IFN-gamma induction of p21(WAF1) is required for cell cycle inhibition and suppression of apoptosis

c-Myc uses Cul4b to preserve genome integrity and promote antiviral CD8+ T cell immunity

During infection, virus-specific CD8+ T cells undergo rapid bursts of proliferation and differentiate into effector cells that kill virus-infected cells and reduce viral load. This rapid clonal expansion can put T cells at significant risk for replication-induced DNA damage. Here, we find that c-Myc links CD8+ T cell expansion to DNA damage response pathways though the E3 ubiquitin ligase, Cullin 4b (Cul4b). Following activation, c-Myc increases the levels of Cul4b and other members of the Cullin RING Ligase 4 (CRL4) complex. Despite expressing c-Myc at high levels, Cul4b-deficient CD8+ T cells do not expand and clear the Armstrong strain of lymphocytic choriomeningitis virus (LCMV) in vivo. Cul4b-deficient CD8+ T cells accrue DNA damage and succumb to proliferative catastrophe early after antigen encounter. Mechanistically, Cul4b knockout induces an accumulation of p21 and Cyclin E2, resulting in replication stress. Our data show that c-Myc supports cell proliferation by maintaining genome stability via Cul4b, thereby directly coupling these two interdependent pathways. These data clarify how CD8+ T cells use c-Myc and Cul4b to sustain their potential for extraordinary population expansion, longevity and antiviral responses.

NMI: a potential biomarker for tumor prognosis and immunotherapy

N-Myc and STAT Interactor protein (NMI) is an interferon inducible protein participating in various cellular activities, and is widely involved in the process of tumorigenesis and progression. Studies have shown that the loss of NMI expression in breast cancer can promote its progression by inducing epithelial-mesenchymal transition (EMT). However, the expression level of NMI in other tumors and its impact on immune cell infiltration, patient prognosis, and drug treatment are still unclear. Here, we analyzed the role of NMI in pan-cancer through multiple omics data. We found that NMI was abnormally expressed in a variety of tumor tissues. The expression of NMI was closely related to the unique molecular and immunotyping, diagnosis and prognosis of various tumor tissues. In addition, we identified the main proteins that interact with NMI, and focused on the relationship between the clinical parameters of lower grade glioma (LGG) and NMI expression. Subsequently, we found that the expression of NMI was correlated with the infiltration of multiple immune cells and the expression of immune checkpoints. Finally, we also found that the expression of NMI was correlated with the sensitivity to multiple antitumor drugs. In conclusion, our comprehensive pan-cancer analysis of NMI revealed that it is a potential molecular marker for tumor diagnosis and treatment, plays an important role in tumor immunity, and is a promising molecular target for cancer treatment.

Investigation of the inhibition effect of 1,2,3,4,6-pentagalloyl-β-D-glucose on gastric cancer cells based on a network pharmacology approach and experimental validation

Background

Gastric cancer (GC) is ranked as the third leading cause of cancer-related mortality worldwide. 1,2,3,4,6-Pentagalloyl-β-D-glucose (β-PGG) has various pharmacological activities and has been shown to suppress cancer development. However, the mechanism by which β-PGG inhibits gastric cancer has not been elucidated.

Objective

This study explored the potential targets and mechanism of β-PGG in GC using the network pharmacology approach combined with in-vitro experiments.

Methods

The PharmMapper software was used to predict the potential targets of β-PGG, and GC-related genes were identified on the GeneCards database. PPI analysis of common genes was performed using the STRING database. The potential regulatory mechanism of β-PGG in GC was explored through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. The binding ability of key genes and target proteins was verified by molecular docking. The effects of β-PGG on genes and proteins were evaluated using the CCK-8 assay, cell cycle analysis, apoptosis assay, real-time fluorescence quantification polymerase chain reaction (qRT-PCR), and Western blotting.

Results

Eight hub genes involved in cell cycle progression and apoptosis were identified. Cancer-related signaling pathways were identified using the Cytoscape tool. Some of those genes were significantly enriched in the p53 signaling pathway. The CCK-8 assay showed that β-PGG inhibited the proliferation of GC cells. Cell cycle and apoptosis experiments revealed that β-PGG induced cell cycle arrest and apoptosis of gastric cancer cells. qRT-PCR and Western blot analysis showed that β-PGG inhibited β-PGG cells by modulating the p53 signaling pathway.

Conclusion

In the present study, the targets and mechanism of β-PGG in gastric cancer were explored. The results indicate that β-PGG can be used to develop treatments for GC.

Rb-E2F-HDAC Repressor Complexes Control Interferon-Induced Repression of Adenovirus To Promote Persistent Infection

Interferons (IFNs) are cytokines that induce a global change in the cell to establish antiviral immunity. We previously demonstrated that human adenovirus (HAdV) exploits IFN-induced viral repression to persist in infected cells. Although this in vitro persistence model has been described, the mechanism behind how persistent HAdV infection is established is not well understood. In this study, we demonstrate that IFN signaling is essential for viral repression and promoting persistent infection. Cyclin-dependent kinase 4 (CDK4), an antagonist of retinoblastoma (Rb) family proteins, was shown to disrupt the viral repression induced by IFNs. Consistent with this result, knockout of the Rb family proteins pRb, p107, and/or p130 drastically reduced the effect of IFNs on viral replication. The pRb protein specifically contributed the greatest effect to IFN inhibition of viral replication. Interestingly, IFNs did not impact pRb through direct changes in protein or phosphorylation levels. Cells treated with IFNs continued to cycle normally, consistent with observations that persistently infected cells remain for long periods of time in the host and in our in vitro persistent infection model. Finally, we observed that histone deacetylase (HDAC) inhibitors activated productive viral replication in persistently infected cells in the presence of IFN. Thus, HDACs, specifically class I HDACs, which are commonly associated with Rb family proteins, play a major role in the maintenance of persistent HAdV infection in vitro. This study uncovers the critical role of pRb and class I HDACs in the IFN-induced formation of a repressor complex that promotes persistent HAdV infections. IMPORTANCE Adenoviruses are ubiquitous viruses infecting more than 90% of the human population. HAdVs cause persistent infections that may lead to serious complications in immunocompromised patients. Therefore, exploring how HAdVs establish persistent infections is critical for understanding viral reactivation in immunosuppressed individuals. The mechanism underlying HAdV persistence has not been fully explored. Here, we provide insight into the contributions of the host cell to IFN-mediated persistent HAdV infection. We found that HAdV-C5 productive infection is inhibited by an Rb-E2F-HDAC repressor complex. Treatment with HDAC inhibitors converted a persistent infection to a lytic infection. Our results suggest that this process involves the noncanonical regulation of Rb-E2F signaling. This study provides insight into a highly prevalent human pathogen, bringing a new level of complexity and understanding to the replicative cycle.

Atmospheric Ammonia Causes Histopathological Lesions, Cell Cycle Blockage and Apoptosis of Spleen in Chickens

The experiment was conducted to investigate the effect of atmospheric ammonia (NH3) on histological changes, cell cycle distribution, and apoptosis of spleen in chickens. 240 chickens were randomly allocated to control group (without NH3 challenge) and NH3 group (70±5 ppm NH3). The experiment lasted for eight days. The results showed that NH3 exposure caused the decreased relative weight (P<0.05), dysplasia of lymphatic follicle, up-regulation of G0G1 phase cells, excessive apoptosis, and increase of reactive oxygen spcecies (ROS) activated cells (P<0.05) in the spleen. The mechanisms of cell cycle blockage were closely related to the upregulation of p53, p21 gene (P<0.05), the downregulation of cyclinD1, cdk6 gene (P<0.05), and the decrease of Proliferating Cell Nuclear Antigen (PCNA) protein (P<0.05). The activated apoptosis could resulted from the increased gene and protein expressions of bax and caspase-3 (P<0.05), and the decreased gene and protein expressions of bcl-2 (P<0.05). The results suggested that 70±5 ppm NH3 caused the spleen dysplasia, which were closely related to the cell cycle arrest and mitochondria apoptotic pathway activation.

Transcriptome analysis of signaling pathways targeted by Ellagic acid in hepatocellular carcinoma cells

BACKGROUND

Ellagic acid (EA) possesses prominent inhibitory activities against various cancers, including hepatocellular carcinoma (HCC). Our recent study demonstrated EA's activities in reducing HCC cell proliferation and tumor formation. However, the mechanisms of EA to exert its anticancer activities and its primary targets in cancer cells have not been systematically explored.

METHODS

Cell proliferation assay and flow cytometric analysis were used to examine the effects of EA treatment on viability and apoptosis, respectively, of HepG2 cells. RNA-seq studies and associated pathway analyses by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were employed to determine EA's primary targets. Differentially expressed genes (DEG) in EA-treated HepG2 cells were verified by RT-qPCR and Western blot. Integrative analyses of the RNA-seq dataset with a TCGA dataset derived from HCC patients were conducted to verify EA-targeted genes and signaling pathways. Interaction network analysis of the DEGs, shRNA-mediated knockdown, cell viability assay, and colony formation assay were used to validate EA's primary targets.

RESULTS

EA reduced cell viability, caused DNA damage, and induced cell cycle arrest at G1 phase of HepG2 cells. We identified 5765 DEGs encoding proteins with over 2.0-fold changes in EA-treated HepG2 cells by DESeq2. These DEGs showed significant enrichment in the pathways regulating DNA replication and cell cycle progression. As primary targets, p21 was significantly upregulated, while MCM2-7 were uniformly downregulated in response to EA treatment. Consistently, p21 knockdown desensitized liver cells to EA in cell viability and colony formation assays.

CONCLUSION

EA induced G1 phase arrest and promoted apoptosis of HCC cells through activating the p21 gene and downregulating the MCM2-7 genes, respectively.

GENERAL SIGNIFICANCE

The discoveries in this study provide helpful insights into developing novel strategies in the therapeutic treatment of HCC patients.

IFN-γ and CD38 in Hyperprogressive Cancer Development

Immune checkpoint inhibitors (ICIs) improve the survival of patients with multiple types of cancer. However, low response rates and atypical responses limit their success in clinical applications. The paradoxical acceleration of tumor growth after treatment, defined as hyperprogressive disease (HPD), is the most difficult problem facing clinicians and patients alike. The mechanisms that underlie hyperprogression (HP) are still unclear and controversial, although different factors are associated with the phenomenon. In this review, we propose two factors that have not yet been demonstrated to be directly associated with HP, but upon which it is important to focus attention. IFN-γ is a key cytokine in antitumor response and its levels increase during ICI therapy, whereas CD38 is an alternative immune checkpoint that is involved in immunosuppressive responses. As both factors are associated with resistance to ICI therapy, we have discussed their possible involvement in HPD with the conclusion that IFN-γ may contribute to HP onset through the activation of the inflammasome pathway, immunosuppressive enzyme IDO1 and activation-induced cell death (AICD) in effector T cells, while the role of CD38 in HP may be associated with the activation of adenosine receptors, hypoxia pathways and AICD-dependent T-cell depletion.

Acquired Resistance to Immune Checkpoint Blockade Therapies

Immune checkpoint blockade therapy (ICBT) has revolutionized the treatment and management of numerous cancers, yet a substantial proportion of patients who initially respond to ICBT subsequently develop resistance. Comprehensive genomic analysis of samples from recent clinical trials and pre-clinical investigation in mouse models of cancer provide insight into how tumors evade ICBT after an initial response to treatment. Here, we summarize our current knowledge on the development of acquired ICBT resistance, by examining the mechanisms related to tumor-intrinsic properties, T-cell function, and tumor-immune cell interactions. We discuss current and future management of ICBT resistance, and consider crucial questions remaining in this field of acquired resistance to immune checkpoint blockade therapies.

Class A CpG oligodeoxynucleotide inhibits IFN-γ-induced signaling and apoptosis in lung cancer

Background

Currently, anticancer immunotherapy based on PD‐1/PD‐L1 blockade with immune checkpoint inhibitors (ICIs) is being used as a standard therapy for non‐small cell lung cancer (NSCLC). However, more effective treatments are required as these tumors are often resistant and refractory. Here, we aimed to determine the effects of immunomodulatory oligodeoxynucleotides (ODNs) in terms of the presence or absence of CpG motifs and the number of consecutive guanosines.

Methods

Western blots were used to measure the molecules which regulate the expression of PD‐L1 in human lung cancer cell lines after incubation with several cytokines and ODNs. The expression of PD‐L1 and β2‐microglobulin (β2‐MG) on A549 cells, and IFN‐γ‐induced apoptosis with ODNs were examined by flow cytometry. The relationship between IFN‐γ receptor and ODN was analyzed by ELISA and immunofluorescence chemistry.

Results

Our results verified that A‐CpG ODNs suppress the upregulation of IFN‐γ‐induced PD‐L1 and β2‐MG expression. In addition, we found that ODNs with six or more consecutive guanosines (ODNs with poly‐G sequences) may competitively inhibit the IFN‐γ receptor and abolish the effect of IFN‐γ, thereby suppressing apoptosis and indoleamine 2,3‐dioxygenase 1 expression in human lung cancer cells. The tumor microenvironment regulates whether this action will promote or suppress tumor immunity. Thus, in immunotherapy with CpG ODNs, it is essential to consider the effect of ODNs with poly‐G sequences.

Conclusions

This study suggests that ODNs containing six or more consecutive guanosines may inhibit the binding of IFN‐γ to IFN‐γ receptor. However, it does not directly show that ODNs containing six or more consecutive guanosines competitively inhibit the IFN‐γ receptor, and further studies are warranted to confirm this finding.

Key points

Significant findings of the study: Oligodeoxynucleotides with a contiguous sequence of six or more guanosines may competitively inhibit the IFN‐γ receptor and abolish the action of IFN‐γ. This may suppress IFN‐γ‐induced apoptosis and indoleamine‐2,3‐dioxygenase‐1 expression in human lung cancer cells.

What this study adds: A‐CpG and poly‐G ODN may overcome tolerance if the cause of ICI tolerance is high IDO expression. However, IFN‐γ also has the effect of suppressing apoptosis of cancer cells, and it is necessary to identify the cause of resistance.

JAK-STAT Signaling: A Double-Edged Sword of Immune Regulation and Cancer Progression

Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling mediates almost all immune regulatory processes, including those that are involved in tumor cell recognition and tumor-driven immune escape. Antitumor immune responses are largely driven by STAT1 and STAT2 induction of type I and II interferons (IFNs) and the downstream programs IFNs potentiate. Conversely, STAT3 has been widely linked to cancer cell survival, immunosuppression, and sustained inflammation in the tumor microenvironment. The discovery of JAK-STAT cross-regulatory mechanisms, post-translational control, and non-canonical signal transduction has added a new level of complexity to JAK-STAT governance over tumor initiation and progression. Endeavors to better understand the vast effects of JAK-STAT signaling on antitumor immunity have unearthed a wide range of targets, including oncogenes, miRNAs, and other co-regulatory factors, which direct specific phenotypical outcomes subsequent to JAK-STAT stimulation. Yet, the rapidly expanding field of therapeutic developments aimed to resolve JAK-STAT aberrations commonly reported in a multitude of cancers has been marred by off-target effects. Here, we discuss JAK-STAT biology in the context of immunity and cancer, the consequences of pathway perturbations and current therapeutic interventions, to provide insight and consideration for future targeting innovations.

ISG15 Deficiency Enhances HIV-1 Infection by Accumulating Misfolded p53

HIV-1 has evolved many strategies to circumvent the host’s antiviral innate immune responses and establishes disseminated infection; the molecular mechanisms of these strategies are not entirely clear. We showed previously that USP18 contributes to HIV-1 replication by abrogating p21 antiviral function. Here, we demonstrate a mechanism by which USP18 mediates p21 downregulation in myeloid cells. USP18, by its protease activity, accumulates misfolded p53, which requires ISG15 for clearance. Depletion of ISG15 causes accumulation of misfolded dominant negative p53, which supports HIV-1 replication. This work clarifies the function and consequences of p53 modification by ISG15 and implicates USP18 in HIV-1 infection and potentially in carcinogenesis.

Macrophages and dendritic cells dominate early immune responses to lentiviruses. HIV-1 sensing by pathogen recognition receptors induces signaling cascades that culminate in type I alpha/beta interferon (IFN-α/β) induction. IFN-α/β signals back via the IFN-α/β receptors, inducing a plethora of IFN-stimulated gene (ISGs), including ISG15, p53, and p21^Cip1. p21 inhibits HIV-1 replication by inactivating the deoxynucleoside triphosphate (dNTP) biosynthesis pathway and activating the restriction factor SAMHD1. p21 is induced by functional p53. ISG15-specific isopeptidase USP18 negatively regulates IFN signaling. We showed previously that USP18 contributes to HIV-1 replication by abrogating p21 antiviral function. Here, we demonstrate a mechanism by which USP18 mediates p21 downregulation in myeloid cells. USP18, by its protease activity, accumulates misfolded p53, which requires ISG15 for its degradation. Depletion of ISG15 causes accumulation of misfolded dominant negative p53, which enhances HIV-1 replication. This work clarifies the function and consequences of p53 modification by ISG15 and implicates USP18 in HIV-1 infection and potentially in carcinogenesis.

Potent Activation of Human T Cells by mRNA Encoding Constitutively Active CD40

New strategies for augmenting the actual performance of therapeutic T cells in vivo are needed for improving clinical outcome of adoptive cell therapy. Cumulative findings suggest that CD40 plays an intrinsic role in T cell costimulation. Recently, we demonstrated the ability of truncated, auto-oligomerizing CD40 derivatives to induce strong activation of APCs in a ligand-independent manner. We reasoned that constitutively active CD40 (caCD40) can similarly exert enhancing effects on human antitumor T cells. To test this assumption, we transfected human T cells with in vitro-transcribed caCD40 mRNA. In polyclonal T cells, caCD40 triggered IFN-γ secretion and upregulated CD25 and 4-1BB. In antimelanoma tumor-infiltrating lymphocytes (TILs), caCD40 induced massive production of IFN-γ, exerting a pronounced synergistic effect when coexpressed with constitutively active TLR4 devoid of its extracellular ligand binding. In unselected "young" TILs, caCD40 reproducibly increased surface expression of CD25, OX40, 4-1BB, CD127, and CD28. Three days post-mRNA electroporation of CD8 TILs, caCD40 elevated IFN-γ and TNF-α production and cytolytic activity in the presence of autologous but not HLA-I-mismatched melanoma. Enhanced killing of autologous melanoma by young TILs was observed 4 d posttransfection. These findings suggest that caCD40 can function as a potent T cell adjuvant and provide essential guidelines for similar manipulation of other key members of the TNFR family.

USP18 (UBP43) Abrogates p21-Mediated Inhibition of HIV-1

The host intrinsic innate immune system drives antiviral defenses and viral restriction, which includes the production of soluble factors, such as type I and III interferon (IFN), and activation of restriction factors, including SAMHD1, a deoxynucleoside triphosphohydrolase. Interferon-stimulated gene 15 (ISG15)-specific ubiquitin-like protease 43 (USP18) abrogates IFN signaling pathways. The cyclin-dependent kinase inhibitor p21 (CIP1/WAF1), which is involved in the differentiation and maturation of monocytes, inhibits human immunodeficiency virus type 1 (HIV-1) in macrophages and dendritic cells. p21 inhibition of HIV-1 replication is thought to occur at the reverse transcription step, likely by suppressing cellular deoxynucleoside triphosphate (dNTP) biosynthesis and increasing the amount of antivirally active form of SAMHD1. SAMHD1 strongly inhibits HIV-1 replication in myeloid and resting CD4⁺ T cells. Here, we studied how USP18 influences HIV-1 replication in human myeloid THP-1 cells. We found that USP18 has the novel ability to inhibit the antiviral function of p21 in differentiated THP-1 cells. USP18 enhanced reverse transcription of HIV-1 by downregulating p21 expression and upregulating intracellular dNTP levels. p21 downregulation by USP18 was associated with the active form of SAMHD1, phosphorylated at T592. USP18 formed a complex with the E3 ubiquitin ligase recognition factor SKP2 (S-phase kinase associated protein 2) and SAMHD1. CRISPR-Cas9 knockout of USP18 increased p21 protein expression and blocked HIV-1 replication. Overall, we propose USP18 as a regulator of p21 antiviral function in differentiated myeloid THP-1 cells.IMPORTANCE Macrophages and dendritic cells are usually the first point of contact with pathogens, including lentiviruses. Host restriction factors, including SAMHD1, mediate the innate immune response against these viruses. However, HIV-1 has evolved to circumvent the innate immune response and establishes disseminated infection. The cyclin-dependent kinase inhibitor p21, which is involved in differentiation and maturation of monocytes, blocks HIV-1 replication at the reverse transcription step. p21 is thought to suppress key enzymes involved in dNTP biosynthesis and activates SAMHD1 antiviral function. We report here that the human USP18 protein is a novel factor potentially contributing to HIV replication by blocking the antiviral function of p21 in differentiated human myeloid cells. USP18 downregulates p21 protein expression, which correlates with upregulated intracellular dNTP levels and the antiviral inactive form of SAMHD1. Depletion of USP18 stabilizes p21 protein expression, which correlates with dephosphorylated SAMHD1 and a block to HIV-1 replication.

Ambiguous roles of innate lymphoid cells in chronic development of liver diseases

Innate lymphoid cells (ILCs) are defined as a distinct arm of innate immunity. According to their profile of secreted cytokines and lineage-specific transcriptional factors, ILCs can be categorized into the following three groups: group 1 ILCs (including natural killer (NK) cells and ILC1s) are dependent on T-bet and can produce interferon-γ; group 2 ILCs (ILC2s) are dependent on GATA3 and can produce type 2 cytokines, including interleukin (IL)-5 and IL-13; and, group 3 ILCs (including lymphoid tissue-like cells and ILC3s) are dependent on RORγt and can produce IL-22 and IL-17. Collaborative with adaptive immunity, ILCs are highly reactive innate effectors that promptly orchestrate immunity, inflammation and tissue repair. Dysregulation of ILCs might result in inflammatory disorders. Evidence regarding the function of intrahepatic ILCs is emerging from longitudinal studies of inflammatory liver diseases wherein they exert both physiological and pathological functions, including immune homeostasis, defenses and surveillance. Their overall effect on the liver depends on the balance of their proinflammatory and antiinflammatory populations, specific microenvironment and stages of immune responses. Here, we review the current data about ILCs in chronic liver disease progression, to reveal their roles in different stages as well as to discuss their therapeutic potency as intervention targets.

Superantigens: The Good, the Bad, and the Ugly

Increasing evidence suggests that superantigens play a role in Immune-mediated diseases. Superantigens are potent activators of CD4* T cells, causing rapid and massive proliferation of cells and cytokine production. This characteristic of superantigens can be exploited in diseases where strong immunologic responses are required, such as in the B16F10 animal model of melanoma. Superantigen administration is able to significantly enhance Ineffective anti-tumor Immune responses, resulting in potent and long-lived protective anti-tumor immunity. However, superantigens are more well-known for the role they play in diseases. Studies using an animal model for neurologic demy-elinatlng diseases such as multiple sclerosis show that superantigens can induce severe relapses and activate auto-reactive T cells not involved in the Initial bout of disease. This may also involve epitope spreading of disease. Superantigens have also been implicated in acute diseases such as food poisoning and TSS, and in chronic diseases such as psoriasis and rheumatoid arthritis. Viral superantigens are also involved in the disease process, including superantigens derived from human Immunodeficiency virus and mouse mammary tumor virus. Finally, immunotherapies that ameliorate the role played by superantigens in disease are discussed.

The Yin and Yang of Innate Lymphoid Cells in Cancer

The recent appreciation of novel subsets of innate lymphoid cells (ILCs) as important regulators of tissue homeostasis, inflammation and repair, raise questions regarding the presence and role of these cells in cancer tissues. In addition to natural killer and fetal lymphoid tissue inducer (LTi) cells, the ILC family comprises non-cytolytic, cytokine-producing cells that are classified into ILC1, ILC2 and ILC3 based on phenotypic and functional characteristics. Differently from natural killer cells, which are the prototypical members of ILC1 and whose role in tumors is better established, the involvement of other ILC subsets in cancer progression or resistance is still fuzzy and in several instances controversial, since current studies indicate both context-dependent beneficial or pathogenic effects. Here, we review the current knowledge regarding the involvement of these novel ILC subsets in the context of tumor immunology, highlighting how ILC subsets might behave either as friends or foes.

CXCL16-positive dendritic cells enhance invariant natural killer T cell-dependent IFNγ production and tumor control

Crosstalk interactions between dendritic cells (DCs) and invariant natural killer T (iNKT) cells are important in regulating antitumor responses elicited by glycolipid antigens. iNKT cells constitutively express the chemokine receptor CXCR6, while cytokine-activated DCs upregulate the transmembrane chemokine ligand, CXCL16. This study examined the co-stimulatory role of CXCR6/CXCL16 interactions in glycolipid-dependent iNKT cell activation and tumor control. Spleen and liver DCs in wild-type mice, but not iNKT cell deficient (Jα18^−/−) mice, transiently upregulated surface CXCL16 following in vivo administration of the glycolipid antigen α-galactosylceramide. Recombinant CXCL16 did not directly induce iNKT cell activation in vitro but enhanced interferon (IFN)-γ production when mouse or human iNKT cells were stimulated with plate-bound anti-CD3. Compared with glycolipid-loaded CXCL16^neg DCs, CXCL16^hi DCs induced higher levels of IFNγ production in iNKT cell cultures and following adoptive transfer in vivo. The number of IFNγ⁺ iNKT cells and expansion of T-bet⁺ iNKT cells were reduced in vivo when CXCL16^−/− DCs were used to activate iNKT cells. Enhanced IFNγ production in vivo was not dependent on CXCR6 expression on natural killer (NK) cells. Adoptive transfer of glycolipid-loaded CXCL16^hi DCs provided superior protection against tumor metastasis compared to CXCL16^neg DC transfers. Similarly, wild-type DCs provided superior protection against metastasis compared with CXCL16^−/− DCs. These experiments implicate an important role for CXCR6/CXCL16 interactions in regulating iNKT cell IFNγ production and tumor control. The selective use of CXCL16^hi DCs in adoptive transfer immunotherapies may prove useful for enhancing T helper (Th) type 1 responses and clinical outcomes in cancer patients.

The good and the bad faces of STAT1 in solid tumours

Signal transducer and activator of transcription (STAT) 1 is part of the Janus kinase (JAK)/STAT signalling cascade and is best known for its essential role in mediating responses to all types of interferons (IFN). STAT1 regulates a variety of cellular processes, such as antimicrobial activities, cell proliferation and cell death. It exerts important immune modulatory activities both in the innate and the adaptive arm of the immune system. Based on studies in mice and data from human patients, STAT1 is generally considered a tumour suppressor but there is growing evidence that it can also act as a tumour promoter. This review aims at contrasting the two faces of STAT1 in tumourigenesis and providing an overview on the current knowledge of the underlying mechanisms or pathways.

Genomic regulation of senescence and innate immunity signaling in the retinal pigment epithelium

The tumor suppressor p53 is a major regulator of genes important for cell cycle arrest, senescence, apoptosis, and innate immunity, and has recently been implicated in retinal aging. In this study we sought to identify the genetic networks that regulate p53 function in the retina using quantitative trait locus (QTL) analysis. First we examined age-associated changes in the activation and expression levels of p53; known p53 target proteins and markers of innate immune system activation in primary retinal pigment epithelial (RPE) cells that were harvested from young and aged human donors. We observed increased expression of p53, activated caspase-1, CDKN1A, CDKN2A (p16INK4a), TLR4, and IFNα in aged primary RPE cell lines. We used the Hamilton Eye Institute (HEI) retinal dataset ( www.genenetwork.org ) to identify genomic loci that modulate expression of genes in the p53 pathway in recombinant inbred BXD mouse strains using a QTL systems biology-based approach. We identified a significant trans-QTL on chromosome 1 (region 172-177 Mb) that regulates the expression of Cdkn1a. Many of the genes in this QTL locus are involved in innate immune responses, including Fc receptors, interferon-inducible family genes, and formin 2. Importantly, we found an age-related increase in FCGR3A and FMN2 and a decrease in IFI16 levels in RPE cultures. There is a complex multigenic innate immunity locus that controls expression of genes in the p53 pathway in the RPE, which may play an important role in modulating age-related changes in the retina.

Cancer-targeted IL-12 controls human rhabdomyosarcoma by senescence induction and myogenic differentiation

Stimulating the immune system to attack cancer is a promising approach, even for the control of advanced cancers. Several cytokines that promote interferon-γ-dominated immune responses show antitumor activity, with interleukin 12 (IL-12) being of major importance. Here, we used an antibody-IL-12 fusion protein (NHS-IL12) that binds histones of necrotic cells to treat human sarcoma in humanized mice. Following sarcoma engraftment, NHS-IL12 therapy was combined with either engineered IL-7 (FcIL-7) or IL-2 (IL-2MAB602) for continuous cytokine bioavailability. NHS-IL12 strongly induced innate and adaptive antitumor immunity when combined with IL-7 or IL-2. NHS-IL12 therapy significantly improved survival of sarcoma-bearing mice and caused long-term remissions when combined with IL-2. NHS-IL12 induced pronounced cancer cell senescence, as documented by strong expression of senescence-associated p16^INK4a and nuclear translocation of p-HP1γ, and permanent arrest of cancer cell proliferation. In addition, this cancer immunotherapy initiated the induction of myogenic differentiation, further promoting the hypothesis that efficient antitumor immunity includes mechanisms different from cytotoxicity for efficient cancer control in vivo.

Exposure to the polyester PET precursor--terephthalic acid induces and perpetuates DNA damage-harboring non-malignant human breast cells

Accurate assessment of the biological impact of xenoestrogens could assist breast cancer prevention. Effects on DNA integrity of breast epithelium, which might be missed in common chemical test screens, underscore the importance of endpoints beyond estrogen receptor interaction and cell proliferation.

Identification of early perturbations induced in cells from non-cancerous breast tissue is critical for understanding possible breast cancer risk from chemical exposure. We have demonstrated previously that exposure to the ubiquitous xenoestrogens, bisphenol A (BPA) and methyl paraben, promotes the hallmarks of cancer in non-malignant human high-risk donor breast epithelial cells (HRBECs) isolated from several donors. Here we show that terephthalic acid (TPA), a major chemical precursor of polyethylene terephthalate (PET) containers used for the storage of food and beverages, increased the ERα: ERβ ratio in multiple HRBEC samples, suggesting an estrogenic effect. Although, like BPA and methyl paraben, TPA also promoted resistance to tamoxifen-induced apoptosis, unlike these chemicals instead of inducing an increased S-phase fraction, TPA treatment arrested cell proliferation. DNA-PK, ATM and members of the MRN complex, known to be involved in DNA damage sensor and effector proteins, were elevated indicating induction of DNA strand breaks. Early DNA damage checkpoint response, mediated through p53/p21, led to G₁ arrest in TPA-exposed cells. Removal of TPA from the growth medium resulted in the rapid induction of BCL2, increasing the ratio of anti-: pro-apoptotic proteins, together with overexpression of Cyclin A/CDK2 proteins. Consequently, despite elevated p53^pSer15 and H2AX^pSer139, indicating sustained DNA damage, TPA exposed cells resumed robust growth rates seen prior to TPA exposure. The propensity for the perpetuation of DNA aberrations that activate DNA damage pathways in non-malignant breast cells justifies careful consideration of human exposure to TPA, particularly at vulnerable life stages.

Cytotoxic T lymphocytes block tumor growth both by lytic activity and IFNγ-dependent cell-cycle arrest

To understand global effector mechanisms of CTL therapy, we performed microarray gene expression analysis in a murine model using pmel-1 T-cell receptor (TCR) transgenic T cells as effectors and B16 melanoma cells as targets. In addition to upregulation of genes related to antigen presentation and the MHC class I pathway, and cytotoxic effector molecules, cell-cycle-promoting genes were downregulated in the tumor on days 3 and 5 after CTL transfer. To investigate the impact of CTL therapy on the cell cycle of tumor cells in situ, we generated B16 cells expressing a fluorescent ubiquitination-based cell-cycle indicator (B16-fucci) and performed CTL therapy in mice bearing B16-fucci tumors. Three days after CTL transfer, we observed diffuse infiltration of CTLs into the tumor with a large number of tumor cells arrested at the G1 phase of the cell cycle, and the presence of spotty apoptotic or necrotic areas. Thus, tumor growth suppression was largely dependent on G1 cell-cycle arrest rather than killing by CTLs. Neutralizing antibody to IFNγ prevented both tumor growth inhibition and G1 arrest. The mechanism of G1 arrest involved the downregulation of S-phase kinase-associated protein 2 (Skp2) and the accumulation of its target cyclin-dependent kinase inhibitor p27 in the B16-fucci tumor cells. Because tumor-infiltrating CTLs are far fewer in number than the tumor cells, we propose that CTLs predominantly regulate tumor growth via IFNγ-mediated profound cytostatic effects rather than via cytotoxicity. This dominance of G1 arrest over other mechanisms may be widespread but not universal because IFNγ sensitivity varied among tumors.

IL6 sensitizes prostate cancer to the antiproliferative effect of IFNα2 through IRF9

Development and progression of prostate cancer (PCa) are associated with chronic inflammation. The cytokine interleukin 6 (IL6) can influence progression, differentiation, survival, and angiogenesis of PCa. To identify novel pathways that are triggered by IL6, we performed a gene expression profiling of two PCa cell lines, LNCaP and MDA PCa 2b, treated with 5 ng/ml IL6. Interferon (IFN) regulatory factor 9 (IRF9) was identified as one of the most prevalent IL6-regulated genes in both cell lines. IRF9 is a mediator of type I IFN signaling and acts together with STAT1 and 2 to activate transcription of IFN-responsive genes. The IL6 regulation of IRF9 was confirmed at mRNA and protein levels by quantitative real-time PCR and western blot respectively in both cell lines and could be blocked by the anti-IL6 antibody Siltuximab. Three PCa cell lines, PC3, Du-145, and LNCaP-IL6+, with an autocrine IL6 loop displayed high expression of IRF9. A tissue microarray with 36 PCa tissues showed that IRF9 protein expression is moderately elevated in malignant areas and positively correlates with the tissue expression of IL6. Downregulation and overexpression of IRF9 provided evidence for an IFN-independent role of IRF9 in cellular proliferation of different PCa cell lines. Furthermore, expression of IRF9 was essential to mediate the antiproliferative effects of IFNα2. We concluded that IL6 is an inducer of IRF9 expression in PCa and a sensitizer for the antiproliferative effects of IFNα2.

Expanding roles for CD4 T cells and their subpopulations in tumor immunity and therapy

The importance of CD4 T cells in orchestrating the immune system and their role in inducing effective T cell-mediated therapies for the treatment of patients with select established malignancies are undisputable. Through a complex and balanced array of direct and indirect mechanisms of cellular activation and regulation, this functionally diverse family of lymphocytes can potentially promote tumor eradication, long-term tumor immunity, and aid in establishing and/or rebalancing immune cell homeostasis through interaction with other immune cell populations within the highly dynamic tumor environment. However, recent studies have uncovered additional functions and roles for CD4 T cells, some of which are independent of other lymphocytes, that can not only influence and contribute to tumor immunity but paradoxically promote tumor growth and progression. Here, we review the recent advances in our understanding of the various CD4 T cell lineages and their signature cytokines in disease progression and/or regression. We discuss their direct and indirect mechanistic interplay among themselves and with other responding cells of the antitumor response, their potential roles and abilities for "plasticity" and memory cell generation within the hostile tumor environment, and their potentials in cancer treatment and immunotherapy.

Novel molecular, cytotoxical, and immunological study on promising and selective anticancer activity of mung bean sprouts

BACKGROUND

The anticancer and immunomodulatory activity of mung bean sprouts (MBS) and the underlying mechanisms against human cervical and hepatocarcinoma cancer cells were explored.

METHODS

MBS cytotoxicity and MBS-induced anticancer cytokines, TNF-α and IFN-β from cancer cells, and immunological cytokines, IL-4, IFN-γ, and IL-10 from peripheral mononuclear cells (PMNC) were assessed by MTS and ELISA assays. Apoptotic cells were investigated by flow cytometry. The expression level of apoptotic genes (Bax, BCL-2, Capsases 7-9) and cell cycle regulatory genes (cyclin D, E, and A) and tumor suppressor proteins (p27, p21, and p53) was assessed by real-time qPCR in the cancer cells treated with extract IC50.

RESULTS

The cytotoxicity on normal human cells was significantly different from HeLa and HepG2 cells, 163.97 ± 5.73, 13.3 ± 0.89, and 14.04 ± 1.5 mg/ml, respectively. The selectivity index (SI) was 12.44 ± 0.83 for HeLa and 11.94 ± 1.2 for HepG2 cells. Increased levels of TNF-α and IFN-β were observed in the treated HeLa and HepG2 culture supernatants when compared with untreated cells. MBS extract was shown to be an immunopolarizing agent by inducing IFNγ and inhibiting IL-4 production by PBMC; this leads to triggering of CMI and cellular cytotoxicity. The extract induced apoptosis, in a dose and time dependent manner, in treated HeLa and HepG2, but not in untreated, cells (P < 0.05). The treatment significantly induced cell cycle arrest in G0/G1 in HeLa cells. The percentage of cells in G0/G1 phase of the treated HeLa cells increased from 62.87 ± 2.1%, in untreated cells, to 80.48 ± 2.97%. Interestingly, MBS IC50 induced the expression of apoptosis and tumor suppressor related genes in both HeLa and HepG2 cells. MBS extract succeeded in inducing cdk-inhibitors, p21, p53, and p27 in HeLa cells while it induced only p53 in HepG2 cells (P < 0.05). This is a clue for the cell type- specific interaction of the studied extract. These proteins inhibit the cyclin-cdk complexes apart from the presence of some other components that might stimulate some cyclins such as cyclin E, A, and D.

CONCLUSION

MBS extract was shown to be a potent anticancer agent granting new prospects of anticancer therapy using natural products.

Exploration of the correlations between interferon-γ in patient serum and HEPACAM in bladder transitional cell carcinoma, and the interferon-γ mechanism inhibiting BIU-87 proliferation

PURPOSE

Interferon-γ inhibits cancer cell proliferation and induces re-expression of different tumor suppressor genes. As a candidate, HEPACAM is almost lost in bladder transitional cell carcinoma. To our knowledge whether interferon-γ inhibits BIU-87 proliferation and re-expresses HEPACAM mRNA is still unknown. Thus, we probed the mechanism and examined the correlations between interferon-γ in patient serum and HEPACAM in bladder transitional cell carcinoma.

MATERIALS AND METHODS

Using enzyme-linked immunosorbent assay we measured serum interferon-γ in 27 men and 6 women, and 15 volunteers. Disease was Ta-T1 in 12 patients, T2-T4 in 21, low grade in 25, high grade in 8, primary in 13 and recurrent in 20. A total of 33 cancer and 26 adjacent tissues were examined by immunohistochemistry to detect HEPACAM protein and ensure the position. Under interferon-γ stimulation we detected BIU-87 proliferation by MTT assay. Cell cycles were examined by flow cytometry. HEPACAM mRNA expression was determined by reverse transcription-polymerase chain reaction. Western blot was used to detect p21(WAF1).

RESULTS

Interferon-γ was remarkably low in patients with bladder transitional cell carcinoma vs volunteers (p <0.01). HEPACAM protein was highly expressed in adjacent tissue, mainly at the cytomembrane, but it was almost absent in bladder transitional cell carcinoma (p <0.01). The interferon-γ decrease in the serum of patients with bladder transitional cell carcinoma and the low HEPACAM expression in tumors correlated linearly (r = 0.899, p <0.01). In vitro interferon-γ inhibited BIU-87 proliferation (p <0.01) and slightly re-expressed HEPACAM mRNA (p <0.05). The cell cycle was arrested at G(0)/G(1) and p21(WAF1) was concurrently increased in response to interferon-γ (p <0.01).

CONCLUSIONS

Results suggest an important connection between HEPACAM and interferon-γ, which may inhibit BIU-87 proliferation through HEPACAM re-expression and p21(WAF1) up-regulation to arrest cells at the G(0)/G(1) phase.

Interferon-gamma enhances radiation-induced cell death via downregulation of Chk1

Interferon-gamma (IFNγ) is a cytokine with roles in immune responses as well as in tumor control. Interferon is often used in cancer treatment together with other therapies. Here we report a novel approach to enhancement of cancer cell killing by combined treatment of IFNγ with ionizing radiation. We found that IFNγ treatment alone in HeLa cells induced phosphorylation of Chk1 in a time- and dose-dependent manner, and resulted in cell arrest. Moreover IFNγ treatment was correlated with attenuation of Chk1 as the treatment shortened protein half-life of Chk1. As Chk1 is an essential cell cycle regulator for viability after DNA damage, attenuation of Chk1 by IFNγ pre-treatment in HeLa cells resulted in increased cell death following ionizing radiation about 2-folds than ionizing radiation treatment alone whereas IFNγ treatment alone had little effect on cell death. X-linked inhibitor of apoptosis-associated factor 1 (XAF1), an IFN-induced gene, seems to partly regulate IFNγ-induced Chk1 destabilization and radiation sensitivity because transient depletion of XAF1 by siRNA prevented IFNγ-induced Chk1 attenuation and partly protected cells from IFNγ-enhanced radiation cell killing. Therefore the results provide a novel rationale to combine IFNγ pretreatment and DNA-damaging anti-cancer drugs such as ionizing radiation to enhance cancer cell killing.

Atorvastatin synergizes with IFN-γ in treating human non-small cell lung carcinomas via potent inhibition of RhoA activity

Interferon-γ (IFN-γ) has been widely used to treat various malignant tumors including human non-small-cell-lung carcinomas (NSCLCs). However, the tumor-inhibitory effect of IFN-γ displays not satisfactory in NSCLC treatment due to the lack of immunogenicity of NSCLCs. This study demonstrated that inhibition of RhoA activity led to significant inhibition of NSCLC cell growth accompanied by decreased expression of c-myc and cyclin D1 and increased levels of major histocompatibility complex (MHC) class I and peptide transporter protein 1 (TAP1) which are involved in tumor immunity. Combination treatment of atorvastatin and IFN-γ resulted in a synergistic inhibition of NSCLC cell growth both in vitro and in vivo. Though IFN-γ alone exerted minimal inhibitory effect on RhoA activity, additional administration of atorvastatin could result in a significant inhibition of RhoA activity, thus substantially suppressing NSCLC cell growth. Specifically, atorvastatin could induce specific deposition of endogenous IFN-γ in tumors while not in other normal tissues in LLC-harbored mice. In conclusion, atorvastatin can enhance IFN-γ sensitivity in NSCLCs both in vitro and in vivo, probably through induction of a synergistic inhibitory effect on RhoA activity. This study also suggests a potential alternative of combination of atorvastatin and IFN-γ in clinical therapy against NSCLCs.

The two faces of interferon-γ in cancer

Interferon-γ is a cytokine whose biological activity is conventionally associated with cytostatic/cytotoxic and antitumor mechanisms during cell-mediated adaptive immune response. It has been used clinically to treat a variety of malignancies, albeit with mixed results and side effects that can be severe. Despite ample evidence implicating a role for IFN-γ in tumor immune surveillance, a steady flow of reports has suggested that it may also have protumorigenic effects under certain circumstances. We propose that, in fact, IFN-γ treatment is a double-edged sword whose anti- and protumorigenic activities are dependent on the cellular, microenvironmental, and/or molecular context. As such, inhibition of the IFN-γ/IFN-γ receptor pathway may prove to be a viable new therapeutic target for a subset of malignancies.

In vivo tumor suppression activity by T cell-specific T-bet restoration

T-box-containing protein expressed in T cells (T-bet) is a master transcription factor for the development of interferon (IFN) gamma-producing T helper 1 (Th1) cells and also functions in other immune cells including natural killer (NK), cytotoxic T lymphocytes and dendritic cells. T-bet-deficient mice increased susceptibility to viral infection and tumor development due to the defective functions of immune cells. T-bet is known to play a key role in NK-mediated antimetastatic response; however, it remains to be characterized whether T-bet is essential for in vivo tumor suppression mediated by T cells. Here, we have investigated in vivo tumor suppression effect of T-bet-restored T cells using T cell-specific and inducible T-bet transgenic mice generated in a T-bet-deficient background. T-bet-null mice increased susceptibility to tumor development, whereas induction of T cell-specific T-bet expression upon melanoma cell injection substantially suppressed tumor development by inducing IFNgamma production in T cells and tumor cell apoptosis. Late induction of T-bet expression in tumor-bearing mice produced comparable amounts of IFNgamma with control and significantly decreased tumor volume. In addition, increased melanoma lung metastasis in T-bet-deficient mice was strikingly inhibited by T-bet restoration in T cells. Intravenous injection of activated Th1 cells, not T-bet-null Th1 cells, attenuated metastatic melanoma progression, in addition, restoration of T-bet in T-bet-null Th1 cells certainly retrieved antimetastatic activity. These results suggest that T-bet expression in T cells is crucial for the control of tumor development and antimetastatic activity.

Gene modulation and immunoregulatory roles of interferon gamma

Interferon-gamma (IFNgamma) is a central regulator of the immune response and signals via the Janus Activated Kinase (JAK)-Signal Transducer and Activator of Transcription (STAT) pathway. Phosphorylated STAT1 homodimers translocate to the nucleus, bind to Gamma Activating Sequence (GAS) and recruit additional factors to modulate gene expression. A bioinformatics analysis revealed that greater number of putative promoters of immune related genes and also those not directly involved in immunity contain GAS compared to response elements (RE) for Interferon Regulatory Factor (IRF)1, Nuclear factor kappa B (NFkappaB) and Activator Protein (AP)1. GAS is present in putative promoters of well known IFNgamma-induced genes, IRF1, GBP1, CXCL10, and other genes identified were TLR3, VCAM1, CASP4, etc. Analysis of three microarray studies revealed that the expression of a subset of only GAS containing immune genes were modulated by IFNgamma. As a significant correlation exists between GAS containing immune genes and IFNgamma-regulated gene expression, this strategy may identify novel IFNgamma-responsive immune genes. This analysis is integrated with the literature on the roles of IFNgamma in mediating a plethora of functions: anti-microbial responses, antigen processing, inflammation, growth suppression, cell death, tumor immunity and autoimmunity. Overall, this review summarizes our present knowledge on IFNgamma mediated signaling and functions.

Regulation of apoptosis by type III interferons

OBJECTIVE

Two types of interferons (IFNs), type I (IFN-alpha/beta) and type III (IFN-lambdas), utilize distinct receptor complexes to induce similar signalling and biological activities, including recently demonstrated for IFN-lambdas antitumour activity. However, ability of type III IFNs to regulate cell population growth remains largely uncharacterized.

MATERIALS AND METHODS

Intact and modified human colorectal adenocarcinoma HT29 cells were used to study regulation of apoptosis by IFN-lambdas.

RESULTS AND CONCLUSIONS

We report that the IFN-lambdaR1 chain of the type III IFN receptor complex possesses an intrinsic ability to trigger apoptosis in cells. Signalling induced through the intracellular domain of IFN-lambdaR1 resulted in G(1)/G(0) phase cell cycle arrest, phosphatidylserine surfacing and chromosomal DNA fragmentation. Caspase-3, caspase-8 and caspase-9 were activated; however, pancaspase inhibitor Z-VAD-FMK did not prevent apoptosis. In addition, the extent of apoptosis correlated with the level of receptor expression and was associated with prolonged IFN-lambda signalling. We also demonstrated that the ability to trigger apoptosis is a unique intrinsic function of all IFN receptors. However, more robust apoptosis was induced by signalling through type III IFN receptor than through type I or type II (IFN-gamma) receptors, suggesting higher cytotoxic potential of type III IFNs. In addition, we observed that IFN-gamma treatment sensitized HT29 cells to IFN-lambda-mediated apoptosis. These results provide evidence that type III IFNs, alone or in combination with other stimuli, have the potential to induce apoptosis.

T cell tolerance induced by histone deacetylase inhibitor is mediated by P21cip1

MEB [n-butyrate 2-(4-morpholinyl) ethyl butyrate hydrochloride], a histone deacetylase inhibitor and G1 blocker, has been shown to induce unresponsiveness in antigen-activated Th1 cells. MEB was tested for here for its ability to inactivate naive alloantigen-specific T cells from DBA/2 and C57BL/10 mice. Since T cells from these two strains of mice have been shown to differ in their cell cycle regulation, it we hoped that this comparison would provide information concerning the role of cycle regulatory proteins in mediating MEB-induced T cell unresponsiveness. MEB inhibited proliferation in a one-way mixed lymphocyte reaction (MLR) in which spleen cells from DBA/2 mice (H-2d) or C57BL/10 mice (H-2b) were stimulated with spleen cells from C57BL/10 or DBA/2 mice, respectively. C57BL/10 responder T cells isolated from the MEB-treated primary MLR remained unresponsive to alloantigen following restimulation in a secondary MLR that did not contain MEB. T cells from DBA/2 mice were less sensitive to MEB-induced unresponsiveness and required a longer exposure or pretreatment with IL-2 to become tolerant. In all cases responsiveness to MEB-induced tolerance in the alloantigen-stimulated T cells corresponded with the levels of the cyclin-dependent kinase inhibitor p21cip1. Additional experiments showed that T cells from p21cip1-deficient mice, unlike T cells from p21cip1 wild-type littermates, were resistant to MEB-induced tolerance. These results underscore the role of p21cip1 in mediating T cell tolerance induced by the histone deacetylase inhibitor MEB.

Revisiting immunosurveillance and immunostimulation: Implications for cancer immunotherapy

Experimental and clinical experience demonstrates that the resolution of a pathogenic challenge depends not only on the presence or absence of an immune reaction, but also on the initiation of the proper type of immune reaction. The initiation of a non-protective type of immune reaction will not only result in a lack of protection, but may also exacerbate the underlying condition. For example, in cancer, constituents of the immune system have been shown to augment tumor proliferation, angiogenesis, and metastases. This review discusses the duality of the role of the immune system in cancer, from the theories of immunosurveillance and immunostimulation to current studies, which illustrate that the immune system has both a protective role and a tumor-promoting role in neoplasia. The potential of using chemotherapy to inhibit a tumor-promoting immune reaction is also discussed.

P21Cip1 is a critical mediator of the cytotoxic action of thymidylate synthase inhibitors in colorectal carcinoma cells

We have demonstrated previously that interferon (IFN)-gamma sensitizes human colon carcinoma cell lines to the cytotoxic effects of 5-fluorouracil combined with leucovorin and to the thymidylate synthase inhibitor, ZD9331, dependent on thymineless stress-induced DNA damage, independent of p53. Here we demonstrate that the cyclin-dependent kinase (CDK) inhibitor p21(Cip1) regulates thymineless stress-induced cytotoxicity in these cells. HCT116 wild-type (wt) and p53-/- cells underwent apoptosis and loss in clonogenic survival when exposed to ZD9331, whereas p21Cip1-/- cells were resistant. In contrast, IFN-gamma induced marked cytotoxicity in p21Cip1-/- cells only. ZD9331 induced p21Cip1 up-regulation in all of the cell lines examined, as did thymidine deprivation in thymidylate synthase-deficient (thymidylate synthase-) cells. Furthermore, selective induction of p21Cip1 in RKO was sufficient to induce apoptosis. P21Cip1, cdk1, cdk2, and cyclin E mRNA expression increased coincident with S-phase accumulation in HT29 cells treated with ZD9331 or 5fluorouracil/leucovorin, as demonstrated by cDNA microarray analyses. Cell cycle analyses revealed that HCT116 wt and p21Cip1 -/- cells accumulated in S phase within 24 h of ZD9331 exposure; however, wt cells exited S-phase more rapidly, where apoptosis occurred before mitosis, either in late S or G2. Finally, the CDK inhibitor roscovitine potentiated the cytotoxic activity of ZD9331 in both wt and p21Cip1-/- cells, strongly suggesting a role for p21Cip1-dependent CDK inhibition in cytotoxicity induced by thymidylate synthase inhibition. In summary, p21Cip1 positively regulates the cytotoxic action of thymidylate synthase inhibitors, negatively regulates the cytotoxic action of IFN-gamma, and enhances S-phase exit after thymineless stress, possibly via interaction with CDK-cyclin complexes.

Deficiency of the cyclin kinase inhibitor p21(WAF-1/CIP-1) promotes apoptosis of activated/memory T cells and inhibits spontaneous systemic autoimmunity

A characteristic feature of systemic lupus erythematosus is the accumulation of activated/memory T and B cells. These G₀/G₁-arrested cells express high levels of cyclin-dependent kinase inhibitors such as p21, are resistant to proliferation and apoptosis, and produce large amounts of proinflammatory cytokines. Herein, we show that ablation of p21 in lupus-prone mice allows these cells to reenter the cell cycle and undergo apoptosis, leading to autoimmune disease reduction. Absence of p21 resulted in enhanced Fas/FasL-mediated activation-induced T cell death, increased activation of procaspases 8 and 3, and loss of mitochondrial transmembrane potential. Increased apoptosis was also associated with p53 up-regulation and a modest shift in the ratio of Bax/Bcl-2 toward the proapoptotic Bax. Proliferation and apoptosis of B cells were also increased in p21^−/− lupus mice. Thus, modulation of the cell cycle pathway may be a novel approach to reduce apoptosis-resistant pathogenic lymphocytes and to ameliorate systemic autoimmunity.

Interferon-γ-Mediated Growth Regulation of Melanoma Cells: Involvement of STAT1-Dependent and STAT1-Independent Signals

Interferon-gamma, a known inhibitor of tumor cell growth, has been used in several protocols for the treatment of melanoma. We have studied the molecular events underlying interferon-gamma-induced G0/G1 arrest in four metastatic melanoma cell lines with different responsiveness to interferon-gamma. The growth arrest did not result from enhanced expression of cyclin-dependent kinase inhibitors p21 and p27. Instead, it correlated with downregulation of cyclin E and cyclin A and inhibition of their associated kinase activities. We show that interferon-gamma-induced growth inhibition could be abrogated by overexpression of dominant negative STAT1 (signal transducer and activator of transcription 1) in the melanoma cell line A375, suggesting that STAT1 plays a crucial part for the anti-proliferative effect. Erythropoietin stimulation of a chimeric receptor led to a concentration-dependent STAT1 activation and concomitant growth arrest when it contained the STAT recruitment motif Y440 of the interferon-gamma receptor 1. In contrast, dose-response studies for interferon-gamma revealed a discrepancy between levels of STAT1 activation and the extent of growth inhibition; whereas STAT1 was activated by low doses of interferon-gamma (10 U per mL), growth inhibitory effects were only visible with 100-fold higher concentrations. Our results suggest the presence of additional signals emanating from the interferon-gamma receptor, which may counteract the anti-proliferative function of STAT1.

rIFN-gamma-mediated growth suppression of platinum-sensitive and -resistant ovarian tumor cell lines not dependent upon arginase inhibition

Background

Arginine metabolism in tumor cell lines can be influenced by various cytokines, including recombinant human interferon-γ (rIFN-γ), a cytokine that shows promising clinical activity in epithelial ovarian cancer (EOC).

Methods

We examined EOC cell lines for the expression of arginase in an enzymatic assay and for transcripts of arginase I and II, inducible nitric oxide synthase (iNOS), and indoleamine 2,3-dioxygenase (IDO) by reverse transcription-polymerase chain reaction. The effects of rIFN-γ on arginase activity and on tumor cell growth inhibition were determined by measuring [³H]thymidine uptake.

Results

Elevated arginase activity was detected in 5 of 8 tumor cell lines, and analysis at the transcriptional level showed that arginase II was involved but arginase I was not. rIFN-γ reduced arginase activity in 3 EOC cell lines but increased activity in the 2008 cell line and its platinum-resistant subline, 2008.C13. iNOS transcripts were not detected in rIFN-γ-treated or untreated cell lines. In contrast, IDO activity was induced or increased by rIFN-γ. Suppression of arginase activity by rIFN-γ in certain cell lines suggested that such inhibition might contribute to its antiproliferative effects. However, supplementation of the medium with polyamine pathway products did not interfere with the growth-inhibitory effects of rIFN-γ EOC cells.

Conclusions

Increased arginase activity, specifically identified with arginase II, is present in most of the tested EOC cell lines. rIFN-γ inhibits or stimulates arginase activity in certain EOC cell lines, though the decrease in arginase activity does not appear to be associated with the in vitro antiproliferative activity of rIFN-γ. Since cells within the stroma of EOC tissues could also contribute to arginine metabolism following treatment with rIFN-γ or rIFN-γ-inducers, it would be helpful to examine these effects in vivo.

Interferons and apoptosis

The interferons (IFNs), in addition to their well-known antiviral activities, have important roles in the control of cell proliferation and are effective agents for the treatment of a limited number of malignant diseases. IFNs not only regulate cell growth and division but also influence cell survival through their effects on apoptosis. This review describes the current state of knowledge about the mechanisms of action of these cytokines on the apoptotic machinery, with particular emphasis on the synergism that exists between the IFNs and other proapoptotic agents, such as members of the tumor necrosis factor (TNF) family. The review also discusses the physiologic and clinical implications of the effects of the IFNs on apoptosis for regulation of viral infection and tumor growth.

Vitamin E supplementation does not alter azoxymethane-induced colonic aberrant crypt foci formation in young or old mice

Vitamin E, part of the body's primary lipid-soluble defense against free radicals and reactive oxygen molecules, has been suggested to reduce the risk for some cancers. However, the role of vitamin E in the etiology and prevention of colon cancer, especially in the highest risk group, the aged, is not clear. Thus, this study was conducted to elucidate the effect of vitamin E supplementation on susceptibility to colon cancer by examining azoxymethane (AOM)-induced aberrant crypt foci (ACF) formation, a surrogate biomarker of colon cancer. Young (3-4 mo) and old (19-20 mo) C57BL/6JNIA mice were fed either a control diet (30 mg dl-alpha-tocopheryl acetate/kg diet) or a vitamin E-supplemented diet (500 mg dl-alpha-tocopheryl acetate/kg diet) for 16 wk. After 6 wk of dietary supplementation, young and old mice were injected with saline or AOM weekly for 5 wk to receive the same total dose of AOM (2.2 mg) and killed 10 wk after the first AOM injection. Vitamin E supplementation had no effect on the number of AOM-induced ACF in young or old mice. In addition, vitamin E supplementation did not have an effect on splenocyte interferon-gamma, interluekin-6 and tumor necrosis factor-alpha levels, natural killer cell killing activity or colonic cell proliferation in young or old mice. Thus, alpha-tocopherol does not seem to affect the initiation and early promotion stages of AOM-induced colon carcinogenesis in young or old mice. Whether vitamin E supplementation might be effective in reducing AOM-induced colon tumors is unclear.

Cell death inhibiting RNA (CDIR) derived from a 3'-untranslated region binds AUF1 and heat shock protein 27

Regulators of programmed cell death were previously identified using a technical knockout genetic screen. Among the elements that inhibited interferon-gamma-induced apoptosis of HeLa cells was a 441-nucleotide fragment derived from the 3'-untranslated region (UTR) of KIAA0425, a gene of unknown function. This fragment was termed cell death inhibiting RNA (CDIR). Deletion and mutation analyses of CDIR were employed to identify the features required for its anti-apoptotic activity. Single nucleotide alterations within either copy of the duplicated U-rich motif found in the CDIR sequence abolished the anti-apoptotic activity of CDIR and altered its in vitro association with a protein complex. Further analysis of the CDIR-binding complex indicated that it contained heat shock protein 27 (Hsp27) and the regulator of mRNA turnover AUF1 (heterogeneous nuclear ribonucleoprotein D). In addition, recombinant AUF1 bound directly to CDIR. Furthermore, expression of another AUF1-binding RNA element, derived from the 3'-UTR of c-myc, inhibited apoptosis. We also demonstrate that the level and the stability of p21(waf1/Cip1/sdi1) mRNA, a target of AUF1 with anti-apoptotic activity, were increased in CDIR-transfected cells. The level of mRNA and protein of Bcl-2, another anti-apoptotic gene, containing an AUF1 binding site in its 3'-UTR was also increased in CDIR-transfected cells. Our data suggest that AUF1 regulates apoptosis by altering mRNA turnover. We propose that CDIR inhibits apoptosis by acting as a competitive inhibitor of AUF1, preventing AUF1 from binding to its targets.

Role of cyclin kinase inhibitor p21 in systemic autoimmunity

The cyclin kinase inhibitor protein p21 affects multiple processes relevant to the immune system, including cell cycle progression, replicative senescence, hemopoietic stem cell quiescence, and apoptosis. Therefore, malfunction of this protein may be a contributor to the pathogenesis of systemic autoimmunity. Here, we report that mixed background p21-deficient 129/Sv x C57BL/6 mice showed increased in vitro and in vivo T cell cycling and activation, moderate hypergammaglobulinemia and, at low penetrance, anti-chromatin autoantibodies. Homeostatic anti-self MHC/peptide ligand-induced proliferation of p21-deficient T cells was also enhanced. However, lymphoid organ enlargement was very mild, presumably due to increased apoptosis of the rapidly dividing cells. Moreover, the older p21-deficient mice had kidney pathology representing a similar, but slightly more advanced, state than that seen in the control mice. The timing and severity of the above serologic, cellular, and histologic manifestations in p21-deficient mice were unaffected by gender. Thus, p21 deficiency significantly enhances T cell activation and homeostatic proliferation, and can induce mild autoimmune manifestations at a low incidence without gender bias, but does not in itself generate the full spectrum of lupus-like disease.

Functional interaction between p53 and the interferon-inducible nucleoprotein IFI 16

Interferons are important in regulating cell growth and differentiation, immune function and initiating anti-viral responses. While the pleotrophic actions of interferons have been well documented, the molecular mechanisms underpinning their biological effects have not been fully characterized. IFI 16 is a member of the interferon-inducible HIN-200 family of nuclear proteins, which we have recently shown can function as a potent transcriptional repressor. A murine member of the HIN-200 family, p202, can indirectly interact with p53 via the p53 binding protein (p53bp) and inhibit p53-mediated transcriptional activation. The binding activity of p202 to p53bp was shown to require the conserved MFHATVAT motif present in all 200 amino acid repeat regions of HIN-200 proteins. Given that IFI 16 contains two MFHATVAT motifs, we sought to determine whether IFI 16 may form a complex with p53 and if so to ascertain the functional significance of this interaction. We demonstrate that IFI 16 can directly bind to the C-terminal region of p53 and augment p53-mediated transcriptional activation without altering the steady state levels of p53. Thus, in addition to its ability to directly regulate gene expression, IFI 16 can also modulate the transcription function of other cellular transcription factors. These findings demonstrate a possible link between gene induction following interferon stimulation and p53-mediated cellular events.

New insights into p53 regulation and gene therapy for cancer

Due to its critical involvement in cell cycle control and apoptotic signaling, the transcription factor p53 has become the most important tumor suppressor currently under investigation. TP53 is the most frequently mutated gene in human cancers and is thought to play a crucial role in malignant transformation. Therefore, p53 appears to be an appealing target for gene therapy. Adenoviral-based p53 gene transfection is now being introduced in large clinical trials. Viral cell entry was found to be the rate-limiting step of gene delivery and thus of therapeutic efficiency. Attachment of adenoviruses to the target cell surface is mediated through the coxsackie-adenovirus receptor, and internalization is achieved via interactions with integrins of the alpha v beta(3) and alpha v beta(5) class. The assumption that the restitution of the p53-dependent apoptotic pathway results in a higher responsiveness of solid tumors to cytostatic agents remains a major matter of debate. Combinations of p53-based gene therapy with other components involved in apoptosis, such as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/APO2L, or agents neutralizing tumor-promoting antiapoptotic signals, such as humanized anti-growth factor antibodies, should further improve the effectiveness of cancer treatment in the future.