The Molecular Mechanisms behind Advanced Breast Cancer Metabolism: Warburg Effect, OXPHOS, and Calcium

Altered metabolism represents a fundamental difference between cancer cells and normal cells. Cancer cells have a unique ability to reprogram their metabolism by deviating their reliance from primarily oxidative phosphorylation (OXPHOS) to glycolysis, in order to support their survival. This metabolic phenotype is referred to as the "Warburg effect" and is associated with an increase in glucose uptake, and a diversion of glycolytic intermediates to alternative pathways that support anabolic processes. These processes include synthesis of nucleic acids, lipids, and proteins, necessary for the rapidly dividing cancer cells, sustaining their growth, proliferation, and capacity for successful metastasis. Triple-negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer, with the poorest patient outcome due to its high rate of metastasis. TNBC is characterized by elevated glycolysis and in certain instances, low OXPHOS. This metabolic dysregulation is linked to chemotherapeutic resistance in TNBC research models and patient samples. There is more than a single mechanism by which this metabolic switch occurs and here, we review the current knowledge of relevant molecular mechanisms involved in advanced breast cancer metabolism, focusing on TNBC. These mechanisms include the Warburg effect, glycolytic adaptations, microRNA regulation, mitochondrial involvement, mitochondrial calcium signaling, and a more recent player in metabolic regulation, JAK/STAT signaling. In addition, we explore some of the drugs and compounds targeting cancer metabolic reprogramming. Research on these mechanisms is highly promising and could ultimately offer new opportunities for the development of innovative therapies to treat advanced breast cancer characterized by dysregulated metabolism.

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.

Abstract A109: MicroRNA-4719 and microRNA-6756-5p correlate with aggressive prostate cancer progression in African American men through regulation of Interleukin-24

Prostate cancer (PCa) incidence and mortality are highest in African American men (AAM) and the molecular mechanisms underlying the racial disparities in PCa are unclear. Interleukin-24 (IL-24), a tumor suppressor whose expression is lost in most human cancers, correlates with cancer progression. Also, microRNAs (miRs) are dysregulated in cancers. microRNA target prediction algorithm tools identified miRs, miR-4719 and miR-6556-5p, as putative regulators of IL-24. This study elucidates the expression profile and role of miR-4719 and miR-6756-5p as regulators of IL-24 in PCa biology of AAM. Our work compares five different PCa cell lines: E006AA (AAM, indolent), E006AA-hT (AAM, aggressive), DU-145 (CM, aggressive), PC-3 (CM, aggressive) to a nontumorigenic prostate epithelial cell line, RWPE1 (CM). qRT-PCR analysis shows that miR-4719 and miR-6756-5p are significantly overexpressed in all PCa cell lines (by >2-fold) compared to RWPE-1. Both miR-4719 (>2 fold) and miR-6756-5p (>50%) are higher in aggressive PCa compared to the indolent PCa, indicating their gain could be an early event in PCa progression. Moreover, miR-4719 and miR-6756-5p are significantly overexpressed in the aggressive PCa of AAM (E006AA-hT) compared to aggressive PCas for CM (PC-3 and DU-145). Interestingly, both miR-4719 and miR-6756-5p expression were higher by (>3-fold) in the aggressive AAM cell line E006AA-hT compared to indolent AAM cell line- E006AA. Thus, miR-4719 and miR-6756-5p may play a role in racial disparity. Using oligonucleotide mimics and inhibitors, we evaluated the functional role of these miRs in the AAM cell lines, E006AA and E006AA-hT. MTT assays revealed that inhibition of miR-4719 and miR-6756-5p significantly decreases proliferation (>40%), while overexpression of both miRs increases proliferation (>20%). Inhibition of miR-4719 and miR-6756-5p further decreased the proliferation of the aggressive E006AA-hT by an extra 20%, compared to indolent E006AA. In contrast, overexpression of both miRs further increased the proliferation of E006AA-hT also by an extra 20%, compared to E006AA. Wound healing assays reveal that inhibition of miR-4719 and miR-6756-5p reduced migration by ~50% compared to the negative control (NC). Strikingly, overexpression of both miRs increased migration by at least 2- and 4-fold, respectively. We observed that IL-24 was downregulated in all PCa cells compared to RWPE-1, suggesting a possible role of these miRs in suppressing IL-24. qRT-PCR analysis show inhibition of miR-4719 and miR-6756-5p significantly increases the expression of IL-24 (by ~2-fold) in PCa cells compared to the NC. In contrast, overexpression of both miRs reduces the expression of IL-24. Our findings indicate that miR-4719 and miR-6756-5p may regulate IL-24 expression and may be biomarkers that can differentiate between indolent and aggressive PCa in AAM. Strategies to inhibit miR-4719 and miR-6756-5p expression to increase IL-24 in PCa could have therapeutic efficacy in AAM.

Citation Format: Dibash K. Das, Leah Persaud, Moira Sauane. MicroRNA-4719 and microRNA-6756-5p correlate with aggressive prostate cancer progression in African American men through regulation of Interleukin-24 [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr A109.

Analysis of Adult Neural Retina Extracellular Vesicle Release, RNA Transport and Proteomic Cargo

Purpose

Extracellular vesicles (EVs) contain RNA and protein cargo reflective of the genotype and phenotype of the releasing cell of origin. Adult neural retina EV release, RNA transfer, and proteomic cargo are the focus of this study.

Methods

Adult wild-type mouse retinae were cultured and released EV diameters and concentrations quantified using Nanosight. Immunogold transmission electron microscopy (TEM) was used to image EV ultrastructure and marker protein localization. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to analyze retinal cell transcripts present in EVs. Super-resolution microscopy was used to image fluorescent (green) RNA and (red) lipid membrane labeled EVs, released by adult retina, and internalized by isolated retinal cells. Mass spectrometry was used to characterize the proteomes of adult retina and EVs.

Results

Adult neural retina released EVs at a rate of 1.42 +/- 0.08 × 108/mL over 5 days, with diameters ranging from 30 to 910 nm. The canonical EV markers CD63 and Tsg101 localized to retinal EVs. Adult retinal and neuronal mRNA species present in both retina and EVs included rhodopsin and the neuronal nuclei marker NeuN. Fluorescently labeled RNA in retinal cells was enclosed in EVs, transported to, and uptaken by co-cultured adult retinal cells. Proteomic analysis revealed 1696 protein species detected only in retinal cells, 957 species shared between retina and EVs, and 82 detected only in EVs.

Conclusions

The adult neural retina constitutively releases EVs with molecular cargo capable of intercellular transport and predicted involvement in biological processes including retinal physiology, mRNA processing, and transcription regulation within the retinal microenvironment.

Modulation of the Pol II CTD Phosphorylation Code by Rac1 and Cdc42 Small GTPases in Cultured Human Cancer Cells and Its Implication for Developing a Synthetic-Lethal Cancer Therapy

Rho GTPases, including Rho, Cdc42, Rac and ROP subfamilies, are key signaling molecules in RNA polymerase II (Pol II) transcriptional control. Our prior work has shown that plant ROP and yeast Cdc42 GTPases similarly modulate Ser2 and Ser5 phosphorylation status of the C-terminal domain (CTD) of the Pol II largest subunit by regulating CTD phosphatase degradation. Here, we present genetic and pharmacological evidence showing that Cdc42 and Rac1 GTPase signaling modulates a similar CTD Ser2 and Ser5 phosphorylation code in cultured human cancer cells. While siRNA knockdown of Cdc42 and Rac1, respectively, in HeLa cells increased the level of CTD Ser phosphatases RPAP2 and FCP1, they both decreased the level of CTD kinases CDK7 and CDK13. In addition, the protein degradation inhibitor MG132 reversed the effect of THZ1, a CDK7 inhibitor which could decrease the cell number and amount of CDK7 and CDK13, accompanied by a reduction in the level of CTD Ser2 and Ser5 phosphorylation and DOCK4 and DOCK9 (the activators for Rac1 and Cdc42, respectively). Conversely, treatments of Torin1 or serum deprivation, both of which promote protein degradation, could enhance the effect of THZ1, indicating the involvement of protein degradation in controlling CDK7 and CDK13. Our results support an evolutionarily conserved signaling shortcut model linking Rho GTPases to Pol II transcription across three kingdoms, Fungi, Plantae and Animalia, and could lead to the development of a potential synthetic-lethal strategy in controlling cancer cell proliferation or death.

A Self-degradable Curcumin Polymer with Anti-cancer Activity

Curcumin is a widely researched and utilized natural product used for a variety of ailments including as a gastrointestinal aide and an anticancer agent. Curcumin however suffers from poor bioavailability. A strategy to circumvent poor bioavailability is to administer with an adjuvant or by synthetic modification. Herein we demonstrate the incorporation of curcumin into a self-degradable polymer by condensation with N,N'-di-Boc-L-cystine. The polymer is made self-degradable upon deprotection of the cystine amines. Degradation is confirmed by thermogravimetric analysis and differential scanning calorimetry. Curcumin retains its anti-cancer activity within the polymer showing activity against HT29 human colon cancer cells and DU-145 prostate cancer cells. The self-degrading polymer showed enhanced activity against HT29 cells compared to that of curcumin.

IL-24 Promotes Apoptosis through cAMP-Dependent PKA Pathways in Human Breast Cancer Cells

Interleukin 24 (IL-24) is a tumor-suppressing protein, which inhibits angiogenesis and induces cancer cell-specific apoptosis. We have shown that IL-24 regulates apoptosis through phosphorylated eukaryotic initiation factor 2 alpha (eIF2α) during endoplasmic reticulum (ER) stress in cancer. Although multiple stresses converge on eIF2α phosphorylation, the cellular outcome is not always the same. In particular, ER stress-induced apoptosis is primarily regulated through the extent of eIF2α phosphorylation and activating transcription factor 4 (ATF4) action. Our studies show for the first time that cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) activation is required for IL-24-induced cell death in a variety of breast cancer cell lines and this event increases ATF4 activity. We demonstrate an undocumented role for PKA in regulating IL-24-induced cell death, whereby PKA stimulates phosphorylation of p38 mitogen-activated protein kinase and upregulates extrinsic apoptotic factors of the Fas/FasL signaling pathway and death receptor 4 expression. We also demonstrate that phosphorylation and nuclear import of tumor suppressor TP53 occurs downstream of IL-24-mediated PKA activation. These discoveries provide the first mechanistic insights into the function of PKA as a key regulator of the extrinsic pathway, ER stress, and TP53 activation triggered by IL-24.

Eukaryotic Translation Initiation Factor 4A Down-Regulation Mediates Interleukin-24-Induced Apoptosis through Inhibition of Translation

Dysregulated activity of helicase eIF4A drives transformation to and maintenance of cancer cell phenotype by reprogramming cellular translation. Interleukin 24 (IL-24) is a tumor-suppressing protein, which has the ability to inhibit angiogenesis, sensitize cancer cells to chemotherapy, and induce cancer cell-specific apoptosis. In this study, we found that eIF4A is inhibited by IL-24. Consequently, selective reduction of translation was observed for mRNAs harboring strong secondary structures in their 5′-untranslated regions (5′UTRs). These mRNAs encode proteins, which function in cell survival and proliferation. Consistently, overexpression of eIF4A conferred cancer cells with resistance to IL-24-induced cell death. It has been established that inhibition of eIF4A triggers mitochondrial-mediated apoptosis. We showed that IL-24 induces eIF4A-dependent mitochondrial depolarization. We also showed that IL-24 induces Sigma 1 Receptor-dependent eIF4A down-regulation and mitochondrial depolarization. Thus, the progress of apoptosis triggered by IL-24 is characterized by a complex program of changes in regulation of several initiation factors, including the eIF4A.

Translation Control by p53

The translation of mRNAs plays a critical role in the regulation of gene expression and therefore, in the regulation of cell proliferation, differentiation and apoptosis. Unrestricted initiation of translation causes malignant transformation and plays a key role in the maintenance and progression of cancers. Translation initiation is regulated by the ternary complex and the eukaryotic initiation factor 4F (eIF4F) complex. The p53 tumor suppressor protein is the most well studied mammalian transcription factor that mediates a variety of anti-proliferative processes. Post-transcriptional mechanisms of gene expression in general and those of translation in particular play a major role in shaping the protein composition of the cell. The p53 protein regulates transcription and controls eIF4F, the ternary complex and the synthesis of ribosomal components, including the down-regulation of rRNA genes. In summary, the induction of p53 regulates protein synthesis and translational control to inhibit cell growth.

eIF2α Phosphorylation Mediates IL24-Induced Apoptosis through Inhibition of Translation

IL24 is an immunomodulatory cytokine that also displays broad cancer-specific suppressor effects. The tumor-suppressor activities of IL24 include inhibition of angiogenesis, sensitization to chemotherapy, and cancer-specific apoptosis. Supra-physiologic activation and/or overexpression of translation initiation factors are implicated in the initiation and progression of cancer animal models as well as a subset of human cancers. Activation and/or overexpression of translation initiation factors correlate with aggressiveness of cancer and poor prognosis. Two rate-limiting translation initiation complexes, the ternary complex and the eIF4F complex, are regulated by eIF2α and 4E-BP1 phosphorylation, respectively. The work reported here provides direct evidence that IL24 induces inhibition of translation initiation leading to apoptosis in squamous cell carcinoma. A dominant constitutively active mutant of eIF2α, which is resistant to phosphorylation, was used to determine the involvement of eIF2α in IL24-induced apoptosis. Treatment with IL24 resulted in inhibition of protein synthesis, expression of downstream biomarkers of ternary complex depletion such as CHOP, and induction of apoptosis in cancer cells. The constitutively active nonphosphorylatable mutant of eIF2α, eIF2α-S51A, reversed both the IL24-mediated translational block and IL24-induced apoptosis. Intriguingly, IL24 treatment also caused hypophosphorylation of 4E-BP1, which binds to eIF4E with high affinity, thus preventing its association with eIF4G and therefore preventing elF4F complex assembly.Implications: These results demonstrate a previously unrecognized role of IL24 in inhibition of translation, mediated through both phosphorylation of eIF2α and dephosphorylation of 4E-BP1, and provide the first direct evidence for translation control of gene-specific expression by IL24. Mol Cancer Res; 15(8); 1117-24. ©2017 AACR.

Predicted molecular signaling guiding photoreceptor cell migration following transplantation into damaged retina

To replace photoreceptors lost to disease or trauma and restore vision, laboratories around the world are investigating photoreceptor replacement strategies using subretinal transplantation of photoreceptor precursor cells (PPCs) and retinal progenitor cells (RPCs). Significant obstacles to advancement of photoreceptor cell-replacement include low migration rates of transplanted cells into host retina and an absence of data describing chemotactic signaling guiding migration of transplanted cells in the damaged retinal microenvironment. To elucidate chemotactic signaling guiding transplanted cell migration, bioinformatics modeling of PPC transplantation into light-damaged retina was performed. The bioinformatics modeling analyzed whole-genome expression data and matched PPC chemotactic cell-surface receptors to cognate ligands expressed in the light-damaged retinal microenvironment. A library of significantly predicted chemotactic ligand-receptor pairs, as well as downstream signaling networks was generated. PPC and RPC migration in microfluidic ligand gradients were analyzed using a highly predicted ligand-receptor pair, SDF-1α – CXCR4, and both PPCs and RPCs exhibited significant chemotaxis. This work present a systems level model and begins to elucidate molecular mechanisms involved in PPC and RPC migration within the damaged retinal microenvironment.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) activates caspases in human prostate cancer cells through sigma 1 receptor

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-based therapy is currently evaluated in clinical studies as a tumor cell-selective pro-apoptotic approach. Unfortunately, many clinical studies have shown that cancer cells acquire TRAIL resistance and finally avoid TRAIL-induced apoptosis. Therefore, defining the mechanisms that permit TRAIL to activate apoptosis is critical for the development of strategies that maximize the potential effectiveness of TRAIL in clinical applications. This study aims at understanding the molecular mechanisms underlying TRAIL-induced apoptosis and unraveling signaling pathways that could revert sensitivity to apoptosis stimuli. Our current study demonstrates for the first time that Sigma 1 Receptor (Sig1R), a ligand-regulated protein chaperone, contributes to TRAIL induction of apoptosis. We show that Sig1R agonist (+)-SKF10047 action or increasing Sig1R expression, significantly reduced apoptosis by TRAIL in prostate cell lines, indicating the importance of Sig1R and signifying that higher levels of Sig1R in prostate cancer cells make them more resistant to TRAIL treatment. Here we show that Sig1R is critically involved in TRAIL-induced caspase activation. Furthermore, we show that Sig1R protein is degraded upon TRAIL treatment. Knockdown of Sig1R, by siRNA transfection increased the sensitivity of breast cancer cells to TRAIL. These results indicate that Sig1R could represent a promising molecule to sensitize human breast cancers to TRAIL. Collectively, these studies define Sig1R as a key mediator of TRAIL induction of cancer-specific killing.

Sigma 1 Receptor antagonist potentiates the anti-cancer effect of p53 by regulating ER stress, ROS production, Bax levels, and caspase-3 activation

Over the last years, many improvements have been made in the treatment of breast cancer; however, novel and less toxic therapies are still needed, especially for relapsing and chemo-resistant patients. Here, we analyzed the therapeutic potential of p53 and Rimcazole, a Sigma 1 Receptor antagonist. Rimcazole and p53 are being evaluated in preclinical and clinical trials, respectively. While p53 is a promising antitumor therapeutic agent, antagonists of Sigma 1 Receptor also inhibit tumor cell survival and induce apoptosis. Our current study demonstrates for the first time the synergistic effect of p53 in combination with the Sigma 1 Receptor antagonist Rimcazole. Furthermore, we show that shRNA knockdown of Sigma 1 Receptor in combination with p53, lead to a similar synergistic effect, and that this synergistic effect, in breast cancer growth suppression occurs independent of p53 status. Furthermore, this combination treatment induced ER stress, p38 MAPK activation, ROS production, and proteins involved in apoptosis (caspases-3, Bax) in breast cancer cells. Combining these therapeutic anti-cancer molecules provides an innovative approach for potentially treating human breast cancer.

Microfluidic generated EGF-gradients induce chemokinesis of transplantable retinal progenitor cells via the JAK/STAT and PI3kinase signaling pathways

A growing number of studies are evaluating retinal progenitor cell (RPC) transplantation as an approach to repair retinal degeneration and restore visual function. To advance cell-replacement strategies for a practical retinal therapy, it is important to define the molecular and biochemical mechanisms guiding RPC motility. We have analyzed RPC expression of the epidermal growth factor receptor (EGFR) and evaluated whether exposure to epidermal growth factor (EGF) can coordinate motogenic activity in vitro. Using Boyden chamber analysis as an initial high-throughput screen, we determined that RPC motility was optimally stimulated by EGF concentrations in the range of 20-400 ng/ml, with decreased stimulation at higher concentrations, suggesting concentration-dependence of EGF-induced motility. Using bioinformatics analysis of the EGF ligand in a retina-specific gene network pathway, we predicted a chemotactic function for EGF involving the MAPK and JAK-STAT intracellular signaling pathways. Based on targeted inhibition studies, we show that ligand binding, phosphorylation of EGFR and activation of the intracellular STAT3 and PI3kinase signaling pathways are necessary to drive RPC motility. Using engineered microfluidic devices to generate quantifiable steady-state gradients of EGF coupled with live-cell tracking, we analyzed the dynamics of individual RPC motility. Microfluidic analysis, including center of mass and maximum accumulated distance, revealed that EGF induced motility is chemokinetic with optimal activity observed in response to low concentration gradients. Our combined results show that EGFR expressing RPCs exhibit enhanced chemokinetic motility in the presence of low nanomole levels of EGF. These findings may serve to inform further studies evaluating the extent to which EGFR activity, in response to endogenous ligand, drives motility and migration of RPCs in retinal transplantation paradigms.

Sigma 1 Receptor plays a prominent role in IL-24-induced cancer-specific apoptosis

Interleukin-24 (IL-24), a member of the IL-10 cytokine family, is an immunomodulatory cytokine that also displays broad cancer-specific suppressor effects. The tumor suppressor activities of IL-24 include inhibition of angiogenesis, sensitization to chemotherapy, and cancer-specific apoptosis. We show that Sigma 1 Receptor (S1R), a ligand-regulated protein chaperone contributes to IL-24 induction of apoptosis. IL-24 generated from an adenovirus expressing IL-24 (Ad.IL-24) induces cancer-specific apoptosis by inducing an endoplasmic reticulum (ER) stress, reactive oxygen species production, and calcium mobilization. The present studies reveals that S1R is required for Ad.IL-24-induced cell death. We provide several lines of evidence to confirm a physical and functional interaction between IL-24 and S1R including: (a) S1R and IL-24 co-localize, as judged by immunocytochemical analysis studies; (b) S1R and IL-24 co-immunoprecipitate using either S1R or IL-24 antibody; (c) S1R agonist (+)-SKF10047 inhibits apoptosis by Ad.IL-24; (d) (+)-SKF10047-mediated inhibition of Ad.IL-24 results in: diminished ER stress protein expression; (e) Calcium mobilization; and (f) ROS production. Collectively, these data demonstrate that S1R interacts with IL-24 and suggest that IL-24:S1R interaction determines apoptosis induction by Ad.IL-24. These studies define Sigma 1 Receptor as a key initial mediator of IL-24 induction of cancer-specific killing. These findings have important implications for our understanding of IL-24 as a tumor suppressor protein as well as an immune modulating cytokine.

The development of MDA-7/IL-24 as a cancer therapeutic

The cytokine melanoma differentiation associated gene 7 (mda-7) was identified by subtractive hybridization as a protein whose expression increased during the induction of terminal differentiation, and that was either not expressed or was present at low levels in tumor cells compared to non-transformed cells. Based on conserved structure, chromosomal location and cytokine-like properties, MDA-7, was classified as a member of the interleukin (IL)-10 gene family and designated as MDA-7/IL-24. Multiple studies have demonstrated that expression of MDA-7/IL-24 in a wide variety of tumor cell types, but not in corresponding equivalent non-transformed cells, causes their growth arrest and rapid cell death. In addition, MDA-7/IL-24 has been noted to radiosensitize tumor cells which in part is due to the generation of reactive oxygen species (ROS) and ceramide that cause endoplasmic reticulum stress and suppress protein translation. Phase I clinical trial data has shown that a recombinant adenovirus expressing MDA-7/IL-24 (Ad.mda-7 (INGN-241)) was safe and had measurable tumoricidal effects in over 40% of patients, strongly arguing that MDA-7/IL-24 could have significant therapeutic value. This review describes what is presently known about the impact of MDA-7/IL-24 on tumor cell biology and its potential therapeutic applications.

MDA-7/IL-24 as a cancer therapeutic: from bench to bedside

The novel cytokine melanoma differentiation associated gene-7 (mda-7) was identified by subtractive hybridization in the mid-1990s as a protein whose expression increased during the induction of terminal differentiation, and that was either not expressed or was present at low levels in tumor cells compared with non-transformed cells. On the basis of conserved structure, chromosomal location and cytokine-like properties, MDA-7, has now been classified as a member of the expanding interleukin (IL)-10 gene family and designated as MDA-7/IL-24. Multiple studies have shown that the expression of MDA-7/IL-24 in a wide variety of tumor cell types, but not in the corresponding equivalent non-transformed cells, causes their growth arrest and ultimately cell death. In addition, MDA-7/IL-24 has been noted to be a radiosensitizing cytokine, which is partly because of the generation of reactive oxygen species and ceramide that cause endoplasmic reticulum stress. Phase I clinical trial data has shown that a recombinant adenovirus expressing MDA-7/IL-24 [Ad.mda-7 (INGN-241)] was safe and had measurable tumoricidal effects in over 40% of patients, which strongly argues that MDA-7/IL-24 may have significant therapeutic value. This review describes what is known about the impact of MDA-7/IL-24 on tumor cell biology and its potential therapeutic applications.

Ceramide plays a prominent role in MDA-7/IL-24-induced cancer-specific apoptosis

Melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) uniquely displays broad cancer-specific apoptosis-inducing activity through induction of endoplasmic reticulum (ER) stress. We hypothesize that ceramide, a promoter of apoptosis, might contribute to mda-7/IL-24 induction of apoptosis. Ad.mda-7-infected tumor cells, but not normal cells, showed increased ceramide accumulation. Infection with Ad.mda-7 induced a marked increase in various ceramides (C16, C24, C24:1) selectively in prostate cancer cells. Inhibiting the enzyme serine palmitoyltransferase (SPT) using the potent SPT inhibitor myriocin (ISP1), impaired mda-7/IL-24-induced apoptosis and ceramide production, suggesting that ceramide formation caused by Ad.mda-7 occurs through de novo synthesis of ceramide and that ceramide is required for mda-7/IL-24-induced cell death. Fumonisin B1 (FB1) elevated ceramide formation as well as apoptosis induced by Ad.mda-7, suggesting that ceramide formation may also occur through the salvage pathway. Additionally, Ad.mda-7 infection enhanced expression of acid sphingomyelinase (ASMase) with a concomitant increase in ASMase activity and decreased sphingomyelin in cancer cells. ASMase silencing by RNA interference inhibited the decreased cell viability and ceramide formation after Ad.mda-7 infection. Ad.mda-7 activated protein phosphatase 2A (PP2A) and promoted dephosphorylation of the anti-apoptotic molecule BCL-2, a downstream ceramide-mediated pathway of mda-7/IL-24 action. Pretreatment of cells with FB1 or ISP-1 abolished the induction of ER stress markers (BiP/GRP78, GADD153 and pospho-eIF2alpha) triggered by Ad.mda-7 infection indicating that ceramide mediates ER stress induction by Ad.mda-7. Additionally, recombinant MDA-7/IL-24 protein induced cancer-specific production of ceramide. These studies define ceramide as a key mediator of an ER stress pathway that may underlie mda-7/IL-24 induction of cancer-specific killing.

Historical perspective and recent insights into our understanding of the molecular and biochemical basis of the antitumor properties of mda-7/IL-24

A subtraction hybridization approach combined with a differentiation therapy model of human melanoma identified melanoma differentiation associated gene-7 (mda-7) as a gene upregulated during induction of terminal differentiation. Based on conserved structure, chromosomal location and cytokine-like properties, mda-7, has now been classified as a member of the expanding interleukin (IL)-10 gene family and designated as mda-7/IL-24. Extensive in vitro and in vivo human tumor xenograft studies confirm that mda-7/IL-24 induces apoptosis specifically in tumor cells without harming normal cells. Unique properties of mda-7/IL-24 action also include potent "bystander antitumor" activity, an ability to exert anti-angiogenic effects, immune modulating ability and a capacity to enhance the sensitivity of tumor cells to radiotherapy, chemotherapy and monoclonal antibody therapy. Very recent studies from our groups further reveal autocrine regulation and chemoprevention facilitating properties of mda-7/IL-24. Based on these remarkable antitumor attributes, mda-7/IL-24 was evaluated by intratumoral injection with a replication incompetent adenovirus expressing this gene (Ad.mda-7; INGN 241) in a phase I clinical trial in patients with metastatic melanomas and other advanced solid cancers. mda-7/IL-24 was well tolerated with significant clinical activity. This review highlights our current understanding of the molecular and biochemical basis of mda-7/IL-24 antitumor properties and highlights its potential as a viable gene-based therapy for a wide spectrum of primary and advanced cancers.

Caspase-, cathepsin-, and PERK-dependent regulation of MDA-7/IL-24-induced cell killing in primary human glioma cells

Melanoma differentiation-associated gene-7/interleukin-24 (mda-7/IL-24) is a novel cytokine displaying selective apoptosis-inducing activity in transformed cells without harming normal cells. The present studies focused on defining the mechanism(s) by which a GST-MDA-7 fusion protein inhibits cell survival of primary human glioma cells in vitro. GST-MDA-7 killed glioma cells with diverse genetic characteristics that correlated with inactivation of ERK1/2 and activation of JNK1-3. Activation of JNK1-3 was dependent on protein kinase R-like endoplasmic reticulum kinase (PERK), and GST-MDA-7 lethality was suppressed in PERK-/- cells. JNK1-3 signaling activated BAX, whereas inhibition of JNK1-3, deletion of BAX, or expression of dominant-negative caspase-9 suppressed lethality. GST-MDA-7 also promoted a PERK-, JNK-, and cathepsin B-dependent cleavage of BID; loss of BID function promoted survival. GST-MDA-7 suppressed BAD and BIM phosphorylation and heat shock protein 70 (HSP70) expression. GST-MDA-7 caused PERK-dependent vacuolization of LC3-expressing endosomes whose formation was suppressed by incubation with 3-methyladenine, expression of HSP70 or BiP/GRP78, or knockdown of ATG5 or Beclin-1 expression but not by inhibition of the JNK1-3 pathway. Knockdown of ATG5 or Beclin-1 expression or overexpression of HSP70 reduced GST-MDA-7 lethality. Our data show that GST-MDA-7 induces an endoplasmic reticulum stress response that is causal in the activation of multiple proapoptotic pathways, which converge on the mitochondrion and highlight the complexity of signaling pathways altered by mda-7/IL-24 in glioma cells that ultimately culminate in decreased tumor cell survival.

mda-7/IL-24, novel anticancer cytokine: focus on bystander antitumor, radiosensitization and antiangiogenic properties and overview of the phase I clinical experience (Review)

Subtraction hybridization applied to a 'differentiation therapy' model of cancer employing human melanoma cells resulted in the cloning of melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24). Initial studies confirm an inverse correlation between mda-7 expression and melanoma development and progression. Forced expression of mda-7 by means of a plasmid or via a replication incompetent adenovirus (Ad.mda-7) promotes growth suppression and induces apoptosis in a broad array of human cancers. In contrast, mda-7 does not induce growth suppressive or toxic effects in normal cells. Based on structure (containing an IL-10 signature motif), secretion by cells (including subsets of T-cells) and location on chromosome 1q (in an area containing IL-10-family genes), mda-7 has now been renamed mda-7/IL-24. Studies by several laboratories have uncovered many of mda-7/IL-24's unique properties, including cancer-specific apoptosis-induction, cell cycle regulation, an ability to inhibit angiogenesis, potent 'bystander antitumor activity' and a capacity to enhance the sensitivity of tumor cells to radiation, chemotherapy and monoclonal antibody therapy. Moreover, based on its profound cancer tropism, substantiated by in vivo human xenograft studies in nude mice, mda-7/IL-24 (administered as Ad.mda-7) was evaluated in a phase I clinical trial in patients with melanomas and solid cancers. These studies document that mda-7/IL-24 is well tolerated and demonstrates evidence of significant clinical activity. In these contexts, mda-7/IL-24 represents a unique cytokine gene with potential for therapy of human cancers. The present review focuses on three unique properties of mda-7/IL-24, namely its potent 'bystander antitumor activity', ability to sensitize tumor cells to radiation, and its antiangiogenesis properties. Additionally, an overview of the phase I clinical trial is provided. These studies affirm that mda-7/IL-24 has promise for the management of diverse cancers.

Melanoma differentiation associated gene-7 (mda-7)/IL-24: a 'magic bullet' for cancer therapy?

An ideal cancer gene therapy would selectively kill cancer cells without harming normal cells and induce multipronged 'bystander' antitumor effects, facilitating eradication of both primary and metastatic tumors. Melanoma differentiation associated gene-7 (mda-7)/interleukin-24 (IL-24) exhibits all of these attributes and more. It induces cancer-selective apoptosis, inhibits angiogenesis, stimulates an antitumor immune response, sensitizes cancer cells to radiation and other modalities of conventional therapies, and exhibits profound 'bystander' activity eliminating both primary and distant tumors in animal models. Moreover, a replication-incompetent adenovirus expressing mda-7/IL-24, Ad.mda-7 (INGN-241), has now undergone evaluation in a Phase I clinical trial for multiple solid tumors, including melanomas, and has demonstrated safety and significant objective clinical activity. Considering these exciting observations, mda-7/IL-24 is being hailed as a 'magic bullet' for cancer gene therapy. This review elaborates on the pleiotropic properties of mda-7/IL-24 and unravels novel aspects of the molecule mandating future studies and expanded clinical applications.

Prostate-derived ETS factor is a mediator of metastatic potential through the inhibition of migration and invasion in breast cancer

Cell migration and invasion are critical events during the progression to metastasis. Without motile function, cancer cells are unable to leave the primary tumor site, invade through the basement membrane, and form secondary tumors. Expression of the epithelial-specific ETS factor prostate-derived ETS factor (PDEF) is reduced in human invasive breast tissue and lost in invasive breast cancer cell lines. Gain-of-function studies that examine different aspects of cell migration show that constitutive or inducible PDEF reexpression inhibits migration and invasion in multiple breast cancer cell lines, and loss-of-function studies show a stimulation of migration in noninvasive breast cancer cells. Furthermore, the introduction of PDEF into invasive breast cancer cells led to a remodeling of the actin cytoskeleton and altered focal adhesion localization and adherence levels. Cells expressing PDEF no longer form the defined morphologic polarity required for efficient, directional migration. Collectively, these data indicate that PDEF down-regulation in invasive breast cancer may promote actin-mediated cell migration through the extracellular matrix.

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.

Melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24): novel gene therapeutic for metastatic melanoma

A potentially less toxic approach for cancer therapy comprises induction of tumor cells to lose growth potential irreversibly and terminally differentiate. Combining this scheme termed 'differentiation therapy of cancer' with subtraction hybridization to human melanoma cells resulted in the cloning of melanoma differentiation associated (mda) genes displaying elevated expression as a consequence of induction of terminal differentiation. One originally novel gene, mda-7, was found to display elevated expression in normal melanocytes and nevi with progressive loss of expression as a consequence of melanoma development and progression to metastasis. Based on structure, biochemical properties and chromosomal location, mda-7 has now been reclassified as interleukin (IL)-24, a member of the expanding IL-10 family of cytokines. In vitro cell culture and in vivo animal studies indicate that mda-7/IL-24 selectively induces programmed cell death (apoptosis) in multiple human cancers (including melanomas), without harming normal cells, and promotes profound anti-tumor activity in nude mice containing human tumor xenografts. Based on these remarkable properties, a Phase I clinical trial was conducted to test the safety of administration of mda-7/IL-24 by a replication incompetent adenovirus (Ad.mda-7; INGN 241) in patients with advanced solid cancers including melanoma. mda-7/IL-24 was found to be safe and to promote significant clinical activity, particularly in the context of patients with metastatic melanoma. These results provide an impetus for further clinical studies and document a central paradigm of cancer therapy, namely translation of basic science from the "bench to the bedside."

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.

Leukemia Inhibitory Factor Induces DNA Synthesis in Swiss Mouse 3T3 Cells Independently of Cyclin D1 Expression through a Mechanism Involving MEK/ERK1/2 Activation

Leukemia inhibitory factor (LIF) and oncostatin M (OSM) induce DNA synthesis in Swiss 3T3 cells through common signaling mechanism(s), whereas other related cytokines such as interleukin-6 and ciliary neurotrophic factor do not cause this response. Induction of DNA replication by LIF or prostaglandin F2alpha (PGF2alpha) occurs, in part, through different signaling events. LIF and OSM specifically trigger STAT1 cytoplasmic to nuclear translocation, whereas PGF2alpha fails to do so. However, LIF and PGF2alpha can trigger increases in ERK1/2 activity, which are required for their mitogenic responses because U0126, a MEK1/2 inhibitor, prevents both ERK1/2 activation and induction of DNA synthesis by LIF or PGF2alpha treatment. PGF2alpha induces cyclin D expression and full phosphorylation of retinoblastoma protein. In contrast, LIF fails to promote increases in cyclin D mRNA/protein levels; consequently, LIF induces DNA synthesis without promoting full phosphorylation of retinoblastoma protein (Rb). However, both LIF and PGF2alpha increase cyclin E expression. Furthermore, LIF mitogenic action does not involve protein kinase C (PKC) activation, because a PKC inhibitor does not block this effect. In contrast, PKC activity is required for PGF2alpha mitogenic action. More importantly, the synergistic effect between LIF and PGF2alpha to promote S phase entry is independent of PKC activation. These results show fundamental differences between LIF- and PGF2alpha-dependent mechanism(s) that induce cellular entry into S phase. These findings are critical in understanding how LIF and other related cytokine-regulated events participate in normal cell cycle control and may also provide clues to unravel crucial processes underlying cancerous cell division.

Unique aspects of mda-7/IL-24 antitumor bystander activity: establishing a role for secretion of MDA-7/IL-24 protein by normal cells

Melanoma differentiation associated gene-7 (mda-7) was cloned using subtraction hybridization from terminally differentiated human melanoma cells. Based on structural and functional properties, mda-7 is now recognized as interleukin-24 (IL-24), a new member of the expanding IL-10 gene family. Unique properties of mda-7/IL-24 include its ability to selectively induce growth suppression, apoptosis and radiosensitization in diverse human cancer cells, without causing similar effects in normal cells. The utility of mda-7/IL-24, administered by means of a replication-incompetent adenovirus, as a gene therapy for cancer has recently received validation in patients, highlighting an important phenomenon initially observed in pancreatic tumor cells, namely a 'potent bystander apoptosis-inducing effect' in adjacent tumor cells not initially receiving this gene product. We presently investigated the contribution of mda-7/IL-24 secreted by normal cells in mediating this 'bystander effect', and document that normal cells induced to produce mda-7/IL-24 following infection with recombinant adenoviruses expressing this cytokine secrete mda-7/IL-24, which modifies the anchorage-independent growth, invasiveness, survival and sensitivity to radiation of cancer cells that contain functional IL-20/IL-22 receptors, but not in cancer cells that lack a complete set of receptors. Moreover, the combination of secreted mda-7/IL-24 and radiation engenders a 'bystander antitumor effect' not only in inherently mda-7/IL-24 or radiation-sensitive cancer cells, but also in tumor cells overexpressing the antiapoptotic proteins bcl-2 or bcl-x(L) and displaying resistance to either treatment alone. The present studies provide definitive evidence that secreted mda-7/IL-24 from normal cells can induce direct antitumor and radiation-enhancing effects that are dependent on the presence of canonical receptors for this cytokine on tumor cells. Moreover, we now describe a novel means of enhancing mda-7/IL-24's therapeutic potential by targeting normal cells to produce and release this cancer-specific apoptosis-inducing cytokine, a strategy that could be employed as an innovative way of using this unique gene product for treating metastatic disease.

Cytokine and tumor cell apoptosis inducing activity of mda-7/IL-24

Melanoma Differentiation Associated gene-7 (mda-7)/IL-24 has shown potent tumor cell apoptosis inducing capacity in multiple cancers, making it a strong candidate for use as a human cancer gene therapeutic. Several independent studies have currently documented and confirmed mda-7/IL-24's cytokine nature including presence of a canonical secretory signal peptide, processing and secretion of the molecule by cells and it's binding to specific interleukin receptors on the cell surface. Receptor binding has been shown to activate the JAK/STAT signal transduction pathway with concomitant stimulation of STAT 1 and 3 transactivators. The physiological role(s) of this molecule in modulating immune responses, as a member of the IL-10 family of cytokines, is not well documented and most current information pertains to its apparently restricted expression patterns in specific cell types with immunomodulatory activity. On the other hand, several additional signal transduction pathways were modulated when cells overexpress mda-7/IL-24, not all of which are necessarily downstream of mda-7/IL-24 induced JAK/STAT activation. A summary of the current status of information is presented to provide a perspective for the cytokine-related properties of mda-7/IL-24 in correlation to its tumor cell apoptosis inducing activity. Moreover, new evidence has surfaced pointing toward apoptosis induction via mechanisms independent of cytokine activity-related JAK/STAT activation.

mda-7/IL-24: exploiting cancer's Achilles' heel

The mda-7/IL-24 cDNA was isolated almost a decade ago in a screen for genes differentially upregulated following growth arrest and terminal differentiation of a human melanoma cell line employed as an in vitro cell differentiation model. The underlying rationale for the screen was that oncogenesis arises from a cellular dedifferentiation process culminating in uncontrolled proliferation and acquisition of invasive and metastatic potential. Identification of genes upregulated during the process of reactivation of faulty or inoperational differentiation maintenance programs was postulated to have cancer gene therapeutic potential. In this context, it is heartening to note that mda-7/IL-24 has made a methodical and progressive journey, from an unidentified novel sequence with little homology to known genes at its time of isolation to currently having the status of a molecule belonging to the IL-10-related family of cytokines, with considerable cancer gene therapeutic potential. Extensive in vitro and in vivo human tumor xenograft studies have established its transformed cell apoptosis-inducing capacity in various model systems. It has recently taken an important step for a candidate cancer gene therapeutic molecule, in the ultimate goal of benchtop to clinic, by being currently utilized in human Phase I/II clinical trials. This review provides a current perspective of our understanding of mda-7/IL-24, including established and more recent information about the molecular properties, specificity of anti-tumor-cell apoptosis-inducing activity, and underlying mechanisms of this action relative to its cancer gene therapeutic potential.

Mechanistic aspects of mda-7/IL-24 cancer cell selectivity analysed via a bacterial fusion protein

The human mda-7/IL-24 gene product is normally expressed in melanocytes and certain lymphocyte populations. Loss of expression, a distinctive feature of many tumor suppressor genes, has been documented at RNA and protein levels in association with melanoma progression both in vitro as well as in human tumor-derived material. The MDA-7/IL-24 protein undergoes post-translational processing, including removal of an amino-terminal 48-residue signal peptide and extensive glycosylation prior to its secretion by producing cells. Its inherent cytokine properties have been documented in multiple reports, which have identified and characterized its cognate receptors and activation of the JAK/STAT signaling pathway following ligand/receptor docking. A notable and incompletely understood property of MDA-7/IL-24 is its ability to induce apoptosis in transformed cells, while having marginal growth suppressive effects on normal primary or immortalized cell lines. MDA-7/IL-24 has been delivered to cells, tumor xenografts and patients in clinical trials via a nonreplicating adenovirus (Ad.mda-7). Studies utilizing eukaryotically expressed and purified MDA-7/IL-24 protein from several sources have recapitulated some of the molecule's reported properties including receptor binding and JAK/STAT activation. Here, we report the properties and characteristics of a bacterially expressed and purified GST-MDA-7 fusion protein. These studies reveal that GST-MDA-7 retains its cancer-selective apoptosis-inducing properties, thereby providing a new reagent that will assist in defining the mechanism of action of this novel cytokine. In addition, retention of tumor-specific activity of GST-MDA-7 suggests that this protein may also have therapeutic applications.

Melanoma differentiation associated gene-7/interleukin-24 promotes tumor cell-specific apoptosis through both secretory and nonsecretory pathways

Melanoma differentiation associated gene-7/interleukin-24 (Mda-7/IL-24), a novel member of the IL-10 family of cytokines, uniquely displays cancer-specific apoptosis-inducing activity. Positive results in ongoing phase I/II clinical trials have strengthened the possibility of its utilization as a cancer gene therapeutic. Previous studies document that signaling events leading to Ad.mda-7-induced transformed cell apoptosis are tyrosine kinase-independent. These results suggest that mda-7/IL-24 cancer cell-specific activity could occur through mechanisms independent of binding to its currently recognized cognate receptors and might even occur independent of receptor function. An adenovirus vector expressing a nonsecreted version of MDA-7/IL-24 protein was generated via deletion of its signal peptide. This nonsecreted protein was as effective as wild-type secreted MDA-7/IL-24 in inducing apoptosis in prostate carcinoma cell lines and displayed transformed cell specificity and localization of MDA-7/IL-24 in the Golgi/endoplasmic reticulum compartments. Our results indicate that mda-7/IL-24-mediated apoptosis can be triggered through a combination of intracellular as well as secretory mechanisms and can occur efficiently in the absence of protein secretion.

Leukaemia inhibitory factor or Oncostatin M induction of Swiss 3T3 cells does not require mevalonic acid synthesis nor protein isoprenylation to initiate DNA replication

Leukaemia inhibitory factor (LIF) or Oncostatin M (OSM), both mitogens for Swiss mouse 3T3 cells, triggers initiation of DNA synthesis without the requirement for mevalonic acid. Thus, Lovastatin (LOV), an inhibitor of the hydroxy methylglutaryl CoA (HMGCoA) reductase, does not block LIF or OSM induced DNA replication and cell multiplication. In contrast, increasing concentrations of LOV from 1 to 60 microM block the mitogenic action of PGF(2alpha) by decreasing the number of cells capable of entering S-phase and dividing. This inhibition by LOV can be reversed by addition of mevanolactone (MEV), an analogue of mevalonic acid. Thus, LIF or OSM triggers initiation of DNA replication independently of mevalonic acid synthesis and therefore without the involvement of isoprenylation of various signalling proteins.

Mda-7/IL-24 induces apoptosis of diverse cancer cell lines through JAK/STAT-independent pathways

Experimental evidence documents that the MDA-7/IL-24 protein (an IL-10 family cytokine) binds to IL-20 and IL-22 receptor complexes resulting in the activation of JAK/STAT signaling pathways. Recent published reports utilizing human blood derived primary lymphocytes have provided additional confirmatory evidence relating to the cytokine properties of this molecule. A notable attribute of mda-7/IL-24 is its cancer cell-specific apoptosis inducing capacity, which currently remains incompletely understood. Treatment with distinctive tyrosine kinase inhibitors (Genistein and AG18) or a JAK-selective inhibitor (AG490) did not prevent Ad.mda-7 induced apoptosis in diverse cell lines. In addition, there is no apparent correlation between patterns of expression of IL-20R1, IL-20R2, and IL-22R mRNA and susceptibility to Ad.mda-7 in different cell lines. Furthermore, Ad.mda-7 is able to induce killing in STAT/JAK deficient cells. In contrast, treatment with the p38(MAPK) selective inhibitor SB203580, partially inhibited apoptosis induced by Ad.mda-7 in different cell lines. These results demonstrate for the first time that signaling events leading to susceptibility to Ad.mda-7 induced apoptosis, might be tyrosine kinase independent and can thus be distinguished from its cytokine function related properties mediated by the IL-20/IL-22 receptor complexes that require JAK/STAT kinase activity.

Melanoma differentiation associated gene-7, mda-7/IL-24, selectively induces growth suppression, apoptosis and radiosensitization in malignant gliomas in a p53-independent manner

Malignant gliomas are extremely aggressive cancers currently lacking effective treatment modalities. Gene therapy represents a promising approach for this disease. A requisite component for improving gene-based therapies of brain cancer includes tumor suppressor genes that exhibit cancer constrained inhibitory activity. Subtraction hybridization identified melanoma differentiation associated gene-7 (mda-7) as a gene associated with melanoma cell growth, differentiation and progression. Ectopic expression of mda-7 by means of a replication-incompetent adenovirus (Ad), Ad.mda-7, induces growth suppression and apoptosis selectively in diverse human cancers, without producing any apparent harmful effect in normal cells. We presently demonstrate that Ad.mda-7 induces growth inhibition and apoptosis in malignant human gliomas expressing both mutant and wild-type p53, and these effects correlate with an elevation in expression of members of the growth arrest and DNA damage (GADD) gene family. In contrast, infection with a recombinant Ad expressing wild-type p53, Ad.wtp53, specifically affects mutant p53 expressing gliomas. When tested in early passage normal and immortal human fetal astrocytes, growth inhibition resulting from infection with Ad.mda-7 or Ad.wtp53 is significantly less than in malignant gliomas and no toxicity is evident in these normal cells. Moreover, infection of gliomas with Ad.mda-7 or treatment with purified GST-MDA-7 protein sensitizes both wild-type and mutant p53 expressing tumor cells to the growth inhibitory and antisurvival effects of ionizing radiation, and this response correlates with increased expression of specific members of the GADD gene family. Since heterogeneity in p53 expression is common in evolving gliomas, the present findings suggest that Ad.mda-7 may, in many instances, prove more beneficial for the gene-based therapy of malignant gliomas than administration of wild-type p53.

MDA-7/IL-24: novel cancer growth suppressing and apoptosis inducing cytokine

The melanoma differentiation-associated gene-7 (mda-7) was cloned by subtraction hybridization as a molecule whose expression is elevated in terminally differentiated human melanoma cells. Current information based on structural and sequence homology, has led to the recognition of MDA-7 as an IL-10 family cytokine member and its renaming as IL-24. Northern blot analysis revealed mda-7/IL-24 expression in human tissues associated with the immune system such as spleen, thymus, peripheral blood leukocytes and normal melanocytes. The MDA-7/IL-24 mouse counterpart, FISP, appears to be a Th2-specific protein and the rat counterpart, C49A/MOB-5, is associated with wound healing and is also induced as a consequence of ras-transformation. A notable property of MDA-7/IL-24 is its ability to induce apoptosis in a large spectrum of human cancer derived cell lines, in mouse xenografts and upon intratumoral injection in human tumors (phase I clinical trials). Various aspects of this intriguing molecule including its cytokine and anti-tumoral effects are described and discussed.

mda-7 (IL-24): signaling and functional roles

One hallmark of neoplasia is abnormal differentiation. Induction of differentiation, by chemical or biological methods, provides a possible therapeutic intervention. "Differentiation therapy" is well documented in several model systems. These include melanoma, in which treatment with interferon-beta and the protein kinase C activator mezerein induces irreversible growth arrest and terminal differentiation culminating in programmed cell death. Subtraction hybridization between terminally differentiated and untreated melanoma cells identified melanoma differentiation-associated gene-7 (mda-7), which is selectively induced during the process of melanoma terminal differentiation. Since its identification seven years ago, mda-7 has been the object of intense focus because of its unique biological properties. Firstly, mda-7 is a secreted protein having cytokine-like properties and belonging to the IL-10 cytokine family. Based on this consideration, mda-7 was renamed IL-24. Secondly if delivered by means of an adenoviral vector, mda-7 induces selective apoptosis in cancer cells of diverse origin, while sparing their normal cellular counterparts. As such, mda-7 has become a novel tool for cancer gene therapy and is currently undergoing phase II clinical trials to determine its clinical efficacy in patients. The present review examines the biological properties of mda-7 and the signaling pathways that contribute to its unique cancer-specific apoptosis-inducing properties.

mda-7 (IL-24) Mediates selective apoptosis in human melanoma cells by inducing the coordinated overexpression of the GADD family of genes by means of p38 MAPK

Subtraction hybridization identified melanoma differentiation-associated gene-7 (mda-7) as a gene induced during terminal differentiation in human melanoma cells. On the basis of structure, chromosomal localization and cytokine-like properties, mda-7 is classified as IL-24. Administration of mda-7/IL-24 by means of a replication-incompetent adenovirus (Ad.mda-7) induces apoptosis selectively in diverse human cancer cells without inducing harmful effects in normal fibroblast or epithelial cells. The present studies investigated the mechanism underlying this differential apoptotic effect. Infection of melanoma cells, but not normal immortal melanocytes, with Ad.mda-7 induced a time- and dose-dependent increase in expression, mRNA and protein, of a family of growth arrest and DNA damage (GADD)-inducible genes, which correlated with induction of apoptosis. Among the members of the GADD family of genes, GADD153, GADD45 alpha, and GADD34 displayed marked, and GADD45 gamma showed minimal induction. Treatment of melanoma cells with SB203580, a selective inhibitor of the p38 mitogen-activated protein kinase (MAPK) pathway, effectively inhibited Ad.mda-7-induced apoptosis. Additional support for an involvement of the p38 MAPK pathway in Ad.mda-7-mediated apoptosis was documented by using an adenovirus expressing a dominant negative mutant of p38 MAPK. Infection with Ad.mda-7 increased the phosphorylation of p38 MAPK and heat shock protein 27 in melanoma cells but not in normal immortal melanocytes. In addition, SB203580 effectively inhibited Ad.mda-7-mediated induction of the GADD family of genes in a time- and dose-dependent manner, and it effectively blocked Ad.mda-7-mediated down-regulation of the antiapoptotic protein BCL-2. Inhibition of GADD genes by an antisense approach either alone or in combination also effectively blocked Ad.mda-7-induced apoptosis in melanoma cells. These results support the hypothesis that Ad.mda-7 mediates induction of the GADD family of genes by means of the p38 MAPK pathway, thereby resulting in the selective induction of apoptosis in human melanoma cells.

Prostaglandin F(2alpha) (PGF(2alpha)) induces cyclin D1 expression and DNA synthesis via early signaling mechanisms in Swiss mouse 3T3 cells

Prostaglandin F(2alpha) (PGF(2alpha)), a mitogen for Swiss 3T3 cells, triggers cyclin D1 mRNA/protein expression prior to cellular entry into the S phase, but fails to raise cdk4 or cyclin D3 levels, while 1-oleoyl-2-diacylglycerol (OAG), a protein kinase C (PKC) and tyrosine kinase (TK) activator, induces only cyclin D1 expression with no mitogenic response. In contrast, in PKC-depleted or -inhibited cells, PGF(2alpha), but not OAG, increases cyclin D1 expression with no mitogenic response. Finally, OAG, in the presence of orthovanadate (Na(3)VO(4)) or TGF(beta1), induces DNA synthesis. Thus, it appears that PGF(2alpha) triggers cyclin D1 expression via two independent signaling events that complement with TGF(beta1)-triggered events to induce DNA synthesis.

Leukaemia inhibitory factor induces mitogenesis in Swiss 3T3 cells and selective enhancement via a variety of signalling events

Leukaemia inhibitory factor (LIF) stimulates cellular DNA synthesis in confluent quiescent Swiss 3T3 cells. Insulin and prostaglandin E1 (PGE1), which fail to stimulate DNA synthesis alone, potentiate this effect. Prostaglandin F2alpha (PGF2alpha), which is mitogenic in these cells, enhances the effect of LIF on DNA synthesis. TGFbeta1 increases the effect of PGF2alpha but not that of LIF. R-59022, a diacylglycerol kinase inhibitor which increases protein kinase C (PKC) activity, enhances only the PGF2alpha response. 13-Tetradecanoyl-12-phorbolacetate-mediated PKC depletion prevents the action of PGF2alpha but not that of LIF, nor the PGF2alpha potentiation of LIF-stimulated DNA synthesis. 1-Oleoyl-2acetylglycerol, a PKC and tyrosine kinase (TK) activator which mimics some of the PGF2alpha effects, enhances only LIF-induced DNA synthesis in cells possessing intact PKC activity. These results suggest that stimulation of DNA synthesis by LIF, as well as its enhancement by PGF2alpha, may occur via a signalling pathway independent of PKC activation.

Inhibition of nucleoside diphosphate kinase activity by in vitro phosphorylation by protein kinase CK2. Differential phosphorylation of NDP kinases in HeLa cells in culture

Although a number of nucleoside diphosphate kinases (NDPKs) have been reported to act as inhibitors of metastasis or as a transcription factor in mammals, it is not known whether these functions are linked to their enzymatic activity or how this protein is regulated. In this report, we show that in vitro protein kinase CK2 catalyzed phosphorylation of human NDPK A inhibits its enzymatic activity by inhibiting the first step of its ping-pong mechanism of catalysis: its autophosphorylation. Upon in vivo 32P labeling of HeLa cells, we observed that both human NDPKs, A and B, were autophosphorylated on histidine residues, however, only the B isoform appeared to be serine phosphorylated.