Coordination of JNK1 and JNK2 is critical for GADD45alpha induction and its mediated cell apoptosis in arsenite responses

Alternative Splicing of MAPKs in the Regulation of Signaling Specificity

The mitogen-activated protein kinase (MAPK) cascades transmit signals from extracellular stimuli to a variety of distinct cellular processes. The MAPKKs in each cascade specifically phosphorylate and activate their cognate MAPKs, indicating that this step funnels various signals into a seemingly linear pathway. Still, the effects of these cascades vary significantly, depending on the identity of the extracellular signals, which gives rise to proper outcomes. Therefore, it is clear that the specificity of the signals transmitted through the cascades is tightly regulated in order to secure the desired cell fate. Indeed, many regulatory components or processes that extend the specificity of the cascades have been identified. Here, we focus on a less discussed mechanism, that is, the role of distinct components in each tier of the cascade in extending the signaling specificity. We cover the role of distinct genes, and the alternatively spliced isoforms of MAPKKs and MAPKs, in the signaling specificity. The alternatively spliced MEK1b and ERK1c, which form an independent signaling route, are used as the main example. Unlike MEK1/2 and ERK1/2, this route’s functions are limited, including mainly the regulation of mitotic Golgi fragmentation. The unique roles of the alternatively spliced isoforms indicate that these components play an essential role in determining the proper cell fate in response to distinct stimulations.

p85α Inactivates MMP-2 and Suppresses Bladder Cancer Invasion by Inhibiting MMP-14 Transcription and TIMP-2 Degradation

Recent studies show p85α up-regulates epidermal growth factor (EGF) receptor, thereby promoting malignant cell transformation and migration in normal mouse embryonic fibroblasts (MEFs). However, the potential role of p85α in human bladder cancer (BC) remains unknown. Here, we show that p85α is down-regulated in BC tumor tissues. Ectopic expression of p85α inhibited cell invasion, but not migration, whereas p85α knockdown promoted invasion in BC cells, revealing that p85α inhibits BC invasion. Overexpression of kinase-deficient p110 in T24 T(p85α) cells inhibited BC cell migration, but not invasion, suggesting that the inhibition of p85α on invasion is independent of PI3K activity. The effect of p85α on inhibiting BC invasion was mediated by the inactivation of MMP-2 concomitant with the up-regulation of TIMP-2 and down-regulation of MMP-14. Mechanistic studies revealed c-Jun inactivation was associated with p85α knockdown-induced MMP-14 expression, and down-regulated miR-190, leading to ATG7 mRNA degradation. This suppressed the autophagy-dependent removal of TIMP-2 in human BC cells. The present results identify a novel function of p85α and clarify the mechanisms underlying its inhibition of BC invasion, providing insight into the role of p85α in normal and cancer cells.

The RING domain in the anti-apoptotic protein XIAP stabilizes c-Myc protein and preserves anchorage-independent growth of bladder cancer cells

X-linked inhibitor of apoptosis protein (XIAP) suppresses apoptosis and plays key roles in the development, growth, migration, and invasion of cancer cells. Therefore, XIAP has recently attracted much attention as a potential antineoplastic therapeutic target, requiring elucidation of the molecular mechanisms underlying its biological activities. Here, using shRNA-mediated gene silencing, immunoblotting, quantitative RT-PCR, anchorage-independent growth assay, and invasive assay, we found that XIAP's RING domain, but not its BIR domain, is crucial for XIAP-mediated up-regulation of c-Myc protein expression in human bladder cancer (BC) cells. Mechanistically, we observed that the RING domain stabilizes c-Myc by inhibiting its phosphorylation at Thr-58 and that this inhibition is due to activated ERK1/2-mediated phosphorylation of glycogen synthase kinase-3β (GSK-3β) at Ser-9. Functional studies further revealed that c-Myc protein promotes anchorage-independent growth and invasion stimulated by the XIAP RING domain in human BC cells. Collectively, the findings in our study uncover that the RING domain of XIAP supports c-Myc protein stability, providing insight into the molecular mechanism and role of c-Myc overexpression in cancer progression. Our observations support the notion of targeting XIAP's RING domain and c-Myc in cancer therapy.

MEG3, as a Competing Endogenous RNA, Binds with miR-27a to Promote PHLPP2 Protein Translation and Impairs Bladder Cancer Invasion

Muscle-invasive and metastatic bladder cancer have an extremely poor 5-year survival rate of 5%. In comparison, all other bladder cancers (BCs) have a 5-year survival rate of 77%. This striking contrast indicates that one of the therapeutic kernels for bladder cancer is to elucidate the molecular mechanisms underlying its invasiveness and metastasis. In the current study, we demonstrated that maternally expressed gene 3 (MEG3) is significantly downregulated in human invasive bladder cancers in comparison to non-invasive bladder cancers, and that ectopic expression of MEG3 dramatically inhibits the invasiveness of human bladder cancer cells. Consistently, ectopic expression of MEG3 also attenuates metastatic ability of T24T cells, a cell line derived from T24 cells, in the lungs of nude mice. Our mechanistic studies reveal that MEG3, as a ceRNA, inhibits the invasiveness of human bladder cancer cells via negative regulation of c-Myc by competing with PHLPP2 mRNA for miR-27a. These findings not only provide a novel insight into understanding the mechanisms behind the MEG3 inhibition of bladder cancer cell invasion, but also reveal the potential for use of MEG3 as a tool for the prevention and therapy of invasive bladder cancer.

Cheliensisin A (Chel A) induces apoptosis in human bladder cancer cells by promoting PHLPP2 protein degradation

Cheliensisin A (Chel A), a styryl-lactone compound extracted from Goniothalamus cheliensis, is reported to have significant anti-cancer effects in various cancer cells. Here we demonstrated that Chel A treatment resulted in apoptosis and an inhibition of anchorage-independent growth in human bladder cancer T24, T24T and U5637 cells. Mechanistic studies showed that such effect is mediated by PH domain and Leucine rich repeat Protein Phosphatases (PHLPP2) protein. Chel A treatment led to PHLPP2 degradation and subsequently increased in c-Jun phosphorylation. Moreover PHLPP2 degradation could be attenuated by inhibition of autophagy, which was mediated by Beclin 1. Collectively, we discover that Chel A treatment induces Beclin-dependent autophagy, consequently mediates PHLPP2 degradation and JNK/C-Jun phosphorylation and activation, further in turn contributing to apoptosis in human bladder cancer cells. Current studies provide a significant insight into understanding of anticancer effect of Chel A in treatment of human bladder cancer.

XIAP BIR domain suppresses miR-200a expression and subsequently promotes EGFR protein translation and anchorage-independent growth of bladder cancer cell

BACKGROUND

The X-linked inhibitor of apoptosis protein (XIAP) is a well-known potent apoptosis suppressor and also participates in cancer cell biological behaviors, therefore attracting great attentions as a potential antineoplastic therapeutic target for past years. Anti-IAP therapy is reported to be closely related to epidermal growth factor receptor (EGFR) expression level. However, whether and how XIAP modulates EGFR expression remains largely unknown.

METHODS

Human XIAP was knockdown with short-hairpin RNA in two different bladder cancer cell lines, T24T and UMUC3. Two XIAP mutants, XIAP ∆BIR (deletion of N-terminal three BIR domains) and XIAP ∆RING (deletion of C-terminal RING domain and keeping the function of BIR domains), were generated to determine which domain is involved in regulating EGFR.

RESULTS

We found here that lacking of XIAP expression resulted in a remarkable suppression of EGFR expression, consequently leading to the deficiency of anchorage-independent cell growth. Further study demonstrated that BIR domain of XIAP was crucial for regulating the EGFR translation by suppressing the transcription and expression of miR-200a. Mechanistic studies indicated that BIR domain activated the protein phosphatase 2 (PP2A) activity by decreasing the phosphorylation of PP2A at Tyr307 in its catalytic subunit, PP2A-C. Such activated PP2A prevented the deviant phosphorylation and activation of MAPK kinases/MAPKs, their downstream effector c-Jun, and in turn inhibiting transcription of c-Jun-regulated the miR-200a.

CONCLUSIONS

Our study uncovered a novel function of BIR domain of XIAP in regulating the EGFR translation, providing significant insight into the understanding of the XIAP overexpression in the cancer development and progression, further offering a new theoretical support for using XIAP BIR domain and EGFR as targets for cancer therapy.

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.

SESN2/sestrin 2 induction-mediated autophagy and inhibitory effect of isorhapontigenin (ISO) on human bladder cancers

Isorhapontigenin (ISO) is a new derivative of stilbene isolated from the Chinese herb Gnetum cleistostachyum. Our recent studies have revealed that ISO treatment at doses ranging from 20 to 80 μM triggers apoptosis in multiple human cancer cell lines. In the present study, we evaluated the potential effect of ISO on autophagy induction. We found that ISO treatment at sublethal doses induced autophagy effectively in human bladder cancer cells, which contributed to the inhibition of anchorage-independent growth of cancer cells. In addition, our studies revealed that ISO-mediated autophagy induction occurred in a SESN2 (sestrin 2)-dependent and BECN1 (Beclin 1, autophagy related)-independent manner. Furthermore, we identified that ISO treatment induced SESN2 expression via a MAPK8/JNK1 (mitogen-activated protein kinase 8)/JUN-dependent mechanism, in which ISO triggered MAPK8-dependent JUN activation and facilitated the binding of JUN to a consensus AP-1 binding site in the SESN2 promoter region, thereby led to a significant transcriptional induction of SESN2. Importantly, we found that SESN2 expression was dramatically downregulated or even lost in human bladder cancer tissues as compared to their paired adjacent normal tissues. Collectively, our results demonstrate that ISO treatment induces autophagy and inhibits bladder cancer growth through MAPK8-JUN-dependent transcriptional induction of SESN2, which provides a novel mechanistic insight into understanding the inhibitory effect of ISO on bladder cancers and suggests that ISO might act as a promising preventive and/or therapeutic drug against human bladder cancer.

A novel post-translational modification of nucleolin, SUMOylation at Lys-294, mediates arsenite-induced cell death by regulating gadd45α mRNA stability

Nucleolin is a ubiquitously expressed protein and participates in many important biological processes, such as cell cycle regulation and ribosomal biogenesis. The activity of nucleolin is regulated by intracellular localization and post-translational modifications, including phosphorylation, methylation, and ADP-ribosylation. Small ubiquitin-like modifier (SUMO) is a category of recently verified forms of post-translational modifications and exerts various effects on the target proteins. In the studies reported here, we discovered SUMOylational modification of human nucleolin protein at Lys-294, which facilitated the mRNA binding property of nucleolin by maintaining its nuclear localization. In response to arsenic exposure, nucleolin-SUMO was induced and promoted its binding with gadd45α mRNA, which increased gadd45α mRNA stability and protein expression, subsequently causing GADD45α-mediated cell death. On the other hand, ectopic expression of Mn-SOD attenuated the arsenite-generated superoxide radical level, abrogated nucleolin-SUMO, and in turn inhibited arsenite-induced apoptosis by reducing GADD45α expression. Collectively, our results for the first time demonstrate that nucleolin-SUMO at K294R plays a critical role in its nucleus sequestration and gadd45α mRNA binding activity. This novel biological function of nucleolin is distinct from its conventional role as a proto-oncogene. Therefore, our findings here not only reveal a new modification of nucleolin protein and its novel functional paradigm in mRNA metabolism but also expand our understanding of the dichotomous roles of nucleolin in terms of cancer development, which are dependent on multiple intracellular conditions and consequently the appropriate regulations of its modifications, including SUMOylation.

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.

The Chinese herb isolate yuanhuacine (YHL-14) induces G2/M arrest in human cancer cells by up-regulating p21 protein expression through an p53 protein-independent cascade

Yuanhuacine (YHL-14), the major component of daphnane diterpene ester isolated from the flower buds of Daphne genkwa, has been reported to have activity against cell proliferation in various cancer cell lines. Nevertheless, the potential mechanism has not been explored yet. Here we demonstrate that YHL-14 inhibits bladder and colon cancer cell growth through up-regulation of p21 expression in an Sp1-dependent manner. We found that YHL-14 treatment resulted in up-regulation of p21 expression and a significant G2/M phase arrest in T24T and HCT116 cells without affecting p53 protein expression and activation. Further studies indicate that p21 induction by YHL-14 occurs at the transcriptional level via up-regulation of Sp1 protein expression. Moreover, our results show that p38 is essential for YHL-14-mediated Sp1 protein stabilization, G2/M growth arrest induction, and anchorage-independent growth inhibition of cancer cells. Taken together, our studies demonstrate a novel mechanism of YHL-14 against cancer cell growth in bladder and colon cancer cell lines, which provides valuable information for the design and synthesis of other new conformation-constrained derivatives on the basis of the structure of YHL-14 for cancer therapy.

SUMOylation of RhoGDIα is required for its repression of cyclin D1 expression and anchorage-independent growth of cancer cells

Selective activation of Rho GTPase cascade requires the release of Rho from RhoGDI (GDP-dissociation inhibitors) complexes. Our previous studies identified RhoGDIα SUMOylation at Lys-138 and its function in the regulation of cancer cell invasion. In the current study, we demonstrate that RhoGDIα SUMOylation has a crucial role in the suppression of cancer cell anchorage-independent growth as well as the molecular mechanisms underlying this suppression. We found that ectopic expression of RhoGDIα resulted in marked inhibition of an anchorage-independent growth with induction of G0/G1 cell cycle arrest, while point mutation of RhoGDIα SUMOylation at residue Lys-138 (K138R) abrogated this growth suppression and G0/G1 cell cycle arrest in cancer cells. Further studies showed that SUMOylation at Lys-138 was critical for RhoGDIα down-regulation of cyclin D1 protein expression and that MEK1/2-Erk was a specific downstream target of SUMOylated RhoGDIα for its inhibition of C-Jun/AP-1 cascade, cyclin d1 transcription, and cell cycle progression. These results strongly demonstrate that SUMOylated RhoGDIα suppressed C-Jun/AP-1-dependent transactivation specifically via targeting MEK1/2-Erk, subsequently leading to the down-regulation of cyclin D1 expression and anti-cancer activity. Our results provide new mechanistic insights into the understanding of essential role of SUMOylation at Lys-138 in RhoGDIα's biological function.

X-linked inhibitor of apoptosis protein (XIAP) regulation of cyclin D1 protein expression and cancer cell anchorage-independent growth via its E3 ligase-mediated protein phosphatase 2A/c-Jun axis

The X-linked inhibitor of apoptosis protein (XIAP) is a well known potent inhibitor of apoptosis; however, it is also involved in other cancer cell biological behavior. In the current study, we discovered that XIAP and its E3 ligase played a crucial role in regulation of cyclin D1 expression in cancer cells. We found that deficiency of XIAP expression resulted in a marked reduction in cyclin D1 expression. Consistently, cell cycle transition and anchorage-independent cell growth were also attenuated in XIAP-deficient cancer cells compared with those of the parental wild-type cells. Subsequent studies demonstrated that E3 ligase activity within the RING domain of XIAP is crucial for its ability to regulate cyclin D1 transcription, cell cycle transition, and anchorage-independent cell growth by up-regulating transactivation of c-Jun/AP-1. Moreover, we found that E3 ligase within RING domain was required for XIAP inhibition of phosphatase PP2A activity by up-regulation of PP2A phosphorylation at Tyr-307 in its catalytic subunit. Such PP2A phosphorylation and inactivation resulted in phosphorylation and activation of its downstream target c-Jun in turn leading to cyclin D1 expression. Collectively, our studies uncovered a novel function of E3 ligase activity of XIAP in the up-regulation of cyclin D1 expression, providing significant insight into the understanding of the biomedical significance of overexpressed XIAP in cancer development, further offering a new molecular basis for utilizing XIAP E3 ligase as a cancer therapeutic target.

p27 suppresses cyclooxygenase-2 expression by inhibiting p38β and p38δ-mediated CREB phosphorylation upon arsenite exposure

p27 is a cyclin-dependent kinase (CDK) inhibitor that suppresses a cell's transition from G0 to S phase, therefore acting as a tumor suppressor. Our most recent studies demonstrate that upon arsenite exposure, p27 suppresses Hsp27 and Hsp70 expressions through the JNK2/c-Jun- and HSF-1-dependent pathways, suggesting a novel molecular mechanism underlying the tumor suppressive function of p27 in a CDK-independent manner. We found that p27-deficiency (p27-/-) resulted in the elevation of cyclooxygenase-2 (COX-2) expression at transcriptional level, whereas the introduction of p27 brought back COX-2 expression to a level similar to that of p27+/+ cells, suggesting that p27 exhibits an inhibitory effect on COX-2 expression. Further studies identified that p27 inhibition of COX-2 expression was specifically due to phosphorylation of transcription factor cAMP response element binding (CREB) phosphorylation mediated by p38β and p38δ. These results demonstrate a novel mechanism underlying tumor suppression effect of p27 and will contribute to the understanding of the overall mechanism of p27 tumor suppression in a CDK-independent manner.

GADD45α induction by nickel negatively regulates JNKs/p38 activation via promoting PP2Cα expression

Growth arrest and DNA damage (GADD) 45α is a member of GADD inducible gene family, and is inducible in cell response to oxidative stress. GADD45α upregulation induces MKK4/JNK activation in some published experimental systems. However, we found here that the depletion of GADD45α (GADD45α−/−) in mouse embryonic fibroblasts (MEFs) resulted in an increase in the phosphorylation of MKK4/7, MKK3/6 and consequently specific up-regulated the activation of JNK/p38 and their downstream transcription factors, such as c-Jun and ATF2, in comparison to those in GADD45α+/+ MEFs cell following nickel exposure. This up-regulation of MKK-JNK/p38 pathway in GADD45α−/− cell could be rescued by the reconstitutional expression of HA-GADD45α in GADD45α−/− MEFs, GADD45α−/−(HA-GADD45α). Subsequent studies indicated that GADD45α deletion repressed expression of PP2Cα, the phosphotase of MKK3/6 and MKK4/7, whereas ectopic expression of HA-PP2Cα in GADD45α−/− cells attenuated activation of MKK3/6-p38 and MKK4/7-JNK pathways. Collectively, our results demonstrate a novel function and mechanism responsible for GADD45α regulation of MKK/MAPK pathway, further provides insight into understanding the big picture of GADD45α in the regulation of cellular responses to oxidative stress and environmental carcinogens.

c-Jun N-terminal kinase is required for thermotherapy-induced apoptosis in human gastric cancer cells

AIM: To investigate the role of c-Jun N-terminal kinase (JNK) in thermotherapy-induced apoptosis in human gastric cancer SGC-7901 cells.

METHODS: Human gastric cancer SGC-7901 cells were cultured in vitro. Following thermotherapy at 43 °C for 0, 0.5, 1, 2 or 3 h, the cells were cultured for a further 24 h with or without the JNK specific inhibitor, SP600125 for 2 h. Apoptosis was evaluated by immunohistochemistry [terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)] and flow cytometry (Annexin vs propidium iodide). Cell proliferation was determined by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. The production of p-JNK, Bcl-2, Bax and caspase-3 proteins was evaluated by Western blotting. The expression of JNK at mRNA level was determined by reverse transcription polymerase chain reaction.

RESULTS: The proliferation of gastric carcinoma SGC-7901 cells was significantly inhibited following thermotherapy, and was 32.7%, 30.6%, 43.8% and 52.9% at 0.5, 1, 2 and 3 h post-thermotherapy, respectively. Flow cytometry analysis revealed an increased population of SGC-790l cells in G0/G1 phase, but a reduced population in S phase following thermotherapy for 1 or 2 h, compared to untreated cells (P < 0.05). The increased number of SGC-790l cells in G0/G1 phase was consistent with induced apoptosis (flow cytometry) following thermotherapy for 0.5, 1, 2 or 3 h, compared to the untreated group (46.5% ± 0.23%, 39.9% ± 0.53%, 56.6% ± 0.35% and 50.4% ± 0.29% vs 7.3% ± 0.10%, P < 0.01), respectively. This was supported by the TUNEL assay (48.2% ± 0.4%, 40.1% ± 0.2%, 61.2% ± 0.29% and 52.0% ± 0.42% vs 12.2% ± 0.22%, P < 0.01) respectively. More importantly, the expression of p-JNK protein and JNK mRNA levels were significantly higher at 0.5 h than at 0 h post-treatment (P < 0.01), and peaked at 2 h. A similar pattern was detected for Bax and caspase-3 proteins. Bcl-2 increased at 0.5 h, peaked at 1 h, and then decreased. Furthermore, the JNK specific inhibitor, SP600125, suppressed p-JNK, Bax and caspase-3 at the protein level in SGC790l cells following thermotherapy, compared to mock-inhibitor treatment, which was in line with the decreased rate of apoptosis. The expression of Bcl-2 was consistent with thermotherapy alone.

CONCLUSION: Thermotherapy induced apoptosis in gastric cancer cells by promoting p-JNK at the mRNA and protein levels, and up-regulated the expression of Bax and caspase-3 proteins. Bcl-2 may play a protective role during thermotherapy. Activation of JNK via the Bax-caspase-3 pathway may be important in thermotherapy-induced apoptosis in gastric cancer cells.

APRIL binding to BCMA activates a JNK2-FOXO3-GADD45 pathway and induces a G2/M cell growth arrest in liver cells

The TNF superfamily ligands APRIL and BAFF bind with different affinity to two receptors, BCMA and TACI, and induce cell survival and/or proliferation, whereas BAFF also binds specifically to BAFFR. These molecules were considered specific for the immune system. Recently, however, they were also found in epithelial and mesenchymal noncancerous and cancerous tissues and cell lines. In this article, we report that hepatocellular carcinoma (HCC) cell lines HepG2 and Hep3B and HCC specimens express APRIL and BAFF and their receptors BCMA and BAFFR, but not TACI; APRIL/BCMA is enhanced in HCC, compared with normal liver tissue. In contrast to previous reports, APRIL binding to BCMA decreases cell proliferation by inducing G(2)/M cell cycle arrest, whereas BAFF has no effect on cell growth. HCC cells therefore represent a rare system in which these two ligands (APRIL and BAFF) exert a differential effect and may serve as a model for specific APRIL/BCMA actions. We show that the effect of APRIL is mediated via BCMA, which does not activate the classical NF-κB pathway, whereas it induces a novel signaling pathway, which involves JNK2 phosphorylation, FOXO3A activation, and GADD45 transcription. In addition, JNK2 mediates the phosphorylation of Akt, which is activated but does not participate in the antiproliferative effect of APRIL. Furthermore, transcriptome analysis revealed that APRIL modifies genes specifically related to cell cycle modulation, including MCM2/4/5/6, CDC6, PCNA, and POLE2. Our data, therefore, identify a novel APRIL/BCMA signaling pathway in HCC and suggest that APRIL could have a pleiotropic role in tumor biology.

The requirement of c-Jun N-terminal kinase 2 in regulation of hypoxia-inducing factor-1α mRNA stability

The mRNA of hif-1α is considered as being constitutively and ubiquitously expressed, regardless of the level of oxygen tension. However many recent reports have showed that hif-1α mRNA could be regulated by natural antisense transcripts, potential microRNAs, and low O(2). In this study, it was found that a deficiency of JNK2 expression reduced HIF-1α protein induction in response to nickel treatment resulting from the impaired expression of hif-1α mRNA. Both the promoter luciferase assay and mRNA degradation assay clearly showed that depletion of JNK2 affected stability of hif-1α mRNA, rather than regulated its transcription. In addition, nucleolin, a classic histone chaperone, was demonstrated to physically bind to hif-1α mRNA and maintain its stability. Further investigation indicated that JNK2 regulated nucleolin expression and might in turn stabilize hif-1α mRNA. Collectively, we provided one more piece of evidence for the oncogenic role of JNK2 and nucleolin in regulating the cancer microenvironments by controlling HIF-1α expression.

Targeting JNK for therapeutic depletion of stem-like glioblastoma cells

Control of the stem-like tumour cell population is considered key to realizing the long-term survival of patients with glioblastoma, one of the most devastating human malignancies. To date, possible therapeutic targets and targeting methods have been described, but none has yet proven to target stem-like glioblastoma cells in the brain to the extent necessary to provide a survival benefit. Here we show that targeting JNK in vivo, the activity of which is required for the maintenance of stem-like glioblastoma cells, via transient, systemic administration of a small-molecule JNK inhibitor depletes the self-renewing and tumour-initiating populations within established tumours, inhibits tumour formation by stem-like glioblastoma cells in the brain, and provide substantial survival benefit without evidence of adverse events. Our findings not only implicate JNK in the maintenance of stem-like glioblastoma cells but also demonstrate that JNK is a viable, clinically relevant therapeutic target in the control of stem-like glioblastoma cells.

Sodium fluoride induces apoptosis in mouse embryonic stem cells through ROS-dependent and caspase- and JNK-mediated pathways

Sodium fluoride (NaF) is used as a source of fluoride ions in diverse applications. Fluoride salt is an effective prophylactic for dental caries and is an essential element required for bone health. However, fluoride is known to cause cytotoxicity in a concentration-dependent manner. Further, no information is available on the effects of NaF on mouse embryonic stem cells (mESCs). We investigated the mode of cell death induced by NaF and the mechanisms involved. NaF treatment greater than 1mM reduced viability and DNA synthesis in mESCs and induced cell cycle arrest in the G(2)/M phase. The addition of NaF induced cell death mainly by apoptosis rather than necrosis. Catalase (CAT) treatment significantly inhibited the NaF-mediated cell death and also suppressed the NaF-mediated increase in phospho-c-Jun N-terminal kinase (p-JNK) levels. Pre-treatment with SP600125 or z-VAD-fmk significantly attenuated the NaF-mediated reduction in cell viability. In contrast, intracellular free calcium chelator, but not of sodium or calcium ion channel blockers, facilitated NaF-induced toxicity in the cells. A JNK specific inhibitor (SP600125) prevented the NaF-induced increase in growth arrest and the DNA damage-inducible protein 45α. Further, NaF-mediated loss of mitochondrial membrane potential was apparently inhibited by pifithrin-α or CAT inhibitor. These findings suggest that NaF affects viability of mESCs in a concentration-dependent manner, where more than 1mM NaF causes apoptosis through hydroxyl radical-dependent and caspase- and JNK-mediated pathways.

GADD45α and annexin A1 are involved in the apoptosis of HL-60 induced by resveratrol

Resveratrol (3,4',5-trihydroxy-trans-stilbene), one of secondary metabolites of low molecular weight present in plant, has various important biological effects. It can induce apoptosis in human leukemia cell types in vitro, although the mechanism is not fully understood. In the present study, we demonstrated reduced viability and DNA synthesis, as well as increased proportion of the subdiploid cell population, in HL-60 cells as determined by cell cycle analysis with resveratrol. Resveratrol treatment resulted in a gradual time-dependent decrease in the expression of anti-apoptotic Bcl-2 and increase in that of Bax, annexin A1, growth arrest- and DNA damage-induced gene 45α (GADD45α), and cleaved caspase-3. In addition, resveratrol markedly increased caspase-3 activity in cells. Our results suggest that resveratrol could inhibit the proliferation and induce apoptosis of HL-60 cells through a GADD45α and annexin A1/caspase-3 pathway.

GADD45alpha mediates arsenite-induced cell apoptotic effect in human hepatoma cells via JNKs/AP-1-dependent pathway

Arsenite (As(III)), an effective chemotherapeutic agent for the acute promyelocytic leukemia (APL) and multiple myeloma (MM), might be also a promise for the therapy of other cancers, including the solid tumors. However, the molecular bases of arsenite-induced cytotoxicity in the tumor cells have not been fully defined. In this study, we have disclosed that arsenite effectively induces the apoptotic response in the HepG2 human hepatoma cells by triggering GADD45alpha induction and the subsequent activation of JNKs/AP-1 cell death pathway. However, signaling events relating to GADD45alpha/JNKs/AP-1 pathway activation have not been observed in HL7702 human diploid hepatic cells under the same arsenite exposure condition. Our results thus have illustrated the selective pro-apoptotic role of arsenite in the hepatoma cells by activating GADD45alpha-dependent cell death pathway whereas with little effect on the normal hepatic cells. The approaches to up-regulate GADD45alpha levels might be helpful in improving the chemotherapeutic action of arsenite on certain solid tumors including hepatoma.

p27 suppresses arsenite-induced Hsp27/Hsp70 expression through inhibiting JNK2/c-Jun- and HSF-1-dependent pathways

p27 is an atypical tumor suppressor that can regulate the activity of cyclin-dependent kinases and G(0)-to-S phase transitions. More recent studies reveal that p27 may also exhibit its tumor-suppressive function through regulating many other essential cellular events. However, the molecular mechanisms underlying these anticancer effects of p27 are largely unknown. In this study, we found that depletion of p27 expression by either gene knock-out or knockdown approaches resulted in up-regulation of both Hsp27 and Hsp70 expression at mRNA- and promoter-derived transcription as well as protein levels upon arsenite exposure, indicating that p27 provides a negative signal for regulating the expression of Hsp27 and Hsp70. Consistently, arsenite-induced activation of JNK2/c-Jun and HSF-1 pathways was also markedly elevated in p27 knock-out (p27(-/-)) and knockdown (p27 shRNA) cells. Moreover, interference with the expression or function of JNK2, c-Jun, and HSF-1, but not JNK1, led to dramatic inhibition of arsenite-induced Hsp27 and Hsp70 expression. Collectively, our results demonstrate that p27 suppresses Hsp27 and Hsp70 expression at the transcriptional level specifically through JNK2/c-Jun- and HSF-1-dependent pathways upon arsenite exposure, which provides additional important molecular mechanisms for the tumor-suppressive function of p27.

JNK1 mediates degradation HIF-1alpha by a VHL-independent mechanism that involves the chaperones Hsp90/Hsp70

Hypoxia-inducible factor-1alpha (HIF-1alpha) is a master transcription factor that is critical for the regulation of a variety of cellular functions. HIF-1alpha is rapidly degraded under normoxic conditions by ubiquitin-mediated proteasome pathway controlled by the tumor suppressor von Hippel Lindau (VHL). Several recent studies reveal that heat-shock proteins (Hsp) can regulate HIF-1alpha protein degradation by a VHL-independent pathway. Here, we demonstrate that the stress kinase c-Jun NH(2)-terminal kinase 1 (JNK1) is required for Hsp-dependent regulation of HIF-1alpha. Stabilization of HIF-1alpha was impaired in JNK1-/- cells but could be rescued by JNK1 reconstitution under hypoxic conditions. These effects could be phenocopied in other cell settings by JNK1 silencing. Accordingly, HIF-1 transcriptional activity and target gene expression were dramatically reduced in JNK1-/- cells. Further, decreased levels of endogenous Hsp90/Hsp70 proteins in JNK1-/- cells affected the protective roles of these chaperones in stabilizing newly synthesized HIF-1alpha, whereas enforced expression of Hsp90/Hsp70 in JNK1-/- cells increased HIF-1alpha stability relative to parental control cells. Furthering this connection, we also found that defective expression of the Hsp90 acetyltransferase HDAC6 in JNK1-/- cells was associated with reduced Hsp90 chaperone activity. Taken together, our studies define a novel function for JNK1 in regulating HIF-1alpha turnover by a VHL-independent mechanism.

Cadmium induces intracellular Ca2+- and H2O2-dependent apoptosis through JNK- and p53-mediated pathways in skin epidermal cell line

Cadmium is a toxic heavy metal and has been widely used in industry. The skin is an important target for this metal. The mechanisms by which cadmium leads to damage to the skin are unclear at present. The aims of this study were to examine whether cadmium induces apoptosis in mouse skin epidermal cell line, JB6 Cl41 cells, and to investigate the cellular mechanisms by which cadmium causes cytotoxicity in the cells. The present study showed that cadmium induced cell death by apoptosis in a dose-dependent manner, as proven by the appearance of cell shrinkage, the increase of Annexin V positively stained cells, and the formation of nuclear DNA ladders. Cadmium-induced apoptosis involved a mitochondria-mediated mechanism but not caspase-dependent pathway in that the critical apoptotic events induced by cadmium, such as the decrease of Bcl-2/Bcl-xL, the increase of GADD45alpha, and the nuclear translocation of apoptosis inducing factor, were not affected by the inhibition of executive caspases. In contrast, blockage of p53 and JNK by pharmacological inhibitors or small interference RNA transfection suppressed the cadmium-induced apoptosis with the concomitant inhibition of antiapoptotic Bcl-2 family proteins and GADD45alpha, respectively. Furthermore, the activation of p53 and JNK and their downstream proteins in cadmium-exposed cells were inhibited by individual treatment with catalase and Bapta-acetoxymethyl. These results suggest that cadmium induces apoptosis via the activation of JNK- and p53-mediated signaling, where calcium ion and hydrogen peroxide act as the pivotal mediators of the apoptotic signaling.

The biological functions of NF-kappaB1 (p50) and its potential as an anti-cancer target

Nuclear factor-kappaB (NF-kappaB) is a key transcriptional factor family that consists of five members in mammalian cells, including NF-kappaB1 (p50), NF-kappaB2 (p52), RelA (p65), RelB and c-Rel. NF-kappaB is implicated in multiple physiological and pathological processes, including cell proliferation and differentiation, inflammatory and immune response, cell survival and apoptosis, cellular stress reactions and tumorigenesis. Recent studies by our group and others have highlighted the novel functions of the p50 protein. In this review, we will focus on the regulation and functions of NF-kappaB p50.

Effect of burn injury on apoptosis and expression of apoptosis-related genes/proteins in skeletal muscles of rats

The purpose of this study was to investigate the occurrence and possible mechanisms of apoptosis in skeletal muscles after burn injury. After a 40% body surface area burn to rats, TA muscles were examined for apoptosis at varying times by TEM, TUNEL and cell death ELISA assay. Thermal injury was found to induce apoptosis in skeletal muscle on the first day and maximal apoptosis appeared 4 days post-injury. Apoptotic ligands in serum assessed by ELISA revealed rapidly increase of TNF-alpha and subsequent increase of sFasL to sFas ratio after burn injury. It implied TNF-alpha induced apoptosis in early stage and FasL induced apoptosis in later stage after burn injury. Apoptosis-related genes/proteins in skeletal muscles examined by real-time PCR array and Western blotting showed pro-apoptotic genes/proteins, including Tnfrsf1a, Tnfrsf1b and Tnfsf6 in TNF ligand and receptor family, Bax and Bid in Bcl-2 family, caspase-3 and caspase-6 in caspase family, Dapk1, FADD and Cidea in death and CIDE domain family, Apaf-1 in CARD family, and Gadd45a were up-regulated, while anti-apoptotic gene Bnip1 was down-regulated compared with that of time-matched controls. In addition, increment of caspase-3, caspase-8 and caspase-9 activity provided further evidence for their role in apoptosis in skeletal muscle. Significant increase in expression in pro-apoptotic genes/proteins and activity of caspases suggested that death receptor-mediated signaling pathways and other apoptotic related pathways participated in apoptosis in skeletal muscle after burn injury. However, it was found that some anti-apoptotic genes such as Bcl2l1, Mcl-1, Nol-3, Il-10 and Prok2 were also up-regulated, which might imply the co-existence of protective response of the body after burns. In conclusion, the data suggest that apoptosis and pro-apoptotic signaling are enhanced in muscles of burned rats. To further elucidate the underlying apoptotic mechanisms mediating the atrophic response is important in establishing potential therapeutic interventions that could prevent and/or reduce skeletal muscle wasting and preserve its physiological function.

Decitabine-induced demethylation of 5' CpG island in GADD45A leads to apoptosis in osteosarcoma cells

GADD45 genes are epigenetically inactivated in various types of cancer and tumor cell lines. To date, defects of the GADD45 gene family have not been implicated in osteosarcoma (OS) oncogenesis, and the role of this pathway in regulating apoptosis in this tumor is unknown. The therapeutic potential of Gadd45 in OS emerged when our previous studies showed that GADD45A was reexpressed by treatment with the demethylation drug decitabine. In this study, we analyze the OS cell lines MG63 and U2OS and show that on treatment with decitabine, a significant loss of DNA methylation of GADD45A was associated with elevated expression and induction of apoptosis. In vivo affects of decitabine treatment in mice showed that untreated control xenografts exhibited low nuclear staining for Gadd45a protein, whereas the nuclei from xenografts in decitabine-treated mice exhibited increased amounts of protein and elevated apoptosis. To show the specificity of this gene for decitabine-induced apoptosis in OS, GADD45A mRNAs were disrupted using short interference RNA, and the ability of the drug to induce apoptosis was reduced. Understanding the role of demethylation of GADD45A in reexpression of this pathway and restoration of apoptotic control is important for understanding OS oncogenesis and for more targeted therapeutic approaches.

Relationship between differentially expressed genes and epigenetic modification during the early stage of esophageal carcinoma induced by nitrosamine

AIM: To detect the differentially expressed genes in the process of esophageal carcinoma induced by nitrosamine, and analyze the property of gene expression at different stages, especially the relationship between differentially expressed genes and DNA methylation.

METHODS: One hundred and ten mice were randomly divided into group A (n = 40) and B (n = 70). The mice in group A were fed with distilled water, while those in group B were fed with carcinoma-inducing mixture containing 20 g/L sodium nitrite and 200 g/L N, N-dimethyl benzyl amine. At the 4, 8, and 20 wk of induction stages, the total RNA from esophageal tissues was isolated and reversely transcripted, and then hybridization with gene-chip was performed. The differentially expressed genes of the two groups were analyzed.

RESULTS: During the process of induction, the number of up-regulated oncogenes increased in a step-by-step fashion in group B as compared with that in group A, and the phase-specificity of oncogenes was observed. But most antioncogenes did not change remarkably. Most genes of DNA methylation did not change at 4 wk, but were up-regulated at 8 and 20 wk. The DNA demethylation gene Mdb2b was up-regulated from the 8 wk, but Gadd45a was up-regulated from the 4 wk and maintained a high level at 8 and 20 wk. Genes of histone acetylation, which were changed obviously, were not found.

CONCLUSION: During the process of nitrosamine-induced esophageal carcinoma, up-regulation of numerous genes may associate with the demethylation of genomic DNA at the early stage. Gadd45a may be involved in the demethylation during the early weeks.

Sensitivity to sodium arsenite in human melanoma cells depends upon susceptibility to arsenite-induced mitotic arrest

Arsenic induces clinical remission in patients with acute promyelocytic leukemia and has potential for treatment of other cancers. The current study examines factors influencing sensitivity to arsenic using human malignant melanoma cell lines. A375 and SK-Mel-2 cells were sensitive to clinically achievable concentrations of arsenite, whereas SK-Mel-3 and SK-Mel-28 cells required supratherapeutic levels for toxicity. Inhibition of glutathione synthesis, glutathione S-transferase (GST) activity, and multidrug resistance protein (MRP) transporter function attenuated arsenite resistance, consistent with studies suggesting that arsenite is extruded from the cell as a glutathione conjugate by MRP-1. However, MRP-1 was not overexpressed in resistant lines and GST-pi was only slightly elevated. ICP-MS analysis indicated that arsenite-resistant SK-Mel-28 cells did not accumulate less arsenic than arsenite-sensitive A375 cells, suggesting that resistance was not attributable to reduced arsenic accumulation but rather to intrinsic properties of resistant cell lines. The mode of arsenite-induced cell death was apoptosis. Arsenite-induced apoptosis is associated with cell cycle alterations. Cell cycle analysis revealed arsenite-sensitive cells arrested in mitosis whereas arsenite-resistant cells did not, suggesting that induction of mitotic arrest occurs at lower intracellular arsenic concentrations. Higher intracellular arsenic levels induced cell cycle arrest in the S-phase and G(2)-phase in SK-Mel-3 and SK-Mel-28 cells, respectively. The lack of arsenite-induced mitotic arrest in resistant cell lines was associated with a weakened spindle checkpoint resulting from reduced expression of spindle checkpoint protein BUBR1. These data suggest that arsenite has potential for treatment of solid tumors but a functional spindle checkpoint is a prerequisite for a positive response to its clinical application.

MLH1- and ATM-dependent MAPK signaling is activated through c-Abl in response to the alkylator N-methyl-N'-nitro-N'-nitrosoguanidine

N-Methyl-N'-nitro-N'-nitrosoguanidine (MNNG) is a DNA-methylating agent, and deficiency in mismatch repair (MMR) results in lack of sensitivity to this genotoxin (termed alkylation tolerance). A number of DNA damage response pathways are activated in a MMR-dependent manner following MNNG, and several also require ATM kinase activity. Here we show that activation of the transcription factor c-Jun is dependent upon both the MMR component MLH1 and ATM, but not ATR, in response to MNNG. In addition to c-Jun, the upstream MAPKs JNK and MKK4 are also activated in a MLH1- and ATM-dependent manner. We document that c-Jun activation is dependent on the MAPK kinase kinase MEKK1. Additionally, the tyrosine kinase c-Abl is required to activate this signaling cascade and forms a complex with MEKK1 and MLH1. This study indicates that an arm of DNA damage-activated MAPK signaling is activated in an MLH1- and ATM-dependent manner in response to MNNG and perhaps suggests that dysregulation of this signaling is responsible, in part, for alkylation tolerance.