Cellular transformation and malignancy induced by ras require c-jun

The molecular mechanism underlying KRAS regulation on STK31 expression in pancreatic ductal adenocarcinoma

KRAS gene mutations are common in pancreatic ductal adenocarcinoma (PDAC), but targeting mutant KRAS is still challenging. Here, an endoribonuclease-prepared small interfering RNA (esiRNA) library was used to screen new kinases that play critical roles in PDAC driven by KRAS gene mutations, and serine/threonine kinase 31 (STK31) was identified and characterized as a potential therapeutic target for KRAS-mutant PDAC. Our results showed that STK31 was upregulated in KRAS-mutant PDAC patients with poor survival and highly expressed in PDAC cell lines with KRASG12D mutation. Inhibition of STK31 in KRAS-mutant cell lines significantly reduced PDAC cell growth in vitro and hindered tumor growth in vivo. Gain and loss of function experiments revealed that STK31 is a downstream target of KRAS in PDAC. A pharmacological inhibition assay showed MAPK/ERK signaling involved in STK31 regulation. The further mechanistic study validated that c-Jun, regulated by KRAS/MAPK signaling, directly modulates the transcription level of STK31 by binding to its promoter region. Through RNA sequencing, we found that the cell cycle regulators CCNB1 and CDC25C are downstream targets of STK31. Taken together, our results indicate that STK31, which is the downstream target of the KRAS/MAPK/ERK/c-Jun signaling pathway in KRAS-mutant PDAC, promotes PDAC cell growth by modulating the expression of the cell cycle regulators CCNB1 and CDC25C.

The role of c-Jun for beating cardiomycyte formation in prepared embryonic body

BACKGROUND

Morbidity and mortality associated with cardiovascular diseases, such as myocardial infarction, stem from the inability of terminally differentiated cardiomyocytes to regenerate, and thus repair the damaged myocardial tissue structure. The molecular biological mechanisms behind the lack of regenerative capacity for those cardiomyocytes remains to be fully elucidated. Recent studies have shown that c-Jun serves as a cell cycle regulator for somatic cell fates, playing a key role in multiple molecular pathways, including the inhibition of cellular reprogramming, promoting angiogenesis, and aggravation of cardiac hypertrophy, but its role in cardiac development is largely unknown. This study aims to delineate the role of c-Jun in promoting early-stage cardiac differentiation.

METHODS

The c-Jun gene in mouse embryonic stem cells (mESCs) was knocked out with CRISPR-Cas9, and the hanging drop method used to prepare the resulting embryoid bodies. Cardiac differentiation was evaluated up to 9 days after c-Jun knockout (ko) via immunofluorescence, flow cytometric, and qPCR analyses.

RESULTS

Compared to the wild-type control group, obvious beating was observed among the c-Jun-ko mESCs after 6 days, which was also associated with significant increases in myocardial marker expression. Additionally, markers associated with mesoderm and endoderm cell layer development, essential for further differentiation of ESCs into cardiomyocytes, were also up-regulated in the c-Jun-ko cell group.

CONCLUSIONS

Knocking out c-Jun directs ESCs toward a meso-endodermal cell lineage fate, in turn leading to generation of beating myocardial cells. Thus, c-Jun plays an important role in regulating early cardiac cell development.

The potential of activator protein 1 (AP-1) in cancer targeted therapy

Activator protein-1 (AP-1) is a transcription factor that consists of a diverse group of members including Jun, Fos, Maf, and ATF. AP-1 involves a number of processes such as proliferation, migration, and invasion in cells. Dysfunctional AP-1 activity is associated with cancer initiation, development, invasion, migration and drug resistance. Therefore, AP-1 is a potential target for cancer targeted therapy. Currently, some small molecule inhibitors targeting AP-1 have been developed and tested, showing some anticancer effects. However, AP-1 is complex and diverse in its structure and function, and different dimers may play different roles in different type of cancers. Therefore, more research is needed to reveal the specific mechanisms of AP-1 in cancer, and how to select appropriate inhibitors and treatment strategies. Ultimately, this review summarizes the potential of combination therapy for cancer.

[Phosphoproteomic analysis of human umbilical venous endothelial cells with DENV-2 infection]

OBJECTIVE

To analyze the differentially phosphorylated proteins in DENV-2-infected human umbilical venous endothelial cells (HUVECs) and explore the possible pathogenic mechanism of DENV-2 infection.

METHODS

The total proteins were extracted from DENV-2-infected HUVECs and blank control HUVEC using SDT lysis method. The phosphorylated proteins were qualitatively and quantitatively analyzed using tandem mass spectrometry (TMT). The identified differentially phosphorylated proteins were analyzed by bioinformatics analyses such as subcellular localization analysis, GO enrichment analysis, KEGG pathway analysis and protein-protein interaction (PPI) analysis. Western blotting was used to detect the expressions of phosphorylated Jun, map2k2 and AKT1 proteins in DENV-2-infected HUVECs.

RESULTS

A total of 2918 modified peptides on 1385 different proteins were detected, and among them 1346 were significantly upregulated (FC > 1.2, P < 0.05) and 1572 were significantly downregulated (FC < 0.83, P < 0.05). A total of 49 phosphorylated conserved motifs were obtained by amino acid conservative motif analysis. The most abundant differentially phosphorylated peptides in protein domain analysis included RNA recognition motif, protein kinase domain and PH domain. Subcellular localization analysis showed that the differentially modified peptides were mainly localized in the nucleus and cytoplasm. GO enrichment and KEGG pathway analysis showed that the differential peptides were mainly enriched in the regulation of stimulation response, biosynthesis of small molecules containing nuclear bases, and migration of phagosomes and leukocytes across the endothelium. PPI and KEGG joint analysis showed that the up-regulated and down-regulated differentially phosphorylated proteins were enriched in 15 pathways. In DENV-2-infected HUVECs, Western blotting detected differential expressions of phosphorylated proteins related with the autophagy pathway, namely JUN, MAP2K2 and AKT1, and among them p-JUN was significantly down-regulated and p-AKT1 and p-MAP2K2 were significantly upregulated (P < 0.01).

CONCLUSION

DENV-2 infected HUVECs show numerous differentially expressed proteins. The downregulation of p-JUN and upregulation of p-MAP2K2 and p-AKT1 suggest their potential roles in regulating autophagy, which is probably involved in the mechanism of DENV-2 infection.

JNK inhibitor IX restrains pancreatic cancer through p53 and p21

Novel treatment options for pancreatic cancer are desperately needed. De-regulated kinases can be regularly detected in pancreatic cancer. Multiple pathway inhibitors were developed to exploit these features, among them selective inhibitors of the c-Jun N-terminal kinase isoforms 1 and 2 (JNK1 and 2). We evaluated the effectiveness of four different JNK inhibitors on pancreatic cancer cell lines. Cell mobility and migration were evaluated in scratch assay and Boyden chamber assay. Mechanism of cell death was analyzed via apoptosis assays in FACS and immunoblotting as well as cell cycle analysis via FACS, and qPCR. JNK2 knockout cells were generated using siRNA transfection. Among the inhibitors, JNK inhibitor IX (JNK-in-IX), designed as specific inhibitor against JNK2 was proven highly effective in inhibiting cell growth, mobility and migration. We were able to show that JNK-in-IX caused DNA damage resulting in G2 arrest mediated through p53 and p21. Interestingly, JNK-in-IX acted independently of its primary target JNK2. In summary, JNK-in-IX was shown highly effective in pancreatic cancer. This study underlines the need for modeling systems in testing therapeutic options as JNK2 was previously not indicated as a potential target.

Stress-activated kinases as therapeutic targets in pancreatic cancer

Pancreatic cancer is a dismal disease with high incidence and poor survival rates. With the aim to improve overall survival of pancreatic cancer patients, new therapeutic approaches are urgently needed. Protein kinases are key regulatory players in basically all stages of development, maintaining physiologic functions but also being involved in pathogenic processes. c-Jun N-terminal kinases (JNK) and p38 kinases, representatives of the mitogen-activated protein kinases, as well as the casein kinase 1 (CK1) family of protein kinases are important mediators of adequate response to cellular stress following inflammatory and metabolic stressors, DNA damage, and others. In their physiologic roles, they are responsible for the regulation of cell cycle progression, cell proliferation and differentiation, and apoptosis. Dysregulation of the underlying pathways consequently has been identified in various cancer types, including pancreatic cancer. Pharmacological targeting of those pathways has been the field of interest for several years. While success in earlier studies was limited due to lacking specificity and off-target effects, more recent improvements in small molecule inhibitor design against stress-activated protein kinases and their use in combination therapies have shown promising in vitro results. Consequently, targeting of JNK, p38, and CK1 protein kinase family members may actually be of particular interest in the field of precision medicine in patients with highly deregulated kinase pathways related to these kinases. However, further studies are warranted, especially involving in vivo investigation and clinical trials, in order to advance inhibition of stress-activated kinases to the field of translational medicine.

JunD, not c-Jun, is the AP-1 transcription factor required for Ras-induced lung cancer

The AP-1 transcription factor c-Jun is required for Ras-driven tumorigenesis in many tissues and is considered as a classical proto-oncogene. To determine the requirement for c-Jun in a mouse model of K-RasG12D-induced lung adenocarcinoma, we inducibly deleted c-Jun in the adult lung. Surprisingly, we found that inactivation of c-Jun, or mutation of its JNK phosphorylation sites, actually increased lung tumor burden. Mechanistically, we found that protein levels of the Jun family member JunD were increased in the absence of c-Jun. In c-Jun-deficient cells, JunD phosphorylation was increased, and expression of a dominant-active JNKK2-JNK1 transgene further increased lung tumor formation. Strikingly, deletion of JunD completely abolished Ras-driven lung tumorigenesis. This work identifies JunD, not c-Jun, as the crucial substrate of JNK signaling and oncogene required for Ras-induced lung cancer.

WITHDRAWN: Knocking out c-Jun promotes cardiomyocyte differentiation from embryonic stem cells

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Multi-omics analysis revealed crucial genes and pathways associated with black carp antiviral innate immunity

Multi-omics strategy contributes as an indispensable and efficient approach for the investigation of the innate immunity in vertebrates. To explore the crucial genes and pathways involved in the antiviral innate immunity of black carp (Mylopharyngodon piceus), the comparative phosphoproteomics and transcriptomics of Mylopharyngodon piceus kidney (MPK) cells with/without GCRV infection were performed in this manuscript. In phosphoproteomics analysis, 2637 phosphosites corresponding to 1532 proteins were identified and quantified, in which 1372 proteins were identified as differentially expressed proteins (DEPs) with 683 upregulated and 689 downregulated in GCRV infected cells. Functional annotation, enrichment analysis and pathway analysis highlighted that a large number of DEPs were enriched in immune related pathways including TLR pathway and NLR pathway. In transcriptomics analysis, a total of 2936 genes were identified as differentially expressed genes (DEGs), in which 2290 and 646 genes were upregulated and downregulated respectively after GCRV infection. As expected, pathway analysis based on DEGs also showed that a large proportion of DEGs were enriched in immune related pathways including TLR and RLR pathway. A combined list of DEPs and DEGs that enriched in above pathways were imported in Cytoscape for network analysis, reconstruction and visualization. The integrative study suggested that several significant DEPs and DEGs, such as MAP3K7 (TAK1), JUN, MAP2K2, CASP8, IL8 and IRF7 might be functionally crucial in host antiviral innate immunity. Thus, this study contributes as an indispensable reference map for the further investigation of the innate immune system of black carp.

The splice 1 variant of HTLV-1 bZIP factor stabilizes c-Jun

HBZ is expressed by the complex retrovirus, Human T-cell Leukemia Virus type 1, and implicated in pathological effects associated with viral infection. From the nucleus, HBZ alters gene expression by interacting with a variety of transcriptional regulatory proteins, among which is c-Jun. Previously, one of the three HBZ variants, HBZ_US, was reported to decrease c-Jun expression by promoting its degradation. Here we show that another variant, HBZ_S1, produces the opposite effect. In the presence of HBZ_S1, c-Jun expression increases due to its stabilization. Our data suggest that this effect requires the ability of HBZ_S1 to interact with c-Jun. We provide evidence that HBZ_S1 inhibits the proteosomal degradation of c-Jun initiated by the Cop1-containing ubiquitin ligase complex. HBZ_S1 is the most abundant variant in HTLV-1-infected T-cells, and our data indicate that levels of c-Jun expression in infected cells are consistent with effects of HBZ_S1.

Irreversible JNK1-JUN inhibition by JNK-IN-8 sensitizes pancreatic cancer to 5-FU/FOLFOX chemotherapy

Over 55,000 people in the United States are diagnosed with pancreatic ductal adenocarcinoma (PDAC) yearly, and fewer than 20% of these patients survive a year beyond diagnosis. Chemotherapies are considered or used in nearly every PDAC case, but there is limited understanding of the complex signaling responses underlying resistance to these common treatments. Here, we take an unbiased approach to study protein kinase network changes following chemotherapies in patient-derived xenograft (PDX) models of PDAC to facilitate design of rational drug combinations. Proteomics profiling following chemotherapy regimens reveals that activation of JNK-JUN signaling occurs after 5-fluorouracil plus leucovorin (5-FU + LEU) and FOLFOX (5-FU + LEU plus oxaliplatin [OX]), but not after OX alone or gemcitabine. Cell and tumor growth assays with the irreversible inhibitor JNK-IN-8 and genetic manipulations demonstrate that JNK and JUN each contribute to chemoresistance and cancer cell survival after FOLFOX. Active JNK1 and JUN are specifically implicated in these effects, and synergy with JNK-IN-8 is linked to FOLFOX-mediated JUN activation, cell cycle dysregulation, and DNA damage response. This study highlights the potential for JNK-IN-8 as a biological tool and potential combination therapy with FOLFOX in PDAC and reinforces the need to tailor treatment to functional characteristics of individual tumors.

Structure of the RNA Specialized Translation Initiation Element that Recruits eIF3 to the 5'-UTR of c-Jun

Specialized translation initiation is a novel form of regulation of protein synthesis, whereby RNA structures within the 5'-UTR regulate translation rates of specific mRNAs. Similar to internal ribosome entry sites (IRESs), specialized translation initiation requires the recruitment of eukaryotic initiation factor 3 (eIF3), but also requires cap recognition by eIF3d, a new 5'-m7GTP recognizing protein. How these RNA structures mediate eIF3 recruitment to affect translation of specific mRNAs remains unclear. Here, we report the nuclear magnetic resonance (NMR) structure of a stem-loop within the c-JUN 5' UTR recognized by eIF3 and essential for specialized translation initiation of this well-known oncogene. The structure exhibits similarity to eIF3 recognizing motifs found in hepatitis C virus (HCV)-like IRESs, suggesting mechanistic similarities. This work establishes the RNA structural features involved in c-JUN specialized translation initiation and provides a basis to search for small molecule inhibitors of aberrant expression of the proto-oncogenic c-JUN.

Toll-like Receptors from the Perspective of Cancer Treatment

Toll-like receptors (TLRs) represent a family of pattern recognition receptors that recognize certain pathogen-associated molecular patterns and damage-associated molecular patterns. TLRs are highly interesting to researchers including immunologists because of the involvement in various diseases including cancers, allergies, autoimmunity, infections, and inflammation. After ligand engagement, TLRs trigger multiple signaling pathways involving nuclear factor-κB (NF-κB), interferon-regulatory factors (IRFs), and mitogen-activated protein kinases (MAPKs) for the production of various cytokines that play an important role in diseases like cancer. TLR activation in immune as well as cancer cells may prevent the formation and growth of a tumor. Nonetheless, under certain conditions, either hyperactivation or hypoactivation of TLRs supports the survival and metastasis of a tumor. Therefore, the design of TLR-targeting agonists as well as antagonists is a promising immunotherapeutic approach to cancer. In this review, we mainly describe TLRs, their involvement in cancer, and their promising properties for anticancer drug discovery.

DDX21 promotes gastric cancer proliferation by regulating cell cycle

DEAD (Asp-Glu-Ala-Asp) cassette helicase 21 (DDX21) is an ATP-dependent RNA helicase that is overexpressed in various malignancies. There is increasing evidence that DDX21 is involved in carcinogenesis and cancer progression by promoting cell proliferation. However, the functional role of DDX21 in gastric cancer is largely unknown. In this study, we observed that DDX21 was significantly up-regulated in gastric cancer tissues compared to paired adjacent normal tissues. The expression of DDX21 was closely related to the pathological stage of gastric cancer. In vitro and in vivo studies had shown that knockdown of DDX21 inhibited gastric cancer cell proliferation, colony formation, G1/S cell cycle transition and xenograft growth, while ectopic expression of DDX21 promoted these cell functions. Mechanically, DDX21 induced gastric cancer cell growth by up-regulating levels of Cyclin D1 and CDK2. Taken together, these results revealed a novel role for DDX21 in the proliferation of gastric cancer cells via the Cyclin D1 and CDK2 pathways. Therefore, DDX21 can be used as a therapeutic target for gastric cancer.

Phospho-proteomic analysis of primary human colon epithelial cells during the early Trypanosoma cruzi infection phase

The protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease, causes severe morbidity and mortality in afflicted individuals. About 30% of T. cruzi-infected individuals present with cardiac, gastrointestinal tract, and/or neurological disorders. Megacolon, one of the major pathologies of Chagas disease, is accompanied by gastrointestinal motility disorders. The molecular mechanism of T. cruzi-mediated megacolon in Chagas disease is currently unknown. To decipher the molecular mechanism of T. cruzi-induced alteration in the colon during the early infection phase, we exposed primary human colonic epithelial cells (HCoEpiC) to invasive T. cruzi trypomastigotes at multiple time points to determine changes in the phosphoprotein networks in the cells following infection using proteome profiler Human phospho-kinase arrays. We found significant changes in the phosphorylation pattern that can mediate cellular deregulations in colonic epithelial cells after infection. We detected a significant increase in the levels of phosphorylated heat shock protein (p-HSP) 27 and transcription factors that regulate various cellular functions, including c-Jun and CREB. Our study confirmed significant upregulation of phospho (p-) Akt S473, p-JNK, which may directly or indirectly modulate CREB and c-Jun phosphorylation, respectively. We also observed increased levels of phosphorylated CREB and c-Jun in the nucleus. Furthermore, we found that p-c-Jun and p-CREB co-localized in the nucleus at 180 minutes post infection, with a maximum Pearson correlation coefficient of 0.76±0.02. Increased p-c-Jun and p-CREB have been linked to inflammatory and profibrotic responses. T. cruzi infection of HCoEpiC induces an increased expression of thrombospondin-1 (TSP-1), which is fibrogenic at elevated levels. We also found that T. cruzi infection modulates the expression of NF-kB and JAK2-STAT1 signaling molecules which can increase pro-inflammatory flux. Bioinformatics analysis of the phosphoprotein networks derived using the phospho-protein data serves as a blueprint for T. cruzi-mediated cellular transformation of primary human colonic cells during the early phase of T. cruzi infection.

Oncogenic N-Ras Stimulates SRF-Mediated Transactivation via H3 Acetylation at Lysine 9

Signal transduction pathways regulate the gene expression by altering chromatin dynamics in response to mitogens. Ras proteins are key regulators linking extracellular stimuli to a diverse range of biological responses associated with gene regulation. In mammals, the three ras genes encode four Ras protein isoforms: H-Ras, K-Ras4A, K-Ras4B, and N-Ras. Although emerging evidence suggests that Ras isoforms differentially regulate gene expressions and are functionally nonredundant, the mechanisms underlying Ras specificity and Ras signaling effects on gene expression remain unclear. Here, we show that oncogenic N-Ras acts as the most potent regulator of SRF-, NF-κB-, and AP-1-dependent transcription. N-Ras-RGL2 axis is a distinct signaling pathway for SRF target gene expression such as Egr1 and JunB, as RGL2 Ras binding domain (RBD) significantly impaired oncogenic N-Ras-induced SRE activation. By monitoring the effect of Ras isoforms upon the change of global histone modifications in oncogenic Ras-overexpressed cells, we discovered that oncogenic N-Ras elevates H3K9ac/H3K23ac levels globally in the chromatin context. Importantly, chromatin immunoprecipitation (ChIP) assays revealed that H3K9ac is significantly enriched at the promoter and coding regions of Egr1 and JunB. Collectively, our findings define an undocumented role of N-Ras in modulating of H3 acetylation and in gene regulation.

BRAF-Oncogene-Induced Senescence and the Role of Thyroid-Stimulating Hormone Signaling in the Progression of Papillary Thyroid Carcinoma

Oncogene-induced senescence (OIS) explains the phenomenon of cellular senescence triggered by the action of oncogenes. It is a mechanism adopted by a cell to inhibit progression of benign tumors into malignancy, occurs in premalignant lesions, and is almost never present in malignant lesions. BRAF mutations occur in about 40-45% of all papillary thyroid carcinomas (PTCs) and of which 99.7% is the BRAFV600E mutation. A unique phenotype of the BRAFV600E mutation is the upregulation of the thyroid-stimulating hormone receptor (TSHR) on thyrocyte membranes. Despite the overexpression of the receptor, BRAFV600E cells undergo cell cycle arrest leading to OIS via a negative feedback signaling mechanism. A simultaneous increase in serum thyroid-stimulating hormone (TSH) in response to hypothyroidism (common in autoimmune diseases such as Hashimoto's thyroiditis) would cause senescent tumor cells to overcome OIS and proceed towards malignancy, hence showing the importance of TSH/TSHR signaling in the development of PTCs. Increase in TSH/TSHR signaling triggers an increase in levels of downstream enzymes such as manganese superoxide dismutase (MnSOD) and dual-specific phosphatase 6 (DUSP6) which eventually results in the production of oncogenic proteins such as c-Myc. Therefore, the detection of these genetic alterations as effective biomarkers for premalignant lesions of PTC is important in clinical settings and techniques such as polymerase chain reaction-mediated restriction fragment length polymorphism (PCR-RFLP) and real-time PCR can be used to detect the BRAFV600E point mutation and overexpression of TSHR, MnSOD, and DUSP6, respectively.

JunD/AP-1 Antagonizes the Induction of DAPK1 To Promote the Survival of v-Src-Transformed Cells

The increase in AP-1 activity is a hallmark of cell transformation by tyrosine kinases. Previously, we reported that blocking AP-1 using the c-Jun dominant negative mutant TAM67 induced senescence, adipogenesis, or apoptosis in v-Src-transformed chicken embryo fibroblasts (CEFs) whereas inhibition of JunD by short hairpin RNA (shRNA) specifically induced apoptosis. To investigate the role of AP-1 in Src-mediated transformation, we undertook a gene profiling study to characterize the transcriptomes of v-Src-transformed CEFs expressing either TAM67 or the JunD shRNA. Our study revealed a cluster of 18 probe sets upregulated exclusively in response to AP-1/JunD impairment and v-Src transformation. Four of these probe sets correspond to genes involved in the interferon pathway. One gene in particular, death-associated protein kinase 1 (DAPK1), is a C/EBPβ-regulated mediator of apoptosis in gamma interferon (IFN-γ)-induced cell death. Here, we show that inhibition of DAPK1 abrogates cell death in v-Src-transformed cells expressing the JunD shRNA. Chromatin immunoprecipitation data indicated that C/EBPβ was recruited to the DAPK1 promoter while the expression of a dominant negative mutant of C/EBPβ abrogated the induction of DAPK1 in response to the inhibition of AP-1. In contrast, as determined by chromatin immunoprecipitation (ChIP) assays, JunD was not detected on the DAPK1 promoter under any conditions, suggesting that JunD promotes survival by indirectly antagonizing the expression of DAPK1 in v-Src transformed cells.

IMPORTANCE

Transformation by the v-Src oncoprotein causes extensive changes in gene expression in primary cells such as chicken embryo fibroblasts. These changes, determining the properties of transformed cells, are controlled in part at the transcriptional level. Much attention has been devoted to transcription factors such as AP-1 and NF-κB and the control of genes associated with a more aggressive phenotype. In this report, we describe a novel mechanism of action determined by the JunD component of AP-1, a factor enhancing cell survival in v-Src-transformed cells. We show that the loss of JunD results in the aberrant activation of a genetic program leading to cell death. This program requires the activation of the tumor suppressor death-associated protein kinase 1 (DAPK1). Since DAPK1 is phosphorylated and inhibited by v-Src, these results highlight the importance of this kinase and the multiple mechanisms controlled by v-Src to antagonize the tumor suppressor function of DAPK1.

T Cell Deficiency Leads to Liver Carcinogenesis in Azoxymethane-Treated Rats

There is an increasing amount of evidence suggesting that T cell deficiency contributes to tumor development. However, it is unclear whether T cell deficiency leads to liver and colon carcinogenesis. The aim of this study was to investigate the role of T cells on liver and colon carcinogenesis. Athymic F344/N Jcl-rnu/- (nu/nu) rats and euthymic F344/N Jcl-rnu/+ (nu/+) rats were administered the carcinogen azoxymethane (AOM) at a dose of 15 mg/kg body wt once a week for 2 weeks. At 48 weeks after the second carcinogen treatment, the rats were sacrificed, and livers and colons were examined. Apoptosis and cell proliferation were evaluated by DNA fragmentation and proliferating cell nuclear antigen assays, respectively. Wild-type p53 and members of the Jun and Fos oncogene families were detected by Western blotting. AOM treatment induced 100% liver tumor and 63.6% colon tumor incidence in T cell–deficient nu/nu rats, compared with 0% and 38.5% incidence in nu/+ rats. T cell deficiency promoted the inhibitory action of AOM on apoptosis in both liver and colon at 48 weeks. In contrast, T cell deficiency increased cell proliferation after AOM treatment in both tissues. Wild-type p53 was reduced in both tissues of T cell–deficient rats. AOM treatment induced c-Jun and c-Fos expressions in the liver but increased only Fos B in the colon, whereas T cell deficiency enhanced c-Jun overexpression in the liver. These results suggest that T cell deficiency leads to liver carcinogenesis partly by a reduction in wild-type p53 and increasing c-Jun expression in AOM-treated rats.

Suppression of MicroRNA 200 Family Expression by Oncogenic KRAS Activation Promotes Cell Survival and Epithelial-Mesenchymal Transition in KRAS-Driven Cancer

Oncogenic KRAS contributes to malignant transformation, antiapoptosis, and metastasis in multiple human cancers, such as lung, colon, and pancreatic cancers and melanoma. MicroRNAs (miRNAs) are endogenous 18- to 25-nucleotide noncoding small RNAs that regulate gene expression in a sequence-specific manner via the degradation of target mRNAs or inhibition of protein translation. In the present study, using array-based miRNA profiling in IMR90 and MCF10A cells expressing oncogenic KRAS, we identified that the expression of the microRNA 200 (mir-200) family was suppressed by KRAS activation and that this suppression was mediated by the transcription factors JUN and SP1 in addition to ZEB1. Restoration of mir-200 expression compromised KRAS-induced cellular transformation in vitro and tumor formation in vivo In addition, we found that enforced expression of mir-200 abrogated KRAS-induced resistance to apoptosis by directly targeting the antiapoptotic gene BCL2 Finally, mir-200 was able to antagonize the epithelial-mesenchymal transition (EMT) driven by mutant KRAS. Collectively, our results suggest that repression of endogenous mir-200 expression is one of the important cellular responses to KRAS activation during tumor initiation and progression.

Regulatory Roles of MAPK Phosphatases in Cancer

The mitogen-activated protein kinases (MAPKs) are key regulators of cell growth and survival in physiological and pathological processes. Aberrant MAPK signaling plays a critical role in the development and progression of human cancer, as well as in determining responses to cancer treatment. The MAPK phosphatases (MKPs), also known as dual-specificity phosphatases (DUSPs), are a family of proteins that function as major negative regulators of MAPK activities in mammalian cells. Studies using mice deficient in specific MKPs including MKP1/DUSP1, PAC-1/DUSP2, MKP2/DUSP4, MKP5/DUSP10 and MKP7/DUSP16 demonstrated that these molecules are important not only for both innate and adaptive immune responses, but also for metabolic homeostasis. In addition, the consequences of the gain or loss of function of the MKPs in normal and malignant tissues have highlighted the importance of these phosphatases in the pathogenesis of cancers. The involvement of the MKPs in resistance to cancer therapy has also gained prominence, making the MKPs a potential target for anti-cancer therapy. This review will summarize the current knowledge of the MKPs in cancer development, progression and treatment outcomes.

Phosphorylation of Glutathione S-Transferase P1 (GSTP1) by Epidermal Growth Factor Receptor (EGFR) Promotes Formation of the GSTP1-c-Jun N-terminal kinase (JNK) Complex and Suppresses JNK Downstream Signaling and Apoptosis in Brain Tumor Cells

Under normal physiologic conditions, the glutathione S-transferase P1 (GSTP1) protein exists intracellularly as a dimer in reversible equilibrium with its monomeric subunits. In the latter form, GSTP1 binds to the mitogen-activated protein kinase, JNK, and inhibits JNK downstream signaling. In tumor cells, which frequently are characterized by constitutively high GSTP1 expression, GSTP1 undergoes phosphorylation by epidermal growth factor receptor (EGFR) at tyrosine residues 3, 7, and 198. Here we report on the effect of this EGFR-dependent GSTP1 tyrosine phosphorylation on the interaction of GSTP1 with JNK, on the regulation of JNK downstream signaling by GSTP1, and on tumor cell survival. Using in vitro and in vivo growing human brain tumors, we show that tyrosine phosphorylation shifts the GSTP1 dimer-monomer equilibrium to the monomeric state and facilitates the formation of the GSTP1-JNK complex, in which JNK is functionally inhibited. Targeted mutagenesis and functional analysis demonstrated that the increased GSTP1 binding to JNK results from phosphorylation of the GSTP1 C-terminal Tyr-198 by EGFR and is associated with a >2.5-fold decrease in JNK downstream signaling and a significant suppression of both spontaneous and drug-induced apoptosis in the tumor cells. The findings define a novel mechanism of regulatory control of JNK signaling that is mediated by the EGFR/GSTP1 cross-talk and provides a survival advantage for tumors with activated EGFR and high GSTP1 expression. The results lay the foundation for a novel strategy of dual EGFR/GSTP1 for treating EGFR+ve, GSTP1 expressing GBMs.

The oncogene c-Jun impedes somatic cell reprogramming

Oncogenic transcription factors are known to mediate the conversion of somatic cells to tumour or induced pluripotent stem cells (iPSCs). Here we report c-Jun as a barrier for iPSC formation. c-Jun is expressed by and required for the proliferation of mouse embryonic fibroblasts (MEFs), but not mouse embryonic stem cells (mESCs). Consistently, c-Jun is induced during mESC differentiation, drives mESCs towards the endoderm lineage and completely blocks the generation of iPSCs from MEFs. Mechanistically, c-Jun activates mesenchymal-related genes, broadly suppresses the pluripotent ones, and derails the obligatory mesenchymal to epithelial transition during reprogramming. Furthermore, inhibition of c-Jun by shRNA, dominant-negative c-Jun or Jdp2 enhances reprogramming and replaces Oct4 among the Yamanaka factors. Finally, Jdp2 anchors 5 non-Yamanaka factors (Id1, Jhdm1b, Lrh1, Sall4 and Glis1) to reprogram MEFs into iPSCs. Our studies reveal c-Jun as a guardian of somatic cell fate and its suppression opens the gate to pluripotency.

The phosphatidylinositol 3-kinase/Akt and c-Jun N-terminal kinase signaling in cancer: Alliance or contradiction? (Review)

The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway and c-Jun N-terminal kinase (JNK) pathway are responsible for regulating a variety of cellular processes including cell growth, migration, invasion and apoptosis. These two pathways are essential to the development and progression of tumors. The dual roles of JNK signaling in apoptosis and tumor development determine the different interactions between the PI3K/Akt and JNK pathways. Activation of PI3K/Akt signaling can inhibit stress- and cytokine-induced JNK activation through Akt antagonizing and the formation of the JIP1-JNK module, as well as the activities of upstream kinases ASK1, MKK4/7 and MLK. On the other hand, hyperactivation of Akt and JNK is also found in cancers that harbor EGFR overexpression or loss of PTEN. Understanding the activation mechanism of PI3K/Akt and JNK pathways, as well as the interplays between these two pathways in cancer may contribute to the identification of novel therapeutic targets. In the present report, we summarized the current understanding of the PI3K/Akt and JNK signaling networks, as well as their biological roles in cancers. In addition, the interactions and regulatory network between PI3K/Akt and JNK pathways in cancer were discussed.

Mitogen- and stress-activated Kinase 1 mediates Epstein-Barr virus latent membrane protein 1-promoted cell transformation in nasopharyngeal carcinoma through its induction of Fra-1 and c-Jun genes

BACKGROUND

Mitogen- and Stress-Activated Kinase 1 (MSK1) is a nuclear kinase that serves as active link between extracellular signals and the primary response of gene expression. However, the involvement of MSK1 in malignant transformation and cancer development is not well understood. In this study, we aimed to explore the role of MSK1 in Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1)-promoted carcinogenesis of nasopharyngeal carcinoma (NPC).

METHODS

The level of MSK1 phosphorylation at Thr581 was detected by the immunohistochemical analysis in NPC tissues and normal nasopharynx tissues, and its correlation with LMP1 was analyzed in NPC tissues and cell lines. Using MSK1 inhibitor H89 or small interfering RNA (siRNA)-MSK1, the effects of MSK1 on LMP1-promoted CNE1 cell proliferation and transformation were evaluated by CCK-8 assay, flow cytometry and focus-forming assay respectively. Furthermore, the regulatory role of MSK1-mediated histone H3 phosphorylation at Ser10 on the promoter activity and expression of Fra-1 or c-Jun was determined by reporter gene assay and western blotting analysis.

RESULTS

Immunohistochemical analysis revealed that the level of MSK1 phosphorylation at Thr581 was significantly higher in the poorly differentiated NPC tissues than that in normal nasopharynx tissues (P < 0.001). Moreover, high level of phosphorylated MSK1 was positively correlated with the expression of LMP1 in NPC tissues (r = 0.393, P = 0.002) and cell lines. MSK1 inhibitor H89 or knockdown of MSK1 by siRNA dramatically suppressed LMP1-promoted CNE1 cell proliferation, which was associated with the induction of cell cycle arrest at G0/G1 phase. In addition, the anchorage-independent growth promoted by LMP1 was blocked in MSK1 knockdown cells. When the activity or expression of MSK1 was inhibited, LMP1-induced promoter activities of Fra-1 and c-Jun as well as their protein levels were greatly reduced. It was found that only H3 WT, but not mutant H3 S10A, dramatically increased LMP1 induction of Fra-1 and c-Jun genes compared with mock cells.

CONCLUSION

Increased MSK1 activity is critically important for LMP1-promoted cell proliferation and transformation in NPC, which may be correlated with its induction of Fra-1 and c-Jun through phosphorylation of histone H3 at Ser10.

The E3 ubiquitin ligase Trim7 mediates c-Jun/AP-1 activation by Ras signalling

The c-Jun/AP-1 transcription factor controls key cellular behaviours, including proliferation and apoptosis, in response to JNK and Ras/MAPK signalling. While the JNK pathway has been well characterized, the mechanism of activation by Ras was elusive. Here we identify the uncharacterized ubiquitin ligase Trim7 as a critical component of AP-1 activation via Ras. We found that MSK1 directly phosphorylates Trim7 in response to direct activation by the Ras-Raf-MEK-ERK pathway, and this modification stimulates Trim7 E3 ubiquitin ligase activity. Trim7 mediates Lys63-linked ubiquitination of the AP-1 co-activator RACO-1, leading to RACO-1 protein stabilization. Consequently, Trim7 depletion reduces RACO-1 levels and AP-1-dependent gene expression. Moreover, transgenic overexpression of Trim7 increases lung tumour burden in a Ras-driven cancer model, and knockdown of Trim7 in established xenografts reduces tumour growth. Thus, phosphorylation-ubiquitination crosstalk between MSK1, Trim7 and RACO-1 completes the long sought-after mechanism linking growth factor signalling and AP-1 activation.

eIF3 targets cell-proliferation messenger RNAs for translational activation or repression

Regulation of protein synthesis is fundamental for all aspects of eukaryotic biology by controlling development, homeostasis and stress responses. The 13-subunit, 800-kilodalton eukaryotic initiation factor 3 (eIF3) organizes initiation factor and ribosome interactions required for productive translation. However, current understanding of eIF3 function does not explain genetic evidence correlating eIF3 deregulation with tissue-specific cancers and developmental defects. Here we report the genome-wide discovery of human transcripts that interact with eIF3 using photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (PAR-CLIP). eIF3 binds to a highly specific program of messenger RNAs involved in cell growth control processes, including cell cycling, differentiation and apoptosis, via the mRNA 5' untranslated region. Surprisingly, functional analysis of the interaction between eIF3 and two mRNAs encoding the cell proliferation regulators c-JUN and BTG1 reveals that eIF3 uses different modes of RNA stem-loop binding to exert either translational activation or repression. Our findings illuminate a new role for eIF3 in governing a specialized repertoire of gene expression and suggest that binding of eIF3 to specific mRNAs could be targeted to control carcinogenesis.

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.

The interruption of PKC-ι signaling and TRAIL combination therapy against glioblastoma cells

Glioblastoma is a highly aggressive type of brain cancer which currently has limited options for treatment. It is imperative to develop combination therapies that could cause apoptosis in glioblastoma. The aim of this study was to characterize the affect of modified ICA-1, a PKC-iota inhibitor, on the growth pattern of various glioblastoma cell lines. T98G and U87 glioblastoma cells were treated with ICA-1 alone and the absolute cell numbers of each group were determined for cell growth expansion analysis, cell viability analysis, and cell death analysis. Low dose ICA-1 treatment alone significantly inhibited cell growth expansion of high density glioblastoma cells without inducing cell death. However, the high dose ICA-1 treatment regimen provided significant apoptosis for glioblastoma cells. Furthermore, this study was conducted to use a two layer molecular level approach for treating glioblastoma cells with ICA-1 plus an apoptosis agent, tumor-necrosis factor-related apoptosis-inducing ligand (TRAIL), to induce apoptosis in such chemo-refractory cancer cells. Following ICA-1 plus TRAIL treatment, apoptosis was detected in glioblastoma cells via the TUNEL assay and via flow cytometric analysis using Annexin-V FITC/PI. This study offers the first evidence for ICA-1 alone to inhibit glioblastoma cell proliferation as well as the novel combination of ICA-1 with TRAIL to cause robust apoptosis in a caspase-3 mediated mechanism. Furthermore, ICA-1 plus TRAIL simultaneously modulates down-regulation of PKC-iota and c-Jun.

The 2 Faces of JNK Signaling in Cancer

c-Jun NH2-terminal kinase (JNK) was discovered almost 20 years ago as the protein kinase responsible for phosphorylating c-Jun at Ser-63 and Ser-73. These sites had previously been demonstrated to be essential for the stimulation of c-Jun activity and for cooperation with Ha-ras in oncogenic transformation. This led to the idea that JNK was a positive regulator of cellular transformation. However, the analysis of jnk gene deletion in various mouse models of cancer has produced conflicting findings, with some studies supporting the pro-oncogenic function of JNK and others providing evidence that JNK acts as a tumor suppressor. This review will discuss how these unexpected findings have increased our understanding of the role of JNK signaling in cancer and have provided a source of new working hypotheses.

Acute and chronic cadmium exposure promotes E-cadherin degradation in MCF7 breast cancer cells

Cadmium is an environmental carcinogen that usually enters the body at minute concentrations through diet or cigarette smoke and bioaccumulates in soft tissues. In past studies, cadmium has been shown to contribute to the development of more aggressive cancer phenotypes including increased cell migration and invasion. This study aims to determine if cadmium exposure-both acute and chronic-contributes to breast cancer progression by interfering with the normal functional relationship between E-cadherin and β-catenin. An MCF7 breast cancer cell line (MCF7-Cd) chronically exposed to 10(-7)  M CdCl2 was previously developed and used as a model system to study chronic exposures, whereas parental MCF7 cells exposed to 10(-6)  M CdCl2 for short periods of time were used to study acute exposures. Cadmium exposure of MCF7 cells led to the degradation of the E-cadherin protein via the ubiquitination pathway. This resulted in fewer E-cadherin/β-catenin complexes and the relocation of active β-catenin to the nucleus, where it interacted with transcription factor TCF-4 to modulate gene expression. Interestingly, only cells chronically exposed to cadmium showed a significant decrease in the localization of β-catenin to the plasma membrane and an increased distance between cells. Our data suggest that cadmium exposure promotes breast cancer progression by (1) down-regulating E-cadherin, thus decreasing the number of E-cadherin/β-catenin adhesion complexes, and (2) enhancing the nuclear translocation of β-catenin to increase expression of cancer-promoting proteins (i.e., c-Jun and cyclin D1).

Ras inhibition boosts galectin-7 at the expense of galectin-1 to sensitize cells to apoptosis

Galectins are a family of β-galactoside-binding lectins that exert diverse extracellular and intracellular effects. Galectin-7 and galectin-1 show opposing effects on proliferation and survival in different cell types. Galectin-7 is a p53-induced gene and an enhancer of apoptosis, whereas galectin-1 induces tumorigenicity and resistance to apoptosis in several types of cancers. We show here that in cells derived from neurofibromin-deficient (Nf1^−/−) malignant peripheral nerve sheath tumors (MPNSTs), Ras inhibition by S-trans,trans-farnesylthiosalicylic-acid (FTS; Salirasib) shifts the pattern of galectin expression. Whereas FTS decreased levels of both active Ras and galectin-1 expression, it dramatically increased both the mRNA and protein expression levels of galectin-7. Galectin-7 accumulation was mediated through JNK inhibition presumably resulting from the observed induction of p53, and was negatively regulated by the AP-1 inhibitor JDP2. Expression of galectin-7 by itself decreased Ras activation in ST88-14 cells and rendered them sensitive to apoptosis. This observed shift in galectin expression pattern together with the accompanying shift from cell proliferation to apoptosis represents a novel pattern of Ras inhibition by FTS. This seems likely to be an important phenomenon in view of the fact that both enhanced cell proliferation and defects of apoptosis constitute major hallmarks of human cancers and play a central role in the resistance of MPNSTs to anti-cancer treatments. These findings suggest that FTS, alone or in combination with chemotherapy agents, may be worth developing as a possible treatment for MPNSTs.

Interaction between c-jun and androgen receptor determines the outcome of taxane therapy in castration resistant prostate cancer

Taxane based chemotherapy is the standard of care treatment in castration resistant prostate cancer (CRPC). There is convincing evidence that taxane therapy affects androgen receptor (AR) but the exact mechanisms have to be further elucidated. Our studies identified c-jun as a crucial key player which interacts with AR and thus determines the outcome of the taxane therapy given. Docetaxel (Doc) and paclitaxel (Pac) agents showed different effects on LNCaP and LNb4 evidenced by alteration in the protein and mRNA levels of c-jun, AR and PSA. Docetaxel-induced phophorylation of c-jun occurred before JNK phosphorylation which suggests that c-jun phosphorylation is independent of JNK pathways in prostate cancer cells. A xenograft study showed that mice treated with Pac and bicalutamide showed worse outcome supporting our hypothesis that upregulation of c-jun might act as a potent antiapoptotic factor. We observed in our in vitro studies an inverse regulation of PSA- and AR-mRNA levels in Doc treated LNb4 cells. This was also seen for kallikrein 2 (KLK 2) which followed the same pattern. Given the fact that response to taxane therapy is measured by PSA decrease we have to consider that this might not reflect the true activity of AR in CRPC patients.

Repeated H2 O2 exposure drives cell cycle progression in an in vitro model of ulcerative colitis

The production of hydrogen peroxide (H₂O₂) drives tumourigenesis in ulcerative colitis (UC). Recently, we showed that H₂O₂ activates DNA damage checkpoints in human colonic epithelial cells (HCEC) through c-Jun N-terminal Kinases (JNK) that induces p21^WAF1. Moreover, caspases circumvented the G1/S and intra-S checkpoints, and cells accumulated in G2/M. The latter observation raised the question of whether repeated H₂O₂ exposures alter JNK activation, thereby promoting a direct passage of cells from G2/M arrest to driven cell cycle progression. Here, we report that increased proliferation of repeatedly H₂O₂-exposed HCEC cells (C-cell cultures) was associated with (i) increased phospho-p46 JNK, (ii) decreased total JNK and phospho-p54 JNK and (iii) p21^WAF1 down-regulation. Altered JNK activation and p21^WAF1 down-regulation were accompanied by defects in maintaining G2/M and mitotic spindle checkpoints through adaptation, as well as by apoptosis resistance following H₂O₂ exposure. This may cause increased proliferation of C-cell cultures, a defining initiating feature in the inflammation-carcinoma pathway in UC. We further suggest that dysregulated JNK activation is attributed to a non-apoptotic function of caspases, causing checkpoint adaptation in C-cell cultures. Additionally, loss of cell-contact inhibition and the overcoming of senescence, hallmarks of cancer, contributed to increased proliferation. Furthermore, there was evidence that p54 JNK inactivation is responsible for loss of cell-contact inhibition. We present a cellular model of UC and suggest a sinusoidal pattern of proliferation, which is triggered by H₂O₂-induced reactive oxygen species generation, involving an interplay between JNK activation/inactivation, p21^WAF1, c-Fos, c-Jun/phospho-c-Jun, ATF2/phospho-ATF2, β-catenin/TCF4-signalling, c-Myc, CDK6 and Cyclin D2, leading to driven cell cycle progression.

Radiation-induced acid ceramidase confers prostate cancer resistance and tumor relapse

Escape of prostate cancer (PCa) cells from ionizing radiation-induced (IR-induced) killing leads to disease progression and cancer relapse. The influence of sphingolipids, such as ceramide and its metabolite sphingosine 1-phosphate, on signal transduction pathways under cell stress is important to survival adaptation responses. In this study, we demonstrate that ceramide-deacylating enzyme acid ceramidase (AC) was preferentially upregulated in irradiated PCa cells. Radiation-induced AC gene transactivation by activator protein 1 (AP-1) binding on the proximal promoter was sensitive to inhibition of de novo ceramide biosynthesis, as demonstrated by promoter reporter and ChIP-qPCR analyses. Our data indicate that a protective feedback mechanism mitigates the apoptotic effect of IR-induced ceramide generation. We found that deregulation of c-Jun induced marked radiosensitization in vivo and in vitro, which was rescued by ectopic AC overexpression. AC overexpression in PCa clonogens that survived a fractionated 80-Gy IR course was associated with increased radioresistance and proliferation, suggesting a role for AC in radiotherapy failure and relapse. Immunohistochemical analysis of human PCa tissues revealed higher levels of AC after radiotherapy failure than those in therapy-naive PCa, prostatic intraepithelial neoplasia, or benign tissues. Addition of an AC inhibitor to an animal model of xenograft irradiation produced radiosensitization and prevention of relapse. These data indicate that AC is a potentially tractable target for adjuvant radiotherapy.

Arginine methylation of the c-Jun coactivator RACO-1 is required for c-Jun/AP-1 activation

c-Jun, the major component of the AP-1 transcription factor complex, has important functions in cellular proliferation and oncogenic transformation. The RING domain-containing protein RACO-1 functions as a c-Jun coactivator that molecularly links growth factor signalling to AP-1 transactivation. Here we demonstrate that RACO-1 is present as a nuclear dimer and that c-Jun specifically interacts with dimeric RACO-1. Moreover, RACO-1 is identified as a substrate of the arginine methyltransferase PRMT1, which methylates RACO-1 on two arginine residues. Arginine methylation of RACO-1 promotes a conformational change that stabilises RACO-1 by facilitating K63-linked ubiquitin chain formation, and enables RACO-1 dimerisation and c-Jun interaction. Abrogation of PRMT1 function impairs AP-1 activity and results in decreased expression of a large percentage of c-Jun target genes. These results demonstrate that arginine methylation of RACO-1 is required for efficient transcriptional activation by c-Jun/AP-1 and thus identify PRMT1 as an important regulator of c-Jun/AP-1 function.

Head and neck cancer cells and xenografts are very sensitive to palytoxin: decrease of c-jun n-terminale kinase-3 expression enhances palytoxin toxicity

Objectives

Palytoxin (PTX), a marine toxin isolated from the Cnidaria (zooanthid) Palythoa caribaeorum is one of the most potent non-protein substances known. It is a very complex molecule that presents both lipophilic and hydrophilic areas. The effect of PTX was investigated in a series of experiments conducted in head and neck squamous cell carcinoma (HNSCC) cell lines and xenografts.

Materials and methods

Cell viability, and gene expression of the sodium/potassium-transporting ATPase subumit alpha1 (ATP1AL1) and GAPDH were analyzed in HNSCC cells and normal epithelial cells after treatment with PTX using cytotoxicity-, clonogenic-, and enzyme inhibitor assays as well as RT-PCR and Northern Blotting. For xenograft experiments severe combined immunodeficient (SCID) mice were used to analyze tumor regression. The data were statistically analyzed using One-Way Annova (SPSS vs20).

Results

Significant toxic effects were observed in tumor cells treated with PTX (LD50 of 1.5 to 3.5 ng/ml) in contrast to normal cells. In tumor cells PTX affected both the release of LDH and the expression of the sodium/potassium-transporting ATPase subunit alpha1 gene suggesting loss of cellular integrity, primarily of the plasma membrane. Furthermore, strong repression of the c-Jun N-terminal kinase 3 (JNK3) mRNA expression was found in carcinoma cells which correlated with enhanced toxicity of PTX suggesting an essential role of the mitogen activated protein kinase (MAPK)/JNK signalling cascades pathway in the mechanisms of HNSCC cell resistance to PTX. In mice inoculated with carcinoma cells, injections of PTX into the xenografted tumors resulted within 24 days in extensive tumor destruction in 75% of the treated animals (LD50 of 68 ng/kg to 83 ng/kg) while no tumor regression occurred in control animals.

Conclusions

These results clearly provide evidence that PTX possesses preferential toxicity for head and neck carcinoma cells and therefore it is worth further studying its impact which may extend our knowledge of the biology of head and neck cancer.

Pathophysiological Significance of Hepatic Apoptosis

Apoptosis is a classical pathological feature in liver diseases caused by various etiological factors such as drugs, viruses, alcohol, and cholestasis. Hepatic apoptosis and its deleterious effects exacerbate liver function as well as involvement in fibrosis/cirrhosis and carcinogenesis. An imbalance between apoptotic and antiapoptotic capabilities is a prominent characteristic of liver injury. The regulation of apoptosis and antiapoptosis can be a pivotal step in the treatment of liver diseases.

Adipogenesis

Adipose tissue is an important site for lipid storage, energy homeostasis, and whole-body insulin sensitivity. It is important to understand the mechanisms involved in adipose tissue development and function, which can be regulated by the endocrine actions of various peptide and steroid hormones. Recent studies have revealed that white and brown adipocytes can be derived from distinct precursor cells. This review will focus on transcriptional control of adipogenesis and its regulation by several endocrine hormones. The general functions and cellular origins of adipose tissue and how the modulation of adipocyte development pertains to metabolic disease states will also be considered.

c-JUN prevents methylation of p16(INK4a) (and Cdk6): the villain turned bodyguard

A novel way by which the AP-1 factor c-JUN interferes with tumorigenesis has recently been elucidated [1]. In a model of murine leukemia, c-JUN prevents the epigenetic silencing of the cell cycle kinase CDK6. In the absence of c-JUN, CDK6 is down-regulated and the 5'region of the gene is methylated. Down-regulation of CDK6 results in significantly delayed leukemia formation. Here we show that c-JUN is also involved in protecting the promoter region of the tumor suppressor p16^INK4a, which is consistently methylated over time in c-JUN deficient cells. In cells expressing c-JUN, p16^INK4a promoter methylation is a less frequent event. Our study unravels a novel mechanism by which the AP-1 factor c-JUN acts as a “bodyguard”, and preventing methylation of a distinct set of genes after oncogenic transformation.

MUC16 induced rapid G2/M transition via interactions with JAK2 for increased proliferation and anti-apoptosis in breast cancer cells

MUC16/CA125 is a tumor marker currently used in clinics for the follow-up of patients with ovarian cancer. However, MUC16 expression is not entirely restricted to ovarian malignancies and has been reported in other cancers including breast cancer. Although it is well established as a biomarker, function of MUC16 in cancer remains to be elucidated. In the present study, we investigated the role of MUC16 in breast cancer and its underlying mechanisms. Interestingly, our results showed that MUC16 is overexpressed in breast cancer tissues whereas not expressed in non-neoplastic ducts. Further, stable knockdown of MUC16 in breast cancer cells (MDA MB 231 and HBL100) resulted in significant decrease in the rate of cell growth, tumorigenicity and increased apoptosis. In search of a mechanism for breast cancer cell proliferation we found that MUC16 interacts with the ezrin/radixin/moesin domain-containing protein of Janus kinase (JAK2) as demonstrated by the reciprocal immunoprecipitation method. These interactions mediate phosphorylation of STAT3 (Tyr705), which might be a potential mechanism for MUC16-induced proliferation of breast cancer cells by a subsequent co-transactivation of transcription factor c-Jun. Furthermore, silencing of MUC16 induced G2/M arrest in breast cancer cells through downregulation of Cyclin B1 and decreased phosphorylation of Aurora kinase A. This in turn led to enhanced apoptosis in the MUC16-knockdown breast cancer cells through Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated extrinsic apoptotic pathway with the help of c-Jun N-terminal kinase signaling. Collectively, our results suggest that MUC16 has a dual role in breast cancer cell proliferation by interacting with JAK2 and by inhibiting the apoptotic process through downregulation of TRAIL.

Activating transcription factor 2 targets c-Fos, but not c-Jun, in growth plate chondrocytes

Activating transcription factor 2 (ATF-2), c-Fos, and c-Jun belong to the bZIP family of transcription factors. Promoters of c-Fos, c-Jun, cyclin D1, and cyclin A are targets of ATF-2 in primary mouse chondrocytes. An ATF-2 expression vector was co-transfected with either c-Fos or c-Jun promoters in mutant ATF-2 chondrocytes in order to show by luciferase assay that ATF-2 increased promoter activity of c-Fos, but not c-Jun. Chromatin immunoprecipitation (ChIP) assays revealed that ATF-2 bound with the c-Fos promoter at the -294 cyclic AMP response element (CRE) site, but did not bind to the TPA responsive element (TRE) or activating protein-1 (AP1) sites of the c-Jun promoter. Dominant-negative (dn) c-Fos inhibited cyclin D1 promoter activity. However, dn c-Jun had minimal effect on this same promoter activity. c-Fos was capable of interactions with both the cyclin D1 CRE and AP1 sites, while c-Jun co-operated specifically with the cyclin D1 CRE site. Neither c-Fos nor c-Jun had any effect on cyclin A promoter activity. c-Fos was unable to bind to the cyclin A AP1 or CRE sites. In contrast c-Jun was competent in interactions with cyclin A AP1-2 as well as the CRE.

Identification of a c-Jun N-terminal kinase-2-dependent signal amplification cascade that regulates c-Myc levels in ras transformation

Ras is one of the most frequently activated oncogenes in cancer. Two mitogen-activated protein kinases (MAPKs) are important for ras transformation: extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase 2 (JNK2). Here we present a downstream signal amplification cascade that is critical for ras transformation in murine embryonic fibroblasts. This cascade is coordinated by ERK and JNK2 MAPKs, whose Ras-mediated activation leads to the enhanced levels of three oncogenic transcription factors, namely, c-Myc, activating transcription factor 2 (ATF2) and ATF3, all of which are essential for ras transformation. Previous studies show that ERK-mediated serine 62 phosphorylation protects c-Myc from proteasomal degradation. ERK is, however, not alone sufficient to stabilize c-Myc but requires the cooperation of cancerous inhibitor of protein phosphatase 2A (CIP2A), an oncogene that counteracts protein phosphatase 2A-mediated dephosphorylation of c-Myc. Here we show that JNK2 regulates Cip2a transcription via ATF2. ATF2 and c-Myc cooperate to activate the transcription of ATF3. Remarkably, not only ectopic JNK2, but also ectopic ATF2, CIP2A, c-Myc and ATF3 are sufficient to rescue the defective ras transformation of JNK2-deficient cells. Thus, these data identify the key signal converging point of JNK2 and ERK pathways and underline the central role of CIP2A in ras transformation.

Pleiotropic action of AP-1 in v-Src-transformed cells

The activation of AP-1 is a hallmark of cell transformation by tyrosine kinases. In this study, we characterize the role of AP-1 proteins in the transformation of chicken embryo fibroblasts (CEF) by v-Src. In normal CEF, the expression of a dominant negative mutant of c-Jun (TAM67) induced senescence. In contrast, three distinct phenotypes were observed when TAM67 was expressed in v-Src-transformed CEF. While senescent cells were also present, the inhibition of AP-1 caused apoptosis in a fraction of the v-Src-transformed cells. In addition, cells containing lipid-rich vesicles accumulated, suggesting that a subpopulation of the v-Src-transformed cells underwent differentiation in response to the inhibition of AP-1. JunD and Fra-2 were the main components of this factor, while c-Jun accounted for a minor fraction of AP-1 in v-Src-transformed CEF. The downregulation of c-Jun expression by short hairpin RNA (shRNA) induced senescence in normal and v-Src-transformed cells. In contrast, a high incidence of apoptosis was caused by the downregulation of JunD, suggesting that it is required for the survival of v-Src-transformed CEF. Levels of the p53 tumor suppressor were elevated under conditions of JunD inhibition. Repression of p53 by shRNA enhanced the survival and anchorage-independent proliferation of v-Src-transformed CEF with JunD/AP-1 inhibition. The inhibition of Fra-2 had no visible phenotype in normal CEF but caused the appearance of lipid-rich vesicles in v-Src-transformed CEF. Therefore, AP-1 facilitated transformation by acting as a survival factor, by inhibiting premature entry into senescence, and by blocking the differentiation of v-Src-transformed CEF.

5'-Nitro-indirubinoxime inhibits epidermal growth factor- and phorbol ester-induced AP-1 activity and cell transformation through inhibition of phosphorylation of Pin1

5'-Nitro-indirubinoxime (5'-NIO), a derivative of indirubin, exhibits anti-cancer activity in a variety of human cancer cells. However, the underlying molecular mechanisms and molecular target(s) of the chemopreventive activities of 5'-NIO remain unknown. Here, we report that 5'-NIO inhibited the epidermal growth factor (EGF) or 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced neoplastic cell transformation of JB6 Cl41 mouse skin epidermal cells without any cytotoxic effects. Western blot analysis revealed that 5'-NIO inhibited activities of Raf-1 (S338), MEK1/2, ERK1/2, JNK, and c-Jun induced by EGF or TPA, respectively, whereas it did not affect autophosphorylation of epidermal growth factor receptor (EGFR) induced by EGF or TPA. In addition, 5'-NIO exerted strong inhibitory effects on the EGF- or TPA-induced c-fos or c-jun transcriptional activity, and thereby inhibited the associated activator protein-1 (AP-1) transactivation activity induced by EGF or TPA. Importantly, 5'-NIO inhibited Pin1 phosphorylation at serine 16 induced by EGF or TPA, respectively, resulted in the inhibition of interaction between Pin1 and Raf-1. Immunoprecipitation/immunoblot analysis revealed that 5'-NIO bound with Pin1. Together, these findings suggest that 5'-NIO might act as an anticarcinogene in EGF- or TPA-induced carcinogenesis through the inhibition of interaction between Pin1 and Raf-1. © 2011 Wiley Periodicals, Inc.

Identification of a co-activator that links growth factor signalling to c-Jun/AP-1 activation

The AP-1 transcription factor c-Jun is essential for cellular proliferation in many cell types, but the molecular link between growth factors and c-Jun activation has been enigmatic. In this study we identify a previously uncharacterized RING-domain-containing protein, RACO-1 (RING domain AP-1 co-activator-1), as a c-Jun co-activator that is regulated by growth factor signalling. RACO-1 interacted with c-Jun independently of amino-terminal phosphorylation, and was both necessary and sufficient for c-Jun/AP-1 activation. Growth factor-mediated stimulation of AP-1 was attributable to MEK/ERK-dependent stabilization of RACO-1 protein. Stimulation of the MEK/ERK pathway strongly promoted Lys 63-linked ubiquitylation of RACO-1, which antagonized Lys 48-linked degradative auto-ubiquitylation of the same Lys residues. RACO-1 depletion reduced cellular proliferation and decreased expression of several growth-associated AP-1 target genes, such as cdc2, cyclinD1 and hb-egf. Moreover, transgenic overexpression of RACO-1 augmented intestinal tumour formation triggered by aberrant Wnt signalling and cooperated with oncogenic Ras in colonic hyperproliferation. Thus RACO-1 is a co-activator that links c-Jun to growth factor signalling and is essential for AP-1 function in proliferation.