Biologic sequelae of c-Jun NH(2)-terminal kinase (JNK) activation in multiple myeloma cell lines

The Role of the Dysregulated JNK Signaling Pathway in the Pathogenesis of Human Diseases and Its Potential Therapeutic Strategies: A Comprehensive Review

JNK is named after c-Jun N-terminal kinase, as it is responsible for phosphorylating c-Jun. As a member of the mitogen-activated protein kinase (MAPK) family, JNK is also known as stress-activated kinase (SAPK) because it can be activated by extracellular stresses including growth factor, UV irradiation, and virus infection. Functionally, JNK regulates various cell behaviors such as cell differentiation, proliferation, survival, and metabolic reprogramming. Dysregulated JNK signaling contributes to several types of human diseases. Although the role of the JNK pathway in a single disease has been summarized in several previous publications, a comprehensive review of its role in multiple kinds of human diseases is missing. In this review, we begin by introducing the landmark discoveries, structures, tissue expression, and activation mechanisms of the JNK pathway. Next, we come to the focus of this work: a comprehensive summary of the role of the deregulated JNK pathway in multiple kinds of diseases. Beyond that, we also discuss the current strategies for targeting the JNK pathway for therapeutic intervention and summarize the application of JNK inhibitors as well as several challenges now faced. We expect that this review can provide a more comprehensive insight into the critical role of the JNK pathway in the pathogenesis of human diseases and hope that it also provides important clues for ameliorating disease conditions.

Effects of Holliday Junction-Recognition Protein-Mediated C-Jun N-Terminal Kinase/ Signal Transducer and Activator of Transcription 3 Signaling Pathway on Cell Proliferation, Cell Cycle and Cell Apoptosis in Bladder Urothelial Carcinoma

The Holliday Junction-Recognition Protein (HJURP) was upregulated in several tumors, which was associated with poor outcome. This study investigated the effects of the HJURP-mediated c-Jun N-terminal kinase (JNK)/ signal transducer and activator of transcription 3 (STAT3) pathway on bladder urothelial carcinoma (BLUC). Online databases were used to analyze HJURP expression in BLUC and the correlation of HJURP to JNK1 [mitogen-activated protein kinase 8 (MAPK8)], JNK2 (MAPK9), STAT3, marker of proliferation Ki-67 (MKI67), proliferating cell nuclear antigen (PCNA), cyclin dependent kinase 2 (CDK2), CDK4 and CDK6. HJURP expression was detected in BLUC cells and human normal primary bladder epithelial cells (BdECs). BLUC cells were treated with HJURP lentivirus activation /shRNA lentivirus particles or JNK inhibitor SP600125. HJURP was upregulated in BLUC tissues and correlated with poor prognosis of patients (all P < 0.05). HJURP in tumor positively correlated with MAPK8 (R = 0.30), MAPK9 (R = 0.30), STAT3 (R = 0.15), MKI67 (R = 0.60), PCNA (R = 0.46), CDK2 (R = 0.39), CDK4 (R = 0.24) and CDK6 (R = 0.21). The JNK inhibitor SP600125 decreased p-JNK/JNK and p-STAT3/STAT3 in BLUC cells, which was reversed by HJURP overexpression (P < 0.05). The HJURP-mediated JNK/STAT3 pathway promoted BLUC cell proliferation and inhibited cell apoptosis (P < 0.05). HJURP reversed the arrested G0/G1 phase of BLUC cells by SP600125. HJURP acted as an oncogene to regulate BLUC cell proliferation, apoptosis and the cell cycle by mediating the JNK/STAT3 pathway. Therefore, HJURP targeting might be an attractive novel therapeutic target for early diagnosis and treatment in BLUC.

Looking into Endoplasmic Reticulum Stress: The Key to Drug-Resistance of Multiple Myeloma?

Multiple myeloma (MM) is the second most common hematologic malignancy, resulting from the clonal proliferation of malignant plasma cells within the bone marrow. Despite significant advances that have been made with novel drugs over the past two decades, MM patients often develop therapy resistance, especially to bortezomib, the first-in-class proteasome inhibitor that was approved for treatment of MM. As highly secretory monoclonal protein-producing cells, MM cells are characterized by uploaded endoplasmic reticulum stress (ERS), and rely heavily on the ERS response for survival. Great efforts have been made to illustrate how MM cells adapt to therapeutic stresses through modulating the ERS response. In this review, we summarize current knowledge on the mechanisms by which ERS response pathways influence MM cell fate and response to treatment. Moreover, based on promising results obtained in preclinical studies, we discuss the prospect of applying ERS modulators to overcome drug resistance in MM.

Phospho-Specific Flow Cytometry Reveals Signaling Heterogeneity in T-Cell Acute Lymphoblastic Leukemia Cell Lines

Several signaling pathways are aberrantly activated in T-ALL due to genetic alterations of their components and in response to external microenvironmental cues. To functionally characterize elements of the signaling network in T-ALL, here we analyzed ten signaling proteins that are frequently altered in T-ALL -namely Akt, Erk1/2, JNK, Lck, NF-κB p65, p38, STAT3, STAT5, ZAP70, Rb- in Jurkat, CEM and MOLT4 cell lines, using phospho-specific flow cytometry. Phosphorylation statuses of signaling proteins were measured in the basal condition or under modulation with H₂O₂, PMA, CXCL12 or IL7. Signaling profiles are characterized by a high variability across the analyzed T-ALL cell lines. Hierarchical clustering analysis documents that higher intrinsic phosphorylation of Erk1/2, Lck, ZAP70, and Akt, together with ZAP70 phosphorylation induced by H₂O₂, identifies Jurkat cells. In contrast, CEM are characterized by higher intrinsic phosphorylation of JNK and Rb and higher responsiveness of Akt to external stimuli. MOLT4 cells are characterized by higher basal STAT3 phosphorylation. These data document that phospho-specific flow cytometry reveals a high variability in intrinsic as well as modulated signaling networks across different T-ALL cell lines. Characterizing signaling network profiles across individual leukemia could provide the basis to identify molecular targets for personalized T-ALL therapy.

Overcoming drug resistance by targeting protein homeostasis in multiple myeloma

Multiple myeloma (MM) is a plasma cell disorder typically characterized by abundant synthesis of clonal immunoglobulin or free light chains. Although incurable, a deeper understanding of MM pathobiology has fueled major therapeutical advances over the past two decades, significantly improving patient outcomes. Proteasome inhibitors, immunomodulatory drugs, and monoclonal antibodies are among the most effective anti-MM drugs, targeting not only the cancerous cells, but also the bone marrow microenvironment. However, de novo resistance has been reported, and acquired resistance is inevitable for most patients over time, leading to relapsed/refractory disease and poor outcomes. Sustained protein synthesis coupled with impaired/insufficient proteolytic mechanisms makes MM cells exquisitely sensitive to perturbations in protein homeostasis, offering us the opportunity to target this intrinsic vulnerability for therapeutic purposes. This review highlights the scientific rationale for the clinical use of FDA-approved and investigational agents targeting protein homeostasis in MM.

Pathophysiological Significance of WDR62 and JNK Signaling in Human Diseases

The c-Jun N-terminal kinase (JNK) is highly evolutionarily conserved and plays important roles in a broad range of physiological and pathological processes. The WD40-repeat protein 62 (WDR62) is a scaffold protein that recruits different components of the JNK signaling pathway to regulate several human diseases including neurological disorders, infertility, and tumorigenesis. Recent studies revealed that WDR62 regulates the process of neural stem cell mitosis and germ cell meiosis through JNK signaling. In this review we summarize the roles of WDR62 and JNK signaling in neuronal and non-neuronal contexts and discuss how JNK-dependent signaling regulates both processes. WDR62 is involved in various human disorders via JNK signaling regulation, and may represent a promising therapeutic strategy for the treatment of related diseases.

JNK signaling as a target for anticancer therapy

The JNKs are members of mitogen-activated protein kinases (MAPK) which regulate many physiological processes including inflammatory responses, macrophages, cell proliferation, differentiation, survival, and death. It is increasingly clear that the continuous activation of JNKs has a role in cancer development and progression. Therefore, JNKs represent attractive oncogenic targets for cancer therapy using small molecule kinase inhibitors. Studies showed that the two major JNK proteins JNK1 and JNK2 have opposite functions in different types of cancers, which need more specification in the design of JNK inhibitors. Some of ATP- competitive and ATP non-competitive inhibitors have been developed and widely used in vitro, but this type of inhibitors lack selectivity and inhibits phosphorylation of all JNK substrates and may lead to cellular toxicity. In this review, we summarized and discussed the strategies of JNK binding inhibitors and the role of JNK signaling in the pathogenesis of different solid and hematological malignancies.

NOD2/c-Jun NH2-Terminal Kinase Triggers Mycoplasma ovipneumoniae-Induced Macrophage Autophagy

Mycoplasma ovipneumoniae belongs to Mycoplasma, a genus containing the smallest self-replicating microorganisms, and causes infectious pleuropneumonia in goats and sheep. Nucleotide-binding oligomerization domain-containing protein (NOD2), an intracellular pattern recognition receptor, interacts with muramyl dipeptide (MDP) to recognize bacterial peptidoglycans and is involved in autophagy induction. However, there have been no reports about NOD recognition of mycoplasmas or M. ovipneumoniae-induced autophagy. In this study, we sought to determine the role of NOD2 in M. ovipneumoniae-induced autophagy using Western blotting, immunofluorescence, real-time PCR (RT-PCR), and color-changing unit (CCU) analysis. M. ovipneumoniae infection markedly increased NOD2 but did not increase NOD1 expression in RAW 264.7 cells. Treating RAW 264.7 cells with MDP significantly increased colocalization of M. ovipneumoniae and LC3, whereas treatment with NOD inhibitor, NOD-IN-1, decreased colocalization of M. ovipneumoniae and LC3. Furthermore, suppressing NOD2 expression with small interfering RNA (siRNA)-NOD2 failed to trigger M. ovipneumoniae-induced autophagy by detecting autophagy markers Atg5, beclin1, and LC3-II. In addition, M. ovipneumoniae infection significantly increased the phosphorylated c-Jun NH₂-terminal kinase (p-JNK)/JNK, p-Bcl-2/Bcl-2, beclin1, Atg5, and LC3-II ratios in RAW 264.7 cells. Treatment with JNK inhibitor, SP600126, or siRNA-NOD2 did not increase this reaction. These findings suggested that M. ovipneumoniae infection activated NOD2, and both NOD2 and JNK pathway activation promoted M. ovipneumoniae-induced autophagy. This study provides new insight into the NOD2 reorganization mechanism and the pathogenesis of M. ovipneumoniae infection.IMPORTANCE M. ovipneumoniae, which lacks a cell wall, causes infectious pleuropneumonia in goats and sheep. In the present study, we focused on the interaction between NOD and M. ovipneumoniae, as well as its association with autophagy. We showed for the first time that NOD2 was activated by M. ovipneumoniae even when peptidoglycans were not present. We also observed that both NOD2 and JNK pathway activation promoted M. ovipneumoniae-induced autophagy.

Acute immune stress improves cell resistance to chemical poison damage in SP600125-induced polyploidy of fish cells in vitro

Previous research has indicated that the small compound, SP600125, could induce polyploidy of fish cells, and has established a stable tetraploid cell line from diploid fish cells. In order to explore how fish cells maintain homeostasis under SP600125-stress in vitro, this study investigates impacts of SP600125-stress on intracellular pathways, as well as on regulation of the cellular homeostasis feedback in fish cells. Transcriptomes are obtained from the SP600125-treated cells. Compared with unigenes expressed in control group (crucial carp fin cells), a total of 2670 and 1846 unigenes are significantly upregulated and downregulated in these cells, respectively. Differentially expressed genes are found, which are involved in innate defense, inflammatory pathways and cell adhesion molecules-related pathways. The SP600125-stress enhances cell-mediated immunity, characterized by significantly increasing expression of multiple immune genes. These enhanced immune genes include the pro-inflammatory cytokines (IL-1β, TNF-ɑ, IL-6R), the adaptor signal transducers (STAT, IκBɑ), and the integrins (ɑ2β1, ɑMβ2). Furthermore, mitochondria are contributed to the cellular homeostasis regulation upon the SP600125-stress. The results show that acute inflammation is an adaptive and controlled response to the SP600125-stress, which is beneficial for alleviating toxicity by SP600125. They provide a potential way of breeding fish polyploidy induced by SP600125 in the future research.

Effect of JNK inhibitor SP600125 on hair cell regeneration in zebrafish (Danio rerio) larvae

The c-Jun amino-terminal kinase (JNK) proteins are a subgroup of the mitogen-activated protein kinase family. They play a complex role in cell proliferation, survival, and apoptosis. Here, we report a novel role of JNK signalling in hair cell regeneration. We eliminated hair cells of 5-day post-fertilization zebrafish larvae using neomycin followed by JNK inhibition with SP600125. JNK inhibition strongly decreased the number of regenerated hair cells in response to neomycin damage. These changes were associated with reduced proliferation. JNK inhibition also increased cleaved caspase-3 activity and induced apoptosis in regenerating neuromasts. Finally, JNK inhibition with SP600125 decreased the expression of genes related to Wnt. Over-activation of the Wnt signalling pathway partly rescued the hair cell regeneration defects induced by JNK inhibition. Together, our findings provide novel insights into the function of JNK and show that JNK inhibition blocks hair cell regeneration by controlling the Wnt signalling pathway.

Effect of SP600125 on the mitotic spindle in HeLa Cells, leading to mitotic arrest, endoreduplication and apoptosis

BACKGROUND

The JNK inhibitor SP600125 strongly inhibits cell proliferation in many human cancer cells by blocking mitosis progression and inducing cell death. Despite, all this study, the mechanism by which SP600125 inhibits mitosis-related effects in human cervical cells (HeLa cells) remains unclear. In this study, we investigated the effects of SP600125 on the cell viability, cell cycle, and on the spindle assembly during mitosis in HeLa cells.

METHODS

To explore this approach, we used a viability test, an immunofluorescence microscopy to detect Histone phosphorylation and mitotic spindle aberrations. Apoptosis was characterised using Western Blotting.

RESULTS

Treatment of HeLa cells with varying concentrations of SP600125 induces significant G2/M cell cycle arrest with elevated phosphorylation of histone H3 within 48 h, and endoreduplication after 48 h. SP600125 also induces significant abnormal mitotic spindle. High concentrations of SP600125 (20 μM) induce disturbing microtubule assembly in vitro. Additionally, SP600125- induced delayed apoptosis and cell death was accompanied by significant poly ADP-ribose polymerase (PARP) cleavage and caspase-3 activation in the late phase (at 72 h).

CONCLUSION

Our results confirmed that SP600125 induce mitosis arrest in G2/M, endoreduplication, mitotic spindle aberrations and apoptosis.

JNK Inhibition Inhibits Lateral Line Neuromast Hair Cell Development

JNK signaling is known to play a role in regulating cell behaviors such as cell cycle progression, cell proliferation, and apoptosis, and recent studies have suggested important roles for JNK signaling in embryonic development. However, the precise function of JNK signaling in hair cell development remains poorly studied. In this study, we used the small molecule JNK inhibitor SP600125 to examine the effect of JNK signaling abrogation on the development of hair cells in the zebrafish lateral line neuromast. Our results showed that SP600125 reduced the numbers of both hair cells and supporting cells in neuromasts during larval development in a dose-dependent manner. Additionally, JNK inhibition strongly inhibited the proliferation of neuromast cells, which likely explains the decrease in the number of differentiated hair cells in inhibitor-treated larvae. Furthermore, western blot and in situ analysis showed that JNK inhibition induced cell cycle arrest through induction of p21 expression. We also showed that SP600125 induced cell death in developing neuromasts as measured by cleaved caspase-3 immunohistochemistry, and this was accompanied with an induction of p53 gene expression. Together these results indicate that JNK might be an important regulator in the development of hair cells in the lateral line in zebrafish by controlling both cell cycle progression and apoptosis.

Thromboxane A2 Receptor Inhibition Suppresses Multiple Myeloma Cell Proliferation by Inducing p38/c-Jun N-terminal Kinase (JNK) Mitogen-activated Protein Kinase (MAPK)-mediated G2/M Progression Delay and Cell Apoptosis

Multiple myeloma (MM) is a plasma cell malignancy without effective therapeutics. Thromboxane A2 (TxA2)/TxA2 receptor (T prostanoid receptor (TP)) modulates the progression of some carcinomas; however, its effects on MM cell proliferation remain unclear. In this study, we evaluated cyclooxygenase (COX) enzymes and downstream prostaglandin profiles in human myeloma cell lines RPMI-8226 and U-266 and analyzed the effects of COX-1/-2 inhibitors SC-560 and NS-398 on MM cell proliferation. Our observations implicate COX-2 as being involved in modulating cell proliferation. We further incubated MM cells with prostaglandin receptor antagonists or agonists and found that only the TP antagonist, SQ29548, suppressed MM cell proliferation. TP silencing and the TP agonist, U46619, further confirmed this finding. Moreover, SQ29548 and TP silencing promoted MM cell G2/M phase delay accompanied by reducing cyclin B1/cyclin-dependent kinase-1 (CDK1) mRNA and protein expression. Notably, cyclin B1 overexpression rescued MM cells from G2/M arrest. We also found that the TP agonist activated JNK and p38 MAPK phosphorylation, and inhibitors of JNK and p38 MAPK depressed U46619-induced proliferation and cyclin B1/CDK1 protein expression. In addition, SQ29548 and TP silencing led to the MM cell apoptotic rate increasing with improving caspase 3 activity. The knockdown of caspase 3 reversed the apoptotic rate. Taken together, our results suggest that TxA2/TP promotes MM cell proliferation by reducing cell delay at G2/M phase via elevating p38 MAPK/JNK-mediated cyclin B1/CDK1 expression and hindering cell apoptosis. The TP inhibitor has potential as a novel agent to target kinase cascades for MM therapy.

Krüppel-like factor 6 interferes with cellular transformation induced by the H-ras oncogene

KLF6 is a member of the Krüppel-like factor family of transcription factors, with diverse roles in the regulation of cell physiology, including proliferation, signal transduction, and apoptosis. Mutations or down-regulation of KLF6 have been described in several human cancers. In this work, we found that KLF6-knockdown resulted in the formation of transformed foci and allowed the spontaneous conversion of NIH3T3 cells to a tumorigenic state. We further assessed the role of KLF6 in the context of oncogenic Ras. We showed that KLF6 was up-regulated by H-Ras(G12V) expression in a Jun N-terminal kinase (JNK)-dependent manner, correlated with enhanced klf6 promoter activity. We found that ectopic KLF6 expression induced a G1-phase cell cycle arrest, thereby decreasing the cell proliferation rate. In addition, constitutive KLF6 expression impaired H-Ras(G12V)-mediated loss of density-dependent growth inhibition and anchorage-independent growth. Moreover, growth of H-Ras(G12V)-driven tumors was reduced in mice challenged with cells stably expressing KLF6. KLF6 expression correlated with the up-regulation of p21, whereas neither p53 induction nor apoptotic cell death was detected. Further, p21 knockdown impaired KLF6-induced cell cycle arrest. These findings provide novel evidence highlighting KLF6 function in response to malignant transformation, suggesting the relevance of KLF6 in controlling cell proliferation and hindering tumorigenesis.

JNK signalling in cancer: in need of new, smarter therapeutic targets

The JNKs are master protein kinases that regulate many physiological processes, including inflammatory responses, morphogenesis, cell proliferation, differentiation, survival and death. It is increasingly apparent that persistent activation of JNKs is involved in cancer development and progression. Therefore, JNKs represent attractive targets for therapeutic intervention with small molecule kinase inhibitors. However, evidence supportive of a tumour suppressor role for the JNK proteins has also been documented. Recent studies showed that the two major JNK proteins, JNK1 and JNK2, have distinct or even opposing functions in different types of cancer. As such, close consideration of which JNK proteins are beneficial targets and, more importantly, what effect small molecule inhibitors of JNKs have on physiological processes, are essential. A number of ATP-competitive and ATP-non-competitive JNK inhibitors have been developed, but have several limitations such as a lack of specificity and cellular toxicity. In this review, we summarize the accumulating evidence supporting a role for the JNK proteins in the pathogenesis of different solid and haematological malignancies, and discuss many challenges and scientific opportunities in the targeting of JNKs in cancer.

Poly(ADP-ribose) polymerase family member 14 (PARP14) is a novel effector of the JNK2-dependent pro-survival signal in multiple myeloma

Regulation of cell survival is a key part of the pathogenesis of multiple myeloma (MM). Jun N-terminal kinase (JNK) signaling has been implicated in MM pathogenesis, but its function is unclear. To elucidate the role of JNK in MM, we evaluated the specific functions of the two major JNK proteins, JNK1 and JNK2. We show here that JNK2 is constitutively activated in a panel of MM cell lines and primary tumors. Using loss-of-function studies, we demonstrate that JNK2 is required for the survival of myeloma cells and constitutively suppresses JNK1-mediated apoptosis by affecting expression of poly(ADP-ribose) polymerase (PARP)14, a key regulator of B-cell survival. Strikingly, we found that PARP14 is highly expressed in myeloma plasma cells and associated with disease progression and poor survival. Overexpression of PARP14 completely rescued myeloma cells from apoptosis induced by JNK2 knockdown, indicating that PARP14 is critically involved in JNK2-dependent survival. Mechanistically, PARP14 was found to promote the survival of myeloma cells by binding and inhibiting JNK1. Moreover, inhibition of PARP14 enhances the sensitization of MM cells to anti-myeloma agents. Our findings reveal a novel regulatory pathway in myeloma cells through which JNK2 signals cell survival via PARP14, and identify PARP14 as a potential therapeutic target in myeloma.

Inhibition of c-Jun NH2-terminal kinase stimulates mu opioid receptor expression via p38 MAPK-mediated nuclear NF-κB activation in neuronal and non-neuronal cells

Despite its potential side effects of addiction, tolerance and withdrawal symptoms, morphine is widely used for reducing moderate and severe pain. Previous studies have shown that the analgesic effect of morphine depends on mu opioid receptor (MOR) expression levels, but the regulatory mechanism of MOR is not yet fully understood. Several in vivo and in vitro studies have shown that the c-Jun NH2-terminal kinase (JNK) pathway is closely associated with neuropathic hyperalgesia, which closely resembles the neuroplastic changes observed with morphine antinociceptive tolerance. In this study, we show that inhibition of JNK by SP600125, its inhibitory peptide, or JNK-1 siRNA induced MOR at both mRNA and protein levels in neuronal cells. This increase in MOR expression was reversed by inhibition of the p38 mitogen-activated protein kinase (MAPK) pathway, but not by inhibition of the mitogen-activated protein/extracellular signal-regulated kinase (MEK) pathway. Further experiments using cell signaling inhibitors showed that MOR upregulation by JNK inhibition involved nuclear factor-kappa B (NF-κB). The p38 MAPK dependent phosphorylation of p65 NF-κB subunit in the nucleus was increased by SP600125 treatment. We also observed by chromatin immunoprecipitation (ChIP) analysis that JNK inhibition led to increased bindings of CBP and histone-3 dimethyl K4, and decreased bindings of HDAC-2, MeCP2, and histone-3 trimethyl K9 to the MOR promoter indicating a transcriptional regulation of MOR by JNK inhibition. All these results suggest a regulatory role of the p38 MAPK and NF-κB pathways in MOR gene expression and aid to our better understanding of the MOR gene regulation.

Targeting early B-cell receptor signaling induces apoptosis in leukemic mantle cell lymphoma

BACKGROUND

We previously showed that B-cell receptor (BCR) signaling pathways are important for in vitro survival of mantle cell lymphoma (MCL) cells. To further identify early BCR-activated signaling pathways involved in MCL cell survival, we focused our study on BCR-proximal kinases such as LYN whose dysregulations could contribute to the aggressive course of MCL.

METHODS

Primary MCL cells were isolated from 14 leukemic patients. Early BCR-induced genes were identified by qRT-PCR array. The basal and BCR-induced phosphorylation of LYN and JNK were evaluated by immunoblottting. Cell survival signals were evaluated by apoptosis using flow cytometry.

RESULTS

We showed that LYN was constitutively phosphorylated in MCL cell lines and in 9/10 leukemic MCL cases. Treatment with dasatinib or with a specific inhibitor of Src kinases such as PP2 suppressed constitutive LYN activation and increased in vitro spontaneous apoptosis of primary MCL cells. BCR engagement resulted in an increase of LYN phosphorylation leading to activation of c-JUN NH2-terminal kinase (JNK) and over-expression of the early growth response gene-1 (EGR-1). Inhibition of JNK with SP600125 induced apoptosis and reduced level of basal and BCR-induced expression of EGR-1. Furthermore, decreasing EGR1 expression by siRNA reduced BCR-induced cell survival. Treatment with PP2 or with dasatinib suppressed BCR-induced LYN and JNK phosphorylation as well as EGR-1 upregulation and is associated with a decrease of cell survival in all cases analysed.

CONCLUSIONS

This study highlights the importance of BCR signaling in MCL cell survival and points out to the efficiency of kinase inhibitors in suppressing proximal BCR signaling events and in inducing apoptosis.

Toosendanin induces apoptosis through suppression of JNK signaling pathway in HL-60 cells

Toosendanin (TSN), a triterpenoid isolated from Melia toosendan Sieb. et Zucc., has been found to suppress proliferation and induce apoptosis in a variety of human cancer cells. However, the mechanism how TSN induces apoptosis remains poorly understood. In this study, we examined the effects of TSN on the growth, cell cycle arrest, induction of apoptosis and the involved signaling pathway in human promyelocytic leukemia HL-60 cells. Proliferation of HL-60 cells was inhibited in a dose-dependent manner with the IC(50 (48 h)) of 28 ng/mL. The growth inhibition was due primarily to the S phase arrest and cell apoptosis. Cell apoptosis induced by TSN was confirmed by Annexin V-FITC/propidium iodide staining. The increase of the pro-apoptotic protein Bax, cleaved PARP and caspase-3, and the decrease of anti-apoptotic protein Bcl-2 were observed. Western blot analysis indicated that TSN inhibits the CDC42/MEKK1/JNK pathway. Taken together, our study suggested, for the first time, that the pro-apoptotic effects of TSN on HL-60 cells were mediated through JNK signaling pathway.

Toll-like receptor 4 activates NF-κB and MAP kinase pathways to regulate expression of proinflammatory COX-2 in renal medullary collecting duct cells

Binding of bacterial LPS to the Toll-like receptor 4 (TLR4) complex of inner medullary collecting duct (IMCD) cells plays a central role in recognition of ascending bacterial infections and activation of proinflammatory responses. Since proinflammatory cyclooxygenase (COX)-2 is induced in IMCD cells upon LPS exposure, the present study addressed the question of whether TLR4 mediates COX-2 induction in IMCD cells and characterized the underlying signaling mechanisms. Enhanced COX-2 expression and activity in the presence of LPS was diminished by TLR4 inhibition. LPS induced a TLR4-dependent stimulation of NF-κB and the MAPKs p38, ERK1/2, and JNK. Activation of NF-κB was under negative control of JNK, as inhibition of JNK increased NF-κB activity and COX-2 expression. Phosphorylation of p38 and ERK1/2 required TLR4-dependent release of TGF-α with subsequent activation of the epidermal growth factor receptor (EGFR), whereas JNK activation was EGFR independent. Inhibition of p38 or ERK1/2 had no significant effect on LPS-induced NF-κB activation, nor on activator protein 1-, cAMP response element-, or serum response element-driven reporter constructs. However, the transcriptional regulator SP-1 appears to contribute to COX-2 expression after LPS exposure. In conclusion, these results propose that LPS mediates enhanced COX-2 expression in IMCD cells by 1) TLR4-mediated activation of the NF-κB signaling pathway, 2) TLR4-dependent release of TGF-α with subsequent activation of the EGFR and downstream MAPKs p38 and ERK1/2, and 3) TLR4-mediated, EGFR-independent activation of JNK that negatively regulates NF-κB activation.

Role of p21 in SP600125-induced cell cycle arrest, endoreduplication, and apoptosis

The anti-cancer effect of the c-Jun N-terminal kinase (JNK) inhibitor SP600125 has been well evaluated in human cancer cells. However the role of p21 in SP600125-mediated G(2)/M distribution is not fully understood. Our results showed that the transcriptional activation of p21 by SP600125 is mediated through the proximal regions of multiple Sp1 sites in the p21 promoter following ERK-dependent phosphorylation of Sp1. In this process, p21 induces endoreduplication through the inhibition of cyclin E/Cdk2 activity at 24 h but does not directly regulate cyclin B1/Cdc2 activity. Furthermore, SP600125 induces the phosphorylation of p21 at Thr 145 through the PI3K/Akt pathway. Akt-mediated phosphorylation of p21 and protection of apoptosis are completely abolished by inhibitors of PI3K and Akt. In summary using time points, we identified the dual functions of p21 as an inhibitor of cell-cycle progression at 24 h and as an anti-apoptotic factor at 48 h.

Novel IkB kinase inhibitors for treatment of nuclear factor-kB-related diseases

INTRODUCTION

NF-kB is a key regulator of inflammation and immunity in cancer development. The IkB kinase (IKK) is a multisubunit complex containing catalytic subunits termed IKK-α, -β and -γ. It is well known that many pro-inflammatory stimuli require the IKK-β subunit for NF-kB activation.

AREAS COVERED

NF-kB affects the progression of inflammation-related diseases,such as myocardial ischemia, bronchial asthma, arthritis, cancer and other diseases. We review the characteristics and effects of these inhibitors on inflammatory and other diseases.

EXPERT OPINION

Various synthesized IKK inhibitors have been developed and they will be used clinically in the near future.

Transcriptional Factor NF-κB as a Target for Therapy in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative condition characterized by chronic inflammation. Nuclear factor κB (NF-κB) is a family of inducible transcription factors that are expressed in a wide variety of cells and tissues, including microglia, astrocytes, and neurons, and the classical NF-κB pathway plays a key role in the activation and regulation of inflammatory mediator production during inflammation. Activation of the classical NF-κB pathway is mediated through the activity of the IKK kinase complex, which consists of a heterotrimer of IKKα, IKKβ, and IKKγ subunits. Targeting NF-κB has been proposed as an approach to the treatment of acute and chronic inflammatory conditions, and the use of inhibitors specific for either IKKβ or IKKγ has now been found to inhibit neurodegeneration of TH+ DA-producing neurons in murine and primate models of Parkinson's disease. These studies suggest that targeting the classical pathway of NF-κB through the inhibition of the IKK complex can serve as a useful therapeutic approach to the treatment of PD.

Novel agents to improve outcome of allogeneic transplantation for patients with multiple myeloma

Over the last few decades therapy for multiple myeloma has improved remarkably. In particular, the introduction of novel agents has allowed improved response rates prior to, and after, stem cell transplantation with extension of progression-free survival in high-risk patients. Nevertheless, most patients relapse, leaving multiple myeloma an incurable disease. Despite being the only treatment option that has real curative potential, allogeneic transplantation has not shown its superiority to autologous transplantation due to its high morbidity and mortality rates. This review highlights how novel agents might help to reduce treatment-related mortality and to improve tumor control prior to and post-allogeneic stem cell transplant, which will hopefully result in significantly improved long-term disease control, and maybe a cure following this treatment modality.

Basal c-Jun NH2-terminal protein kinase activity is essential for survival and proliferation of T-cell acute lymphoblastic leukemia cells

Hyperactivation of c-Jun NH2-terminal protein kinase (JNK) has been found in various malignant lymphocytes and inhibition of JNK activity leads to cell cycle arrest and apoptosis. However, the role of JNK activity in the oncogenic growth of T-cell acute lymphoblastic leukemia (T-ALL) cells remains largely unknown. Here, we report that treatment of T-ALL cells with JNK inhibitors led to cell cycle arrest and apoptosis and increased sensitivity to Fas-mediated apoptosis, whereas weak ectopic expression of MKK7-JNK1 fusion protein, which shows constitutive JNK activity, in T-ALL cells resulted in accelerated cell cycle progression and resistance to Fas-mediated apoptosis. The protein levels of c-Myc and Bcl-2 were reduced in the presence of JNK inhibitors but were enhanced with MKK7-JNK1. Small interfering RNA against JNK1, but not JNK2, exhibited similar effects to JNK inhibitors. These findings suggest that targeting JNK, especially JNK1 isoform, may have some important therapeutic implications in the treatment of T-ALL. Further exploration revealed that JNK protein and basal JNK activity in T-ALL cells showed aberrant subcellular localization, but no hyperactivation of JNK was observed. Thus, our work suggests that there might be novel mechanism(s) other than hyperactivation underlying the protumorigenic role of JNK activity.

JNK inhibitor SP600125 promotes the formation of polymerized tubulin, leading to G2/M phase arrest, endoreduplication, and delayed apoptosis

The JNK inhibitor SP600125 strongly inhibits cell proliferation in many human cancer cells by blocking cell-cycle progression and inducing apoptosis. Despite extensive study, the mechanism by which SP600125 inhibits mitosis-related effects in human leukemia cells remains unclear. We investigated the effects of SP600125 on the inhibition of cell proliferation and the cell cycle, and on microtubule dynamics in vivo and in vitro. Treatment of synchronized leukemia cells with varying concentrations of SP600125 results in significant G2/M cell cycle arrest with elevated p21 levels, phosphorylation of histone H3 within 24 h, and endoreduplication with elevated Cdk2 protein levels after 48 h. SP600125 also induces significant abnormal microtubule dynamics in vivo. High concentrations of SP600125 (200 microM) were required to disorganize microtubule polymerization in vitro. Additionally, SP600125- induced delayed apoptosis and cell death was accompanied by significant poly ADP-ribose polymerase (PARP) cleavage and caspase-3 activity in the late phase (at 72 h). Endoreduplication showed a greater increase in ectopic Bcl-2-expressing U937 cells at 72 h than in wild-type U937 cells without delayed apoptosis. These results indicate that Bcl-2 suppresses apoptosis and SP600125-induced G2/M arrest and endoreduplication. Therefore, we suggest that SP600125 induces mitotic arrest by inducing abnormal spindle microtubule dynamics.

A JNK inhibitor SP600125 induces defective cytokinesis and enlargement in P19 embryonal carcinoma cells

While analyzing the role of c-Jun NH(2)-terminal kinase (JNK) in neurogenesis in P19 embryonal carcinoma cells, we noticed that treatment with SP600125, a JNK inhibitor, increased the cell size markedly. SP600125-induced enlargement of P19 cells was time- and dose-dependent. The increased cell size in response to SP600125 was also detected in B6mt-1 embryonic stem cells. SP600125 treatment inhibited cell growth and increased DNA contents, indicating the inhibition of cell proliferation resulting from endoreduplication. Concurrently, the gene expression of p21, a regulator of G2/M arrest as well as G1 arrest, was increased in cells treated with SP600125. The increased cell size in response to SP600125 was detected even in P19 cells treated with colcemide, an inhibitor of cell cycle progression at the metaphase. The present study suggests that treatment with SP600125 progresses the cell cycle, skipping cytokinesis in P19 cells.

The links between transcription, beta-catenin/JNK signaling, and carcinogenesis

Interactions between transcription and signaling are fundamentally important for understanding both the structure and function of genetic pathways and their role in diseases such as cancer. The finding that beta-catenin/TCF4 and JNK/c-Jun cooperate has important implications in carcinogenesis. Previously, we found that binding of c-Jun and beta-catenin/TCF4 to the c-jun promoter is dependent upon JNK activity, thus one role for this complex is to contribute to the repression and/or activation of genes that may mediate cell maintenance, proliferation, differentiation, and death, whereas deregulation of these signals may contribute to carcinogenesis. Here we address the functional links reported between activated beta-catenin/JNK signaling pathways, their component genes, and their common targets, and discuss how alterations in the properties of these genes lead to the development of cancer.

JNK is constitutively active in mantle cell lymphoma: cell cycle deregulation and polyploidy by JNK inhibitor SP600125

Mantle cell lymphoma (MCL) is characterized by genetic instability and a poor prognosis. Many blastoid variants are (hypo)tetraploid and have an even worse prognosis. We investigated the role of signalling by mitogen-activated protein kinases (MAPKs) in MCL. As compared to normal tonsil B cells, MCL cells showed higher activation of the JNK MAPK in both an MAPK array and a sandwich ELISA assay. Immunohistochemistry showed overexpression of phospho (p)-JNK (Thr183/Tyr185) in 30 of 37 MCL cases. Inhibition of p-JNK with SP600125 resulted in growth arrest in all four MCL cell lines (Jeko-1, HBL-2, UPN-1, Granta-519), which could be partly reversed by the addition of CD40L and IL-4. Furthermore, SP600125 led to G2/M phase arrest on day 1 and a striking increase in endoreduplication on day 2 and day 3, which was confirmed by karyotype analysis. G2/M arrest was associated with down-regulation of EGR1 and p21 protein expression. SP600125-induced polyploidy could be blocked by the BCL-2 inhibitor YC137. These data suggest that constitutive JNK activity is necessary to promote proliferation and maintain diploidy in MCL. JNK inhibition leads to cell cycle deregulation and endoreduplication, mimicking the tetraploid state seen in a subset of MCL cases. Thus, our data also provide an experimental model to study polyploid MCL cells.

Mechanisms regulating the susceptibility of hematopoietic malignancies to glucocorticoid-induced apoptosis

Glucocorticoids (GCs) are commonly used in the treatment of hematopoietic malignancies owing to their ability to induce apoptosis of these cancerous cells. Whereas some types of lymphoma and leukemia respond well to this drug, others are resistant. Also, GC-resistance gradually develops upon repeated treatments ultimately leading to refractory relapsed disease. Understanding the mechanisms regulating GC-induced apoptosis is therefore uttermost important for designing novel treatment strategies that overcome GC-resistance. This review discusses updated data describing the complex regulation of the cell's susceptibility to apoptosis triggered by GCs. We address both the genomic and nongenomic effects involved in promoting the apoptotic signals as well as the resistance mechanisms opposing these signals. Eventually we address potential strategies of clinical relevance that sensitize GC-resistant lymphoma and leukemia cells to this drug. The major target is the nongenomic signal transduction machinery where the interplay between protein kinases determines the cell fate. Shifting the balance of the kinome towards a state where Glycogen synthase kinase 3alpha (GSK3alpha) is kept active, favors an apoptotic response. Accumulating data show that it is possible to therapeutically modulate GC-resistance in patients, thereby improving the response to GC therapy.

Oral administration of blueberry inhibits angiogenic tumor growth and enhances survival of mice with endothelial cell neoplasm

Endothelial cell neoplasms are the most common soft tissue tumor in infants. Subcutaneous injection of spontaneously transformed murine endothelial (EOMA) cells results in development of hemangioendothelioma (HE). We have previously shown that blueberry extract (BBE) treatment of EOMA cells in vitro prior to injection in vivo can significantly inhibit the incidence and size of developing HE. In this study, we sought to determine whether oral BBE could be effective in managing HE and to investigate the mechanisms through which BBE exerts its effects on endothelial cells. A dose-dependent decrease in HE tumor size was observed in mice receiving daily oral gavage feeds of BBE. Kaplan-Meier survival curve showed significantly enhanced survival for mice with HE tumors given BBE, compared to control. BBE treatment of EOMA cells inhibited both c-Jun N-terminal kinase (JNK) and NF-kappaB signaling pathways that culminate in monocyte chemoattractant protein-1 (MCP-1) expression required for HE development. Antiangiogenic effects of BBE on EOMA cells included decreased proliferation by BrdU assay, decreased sprouting on Matrigel, and decreased transwell migration. Thus, this work provides first evidence demonstrating that BBE can limit tumor formation through antiangiogenic effects and inhibition of JNK and NF-kappaB signaling pathways. Oral administration of BBE represents a potential therapeutic antiangiogenic strategy for treating endothelial cell neoplasms in children.

Blockage of interleukin-6 signaling with 6-amino-4-quinazoline synergistically induces the inhibitory effect of bortezomib in human U266 cells

The transcription factor nuclear factor-kappa B (NF-kappaB) regulates the transcription of a number of genes involved in a variety of cellular responses, including cell survival, inflammation, and differentiation. NF-kappaB is activated by a variety of stimuli, proinflammatory cytokines, mitogens, growth factors, and stress-inducing agents. Aberrant NF-kappaB expression is considered to be one of the oncogenic factors of cancer and the constitutive activation of NF-kappaB is observed in several hematologic disorders [classic Hodgkin's lymphoma, diffuse large B cell lymphoma, and multiple myeloma (MM)], and the modulation of NF-kappaB activation is emerging as a promising novel anticancer therapeutic strategy.Therefore, we focused on the regulation of NF-kappaB activation in MM. When U266 cells were treated with 6-amino-4-quinazoline, an NF-kappaB activation inhibitor, we determined that it most effectively blocked the interleukin (IL)-6-induced activation of MAPK and JAK/STAT pathways among different signaling inhibitors. The results of the luciferase assay indicated that 6-amino-4-quinazoline inhibited NF-kappaB activation with diminished NF-kappaB protein bound to NF-kappaB DNA binding sites. In addition, 6-amino-4-quinazoline suppressed the production of IL-6, which affected MM cell proliferation. Furthermore, combined treatment with bortezomib and 6-amino-4-quinazoline effectively inhibited the IL-6 and soluble IL-6R-induced activation of STAT3 and extracellular signal-regulated kinase phosphorylation. Our data showed that the inhibition of NF-kappaB activation abrogated MM cell proliferation induced by the IL-6 pathway, and might represent a promising therapeutic strategy for the treatment of MM.

Erythropoietin enhancement of rat pancreatic tumor cell proliferation requires the activation of ERK and JNK signals

Erythropoietin (EPO) regulates the proliferation and differentiation of erythroid cells by binding to its specific transmembrane receptor EPOR. Recent studies, however, have shown that the EPOR is additionally present in various cancer cells and EPO induces the proliferation of these cells, suggesting a different function for EPO other than erythropoiesis. Therefore, the purpose of the present study was to examine EPOR expression and the role of EPO in the proliferation and signaling cascades involved in this process, using the rat pancreatic tumor cell line AR42J. Our results showed that AR42J cells expressed EPOR, and EPO significantly enhanced their proliferation. Cell cycle analysis of EPO-treated cells indicated an increased percentage of cells in the S phase, whereas cell numbers in G0/G1 phase were significantly reduced. Phosphorylation of extracellular regulatory kinase 1/2 (ERK1/2) and c-Jun NH2terminal kinase 1/2 (JNK1/2) was rapidly stimulated and sustained after EPO addition. Treatment of cells with mitogen-activated protein/ERK kinase (MEK) inhibitor PD98059 or JNK inhibitor SP600125 significantly inhibited EPO-enhanced proliferation and also increased the fraction of cells in G0/G1 phase. Furthermore, the inhibition of JNK using small interference RNA (siRNA) suppressed EPO-enhanced proliferation of AR42J cells. Taken together, our results indicate that AR42J cells express EPOR and that the activation of both ERK1/2 and JNK1/2 by EPO is essential in regulating proliferation and the cell cycle. Thus both appear to play a key role in EPO-enhanced proliferation and suggest that the presence of both is required for EPO-mediated proliferation of AR42J cells.

Knockdown of Snail, a novel zinc finger transcription factor, via RNA interference increases A549 cell sensitivity to cisplatin via JNK/mitochondrial pathway

Previous reports have implicated epithelial-mesenchymal transition (EMT) as a major cause of cancer. Snail, a novel zinc finger transcription factor, was suggested to be an important inducer of EMT and therefore be involved in different phases of tumorigenicity. However, whether Snail could increase chemoresistance of cancer cells to chemotherapeutic agent remains unclear. To evaluate the roles and possible mechanisms of Snail in chemoresistance of lung cancer cells to cisplatin, we utilized RNA interference to knockdown Snail expression in A549 cells and further assessed the cell viability and apoptosis as well as possible signaling transduction pathways. The data showed that Snail depletion sensitized A549 cells to cisplatin possibly by inducing activation of JNK/mitochondrial pathway, suggesting critical roles of Snail in A549 cell chemoresistance to cisplatin and raising the possibility of Snail depletion as a promising approach to lung cancer therapy.

Bcl-2 overexpression attenuates SP600125-induced apoptosis in human leukemia U937 cells

SP600125 is a specific inhibitor of c-Jun N-terminal kinase (JNK) that is known to strongly induce apoptosis and block cell cycle progression in G2/M phase. In this study, we demonstrated that treatment of U937 cells with SP600125 resulted in significant G2/M cell cycle arrest that was due to decreased cyclin B1 and cdc25c protein levels. Moreover, SP600125 promoted LDH release and DNA fragmentation that was associated with caspase-3 activation and degradation of its substrates. In contrast, overexpression of the antiapoptotic protein Bcl-2 rendered leukemia cells resistant to SP600125-induced apoptosis, but more sensitive to G2/M phase arrest and endoreduplication (>4N DNA). Overexpression of Bcl-2 significantly inhibited SP600125-induced caspase-3 activation and degradation of its substrates, and sustained expression levels of the IAP-2 proteins following SP600125 treatment. The inhibitory effect of Bcl-2 on apoptosis was attenuated by treatment with the small molecule Bcl-2 inhibitor, HA14-1. These data provide important mechanistic insights related to Bcl-2-mediated resistance to SP600125-induced apoptosis, and induction of G2/M phase arrest and endoreduplication.

Polarity proteins PAR6 and aPKC regulate cell death through GSK-3beta in 3D epithelial morphogenesis

Epithelial cells are polarized, with an apical surface facing a lumen or outer surface and a basolateral surface facing other cells and extracellular matrix (ECM). Hallmarks of epithelial carcinogenesis include loss of polarity, as well as uncontrolled proliferation and resistance to apoptosis. Are these features controlled by a common molecular mechanism? The partitioning-defective 3 (PAR3)-PAR6-atypical PKC (aPKC) complex is a master regulator that controls polarization in many animal cells. Here we show that PAR6 is involved in apoptosis by regulating aPKC and glycogen synthase kinase 3beta (GSK-3beta) activity. During epithelial morphogenesis in 3D culture of Madin-Darby canine kidney (MDCK) cells, expression of an N-terminally deleted PAR6 (PAR6DeltaN) leads to a significant increase in caspase-dependent cell death by downregulating aPKC activity. Accordingly, inhibition of aPKC in wild-type (WT) MDCK cells with either a cell-permeable PKCzeta pseudosubstrate or RNAi promotes apoptosis, which suggests that PAR6 regulates apoptosis via an aPKC-mediated pathway. GSK-3beta, a substrate of aPKC, is hyper-activated by expressing PAR6DeltaN. GSK-3beta inhibitors block PAR6DeltaN-induced apoptosis while expression of constitutively active GSK-3beta (S9A) promotes apoptosis, which is rescued by ectopic expression of aPKC. We conclude that a PAR6-aPKC-GSK-3beta mechanism links cell polarity and apoptosis.

A pathogenic role for JNK signaling in experimental anti-GBM glomerulonephritis

Activation of the c-Jun NH2-terminal kinase (JNK) signaling pathway is involved in the immune response; however, little is known of its role in immune-induced renal injury. In this study, we examine JNK signaling in the rat anti-glomerular basement membrane (GBM) disease model using CC-401, a specific JNK inhibitor. Animals were given CC-401, vehicle alone or no treatment starting before anti-GBM serum injection and continued treatment until killing. In acute disease, CC-401 blocked JNK signaling and reduced proteinuria in the first 24 h. The transient neutrophil influx seen at 3 h of disease was not affected, however. Continued CC-401 treatment suppressed glomerular and tubulointerstitial damage usually seen at 14 days. The protective effect may be due to modulation of macrophage activation, as CC-401 had no effect upon glomerular macrophage infiltration at day 14 despite the suppression of glomerular lesions and a marked reduction in renal tumor necrosis factor-alpha and inducible nitric oxide synthase messenger RNA levels. Treatment with CC-401 had no apparent effect on T cell or humoral immune responses. These studies suggest that JNK signaling promotes renal injury in acute and progressive rat anti-GBM disease. JNK inhibitors may be a novel therapeutic approach for the treatment of human glomerulonephritis.

Regulation of PTEN expression in intestinal epithelial cells by c-Jun NH2-terminal kinase activation and nuclear factor-kappaB inhibition

The tumor suppressor protein phosphatase and tensin homologue deleted on chromosome ten (PTEN) plays an important role in intestinal cell proliferation and differentiation and tumor suppression by antagonizing phosphatidylinositol 3-kinase. Despite its importance, the molecular mechanisms regulating PTEN expression are largely undefined. Here, we show that treatment of the colon cancer cell line HT29 with the differentiating agent sodium butyrate (NaBT) increased PTEN protein and mRNA expression and induced c-Jun NH2-terminal kinase (JNK) activation. Inhibition of JNK by chemical or genetic methods attenuated NaBT-induced PTEN expression. In addition, our findings showed a cross-talk between nuclear factor kappaB (NF-kappaB) and JNK with respect to PTEN regulation. Overexpression of the NF-kappaB superrepressor increased PTEN expression and JNK activity, whereas overexpression of the p65 NF-kappaB subunit reduced both basal and NaBT-mediated JNK activation and PTEN expression. Moreover, we showed that overexpression of PTEN or treatment with NaBT increased expression of the cyclin-dependent kinase inhibitor p27(kip1) in HT29 cells; this induction was attenuated by inhibition of PTEN or JNK expression or overexpression of p65. Finally, we show a role for PTEN in NaBT-mediated cell death and differentiation. Our findings suggest that the JNK/PTEN and NF-kappaB/PTEN pathways play a critical role in normal intestinal homeostasis and colon carcinogenesis.

Bortezomib inhibits human osteoclastogenesis

In multiple myeloma, the overexpression of receptor activator of nuclear factor kappa B (NF-kappaB) ligand (RANKL) leads to the induction of NF-kappaB and activator protein-1 (AP-1)-related osteoclast activation and enhanced bone resorption. The purpose of this study was to examine the molecular and functional effects of proteasome inhibition in RANKL-induced osteoclastogenesis. Furthermore, we aimed to compare the outcome of proteasome versus selective NF-kappaB inhibition using bortezomib (PS-341) and I-kappaB kinase inhibitor PS-1145. Primary human osteoclasts were derived from CD14+ precursors in presence of RANKL and macrophage colony-stimulating factor (M-CSF). Both bortezomib and PS-1145 inhibited osteoclast differentiation in a dose- and time-dependent manner and furthermore, the bone resorption activity of osteoclasts. The mechanisms of action involved in early osteoclast differentiation were found to be related to the inhibition of p38 mitogen-activated protein kinase pathways, whereas the later phase of differentiation and activation occurred due to inhibition of p38, AP-1 and NF-kappaB activation. The AP-1 blockade contributed to significant reduction of osteoclastic vascular endothelial growth factor production. In conclusion, our data demonstrate that proteasomal inhibition should be considered as a novel therapeutic option of cancer-induced lytic bone disease.

The oxidative stress response regulates DKK1 expression through the JNK signaling cascade in multiple myeloma plasma cells

Multiple myeloma (MM) plasma cells, but not those from healthy donors and patients with monoclonal gammopathy of undetermined significance or other plasma cell dyscrasias involving the bone marrow, express the Wnt-signaling antagonist DKK1. We previously reported that secretion of DKK1 by MM cells likely contributes to osteolytic lesions in this disease by inhibiting Wnt signaling, which is essential for osteoblast differentiation and survival. The mechanisms responsible for activation and regulation of DKK1 expression in MM are not known. Herein, we could trace DKK1 expression changes in MM cells to perturbations in the JNK signaling cascade, which is differentially modulated through oxidative stress and interactions between MM cells with osteoclasts in vitro. Despite its role as a tumor suppressor and mediator of apoptosis in other cell types including osteoblasts, our data suggest that DKK1, a stress-responsive gene in MM, does not mediate apoptotic signaling, is not activated by TP53, and its forced overexpression could not inhibit cell growth or sensitize MM cells to apoptosis following treatment with thalidomide or lenalidomide. We conclude that specific strategies to modulate persistent activation of the JNK pathway may be beneficial in preventing disease progression and treating myeloma-associated bone disease by inhibiting DKK1 expression.

Targeted therapy of multiple myeloma based upon tumor-microenvironmental interactions

Multiple myeloma (MM) remains incurable, but recent advances in genomics and proteomics have allowed for advances in our understanding of disease pathogenesis, identified novel therapeutic targets, allowed for molecular classification, and provided the scientific rationale for combining targeted therapies to increase tumor cell cytotoxicity and abrogate drug resistance. Besides these advances, recognition of the role of the bone marrow (BM) milieu in conferring growth, survival, and drug resistance in MM cells, both in laboratory and animal models, has allowed for the establishment of a new treatment paradigm targeting the tumor cell and its microenvironment to overcome drug resistance and improve patient outcomes in MM. In particular, thalidomide, bortezomib, and lenalidamide all overcome conventional drug resistance, not only by directly inducing tumor cell cytotoxicity, but by inhibiting adhesion of MM cells to BM. This abrogates constitutive and MM-binding-induced transcription and secretion of cytokines, inhibits angiogenesis, and augments host anti-MM immunity. These three drugs have rapidly translated from bench to bedside and in treatment protocols of MM, first in patients with relapsed refractory disease, and then alone and in combination in newly diagnosed patients. Promising novel targeted agents include the novel proteasome inhibitor NPI-0052 and the heat shock protein inhibitor KOS-953. Importantly, gene-array, proteomic, and cell-signaling studies have not only helped to identify in vivo mechanisms of action and drug resistance to novel agents, but also aided in the design of promising combination-therapy protocols.

NPM-ALK oncogenic kinase promotes cell-cycle progression through activation of JNK/cJun signaling in anaplastic large-cell lymphoma

Anaplastic large-cell lymphoma (ALCL) frequently carries the t(2;5)(p23;q35), resulting in aberrant expression of nucleophosmin-anaplastic lymphoma kinase (NPM-ALK). We show that in 293T and Jurkat cells, forced expression of active NPM-ALK, but not kinase-dead mutant NPM-ALK (210K>R), induced JNK and cJun phosphorylation, and this was linked to a dramatic increase in AP-1 transcriptional activity. Conversely, inhibition of ALK activity in NPM-ALK(+) ALCL cells resulted in a concentration-dependent dephosphorylation of JNK and cJun and decreased AP-1 DNA-binding. In addition, JNK physically binds NPM-ALK and is highly activated in cultured and primary NPM-ALK(+) ALCL cells. cJun phosphorylation in NPM-ALK(+) ALCL cells is mediated by JNKs, as shown by selective knocking down of JNK1 and JNK2 genes using siRNA. Inhibition of JNK activity using SP600125 decreased cJun phosphorylation and AP-1 transcriptional activity and this was associated with decreased cell proliferation and G2/M cell-cycle arrest in a dose-dependent manner. Silencing of the cJun gene by siRNA led to a decreased S-phase cell-cycle fraction associated with upregulation of p21 and downregulation of cyclin D3 and cyclin A. Taken together, these findings reveal a novel function of NPM-ALK, phosphorylation and activation of JNK and cJun, which may contribute to uncontrolled cell-cycle progression and oncogenesis.

Pathway interactions between MAPKs, mTOR, PKA, and the glucocorticoid receptor in lymphoid cells

Background

Glucocorticoids are frequently used as a primary chemotherapeutic agent in many types of human lymphoid malignancies because they induce apoptosis through activation of the glucocorticoid receptor, with subsequent alteration of a complex network of cellular mechanisms. Despite clinical usage for over fifty years, the complete mechanism responsible for glucocorticoid-related apoptosis or resistance remains elusive. The mitogen-activated protein kinase pathway is a signal transduction network that influences a variety of cellular responses through phosphorylation of specific target substrates, including the glucocorticoid receptor. In this study we have evaluated the pharmaceutical scenarios which converge on the mitogen-activated protein kinase pathway to alter glucocorticoid sensitivity in clones of human acute lymphoblastic CEM cells sensitive and refractory to apoptosis in response to the synthetic glucocorticoid dexamethasone.

Results

The glucocorticoid-resistant clone CEM-C1-15 displays a combination of high constitutive JNK activity and dexamethasone-induced ERK activity with a weak induction of p38 upon glucocorticoid treatment. The cells become sensitive to glucocorticoid-evoked apoptosis after: (1) inhibition of JNK and ERK activity, (2) stimulation of the cAMP/PKA pathway with forskolin, or (3) inhibition of mTOR with rapamycin. Treatments 1–3 in combination with dexamethasone alter the intracellular balance of phospho-MAPKs by lowering JNK phosphorylation and increasing the level of glucocorticoid receptor phosphorylated at serine 211, a modification known to enhance receptor activity.

Conclusion

Our data support the hypothesis that mitogen-activated protein kinases influence the ability of certain malignant lymphoid cells to undergo apoptosis when treated with glucocorticoid. Activated/phosphorylated JNK and ERK appear to counteract corticoid-dependent apoptosis. Inhibiting these MAPKs restores corticoid sensitivity to a resistant clone of CEM cells. Forskolin, which activates the cAMP pathway, and rapamycin, which inhibits mTOR, also inhibit JNK. Further, the sensitizing treatments result in a largely dexamethasone-dependent increase in the total pool of glucocorticoid receptor phosphorylated at serine 211. The phospho-serine 211 receptor is known to be more potent in activating gene transcription and apoptosis. The interactive effects demonstrated here in reverting resistant cells to corticoid sensitivity could provide therapeutic clinical potential in the treatment of lymphoid malignancies.

Activation of p53 in cervical cancer cells by human papillomavirus E6 RNA interference is transient, but can be sustained by inhibiting endogenous nuclear export-dependent p53 antagonists

p53 is degraded in cervical cancer cells by the human papillomavirus E6 and can be stabilized with short interfering RNA (siRNA) molecules targeting E6 mRNA. In this in vitro study, we show that E6 siRNA-induced p53 activation is transient in HeLa cervical cancer cells despite continuous suppression of E6 mRNA; activation can be sustained if the endogenous p53 antagonists COP1, MDM2, Pirh2, and c-Jun-NH(2)-kinase are also targeted by siRNAs or by inhibiting the nuclear export of p53 with leptomycin B. The direct targeting of any one of these four cellular p53 antagonists had no effect on p53 activity when E6 was intact, but inhibited the fading off of E6 siRNA-induced p53 activation in nonstress conditions. The effect was additive when multiple cellular antagonists were concomitantly inhibited, indicating that all these proteins degrade p53 when E6 is inactivated. The antiproliferative effect induced by E6 silencing was enhanced when the endogenous p53 antagonists were additionally targeted. In conclusion, if human papillomavirus E6 is inhibited under nonstress conditions, the subsequent p53 activation is quickly reversed by the endogenous p53 degenerative machinery. The present results indicate that several cellular p53 antagonists must be inhibited for sustained p53 activity if E6 siRNA therapy is attempted and if no combined genotoxic therapy is applied.