Regulation of c-Myc through phosphorylation at Ser-62 and Ser-71 by c-Jun N-terminal kinase

Open MoA: revealing the mechanism of action (MoA) based on network topology and hierarchy

MOTIVATION

Many approaches in systems biology have been applied in drug repositioning due to the increased availability of the omics data and computational biology tools. Using a multi-omics integrated network, which contains information of various biological interactions, could offer a more comprehensive inspective and interpretation for the drug mechanism of action (MoA).

RESULTS

We developed a computational pipeline for dissecting the hidden MoAs of drugs (Open MoA). Our pipeline computes confidence scores to edges that represent connections between genes/proteins in the integrated network. The interactions showing the highest confidence score could indicate potential drug targets and infer the underlying molecular MoAs. Open MoA was also validated by testing some well-established targets. Additionally, we applied Open MoA to reveal the MoA of a repositioned drug (JNK-IN-5A) that modulates the PKLR expression in HepG2 cells and found STAT1 is the key transcription factor. Overall, Open MoA represents a first-generation tool that could be utilized for predicting the potential MoA of repurposed drugs and dissecting de novo targets for developing effective treatments.

AVAILABILITY AND IMPLEMENTATION

Source code is available at https://github.com/XinmengLiao/Open_MoA.

Single-Cell Evolutionary Analysis Reveals Drivers of Plasticity and Mediators of Chemoresistance in Small Cell Lung Cancer

Small cell lung cancer (SCLC) is often a heterogeneous tumor, where dynamic regulation of key transcription factors can drive multiple populations of phenotypically different cells which contribute differentially to tumor dynamics. This tumor is characterized by a very low 2-year survival rate, high rates of metastasis, and rapid acquisition of chemoresistance. The heterogeneous nature of this tumor makes it difficult to study and to treat, as it is not clear how or when this heterogeneity arises. Here we describe temporal, single-cell analysis of SCLC to investigate tumor initiation and chemoresistance in both SCLC xenografts and an autochthonous SCLC model. We identify an early population of tumor cells with high expression of AP-1 network genes that are critical for tumor growth. Furthermore, we have identified and validated the cancer testis antigens (CTA) PAGE5 and GAGE2A as mediators of chemoresistance in human SCLC. CTAs have been successfully targeted in other tumor types and may be a promising avenue for targeted therapy in SCLC.

IMPLICATIONS

Understanding the evolutionary dynamics of SCLC can shed light on key mechanisms such as cellular plasticity, heterogeneity, and chemoresistance.

Targeting Transcription Factors in Cancer: From "Undruggable" to "Druggable"

Deregulation of transcription factors is critical to hallmarks of cancer. Genetic mutations, gene fusions, amplifications or deletions, epigenetic alternations, and aberrant post-transcriptional modification of transcription factors are involved in the regulation of various stages of carcinogenesis, including cancer initiation, progression, and metastasis. Thus, targeting the dysfunctional transcription factors may lead to new cancer therapeutic strategies. However, transcription factors are conventionally considered as "undruggable." Here, we summarize the recent progresses in understanding the regulation of transcription factors in cancers and strategies to target transcription factors and co-factors for preclinical and clinical drug development, particularly focusing on c-Myc, YAP/TAZ, and β-catenin due to their significance and interplays in cancer.

Hepatitis C virus (HCV)-induced ROS/JNK signaling pathway activates the E3 ubiquitin ligase Itch to promote the release of HCV particles via polyubiquitylation of VPS4A

We previously reported that hepatitis C virus (HCV) infection activates the reactive oxygen species (ROS)/c-Jun N-terminal kinase (JNK) signaling pathway. However, the roles of ROS/JNK activation in the HCV life cycle still remain unclear. We sought to identify a novel role of ROS/JNK signaling pathway in the HCV life cycle. Immunoblot analysis revealed that HCV-induced ROS/JNK activation promoted phosphorylation of Itch, a HECT-type E3 ubiquitin ligase, leading to activation of Itch. The siRNA-knockdown of Itch significantly reduced the extracellular HCV infectivity titers, HCV RNA, and HCV core protein without affecting intracellular HCV infectivity titers, HCV RNA, and HCV proteins, suggesting that Itch is involved in release of HCV particles. HCV-mediated JNK/Itch activation specifically promoted polyubiquitylation of an AAA-type ATPase VPS4A, but not VPS4B, required to form multivesicular bodies. Site-directed mutagenesis revealed that two lysine residues (K23 and K121) on VPS4A were important for VPS4A polyubiquitylation. The siRNA-knockdown of VPS4A, but not VPS4B, significantly reduced extracellular HCV infectivity titers. Co-immunoprecipitation analysis revealed that HCV infection specifically enhanced the interaction between CHMP1B, a subunit of endosomal sorting complexes required for transport (ESCRT)-III complex, and VPS4A, but not VPS4B, whereas VPS4A K23R/K121R greatly reduced the interaction with CHMP1B. HCV infection significantly increased ATPase activity of VPS4A, but not VPS4A K23R/K121R or VPS4B, suggesting that HCV-mediated polyubiquitylation of VPS4A contributes to activation of VPS4A. Taken together, we propose that HCV-induced ROS/JNK/Itch signaling pathway promotes VPS4A polyubiquitylation, leading to enhanced VPS4A-CHMP1B interaction and promotion of VPS4A ATPase activity, thereby promoting the release of HCV particles. IMPORTANCE ROS/JNK signaling pathway contributes to liver diseases, including steatosis, metabolic disorders, and hepatocellular carcinoma. We previously reported that HCV activates the ROS/JNK signaling pathway, leading to the enhancement of hepatic gluconeogenesis and apoptosis induction. This study further demonstrates that HCV-induced ROS/JNK signaling pathway activates the E3 ubiquitin ligase Itch to promote release of HCV particles via polyubiquitylation of VPS4A. We provide evidence suggesting that HCV infection promotes the ROS/JNK/Itch signaling pathway and ESCRT/VPS4A machinery to release infectious HCV particles. Our results may lead to a better understanding of the mechanistic details of HCV particle release.

An insight into crosstalk among multiple signaling pathways contributing to epileptogenesis

Despite the years of research, epilepsy remains uncontrolled in one-third of afflicted individuals and poses a health and economic burden on society. Currently available anti-epileptic drugs mainly target the excitatory-inhibitory imbalance despite targeting the underlying pathophysiology of the disease. Recent research focuses on understanding the pathophysiologic mechanisms that lead to seizure generation and on possible new treatment avenues for preventing epilepsy after a brain injury. Various signaling pathways, including the mechanistic target of rapamycin (mTOR) pathway, mitogen-activated protein kinase (MAP-ERK) pathway, JAK-STAT pathway, wnt/β-catenin signaling, cAMP pathway, and jun kinase pathway, have been suggested to play an essential role in this regard. Recent work suggests that the mTOR pathway intervenes epileptogenesis and proposes that mTOR inhibitors may have antiepileptogenic properties for epilepsy. In the same way, several animal studies have indicated the involvement of the Wnt signaling pathway in neurogenesis and neuronal death induced by seizures in different phases (acute and chronic) of seizure development. Various studies have also documented the activation of JAK-STAT signaling in epilepsy and cAMP involvement in epileptogenesis through CREB (cAMP response element-binding protein). Although studies are there, the mechanism for how components of these pathways mediate epileptogenesis requires further investigation. This review summarises the current role of various signaling pathways involved in epileptogenesis and the crosstalk among them. Furthermore, we will also discuss the mechanical base for the interaction between these pathways and how these interactions could be a new emerging promising target for future epilepsy therapies.

Mechanism of Endoplasmic Reticulum Stress in Cerebral Ischemia

Endoplasmic reticulum (ER) is the main organelle for protein synthesis, trafficking and maintaining intracellular Ca²⁺ homeostasis. The stress response of ER results from the disruption of ER homeostasis in neurological disorders. Among these disorders, cerebral ischemia is a prevalent reason of death and disability in the world. ER stress stemed from ischemic injury initiates unfolded protein response (UPR) regarded as a protection mechanism. Important, disruption of Ca²⁺ homeostasis resulted from cytosolic Ca²⁺ overload and depletion of Ca²⁺ in the lumen of the ER could be a trigger of ER stress and the misfolded protein synthesis. Brain cells including neurons, glial cells and endothelial cells are involved in the complex pathophysiology of ischemic stroke. This is generally important for protein underfolding, but even more for cytosolic Ca²⁺ overload. Mild ER stress promotes cells to break away from danger signals and enter the adaptive procedure with the activation of pro-survival mechanism to rescue ischemic injury, while chronic ER stress generally serves as a detrimental role on nerve cells via triggering diverse pro-apoptotic mechanism. What’s more, the determination of some proteins in UPR during cerebral ischemia to cell fate may have two diametrically opposed results which involves in a specialized set of inflammatory and apoptotic signaling pathways. A reasonable understanding and exploration of the underlying molecular mechanism related to ER stress and cerebral ischemia is a prerequisite for a major breakthrough in stroke treatment in the future. This review focuses on recent findings of the ER stress as well as the progress research of mechanism in ischemic stroke prognosis provide a new treatment idea for recovery of cerebral ischemia.

Oxygen-dependent changes in binding partners and post-translational modifications regulate the abundance and activity of HIF-1α/2α

Cellular adaptation to low-oxygen environments is mediated in part by the hypoxia-inducible factors (HIFs). Like other transcription factors, the stability and transcriptional activity of HIFs-and consequently, the hypoxic response-are regulated by post-translational modifications (PTMs) and changes in protein-protein interactions. Our current understanding of PTM-mediated regulation of HIFs is primarily based on in vitro protein fragment-based studies typically validated in fragment-expressing cells treated with hypoxia-mimicking compounds. Here, we used immunoprecipitation-based mass spectrometry to characterize the PTMs and binding partners for full-length HIF-1α and HIF-2α under normoxic (21% oxygen) and hypoxic (1% oxygen) conditions. Hypoxia substantially altered the complexity and composition of the HIFα protein interaction networks, particularly for HIF-2α, with the hypoxic networks of both isoforms being enriched for mitochondrial proteins. Moreover, both HIFα isoforms were heavily covalently modified. We identified ~40 PTM sites composed of 13 different types of modification on both HIFα isoforms, including multiple cysteine modifications and an unusual phosphocysteine. More than 80% of the PTMs identified were not previously known and about half exhibited oxygen dependency. We further characterized an evolutionarily conserved phosphorylation of Ser31 in HIF-1α as a regulator of its transcriptional function, and we propose functional roles for Thr406, Thr528, and Ser581 in HIF-2α. These data will help to delineate the different physiological roles of these closely related isoforms in fine-tuning the hypoxic response.

OSU-03012 Disrupts Akt Signaling and Prevents Endometrial Carcinoma Progression in vitro and in vivo

Purpose

OSU-03012 is a celecoxib derivative lacking cyclooxygenase-2 inhibitory activity and a potent PDK1 inhibitor which has been shown to inhibit tumor growth in various ways. However, the role of OSU-03012 in endometrial carcinoma (EC) in which the PI3K/Akt signaling pathway highly activated has not been studied. Here, we determined the potency of OSU-03012 in suppressing EC progression in vitro and in vivo, and studied the underlined mechanisms.

Methods

The human EC Ishikawa and HEC-1A cells were used as the in vitro models. CCK8 assay and flow cytometry were conducted to evaluate cell proliferation, cell cycle progression, and apoptosis. The metastatic ability was evaluated using the transwell migration assay. The Ishikawa xenograft tumor model was used to study the inhibitory effects of OSU-03012 on EC growth in vivo. Western blot analysis was performed to evaluate expressions of the cell cycle and apoptosis associated proteins.

Results

OSU-03012 could inhibit the progression of EC both in vitro and in vivo by disrupting Akt signaling. It reduced the metastatic ability of EC, led to G2/M cell cycle arrest and induced apoptosis via the mitochondrial apoptosis pathway.

Conclusion

Our data indicated that OSU-03012 could inhibit the progression of EC in vitro and in vivo. It can potentially be used as the targeted drug for the treatment of EC by inhibiting Akt signaling.

Rhophilin-2 Upregulates Glutamine Synthetase by Stabilizing c-Myc Protein and Confers Resistance to Glutamine Deprivation in Lung Cancer

Introduction

RHPN2, a member of rhophilin family of rho-binding proteins, regulates actin cytoskeleton and vesicular trafficking, and promotes mesenchymal transformation in cancer. We have found that RHPN2 was significantly mutated in lung adenocarcinoma (LUAD). However, the role of RHPN2 in lung cancer is not fully understood.

Methods

In the present study, we investigated the expression of RHPN2 in 125 patients with LUAD by qRT-PCR and correlated its expression with clinical characteristics. The effects of RHPN2 on the proliferation and invasion of lung cancer cells were determined by CCK-8 and in vitro transwell assays, clonogenic assay, and xenograft mouse model. The RhoA pull down assay and Western blotting were performed to elucidate the mechanism of RNPN2 in tumorigenesis of lung cancer.

Results

RHPN2 was overexpressed in tumors from LUAD, and high levels of RHPN2 were associated with poor prognosis of LUAD patients. RHPN2 was required for proliferation and invasion of lung cancer cells. Intriguingly, overexpression of RHPN2 conferred the resistance to glutamine depletion in lung cancer cells. Mechanistic studies revealed that ectopic overexpression of RHPN2 promoted the stability of c-Myc protein via phosphorylation at Ser62 and increased c-Myc target glutamine synthetase (GS). Analysis of GS expression in clinical sample showed that the expression of GS was elevated in tumor cells. Kaplan-Meier analysis revealed that high levels of GS were significantly associated with worse overall survival time of the patients with LUAD.

Conclusions

Taken together, this study suggested that RHPN2 was involved in tumorigenesis of lung cancer via modulating c-Myc stability and the expression of its target GS in lung adenocarcinoma, which links RHPN2 and glutamine metabolism.

Combination therapy of BCR-ABL-positive B cell acute lymphoblastic leukemia by tyrosine kinase inhibitor dasatinib and c-JUN N-terminal kinase inhibition

Background

The Philadelphia chromosome (Ph), which leads to the creation and expression of the fusion gene product BCR-ABL, underlines the pathogenesis of chronic myelogenous leukemia (CML) and a fraction of adult and pediatric acute B-lymphoblastic leukemia (B-ALL). The BCR-ABL tyrosine kinase inhibitors (TKIs) have shown a remarkable clinical activity in patients with CML, but their efficacy in treating Ph⁺ B-ALL is limited. Identifying additional therapeutic targets is important for the effective treatment of Ph⁺ B-ALL.

Methods

Activation of the JNK signaling pathway in human and mouse BCR-ABL⁺ B-ALL cells with or without dasatinib treatment was analyzed by Western blotting. JNK was inhibited either by RNA interference or chemical inhibitors, such as JNK-IN-8. The effect of JNK inhibition with or without BCR-ABL TKI dasatinib on BCR-ABL⁺ B-ALL cells was analyzed by the CellTiter-Glo® Luminescent Cell Viability Assay. The in vivo effects of JNK-IN-8 and dasatinib alone or in combination were tested using a BCR-ABL induced B-ALL mouse model.

Results

We found that the c-JUN N-terminal kinase (JNK) signaling pathway is abnormally activated in both human and mouse BCR-ABL⁺ B-ALL cells, but the BCR-ABL TKI does not inhibit JNK activation in these cells. Inhibition of JNK, either by RNAi-mediated downregulation or by JNK inhibitors, could significantly reduce viability of Ph⁺ B-ALL cells. JNK inhibition by RNAi-mediated downregulation or JNK inhibitors also showed a synergistic effect with the BCR-ABL TKI, dasatinib, in killing Ph⁺ B-ALL cells in vitro. Furthermore, a potent JNK inhibitor, JNK-IN-8, in combination with dasatinib markedly improved the survival of mice with BCR-ABL induced B-ALL, as compared to the treatment with dasatinib alone.

Conclusions

Our findings indicate that simultaneously targeting both BCR-ABL and JNK kinase might serve as a promising therapeutic strategy for Ph⁺ B-ALL.

MicroRNA-466c-3p exerts protective effect on neuronal apoptosis and improves functional recovery post spinal cord injury via mitochondrial apoptotic pathway

Spinal cord injury (SCI) is involved with abnormal expression of miRNAs (miRs) which are responsible for some II^ry injury responses which include apoptosis, inflammation and oxidative stress. Mechanisms involving miRs induced apoptosis still needs to be investigated. In the present work we developed a rat model of SCI, followed by microarray analysis for expression of miRs at various time points after SCI. The locomotor activity was assessed by Basso, Beattie and Bresnahan score, lesion volume was analyzed by cresyl violet staining and TUNEL staining for extent of apoptosis at various time points of post SCI. Numbers of miRs were altered after 2 weeks of SCI among which miR-466c-3p was the most significantly down-regulated. Transfection with miR-466c-3p mimics caused overexpression of miR-466c-3p, also improvement in functional recovery, decrease in apoptosis of neuronal cells and lesion size was observed in SCI rats. The Luciferase assay suggested that miR-466c-3p suppressed the expression of Bcl-2 (apoptosis regulator). It was also evidenced that upon restoring the levels of Bcl-2 with the help of pc-DNA3-Bcl-2 halted the attenuating action of miR-466c-3p in hydrogen peroxide exposed N9 microglia cells. The findings suggested that miR-466c-3p may inhibit mitochondrial apoptotic pathway via blocking Bcl-2 and cleaved capase-9/-3in rats after SCI. Altogether, the results suggested that miR-466c-3p may exert attenuating effect on functional recovery and inhibit the apoptosis of neuronal cells via halting the mitochondrial apoptosis cascade in SCI rats indicating that miR-466c-3p can be attractive therapeutic candidate in treating SCI.

miR-142-3p suppresses apoptosis in spinal cord-injured rats

Introduction

Spinal cord injury (SCI) leads to abnormal expression of miRs, leading to secondary responses such as oxidative stress, inflammation and apoptosis. In the present work, we screened the miRs involved and the associated pathway.

Methods

In a rat model of SCI, the microarray analysis for expression of miRs at various time points post-SCI was done. The locomotor analysis was done by Basso, Beattie and Bresnahan score, and Cresyl violet staining was done for lesion volume and TUNEL assay was done for apoptosis in neuronal cells. The expression of apoptotic proteins was done by the western blot study.

Results

It was evidenced that the expression of the number of miRs was altered on the 14th day post-SCI, and miR-142-3p was found to be the most significantly suppressed miR. The results suggested that overexpression of miR-142-3p by its agomir-attenuated functional recovery decreased lesion size and apoptosis of neuronal cells in rats subjected to SCI. The luciferase assay indicated that miR-142-3p blocked the levels of Bax, which is a significant activator of the mitochondrial apoptotic pathway (MAP) via targeting the 3'UTR region of BV-2 cells, and in addition, pc-DNA-Bax restored Bax and inhibited the correcting role of miR-142-3p in hydrogen peroxide-treated BV-2 cells. The findings suggested that miR-142-3p may inhibit the MAP by inhibiting the expression of cleaved-caspase-3/-9 and Bax in SCI rats.

Conclusion

This study concludes that miR-142-3p may attenuate the functional recovery and decrease apoptosis in neuronal cells via inhibiting the MAP in the spinal cord-injured rats, confirming miR-142-3p as a potential therapeutic target in treating SCI.

Peroxynitrite promotes serine-62 phosphorylation-dependent stabilization of the oncoprotein c-Myc

Stabilization of c-Myc oncoprotein is dependent on post-translational modifications, especially its phosphorylation at serine-62 (S62), which enhances its tumorigenic potential. Herein we report that increase in intracellular superoxide induces phospho-stabilization and activation of c-Myc in cancer cells. Importantly, sustained phospho-S62 c-Myc was necessary for promoting superoxide dependent chemoresistance as non-phosphorylatable S62A c-Myc was insensitive to the redox impact when subjected to chemotherapeutic insults. This redox-dependent sustained S62 phosphorylation occurs through nitrative inhibition of phosphatase, PP2A, brought about by peroxynitrite, a reaction product of superoxide and nitric oxide. We identified a conserved tyrosine residue (Y238) in the c-Myc targeting subunit B56α of PP2A, which is selectively amenable to nitrative inhibition, further preventing holoenzyme assembly. In summary, we have established a novel mechanism wherein the pro-oxidant microenvironment stimulates a pro-survival milieu and reinforces tumor maintenance as a functional consequence of c-Myc activation through its sustained S62 phosphorylation via inhibition of phosphatase PP2A.

Significance statement

Increased peroxynitrite signaling in tumors causes sustained S62 c-Myc phosphorylation by PP2A inhibition. This is critical to promoting c-Myc stabilization and activation which promotes chemoresistance and provides significant proliferative and growth advantages to osteosarcomas.

High-Order Correlation Integration for Single-Cell or Bulk RNA-seq Data Analysis

Quantifying or labeling the sample type with high quality is a challenging task, which is a key step for understanding complex diseases. Reducing noise pollution to data and ensuring the extracted intrinsic patterns in concordance with the primary data structure are important in sample clustering and classification. Here we propose an effective data integration framework named as HCI (High-order Correlation Integration), which takes an advantage of high-order correlation matrix incorporated with pattern fusion analysis (PFA), to realize high-dimensional data feature extraction. On the one hand, the high-order Pearson's correlation coefficient can highlight the latent patterns underlying noisy input datasets and thus improve the accuracy and robustness of the algorithms currently available for sample clustering. On the other hand, the PFA can identify intrinsic sample patterns efficiently from different input matrices by optimally adjusting the signal effects. To validate the effectiveness of our new method, we firstly applied HCI on four single-cell RNA-seq datasets to distinguish the cell types, and we found that HCI is capable of identifying the prior-known cell types of single-cell samples from scRNA-seq data with higher accuracy and robustness than other methods under different conditions. Secondly, we also integrated heterogonous omics data from TCGA datasets and GEO datasets including bulk RNA-seq data, which outperformed the other methods at identifying distinct cancer subtypes. Within an additional case study, we also constructed the mRNA-miRNA regulatory network of colorectal cancer based on the feature weight estimated from HCI, where the differentially expressed mRNAs and miRNAs were significantly enriched in well-known functional sets of colorectal cancer, such as KEGG pathways and IPA disease annotations. All these results supported that HCI has extensive flexibility and applicability on sample clustering with different types and organizations of RNA-seq data.

NLRP12 suppresses hepatocellular carcinoma via downregulation of cJun N-terminal kinase activation in the hepatocyte

Hepatocellular carcinoma (HCC) is a deadly human cancer associated with chronic inflammation. The cytosolic pathogen sensor NLRP12 has emerged as a negative regulator of inflammation, but its role in HCC is unknown. Here we investigated the role of NLRP12 in HCC using mouse models of HCC induced by carcinogen diethylnitrosamine (DEN). Nlrp12^-/- mice were highly susceptible to DEN-induced HCC with increased inflammation, hepatocyte proliferation, and tumor burden. Consistently, Nlrp12^-/- tumors showed higher expression of proto-oncogenes cJun and cMyc and downregulation of tumor suppressor p21. Interestingly, antibiotics treatment dramatically diminished tumorigenesis in Nlrp12^-/- mouse livers. Signaling analyses demonstrated higher JNK activation in Nlrp12^-/- HCC and cultured hepatocytes during stimulation with microbial pattern molecules. JNK inhibition or NLRP12 overexpression reduced proliferative and inflammatory responses of Nlrp12^-/- hepatocytes. In summary, NLRP12 negatively regulates HCC pathogenesis via downregulation of JNK-dependent inflammation and proliferation of hepatocytes.

MicroRNA‑124 improves functional recovery and suppresses Bax‑dependent apoptosis in rats following spinal cord injury

Spinal cord injury (SCI) induces aberrant expression of microRNAs (miRNAs), causing various secondary injury responses, including inflammation, apoptosis and oxidative stress. However, the mechanisms underlying miRNA-mediated apoptosis have not been fully elucidated. In the present study, a rat SCI model was established and a miRNA microarray was analyzed to detect miRNA expression profiles at different times post-SCI. The Basso, Beattie and Bresnahan score, cresyl violet staining and terminal deoxynucleotidyl-transferase-mediated dUTP nick end labeling staining were used to evaluate locomotor activity, lesion volume and neuronal cell apoptosis, respectively, at different time points post-SCI. It was observed that numerous miRNAs were altered at 14 days post-SCI and miR-124 was one of the most notably downregulated miRNAs. The present results demonstrated that overexpression of miR-124 by agomir-124 improves functional recovery, decreases lesion size and suppresses neuronal cell apoptosis in a rat SCI model. Luciferase reporter assay demonstrated that miR-124 inhibited apoptosis regulator BAX (Bax) expression, a key molecule in the activation of the mitochondrial apoptotic pathway, by targeting its 3′-untranslated region in BV-2 cells. Furthermore, restoration of Bax by pc-DNA-Bax inhibits the protective effect of miR-124 in H₂O₂-treated BV-2 cells. Notably, the present results demonstrated that miR-124 may block the mitochondrial apoptotic pathway by inhibiting Bax, cleaved-caspase-9 and cleaved-caspase-3 expression in rats following SCI. Collectively, the present results suggested that miR-124 may improve functional recovery and supress neuronal cell apoptosis by blocking the mitochondrial apoptotic pathway in SCI rats, suggesting that miR-124 may serve as a potential therapeutic target in SCI treatment.

Ursolic acid facilitates apoptosis in rheumatoid arthritis synovial fibroblasts by inducing SP1-mediated Noxa expression and proteasomal degradation of Mcl-1

Rheumatoid arthritis (RA) is characterized by hyperplastic pannus formation mediated by activated synovial fibroblasts (RASFs) that cause joint destruction. We have shown earlier that RASFs exhibit resistance to apoptosis, primarily as a result of enhanced expression of myeloid cell leukemia-1 (Mcl-1). In this study, we discovered that ursolic acid (UA), a plant-derived pentacyclic triterpenoid, selectively induces B-cell lymphoma 2 homology 3-only protein Noxa in human RASFs. We observed that UA-induced Noxa expression was followed by a consequent decrease in Mcl-1 expression in a dose-dependent manner. Subsequent evaluation of the signaling pathways showed that UA-induced Noxa is primarily mediated by the JNK pathway in human RASFs. Chromatin immunoprecipitation (IP) studies into the promoter region of Noxa indicated the role of transcription factor specificity protein 1 in JNK-mediated Noxa expression. Furthermore, the results from IP studies and proximity ligation assays indicated that UA-induced Noxa colocalizes and associates with Mcl-1 to prime it for proteasomal degradation through K48-linked ubiquitination by the selective recruitment of Mcl-1 ubiquitin ligase E3, a homologous to E6-associated protein C terminus domain-containing E3 ubiquitin ligase. These findings unveil a novel mechanism of inducing apoptosis in RASFs and a potential adjunct therapeutic strategy of regulating synovial hyperplasia in RA.-Kim, E. Y., Sudini, K., Singh, A. K., Haque, M., Leaman, D., Khuder, S., Ahmed, S. Ursolic acid facilitates apoptosis in rheumatoid arthritis synovial fibroblasts by inducing SP1-mediated Noxa expression and proteasomal degradation of Mcl-1.

Myc phosphorylation in its basic helix-loop-helix region destabilizes transient α-helical structures, disrupting Max and DNA binding

Myelocytomatosis proto-oncogene transcription factor (Myc) is an intrinsically disordered protein with critical roles in cellular homeostasis and neoplastic transformation. It is tightly regulated in the cell, with Myc phosphorylation playing a major role. In addition to the well-described tandem phosphorylation of Thr-52 and Ser-62 in the Myc transactivation domain linked to its degradation, P21 (RAC1)-activated kinase 2 (PAK2)-mediated phosphorylation of serine and threonine residues in the C-terminal basic helix-loop-helix leucine zipper (bHLH-LZ) region regulates Myc transcriptional activity. Here we report that PAK2 preferentially phosphorylates Myc twice, at Thr-358 and Ser-373, with only a minor fraction being modified at the previously identified Thr-400 site. For transcriptional activity, Myc binds E-box DNA elements, requiring its heterodimerization with Myc-associated factor X (Max) via the bHLH-LZ regions. Using isothermal calorimetry (ITC), we found that Myc phosphorylation destabilizes this ternary protein-DNA complex by decreasing Myc's affinity for Max by 2 orders of magnitude, suggesting a major effect of phosphorylation on this complex. Phosphomimetic substitutions revealed that Ser-373 dominates the effect on Myc-Max heterodimerization. Moreover, a T400D substitution disrupted Myc's affinity for Max. ITC, NMR, and CD analyses of several Myc variants suggested that the effect of phosphorylation on the Myc-Max interaction is caused by secondary structure disruption during heterodimerization rather than by a change in the structurally disordered state of Myc or by phosphorylation-induced electrostatic repulsion in the heterodimer. Our findings provide critical insights into the effects of PAK2-catalyzed phosphorylation of Myc on its interactions with Max and DNA.

Myc inhibits JNK-mediated cell death in vivo

The proto-oncogene Myc is well known for its roles in promoting cell growth, proliferation and apoptosis. However, in this study, we found from a genetic screen that Myc inhibits, rather than promotes, cell death triggered by c-Jun N-terminal kinase (JNK) signaling in Drosophila. Firstly, expression of Drosophila Myc (dMyc) suppresses, whereas loss of dMyc enhances, ectopically activated JNK signaling-induced cell death. Secondly, dMyc impedes physiologically activated JNK pathway-mediated cell death. Thirdly, loss of dMyc triggers JNK pathway activation and JNK-dependent cell death. Finally, the mammalian cMyc gene, when expressed in Drosophila, impedes activated JNK signaling-induced cell death. Thus, besides its well-studied apoptosis promoting function, Myc also antagonizes JNK-mediated cell death in Drosophila, and this function is likely conserved from fly to human.

Upregulation of miR-146a increases cisplatin sensitivity of the non-small cell lung cancer A549 cell line by targeting JNK-2

The aim of the present study was to investigate the effects of microRNA (miR-)146a on the cisplatin sensitivity of the non-small cell lung cancer (NSCLC) A549 cell line and study the underlying molecular mechanism. The differences in expression of miRNAs between A549 and A549/cisplatin (A549/DDP) cells were determined, and miR-146a was selected to study its effect on cisplatin sensitivity of A549/DDP cells. miR-146a mimic and inhibitor transient transfection systems were constructed using vectors, and A549/DDP cells were infected with miR-146a mimic and inhibitor to investigate growth, apoptosis and migration. The directed target of miR-146a was determined and the underlying molecular mechanism was validated in the present study. The results of the present study demonstrated that miR-146a was downregulated in NSCLC A549/DDP cells, compared with A549 cells. The overexpression of miR-146a induced apoptosis and inhibited the growth and invasion of A549/DDP cells, which resulted in increased cisplatin sensitivity in NSCLC cells. The JNK2 gene was determined as the direct target of miR-146a, and may be activated by the overexpression of miR-146a. Additionally, JNK2 activated the expression of p53 and inhibited B cell lymphoma 2. The upregulation of miR-146a increased cisplatin sensitivity of the A549 cell line by targeting JNK2, which may provide a novel method for treating NSCLC cisplatin resistance.

MYC Modulation around the CDK2/p27/SKP2 Axis

MYC is a pleiotropic transcription factor that controls a number of fundamental cellular processes required for the proliferation and survival of normal and malignant cells, including the cell cycle. MYC interacts with several central cell cycle regulators that control the balance between cell cycle progression and temporary or permanent cell cycle arrest (cellular senescence). Among these are the cyclin E/A/cyclin-dependent kinase 2 (CDK2) complexes, the CDK inhibitor p27^KIP1 (p27) and the E3 ubiquitin ligase component S-phase kinase-associated protein 2 (SKP2), which control each other by forming a triangular network. MYC is engaged in bidirectional crosstalk with each of these players; while MYC regulates their expression and/or activity, these factors in turn modulate MYC through protein interactions and post-translational modifications including phosphorylation and ubiquitylation, impacting on MYC's transcriptional output on genes involved in cell cycle progression and senescence. Here we elaborate on these network interactions with MYC and their impact on transcription, cell cycle, replication and stress signaling, and on the role of other players interconnected to this network, such as CDK1, the retinoblastoma protein (pRB), protein phosphatase 2A (PP2A), the F-box proteins FBXW7 and FBXO28, the RAS oncoprotein and the ubiquitin/proteasome system. Finally, we describe how the MYC/CDK2/p27/SKP2 axis impacts on tumor development and discuss possible ways to interfere therapeutically with this system to improve cancer treatment.

Involvement of JNK signaling in IL4-induced M2 macrophage polarization

It has been generally accepted that alternatively activated macrophages (M2), which can be induced by type 2 cytokines such as IL-4, is responsible for tissue repair. However, the function of JNK in IL-4-induced M2 macrophage polarization remains unclear. Here, we demonstrated that M0 macrophages can be polarized into M2 status in response to IL-4 stimulation with the increased expression of the M2-specific molecular markers. We also found that IL-4 induced higher expression of JNK and transcription factor c-Myc in M2 macrophages. Our Q-PCR and Western blot results showed that JNK increased the expression of c-Myc and M2 markers Arg1, Mrc1. We also demonstrated c-Myc was the downstream of IL-4-JNK pathway. Further, the depletion of c-Myc, Arg1 and Mrc1 could inhibit the migration ability of M2 macrophages. Taken together, our data establishes a new role for JNK signaling in IL-4-induced alternative activation of macrophages and may provide a novel strategy for immune therapy.

dMyc is required in retinal progenitors to prevent JNK-mediated retinal glial activation

In the nervous system, glial cells provide crucial insulation and trophic support to neurons and are important for neuronal survival. In reaction to a wide variety of insults, glial cells respond with changes in cell morphology and metabolism to allow repair. Additionally, these cells can acquire migratory and proliferative potential. In particular, after axonal damage or pruning the clearance of axonal debris by glial cells is key for a healthy nervous system. Thus, bidirectional neuron-glial interactions are crucial in development, but little is known about the cellular sensors and signalling pathways involved. In here, we show that decreased cellular fitness in retinal progenitors caused by reduced Drosophila Myc expression triggers non cell-autonomous activation of retinal glia proliferation and overmigration. Glia migration occurs beyond its normal limit near the boundary between differentiated photoreceptors and precursor cells, extending into the progenitor domain. This overmigration is stimulated by JNK activation (and the function of its target Mmp1), while proliferative responses are mediated by Dpp/TGF-β signalling activation.

For a functional nervous system, neurons transmit information from cell to cell while glial cells provide crucial insulation and trophic support to neurons, which is important for neuronal survival. Glial cells are one of the most plastic cell types being able to adapt and respond to changing environmental stimuli. In this work we inhibit the function of the growth regulator dMyc in Drosophila retinal primordium, the eye imaginal discs. Glial cell numbers and migration pattern to the eye disc are tightly controlled but in dMyc-depleted retinas the glial cells overcome their normal barriers and overmigrate into the eye progenitors domain. We show evidence that this process is mediated by JNK activation in the presence of metalloproteinases. We discuss the biological role of overmigrating glia in tissue regeneration and/or confinement of the damaged area.

Chaperone-mediated autophagy prevents cellular transformation by regulating MYC proteasomal degradation

Chaperone-mediated autophagy (CMA), a selective form of protein lysosomal degradation, is maximally activated in stress situations to ensure maintenance of cellular homeostasis. CMA activity decreases with age and in several human chronic disorders, but in contrast, in most cancer cells, CMA is upregulated and required for tumor growth. However, the role of CMA in malignant transformation remains unknown. In this study, we demonstrate that CMA inhibition in fibroblasts augments the efficiency of MYC/c-Myc-driven cellular transformation. CMA blockage contributes to the increase of total and nuclear MYC, leading to enhancement of cell proliferation and colony formation. Impaired CMA functionality accentuates tumorigenesis-related metabolic changes observed upon MYC-transformation. Although not a direct CMA substrate, we have found that CMA regulates cellular MYC levels by controlling its proteasomal degradation. CMA promotes MYC ubiquitination and degradation by regulating the degradation of C330027C09Rik/KIAA1524/CIP2A (referred to hereafter as CIP2A), responsible for MYC stabilization. Ubiquitination and proteasomal degradation of MYC requires dephosphorylation at Ser62, and CIP2A inhibits the phosphatase responsible for this dephosphorylation. Failure to degrade CIP2A upon CMA blockage leads to increased levels of phosphorylated MYC (Ser62) and to stabilization of this oncogene. We demonstrate that this phosphorylation is essential for the CMA-mediated effect, since specific mutation of this site (Ser62 to Ala62) is enough to normalize MYC levels in CMA-incompetent cells. Altogether these data demonstrate that CMA mitigates MYC oncogenic activity by promoting its proteasomal degradation and reveal a novel tumor suppressive role for CMA in nontumorigenic cells.

PIM1 kinase regulates cell death, tumor growth and chemotherapy response in triple-negative breast cancer

Triple-negative breast cancers (TNBCs) have poor prognosis and lack targeted therapies. Here we identified increased copy number and expression of the PIM1 proto-oncogene in genomic data sets of patients with TNBC. TNBC cells, but not nonmalignant mammary epithelial cells, were dependent on PIM1 for proliferation and protection from apoptosis. PIM1 knockdown reduced expression of the anti-apoptotic factor BCL2, and dynamic BH3 profiling of apoptotic priming revealed that PIM1 prevents mitochondrial-mediated apoptosis in TNBC cell lines. In TNBC tumors and their cellular models, PIM1 expression was associated with several transcriptional signatures involving the transcription factor MYC, and PIM1 depletion in TNBC cell lines decreased, in a MYC-dependent manner, cell population growth and expression of the MYC target gene MCL1. Treatment with the pan-PIM kinase inhibitor AZD1208 impaired the growth of both cell line and patient-derived xenografts and sensitized them to standard-of-care chemotherapy. This work identifies PIM1 as a malignant-cell-selective target in TNBC and the potential use of PIM1 inhibitors for sensitizing TNBC to chemotherapy-induced apoptotic cell death.

JNK Signaling: Regulation and Functions Based on Complex Protein-Protein Partnerships

The c-Jun N-terminal kinases (JNKs), as members of the mitogen-activated protein kinase (MAPK) family, mediate eukaryotic cell responses to a wide range of abiotic and biotic stress insults. JNKs also regulate important physiological processes, including neuronal functions, immunological actions, and embryonic development, via their impact on gene expression, cytoskeletal protein dynamics, and cell death/survival pathways. Although the JNK pathway has been under study for >20 years, its complexity is still perplexing, with multiple protein partners of JNKs underlying the diversity of actions. Here we review the current knowledge of JNK structure and isoforms as well as the partnerships of JNKs with a range of intracellular proteins. Many of these proteins are direct substrates of the JNKs. We analyzed almost 100 of these target proteins in detail within a framework of their classification based on their regulation by JNKs. Examples of these JNK substrates include a diverse assortment of nuclear transcription factors (Jun, ATF2, Myc, Elk1), cytoplasmic proteins involved in cytoskeleton regulation (DCX, Tau, WDR62) or vesicular transport (JIP1, JIP3), cell membrane receptors (BMPR2), and mitochondrial proteins (Mcl1, Bim). In addition, because upstream signaling components impact JNK activity, we critically assessed the involvement of signaling scaffolds and the roles of feedback mechanisms in the JNK pathway. Despite a clarification of many regulatory events in JNK-dependent signaling during the past decade, many other structural and mechanistic insights are just beginning to be revealed. These advances open new opportunities to understand the role of JNK signaling in diverse physiological and pathophysiological states.

PIAS1 Promotes Lymphomagenesis through MYC Upregulation

The MYC proto-oncogene is a transcription factor implicated in a broad range of cancers. MYC is regulated by several post-translational modifications including SUMOylation, but the functional impact of this post-translational modification is still unclear. Here, we report that the SUMO E3 ligase PIAS1 SUMOylates MYC. We demonstrate that PIAS1 promotes, in a SUMOylation-dependent manner, MYC phosphorylation at serine 62 and dephosphorylation at threonine 58. These events reduce the MYC turnover, leading to increased transcriptional activity. Furthermore, we find that MYC is SUMOylated in primary B cell lymphomas and that PIAS1 is required for the viability of MYC-dependent B cell lymphoma cells as well as several cancer cell lines of epithelial origin. Finally, Pias1-null mice display endothelial defects reminiscent of Myc-null mice. Taken together, these results indicate that PIAS1 is a positive regulator of MYC.

Eiger-induced cell death relies on Rac1-dependent endocytosis

Signaling via tumor necrosis factor receptor (TNFR) superfamily members regulates cellular life and death decisions. A subset of mammalian TNFR proteins, most notably the p75 neurotrophin receptor (p75NTR), induces cell death through a pathway that requires activation of c-Jun N-terminal kinases (JNKs). However the receptor-proximal signaling events that mediate this remain unclear. Drosophila express a single tumor necrosis factor (TNF) ligand termed Eiger (Egr) that activates JNK-dependent cell death. We have exploited this model to identify phylogenetically conserved signaling events that allow Egr to induce JNK activation and cell death in vivo. Here we report that Rac1, a small GTPase, is specifically required in Egr-mediated cell death. rac1 loss of function blocks Egr-induced cell death, whereas Rac1 overexpression enhances Egr-induced killing. We identify Vav as a GEF for Rac1 in this pathway and demonstrate that dLRRK functions as a negative regulator of Rac1 that normally acts to constrain Egr-induced death. Thus dLRRK loss of function increases Egr-induced cell death in the fly. We further show that Rac1-dependent entry of Egr into early endosomes is a crucial prerequisite for JNK activation and for cell death and show that this entry requires the activity of Rab21 and Rab7. These findings reveal novel regulatory mechanisms that allow Rac1 to contribute to Egr-induced JNK activation and cell death.

JNK1 Deficient Insulin-Producing Cells Are Protected against Interleukin-1β-Induced Apoptosis Associated with Abrogated Myc Expression

The relative contributions of the JNK subtypes in inflammatory β-cell failure and apoptosis are unclear. The JNK protein family consists of JNK1, JNK2, and JNK3 subtypes, encompassing many different isoforms. INS-1 cells express JNK1α1, JNK1α2, JNK1β1, JNK1β2, JNK2α1, JNK2α2, JNK3α1, and JNK3α2 mRNA isoform transcripts translating into 46 and 54 kDa isoform JNK proteins. Utilizing Lentiviral mediated expression of shRNAs against JNK1, JNK2, or JNK3 in insulin-producing INS-1 cells, we investigated the role of individual JNK subtypes in IL-1β-induced β-cell apoptosis. JNK1 knockdown prevented IL-1β-induced INS-1 cell apoptosis associated with decreased 46 kDa isoform JNK protein phosphorylation and attenuated Myc expression. Transient knockdown of Myc also prevented IL-1β-induced apoptosis as well as caspase 3 cleavage. JNK2 shRNA potentiated IL-1β-induced apoptosis and caspase 3 cleavage, whereas JNK3 shRNA did not affect IL-1β-induced β-cell death compared to nonsense shRNA expressing INS-1 cells. In conclusion, JNK1 mediates INS-1 cell death associated with increased Myc expression. These findings underline the importance of differentiated targeting of JNK subtypes in the development of inflammatory β-cell failure and destruction.

ASK1 modulates the expression of microRNA Let7A in microglia under high glucose in vitro condition

Hyperglycemia results in oxidative stress and leads to neuronal apoptosis in the brain. Diabetes studies show that microglia participate in the progression of neuropathogenesis through their involvement in inflammation in vivo and in vitro. In high-glucose-induced inflammation, apoptosis signal regulating kinase 1 (ASK1) triggers the release of apoptosis cytokines and apoptotic gene expression. MicroRNA-Let7A (miR-Let7A) is reported to be a regulator of inflammation. In the present study, we investigated whether miR-Let7A regulates the function of microglia by controlling ASK1 in response to high-glucose-induced oxidative stress. We performed reverse transcription (RT) polymerase chain reaction, Taqman assay, real-time polymerase chain reaction, and immunocytochemistry to confirm the alteration of microglia function. Our results show that miR-Let7A is associated with the activation of ASK1 and the expression of anti-inflammatory cytokine (interleukin (IL)-10) and Mycs (c-Myc and N-Myc). Thus, the relationship between Let-7A and ASK1 could be a novel target for enhancing the beneficial function of microglia in central nervous system (CNS) disorders.

FBXO32 Targets c-Myc for Proteasomal Degradation and Inhibits c-Myc Activity

FBXO32 (MAFbx/Atrogin-1) is an E3 ubiquitin ligase that is markedly up-regulated in muscle atrophy. Although some data indicate that FBXO32 may play an important role in tumorigenesis, the molecular mechanism of FBXO32 in tumorigenesis has been poorly understood. Here, we present evidence that FBXO32 targets the oncogenic protein c-Myc for ubiquitination and degradation through the proteasome pathway. Phosphorylation of c-Myc at Thr-58 and Ser-62 is dispensable for FBXO32 to induce c-Myc degradation. Mutation of the lysine 326 in c-Myc reduces c-Myc ubiquitination and prevents the c-Myc degradation induced by FBXO32. Furthermore, overexpression of FBXO32 suppresses c-Myc activity and inhibits cell growth, but knockdown of FBXO32 enhances c-Myc activity and promotes cell growth. Finally, we show that FBXO32 is a direct downstream target of c-Myc, highlighting a negative feedback regulation loop between c-Myc and FBXO32. Thus, FBXO32 may function by targeting c-Myc. This work explains the function of FBXO32 and highlights its mechanisms in tumorigenesis.

MYC regulates the unfolded protein response and glucose and glutamine uptake in endocrine resistant breast cancer

Background

About 70% of all breast cancers are estrogen receptor alpha positive (ER+) and are treated with antiestrogens. However, 50% of ER + tumors develop resistance to these drugs (endocrine resistance). In endocrine resistant cells, an adaptive pathway called the unfolded protein response (UPR) is elevated that allows cells to tolerate stress more efficiently than in sensitive cells. While the precise mechanism remains unclear, the UPR can trigger both pro-survival and pro-death outcomes that depend on the nature and magnitude of the stress. In this study, we identified MYC, an oncoprotein that is upregulated in endocrine resistant breast cancer, as a regulator of the UPR in glucose-deprived conditions.

Methods

ER+ human breast cancer cell lines (LCC1, LCC1, LY2 and LCC9) and rat mammary tumors were used to confirm upregulation of MYC in endocrine resistance. To evaluate functional relevance of proteins, siRNA-mediated inhibition or small molecule inhibitors were used. Cell density/number was evaluated with crystal violet assay; cell cycle and apoptosis were measured by flow cytometry. Relative quantification of glutamine metabolites were determined by mass spectrometry. Signaling molecules of the UPR, apoptosis or autophagy pathways were investigated by western blotting.

Results

Increased MYC function in resistant cells correlated with increased dependency on glutamine and glucose for survival. Inhibition of MYC reduced cell growth and uptake of both glucose and glutamine in resistant cells. Interestingly, in glucose-deprived conditions, glutamine induced apoptosis and necrosis, arrested autophagy, and triggered the unfolded protein response (UPR) though GRP78-IRE1α with two possible outcomes: (i) inhibition of cell growth by JNK activation in most cells and, (ii) promotion of cell growth by spliced XBP1 in the minority of cells. These disparate effects are regulated, at different signaling junctions, by MYC more robustly in resistant cells.

Conclusions

Endocrine resistant cells overexpress MYC and are better adapted to withstand periods of glucose deprivation and can use glutamine in the short term to maintain adequate metabolism to support cell survival. Our findings reveal a unique role for MYC in regulating cell fate through the UPR, and suggest that targeting glutamine metabolism may be a novel strategy in endocrine resistant breast cancer.

Endogenous cannabinoid anandamide impairs cell growth and induces apoptosis in chondrocytes

Endocannabinoids has been described to be involved in articular degenerative disease by modulating nociception and immune system. However, the role of the endocannabinoid anandamide on chondrocyte cell viability is still unclear. Therefore, we decided to study anandamide's effects on chondrocytes viability and to evaluate its interactions with the catabolic factor TNF (tumor necrosis factor). Chondrocyte vitality was evaluated by MTT assay. We investigated LDH release, chromatin condensation, cleavage of focal adhesion kinase (FAK), and caspases-3, 8, and 9 activation. c-MYC mRNA levels were determined by RT-PCR. We studied by Western blot the activation patterns of AKT, AMPK, ERK, p38, and JNK kinases. Finally, we evaluate the effect of anandamide in TNF-induced caspase-3 cleavage. Anandamide decreased chondrocyte vitality independently of its receptors. It induced AMPK activation without LDH release. Anandamide induced chromatin condensation, activation of caspase-3, 8, and 9, and FAK cleavage. Surprisingly, despite anandamide inhibited cell proliferation, it increased c-MYC expression. Moreover anandamide inhibited AKT activation, whilst it induced a sustained activation of ERK, JNK, and p38. Finally, anandamide synergized with TNF-α in the cleavage of caspase-3. In conclusion, our findings suggest that anandamide, alone or in combination with TNF-α, may be a potential destructive agent in cartilage.

Thrombospondin-1 repression is mediated via distinct mechanisms in fibroblasts and epithelial cells

Tumor-associated angiogenesis is postulated to be regulated by the balance between pro- and anti-angiogenic factors. We demonstrate here that the critical step in establishing the angiogenic capability of human tumor cells is the repression of a key secreted anti-angiogenic factor, thrombospondin-1 (Tsp-1). This repression is essential for tumor formation by mammary epithelial cells and kidney cells engineered to express SV40 early region proteins, hTERT, and H-RasV12. In transformed epithelial cells, a signaling pathway leading from Ras to Tsp-1 repression induces the sequential activation of PI3 kinase, Rho and ROCK, leading to activation of Myc through phosphorylation, thereby enabling Myc to repress Tsp-1 transcription. In transformed fibroblasts, however, the repression of Tsp-1 can be achieved by an alternative mechanism involving inactivation of both p53 and pRb. We thus describe novel mechanisms by which the activation of oncogenes in epithelial cells and the inactivation of tumor suppressors in fibroblasts permits angiogenesis and, in turn, tumor formation.

JNK Signaling in the Control of the Tumor-Initiating Capacity Associated with Cancer Stem Cells

Deregulation of c-Jun NH2-terminal kinase (JNK) signaling occurs frequently in a variety of human cancers, yet the exact role(s) of JNK deregulation in cancer cell biology remains to be fully elucidated. Our recent demonstration that the activity of JNK is required not only for self-renewal of glioma stem cells but also for their tumor initiation has, however, identified a new role for JNK in the control of the stemness and tumor-initiating capacity of cancer cells. Significantly, transient JNK inhibition was sufficient to cause sustained loss of the tumor-initiating capacity of glioma stem cells, suggesting that the phenotype of "lost tumor-initiating capacity" may be as stable as the differentiated state and that the tumor-initiating capacity might therefore be under the control of JNK through an epigenetic mechanism that also governs stemness and differentiation. Here, in this article, we review the role and mechanism of JNK in the control of this "stemness-associated tumor-initiating capacity" (STATIC), a new hypothetical concept we introduce in this review article. Since the idea of STATIC is essentially applicable to both cancer types that do and do not follow the cancer stem cell hypothesis, we also give consideration to the possible involvement of JNK-mediated control of STATIC in a wide range of human cancers in which JNK is aberrantly activated. Theoretically, successful targeting of STATIC through JNK could contribute to long-term control of cancer. Issues to be considered before clinical application of therapies targeting this JNK-STATIC axis are also discussed.

Posttranslational modifications of defined embryonic reprogramming transcription factors

The generation of induced pluripotent stem cells (iPSCs) from somatic cells by expressing ectopic reprogramming transcriptional factors such as Oct3/4, Sox2, Klf4, c-Myc, and Nanog is one of the cutting-edge discoveries in stem cell and cancer research. This discovery has raised several safety issues regarding the use of iPSC technology for human disease research. Tumorigenesis is the major obstacle observed for iPSC-mediated transplantation therapy. Recently, a new method to generate human iPSCs either by a chemical method or by direct delivery of reprogramming factors has become a promising approach for future customized cell therapy of human disorders. These reprogramming transcriptional factors play critical roles in diverse cellular functions such as transactivation, cellular proliferation, differentiation, apoptosis, and tumorigenesis. Posttranslational modifications (PTMs) (phosphorylation, ubiquitination, acetylation, sumoylation, and so on) of these proteins act as a regulatory signal to control protein activity, expression, and stability in a wide variety of cellular processes. We attempt to summarize the accumulated evidence to address the role of PTMs of Oct3/4, Sox2, Klf4, c-Myc, and Nanog in regulating their biological functions. This review allows us to understand the importance of PTMs and their application in developing an efficient and safe reprogramming method without cancer development for cell therapy. Finally, we discuss the importance of PTMs of reprogramming factors in tumor pathogenesis.

Infection by Toxoplasma gondii specifically induces host c-Myc and the genes this pivotal transcription factor regulates

Toxoplasma gondii infection has previously been described to cause dramatic changes in the host transcriptome by manipulating key regulators, including STATs, NF-κB, and microRNAs. Here, we report that Toxoplasma tachyzoites also mediate rapid and sustained induction of another pivotal regulator of host cell transcription, c-Myc. This induction is seen in cells infected with all three canonical types of Toxoplasma but not the closely related apicomplexan parasite Neospora caninum. Coinfection of cells with both Toxoplasma and Neospora still results in an increase in the level of host c-Myc, showing that c-Myc is actively upregulated by Toxoplasma infection (rather than repressed by Neospora). We further demonstrate that this upregulation may be mediated through c-Jun N-terminal protein kinase (JNK) and is unlikely to be a nonspecific host response, as heat-killed Toxoplasma parasites do not induce this increase and neither do nonviable parasites inside the host cell. Finally, we show that the induced c-Myc is active and that transcripts dependent on its function are upregulated, as predicted. Hence, c-Myc represents an additional way in which Toxoplasma tachyzoites have evolved to specifically alter host cell functions during intracellular growth.

OSU-03012, a non-Cox inhibiting celecoxib derivative, induces apoptosis of human esophageal carcinoma cells through a p53/Bax/cytochrome c/caspase-9-dependent pathway

OSU-03012 is a celecoxib derivative devoid of cyclooxygenase-2 inhibitory activity. It was previously reported to inhibit the growth of some tumor cells through the AKT-signaling pathway. In the current study, we assessed the ability of OSU-03012 to induce apoptosis in human esophageal carcinoma cells and the mechanism by which this occurs. A cell proliferation assay indicated that OSU-03012 inhibited the growth of human esophageal carcinoma cell lines with an IC50 below 2 μmol/l and had the most effective cytotoxicity against Eca-109 cells. Terminal deoxynucleotidyl transferase-mediated nick-end labeling assay and flow cytometry analysis showed that OSU-03012 could induce the apoptosis in Eca-109 cells. After treatment of Eca-109 cells with 2 μmol/l OSU-03012 for 24 h, the apoptosis index increased from 14.07 to 53.72%. OSU-03012 treatment resulted in a 30-40% decrease in the mitochondrial membrane potential and caused cytochrome c release into the cytosol. Further studies with caspase-9-specific and caspase-8-specific inhibitors (z-LEHDfmk and z-IETDfmk, respectively) pointed toward the involvement of the caspase-9 pathway, but not the caspase-8 pathway, in the execution of OSU-03012-induced apoptosis. Immunoblot analysis demonstrated that OSU-03012-induced cellular apoptosis was associated with upregulation of Bax, cleaved caspase-3, and cleaved caspase-9. Ser-15 of p53 was phosphorylated after 24 h of treatment of the cancer cells with OSU-03012. This increase in p53 was associated with the decrease in Bcl-2 and increase in Bax. An inhibitor of p53, pifithrin-α, attenuated the anticancer effects of OSU-03012 and downregulated the expression of Bax and cleaved caspase-9. Altogether, our results show that OSU-03012 could induce apoptosis in human esophageal carcinoma cells through a p53/Bax/cytochrome c/caspase-9-dependent pathway.

JNK contributes to temozolomide resistance of stem-like glioblastoma cells via regulation of MGMT expression

While elimination of the cancer stem cell population is increasingly recognized as a key to successful treatment of cancer, the high resistance of cancer stem cells to conventional chemoradiotherapy remains a therapeutic challenge. O6-methylguanine DNA methyltransferase (MGMT), which is frequently expressed in cancer stem cells of glioblastoma, has been implicated in their resistance to temozolomide, the first-line chemotherapeutic agent against newly diagnosed glioblastoma. However, much remains unknown about the molecular regulation that underlies MGMT expression and temozolomide resistance of glioblastoma cancer stem cells. Here, we identified JNK as a novel player in the control of MGMT expression and temozolomide resistance of glioblastoma cancer stem cells. We showed that inhibition of JNK, either pharmacologically or by RNA interference, in stem-like glioblastoma cells derived directly from glioblastoma tissues reduces their MGMT expression and temozolomide resistance. Importantly, sensitization of stem-like glioblastoma cells to temozolomide by JNK inhibition was dependent on MGMT expression, implying that JNK controls temozolomide resistance of stem-like glioblastoma cells through MGMT expression. Our findings suggest that concurrent use of JNK inhibitors with temozolomide may be a rational therapeutic approach to effectively target the cancer stem cell population in the treatment of glioblastoma.

MYC phosphorylation at novel regulatory regions suppresses transforming activity

Despite its central role in human cancer, MYC deregulation is insufficient by itself to transform cells. Because inherent mechanisms of neoplastic control prevent precancerous lesions from becoming fully malignant, identifying transforming alleles of MYC that bypass such controls may provide fundamental insights into tumorigenesis. To date, the only activated allele of MYC known is T58A, the study of which led to identification of the tumor suppressor FBXW7 and its regulator USP28 as a novel therapeutic target. In this study, we screened a panel of MYC phosphorylation mutants for their ability to promote anchorage-independent colony growth of human MCF10A mammary epithelial cells, identifying S71A/S81A and T343A/S344A/S347A/S348A as more potent oncogenic mutants compared with wild-type (WT) MYC. The increased cell-transforming activity of these mutants was confirmed in SH-EP neuroblastoma cells and in three-dimensional MCF10A acini. Mechanistic investigations initiated by a genome-wide mRNA expression analysis of MCF10A acini identified 158 genes regulated by the mutant MYC alleles, compared with only 112 genes regulated by both WT and mutant alleles. Transcriptional gain-of-function was a common feature of the mutant alleles, with many additional genes uniquely dysregulated by individual mutant. Our work identifies novel sites of negative regulation in MYC and thus new sites for its therapeutic attack.

Oppositional regulation of Noxa by JNK1 and JNK2 during apoptosis induced by proteasomal inhibitors

Proteasome inhibitors (PIs) potently induce apoptosis in a variety of tumor cells, but the underlying mechanisms are not fully elucidated. Comparing PI-induced apoptosis susceptibilities of various mouse embryonic fibroblast (MEF) lines differing in their c-jun N-terminal kinase (JNK) 1 and 2 status, we show that several hallmarks of apoptosis were most rapidly detectable in JNK2-/- cells, whereas they appeared only delayed and severely reduced in their intensities in cells expressing JNK2. Consistent with our finding that PI-induced apoptosis requires de novo protein synthesis, the proteasomal inhibitor MG-132 induced expression of the BH3-only protein Noxa at the transcriptional level in a JNK1-dependent, but JNK2-opposing manner. As the knockdown of Noxa blocked only the rapid PI-induced apoptosis of JNK2-/- cells, but not the delayed death occurring in JNK1-/- and JNK1+/+ cells, our data uncover a novel PI-induced apoptosis pathway that is regulated by the JNK1/2-dependent expression of Noxa. Furthermore, several transcription factors known to modulate Noxa expression including ATF3, ATF4, c-Jun, c-Myc, HIF1α, and p53 were found upregulated following MG-132 exposure. From those, only knockdown of c-Myc rescued JNK2-/- cells from PI-induced apoptosis, however, without affecting expression of Noxa. Together, our data not only show that a rapid execution of PI-induced apoptosis requires JNK1 for upregulation of Noxa via an as yet unknown transcription factor, but also that JNK2 controls this event in an oppositional manner.

Activation and crosstalk between the endoplasmic reticulum road and JNK pathway in ischemia-reperfusion brain injury

BACKGROUND

Recent studies suggest that endoplasmic reticulum stress (ERS) is the key process in ischemic brain injury. The JNK pathway is also involved in the process of ischemic brain injury.

METHOD

We established a middle cerebral artery occlusion/reperfusion (MCAO/R) model in rats; detected the changes in c-Jun N-terminal kinase (JNK), GADD153 and caspase-12 at different reperfusion time points by immunohistochemistry, Western blot and double-label immunofluorescence; and observed the effect of JNK inhibitor SP600125 on the expression of JNK, GADD153 and caspase-12 to explore the relationship between the endoplasmic reticulum road and JNK pathway.

RESULTS

The expression of the two hallmarks of ERS-GADD153 and caspase-12-significantly increased, and the activation of JNK also obviously increased. After interference by SP600125, the expression of p-JNk and caspase-12 obviously decreased, whereas the decrease of GADD153 occurred only after 24 h reperfusion.

CONCLUSIONS

Both ERS and JNK pathways are involved in the pathological process of ischemic brain injury. The JNK pathway may be involved in the process of ERS, but perhaps has more effect on the caspase-12 pathway.

Induction of apoptosis by 3-amino-6-(3-aminopropyl)-5,6-dihydro-5,11-dioxo-11H-indeno[1,2-c]isoquinoline via modulation of MAPKs (p38 and c-Jun N-terminal kinase) and c-Myc in HL-60 human leukemia cells

Recently, we reported that 3-amino-6-(3-aminopropyl)-5,6-dihydro-5,11-dioxo-11H-indeno[1,2-c]isoquinoline (AM6-36), sharing structural similarity with naturally occurring isoquinolines, induced activities mediated by retinoid X receptor (RXR) response element accompanied by antiproliferative effects on breast cancer cells. To further characterize the biologic potential of AM6-36, we currently report studies conducted with HL-60 human leukemia cells. AM6-36 significantly inhibited cellular proliferation in a dose- and time-dependent manner with an IC(50) value of 86 nM. When evaluated at low test concentrations (≤0.25 μM), AM6-36 induced arrest in the G2/M phase of the cell cycle. At higher concentrations (1 and 2 μM), the response shifted to apoptosis, which was consistent with the effect of AM6-36 on other apoptotic signatures including an increase of apoptotic annexin V(+) 7-AAD(-) cells, loss of mitochondrial membrane potential, induction of poly(ADP-ribose) polymerase cleavage, and activation of several caspases. These apoptotic effects are potentially due to up-regulation of p38 MAPK and JNK phosphorylation and down-regulation of c-Myc oncogene expression. Taken together, AM6-36 might serve as an effective anticancer agent by inducing G2/M cell cycle arrest and apoptosis through the activation of MAPKs and inhibition of c-Myc.