The Tumor Suppressor Activity of MDA-7/IL-24 Is Mediated by Intracellular Protein Expression in NSCLC Cells

PIKFYVE inhibitors trigger interleukin-24-dependent cell death of autophagy-dependent melanoma

Inhibitors specifically targeting the 1-phosphatidylinositol 3-phosphate 5-kinase (PIKFYVE) disrupt lysosome homeostasis, thereby selectively terminating autophagy-dependent human cancer cells in vivo as well as in vitro without harming the viability of nonmalignant cells. To elucidate the mechanism by which PIKFYVE inhibition induces cell death, autophagy-dependent melanoma cells were compared with normal foreskin fibroblasts. RNA sequence profiling suggested that PIKFYVE inhibitors upregulated an endoplasmic reticulum (ER) stress response involving interleukin-24 (IL24; also known as MDA7) selectively in melanoma cells. Subsequent biochemical and genetic analyses confirmed these results and extended them to tumor xenografts in which tumor formation and expansion were inhibited. IL24 expression was upregulated by the DDIT3/CHOP/CEBPz transcription factor, a component of the PERK-dependent ER-stress response. Ectopic expression of IL24-induced cell death in melanoma cells, but not in foreskin fibroblasts, whereas ablation of the IL24 gene in melanoma cells prevented death. IL24 upregulation was triggered specifically by PIKFYVE inhibition. Thus, unlike thapsigargin and tunicamycin, which induce ER-stress indiscriminately, PIKFYVE inhibitors selectively terminated PIKFYVE-sensitive melanoma by inducing IL24-dependent ER-stress. Moreover, induction of cell death by a PIKFYVE inhibitor together with ectopic expression of IL24 protein was cumulative, thereby confirming the therapeutic potential of PIKFYVE inhibitors in the treatment of melanoma.

IL-24 is the key effector of Th9 cell-mediated tumor immunotherapy

Th9 cells are powerful effector T cells for cancer immunotherapy. However, the underlying antitumor mechanism of Th9 cells still needs to be further elucidated. Here, we show that Th9 cells express high levels of not only IL-9, but also IL-24. We found that knockout of Il24 gene in Th9 cells promotes Th9 cell proliferation in vitro, but decreases Th9 cell survival in vitro and in vivo. Interestingly, knockout of Il24 gene in Th9 cells decreases the tumor-specific cytotoxicity of Th9 cells in vitro. In addition, immunotherapy with Il24 knockout Th9 cells exhibit less tumor inhibition than regular Th9 cells in mouse tumor models. We found that inhibition of Foxo1 by a specific inhibitor downregulates IL-24 expression in Th9 cells and decreases Th9 cell antitumor efficacy in vivo. Our results identify IL-24 as a powerful antitumor effector of Th9 cells and provide a target in Th9 cell-mediated tumor therapy.

Interleukin 24: Signal Transduction Pathways

Interleukin 24 is a member of the IL-10 family with crucial roles in antitumor, wound healing responses, host defense, immune regulation, and inflammation. Interleukin 24 is produced by both immune and nonimmune cells. Its canonical pathway relies on recognition and interaction with specific Interleukin 20 receptors in the plasma membrane and subsequent cytoplasmic Janus protein tyrosine kinases (JAK)/signal transducer and activator of the transcription (STAT) activation. The identification of noncanonical JAK/STAT-independent signaling pathways downstream of IL-24 relies on the interaction of IL-24 with protein kinase R in the cytosol, respiratory chain proteins in the inner mitochondrial membrane, and chaperones such as Sigma 1 Receptor in the endoplasmic reticulum. Numerous studies have shown that enhancing or inhibiting the expression of Interleukin 24 has a therapeutic effect in animal models and clinical trials in different pathologies. Successful drug targeting will require a deeper understanding of the downstream signaling pathways. In this review, we discuss the signaling pathway triggered by IL-24.

Emodin inhibits U87 glioblastoma cells migration by activating aryl hydrocarbon receptor (AhR) signaling pathway

Aryl hydrocarbon receptor (AhR) is a ligand-activated receptor to mediates the biological reactions of many environmental and natural compounds, which is highly expressed in glioblastoma. Although it has been reported that AhR agonist emodin can suppress some kinds of tumors, its inhibitory effect on glioblastoma migration and its relationship with AhR remain unclear. Based on the complexity of tumor pathogenesis and the tissue specificity of AhR, we hope can further understand the effect of emodin on glioblastoma and explore its mechanism. We found that the inhibitory effect of emodin on the migration of U87 glioblastoma cells increased with time, and the cell migration ability was inhibited by about 25% after 36 h exposure. In this process, emodin promoted the expression of the tumor suppressor IL24 by activating the AhR signaling pathway. Reducing the expression of AhR or IL24 by interfering RNA could block or relieve the inhibitory effect of emodin on the U87 cells migration, which indicates the inhibition of emodin on the migration of glioblastoma is mediated by the AhR-IL24 axis. Our data proved the AhR-IL24 signal axis is an important pathway for emodin to inhibit the migration of glioblastoma, and the AhR signaling pathway can be used as a key target to research the regulation effect and its mechanism of compounds on glioblastoma migration.

Insights into the Mechanisms of Action of MDA-7/IL-24: A Ubiquitous Cancer-Suppressing Protein

Melanoma differentiation associated gene-7/interleukin-24 (MDA-7/IL-24), a secreted protein of the IL-10 family, was first identified more than two decades ago as a novel gene differentially expressed in terminally differentiating human metastatic melanoma cells. MDA-7/IL-24 functions as a potent tumor suppressor exerting a diverse array of functions including the inhibition of tumor growth, invasion, angiogenesis, and metastasis, and induction of potent "bystander" antitumor activity and synergy with conventional cancer therapeutics. MDA-7/IL-24 induces cancer-specific cell death through apoptosis or toxic autophagy, which was initially established in vitro and in preclinical animal models in vivo and later in a Phase I clinical trial in patients with advanced cancers. This review summarizes the history and our current understanding of the molecular/biological mechanisms of MDA-7/IL-24 action rendering it a potent cancer suppressor.

A new insight into the role of aryl hydrocarbon receptor (AhR) in the migration of glioblastoma by AhR-IL24 axis regulation

Cancer occurrence and development are closely related to the environment. Aryl hydrocarbon receptor (AhR) is an important receptor mediating the toxic effects of many environmental compounds, and is also involved in regulating tumor cell migration. Glioblastoma is the most malignant glioma and exhibits high motility, but the effects of AhR on the migration of glioblastoma are still unclear. We aimed to understand the role of AhR in the migration of this type of tumor cell and to explore the underlying molecular mechanism. In cultured human neuroblastoma cells (U87), we found that AhR overexpression or knockdown increased or suppressed the migration ability of U87 cells, respectively. Furthermore, inhibition of basal activation of the AhR pathway suppressed migration ability, suggesting a positive correlation between endogenous activity of the AhR pathway and cell migration. When the AhR pathway was activated by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or 6-formyl [3,2-b] carbazole (FICZ), the migration of U87 cells was inhibited by inducing the expression of a tumor suppressor, IL24, which is a downstream responsive gene of AhR activation. Moreover, a similar AhR-IL24-dependent mechanism for migration inhibition of TCDD was documented in a breast cancer cell line and a lung cancer cell line. This study demonstrated that AhR plays important roles in regulating the migration of glioblastoma, and the induction of the AhR-IL24 axis mediates the inhibition of migration in response to TCDD or FICZ treatment.

Interleukin (IL)-24: Reconfiguring the Tumor Microenvironment for Eliciting Antitumor Response

Interleukin (IL)-24 is a member of the IL-10 family of cytokines. Due to its unique ability to function as both a tumor suppressor and cytokine, IL-24-based cancer therapy has been developed for treating a broad spectrum of human cancers. Majority of the studies reported to date have focused on establishing IL-24 as a cancer therapeutic by primarily focusing on tumor cell killing. However, the ability of IL-24 treatment on modulating the tumor microenvironment and immune response is underinvestigated. In this article, we summarize the biological and functional properties of IL-24 and the benefits of applying IL-24-based therapy for cancer.

Role of IL-24 in NK cell activation and its clinical implication in systemic lupus erythematosus

OBJECTIVES

Interleukin (IL)-24 has been considered as an inflammatory cytokine in autoimmune diseases. However, conflicting data exist and its biological function remains controversial. Additionally, little is known about its functional impact on natural killer (NK) cells. The aim of this study was to investigate the role of IL-24 in NK cell activation and its clinical implication in systemic lupus erythematosus (SLE).

METHODS

Serum cohort consisting of 299 SLE patients, 214 RA patients, and 159 healthy controls (HCs) and plasma cohort consisting of 70 SLE patients, 82 RA patients, and 123 HCs were included in evaluating IL-24 concentrations. Impact of IL-24 on NK cell activation was assessed in two NK cell subsets, i.e., CD56^dimCD16⁺ and CD56^brightCD16^- NK cells. Human NK-92 cell line was applied to evaluate functional potential of IL-24 on NK cell migration and invasion.

RESULTS

Serum and plasma levels of IL-24 were comparable between patients with SLE or RA and HCs. While recombinant human (rh) IL-2 consistently induced an increased expression of CD69 on both CD56^dimCD16⁺ and CD56^brightCD16^- cells derived from both healthy subjects and patients with SLE, IL-24 alone was insufficient to activate the CD56^dim and CD56^bright NK cells. Similarly, while the migratory NK-92 cell numbers were significantly increased with rhIL-2 stimulation, IL-24 alone was unable to enhance NK-92 cell migratory and invasive capacity.

CONCLUSION

Our data indicate that there were no significant differences in serum and plasma concentrations of IL-24 between SLE patients and healthy controls. Recombinant IL-24 has no effect on NK cell activation and migration. Key points • This is the first study to investigate functional potential of IL-24 on NK cell activation. • Recombinant IL-24 lacks functional capacity on NK cell activation in either CD56^dimCD16⁺ or CD56^brightCD16^- NK cell subsets derived from both healthy subjects and patients with SLE. • No significant differences in serum and plasma levels of IL-24 between SLE patients and healthy controls.

SUMO-fusion and autoinduction-based combinatorial approach for enhanced production of bioactive human interleukin-24 in Escherichia coli

High-level production of recombinant human interleukin-24 (IL-24), a multifunctional immunomodulatory cytokine, has been challenging due primarily to its aggregation as inclusion bodies in the bacterial host while persistent poor-expression in the insect/mammalian expression systems. The present study presents a robust, vector-host combination (pE-SUMO-IL24), auto-inducible medium (YNG/M9NG), and a simple purification scheme for soluble, bioactive, and cost-effective production of native-like IL-24 (nIL-24) in Escherichia coli. The final protein yield, following a three-step purification scheme (IMAC, SEC, dialysis), was 98 mg/L in shake-flask culture (with scale-up potential), which was several folds higher than reported earlier. In vitro cytotoxicity assays with HeLa and HCT116 cancer cell lines (performed using different concentrations of nIL-24) and the fluorescence activated cell sorting analysis (FACS) revealed a dose- and concentration-dependent increase in the population of pro-apoptotic cells with concomitant, statistically significant drop in the number of cells existent at G_o/G1-, S-, and G2/M-phases (P < 0.002). The bioactive nIL-24, developed through this study, holds promise for use in further functional characterizations/applications. KEY POINTS: • Yeast SUMO fusion partner at N-terminus for improved solubility of an otherwise insoluble IL-24 in E. coli. • Enhanced cell densities with concomitant several-fold increase in protein yield by lactose-inducible media. • Improved inhibition of cervical and colorectal carcinomas by native-like nIL-24 compared with Met-containing IL. • Heterologous nIL-24 may enable better understanding of the functional intricacies linked up with its unique cancer-specific features. Graphical abstract.

Modification of IL-24 by tumor penetrating peptide iRGD enhanced its antitumor efficacy against non-small cell lung cancer

Interleukin-24 (IL-24) is known for its tumor suppressive activity and the selective induction of apoptosis of numerous human cancer cells, while demonstrating little harm to normal cells. However, poor tumor penetration remains a key problem for the efficacy of IL-24 as a treatment. The iRGD (CRGDK/RGPDC) is a novel tumor-specific peptide with unique tumor-penetrating and cell-internalizing properties. To enhance the tumor-penetrating effects of IL-24, the iRGD peptide was fused with the C-terminal domain of IL-24 to generate a novel recombinant protein, IL-24-iRGD. The aim of the present study was to investigate the antitumor effects of IL-24-iRGD in non-small cell lung cancer (NSCLC) cells in vitro and in vivo. It was observed that IL-24-iRGD increased the production of IL-6, TNF-α and INF-γ from human peripheral blood monocyte (PBMC), and suppressed cell growth of A549 in vitro. Then A549 cells were subcutaneously injected into nude mice, and these tumor-bearing mice were immunized with IL-24, IL-24-iRGD or PBS via the tail vein. The IL-24 and IL-24-iRGD-treated groups exhibited tumor growth inhibition rates of 26.2% and 59.1%, respectively, when compared with the PBS-treated group. Protein penetration into tumors was analyzed by immunofluorescence, cell apoptosis was examined by TdT-mediated dUTP nick end labeling, and the expression of cleaved caspase-3 was analyzed by immuno-histochemical staining. The results demonstrated that IL-24-iRGD induced apoptosis and inhibited the growth of A549 cells to a significantly greater extent when compared with IL-24 treatment alone. It may provide an improved strategy for antitumor therapy and the clinical treatment of NSCLC.

MDA-7/interleukin 24 (IL-24) in tumor gene therapy: application of tumor penetrating/homing peptides for improvement of the effects

INTRODUCTION

MDA-7/Interleukin-24 (IL-24), as a pleiotropic cytokine, exhibits a specific tumor suppression property that has attracted a great deal of attention. While its anti-tumor induction is mostly attributed to endogenous gene expression, attachment of secreted MDA-7/IL-24 to cognate receptors also triggers the death of cancerous cell via different pathways. Therefore, precise targeting of secreted MDA-7/IL-24 to tumor cells would render it more efficacy and specificity.

AREAS COVERED

In order to target soluble cytokines, particularly MDA-7/IL-24 to the neighbor tumor sites and enhance their therapeutic efficiency, fusing with cell penetrating peptides (CPPs) or Tumor homing peptides (THPs) seems logical due to the improvement of their bystander effects. Although the detailed anti-tumor mechanisms of endogenous mda-7/IL-24 have been largely investigated, the significance of the secreted form in these activities and methods of its improving by CPPs or THPs need more discussion.

EXPERT OPINION

While the employment of CPPs/THPs for the improvement of cytokine gene therapy is desirable, to create fusions of CPPs/THPs with MDA-7/IL-24, some hurdles are not avoidable. Regarding our expertise, herein, the importance of CPPs/THPs, needs for their elegant designing in a fusion structure, and their applications in cytokine gene therapy are discussed with a special focus on mda-7/IL-24.

Role of MDA-7/IL-24 a Multifunction Protein in Human Diseases

Subtraction hybridization identified genes displaying differential expression as metastatic human melanoma cells terminally differentiated and lost tumorigenic properties by treatment with recombinant fibroblast interferon and mezerein. This approach permitted cloning of multiple genes displaying enhanced expression when melanoma cells terminally differentiated, called melanoma differentiation associated (mda) genes. One mda gene, mda-7, has risen to the top of the list based on its relevance to cancer and now inflammation and other pathological states, which based on presence of a secretory sequence, chromosomal location, and an IL-10 signature motif has been named interleukin-24 (MDA-7/IL-24). Discovered in the early 1990s, MDA-7/IL-24 has proven to be a potent, near ubiquitous cancer suppressor gene capable of inducing cancer cell death through apoptosis and toxic autophagy in cancer cells in vitro and in preclinical animal models in vivo. In addition, MDA-7/IL-24 embodied profound anticancer activity in a Phase I/II clinical trial following direct injection with an adenovirus (Ad.mda-7; INGN-241) in tumors in patients with advanced cancers. In multiple independent studies, MDA-7/IL-24 has been implicated in many pathological states involving inflammation and may play a role in inflammatory bowel disease, psoriasis, cardiovascular disease, rheumatoid arthritis, tuberculosis, and viral infection. This review provides an up-to-date review on the multifunctional gene mda-7/IL-24, which may hold potential for the therapy of not only cancer, but also other pathological states.

Long intergenic non-coding RNA 00152 promotes lung adenocarcinoma proliferation via interacting with EZH2 and repressing IL24 expression

BACKGROUND

Numerous studies have shown that long non-coding RNAs (lncRNAs) behave as a novel class of transcript during multiple cancer processes, such as cell proliferation, apoptosis, migration, and invasion. LINC00152 is located on chromosome 2p11.2, and has a transcript length of 828 nucleotides. The biological role of LINC00152 in LAD(lung adenocarcinoma) remains unknown.

METHODS

Quantitative reverse transcription PCR(qRT-PCR) was used to detect LINC00152 expression in 60 human LAD tissues and paired normal tissues. In vitro and in vivo studies showed the biological function of LINC00152 in tumour progression. RNA transcriptome sequencing technology was performed to identify the downstream suppressor IL24(interleukin 24) which was further examined by qRT-PCR, western bolt and rescue experiments. RNA immunoprecipitation (RIP), RNA pulldown, and Chromatin immunoprecipitation (ChIP) assays were carried out to reveal the interaction between LINC00152, EZH2 and IL24.

RESULTS

LINC00152 expression was upregulated in 60 human LAD tissues and paired normal tissues. High levels of LINC00152 expression were correlated with advanced TNM stage, larger tumor size, and lymph node metastasis, as well as shorter survival time. Silencing of LINC00152 suppressed cell growth and induced cell apoptosis. LINC00152 knockdown altered the expression of many downstream genes, including IL24. LINC00152 could interact with EZH2 and inhibit IL24 transcription. Moreover, the ectopic expression of IL24 repressed cell proliferation and partly reversed LINC00152 overexpression-induced promotion of cell growth in LAD.

CONCLUSIONS

Our study reveals an oncogenic role for LINC00152 in LAD tumorigenesis, suggesting that it could be used as a therapeutic target in LAD treatment.

RNA-binding protein CELF1 promotes tumor growth and alters gene expression in oral squamous cell carcinoma

The RNA binding protein CELF1 (also known as CUGBP1) is emerging as a critical regulator of cancer cell proliferation and apoptosis. Here, to provide a global prospective of CELF1 regulation of oral squamous cell carcinoma, we performed RNA-sequencing in oral cancer cells and CELF1 overexpression analysis in non-malignant human oral keratinocytes. Our approaches identified 1283 mRNAs differentially regulated as a function of CELF1 expression and more importantly CELF1 promoted alternative splicing of several target pre-mRNAs, which are known to be involved in various cancer biological processes. Overexpression of CELF1 in non-malignant human oral keratinocytes protected cells against oxidative damage and altered gene expression patterns. Finally, we provide evidence that reduction of CELF1 protein using a xenograft tumorigenesis mouse model decreased tumor growth. Altogether, these data provided a comprehensive view of the CELF1 mRNA regulatory network in oral cancer and suggests that CELF1 and/or its target mRNAs are viable candidates for therapeutic intervention.

Melanoma Differentiation-associated Gene 7/IL-24 Exerts Cytotoxic Effects by Altering the Alternative Splicing of Bcl-x Pre-mRNA via the SRC/PKCδ Signaling Axis

Melanoma differentiation-associated gene 7 (MDA-7/IL-24) exhibits cytotoxic effects on tumor cells while sparing untransformed cells, and Bcl-x(L) is reported to efficiently block the induction of cell death by MDA-7/IL-24. The expression of Bcl-x(L) is regulated at the level of RNA splicing via alternative 5' splice site selection within exon 2 to produce either the pro-apoptotic Bcl-x(s) or the anti-apoptotic Bcl-x(L). Our laboratory previously reported that Bcl-x RNA splicing is dysregulated in a large percentage of human non-small cell lung cancer (NSCLC) tumors. Therefore, we investigated whether the alternative RNA splicing of Bcl-x pre-mRNA was modulated by MDA-7/IL-24, which would suggest that specific NSCLC tumors are valid targets for this cytokine therapy. Adenovirus-delivered MDA-7/IL-24 (Ad.mda-7) reduced the viability of NSCLC cells of varying oncogenotypes, which was preceded by a decrease in the ratio of Bcl-x(L)/Bcl-x(s) mRNA and Bcl-x(L) protein expression. Importantly, both the expression of Bcl-x(L) and the loss of cell viability were "rescued" in Ad.mda-7-treated cells incubated with Bcl-x(s) siRNA. In addition, NSCLC cells ectopically expressing Bcl-x(s) exhibited significantly reduced Bcl-x(L) expression, which was again restored by Bcl-x(s) siRNA, suggesting the existence of a novel mechanism by which Bcl-x(s) mRNA restrains the expression of Bcl-x(L). In additional mechanistic studies, inhibition of SRC and PKCδ completely ablated the ability of MDA-7/IL-24 to reduce the Bcl-x(L)/(s) mRNA ratio and cell viability. These findings show that Bcl-x(s) expression is an important mediator of MDA-7/IL-24-induced cytotoxicity requiring the SRC/PKCδ signaling axis in NSCLC cells.

Phosphorylation of interleukin (IL)-24 is required for mediating its anti-cancer activity

Interleukin (IL)-24 is a tumor suppressor/cytokine gene that undergoes post-translational modifications (PTMs). Glycosylation and ubiquitination are important for IL-24 protein stabilization and degradation respectively. Little is known about IL-24 protein phosphorylation and its role in IL-24-mediated anti-tumor activities. In this study we conducted molecular studies to determine whether IL-24 phosphorylation is important for IL-24-mediated anti-cancer activity.

Human H1299 lung tumor cell line that was stably transfected with a doxycycline (DOX)-inducible (Tet-on) plasmid vector carrying the cDNA of IL-24-wild-type (IL-24^wt) or IL-24 with all five phosphorylation sites replaced (IL-24^mt) was used in the present study. Inhibition of tumor cell proliferation, cell migration and invasion, and induction of G2/M cell cycle arrest was observed in DOX-induced IL-24^wt-expressing cells but not in IL-24^mt-expressing cells. Secretion of IL-24^mt protein was greatly reduced compared to IL-24^wt protein. Further, IL-24^wt and IL-24^mt proteins markedly differed in their subcellular organelle localization. IL-24^wt but not IL-24^mt inhibited the AKT/mTOR signaling pathway. SiRNA-mediated AKT knockdown and overexpression of myristolyated AKT protein confirmed that IL-24^wt but not IL-24^mt mediated its anti-cancer activity by inhibiting the AKT signaling pathway.

Our results demonstrate that IL-24 phosphorylation is required for inhibiting the AKT/mTOR signaling pathway and exerting its anti-cancer activities.

Indications for distinct pathogenic mechanisms of asbestos and silica through gene expression profiling of the response of lung epithelial cells

Occupational and environmental exposures to airborne asbestos and silica are associated with the development of lung fibrosis in the forms of asbestosis and silicosis, respectively. However, both diseases display distinct pathologic presentations, likely associated with differences in gene expression induced by different mineral structures, composition and bio-persistent properties. We hypothesized that effects of mineral exposure in the airway epithelium may dictate deviating molecular events that may explain the different pathologies of asbestosis versus silicosis. Using robust gene expression-profiling in conjunction with in-depth pathway analysis, we assessed early (24 h) alterations in gene expression associated with crocidolite asbestos or cristobalite silica exposures in primary human bronchial epithelial cells (NHBEs). Observations were confirmed in an immortalized line (BEAS-2B) by QRT-PCR and protein assays. Utilization of overall gene expression, unsupervised hierarchical cluster analysis and integrated pathway analysis revealed gene alterations that were common to both minerals or unique to either mineral. Our findings reveal that both minerals had potent effects on genes governing cell adhesion/migration, inflammation, and cellular stress, key features of fibrosis. Asbestos exposure was most specifically associated with aberrant cell proliferation and carcinogenesis, whereas silica exposure was highly associated with additional inflammatory responses, as well as pattern recognition, and fibrogenesis. These findings illustrate the use of gene-profiling as a means to determine early molecular events that may dictate pathological processes induced by exogenous cellular insults. In addition, it is a useful approach for predicting the pathogenicity of potentially harmful materials.

The role of the IL-22/IL-22R1 axis in cancer

Interleukin-22 (IL-22) is an IL-10 family cytokine produced by T cells and innate lymphoid cells. The IL-22 signaling pathway orchestrates mucosal immune defense and tissue regeneration through pleiotropic effects including pro-survival signaling, cell migration, dysplasia and angiogenesis. While these functions can prevent initial establishment of tumors, they can also be hijacked by aggressive cancers to enhance tumor growth and metastasis. Thus, the role of the IL-22/IL-22R1 axis in cancer is complex and context-specific. Evidence of IL-22 involvement manifests as dysregulation of IL-22 expression and signaling in patients with many common cancers including those of the gut, skin, lung and liver. Unlike other cancer-associated cytokines, IL-22 has restricted tissue specificity as its unique receptor IL-22R1 is exclusively expressed on epithelial and tissue cells, but not immune cells. This makes it an attractive target for therapy as there is potential achieve anti-tumor immunity with fewer side effects. This review summarizes current findings on functions of IL-22 in association with general mechanisms for tumorigenesis as well as specific contributions to particular cancers, and ponders how best to approach further research in the field.

Molecular targets and signaling pathways regulated by interleukin (IL)-24 in mediating its antitumor activities

Cancer remains a major health issue in the world and the effectiveness of current therapies is limited resulting in disease recurrence and resistance to therapy. Therefore to overcome disease recurrence and have improved treatment efficacy there is a continued effort to develop and test new anticancer drugs that are natural or synthetic - (conventional chemotherapeutics, small molecule inhibitors) and biologic (antibody, tumor suppressor genes, oligonucleotide) product. In parallel, efforts for identifying molecular targets and signaling pathways to which cancer cells are "addicted" are underway. By inhibiting critical signaling pathways that is crucial for cancer cell survival, it is expected that the cancer cells will undergo a withdrawal symptom akin to "de-addiction" resulting in cell death. Thus, the key for having an improved and greater control on tumor growth and metastasis is to develop a therapeutic that is able to kill tumor cells efficiently by modulating critical signaling pathways on which cancer cells rely for their survival.Currently several small molecule inhibitors targeted towards unique molecular signaling pathways have been developed and tested in the clinic. Few of these inhibitors have shown efficacy while others have failed. Thus, targeting a single molecule or pathway may be insufficient to completely block cancer cell proliferation and survival. It is therefore important to identify and test an anticancer drug that can inhibit multiple signaling pathways in a cancer cell, control growth of both primary and metastatic tumors and is safe.One biologic agent that has the characteristics of serving as a potent anticancer drug is interleukin (IL)-24. IL-24 suppresses multiple signaling pathways in a broad-spectrum of human cancer cells leading to tumor cell death, inhibition of tumor angiogenesis and metastasis. Additionally, combining IL-24 with other therapies demonstrated additive to synergistic antitumor activity. Clinical testing of IL-24 as a gene-based therapeutic for the treatment of solid tumors demonstrated that IL-24 is efficacious and is safe. The unique features of IL-24 support its further development as an anticancer drug for cancer treatment.In this review we summarize the current understanding on the molecular targets and signaling pathways regulated by IL-24 in mediating its anticancer activity.

IL-24 sensitizes tumor cells to TLR3-mediated apoptosis

Interleukin-24 (IL-24), a member of the IL-10 cytokine family whose physiological function remains largely unknown, has been shown to induce apoptosis when expressed in an adenoviral background. It is yet little understood, why IL-24 alone induced apoptosis only in a limited number of tumor cell lines. Analyzing an influenza A virus vector expressing IL-24 for its oncolytic potential revealed enhanced pro-apoptotic activity of the chimeric virus compared with virus or IL-24 alone. Interestingly, IL-24-mediated enhancement of influenza-A-induced apoptosis did not require viral replication but critically depended on toll-like receptor 3 (TLR3) and caspase-8. Immunoprecipitation of TLR3 showed that infection by influenza A virus induced formation of a TLR3-associated signaling complex containing TRIF, RIP1, FADD, cFLIP and pro-caspase-8. Co-administration of IL-24 decreased the presence of cFLIP in the TLR3-associated complex, converting it into an atypical, TLR3-associated death-inducing signaling complex (TLR3 DISC) that induced apoptosis by enabling caspase-8 activation at this complex. The sensitizing effect of IL-24 on TLR3-induced apoptosis, mediated by influenza A virus or the TLR3-specific agonist poly(I:C), was also evident on tumor spheroids. In conclusion, rather than acting as an apoptosis inducer itself, IL-24 sensitizes cancer cells to TLR-mediated apoptosis by enabling the formation of an atypical DISC which, in the case of influenza A virus or poly(I:C), is associated with TLR3.

Molecular Mechanisms Governing IL-24 Gene Expression

Interleukin-24 (IL-24) belongs to the IL-10 family of cytokines and is well known for its tumor suppressor activity. This cytokine is released by both immune and nonimmune cells and acts on non-hematopoietic tissues such as skin, lung and reproductive tissues. Apart from its ubiquitous tumor suppressor function, IL-24 is also known to be involved in the immunopathology of autoimmune diseases like psoriasis and rheumatoid arthritis. Although the cellular sources and functions of IL-24 are being increasingly investigated, the molecular mechanisms of IL-24 gene expression at the levels of signal transduction, epigenetics and transcription factor binding are still unclear. Understanding the specific molecular events that regulate the production of IL-24 will help to answer the remaining questions that are important for the design of new strategies of immune intervention involving IL-24. Herein, we briefly review the signaling pathways and transcription factors that facilitate, induce, or repress production of this cytokine along with the cellular sources and functions of IL-24.

Enhanced apoptosis-inducing function of MDA-7/IL-24 RGD mutant via the increased adhesion to tumor cells

Melanoma differentiation-associated gene-7 (mda-7)/interleukin-24 (IL-24) has shown potent tumor cell apoptosis inducing capacity in multiple cancers. However, the apoptosis induction capacity of mda-7/IL-24 was low and directly correlated with the adhesion to tumor cells.Cell adhesion molecule integrin α(v)β(3) expressed on the surface of several types of solid tumor cells, and they bind to arginine-glycine-aspartic acid (RGD) which enhanced the adhesion to tumor cells. This rout was exploited to construct a tumor-targeting gene RGD-IL-24 which can express RGD-MDA-7/IL-24 protein that includes the cell adhesive sequence (164)Arg-(165)Gly-(166)Asp (A Glycine residue was inserted into the recombinant MDA-7/IL-24 between Arg164 and Asp165 to form a RGD motif). We successfully got the MDA-7/IL-24 mutant by overlapping polymerase chain reaction (PCR) and evaluated its therapeutic efficacy for tumor cell lines MCF-7, HeLa, HepG2, and normal human lung fibroblast (NHLF) line. And we found that the expression of pCDNA3.1/RGD-IL-24 was same to the expression of pCDNA3.1/IL-24. The RGD-IL-24 enhanced the apoptosis-inducing function in tumor cells, but not in normal cells. In tumor cell lines, the apoptosis-inducing activities of RGD-IL-24 was significantly higher than IL-24 detecting by MTT assay, Annexin V, and Hoechst 33258 analysis. Further, pCDNA3.1/RGD-IL-24 showed a significant increase in the ratio of pro-apoptotic (bax) to anti-apoptotic (bcl-2) proteins in tumor cell lines, but not in NHLF cell line. Together, these results suggest that RGD-IL-24 can enhance the apoptosis of tumor cells and may provide a promising drug in tumor therapy.

mda-7/IL-24: a unique member of the IL-10 gene family promoting cancer-targeted toxicity

Melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) is a unique member of the IL-10 gene family that displays nearly ubiquitous cancer-specific toxicity, with no harmful effects toward normal cells or tissues. mda-7/IL-24 was cloned from human melanoma cells by differentiation induction subtraction hybridization (DISH) and promotes endoplasmic reticulum (ER) stress culminating in apoptosis or toxic autophagy in a broad-spectrum of human cancers, when assayed in cell culture, in vivo in human tumor xenograft mouse models and in a Phase I clinical trial in patients with advanced cancers. This therapeutically active cytokine also induces indirect antitumor activity through inhibition of angiogenesis, stimulation of an antitumor immune response, and sensitization of cancer cells to radiation-, chemotherapy- and antibody-induced killing.

Recombinant adenovirus IL-24-Bax promotes apoptosis of hepatocellular carcinoma cells in vitro and in vivo

Gene therapy promises to become an alternative choice for the treatment of hepatic cancer. In many cancers, the delivery of chimeric proteins by adenovirus vector has been reported to induce apoptosis. This study was performed to evaluate whether the recombinant adenovirus interleukin (IL)-24-Bax can induce apoptosis in hepatocellular carcinoma cells in vitro and in vivo. Several recombinant adenoviruses were constructed, and the expression of their encoded proteins was measured. The effects of the recombinant adenovirus on hepatocellular carcinoma cells and the normal hepatocyte cell line were investigated through cell viability and apoptosis assays after the cells were treated with Ad.Luc, Ad.IL-24, Ad.Bax or Ad.IL-24-Bax. The mechanism involved was also explored. A tumor-bearing mouse model was used to evaluate the effects of the adenovirus on tumor volume and cell apoptosis in vivo. Ad.IL-24-Bax selectively suppressed growth of hepatocellular carcinoma cells and induced apoptosis, but it had little influence on the normal hepatocytes. The mechanism of this response may include the effect of the 10HRE/VEGF385 promoter and the synergistic effect of IL-24 and Bax. Ad.IL-24-Bax also suppressed tumor growth in nude mice and induced apoptosis. Ad.IL-24-Bax may be a useful tool for gene therapy of hepatic cancer.

Down-regulation of BiP/GRP78 sensitizes resistant prostate cancer cells to gene-therapeutic overexpression of REIC/Dkk-3

We have recently shown that an adenovirus carrying REIC/Dkk-3 (Ad-REIC) exhibits a potent tumor-specific cell-killing function for various human cancers. It has also become evident that some human cancers are resistant to Ad-REIC-induced apoptosis. The aim of the present study was to determine the molecular mechanisms of resistance to Ad-REIC. First, we isolated resistant clones from a human prostate cancer cell line, PC3, after repeated exposure to Ad-REIC. Infection efficiency of the adenovirus vector and expression level of REIC/Dkk-3 in the resistant clones were similar to those in the parental PC3 cells. By screening for alteration in levels and functional status of proteins involved in Ad-REIC-induced apoptosis, we found that BiP/GRP78, an ER-residing chaperone protein, was expressed at higher levels consistently among resistant cells. Expression levels of BiP and rates of apoptosis induced by Ad-REIC were inversely correlated. Down-regulation of BiP with siRNA sensitized the resistant cells to Ad-REIC in vivo as well as in culture. These results indicate that BiP is a major determinant of resistance to Ad-REIC-induced apoptosis. Thus BiP is useful for diagnosis of inherent and acquired resistance of cancers and also as a target molecule to overcome resistance to the gene therapeutic Ad-REIC.

Induction of cytokine gene expression in human thyroid epithelial cells irradiated with HZE particles (iron ions)

Gene expression profiles were examined using cDNA microarray technology in human thyroid epithelial (Htori-3) cells exposed to a low, non-toxic dose (10 cGy) of radiation from HZE particles in the form of iron ions in the absence or presence of selenomethionine (SeM). A total of 215 genes were differentially regulated 2 h after exposure to a 10-cGy dose of iron-ion radiation. In the microarray analysis, SeM had profound effects on the radiation-induced expression of several specific genes, which includes PLAU, IGFBP3, FOLR1, B4GALT1 and COL1A1. Of particular interest to us was a gene cluster, "secreted proteins", that was up-regulated after radiation exposure. Seven up-regulated genes of this gene cluster fall within the chemokine/cytokine gene cluster, namely, CXCL1, CXCL2, IL6, IL11, IL8, IL24 and TGFbeta2. In microarray studies, the radiation-induced up-regulated expression of some these genes encoding cytokine/chemokine proteins was significantly decreased by SeM treatment. For IL8, TGFbeta2, CXCL1 and CXCL2, these observations were validated by qPCR techniques. It is concluded that SeM can regulate ionizing radiation-induced gene expression and may serve as an effective countermeasure for some of the acute inflammatory/immune responses induced by low-dose HZE-particle radiation.

Inhibition of autophagy induced by overexpression of mda-7/interleukin-24 strongly augments the antileukemia activity in vitro and in vivo

Melanoma differentiation-associated gene-7/interleukin-24 (mda-7/IL-24) is a novel candidate of tumor suppressor that can selectively induce apoptosis experimentally in a spectrum of human cancer cells including leukemia cells. However, a recent study suggests that mda-7/IL-24 promotes the survival of chronic lymphocytic leukemia B-cells. In this study, we showed that mda-7/IL-24 was constitutively expressed in leukemia cell lines and primary acute myeloid leukemia samples. Using a conditionally replicating adenovirus expressing mda-7/IL-24 (ZD55-IL-24), we showed that enforced expression of mda-7/IL-24 in leukemia cells induced autophagy, which was triggered by the upregulation of Beclin-1. Immunofluorescence and coimmunoprecipitation studies suggested that mda-7/IL-24 protein interacts with Beclin-1. Class III PI3K/Beclin-1 complex was shown involved in the mda-7/IL-24-induced autophagy. Moreover, autophagy inhibition by phosphatidylinositol 3-kinase inhibitor, wortmannin, resulted in a reduced Beclin-1 expression and autophagosome formation associated with significantly enhanced cell death. Importantly, the combination of ZD55-IL-24 with wortmannin elicited a strongly enhanced antileukemia efficacy in established leukemia xenografts. These results suggest that mda-7/IL-24-induced autophagy in leukemia cells may provide survival advantage and mda-7/IL-24 combined with agents that disrupt autophagy is a promising new strategy for the treatment of leukemia.

IL-24: a classic cytokine and/or a potential cure for cancer?

IL-24, a member of the IL-10 family of cytokines, is produced by monocytes and Th2 cells. Interestingly, immune cells do not appear to express specific IL-24 receptor chains (IL-20R1/IL-20R2 and IL-22R/IL-20R2), it is therefore unlikely that IL-24 has classical immune-modulating properties. Skin, on the other hand, seems to represent a major target tissue for IL-24 and related cytokines such as IL-19, -20, and -22. However, the initial interest in IL-24 did not arise from its physiological signalling properties through its cognate receptors but rather because of its tentative ability to selectively kill different cancer cells. In an attempt to further investigate the signalling events underlying the IL-24-induced cancer cell death, we found that melanoma cell lines did not react in the expected and previously described way. Using several different forms and delivery modes of IL-24, we were unable to detect any apoptosis-inducing properties of this cytokine in melanoma cells. In the present ‘Point of view’ we will briefly summarizse these findings and put them in context of published reports stating that IL-24 might be a long sought after treatment for several types of cancer.

Interleukin-24 induces expression of beta4 integrin but suppresses anchorage-independent growth of rat mammary tumor cells by a mechanism that is independent of beta4

Wistar-Furth rats develop multiple mammary adenocarcinomas following initiation with methylnitrosourea, whereas Copenhagen rats are resistant to the development of mammary tumors. We have previously isolated cell lines from tumors induced in resistant Copenhagen x Wistar-Furth F(1) rats by infusion of a retrovirus harboring v-Ha-ras directly into the main mammary ducts. Some of the cell lines were able to grow in soft agar, but a significant number did not display anchorage-independent growth. Here, we compared by microarray analysis genes that are differentially expressed in these cell lines. The expression of interleukin-24 (IL-24) and beta(4) integrin was highly correlated with the inability of cells to grow in soft agar. Ectopic expression of IL-24 in anchorage-independent cells inhibited their growth in monolayer culture, in soft agar, and in nude mice in vivo and inhibited their ability to migrate and invade in in vitro assays. Furthermore, growth suppression by IL-24 was associated with the transcriptional up-regulation of p27(Kip1) via the activation of Stat3. We showed, for the first time, that beta(4) integrin is a downstream target of IL-24. However, beta(4) does not play a direct role in regulating the proliferative capacity of rat mammary tumor cells. Our results show that IL-24 suppresses the growth of rat mammary carcinoma cells and may play a role in the resistance of Copenhagen rats to mammary carcinogenesis.

Gene expression deregulation by KRAS G12D and G12V in a BRAF V600E context

Background

KRAS and BRAF mutations appear of relevance in the genesis and progression of several solid tumor types but the co-occurrence and interaction of these mutations have not yet been fully elucidated. Using a microsatellite stable (MSS) colorectal cancer (CRC) cell line (Colo741) having mutated BRAF and KRAS^WT, we also aimed to investigate the KRAS-BRAF interaction. Gene expression profiles for control KRAS^WT, KRAS^G12V and KRAS^G12D transfected cells were obtained after cell clone selection and RT-PCR screening. Extensive qPCR was performed to confirm microarray data.

Results

We found that the KRAS^G12V state deregulated several genes associated to cell cycle, apoptosis and nitrogen metabolism. These findings indicated a reduced survival and proliferation with respect to the KRAS^WT state. The KRAS^G12D state was, instead, characterized by several other distinct functional changes as for example those related to chromatin organization and cell-cell adhesion without affecting apoptosis related genes.

Conclusion

These data predict that the G12D mutation may be more likely selected in a BRAF mutated context. At the same time, the presence of the KRAS^G12V mutation in the cells escaping apoptosis and inducing angiogenesis via IL8 may confer a more aggressive phenotype. The present results get along with the observations that CRCs with G12V are associated with a worse prognosis with respect to the WT and G12D states and may help identifying novel CRC pathways and biomarkers of clinical relevance.

Inhibition of pancreatic carcinoma growth by adenovirus-mediated human interleukin-24 expression in animal model

Interleukin-24 (IL-24) has been shown to be a tumor-suppressor gene and the protein product found to be constitutively expressed by melanocytes, nerve cells, and some primary melanomas. The potential effect of adenovirus (AdV)-mediated IL-24 gene therapy was explored on human pancreatic carcinoma by using a pancreatic carcinoma cell line, patu8988. A recombinant adenovirus, AdVGFP/IL-24, expressing the marker, green fluorescent protein (GFP), and the tumor-suppressor gene, IL-24, was constructed. AdVGFP/IL-24 treatment of pancreatic carcinoma cells in vitro significantly induced pancreatic carcinoma cell cytotoxicity and apoptosis, compared with AdVGFP without IL-24 expression. In nude mice bearing patu8988 tumors, intratumoral injections of AdVGFP/IL-24 significantly inhibited pancreatic carcinoma growth. In addition, the molecular mechanism of tumor suppression was elucidated by downregulating the expression of vascular endothelial growth factor, CD34, and Bcl-2, as well as inhibiting tumor angiogenesis. Therefore, AdVGFP/IL-24 has the potential to serve as a novel tool for pancreatic carcinoma gene therapy.

Down-regulation of inhibition of differentiation-1 via activation of activating transcription factor 3 and Smad regulates REIC/Dickkopf-3-induced apoptosis

REIC/Dickkopf-3 (Dkk-3), a tumor suppressor gene, has been investigated in gene therapy studies. Our previous study suggested that REIC/Dkk-3-induced apoptosis mainly resulted from phosphorylation of c-Jun-NH(2) kinase (JNK) in prostate cancer cells. However, the precise mechanisms, especially the molecular mechanisms regulating JNK phosphorylation, remain unclear. In this study, we investigated the mechanisms participating in JNK phosphorylation in the context of a refractory cancer disease, malignant mesothelioma (MM). Adenovirus-mediated overexpression of REIC/Dkk-3 induced apoptosis mainly through JNK activation in immortalized MM cells (211H cells). Interestingly, transcriptional down-regulation of inhibition of differentiation-1 (Id-1) was detected in REIC/Dkk-3-overexpressed 211H cells. Moreover, restoration of Id-1 expression antagonized REIC/Dkk-3-induced JNK phosphorylation and apoptosis. Mutagenesis experiments with the 2.1-kb human Id-1 promoter revealed that activating transcription factor 3 (ATF3) and Smad interaction, with their respective binding motifs, was essential for REIC/Dkk-3-mediated suppression of Id-1 promoter activity. ATF3 activation was probably induced by endoplasmic reticulum stress. Finally, we showed strong antitumor effects from REIC/Dkk-3 gene transfer into the pleural cavity in an orthotopic MM mouse model. Relative to control tumor tissue, REIC/Dkk-3-treated tumor tissue showed down-regulated expression of Id-1 mRNA, enhanced expression of phosphorylated JNK, and an increased number of apoptotic cells. In summary, we first showed that both ATF3 and Smad were crucially and synergistically involved in down-regulation of Id-1, which regulated JNK phosphorylation in REIC/Dkk-3-induced apoptosis. Thus, gene therapy with REIC/Dkk-3 may be a promising therapeutic tool for MM.

A novel splicing variant of mouse interleukin (IL)-24 antagonizes IL-24-induced apoptosis

Alternative splicing of mRNA enables functionally diverse protein isoforms to be expressed from a single gene, allowing transcriptome diversification. Interleukin (IL)-24/MDA-7 is a member of the IL-10 gene family, and FISP (IL-4-induced secreted protein), its murine homologue, is selectively expressed and secreted by T helper 2 lymphocytes. A novel splice variant of mouse IL-24/FISP, designated FISP-sp, lacks 29 nucleotides from the 5'-end of exon 4 of FISP. The level of FISP-sp expression is 10% of the level of total primary FISP transcription. Unlike FISP, FISP-sp does not induce growth inhibition and apoptosis. FISP-sp is exclusively localized in endoplasmic reticulum, and its expression is up-regulated by endoplasmic reticulum stress. Our results suggest that the novel splicing variant FISP-sp dimerizes with FISP and blocks its secretion and inhibits FISP-induced apoptosis in vivo.

Adenoviral endoplasmic reticulum-targeted mda-7/interleukin-24 vector enhances human cancer cell killing

We developed several adenoviral vectors designed to target MDA-7 expression to different subcellular compartments [endoplasmic reticulum (ER), mitochondria, nucleus, and cytosol] and evaluated their ability to enhance apoptosis. Adenoviral ER-targeted mda-7/interleukin-24 vector (Ad-ER-mda7) selectively and effectively inhibited the growth and proliferation of lung (A549 and H1299) and esophageal (Seg1 and Bic1) cancer cells by enhancing cell killing. Both Ad-mda7 and Ad-ER-mda7 activated a novel pathway of ER stress-induced apoptosis characterized by unregulated expression of phosphorylated JNK, phosphorylated c-Jun, and phosphorylated RNA-dependent protein kinase. Caspase-4 activation mediated Ad-mda7- and Ad-ER-mda7-induced cell death. In addition, Ad-mda7- and Ad-ER-mda7-mediated growth inhibition correlated with activation of ER molecular markers RNA-dependent protein kinase and JNK both in vitro (in Ad-mda7- or Ad-ER-mda7-treated lung cancer cells) and in vivo. These findings suggest that vectors targeting the ER (Ad-ER-mda7) may be more effective in cancer gene therapy possibly through more effective induction or ER stress pathways.

Recombinant human IL-24 suppresses lung carcinoma cell growth via induction of cell apoptosis and inhibition of tumor angiogenesis

Previous studies have shown that interleukin-24 (IL-24; mda-7) as a novel tumor suppressor gene has tumor-suppressive activity against a broad spectrum of human cancers. However, the therapeutic effect of the recombinant human IL-24 (rhIL-24) protein purified from prokaryotic cells on human lung cancers has not been reported. In this study, we cloned the human gene coding for IL-24 from lipopolysaccharide-activated human peripheral blood mononuclear cells (PBMCs) by reverse-transcriptase polymerase chain reaction and constructed an expression vector pBV220-IL-24. We then transfected Escherichia coli DH5alpha with pBV220-IL-24. The soluble rhIL-24 was obtained from purified insoluble inclusion bodies of transfected cells by a denaturing and renaturing process. We demonstrated that the purified soluble rhIL-24 protein with 18.5 kappaDa was capable of (1) inducing in vitro apoptosis of A549 lung carcinoma cells; (2) activating PBMCs to secrete cytokines such as IL-6, tumor necrosis factor-alpha, and interferon-gamma; (3) inhibiting the formation of blood capillaries on chicken embryonic allantois and in vivo tumor angiogenesis; and (4) inhibiting A549 lung tumor cell growth in vitro and in vivo. Therefore, our results indicate its potent suppressive effect on human lung carcinoma cell line and warrant its further investigation for therapeutic application against human lung cancer.

Recombinant interleukin-24 lacks apoptosis-inducing properties in melanoma cells

IL-24, also known as melanoma differentiation antigen 7 (mda-7), is a member of the IL-10 family of cytokines and is mainly produced by Th(2) cells as well as by activated monocytes. Binding of IL-24 to either of its two possible heterodimeric receptors IL-20R1/IL-20R2 and IL-22R/IL-20R2 activates STAT3 and/or STAT1 in target tissues such as lung, testis, ovary, keratinocytes and skin. To date, the physiological properties of IL-24 are still not well understood but available data suggest that IL-24 affects epidermal functions by increasing proliferation of dermal cells. In stark contrast to its "normal" and physiological behaviour, IL-24 has been reported to selectively and efficiently kill a vast variety of cancer cells, especially melanoma cells, independent of receptor expression and Jak-STAT signalling. These intriguing properties have led to the development of adenovirally-expressed IL-24, which is currently being evaluated in clinical trials. Using three different methods, we have analysed a large panel of melanoma cell lines with respect to IL-24 and IL-24 receptor expression and found that none of the investigated cell lines expressed sufficient amounts of functional receptor pairs and therefore did not react to IL-24 stimulation with Jak/STAT activation. Results for three cell lines contrasted with previous studies, which reported presence of IL-24 receptors and activation of STAT3 following IL-24 stimulation. Furthermore, evaluating four different sources and modes of IL-24 administration (commercial recombinant IL-24, bacterially expressed GST-IL-24 fusion protein, IL-24 produced from transfected Hek cells, transiently over-expressed IL-24) no induction or increase in cell death was detected when compared to appropriate control treatments. Thus, we conclude that the cytokine IL-24 itself has no cancer-specific apoptosis-inducing properties in melanoma cells.

Adenovirus-mediated Il-24 expression suppresses hepatocellular carcinoma growth via induction of cell apoptosis and cycling arrest and reduction of angiogenesis

Previous studies have shown that interleukin (IL)-24 as a novel tumor suppressor gene has tumor-suppressor activity in a broad spectrum of human cancer cells both in vitro and in vivo. In this study, we explored the potential effect of adenovirus-mediated IL-24 gene therapy on human hepatocellular carcinoma (HCC) by using a HCC cell line, SMMC-7721. We constructed a recombinant adenovirus, AdVGFP/IL-24 expressing the marker green fluorescent protein (GFP) and the tumor-suppressor gene, IL-24. We demonstrated that AdVGFP/IL-24 treatment of SMMC-7721 cells in vitro significantly induced HCC cell cytotoxicity and apoptosis, and altered HCC cell cycling with an S-phase reduction and G2/M phase arrest, compared with AdVGFP, without IL-24 expresssion (p < 0.05). Furthermore, we also showed that the treatment of SMMC-7721 tumors by an intratumoral injection of AdVGFP/IL-24 significantly suppressed in vivo HCC growth in athymic nude mice, compared with AdVGFP treatment (p < 0.05). In addition, we also elucidated the molecular mechanism responsible for AdVGFP/IL-24-associated tumor suppression. These include: (1) upregulation of p53-independent apoptosis-associated caspase-3 and (2) downregulation of angiogenesis-associated vascular endothelial growth factor and CD34. Therefore, this study will provide a framework for future clinical applications of AdVGFP/IL-24 in HCC gene therapy.

Expression, purification, and characterization of recombinant human interleukin 24 in Escherichia coli

Interleukin-24 (IL-24) can induce apoptosis of a broad range of tumor cells, and this function of IL-24 is independent of classic tumor suppressor genes, such as p53, Rb and p16. Here, we report the expression, purification and preparation of a recombinant IL-24 protein (rIL-24) without post-translational modifications, which may selectively induce apoptosis of tumor cells in vitro. We found that non-fusion rIL-24 was not able to be expressed by vectors pET11c, 28a, and 22b in Escherichia coli. To obtain recombinant non-fusion IL-24 protein, the encoding region for IL-24 was cloned between KpnI and BamHI in pET32a. The Trx (Thioredoxin)/IL-24 fusion proteins were expressed in the form of inclusion bodies in E. coli host strain BL21 (DE21). The expression level was more than 30% of total cell lysate. Inclusion bodies were disrupted, washed, and isolated at pH 9.0, and were completely dissolved in a buffer containing 2M urea at pH 9.0. After nickel ion metal affinity chromatography, gel filtration chromatography, and renaturation, the refolded fusion proteins with a purity of >96% were obtained. Trx/IL-24 proteins were digested by enterokinase (EK) to both Trx and rIL-24 fragments which then were separated by cation exchange chromatography. Cell proliferation experiments proved that the rIL-24 (98% purity) retains its cancer-selective apoptosis-inducing properties. This result suggested that the rIL-24 may have cancer therapeutic applications.

N-Glycosylation of MDA-7/IL-24 Is Dispensable for Tumor Cell–Specific Apoptosis and “Bystander” Antitumor Activity

Biochemical and genetic mutation-based analyses confirm that the MDA-7/IL-24 protein can induce transformed cell-specific apoptosis through a mechanism involving endoplasmic reticulum (ER) stress-associated pathways. Covalent modifications by N-linked glycans in the ER contribute to the conformational maturation and biological functions of many proteins. Because MDA-7/IL-24 is a glycosylated protein, we investigated the role of glycosylation in mediating the specific biological and "bystander" antitumor activities of this cytokine. An adenovirus vector expressing a nonsecreted and nonglycosylated version of MDA-7/IL-24 protein was generated via deletion of its signal peptide and point mutations of its three N-glycosylated sites. In this study, we showed that this intracellular nonglycosylated protein was as effective as wild-type MDA-7/IL-24 protein in inducing apoptosis in multiple tumor cell lines. Both constructs (a) displayed transformed cell specificity and localization to the ER compartment, (b) mediated apoptosis through JAK/STAT-independent and p38(MAPK)-dependent pathways, (c) induced sustained ER stress as evidenced by expression of ER stress markers (BiP/GRP78, GRP94, XBP-1, and eIF2alpha), and (d) generated proteins that physically interacted with BiP/GRP78. Additionally, an expression construct containing the mda-7/IL-24 signal peptide linked to the mutated nonglycosylated mda-7/IL-24 gene retained the ability to induce bystander antitumor activity. These studies reveal that MDA-7/IL-24 glycosylation is not mandatory for inducing cell death or bystander activities in different cancer cells, providing new insights into the mechanism by which MDA-7/IL-24 induces apoptosis and ER stress.

Soluble Human MDA-7/IL-24: Characterization of the Molecular Form(s) Inhibiting Tumor Growth and Stimulating Monocytes

Interleukin-24 (IL-24), also known as melanoma differentiation-associated gene-7 (mda-7), is a member of the IL-10 family that exhibits both tumor suppressor and proinflammatory properties. We describe the purification of this novel dual-function tumor suppressor/cytokine from the supernatant of IL-24 gene-transfected HEK 293 cells and define the biochemical and functional properties of the soluble human IL-24 protein. Size exclusion chromatography demonstrates that an IL-24 macromolecular complex fractionates in a broad peak with a median of 110 kDa and comprises several IL-24 isoforms, identified by immunoblotting with anti-IL-24 polyclonal antibody after reducing SDS-PAGE analysis. IL-24 was found to associate with two serum components, albumin and C1q. Cation exchange purification results in the isolation of at least two N-linked glycosylated IL-24 dimers covalently associated via intermolecular disulfide bonds. These molecularly defined N-glycosylated IL-24 dimers elicited dose-dependent secretion of tumor necrosis factor-alpha (TNF-alpha) and IL-6 from human monocytes, as well as cytotoxicity to human melanoma cell lines. Thus, we demonstrated that the secreted, glycosylated, dimeric, human IL-24 is immunomodulatory to monocytes and exhibits tumor cell growth inhibition.

Enhancement of adenoviral MDA-7-mediated cell killing in human lung cancer cells by geldanamycin and its 17-allyl- amino-17-demethoxy analogue

Our previous studies demonstrated that adenovirus-mediated overexpression of melanoma differentiation-associated gene-7 (Ad-mda7) leads to rapid induction of double-stranded RNA-dependent protein kinase (PKR) and activation of its downstream targets, resulting in apoptosis induction in human lung cancer cells. Here, we report that Ad-mda7 and the benzoquinone ansamycin geldanamycin (GA) interact in a highly synergistic manner to induce cell death in human lung cancer cells. Co-administration of Ad-mda7 and GA did not modify expression of MDA-7, and was not associated with further PKR induction and activation; instead the enhanced cytotoxicity of this combination was associated with inactivation of AKT by GA. By surface staining using anti-E-cadherin monoclonal antibody and flow cytometry, we found that treatment with the combination of Ad-mda7 and GA increased E-cadherin levels in these cancer cells. Ad-mda7 and GA cotreatment also inhibited lung cancer cell motility by increasing the beta-catenin/E-cadherin association. Moreover, combination of GA derivative 17-allyl-amino, 17-demethoxygeldanamycin (17AAG), with Ad-mda7 resulted in enhancement of cell death in A549 and H460 human lung cancer cells.

mda-7/IL-24: multifunctional cancer-specific apoptosis-inducing cytokine

"Differentiation therapy" provides a unique and potentially effective, less toxic treatment paradigm for cancer. Moreover, combining "differentiation therapy" with molecular approaches presents an unparalleled opportunity to identify and clone genes mediating cancer growth control, differentiation, senescence, and programmed cell death (apoptosis). Subtraction hybridization applied to human melanoma cells induced to terminally differentiate by treatment with fibroblast interferon (IFN-beta) plus mezerein (MEZ) permitted cloning of melanoma differentiation associated (mda) genes. Founded on its novel properties, one particular mda gene, mda-7, now classified as a member of the interleukin (IL)-10 gene family (IL-24) because of conserved structure, chromosomal location, and cytokine-like properties has become the focus of attention of multiple laboratories. When administered by transfection or adenovirus-transduction into a spectrum of tumor cell types, melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) induces apoptosis, whereas no toxicity is apparent in normal cells. mda-7/IL-24 displays potent "bystander antitumor" activity and also has the capacity to enhance radiation lethality, to induce immune-regulatory activities, and to inhibit tumor angiogenesis. Based on these remarkable attributes and effective antitumor therapy in animal models, this cytokine has taken the important step of entering the clinic. In a Phase I clinical trial, intratumoral injections of adenovirus-administered mda-7/IL-24 (Ad.mda-7) was safe, elicited tumor-regulatory and immune-activating processes, and provided clinically significant activity. This review highlights our current understanding of the diverse activities and properties of this novel cytokine, with potential to become a prominent gene therapy for cancer.