Regulation of MCL1 through a serum response factor/Elk-1-mediated mechanism links expression of a viability-promoting member of the BCL2 family to the induction of hematopoietic cell differentiation

Investigation and Characterization of the RAS/RAF/MEK/ERK Pathway and Other Signaling Pathways in Chronic Sinusitis with Nasal Polyps

BACKGROUND

The clinical outcomes of drug treatments and surgical interventions for chronic sinusitis with nasal polyps (CRSwNPs) are suboptimal, and the high recurrence rate remains a significant challenge in clinical practice. Targeted therapies such as biologics provide new perspectives and directions for treating CRSwNP.

SUMMARY

With the continuous investigation of signaling pathways, RAS/RAF/MEK/ERK signaling pathway and other signaling pathways including Hippo, JAK-STAT, Wnt, TGF-β, PI3K, Notch, and NF-κB were confirmed to play an important role in the progression of CRSwNP. Among them, the abnormality of RAS/RAF/MEK/ERK signaling pathway is accompanied by the abnormality of this apoptotic component, which may provide new research directions for targeting the components of signaling pathways to mediate apoptosis.

KEY MESSAGES

Abnormalities in signaling pathways are particularly important in studying the pathogenesis and treatment of CRSwNP. Therefore, this review summarizes the ongoing investigation and characterization of RAS/RAF/MEK/ERK signaling pathway and other signaling pathways in CRSwNP, which provides constructive ideas and directions for improving the treatment of CRSwNP.

NL101 synergizes with the BCL-2 inhibitor venetoclax through PI3K-dependent suppression of c-Myc in acute myeloid leukaemia

BACKGROUND

Acute myeloid leukaemia (AML) comprises a group of heterogeneous and aggressive haematological malignancies with unsatisfactory prognoses and limited treatment options. Treatments targeting B-cell lymphoma-2 (BCL-2) with venetoclax have been approved for patients with AML, and venetoclax-based drug combinations are becoming the standard of care for older patients unfit for intensive chemotherapy. However, the therapeutic duration of either single or combination strategies is limited, and the development of resistance seems inevitable. Therefore, more effective combination regimens are urgently needed.

METHODS

The efficacy of combination therapy with NL101, a SAHA-bendamustine hybrid, and venetoclax was evaluated in preclinical models of AML including established cell lines, primary blasts from patients, and animal models. RNA-sequencing and immunoblotting were used to explore the underlying mechanism.

RESULTS

NL101 significantly potentiated the activity of venetoclax in AML cell lines, as evidenced by the enhanced decrease in viability and induction of apoptosis. Mechanistically, the addition of NL101 to venetoclax decreased the stability of the antiapoptotic protein myeloid cell leukaemia-1 (MCL-1) by inhibiting ERK, thereby facilitating the release of BIM and triggering mitochondrial apoptosis. Moreover, the strong synergy between NL101 and venetoclax also relied on the downregulation of c-Myc via PI3K/Akt/GSK3β signalling. The combination of NL101 and venetoclax synergistically eliminated primary blasts from 10 AML patients and reduced the leukaemia burden in an MV4-11 cell-derived xenograft model.

CONCLUSIONS

Our results encourage the pursuit of clinical trials of combined treatment with NL101 and venetoclax and provide a novel venetoclax-incorporating therapeutic strategy for AML.

Overview of BH3 mimetics in ovarian cancer

Ovarian carcinoma is the leading cause of gynecological cancer-related death, still with a dismal five-year prognosis, mainly due to late diagnosis and the emergence of resistance to cytotoxic and targeted agents. Bcl-2 family proteins have a key role in apoptosis and are associated with tumor development/progression and response to therapy in different cancer types, including ovarian carcinoma. In tumors, evasion of apoptosis is a possible mechanism of resistance to therapy. BH3 mimetics are small molecules that occupy the hydrophobic pocket on pro-survival proteins, allowing the induction of apoptosis, and are currently under study as single agents and/or in combination with cytotoxic and targeted agents in solid tumors. Here, we discuss recent advances in targeting anti-apoptotic proteins of the Bcl-2 family for the treatment of ovarian cancer, focusing on BH3 mimetics, and how these approaches could potentially offer an alternative/complementary way to treat patients and overcome or delay resistance to current treatments.

Repurposing Niclosamide as a plausible neurotherapeutic in autism spectrum disorders, targeting mitochondrial dysfunction: a strong hypothesis

Autism Spectrum Disorders (ASD) are a complex set of neurodevelopmental manifestations which present in the form of social and communication deficits. Affecting a growing proportion of children worldwide, the exact pathogenesis of this disorder is not very well understood, and multiple signaling pathways have been implicated. Among them, the ERK/MAPK pathway is critical in a number of cellular processes, and the normal functioning of neuronal cells also depends on this cascade. As such, recent studies have increasingly focused on the impact this pathway has on the development of autistic symptoms. Improper ERK signaling is suspected to be involved in neurotoxicity, and the same might be implicated in autism spectrum disorders (ASD), through a variety of effects including mitochondrial dysfunction and oxidative stress. Niclosamide, an antihelminthic and anti-inflammatory agent, has shown potential in inhibiting this pathway, and countering the effects shown by its overactivity in inflammation. While it has previously been evaluated in other neurological disorders like Alzheimer's Disease and Parkinson's Disease, as well as various cancers by targeting ERK/MAPK, it's efficacy in autism has not yet been evaluated. In this article, we attempt to discuss the potential role of the ERK/MAPK pathway in the pathogenesis of ASD, specifically through mitochondrial damage, before moving to the therapeutic potential of niclosamide in the disorder, mediated by the inhibition of this pathway and its detrimental effects of neuronal development.

UDCA for Drug-Induced Liver Disease: Clinical and Pathophysiological Basis

Drug-induced liver injury (DILI) is an adverse reaction to medications and other xenobiotics that leads to liver dysfunction. Based on differential clinical patterns of injury, DILI is classified into hepatocellular, cholestatic, and mixed types; although hepatocellular DILI is associated with inflammation, necrosis, and apoptosis, cholestatic DILI is associated with bile plugs and bile duct paucity. Ursodeoxycholic acid (UDCA) has been empirically used as a supportive drug mainly in cholestatic DILI, but both curative and prophylactic beneficial effects have been observed for hepatocellular DILI as well, according to preliminary clinical studies. This could reflect the fact that UDCA has a plethora of beneficial effects potentially useful to treat the wide range of injuries with different etiologies and pathomechanisms occurring in both types of DILI, including anticholestatic, antioxidant, anti-inflammatory, antiapoptotic, antinecrotic, mitoprotective, endoplasmic reticulum stress alleviating, and immunomodulatory properties. In this review, a revision of the literature has been performed to evaluate the efficacy of UDCA across the whole DILI spectrum, and these findings were associated with the multiple mechanisms of UDCA hepatoprotection. This should help better rationalize and systematize the use of this versatile and safe hepatoprotector in each type of DILI scenarios.

USP9X mediates an acute adaptive response to MAPK suppression in pancreatic cancer but creates multiple actionable therapeutic vulnerabilities

Pancreatic ductal adenocarcinomas (PDACs) frequently harbor KRAS mutations. Although MEK inhibitors represent a plausible therapeutic option, most PDACs are innately resistant to these agents. Here, we identify a critical adaptive response that mediates resistance. Specifically, we show that MEK inhibitors upregulate the anti-apoptotic protein Mcl-1 by triggering an association with its deubiquitinase, USP9X, resulting in acute Mcl-1 stabilization and protection from apoptosis. Notably, these findings contrast the canonical positive regulation of Mcl-1 by RAS/ERK. We further show that Mcl-1 inhibitors and cyclin-dependent kinase (CDK) inhibitors, which suppress Mcl-1 transcription, prevent this protective response and induce tumor regression when combined with MEK inhibitors. Finally, we identify USP9X as an additional potential therapeutic target. Together, these studies (1) demonstrate that USP9X regulates a critical mechanism of resistance in PDAC, (2) reveal an unexpected mechanism of Mcl-1 regulation in response to RAS pathway suppression, and (3) provide multiple distinct promising therapeutic strategies for this deadly malignancy.

MCL-1 is a clinically targetable vulnerability in breast cancer

Pro-survival members of the BCL-2 family, including MCL-1, are emerging as important proteins during the development and therapeutic response of solid tumors. Notably, high levels of MCL-1 occur in breast cancer, where functional dependency has been demonstrated using cell lines and mouse models. The utility of restoring apoptosis in cancer cells through inhibition of pro-survival BCL-2 proteins has been realized in the clinic, where the first specific inhibitor of BCL-2 is approved for use in leukemia. A variety of MCL-1 inhibitors are now undergoing clinical trials for blood cancer treatment and application of this new class of drugs is also being tested in solid cancers. On-target compounds specific to MCL-1 have demonstrated promising efficacy in preclinical models of breast cancer and show potential to enhance the anti-tumor effect of conventional therapies. Taken together, this makes MCL-1 an extremely attractive target for clinical evaluation in the context of breast cancer.Abbreviations: ADC (antibody-drug conjugate); AML (Acute myeloid leukemia); APAF1 (apoptotic protease activating factor 1); bCAFs (breast cancer associated fibroblasts); BCL-2 (B-cell lymphoma 2); BH (BCL-2 homology); CLL (chronic lymphocytic leukemia); EGF (epidermal growth factor); EMT (epithelial to mesenchymal transition); ER (estrogen receptor); FDA (food and drug administration); GEMM (genetically engineered mouse model); HER2 (human epidermal growth factor 2); IL6 (interleukin 6); IMM (inner mitochondrial membrane); IMS (intermembrane space); MCL-1 (myeloid cell leukemia-1); MOMP (mitochondrial outer membrane permeabilisation); MM (multiple myeloma); PDX (patient-derived xenograft); OMM (outer mitochondrial membrane); PROTAC (proteolysis-targeting chimeras) TNBC (triple negative breast cancer); UPS (ubiquitin mediated proteolysis system).

Targeting the BCL-2-regulated apoptotic pathway for the treatment of solid cancers

The deregulation of apoptosis is a key contributor to tumourigenesis as it can lead to the unwanted survival of rogue cells. Drugs known as the BH3-mimetics targeting the pro-survival members of the BCL-2 protein family to induce apoptosis in cancer cells have achieved clinical success for the treatment of haematological malignancies. However, despite our increasing knowledge of the pro-survival factors mediating the unwanted survival of solid tumour cells, and our growing BH3-mimetics armamentarium, the application of BH3-mimetic therapy in solid cancers has not reached its full potential. This is mainly attributed to the need to identify clinically safe, yet effective, combination strategies to target the multiple pro-survival proteins that typically mediate the survival of solid tumours. In this review, we discuss current and exciting new developments in the field that has the potential to unleash the full power of BH3-mimetic therapy to treat currently recalcitrant solid malignancies.

Bayesian multi-source regression and monocyte-associated gene expression predict BCL-2 inhibitor resistance in acute myeloid leukemia

The FDA recently approved eight targeted therapies for acute myeloid leukemia (AML), including the BCL-2 inhibitor venetoclax. Maximizing efficacy of these treatments requires refining patient selection. To this end, we analyzed two recent AML studies profiling the gene expression and ex vivo drug response of primary patient samples. We find that ex vivo samples often exhibit a general sensitivity to (any) drug exposure, independent of drug target. We observe that this "general response across drugs" (GRD) is associated with FLT3-ITD mutations, clinical response to standard induction chemotherapy, and overall survival. Further, incorporating GRD into expression-based regression models trained on one of the studies improved their performance in predicting ex vivo response in the second study, thus signifying its relevance to precision oncology efforts. We find that venetoclax response is independent of GRD but instead show that it is linked to expression of monocyte-associated genes by developing and applying a multi-source Bayesian regression approach. The method shares information across studies to robustly identify biomarkers of drug response and is broadly applicable in integrative analyses.

The role of post-translational modifications in the regulation of MCL1

Apoptosis is an evolutionarily conserved form of programed cell death (PCD) that has a vital effect on early embryonic development, tissue homeostasis and clearance of damaged cells. Dysregulation of apoptosis can lead to many diseases, such as Alzheimer's disease, cancer, AIDS and heart disease. The anti-apoptotic protein MCL1, a member of the BCL2 family, plays important roles in these physiological and pathological processes. Its high expression is closely related to drug resistances in the treatment of tumor. This review summarizes the structure and function of MCL1, the types of post-translational modifications of MCL1 and their effects on the functions of MCL1, as well as the treatment strategies targeting MCL1 in cancer therapy. The research on the fine regulation of MCL1 will be favorable to the provision of a promising future for the design and screening of MCL1 inhibitors.

Saga of Mcl-1: regulation from transcription to degradation

The members of the Bcl-2 family are the central regulators of various cell death modalities. Some of these proteins contribute to apoptosis, while others counteract this type of programmed cell death, thus balancing cell demise and survival. A disruption of this balance leads to the development of various diseases, including cancer. Therefore, understanding the mechanisms that underlie the regulation of proteins of the Bcl-2 family is of great importance for biomedical research. Among the members of the Bcl-2 family, antiapoptotic protein Mcl-1 is characterized by a short half-life, which renders this protein highly sensitive to changes in its synthesis or degradation. Hence, the regulation of Mcl-1 is of particular scientific interest, and the study of Mcl-1 modulators could aid in the understanding of the mechanisms of disease development and the ways of their treatment. Here, we summarize the present knowledge regarding the regulation of Mcl-1, from transcription to degradation, focusing on aspects that have not yet been described in detail.

ΗΙF1α, EGR1 and SP1 co-regulate the erythropoietin receptor expression under hypoxia: an essential role in the growth of non-small cell lung cancer cells

BACKGROUND

Overexpression of erythropoietin (EPO) and EPO receptor (EPO-R) is associated with poor prognosis in non-small-cell lung carcinoma (NSCLC). Hypoxia, a potent EPO inducer, is a major stimulating factor in the growth of solid tumors. However, how EPO-R expression is regulated under hypoxia is largely unknown.

METHODS

The role of EPO-R in NSCLC cell proliferation was assessed by RNA interference in vitro. Luciferase reporter assays were performed to map the promoter elements involved in the EPO-R mRNA transcription. Nuclear co-immunoprecipitation and chromatin immunoprecipitation were performed to assess the interaction among transcription factors HIF1α, SP1, and EGR1 in the regulation of EPO-R under hypoxia. The expression of key EPO-R transcription factors in clinical specimens were determined by immunohistochemistry.

RESULTS

Hypoxia induced a dosage and time dependent EPO-R mRNA expression in NSCLC cells. Knockdown of EPO-R reduced NSCLC cell growth under hypoxia (P < 0.05). Mechanistically, a SP1-EGR1 overlapped DNA binding sequence was essential to the hypoxia induced EPO-R transcription. In the early phase of hypoxia, HIF1α interacted with EGR1 that negatively regulated EPO-R. With the exit of EGR1 in late phase, HIF1α positively regulated EPO-R expression through additive interaction with SP1. In clinical NSCLC specimen, SP1 was positively while EGR1 was negatively associated with active EPO-R expression (P < 0.05).

CONCLUSIONS

HIF1α, SP1 and EGR1 mediated EPO-R expression played an essential role in hypoxia-induced NSCLC cell proliferation. Our study presents a novel mechanism of EPO-R regulation in the tumor cells, which may provide information support for NSCLC diagnosis and treatment.

p38 MAPK pathway-dependent SUMOylation of Elk-1 and phosphorylation of PIAS2 correlate with the downregulation of Elk-1 activity in heat-stressed HeLa cells

Stress-activated and mitogen-activated protein kinases (MAPKs) regulate gene expression by post-translational modifications of transcription factors. Elk-1, a transcription factor that regulates the expression of immediate early genes, is amenable to regulation by all the three mammalian MAPKs. In the present report, using inhibitors specific for different MAPK pathways, we show that during exposure of HeLa cells to heat stress, Elk-1 is SUMOylated with SUMO1 by p38 MAPK pathway-dependent mechanisms. Elk-1-phosphorylation levels were significantly reduced under similar conditions. We also show that transcriptional activity of Elk-1 as assessed by luciferase reporter expression and qPCR estimation of the expression of genes regulated by Elk-1 was downregulated upon exposure to heat stress; this downregulation was reversed when heat exposure was performed in the presence of either SB203580 (p38 MAPK inhibitor) or ginkgolic acid (inhibitor of SUMOylation). Elk-1 induced transcription is also regulated by PIAS2 which acts as a coactivator upon the activation of extracellular signal-regulated kinases (ERKs) and as a corepressor upon its phosphorylation by p38 MAPK. Since heat stress activates the p38 MAPK pathway, we determined if PIAS2 was phosphorylated in heat-stressed HeLa cells. Our studies indicate that in HeLa cells exposed to heat stress, PIAS2 is phosphorylated by p38 MAPK pathway-dependent mechanisms. Collectively, the results presented demonstrate that in heat-stressed HeLa cells, p38 MAPK pathway-dependent SUMOylation of Elk-1 and phosphorylation of PIAS2 correlate with the downregulation of transactivation by Elk-1.

Targeting SET to restore PP2A activity disrupts an oncogenic CIP2A-feedforward loop and impairs triple negative breast cancer progression

Background

Triple-negative breast cancer (TNBC) remains difficult to be targeted. SET and cancerous inhibitor of protein phosphatase 2A (CIP2A) are intrinsic protein-interacting inhibitors of protein phosphatase 2A (PP2A) and frequently overexpressed in cancers, whereas reactivating PP2A activity has been postulated as an anti-cancer strategy. Here we explored this strategy in TNBC.

Methods

Data from The Cancer Genome Atlas (TCGA) database was analyzed. TNBC cell lines were used for in vitro studies. Cell viability was examined by MTT assay. The apoptotic cells were examined by flow cytometry and Western blot. A SET-PP2A protein-protein interaction antagonist TD19 was used to disrupt signal transduction. In vivo efficacy of TD19 was tested in MDA-MB-468-xenografted animal model.

Findings

TCGA data revealed upregulation of SET and CIP2A and positive correlation of these two gene expressions in TNBC tumors. Ectopic SET or CIP2A increased cell viability, migration, and invasion of TNBC cells. Notably ERK inhibition increased PP2A activity. ERK activation is known crucial for Elk-1 activity, a transcriptional factor regulating CIP2A expression, we hypothesized an oncogenic feedforward loop consisting of pERK/pElk-1/CIP2A/PP2A. This loop was validated by knockdown of PP2A and ectopic expression of Elk-1, showing reciprocal changes in loop members. In addition, ectopic expression of SET increased pAkt, pERK, pElk-1 and CIP2A expressions, suggesting a positive linkage between SET and CIP2A signaling. Moreover, TD19 disrupted this CIP2A-feedforward loop by restoring PP2A activity, demonstrating in vitro and in vivo anti-cancer activity. Mechanistically, TD19 downregulated CIP2A mRNA via inhibiting pERK-mediated Elk-1 nuclear translocation thereby decreased Elk-1 binding to the CIP2A promoter.

Interpretation

These findings suggested that a novel oncogenic CIP2A-feedforward loop contributes to TNBC progression and targeting SET to disrupt this oncogenic CIP2A loop showed therapeutic potential in TNBC.

Lead Neurotoxicity on Human Neuroblastoma Cell Line SH-SY5Y is Mediated via Transcription Factor EGR1/Zif268 Induced Disrupted in Scherophernia-1 Activation

Lead (Pb²⁺) is a well-known type of neurotoxin and chronic exposure to Pb²⁺ induces cognition dysfunction. In this work, the potential role of early growth response gene 1 (EGR1) in the linkage of Pb²⁺ exposure and disrupted in scherophernia-1 (DISC1) activity was investigated. Human neuroblastoma cell line SH-SY5Y was subjected to different concentrations of lead acetate (PbAc) to determine the effect of Pb²⁺ exposure on the cell viability, apoptosis, and activity of EGR1 and DISC1. Then the expression of EGR1 in SH-SY5Y cells was knocked down with specific siRNA to assess the function of EGR1 in Pb²⁺ induced activation of DISC1. The interaction between EGR1 and DISC1 was further validated with dual luciferase assay, Supershift electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP)-PCR. Administration of PbAc decreased cell viability and induced apoptosis in SH-SY5Y cells in a dose-dependent manner. Additionally, exposure to PbAc also up-regulated expression of EGR1 and DISC1 at all concentrations. Knockdown of EGR1 blocked the effect of PbAc on SH-SY5Y cells, indicating the central role of EGR1 in the function of Pb²⁺ on activity of DISC1. Based on the results of dual luciferase assay, Supershift EMSA, and ChIP-PCR, EGR1 mediated the effect of Pb²⁺ on DISC1 by directly bound to the promoter region of DISC1 gene. The current study elaborated the mechanism involved in the effect of Pb²⁺ exposure on expression of DISC1 for the first time: EGR1 activated by Pb²⁺ substitution of zinc triggered the transcription of DISC1 gene by directly binding to its promoter.

Control of cell death and mitochondrial fission by ERK1/2 MAP kinase signalling

The ERK1/2 signalling pathway is best known for its role in connecting activated growth factor receptors to changes in gene expression due to activated ERK1/2 entering the nucleus and phosphorylating transcription factors. However, active ERK1/2 also translocate to a variety of other organelles including the endoplasmic reticulum, endosomes, golgi and mitochondria to access specific substrates and influence cell physiology. In this article, we review two aspects of ERK1/2 signalling at the mitochondria that are involved in regulating cell fate decisions. First, we describe the prominent role of ERK1/2 in controlling the BCL2-regulated, cell-intrinsic apoptotic pathway. In most cases ERK1/2 signalling promotes cell survival by activating prosurvival BCL2 proteins (BCL2, BCL-xL and MCL1) and repressing prodeath proteins (BAD, BIM, BMF and PUMA). This prosurvival signalling is co-opted by oncogenes to confer cancer cell-specific survival advantages and we describe how this information has been used to develop new drug combinations. However, ERK1/2 can also drive the expression of the prodeath protein NOXA to control 'autophagy or apoptosis' decisions during nutrient starvation. We also describe recent studies demonstrating a link between ERK1/2 signalling, DRP1 and the mitochondrial fission machinery and how this may influence metabolic reprogramming during tumorigenesis and stem cell reprogramming. With advances in subcellular proteomics it is likely that new roles for ERK1/2, and new substrates, remain to be discovered at the mitochondria and other organelles.

miR-596 Modulates Melanoma Growth by Regulating Cell Survival and Death

Tumors grow because cancer cells lack the ability to balance cell survival and death signaling pathways. miR-596, a microRNA located at the 8p23.3 locus, has been shown by the TCGA-Assembler to be deleted in a significant number of melanoma samples. Here, we also validated the low levels of miR-596 in melanoma compared to tissue nevi, and Kaplan-Meier curve analysis revealed that low miR-596 expression was associated with worse overall survival. Moreover, we showed that miR-596 overexpression effectively inhibited MAPK/ERK signaling, cell proliferation, migration, and invasion and increased the cell apoptosis of melanoma cells. In addition, we found that miR-596 directly targets MEK1 and two apoptotic proteins, MCL1, and BCL2L1, in melanoma cells. Our findings indicated that miR-596 is an important miRNA that both negatively regulates the MAPK/ERK signaling pathway by targeting MEK1 and modulates the apoptosis pathway by targeting MCL1 and BCL2L1, suggesting that miR-596 could be a therapeutic candidate for treating melanoma, and a prognostic factor for melanoma patients.

ERK1/2 signalling protects against apoptosis following endoplasmic reticulum stress but cannot provide long-term protection against BAX/BAK-independent cell death

Disruption of protein folding in the endoplasmic reticulum (ER) causes ER stress. Activation of the unfolded protein response (UPR) acts to restore protein homeostasis or, if ER stress is severe or persistent, drive apoptosis, which is thought to proceed through the cell intrinsic, mitochondrial pathway. Indeed, cells that lack the key executioner proteins BAX and BAK are protected from ER stress-induced apoptosis. Here we show that chronic ER stress causes the progressive inhibition of the extracellular signal-regulated kinase (ERK1/2) signalling pathway. This is causally related to ER stress since reactivation of ERK1/2 can protect cells from ER stress-induced apoptosis whilst ERK1/2 pathway inhibition sensitises cells to ER stress. Furthermore, cancer cell lines harbouring constitutively active BRAFV600E are addicted to ERK1/2 signalling for protection against ER stress-induced cell death. ERK1/2 signalling normally represses the pro-death proteins BIM, BMF and PUMA and it has been proposed that ER stress induces BIM-dependent cell death. We found no evidence that ER stress increased the expression of these proteins; furthermore, BIM was not required for ER stress-induced death. Rather, ER stress caused the PERK-dependent inhibition of cap-dependent mRNA translation and the progressive loss of pro-survival proteins including BCL2, BCLXL and MCL1. Despite these observations, neither ERK1/2 activation nor loss of BAX/BAK could confer long-term clonogenic survival to cells exposed to ER stress. Thus, ER stress induces cell death by at least two biochemically and genetically distinct pathways: a classical BAX/BAK-dependent apoptotic response that can be inhibited by ERK1/2 signalling and an alternative ERK1/2- and BAX/BAK-independent cell death pathway.

Myocardin and Stat3 act synergistically to inhibit cardiomyocyte apoptosis

Signal transducer and activator of transcription 3 (Stat3) and Myocardin regulate cardiomyocyte differentiation, proliferation, and apoptosis. We report a novel aspect of the cellular function of Myocardin and Stat3 in the regulation of cardiomyocyte apoptosis. Myocardin and Stat3 showed anti-apoptotic function by increasing the expression of Bcl-2 while reducing expression of the pro-apoptotic genes Bax, Apaf-1, caspase-9, and caspase-3. Moreover, myocardin/Stat3-mediated activation of Bcl-2 and Mcl-1 transcription is contingent on the CArG box. Myocardin and Stat3 synergistically inhibited staurosporine-induced cardiomyocyte apoptosis by up-regulating expression of anti-apoptotic Bcl-2 and Mcl-1 in neonatal rat cardiomyocytes. These results describe a novel anti-apoptotic Myocardin/Stat3 signaling pathway operating during cardiomyocyte apoptosis. This provides a molecular explanation for cardiomyocyte apoptosis inhibition as a critical component of myocardial protection.

Upregulation of SRF Is Associated With Hypoxic Pulmonary Hypertension by Promoting Viability of Smooth Muscle Cells via Increasing Expression of Bcl-2

The aim of study was to investigate the involvement of hypoxia-induced upregulation of serum response factor (SRF) and its downstream effector, B cell leukemia-2 (Bcl-2), in hypoxia-induced pulmonary hypertension (PH). Immunohistochemistry analysis and western blot analysis were used to detect the levels of SRF and Bcl-2 in rats exposed to hypoxia. Furthermore, the regulatory relationship between SRF and Bcl-2 was investigated in PASMCs using real-time PCR and western-blot analysis. We found that mPAP (mean pulmonary arterial pressure) and WA (the ratio of vascular wall area to external diameter) were increased after exposure to hypoxia, while LA (the ratio of vascular lumen area to total area) decreased after exposure to hypoxia. The immunohistochemistry analysis displayed a substantial increase in SRF and Bcl-2 in pulmonary arterial walls after 14 days of hypoxia. And the western blotting showed that SRF and Bcl-2 protein levels were much higher after 7 days of hypoxia and then remained at a high level. And then the levels of SRF and Bcl-2 in pulmonary artery smooth muscle cells (PASMCs) exposed to hypoxia were substantially suppressed following introduction of SRF siRNA, and the level of Bcl-2 was remarkably inhibited by Bcl-2 siRNA, while Bcl-2 siRNA had no effect on SRF level. Finally, SRF siRNA, and Bcl-2 siRNA significantly reduced viability of PASMCs exposed to hypoxia, and enhanced apoptosis of PASMCs exposed to hypoxia. These data validated that SRF responded to hypoxia, which subsequently was involved in pulmonary hypertension by abnormally promoting viability of PASMCs via modulating expression of Bcl-2. J. Cell. Biochem. 118: 2731-2738, 2017. © 2017 Wiley Periodicals, Inc.

Jaceosidin induces apoptosis through Bax activation and down-regulation of Mcl-1 and c-FLIP expression in human renal carcinoma Caki cells

Jaceosidin is a flavonoid isolated from Artemisia vestita that has been reported to possess anti-tumor and anti-proliferative activities in many cancer cells. In this study, we investigated the anti-tumor activity of jaceosodin in renal carcinoma cells. Jaceosidin induced apoptosis in multiple human renal carcinoma cells (Caki, ACHN, A498, and 786-O), lung cancer cells (A549) and glioma cells (U251MG). In contrast, jaceosidin does not induce apoptosis in normal human umbilical vein cells (EA.hy926). Apoptotic cell death was associated with the activation of caspase-3 and cleavage of poly (ADP-ribose) polymerase. Treatment with jaceosidin also caused loss of mitochondrial membrane potential (MMP) and Bax activation, which led to the release of cytochrome c into the cytosol. We also found that jaceosidin downregulated Mcl-1 and c-FLIP expression at the transcriptional level and that ectopic expression of Mcl-1 and c-FLIP blocked jaceosidin-induced apoptosis. Cumulatively, our results suggest that jaceosidin induces apoptosis in renal carcinoma cells through Bax activation and reduces Mcl-1 and c-FLIP expression.

An Elk transcription factor is required for Runx-dependent survival signaling in the sea urchin embryo

Elk proteins are Ets family transcription factors that regulate cell proliferation, survival, and differentiation in response to ERK (extracellular-signal regulated kinase)-mediated phosphorylation. Here we report the embryonic expression and function of Sp-Elk, the single Elk gene of the sea urchin Strongylocentrotus purpuratus. Sp-Elk is zygotically expressed throughout the embryo beginning at late cleavage stage, with peak expression occurring at blastula stage. Morpholino antisense-mediated knockdown of Sp-Elk causes blastula-stage developmental arrest and embryo disintegration due to apoptosis, a phenotype that is rescued by wild-type Elk mRNA. Development is also rescued by Elk mRNA encoding a serine to aspartic acid substitution (S402D) that mimics ERK-mediated phosphorylation of a conserved site that enhances DNA binding, but not by Elk mRNA encoding an alanine substitution at the same site (S402A). This demonstrates both that the apoptotic phenotype of the morphants is specifically caused by Elk depletion, and that phosphorylation of serine 402 of Sp-Elk is critical for its anti-apoptotic function. Knockdown of Sp-Elk results in under-expression of several regulatory genes involved in cell fate specification, cell cycle control, and survival signaling, including the transcriptional regulator Sp-Runt-1 and its target Sp-PKC1, both of which were shown previously to be required for cell survival during embryogenesis. Both Sp-Runt-1 and Sp-PKC1 have sequences upstream of their transcription start sites that specifically bind Sp-Elk. These results indicate that Sp-Elk is the signal-dependent activator of a feed-forward gene regulatory circuit, consisting also of Sp-Runt-1 and Sp-PKC1, which actively suppresses apoptosis in the early embryo.

The Dual MEK/FLT3 Inhibitor E6201 Exerts Cytotoxic Activity against Acute Myeloid Leukemia Cells Harboring Resistance-Conferring FLT3 Mutations

Fms-like tyrosine kinase 3 (FLT3) inhibition has elicited encouraging responses in acute myeloid leukemia (AML) therapy. Unfortunately, unless combined with a bone marrow transplant, disease relapse is frequent. In addition to the acquired point mutations in the FLT3 kinase domain that contribute to FLT3 inhibitor resistance, MEK/ERK signaling is persistently activated in AML cells even when FLT3 phosphorylation is continually suppressed. Thus, concomitant targeting of FLT3 and MAPK may potentially exert synergistic activity to counteract the resistance of AML cells to FLT3-targeted therapy. In this study, we investigated the antileukemia activity of a MEK1 and FLT3 dual inhibitor, E6201, in AML cells resistant to FLT3 inhibition. We found that E6201 exerted profound apoptogenic effects on AML cells harboring resistance-conferring FLT3 mutations. This activity appeared to be p53 dependent, and E6201-induced cytotoxicity was retained under hypoxic culture conditions and during coculture with mesenchymal stem cells that mimic the AML microenvironment. Furthermore, E6201 markedly reduced leukemia burden and improved the survival of mice in a human FLT3-mutated AML model. Collectively, our data provide a preclinical basis for the clinical evaluation of E6201 in AML patients harboring FLT3 mutations, including those who relapse following FLT3-targeted monotherapy.

Preclinical efficacy of sepantronium bromide (YM155) in multiple myeloma is conferred by down regulation of Mcl-1

The inhibitor-of-apoptosis family member survivin has been reported to inhibit apoptosis and regulate mitosis and cytokinesis. In multiple myeloma, survivin has been described to be involved in downstream sequelae of various therapeutic agents. We assessed 1093 samples from previously untreated patients, including two independent cohorts of 392 and 701 patients, respectively. Survivin expression was associated with cell proliferation, adverse prognostic markers, and inferior event-free and overall survival, supporting the evaluation of survivin as a therapeutic target in myeloma. The small molecule suppressant of survivin - YM155 - is in clinical development for the treatment of solid tumors. YM155 potently inhibited proliferation and induced apoptosis in primary myeloma cells and cell lines. Gene expression and protein profiling revealed the critical roles of IL6/STAT3-signaling and the unfolded protein response in the efficacy of YM155. Both pathways converged to down regulate anti-apoptotic Mcl-1 in myeloma cells. Conversely, growth inhibition and apoptotic cell death by YM155 was rescued by ectopic expression of Mcl-1 but not survivin, identifying Mcl-1 as the pivotal downstream target of YM155 in multiple myeloma. Mcl-1 expression was likewise associated with adverse prognostic markers, and inferior survival. Our results strongly support the clinical evaluation of YM155 in patients with multiple myeloma.

Proteinase-activated receptor 2 (PAR2) decreases apoptosis in colonic epithelial cells

Mucosal biopsies from inflamed colon of inflammatory bowel disease patients exhibit elevated epithelial apoptosis compared with those from healthy individuals, disrupting mucosal homeostasis and perpetuating disease. Therapies that decrease intestinal epithelial apoptosis may, therefore, ameliorate inflammatory bowel disease, but treatments that specifically target apoptotic pathways are lacking. Proteinase-activated receptor-2 (PAR2), a G protein-coupled receptor activated by trypsin-like serine proteinases, is expressed on intestinal epithelial cells and stimulates mitogenic pathways upon activation. We sought to determine whether PAR2 activation and signaling could rescue colonic epithelial (HT-29) cells from apoptosis induced by proapoptotic cytokines that are increased during inflammatory bowel disease. The PAR2 agonists 2-furoyl-LIGRLO (2f-LI), SLIGKV and trypsin all significantly reduced cleavage of caspase-3, -8, and -9, poly(ADP-ribose) polymerase, and the externalization of phosphatidylserine after treatment of cells with IFN-γ and TNF-α. Knockdown of PAR2 with siRNA eliminated the anti-apoptotic effect of 2f-LI and increased the sensitivity of HT-29 cells to cytokine-induced apoptosis. Concurrent inhibition of both MEK1/2 and PI3K was necessary to inhibit PAR2-induced survival. 2f-LI was found to increase phosphorylation and inactivation of pro-apoptotic BAD at Ser(112) and Ser(136) by MEK1/2 and PI3K-dependent signaling, respectively. PAR2 activation also increased the expression of anti-apoptotic MCL-1. Simultaneous knockdown of both BAD and MCL-1 had minimal effects on PAR2-induced survival, whereas single knockdown had no effect. We conclude that PAR2 activation reduces cytokine-induced epithelial apoptosis via concurrent stimulation of MEK1/2 and PI3K but little involvement of MCL-1 and BAD. Our findings represent a novel mechanism whereby serine proteinases facilitate epithelial cell survival and may be important in the context of colonic healing.

Transcription factor Elk-1 participates in the interleukin-1β-dependent regulation of expression of immediate early response gene 3 (IER3)

Immediate early response gene 3 (IER3) encodes a protein involved in the regulation of apoptosis and differentiation. Recently the role of IER3 in the regulation of extracellular signal-regulated kinases (ERKs) was discovered. IER3 prolongs ERKs activation by inhibition of phosphatase PP2A. Here we show that interleukin-1β (IL-1β)-induced IER3 expression is mediated by the ERK1/2 target, transcription factor Elk-1. We identified sequences in the IER3 promoter responsible for its ERKs-dependent activation, namely ETS5/6. Elk-1 binds to these sequences and is phosphorylated following IL-1β stimulation. Mutation of ETS5/6 binding site abolishes activation of IER3 promoter by IL-1β as well as by the constitutively active form of Elk-1 (Elk-VP16). Thus IER3 acts not only as a regulator of ERKs activation, but also as a ERKs-Elk-1-dependent downstream effector.

Rational combination of dual PI3K/mTOR blockade and Bcl-2/-xL inhibition in AML

Acute myeloid leukemia (AML) continues to represent an area of critical unmet need with respect to new and effective targeted therapies. The Bcl-2 family of pro- and antiapoptotic proteins stands at the crossroads of cellular survival and death, and the expression of and interactions between these proteins determine tumor cell fate. Malignant cells, which are often primed for apoptosis, are particularly vulnerable to the simultaneous disruption of cooperative survival signaling pathways. Indeed, the single agent activity of agents such as mammalian target of rapamycin (mTOR) and mitogen-activated protein kinase kinase (MEK) inhibitors in AML has been modest. Much work in recent years has focused on strategies to enhance the therapeutic potential of the bona fide BH3-mimetic, ABT-737, which inhibits B-cell lymphoma 2 (Bcl-2) and Bcl-xL. Most of these strategies target Mcl-1, an antiapoptotic protein not inhibited by ABT-737. The phosphatidylinositol-3-kinase (PI3K)/Akt/mTOR and Ras/Raf/MEK/ERK signaling pathways are central to the growth, proliferation, and survival of AML cells, and there is much interest currently in pharmacologically interrupting these pathways. Dual inhibitors of PI3K and mTOR overcome some intrinsic disadvantages of rapamycin and its derivatives, which selectively inhibit mTOR. In this review, we discuss why combining dual PI3K/mTOR blockade with inhibition of Bcl-2 and Bcl-xL, by virtue of allowing coordinate inhibition of three mutually synergistic pathways in AML cells, may be a particularly attractive therapeutic strategy in AML, the success of which may be predicted for by basal Akt activation.

Evaluation of apoptosis induction by concomitant inhibition of MEK, mTOR, and Bcl-2 in human acute myelogenous leukemia cells

Aberrant activation of multiple signaling pathways is common in acute myelogenous leukemia (AML) cells, which can be linked to a poor prognosis for patients with this disease. Previous research with mTOR or MEK inhibitors revealed cytostatic, rather than cytotoxic, effects in in vitro and in vivo AML models. We evaluated the combination effect of the mTOR inhibitor AZD8055 and the MEK inhibitor selumetinib on human AML cell lines and primary AML samples. This combination demonstrated synergistic proapoptotic effects in AML cells with high basal activation of MEK and mTOR. We next incorporated the BH3 mimetic ABT-737 into this combination regimen to block Bcl-2, which further enhanced the apoptogenic effect of MEK/mTOR inhibition. The combination treatment also had a striking proapoptotic effect in CD33(+)/CD34(+) AML progenitor cells from primary AML samples with NRAS mutations. Mechanistically, upregulation of the proapoptotic protein Bim, accompanied by the downregulation of the antiapoptotic protein Mcl-1 (mainly via protein degradation), seemed to play critical roles in enhancing the combination drug effect. Furthermore, the modulation of survivin, Bax, Puma, and X-chromosome-linked inhibitor of apoptosis protein (XIAP) expression suggested a role for mitochondria-mediated apoptosis in the cytotoxicity of the drug combination. Consequently, the concomitant blockade of prosurvival MEK/mTOR signaling and the deactivation of Bcl-2 could provide a mechanism-based integrated therapeutic strategy for the eradication of AML cells.

Regulation of Mcl-1 by constitutive activation of NF-κB contributes to cell viability in human esophageal squamous cell carcinoma cells

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is one of the most lethal malignancies with a 5-year survival rate less than 15%. Understanding of the molecular mechanisms involved in the pathogenesis of ESCC becomes critical to develop more effective treatments.

METHODS

Mcl-1 expression was measured by reverse transcription (RT)-PCR and Western blotting. Human Mcl-1 promoter activity was evaluated by reporter gene assay. The interactions between DNA and transcription factors were confirmed by electrophoretic mobility shift assay (EMSA) in vitro and by chromatin immunoprecipitation (ChIP) assay in cells.

RESULTS

Four human ESCC cell lines, TE-1, Eca109, KYSE150 and KYSE510, are revealed increased levels of Mcl-1 mRNA and protein compare with HaCaT, an immortal non-tumorigenic cell line. Results of reporter gene assays demonstrate that human Mcl-1 promoter activity is decreased by mutation of kappaB binding site, specific NF-kappaB inhibitor Bay11-7082 or dominant inhibitory molecule DNMIkappaBalpha in TE-1 and KYSE150 cell lines. Mcl-1 protein level is also attenuated by Bay11-7082 treatment or co-transfection of DNMIkappaBalpha in TE-1 and KYSE150 cells. EMSA results indicate that NF-kappaB subunits p50 and p65 bind to human Mcl-1-kappaB probe in vitro. ChIP assay further confirm p50 and p65 directly bind to human Mcl-1 promoter in intact cells, by which regulates Mcl-1 expression and contributes to the viability of TE-1 cells.

CONCLUSIONS

Our data provided evidence that one of the mechanisms of Mcl-1 expression in human ESCC is regulated by the activation of NF-kappaB signaling. The newly identified mechanism might provide a scientific basis for developing effective approaches to treatment human ESCC.

The transcription factor Zif268/Egr1, brain plasticity, and memory

The capacity to remember our past experiences and organize our future draws on a number of cognitive processes that allow our brain to form and store neural representations that can be recalled and updated at will. In the brain, these processes require mechanisms of neural plasticity in the activated circuits, brought about by cellular and molecular changes within the neurons activated during learning. At the cellular level, a wealth of experimental data accumulated in recent years provides evidence that signaling from synapses to nucleus and the rapid regulation of the expression of immediate early genes encoding inducible, regulatory transcription factors is a key step in the mechanisms underlying synaptic plasticity and the modification of neural networks required for the laying down of memories. In the activated neurons, these transcriptional events are thought to mediate the activation of selective gene programs and subsequent synthesis of proteins, leading to stable functional and structural remodeling of the activated networks, so that the memory can later be reactivated upon recall. Over the past few decades, novel insights have been gained in identifying key transcriptional regulators that can control the genomic response of synaptically activated neurons. Here, as an example of this approach, we focus on one such activity-dependent transcription factor, Zif268, known to be implicated in neuronal plasticity and memory formation. We summarize current knowledge about the regulation and function of Zif268 in different types of brain plasticity and memory processes.

BCL-2 inhibition with ABT-737 prolongs survival in an NRAS/BCL-2 mouse model of AML by targeting primitive LSK and progenitor cells

Myelodysplastic syndrome (MDS) transforms into an acute myelogenous leukemia (AML) with associated increased bone marrow (BM) blast infiltration. Using a transgenic mouse model, MRP8[NRASD12/hBCL-2], in which the NRAS:BCL-2 complex at the mitochondria induces MDS progressing to AML with dysplastic features, we studied the therapeutic potential of a BCL-2 homology domain 3 mimetic inhibitor, ABT-737. Treatment significantly extended lifespan, increased survival of lethally irradiated secondary recipients transplanted with cells from treated mice compared with cells from untreated mice, with a reduction of BM blasts, Lin-/Sca-1(+)/c-Kit(+), and progenitor populations by increased apoptosis of infiltrating blasts of diseased mice assessed in vivo by technicium-labeled annexin V single photon emission computed tomography and ex vivo by annexin V/7-amino actinomycin D flow cytometry, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling, caspase 3 cleavage, and re-localization of the NRAS:BCL-2 complex from mitochondria to plasma membrane. Phosphoprotein analysis showed restoration of wild-type (WT) AKT or protein kinase B, extracellular signal-regulated kinase 1/2 and mitogen-activated protein kinase patterns in spleen cells after treatment, which showed reduced mitochondrial membrane potential. Exon specific gene expression profiling corroborates the reduction of leukemic cells, with an increase in expression of genes coding for stem cell development and maintenance, myeloid differentiation, and apoptosis. Myelodysplastic features persist underscoring targeting of BCL-2-mediated effects on MDS-AML transformation and survival of leukemic cells.

The F-box protein FBXO25 promotes the proteasome-dependent degradation of ELK-1 protein

FBXO25 is one of the 69 known human F-box proteins that serve as specificity factors for a family of ubiquitin ligases composed of SKP1, Rbx1, Cullin1, and F-box protein (SCF1) that are involved in targeting proteins for degradation across the ubiquitin proteasome system. However, the substrates of most SCF E3 ligases remain unknown. Here, we applied an in chip ubiquitination screen using a human protein microarray to uncover putative substrates for the FBXO25 protein. Among several novel putative targets identified, the c-fos protooncogene regulator ELK-1 was characterized as the first endogenous substrate for SCF1(FBXO25) E3 ligase. FBXO25 interacted with and mediated the ubiquitination and proteasomal degradation of ELK-1 in HEK293T cells. In addition, FBXO25 overexpression suppressed induction of two ELK-1 target genes, c-fos and egr-1, in response to phorbol 12-myristate 13-acetate. Together, our findings show that FBXO25 mediates ELK-1 degradation through the ubiquitin proteasome system and thereby plays a role in regulating the activation of ELK-1 pathway in response to mitogens.

That which does not kill me makes me stronger; combining ERK1/2 pathway inhibitors and BH3 mimetics to kill tumour cells and prevent acquired resistance

Oncogenic mutations in RAS or BRAF can drive the inappropriate activation of the ERK1/2. In many cases, tumour cells adapt to become addicted to this deregulated ERK1/2 signalling for their proliferation, providing a therapeutic window for tumour-selective growth inhibition. As a result, inhibition of ERK1/2 signalling by BRAF or MEK1/2 inhibitors is an attractive therapeutic strategy. Indeed, the first BRAF inhibitor, vemurafenib, has now been approved for clinical use, while clinical evaluation of MEK1/2 inhibitors is at an advanced stage. Despite this progress, it is apparent that tumour cells adapt quickly to these new targeted agents so that tumours with acquired resistance can emerge within 6-9 months of primary treatment. One of the major reasons for this is that tumour cells typically respond to BRAF or MEK1/2 inhibitors by undergoing a G1 cell cycle arrest rather than dying. Indeed, although inhibition of ERK1/2 invariably increases the expression of pro-apoptotic BCL2 family proteins, tumour cells undergo minimal apoptosis. This cytostatic response may simply provide the cell with the opportunity to adapt and acquire resistance. Here we discuss recent studies that demonstrate that combination of BRAF or MEK1/2 inhibitors with inhibitors of pro-survival BCL2 proteins is synthetic lethal for ERK1/2-addicted tumour cells. This combination effectively transforms the cytostatic response of BRAF and MEK1/2 inhibitors into a striking apoptotic cell death response. This not only augments the primary efficacy of BRAF and MEK1/2 inhibitors but delays the onset of acquired resistance to these agents, validating their combination in the clinic.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

Phospho-Ser383-Elk-1 is localized to the mitotic spindles during cell cycle and interacts with mitotic kinase Aurora-A

Elk-1 is a member of the E-twenty-six (ETS) domain superfamily of transcription factors and has been traditionally associated with mitogen-induced immediate early gene transcription upon phosphorylation by mitogen activated protein kinases (ERK/MAPK). Elk-1 is not only upregulated but also phosphorylated in brain tumour cells. However, in this study, we show for the first time that S383-phosphorylated Elk-1 (P-S383-Elk-1) is associated with mitotic spindle poles from metaphase through telophase and relocates to the spindle midbody during cytokinesis, while Thr417Ala mutation is associated with DNA throughout mitosis. Serine 383 phosphorylation appears to be important for polar localization of Elk-1, since exogenous protein including serine-to-alanine mutation was seen to be distributed throughout the spindle fibres. We further show that Elk-1 interacts with the cell cycle kinase Aurora-A, and when Aurora inhibitors are used, P-S383-Elk-1 fails to localize to the poles and remains associated with DNA. Apart from one transcriptional repressor molecule, Kaiso, this is the first time a transactivator was shown to possess such mitotic localization and interaction. The functional significance and detailed mechanism of this cell cycle-related localization of Elk-1 are yet to be determined.

Understanding sensitivity to BH3 mimetics: ABT-737 as a case study to foresee the complexities of personalized medicine

BH3 mimetics such as ABT-737 and navitoclax bind to the BCL-2 family of proteins and induce apoptosis through the intrinsic apoptosis pathway. There is considerable variability in the sensitivity of different cells to these drugs. Understanding the molecular basis of this variability will help to determine which patients will benefit from these drugs. Furthermore, this understanding aids in the design of rational strategies to increase the sensitivity of cells which are otherwise resistant to BH3 mimetics. We discuss how the expression of BCL-2 family proteins regulates the sensitivity to ABT-737. One of these, MCL-1, has been widely described as contributing to resistance to ABT-737 which might suggest a poor response in patients with cancers that express levels of MCL-1. In some cases, resistance to ABT-737 conferred by MCL-1 is overcome by the expression of pro-apoptotic proteins that bind to apoptosis inhibitors such as MCL-1. However, the distribution of the pro-apoptotic proteins amongst the various apoptosis inhibitors also influences sensitivity to ABT-737. Furthermore, the expression of both pro- and anti-apoptotic proteins can change dynamically in response to exposure to ABT-737. Thus, there is significant complexity associated with predicting response to ABT-737. This provides a paradigm for the multiplicity of intricate factors that determine drug sensitivity which must be considered for the full implementation of personalized medicine.

MEK inhibition enhances ABT-737-induced leukemia cell apoptosis via prevention of ERK-activated MCL-1 induction and modulation of MCL-1/BIM complex

Recently, strategies for acute myeloid leukemia (AML) therapy have been developed that target anti-apoptotic BCL2 family members using BH3-mimetic drugs such as ABT-737. Though effective against BCL2 and BCL-X(L), ABT-737 poorly inhibits MCL-1. Here we report that, unexpectedly, ABT-737 induces activation of the extracellular receptor activated kinase and induction of MCL-1 in AML cells. MEK inhibitors such as PD0325901 and CI-1040 have been used successfully to suppress MCL-1. We report that PD0325901 blocked ABT-737-induced MCL-1 expression, and when combined with ABT-737 resulted in potent synergistic killing of AML-derived cell lines, primary AML blast and CD34+38-123+ progenitor/stem cells. Finally, we tested the combination of ABT-737 and CI-1040 in a murine xenograft model using MOLM-13 human leukemia cells.Whereas control mice and CI-1040-treated mice exhibited progressive leukemia growth, ABT-737, and to a significantly greater extent, ABT-737+CI-1040 exerted major anti-leukemia activity. Collectively, results demonstrated unexpected anti-apoptotic interaction between the BCL2 family-targeted BH3-mimetic ABT-737 and mitogen-activated protein kinase signaling in AML cells: the BH3 mimetic is not only restrained in its activity by MCL-1, but also induces its expression. However, concomitant inhibition by BH3 mimetics and MEK inhibitors could abrogate this effect and may be developed into a novel and effective therapeutic strategy for patients with AML.

EGF activates TTP expression by activation of ELK-1 and EGR-1 transcription factors

Background

Tristetraprolin (TTP) is a key mediator of processes such as inflammation resolution, the inhibition of autoimmunity and in cancer. It carries out this role by the binding and degradation of mRNA transcripts, thereby decreasing their half-life. Transcripts modulated by TTP encode proteins such as cytokines, pro-inflammatory agents and immediate-early response proteins. TTP can also modulate neoplastic phenotypes in many cancers. TTP is induced and functionally regulated by a spectrum of both pro- and anti-inflammatory cytokines, mitogens and drugs in a MAPK-dependent manner. So far the contribution of p38 MAPK to the regulation of TTP expression and function has been best described.

Results

Our results demonstrate the induction of the gene coding TTP (ZFP36) by EGF through the ERK1/2-dependent pathway and implicates the transcription factor ELK-1 in this process. We show that ELK-1 regulates ZFP36 expression by two mechanisms: by binding the ZFP36 promoter directly through ETS-binding site (+ 883 to +905 bp) and by inducing expression of EGR-1, which in turn increases ZFP36 expression through sequences located between -111 and -103 bp.

Conclusions

EGF activates TTP expression via ELK-1 and EGR-1 transcription factors.

Coordinated sumoylation and ubiquitination modulate EGF induced EGR1 expression and stability

Background

Human early growth response-1 (EGR1) is a member of the zing-finger family of transcription factors induced by a range of molecular and environmental stimuli including epidermal growth factor (EGF). In a recently published paper we demonstrated that integrin/EGFR cross-talk was required for Egr1 expression through activation of the Erk1/2 and PI3K/Akt/Forkhead pathways. EGR1 activity and stability can be influenced by many different post-translational modifications such as acetylation, phosphorylation, ubiquitination and the recently discovered sumoylation. The aim of this work was to assess the influence of sumoylation on EGF induced Egr1 expression and/or stability.

Methods

We modulated the expression of proteins involved in the sumoylation process in ECV304 cells by transient transfection and evaluated Egr1 expression in response to EGF treatment at mRNA and protein levels.

Results

We demonstrated that in ECV304 cells Egr1 was transiently induced upon EGF treatment and a fraction of the endogenous protein was sumoylated. Moreover, SUMO-1/Ubc9 over-expression stabilized EGF induced ERK1/2 phosphorylation and increased Egr1 gene transcription. Conversely, in SUMO-1/Ubc9 transfected cells, EGR1 protein levels were strongly reduced. Data obtained from protein expression and ubiquitination analysis, in the presence of the proteasome inhibitor MG132, suggested that upon EGF stimuli EGR1 sumoylation enhanced its turnover, increasing ubiquitination and proteasome mediated degradation.

Conclusions

Here we demonstrate that SUMO-1 modification improving EGR1 ubiquitination is involved in the modulation of its stability upon EGF mediated induction.

ELK4 neutralization sensitizes glioblastoma to apoptosis through downregulation of the anti-apoptotic protein Mcl-1

Glioma is the most common adult primary brain tumor. Its most malignant form, glioblastoma multiforme (GBM), is almost invariably fatal, due in part to the intrinsic resistance of GBM to radiation- and chemotherapy-induced apoptosis. We analyzed B-cell leukemia-2 (Bcl-2) anti-apoptotic proteins in GBM and found myeloid cell leukemia-1 (Mcl-1) to be the highest expressed in the majority of malignant gliomas. Mcl-1 was functionally important, as neutralization of Mcl-1 induced apoptosis and increased chemotherapy-induced apoptosis. To determine how Mcl-1 was regulated in glioma, we analyzed the promoter and identified a novel functional single nucleotide polymorphism in an uncharacterized E26 transformation-specific (ETS) binding site. We identified the ETS transcription factor ELK4 as a critical regulator of Mcl-1 in glioma, since ELK4 downregulation was shown to reduce Mcl-1 and increase sensitivity to apoptosis. Importantly the presence of the single nucleotide polymorphism, which ablated ELK4 binding in gliomas, was associated with lower Mcl-1 levels and a greater dependence on Bcl-xL. Furthermore, in vivo, ELK4 downregulation reduced tumor formation in glioblastoma xenograft models. The critical role of ELK4 in Mcl-1 expression and protection from apoptosis in glioma defines ELK4 as a novel potential therapeutic target for GBM.

Vinblastine sensitizes leukemia cells to cyclin-dependent kinase inhibitors, inducing acute cell cycle phase-independent apoptosis

The efficacy of many chemotherapeutic agents can be attenuated by expression of the anti-apoptotic proteins Bcl-2, Bcl-X(L) and Mcl-1. Flavopiridol and dinaciclib are cyclin-dependent kinase 7 and 9 inhibitors that transcriptionally inhibit expression of Mcl-1. We have investigated the ability of flavopiridol and dinaciclib to sensitize a panel of leukemia cell lines to vinblastine and paclitaxel. Both drugs acutely sensitized most of the leukemia lines to vinblastine, with 100% apoptosis in 4 h. Furthermore, dinaciclib sensitized freshly isolated chronic lymphocytic leukemia cells to vinblastine. This rapid induction of apoptosis was attributed to vinblastine-mediated activation of JNK because (a) flavopiridol and dinaciclib failed to induce apoptosis when combined with non-JNK activating concentrations of vinblastine; (b) JNK inhibitors suppressed JNK activity and prevented apoptosis; (c) flavopiridol did not potentiate apoptosis induced by paclitaxel which does not activate JNK in these cells; and (d) Jurkat cells failed to activate JNK in response to vinblastine and were not sensitive to combinations of vinblastine and flavopiridol or dinaciclib. The rapid induction of apoptosis by this combination in multiple cell systems but not in normal lymphocytes provides justification for performing a clinical trial to assess the efficacy in patients.

ETS-domain transcription factor Elk-1 mediates neuronal survival: SMN as a potential target

Elk-1 belongs to the ternary complex factors (TCFs) subfamily of the ETS domain proteins, and plays a critical role in the expression of immediate-early genes (IEGs) upon mitogen stimulation and activation of the mitogen-activated protein kinase (MAPK) cascade. The association of TCFs with serum response elements (SREs) on IEG promoters has been widely studied and a role for Elk-1 in promoting cell cycle entry has been determined. However, the presence of the ETS domain transcription factor Elk-1 in axons and dendrites of post-mitotic adult brain neurons has implications for an alternative function for Elk-1 in neurons other than controlling proliferation. In this study, possible alternative roles for Elk-1 in neurons were investigated, and it was demonstrated that blocking TCF-mediated transactivation in neuronal cells leads to apoptosis through a caspase-dependent mechanism. Indeed RNAi-mediated depletion of endogenous Elk-1 results in increased caspase activity. Conversely, overexpression of either Elk-1 or Elk-VP16 fusion proteins was shown to rescue PC12 cells from chemically-induced apoptosis, and that higher levels of endogenous Elk-1 correlated with longer survival of DRGs in culture. It was shown that Elk-1 regulated the Mcl-1 gene expression required for survival, and that RNAi-mediated degradation of endogenous Elk-1 resulted in elimination of the mcl-1 message. We have further identified the survival-of-motor neuron-1 (SMN1) gene as a novel target of Elk-1, and show that the ets motifs in the SMN1 promoter are involved in this regulation.

Epidermal growth factor regulates Mcl-1 expression through the MAPK-Elk-1 signalling pathway contributing to cell survival in breast cancer

Myeloid cell leukaemia-1 (Mcl-1) is an anti-apoptotic member of the Bcl-2 family that is elevated in a variety of tumour types including breast cancer. In breast tumours, increased Mcl-1 expression correlates with high tumour grade and poor patient survival. We have previously demonstrated that Her-2 levels correspond to increased Mcl-1 expression in breast tumours. Epidermal growth factor (EGF) receptor signalling is frequently deregulated in breast cancer and leads to increased proliferation and survival. Herein, we determined the critical downstream signals responsible for the EGF mediated increase of Mcl-1 and their role in cell survival. We found that both Mcl-1 mRNA and protein levels are rapidly induced upon stimulation with EGF. Promoter analysis revealed that an Elk-1 transcription factor-binding site is critical for EGF activation of the Mcl-1 promoter. Furthermore, we found that knockdown of Elk-1or inhibition of the Erk signalling pathway was sufficient to block EGF upregulation of Mcl-1 and EGF mediated cell survival. Using chromatin immunoprecipitation and biotin labelled probes of the Mcl-1 promoter, we found that Elk-1 and serum response factor are bound to the promoter after EGF stimulation. To determine whether Mcl-1 confers a survival advantage, we found that knockdown of Mcl-1 expression increased apoptosis whereas overexpression of Mcl-1 inhibited drug induced cell death. In human breast tumours, we found a correlation between phosphorylated Elk-1 and Mcl-1 protein levels. These results indicate that the EGF induced activation of Elk-1 is an important mediator of Mcl-1 expression and cell survival and therefore a potential therapeutic target in breast cancer.

Membrane-bound IL-15 stimulation on peripheral blood natural kiler progenitors leads to the generation of an adherent subset co-expressing dendritic cells and natural kiler functional markers

Human peripheral blood natural killer progenitors represent a flexible, heterogeneous population whose phenotype and function are controlled by their membrane-bound IL-15. Indeed, reciprocal membrane-bond IL-15 trans-presentation commits these cells into NK differentiation, while membrane-bound IL-15 stimulation with its soluble ligand (sIL-15Rα) triggers a reverse signal (pERK1/2 and pFAK) that modifies the developmental program of at least two subsets of PB-NKPs. This treatment generates: i) the expansion of an immature NK subset growing in suspension; ii) the appearance of an unprecedented adherent non-proliferative subset with a dendritic morphology co-expressing marker, cytokines and functions typical of myeloid dendritic cells (CD1a(+)/BDCA1(+)/IL-12(+)) and NK cells (CD3-/NKp46(+)/ CD56(+)/IFNγ(+)). The generation of these putative NK/DCs is associated to the rapid inhibition of negative regulators of myelopoiesis (the transcription factors STAT6 and GATA-3) followed by the transient upregulation of inducers of myeloid development, such as the transcription factors (PU.1, GATA-1) and the anti-apoptotic molecule (MCL-1).

Biologic function and clinical potential of telomerase and associated proteins in cardiovascular tissue repair and regeneration

Telomeres comprise long tracts of double-stranded TTAGGG repeats that extend for 9-15 kb in humans. Telomere length is maintained by telomerase, a specialized ribonucleoprotein that prevents the natural ends of linear chromosomes from undergoing inappropriate repair, which could otherwise lead to deleterious chromosomal fusions. During the development of cardiovascular tissues, telomerase activity is strong but diminishes with age in adult hearts. Dysfunction of telomerase is associated with the impairment of tissue repair or regeneration in several pathologic conditions, including heart failure and infarction. Under both physiologic and pathophysiologic conditions, telomerase interacts with promyogenic nuclear transcription factors (e.g. myocardin, serum response factor) to augment the potency of cardiovascular cells during growth, survival, and differentiation. We review recent findings on the biologic function of telomerase and its potential for clinical application in cardiovascular development and repair. Understanding the roles of telomerase and its associated proteins in the functional regulation of cardiovascular cells and their progenitors may lead to new strategies for cardiovascular tissue repair and regeneration.

The fast-mobility isoform of mouse Mcl-1 is a mitochondrial matrix-localized protein with attenuated anti-apoptotic activity

The full-length pro-survival protein Mcl-1 predominantly resides on the outer membrane of mitochondria. Here, we identified a mitochondrial matrix-localized isoform of Mcl-1 that lacks 33 amino acid residues at the N-terminus which serve both as a mitochondrial targeting and processing signal. Ectopically-expressed Mcl-1 without the N-terminal 33 residues failed to enter the mitochondrial matrix but retained wt-like activities both for interaction with BH3-only proteins and anti-apoptosis. In contrast, the mitochondrial matrix-localized isoform failed to interact with BH3-only proteins and manifested an attenuated anti-apoptotic activity. This study reveals that import of Mcl-1 into the mitochondrial matrix results in the attenuation of Mcl-1's anti-apoptotic function.

Mcl-1; the molecular regulation of protein function

Apoptosis, an essential and basic biological phenomenon, is regulated in a complex manner by a multitude of factors. Myeloid cell leukemia 1 (Mcl-1), an anti-apoptotic member of the B-cell lymphoma 2 (Bcl-2) family of apoptosis-regulating proteins, exemplifies a number of the mechanisms by which a protein's contribution to cell fate may be modified. The N-terminus of Mcl-1 is unique amongst the Bcl-2 family, in that it is rich in experimentally confirmed and putative regulatory residues and motifs. These include sites for ubiquitination, cleavage and phosphorylation, which influence the protein's stability, localisation, dimerization and function. Here we review what is known about the regulation of Mcl-1 expression and function, with particular focus on post-translational modifications and how phosphorylation interconnects the complex molecular control of Mcl-1 with cellular state.