Transcriptional regulation of pro-apoptotic Par-4 by NF-kappaB/p65 and its function in controlling cell kinetics during early events in endometrial tumourigenesis

IL-6/STAT3 signaling pathway induces prostate apoptosis response protein-4(PAR-4) to stimulate malignant behaviors of hepatocellular carcinoma cells

INTRODUCTION AND OBJECTIVES

Prostate apoptosis response protein-4(PAR-4) is considered a tumor suppressor. However, the role of PAR-4 in hepatocellular carcinoma(HCC) has rarely been reported. The study explores the role of PAR-4 in the malignant behaviors of HCC cells.

MATERIALS AND METHODS

TCGA database was applied to analyze the expression of PAR-4 in HCC. Evaluated PAR-4 relationship with clinical parameters and prognosis by tissue microarray; Expression of STAT3, p-STAT3, Src and Ras was detected by Western blotting or laser confocal microscopy. Cell scratch and flow cytometry assays were used to observe IL-6 regulation of the malignant behaviors of HCC cells. The tumorigenic potential of HCC cells in vivo was evaluated in a nude mouse tumor model.

RESULTS

Analysis indicated that the expression of PAR-4 in HCC tissues was significantly higher than that in normal liver tissues; and PAR-4 interacted with STAT3. KEGG analysis showed that PAR-4 plays a role in the Janus kinase(JAK)/STAT signaling pathway. The positive expression rate of PAR-4 in HCC tissues was significantly higher than that in adjacent tissues. Positive correlation between IL-6 and PAR-4 expression in the HCC tissues. Exogenous IL-6 significantly promoted the proliferation and migration of HCC cells and up-regulated the expression of PAR-4 and p-STAT3 in HCC cells. Interference of the expression of PAR-4 could reduce the malignant behaviors of HCC cells and inhibit tumorigenesis in a nude mouse tumor model.

CONCLUSIONS

PAR-4 expression is positively correlated with HCC; PAR-4 promotes malignant behavior of HCC cells mediated by the IL-6/STAT3 signaling pathway.

The regulatory mechanisms and inhibitors of isocitrate dehydrogenase 1 in cancer

Reprogramming of energy metabolism is one of the basic characteristics of cancer and has been proved to be an important cancer treatment strategy. Isocitrate dehydrogenases (IDHs) are a class of key proteins in energy metabolism, including IDH1, IDH2, and IDH3, which are involved in the oxidative decarboxylation of isocitrate to yield α-ketoglutarate (α-KG). Mutants of IDH1 or IDH2 can produce d-2-hydroxyglutarate (D-2HG) with α-KG as the substrate, and then mediate the occurrence and development of cancer. At present, no IDH3 mutation has been reported. The results of pan-cancer research showed that IDH1 has a higher mutation frequency and involves more cancer types than IDH2, implying IDH1 as a promising anti-cancer target. Therefore, in this review, we summarized the regulatory mechanisms of IDH1 on cancer from four aspects: metabolic reprogramming, epigenetics, immune microenvironment, and phenotypic changes, which will provide guidance for the understanding of IDH1 and exploring leading-edge targeted treatment strategies. In addition, we also reviewed available IDH1 inhibitors so far. The detailed clinical trial results and diverse structures of preclinical candidates illustrated here will provide a deep insight into the research for the treatment of IDH1-related cancers.

Expression of PAWR predicts prognosis of ovarian cancer

Background

Ovarian cancer greatly threatens the general health of women worldwide. Implementation of predictive prognostic biomarkers aids in ovarian cancer management.

Methods

Using online databases, the general expression profile, target-disease associations, and interaction network of PAWR were explored. To identify the role of PAWR in ovarian cancer, gene correlation analysis, survival analysis, and combined analysis of drug responsiveness and PAWR expression were performed. The predictive prognostic value of PAWR was further validated in clinical samples.

Results

PAWR was widely expressed in normal and cancer tissues, with decreased expression in ovarian cancer tissues compared with normal tissues. PAWR was associated with various cancers including ovarian cancer. PAWR formed a regulatory network with a group of proteins and correlated with several genes, which were both implicated in ovarian cancer and drug responsiveness. High PAWR expression denoted better survival in ovarian cancer patients (OS: HR = 0.84, P = 0.0077; PFS, HR = 0.86, P = 0.049). Expression of PAWR could predict platinum responsiveness in ovarian cancer and there was a positive correlation between PAWR gene effect and paclitaxel sensitivity. In 12 paired clinical samples, the cancerous tissues exhibited significantly lower PAWR expression than matched normal fallopian tubes. The predictive prognostic value of PAWR was maintained in a cohort of 50 ovarian cancer patients.

Conclusions

High PAWR expression indicated better survival and higher drug responsiveness in ovarian cancer patients. PAWR could be exploited as a predictive prognostic biomarker in ovarian cancer.

Potential Therapeutic Agents Against Par-4 Target for Cancer Treatment: Where Are We Going?

One of the greatest challenges of cancer therapeutics nowadays is to find selective targets successfully. Prostate apoptosis response-4 (Par-4) is a selective tumor suppressor protein with an interesting therapeutic potential due to its specificity on inducing apoptosis in cancer cells. Par-4 activity and levels can be downregulated in several tumors and cancer cell types, indicating poor prognosis and treatment resistance. Efforts to increase Par-4 expression levels have been studied, including its use as a therapeutic protein by transfection with adenoviral vectors or plasmids. However, gene therapy is very complex and still presents many hurdles to be overcome. We decided to review molecules and drugs with the capacity to upregulate Par-4 and, thereby, be an alternative to reach this druggable target. In addition, Par-4 localization and function are reviewed in some cancers, clarifying how it can be used as a therapeutic target.

PAR-4 overcomes chemo-resistance in breast cancer cells by antagonizing cIAP1

Most deaths from breast cancer result from tumour recurrence, which is typically an incurable disease. Down-regulation of the pro-apoptotic tumour suppressor protein prostate apoptosis response-4 (PAR-4) is required for breast cancer recurrence and resistance to chemotherapy. Recent advances in the analysis of apoptotic signalling networks have uncovered an important role for activation of caspase-8 following DNA damage by genotoxic drugs. DNA damage induces depletion of IAP proteins and causes caspase-8 activation by promoting the formation of a cytosolic cell death complex. We demonstrate that loss of PAR-4 in triple negative breast cancer cell lines (TNBC) mediates resistance to DNA damage-induced apoptosis and prevents activation of caspase-8. Moreover, loss of PAR-4 prevents DNA damage-induced cIAP1 depletion. PAR-4 functions downstream of caspase-8 by cleavage-induced nuclear translocation of the C-terminal part and we demonstrate that nuclear translocation of the C-terminal PAR-4 fragment leads to depletion of cIAP1 and subsequent caspase-8 activation. Specifically targeting cIAP1 with RNAi or Smac mimetics (LCL161) overcomes chemo-resistance induced by loss of PAR-4 and restores caspase-8 activation. Our data identify cIAP1 as important downstream mediator of PAR-4 and we provide evidence that combining Smac mimetics and genotoxic drugs creates vulnerability for synthetic lethality in TNBC cells lacking PAR-4.

TNF-α and IFN-γ Together Up-Regulates Par-4 Expression and Induce Apoptosis in Human Neuroblastomas

The objective of this study was to examine the combined effect of Interferon-gamma (IFN-γ) and Tumor Necrosis factor-alpha (TNF-α) on cytotoxicity and expression of prostate apoptosis response-4 (Par-4) and Par-4 interacting proteins B-cell lymphoma (Bcl-2), nuclear factor kappa-light-chain-enhancer of activated B cells/p65 subunit (NF-κB/p65), Ak mouse strain thymoma (Akt) in human neuroblastoma (NB) cells. Materials and methods included human neuroblastoma cell lines-SK-N-MC, SK-N-SH, and SH-SY5Y, which were treated with IFN-γ and TNF-α individually, or in combination, and were assessed for viability by tetrazolium (MTT) assay. Apoptosis was monitored by hypodiploid population (by flow cytometry), DNA fragmentation, Poly (ADP-ribose) polymerase (PARP) cleavage, and caspase-8 activity. Transcript level of Par-4 was measured by RT-PCR. Protein levels of Par-4 and suppressor of cytokine signaling 3 (SOCS-3) were assessed by immunoblotting. Cellular localization of Par-4 and p65 was examined by immunofluorescence. Unbiased transcript analysis for IFN-γ, TNF-α, and Par-4 were analyzed from three independent clinical datasets from neuroblastoma patients. In terms of results, SK-N-MC cells treated with a combination of, but not individually with, IFN-γ and TNF-α induced apoptosis characterized by hypodiploidy, DNA fragmentation, PARP cleavage, and increased caspase-8 activity. Apoptosis was associated with up-regulation of Par-4 mRNA and protein expression. Immunofluorescence studies revealed that Par-4 was localized exclusively in cytoplasm in SK-N-MC cells cultured for 24 h. but showed nuclear localization at 48 h. Treatment with IFN-γ and TNF-α together enhanced the intensity of nuclear Par-4. In gene expression, data from human neuroblastoma patients, levels of IFN-γ, and TNF-α have strong synergy with Par-4 expression and provide good survival advantage. The findings also demonstrated that apoptosis was associated with reduced level of pro-survival proteins–Bcl-2 and Akt and NF-κB/p65. Furthermore, the apoptotic effect induced by IFN-γ-induced Signal Transducer and Activator of Transcription-1(STAT-1), and could be due to down-regulation of suppressor of cytokine signaling-3 (SOCS3). The study concludes that a combinatorial approach using IFN-γ and TNF-α can be explored to maximize the effect in chemotherapy in neuroblastoma, and implies a role for Par-4 in the process.

The Role of Prostate Apoptosis Response-4 (Par-4) in Mycobacterium tuberculosis Infected Macrophages

Prostate apoptosis response-4 (Par-4) is a tumor suppressor protein that forms a complex with glucose-regulated protein 78 (GRP78) to induce apoptosis. Previously, we reported that ER stress-induced apoptosis is a critical host defense mechanism against Mycobacterium tuberculosis (Mtb). We sought to understand the role of Par-4 during ER stress-induced apoptosis in response to mycobacterial infection. Par-4 and GRP78 protein levels increased in response Mtb (strain: H37Ra) infection. Furthermore, Par-4 and GRP78 translocate to the surface of Mtb H37Ra-infected macrophages and induce apoptosis via caspase activation. NF-κB activation, Mtb-mediated ER stress, and Par-4 production were significantly diminished in macrophages with inhibited ROS production. To test Par-4 function during mycobacterial infection, we analyzed intracellular survival of Mtb H37Ra in macrophages with Par-4 overexpression or knockdown. Mtb H37Ra growth was significantly reduced in Par-4 overexpressing macrophages and increased in knockdown macrophages. We also observed increased Par-4, GRP78, and caspases activation in Bacillus Calmette-Guérin (BCG)-infected prostate cancer cells. Our data demonstrate that Par-4 is associated with ER stress-induced apoptosis resulting in reduced intracellular survival of mycobacteria. BCG treatment increases Par-4-dependent caspase activation in prostate cancer cells. These results suggest ER stress-induced Par-4 acts as an important defense mechanism against mycobacterial infection and regulates cancer.

Post-translational regulation of the cleaved fragment of Par-4 in ovarian and endometrial cancer cells

We recently reported the caspase3-dependent cleavage of Par-4 resulting in the accumulation of a 25kDa cleaved-Par-4 (cl-Par-4) fragment and we investigated in the present study the mechanisms regulating this fragment using cl-Par-4-expressing stable clones derived from ovarian and endometrial cancer cell lines.Cl-Par-4 protein was weakly express in all stable clones despite constitutive expression. However, upon cisplatin treatment, cl-Par-4 levels increased up to 50-fold relative to baseline conditions. Treatment of stable clones with proteasome and translation inhibitors revealed that cisplatin exposure might in fact protect cl-Par-4 from proteasome-dependent degradation. PI3K and MAPK pathways were also implicated as evidenced by an increase of cl-Par-4 in the presence of PI3K inhibitors and a decrease using MAPK inhibitors. Finally using bioinformatics resources, we found diverse datasets showing similar results to those we observed with the proteasome and cl-Par-4 further supporting our data.These new findings add to the complex mechanisms regulating Par-4 expression and activity, and justify further studies addressing the biological significance of this phenomenon in gynaecological cancer cells.

The tumor suppressor prostate apoptosis response-4 (Par-4) is regulated by mutant IDH1 and kills glioma stem cells

Prostate apoptosis response-4 (Par-4) is an endogenous tumor suppressor that selectively induces apoptosis in a variety of cancers. Although it has been the subject of intensive research in other cancers, less is known about its significance in gliomas, including whether it is regulated by key driver mutations, has therapeutic potential against glioma stem cells (GSCs), and/or is a prognostic marker. We found that patient-derived gliomas with mutant isocitrate dehydrogenase 1 have markedly lower Par-4 expression (P < 0.0001), which was validated by The Cancer Genome Atlas dataset (P = 2.0 E-13). The metabolic product of mutant IDH1, D-2-hydroxyglutarate (2-HG), can suppress Par-4 transcription in vitro via inhibition of promoter activity as well as enhanced mRNA degradation, but interestingly not by direct DNA promoter hypermethylation. The Selective for Apoptosis induction in Cancer cells (SAC) domain within Par-4 is highly active against glioma cells, including orthotopic xenografts of patient-derived primary GSCs (P < 0.0001). Among high-grade gliomas that are IDH1 wild type, those that express more Par-4 have significantly longer median survival (18.4 vs. 8.0 months, P = 0.002), a finding confirmed in two external GBM cohorts. Together, these data suggest that Par-4 is a significant component of the mutant IDH1 phenotype, that the activity of 2-HG is complex and can extend beyond direct DNA hypermethylation, and that Par-4 is a promising therapeutic strategy against GSCs. Furthermore, not every effect of mutant IDH1 necessarily contributes to the overall favorable prognosis seen in such tumors; inhibition of Par-4 may be one such effect.

Prostate apoptosis response-4 mediates TGF-β-induced epithelial-to-mesenchymal transition

A growing body of evidence supports that the epithelial-to-mesenchymal transition (EMT), which occurs during cancer development and progression, has a crucial role in metastasis by enhancing the motility of tumor cells. Transforming growth factor-β (TGF-β) is known to induce EMT in a number of cancer cell types; however, the mechanism underlying this transition process is not fully understood. In this study we have demonstrated that TGF-β upregulates the expression of tumor suppressor protein Par-4 (prostate apoptosis response-4) concomitant with the induction of EMT. Mechanistic investigations revealed that exogenous treatment with each TGF-β isoform upregulates Par-4 mRNA and protein levels in parallel levels of phosphorylated Smad2 and IκB-α increase. Disruption of TGF-β signaling by using ALK5 inhibitor, neutralizing TGF-β antibody or phosphoinositide 3-kinase inhibitor reduces endogenous Par-4 levels, suggesting that both Smad and NF-κB pathways are involved in TGF-β-mediated Par-4 upregulation. NF-κB-binding sites in Par-4 promoter have previously been reported; however, using chromatin immunoprecipitation assay we showed that Par-4 promoter region also contains Smad4-binding site. Furthermore, TGF-β promotes nuclear localization of Par-4. Prolonged TGF-β3 treatment disrupts epithelial cell morphology, promotes cell motility and induces upregulation of Snail, vimentin, zinc-finger E-box binding homeobox 1 and N-Cadherin and downregulation of Claudin-1 and E-Cadherin. Forced expression of Par-4, results in the upregulation of vimentin and Snail expression together with increase in cell migration. In contrast, small interfering RNA-mediated silencing of Par-4 expression results in decrease of vimentin and Snail expression and prevents TGF-β-induced EMT. We have also uncovered a role of X-linked inhibitor of apoptosis protein in the regulation of endogenous Par-4 levels through inhibition of caspase-mediated cleavage. In conclusion, our findings suggest that Par-4 is a novel and essential downstream target of TGF-β signaling and acts as an important factor during TGF-β-induced EMT.