found that the combination treatment of cells with photoactivated hypericin and manumycin resulted in enhanced antiproliferative and apoptotic response compared to the effect of single treatments. This was associated with increased suppression of clonogenic growth, S phase cell cycle arrest, elevated caspase-3/7 activity and time-dependent total cleavage of procaspase-3 and lamin B, cleavage of p21Bax into p18Bax and massive PARP cleavage. Moreover, we found that the apoptosis-inducing factor is implicated in signaling events triggered by photoactivated hypericin. Our results showed the relocalization of apoptosis-inducing factor (AIF) to the nuclei after hypericin treatment. In addition, we discovered that not only manumycin but also photoactivated hypericin induced the reduction of total Ras protein level. Manumycin decreased the amount of farnesylated Ras, and the combination treatment decreased the amount of both farnesylated and non-farnesylated Ras protein more dramatically. The present findings indicate that the inhibition of Ras processing may be the determining factor for enhancing the antiproliferative and apoptotic effects of combination treatment on HT-29 cells.

The extending network of FOXO transcriptional target genes

The evolutionarily conserved Forkhead box O (FOXO) family of transcription factors regulates multiple transcriptional targets involved in various cellular processes, including proliferation, stress resistance, apoptosis, and metabolism. Target gene regulation appears to be controlled in a cell-type-specific manner due to association of FOXO isoforms with specific cofactors. Many of the cellular processes modulated by FOXO are themselves deregulated in tumorigenesis, and deletion of Foxo genes has demonstrated that these transcription factors function as tumor suppressors. Our understanding of the regulation of FOXO activity, and defining specific transcriptional targets, may provide clues to the molecular mechanisms controlling cell fate decisions. In this review we describe the functional consequences of FOXO activation based on our current knowledge of transcriptional targets.

Integrating opposing signals toward Forkhead box O

Transcription factors are the common convergence points of signal transduction pathways to affect gene transcription. Signal transduction activity results in posttranslational modification (PTM) of transcription factors and the sum of these modifications at any given time point will determine the action of the transcription factor. It has been suggested that these PTMs provide a transcription factor code analogous to the histone code. However, the number and variety of these modifications and the lack of knowledge in general of their dynamics precludes at present a concise view of how combinations of PTMs affect transcription factor function. Also, a single type of PTM such as phosphorylation can have opposing effects on transcription factor activity. Transcription factors of the Forkhead box O (FOXO) class are predominantly regulated through signaling, by phosphoinositide 3-kinase/protein kinase B (also known as AKT) pathway and a reactive oxygen species/c-Jun N-terminal kinase pathway. Both pathways result in increased FOXO phosphorylation yet with opposing result. Whereas PKB-mediated phosphorylation inactivates FOXO, c-Jun N-terminal kinase-mediated phosphorylation results in activation of FOXO. Here we discuss regulation of FOXO transcription factors by phosphorylation as an example for understanding integration of signal transduction at the level of transcription activity.

Forkhead homeobox type O transcription factors in the responses to oxidative stress

Reactive oxygen species (ROS) and cellular oxidative stress are involved in many physiological and pathophysiological processes, including cellular and organismal aging, migration, proliferation, senescence or death of normal and cancer cells, and stress resistance of stem cells. The forkhead homeobox type O (FOXO) transcription factors FOXO1, FOXO3a, and FOXO4 are critical mediators of the cellular responses to oxidative stress and have been implicated in many of the above ROS-regulated processes. In cancer cells they converge oxidative stress signaling to cell cycle arrest and cell death or promote a motile phenotype. Dependent on their posttranslational modifications FOXOs can also actively regulate the detoxification of cells from ROS and promote stress resistance. Thus, FOXO transcription factors are of vital importance in processes regulating tumor survival or progression, stem cell maintenance, age-related pathological processes, and lifespan extension.

Gradient descent optimization in gene regulatory pathways

Background

Gene Regulatory Networks (GRNs) have become a major focus of interest in recent years. Elucidating the architecture and dynamics of large scale gene regulatory networks is an important goal in systems biology. The knowledge of the gene regulatory networks further gives insights about gene regulatory pathways. This information leads to many potential applications in medicine and molecular biology, examples of which are identification of metabolic pathways, complex genetic diseases, drug discovery and toxicology analysis. High-throughput technologies allow studying various aspects of gene regulatory networks on a genome-wide scale and we will discuss recent advances as well as limitations and future challenges for gene network modeling. Novel approaches are needed to both infer the causal genes and generate hypothesis on the underlying regulatory mechanisms.

Methodology

In the present article, we introduce a new method for identifying a set of optimal gene regulatory pathways by using structural equations as a tool for modeling gene regulatory networks. The method, first of all, generates data on reaction flows in a pathway. A set of constraints is formulated incorporating weighting coefficients. Finally the gene regulatory pathways are obtained through optimization of an objective function with respect to these weighting coefficients. The effectiveness of the present method is successfully tested on ten gene regulatory networks existing in the literature. A comparative study with the existing extreme pathway analysis also forms a part of this investigation. The results compare favorably with earlier experimental results. The validated pathways point to a combination of previously documented and novel findings.

Conclusions

We show that our method can correctly identify the causal genes and effectively output experimentally verified pathways. The present method has been successful in deriving the optimal regulatory pathways for all the regulatory networks considered. The biological significance and applicability of the optimal pathways has also been discussed. Finally the usefulness of the present method on genetic engineering is depicted with an example.

SYUNZ-16, a newly synthesized alkannin derivative, induces tumor cells apoptosis and suppresses tumor growth through inhibition of PKB/AKT kinase activity and blockade of AKT/FOXO signal pathway

Alkannin is the major bioactive compound of Arnebia euchroma roots, which is used in many therapeutic remedies in Chinese traditional medicine. SYUNZ-16 is a new derivative of alkannin. In this study, anticancer effects of SYUNZ-16 on human lung adenocarcinoma cell line GLC-82 and human hepatocarcinoma cell line Hep3B were tested in vitro. The results showed SYUNZ-16 could obviously inhibit the proliferation of these cancer cell lines via induction of apoptosis, with the evidence of increasing AnnexinV-positive cells and cleaved caspase-3 and PARP fragments. More importantly, we found that SYUNZ-16 could inhibit AKT activity in cell-free system. Treatment of cancer cells with SYUNZ-16 decreased the phosphorylation of AKT. Additionally, SYUNZ-16 partially attenuated the phosphorylation levels of FKHR and FKHRL1 in a dose-dependent and time-dependent fashion, and led to an increase in the nuclear accumulation of exogenous FKHR, and upregulated the mRNA expression of Bim and TRADD in cancer cells. Further study showed that constitutively activated AKT1 transfection could reduce apoptosis induction mediated by SYUNZ-16. The in vivo experiments showed that SYUNZ-16 had inhibitory effects on S-180 sarcoma implanted to mice. And in GLC-82 xenograft models, SYUNZ-16 at 20 mg/kg/qod remarkably inhibited the tumor growth with the T/C value of 45.3%. Taken together, SYUNZ-16 might be a potent inhibitor of AKT signaling pathway in tumor cells. These data provide evidence for the development of SYUNZ-16 as a potential antitumor drug candidate for further research and development.

Reduced tumor necrosis factor receptor-associated death domain expression is associated with prostate cancer progression

By using LNCaP and its derivative cell lines, we first observed an association between tumor necrosis factor-alpha (TNF-alpha) resistance and hormone independence. Moreover, we found that the expression of tumor necrosis factor receptor-associated death domain (TRADD) was reduced in androgen deprivation-independent cells compared with that in androgen deprivation-dependent cells. TRADD is a crucial transducer for TNF-alpha-induced nuclear factor-kappaB (NF-kappaB) activation. Knocking down TRADD expression in LNCaP cells impaired TNF-alpha-induced NF-kappaB activation and androgen receptor repression, whereas overexpression of TRADD in C4-2B cells restored their sensitivity to TNF-alpha. Finally, we found that androgen deprivation reduces TRADD expression in vitro and in vivo, suggesting that androgen deprivation therapy may promote the development of TNF-alpha resistance by reducing TRADD expression during prostate cancer progression.

High levels of tumor necrosis factor-alpha contribute to accelerated loss of cartilage in diabetic fracture healing

Diabetes interferes with fracture repair; therefore, we investigated mechanisms of impaired fracture healing in a model of multiple low-dose streptozotocin-induced diabetes. Microarray and gene set enrichment analysis revealed an up-regulation of gene sets related to inflammation, including tumor necrosis factor (TNF) signaling in the diabetic group, when cartilage is being replaced by bone on day 16, but not on days 12 or 22. This change coincided with elevated osteoclast numbers and accelerated removal of cartilage in the diabetic group (P < 0.05), which was reflected by smaller callus size. When diabetic mice were treated with the TNF-specific inhibitor, pegsunercept, the number of osteoclasts, cartilage loss, and number of TNF-alpha and receptor activator for nuclear factor kB ligand positive chondrocytes were significantly reduced (P < 0.05). The transcription factor forkhead box 01 (FOXO1) was tested for mediating TNF stimulation of osteoclastogenic and inflammatory factors in bone morphogenetic protein 2 pretreated ATDC5 and C3H10T1/2 chondrogenic cells. FOXO1 knockdown by small-interfering RNA significantly reduced TNF-alpha, receptor activator for nuclear factor kB ligand, macrophage colony-stimulating factor, interleukin-1alpha, and interleukin-6 mRNA compared with scrambled small-interfering RNA. An association between FOXO1 and the TNF-alpha promoter was demonstrated by chromatin immunoprecipitation assay. Moreover, diabetes increased FOXO1 nuclear translocation in chondrocytes in vivo and increased FOXO1 DNA binding activity in diabetic fracture calluses (P < 0.05). These results suggest that diabetes-enhanced TNF-alpha increases the expression of resorptive factors in chondrocytes through a process that involves activation of FOXO1 and that TNF-alpha dysregulation leads to enhanced osteoclast formation and accelerated loss of cartilage.

P53 negatively regulates the transcriptional activity of FOXO3a under oxidative stress

Transcription factors P53 and FOXO are both activated in response to stresses via protein-protein interactions, leading to events such as cell survival or apoptosis. To clarify the mechanisms that regulate FOXO activity, we analyzed the intermolecular interaction of FOXO3a and P53. FOXO3a and P53 interacted in COS-7 cells, and transcriptional activity of FOXO3a was suppressed by P53, but P53 was not affected by FOXO3a. RT-PCR revealed that expression of the endogenous apoptosis-inducible genes Bim and Bcl6 was decreased markedly by co-expression of P53 with them, but expression of p27 and CyclinG2 was not. In addition, treatment with 500 microM H2O2 for 30 min to 1h to mimic oxidative stress promoted protein binding. Serum deprivation and drug treatment also affected the binding of FOXO3a and P53. These findings suggest that FOXO3a controls cellular function by changing its molecular interaction with P53 to mediate transcription factor activity under stress stimuli.

FoxO proteins and cardiac pathology

The FoxO family of transcription factors mediate a wide range of cellular responses from cell death to cell survival, growth inhibition and glucose utilization. This complex array of responses is regulated by an equally complex regulatory system, involving phosphorylation, ubiquitinization and acetylation, in addition to interactions with other transcription factors and transcriptional modifiers. In heart, FoxO proteins have been shown to be involved in development in limiting hypertrophic growth responses and in cardioprotection provided by silent information regulator 1 (Sirt1). However, the range of responses mediated by FoxO proteins and the clear evidence for involvement of FoxO regulators in cardiac pathology, suggest that further pathological actions of FoxO family members remain to be elucidated.

TUSC4/NPRL2, a novel PDK1-interacting protein, inhibits PDK1 tyrosine phosphorylation and its downstream signaling

3-Phosphoinositide-dependent protein kinase-1 (PDK1) is a key regulator of cell proliferation and survival signal transduction. PDK1 is known to be constitutively active and is further activated by Src-mediated phosphorylation at the tyrosine-9, -373, and -376 residues. To identify novel regulators of PDK1, we performed E. coli-based two-hybrid screening and revealed that tumor suppressor candidate 4 (TUSC4), also known as nitrogen permease regulator-like 2 (NPRL2), formed a complex with PDK1 and suppressed Src-dependent tyrosine phosphorylation and activation of PDK1 in vitro and in cells. The NH(2)-terminal 133 amino acid residues of TUSC4 were involved in binding to PDK1. The deletion mutant of TUSC4 that lacked the NH(2)-terminal domain showed no inhibitory effects on PDK1 tyrosine phosphorylation or activation. Thus, complex formation is indispensable for TUSC4-mediated PDK1 inactivation. The siRNA-mediated down-regulation of TUSC4 induced cell proliferation, while ectopic TUSC4 expression inactivated the PDK1 downstream signaling pathway, including Akt and p70 ribosomal protein S6 kinase, and increased cancer cell sensitivity to several anticancer drugs. Our results suggest that TUSC4/NPRL2, a novel PDK1-interacting protein, plays a role in regulating the Src/PDK1 signaling pathway and cell sensitivity to multiple cancer chemotherapeutic drugs.

Apoptotic pathways in tumor progression and therapy

Apoptosis is a cell suicide program that plays a critical role in development and tissue homeostasis. The ability of cancer cells to evade this programmed cell death (PCD) is a major characteristic that enables their uncontrolled growth. The efficiency of chemotherapy in killing such cells depends on the successful induction of apoptosis, since defects in apoptosis signaling are a major cause of drug resistance. Over the past decades, much progress has been made in our understanding of apoptotic signaling pathways and their dysregulation in cancer progression and therapy. These advances have provided new molecular targets for proapoptotic cancer therapies that have recently been used in drug development. While most of those therapies are still at the preclinical stage, some of them have shown much promise in the clinic. Here, we review our current knowledge of apoptosis regulation in cancer progression and therapy, as well as the new molecular targeted molecules that are being developed to reinstate cancer cell death.

Nucleobindin 1 Controls the Unfolded Protein Response by Inhibiting ATF6 Activation

In response to endoplasmic reticulum (ER) stress, activating transcription factor 6 (ATF6), an ER membrane-anchored transcription factor, is transported to the Golgi apparatus and cleaved by site-1 protease (S1P) to activate the unfolded protein response (UPR). Here, we identified nucleobindin 1 (NUCB1) as a novel repressor of the S1P-mediated ATF6 activation. NUCB1 is an ER stress-inducible gene with the promoter region having functional cis-elements for transcriptional activation by ATF6. Overexpression of NUCB1 inhibits S1P-mediated ATF6 cleavage without affecting ER-to-Golgi transport of ATF6, whereas knock-down of NUCB1 by siRNA accelerates ATF6 cleavage during ER stress. NUCB1 protein localizes in the Golgi apparatus, and disruption of the Golgi localization results in loss of the ATF6-inhibitiory activity. Consistent with these observations, NUCB1 can suppress physical interaction of S1P-ATF6 during ER stress. Together, our results demonstrate that NUCB1 is the first-identified, Golgi-localized negative feedback regulator in the ATF6-mediated branch of the UPR.

FOXO transcription factor-dependent p15INK4b and p19INK4d expression

FOXO (Forkhead box O) transcription factors are involved in cell-cycle arrest or apoptosis induction by transcripting cell-cycle inhibitor p27(KIP1) or apoptosis-related genes, respectively. Akt/protein kinase B promotes cell proliferation and suppresses apoptosis, in part, by phosphorylating FOXOs. Phosphorylated FOXOs could not exhibit transcriptional activity because of their nuclear export. Here we show that p15(INK4b) and p19(INK4d) transcription is associated with FOXO-mediated G1 cell-cycle arrest. Inhibition of Akt signaling by PI3K inhibitors, a PDK1 inhibitor, or dominant-negative Akt transfection increased expression of p15(INK4b) and p19(INK4d) but not p16(INK4a) and p18(INK4c). Ectopic expression of wild type or active FOXO but not inactive form also increased p15(INK4b) and p19(INK4d) levels. FOXOs bound to promoter regions and induced transcription of these genes. No increase in the G1-arrested cell population, mediated by PI3K inhibitor LY294002, was observed in INK4b-/- or INK4d-/- murine embryonic fibroblasts. In summary, FOXOs are involved in G1 arrest caused by Akt inactivation via p15(INK4b) and p19(INK4d) transcription.

Levels of protein tyrosine phosphatase 1B determine susceptibility to apoptosis in serum-deprived hepatocytes

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of tyrosine kinase growth factor signaling. To assess the importance of PTP1B in the balance between death and survival in the liver, we have developed immortalized neonatal hepatocyte cell lines lacking (PTP1B(-/-)) or overexpressing (PTP1B(+/+PTP1B)) PTP1B. Early activation of caspase-3 occurred in PTP1B(+/+PTP1B) hepatocytes but was nearly abolished in PTP1B(-/-) cells. At the molecular level, PTP1B overexpression/deficiency altered the balance of pro-(Bim) and anti-(Bcl-x(L)) apoptotic members of the Bcl-2 family upon serum withdrawal. Likewise, cytosolic cytochrome C increased rapidly in PTP1B(+/+PTP1B) hepatocytes whereas it was retained in the mitochondria of PTP1B(-/-) cells. DNA fragmentation and the increase of apoptotic cells induced by serum withdrawal in wild-type (PTP1B(+/+)) hepatocytes were absent in PTP1B(-/-) cells. Conversely, overexpression of PTP1B accelerated DNA laddering and increased the number of apoptotic cells. In serum-deprived PTP1B(+/+PTP1B) hepatocytes, a rapid entry of Foxo1 into the nucleus and an earlier activation of caspase-8 was observed. However, both events were suppressed in PTP1B(-/-) hepatocytes. Moreover, PTP1B deficiency conferred resistance to apoptosis induced by activation of Fas and constitutively active Foxo1. Rescue of PTP 1B in deficient hepatocytes recovered the phenotype of wild-type cells whereas reduction of PTP1B by siRNA suppressed apoptosis. Our results reveal a unique role for PTP1B as a mediator of the apoptotic pathways triggered by trophic factors withdrawal in hepatocytes. This novel mechanism may represent an important target in the design of therapeutic strategies for human liver regeneration after pathological damage as well as for treatment of hepatocarcinomas.

Increased expression of Dyrk1a in HPV16 immortalized keratinocytes enable evasion of apoptosis

Immortalization is a critical event in virus-related oncogenesis. No enough information, however, is currently available to elucidate the changes that occur in cellular molecules during immortalization. To identify potential cellular markers or regulators involving in immortalization, a paired-cell model of primary foreskin keratinocytes (FK) and HPV16 immortalized foreskin keratinocytes were established. Using mRNA differential display, RT-PCR and Northern blot methods, we have identified and confirmed that Dyrk1a (dual-specificity tyrosine-phosphorylated and regulated kinase 1A) is present and increased in HPV16 immortalized cells, but is absent in primary keratinocytes. Moreover, transfection of E7 siRNA oligo into immortalized cells leads to a diminishing E7 expression and the eventual disappearance of Dyrk1a. Similar results of Dyrk1a expressional differences could also be seen when tissue specimens were compared using LCM/real-time PCR and immunohistochemistry analysis; malignant cervical lesions contain significantly more DYRK1A than normal tissue. It was also demonstrated that raised DYRK1A could rearrange the cellular localization of FKHR (forkhead in rhabdomyosarcoma), an apoptosis activator, and suppress BAD. Importantly, this phenomenon can be reversed when endogenous Dyrk1a was knocked down in immortalized cells by RNA interference. These results suggest that the raised Dyrk1a in HPV16 immortalized keratinocytes and cervical lesions may serve as a candidate antiapoptotic factor in the FKHR regulated pathway and initiate immortalization and tumorigenesis gradually.

Down-regulation of Bcl-XL by RNA interference suppresses cell growth and induces apoptosis in human esophageal cancer cells

AIM: To determine the inhibitory effect of the vector-generated small interfering RNAs (siRNAs) on the expression of the Bcl-X_L gene in established human esophageal cancer cells, and to investigate the effect of the Bcl-X_L siRNAs on cell growth and apoptosis in esophageal cancer cells.

METHODS: Three siRNA-expressing vectors targeting different sites of the Bcl-X_L gene were constructed from pTZ-U6+1 vector. Cultured esophageal cancer cells were transfected with the siRNA-expressing vector (or the control vector) using lipofectamine 2000. Bcl-X_L gene expression was determined with semiquantitative RT-PCR assay and Western blotting. Among the three siRNA-expressing vectors, the most highly functional vector and its effect on cell growth and apoptosis in esophageal cancer cells was further analyzed.

RESULTS: Of the three siRNA-expressing vectors, siRNA-expressing vector No.1 was the most potent one which suppressed Bcl-X_L mRNA production to 32.5% of that in the untreated esophageal cancer cells. Western blotting analysis showed that siRNA-expressing vector No.1 markedly down-regulated the expression of Bcl-X_L in human esophageal cancer cells. Treatment of esophageal cancer cells with siRNA-expressing vector No.1 resulted in inhibition of cell growth and induction of apoptosis.

CONCLUSION: Down-regulation of Bcl-X_L by vector-generated small interfering RNAs can suppress cell growth and induce apoptosis in human esophageal cancer cells.

Cis-parinaric acid effects, cytotoxicity, c-Jun N-terminal protein kinase, forkhead transcription factor and Mn-SOD differentially in malignant and normal astrocytes

Cis-parinaric acid (c-PNA), a natural four conjugated polyunsaturated fatty acid, increases free radical production and it is preferentially cytotoxic to malignant glial cells compared to normal astrocytes in-vitro. In order to explain the increased cytotoxicity of c-PNA in malignant glial cells, we compared the effects of c-PNA on the oxidative stress-dependent signal transducing events in 36B10 cells, a malignant rat astrocytoma cell line, and in fetal rat astrocytes. Our results show that c-PNA treatment in 36B10 cells caused a persistent activation of c-Jun N-terminal protein kinase (JNK) at RNA and protein levels. Specific inhibitors of the kinase significantly reversed the cytotoxicity of c-PNA. Additionally, c-PNA caused the phosphorylated inactivation of forkhead transcription factor-3a (FKHR-L1, FOXO3a) and drastically decreased the activity of mitochondrial superoxide dismutase (Mn-SOD) that protects cells from oxidative stress. On the other hand, identical c-PNA treatments in normal astrocytes increased the dephosphorylated activation of FKHR-L1, maintained activity of Mn-SOD and failed to phosphorylate JNK. Taken together, the results imply that a selective activation of JNK and the opposite regulation of FKHR-L1 and Mn-SOD contribute to the differential cytotoxicity of c-PNA in malignant and normal glial cells.

FOXO1A Is a Candidate for the 13q14 Tumor Suppressor Gene Inhibiting Androgen Receptor Signaling in Prostate Cancer

Chromosomal deletion is frequent at the region between BRCA2 and RB1 in the q14 band of chromosome 13 (13q14) in human cancers, including prostate cancer, suggesting the presence of a tumor suppressor gene. However, no reasonable candidate has been identified thus far. In this study, we did genetic and functional analyses to identify and evaluate the 13q14 tumor suppressor gene. Hemizygous and homozygous deletions in cell lines/xenografts of prostate cancer mapped the deletion locus to 919 kb, which harbors only one known gene, the FOXO1A transcription factor. Deletion at FOXO1A was detected in 31% to 34% in 6 cell lines, 27 xenografts, and 72 clinical specimens of prostate cancer, and was significantly more frequent than deletions at surrounding loci. In addition, FOXO1A was transcriptionally down-regulated in some prostate cancers. Functionally, ectopic expression of FOXO1A inhibited, and its knockdown promoted, cell proliferation or survival. Furthermore, FOXO1A inhibited androgen- and androgen receptor-mediated gene regulation and cell proliferation. Consistent with the understanding of FOXO1A biology, our findings suggest that FOXO1A is the 13q14 tumor suppressor gene, at least in prostate cancer. As a well-established negative effector in the phosphatidylinositol 3-kinase/AKT signaling pathway, FOXO1A inactivation in cancer would impair the therapeutic effect of phosphatidylinositol 3-kinase/AKT inhibitors in cancer treatment.

4-HPR modulates gene expression in ovarian cells

Ovarian cancer has a high rate of recurrence and subsequent mortality following chemotherapy despite intense efforts to improve treatment outcomes. Recent trials have suggested that retinoids, especially 4-(N-hydroxyphenyl) retinamide (4-HPR), play an important role as a chemopreventive agent and are currently being used in clinical trials for ovarian cancer chemoprevention as well as treatment. This study examines the mechanism of its activity in premalignant and cancer cells. We investigated the modulation of gene expression by 4-HPR in immortalized ovarian surface epithelial (IOSE) cells and ovarian cancer (OVCA433) cells with DNA microarray. Real time RT-PCR and western blotting were used to confirm the microarray results and metabolic changes were examined with optical fluorescence spectroscopy. 4-HPR resulted in an up-regulation of expression of proapoptotic genes and mitochondrial uncoupling protein in OVCA433 cells and modulation of the RXR receptors in IOSE cells, and down-regulation of mutant BRCA genes in both IOSE and OVCA433 cells. 4-HPR had a larger effect on the redox in the 433 cells compared to IOSE. These findings suggest that 4-HPR acts through different mechanisms in premalignant ovarian surface cells and cancer cells, with a preventive effect in premalignant cells and a treatment effect in cancer cells.

Akt/protein kinase B-dependent phosphorylation and inactivation of WEE1Hu promote cell cycle progression at G2/M transition

The serine/threonine kinase Akt is known to promote cell growth by regulating the cell cycle in G1 phase through activation of cyclin/Cdk kinases and inactivation of Cdk inhibitors. However, how the G2/M phase is regulated by Akt remains unclear. Here, we show that Akt counteracts the function of WEE1Hu. Inactivation of Akt by chemotherapeutic drugs or the phosphatidylinositide-3-OH kinase inhibitor LY294002 induced G2/M arrest together with the inhibitory phosphorylation of Cdc2. Because the increased Cdc2 phosphorylation was completely suppressed by wee1hu gene silencing, WEE1Hu was associated with G2/M arrest induced by Akt inactivation. Further analyses revealed that Akt directly bound to and phosphorylated WEE1Hu during the S to G2 phase. Serine-642 was identified as an Akt-dependent phosphorylation site. WEE1Hu kinase activity was not affected by serine-642 phosphorylation. We revealed that serine-642 phosphorylation promoted cytoplasmic localization of WEE1Hu. The nuclear-to-cytoplasmic translocation was mediated by phosphorylation-dependent WEE1Hu binding to 14-3-3theta but not 14-3-3beta or -sigma. These results indicate that Akt promotes G2/M cell cycle progression by inducing phosphorylation-dependent 14-3-3theta binding and cytoplasmic localization of WEE1Hu.

Cyclin D1 represses p300 transactivation through a cyclin-dependent kinase-independent mechanism

Cyclin D1 encodes a regulatory subunit, which with its cyclin-dependent kinase (Cdk)-binding partner forms a holoenzyme that phosphorylates and inactivates the retinoblastoma protein. In addition to its Cdk binding-dependent functions, cyclin D1 regulates cellular differentiation in part by modifying several transcription factors and nuclear receptors. The molecular mechanism through which cyclin D1 regulates the function of transcription factors involved in cellular differentiation remains to be clarified. The histone acetyltransferase protein p300 is a co-integrator required for regulation of multiple transcription factors. Here we show that cyclin D1 physically interacts with p300 and represses p300 transactivation. We demonstrated further that the interaction of the two proteins occurs at the peroxisome proliferator-activated receptor gamma-responsive element of the lipoprotein lipase promoter in the context of the local chromatin structure. We have mapped the domains in p300 and cyclin D1 involved in this interaction. The bromo domain and cysteine- and histidine-rich domains of p300 were required for repression by cyclin D1. Cyclin D1 repression of p300 was independent of the Cdk- and retinoblastoma protein-binding domains of cyclin D1. Cyclin D1 inhibits histone acetyltransferase activity of p300 in vitro. Microarray analysis identified a signature of genes repressed by cyclin D1 and induced by p300 that promotes cellular differentiation and induces cell cycle arrest. Together, our results suggest that cyclin D1 plays an important role in cellular proliferation and differentiation through regulation of p300.

Mutant PIK3CA promotes cell growth and invasion of human cancer cells

PIK3CA is mutated in diverse human cancers, but the functional effects of these mutations have not been defined. To evaluate the consequences of PIK3CA alterations, the two most common mutations were inactivated by gene targeting in colorectal cancer (CRC) cells. Biochemical analyses of these cells showed that mutant PIK3CA selectively regulated the phosphorylation of AKT and the forkhead transcription factors FKHR and FKHRL1. PIK3CA mutations had little effect on growth under standard conditions, but reduced cellular dependence on growth factors. PIK3CA mutations resulted in attenuation of apoptosis and facilitated tumor invasion. Treatment with the PI3K inhibitor LY294002 abrogated PIK3CA signaling and preferentially inhibited growth of PIK3CA mutant cells. These data have important implications for therapy of cancers harboring PIK3CA alterations.

Induction of prosurvival molecules by apoptotic stimuli: involvement of FOXO3a and ROS

Most cancer therapeutics fails to eradicate cancer because cancer cells rapidly develop resistance to its proapoptotic effects. The underlying mechanisms remain incompletely understood. Here we show that three representative apoptotic stimuli, that is, serum starvation, a mitochondrial toxin, and a DNA-damaging agent (etoposide), rapidly induce several distinct classes of prosurvival molecules, in particular, Bcl-2/Bcl-X(L) and superoxide dismutase (SOD; including both MnSOD and Cu/ZnSOD). At the population level, the induction of these prosurvival molecules occurs prior to or concomitant with the induction of proapoptotic molecules such as Bim and Bak. Blocking the induction using siRNAs of the prosurvival or proapoptotic molecules facilitates or inhibits apoptosis, respectively. One master transcription factor, FOXO3a, is involved in the transcriptional activation of some of these prosurvival (e.g., MnSOD) and proapoptotic (e.g., Bim) molecules. Interestingly, in all three apoptotic systems, FOXO3a itself is also upregulated at the transcriptional level. Mechanistic studies indicate that reactive oxygen species (ROS) are rapidly induced upon apoptotic stimulation and that ROS inhibitors/scavengers block the induction of FOXO3a, MnSOD, and Bim. Finally, we show that apoptotic stimuli also upregulate prosurvival molecules in normal diploid human fibroblasts and at subapoptotic concentrations. Taken together, these results suggest that various apoptotic inducers may rapidly mobilize prosurvival mechanisms through ROS-activated master transcription factors such as FOXO3a. The results imply that effective anticancer therapeutics may need to combine both apoptosis-inducing and survival-suppressing strategies.

FOXO1 functions as a master switch that regulates gene expression necessary for tumor necrosis factor-induced fibroblast apoptosis

Tumor necrosis factor-alpha (TNF-alpha) is a potent pro-inflammatory and pro-apoptotic mediator that plays an important role in several normal and disease processes. TNF-induced cell death is one of the principal mechanisms by which cells are removed. Although TNF-mediated apoptosis has been the subject of intense investigation, the transcriptional mechanisms through which it promotes apoptosis are not well understood and, paradoxically, the archetypal TNF-induced nuclear factor NFkappaB is anti-apoptotic. To identify a potential master transcriptional regulator of apoptosis, we examined an array of TNF-alpha-activated transcription factors. Fork-head box class-O 1 (FOXO1) was strongly activated, which was confirmed in vitro and in vivo by electrophoretic mobility shift assay. The central importance of FOXO1 was established in experiments with small inhibitory RNA (siRNA) that specifically silenced FOXO1. When FOXO1 was silenced, fibroblast apoptosis was reduced 76%. Other siRNAs that partially inhibited FOXO1 expression were proportionately effective in reducing apoptosis. Transcriptional profiling was then carried out in conjunction with siRNA to establish mechanisms by which FOXO1 modulated apoptosis. In the absence of FOXO1, TNF-alpha failed to up-regulate a large number of pro-apoptotic gene families including ligands, receptors, adapter molecules, mitochondrial proteins, and caspases. siRNA silencing also blocked down-regulation of anti-apoptotic genes. These results indicate that TNF induces activation of the FOXO1 transcription factor, which acts as a master switch to control apoptosis.

N/A

N/A

IRS-2 mediates the antiapoptotic effect of insulin in neonatal hepatocytes

To assess the role of insulin action and inaction in the liver, immortalized hepatocyte cell lines have been generated from insulin receptor substrate (IRS)-2(-/-) and wild-type mice. Using this model, we have recently demonstrated that the lack of IRS-2 in neonatal hepatocytes resulted in insulin resistance. In the current study, we show that immortalized neonatal hepatocytes undergo apoptosis on serum withdrawal, with caspase-3 activation and DNA laddering occurring earlier in the absence of IRS-2. Insulin rescued wild-type hepatocytes from serum withdrawal-induced caspase-3 activation and DNA fragmentation in a dose-dependent manner, but it failed to rescue hepatocytes lacking IRS-2. In IRS-2(-/-) cells, insulin failed to phosphorylate Bad. Furthermore, in these cells, insulin was unable to translocate Foxo1 from the nucleus to the cytosol. Adenoviral infection of wild-type cells with constitutively active Foxo1 (ADA) induced caspase-8 and caspase-3 activities, proapoptotic gene expression, DNA laddering and apoptosis. Dominant negative Foxo1 regulated the whole pathway in an opposite manner. Prolonged insulin treatment (24 hours) increased expression of antiapoptotic genes (Bcl-xL), downregulated proapoptotic genes (Bim and nuclear Foxo1), and decreased caspase-3 activity in wild-type hepatocytes but not in IRS-2(-/-) cells. Infection of IRS-2(-/-) hepatocytes with adenovirus encoding IRS-2 reconstituted phosphatidylinositol 3-kinase (PI 3-kinase)/Akt/Foxo1 signaling, restored pro- and antiapoptotic gene expression, and decreased caspase-3 activity in response to insulin, thereby blocking apoptosis. In conclusion, IRS-2 signaling is specifically required through PIP3 generation to mediate the survival effects of insulin. Epidermal growth factor, via PIP3/Akt/Foxo1 phosphorylation, was able to rescue IRS-2(-/-) hepatocytes from serum withdrawal-induced apoptosis, modulating pro- and anti-apoptotic gene expression and downregulating caspase-3 activity.

Susceptibility to apoptosis in insulin-like growth factor-I receptor-deficient brown adipocytes

Fetal brown adipocytes are insulin-like growth factor-I (IGF-I) target cells. To assess the importance of the IGF-I receptor (IGF-IR) in brown adipocytes during fetal life, we have generated immortalized brown adipocyte cell lines from the IGF-IR(-/-) mice. Using this experimental model, we demonstrate that the lack of IGF-IR in fetal brown adipocytes increased the susceptibility to apoptosis induced by serum withdrawal. Culture of cells in the absence of serum and growth factors produced rapid DNA fragmentation (4 h) in IGF-IR(-/-) brown adipocytes, compared with the wild type (16 h). Consequently, cell viability was decreased more rapidly in fetal brown adipocytes in the absence of IGF-IR. Furthermore, caspase-3 activity was induced much earlier in cells lacking IGF-IR. At the molecular level, IGF-IR deficiency in fetal brown adipocytes altered the balance of the expression of several proapoptotic (Bcl-xS and Bim) and antiapoptotic (Bcl-2 and Bcl-xL) members of the Bcl-2 family. This imbalance was irreversible even though in IGF-IR-reconstituted cells. Likewise, cytosolic cytochrome c levels increased rapidly in IGF-IR-deficient cells compared with the wild type. A rapid entry of Foxo1 into the nucleus accompanied by a rapid exit from the cytosol and an earlier activation of caspase-8 were observed in brown adipocytes lacking IGF-IR upon serum deprivation. Activation of caspase-8 was inhibited by 50% in both cell types by neutralizing anti-Fas-ligand antibody. Adenoviral infection of wild-type brown adipocytes with constitutively active Foxol (ADA) increased the expression of antiapoptotic genes, decreased Bcl-xL and induced caspase-8 and -3 activities, with the final outcome of DNA fragmentation. Up-regulation of uncoupling protein-1 (UCP-1) expression in IGF-IR-deficient cells by transduction with PGC-1alpha or UCP-1 ameliorated caspase-3 activation, thereby retarding apoptosis. Finally, insulin treatment prevented apoptosis in both cell types. However, the survival effect of insulin on IGF-IR(-/-) brown adipocytes was elicited even in the absence of phosphatidylinositol 3-kinase/Akt signaling. Thus, our results demonstrate for the first time the unique role of IGF-IR in maintaining the balance of death and survival in fetal brown adipocytes.

Inhibition of phosphorylation of a forkhead transcription factor sensitizes human ovarian cancer cells to cisplatin

The Forkhead family transcription factor FKHRL1 is an inducer of apoptosis in its unphosphorylated form and was recently reported to be a substrate of Akt kinase. We studied the roles of FKHRL1 in both cisplatin-resistant Caov-3 (a papillary adenocarcinoma cell line) and cisplatin-sensitive A2780 human ovarian cancer cell lines. Treatment of Caov-3 cells but not A2780 cells with cisplatin transiently stimulated the phosphorylation of FKHRL1. Transfection experiments revealed that a kinase inactive-mutant of Akt or a triple mutant (TM) of FKHRL1, in which all three of the putative Akt phosphorylation sites were converted to alanine, was unable to phosphorylate the FKHRL1 protein in cells treated with cisplatin. Because the phosphorylated form of FKHRL1 is known to be localized in the cytoplasm, we examined whether cisplatin-induced phosphorylation of FKHRL1 might have an effect on the subcellular distribution of FKHRL1. Cisplatin induced the localization of FKHRL1 in the cytoplasm in Caov-3 cells but not in A2790 cells. Moreover, cisplatin induced the association of 14-3-3 protein with phosphorylated-FKHRL1 in Caov-3 cells but not in A2790 cells. Because the unphosphorylated form of FKHRL1 binds the Fas ligand promoter, thereby inducing apoptosis, we further examined the effect of the phosphorylation status of FKHRL1 on the activity of the Fas ligand promoter in the presence of cisplatin. Transfection with the kinase-inactive mutant of Akt or TM of FKHRL1 induced the activity of the Fas ligand promoter in Caov-3 cells. Moreover, exogenous expression of TM of FKHRL1 in Caov-3 cells decreased the cell viability after treatment with cisplatin. Our findings suggest that cisplatin causes the phosphorylation of FKHRL1 via a phosphatidylinositol 3-kinase/Akt cascade, and inhibition of this cascade sensitizes ovarian cancer cells to cisplatin.

FLT3 receptors with internal tandem duplications promote cell viability and proliferation by signaling through Foxo proteins

In about 30% of the patients with acute myeloid leukemia, activating FLT3 receptor mutations have been identified, often as in-frame internal tandem duplications (ITD) at the juxtamembrane domain of the receptor. FLT3-ITD receptors exhibit constitutive tyrosine kinase activity in the absence of FLT3 ligand (FL) binding, and when expressed in cytokine-dependent cell lines and primary hematopoietic cells suppress programmed cell death and increase cell division. However, the signaling pathways important for transformation, in particular the nuclear targets, are unknown. Here we demonstrate that FLT3-ITD expression in Ba/F3 cells results in activation of Akt and concomitant phosphorylation of the Forkhead family member Foxo3a. Phosphorylation of Foxo proteins through FLT3-ITD signaling promotes their translocation from the nucleus into the cytoplasm, which requires the presence of conserved Akt phosphorylation sites in Forkhead transcription factors and PI3K activity. Induction of Foxo3a phosphorylation by FLT3-ITD receptors in Ba/F3 cells correlates with the suppression of Foxo-target genes p27Kip1 and the proapoptotic Bcl-2 family member Bim. Specifically, FLT3-ITD expression prevents Foxo3a-mediated apoptosis and upregulation of p27Kip1 and Bim gene expression. These data indicate that the oncogenic tyrosine kinase FLT3 can negatively regulate Foxo transcription factors, thereby promoting cell survival and proliferation.

PI3K/Akt and apoptosis: size matters

Recent research has examined Akt and Akt-related serine-threonine kinases in signaling cascades that regulate cell survival and are important in the pathogenesis of degenerative diseases and in cancer. We seek to recapitulate the research that has helped to define the current understanding of the role of the Akt pathway under normal and pathologic conditions, also in view of genetic models of Akt function. In particular, we will evaluate the mechanisms of Akt regulation and the role of Akt substrates in Akt-dependent biologic responses in the decisions of cell death and cell survival. Here, we hope to establish the mechanisms of apoptosis suppression by Akt kinase as a framework for a more general understanding of growth factor-dependent regulation of cell survival.

Body language: the function of PML nuclear bodies in apoptosis regulation

Promyelocytic leukaemia (PML) nuclear bodies (NBs) are macromolecular nuclear domains present in virtually every mammalian cell. PML nuclear bodies (PML-NBs) were functionally linked to various fundamental cellular processes, including transcriptional control, tumour suppression and apoptosis regulation. Supporting the important function of PML and its associated NBs in apoptosis regulation, several apoptotic regulators localise to PML-NBs, and cells from PML-deficient mice show severe apoptotic defects, including induction of genotoxic stress and death receptor CD95 (Fas/APO-1) activation. Based on the current literature, we hypothesise that PML-NBs regulate apoptosis through different molecular mechanisms, on the one hand by acting as macromolecular scaffolds for recruitment and post-translational modification of the apoptotic key regulator p53, and on the other by regulating the subcellular bioavailability and quality of some apoptotic signal transducers.

Decisions on life and death: FOXO Forkhead transcription factors are in command when PKB/Akt is off duty

Forkhead transcription factors of the FOXO family are important downstream targets of protein kinase B (PKB)/Akt, a kinase shown to play a decisive role in cell proliferation and cell survival. Direct phosphorylation by PKB/Akt inhibits transcriptional activation by FOXO factors, causing their displacement from the nucleus into the cytoplasm. Work from recent years has shown that this family of transcription factors regulates the expression of a number of genes that are crucial for the proliferative status of a cell, as well as a number of genes involved in programmed cell death. As such, these transcription factors appear to play an essential role in many of the effects of PKB/Akt on cell proliferation and survival. Indeed, in cells of the hematopoietic system, mere activation of a FOXO factor is sufficient to activate a variety of proapoptotic genes and to trigger apoptosis. In contrast, in most other cell types, activation of FOXO blocks cellular proliferation and drives cells into a quiescent state. In such cell types, FOXO factors also provide the protective mechanisms that are required to adapt to the altered metabolic state of quiescent cells. Thus, as PKB/Akt signaling is switched off, FOXO factors take over to determine the fate of a cell, long-term survival in a quiescent state, or programmed cell death. This review summarizes our current understanding of the mechanisms by which PKB/Akt and FOXO factors regulate these decisions.