Interferons and the tumor cell

Tumor inherent interferons: Impact on immune reactivity and immunotherapy

Immunotherapy has revolutionized cancer treatment, with sustained responses to immune checkpoint inhibitors reported in a number of malignancies. Such therapeutics are now being trialed in aggressive or advanced cancers that are heavily reliant on untargeted therapies, such as triple negative breast cancer. However, responses have been underwhelming to date and are very difficult to predict, leading to an inability to accurately weigh up the benefit-to-risk ratio for their implementation. The tumor immune microenvironment has been closely linked to immunotherapeutic response, with superior responses observed in patients with T cell-inflamed or 'hot' tumors. One class of cytokines, the type I interferons, are a major dictator of tumor immune infiltration and activation. Tumor cell inherent interferon signaling dramatically influences the immune microenvironment and the expression of immune checkpoint proteins, hence regulators and targets of this pathway are candidate biomarkers of immunotherapeutic response. In support of a link between IFN signaling and immunotherapeutic response, the combination of type I interferon inducers with checkpoint immunotherapy has recently been demonstrated critical for a sustained anti-tumor response in aggressive breast cancer models. Here we review evidence that links type I interferons with a hot tumor immune microenvironment, response to checkpoint inhibitors and reduced risk of metastasis that supports their use as biomarkers and therapeutics in oncology.

ISG15 inhibits cancer cell growth and promotes apoptosis

Cervical cancer is one of the most common causes of cancer-related mortality in women in developing countries. Interferon (IFN)-α has been widely used in the treatment of various types of cancer, including cervical cancer, and IFN-stimulated gene 15 (ISG15), an ubiquitin-like protein, is upregulated by IFN-α treatment. The anti-virus and antitumor effects of ISG15 have been reported; however, its mechanism of action have not yet been fully elucidated. In this study, HeLa cells were used as a model system to investigate the roles of ISG15 in IFN-α-mediated cancer cell growth inhibition and induction of apoptosis. The results revealed that both p53 and p21 were upregulated in HeLa cells treated with IFN-α or in the HeLa cells overexpressing ISG15. In addition, the expression levels of ubiquitin-like modifier-activating enzyme 7 (UBA7, also known as UBE1L; ISG15 E1-activating enzyme), UBCH8 (ISG15 E2-conjugating enzyme) and HERC5 (ISG15 E3-ligase) were elevated in the HeLa cells treated with IFN-α. The levels of p53 in the HeLa cells were attenuated by transient transfection with small interfering RNA (siRNA) targeting ISG15 (ISG15-siRNA). Cell viability was inhibited by both IFN-α treatment and ISG15 overexpression. However, these effects were significantly diminished when p53 was knocked down, suggesting that the effects of inhibitory effects of ISG15 on HeLa cell growth and the induction of apoptosis were p53-dependent. Taken together, these results suggest the existence of the IFN-α/ISG15/p53 axis in cervical cancer cells and any strategies manipulating the levels of ISG15 may thus prove to be effective in the treatment of cervical cancer.

Apoptosis-inducing factor (AIF) is targeted in IFN-α2a-induced Bid-mediated apoptosis through Bak activation in ovarian cancer cells

Previously we have shown that interferon (IFN)-α induced apoptosis is predominantly mediated by the upregulation of tumor necrosis factor related apoptosis-inducing ligand (TRAIL) via the caspase-8 pathway. It was also shown that recruitment of mitochondria in IFN-α induced apoptosis involves the cleavage of BH3 interacting domain death agonist (Bid) to truncated Bid (tBid). In the present study, we demonstrate that tBid induced by IFN-α2a activates mitochondrial Bak to trigger the loss of mitochondrial membrane integrity, consequently causing release of apoptosis-inducing factor (AIF) in ovarian cancer cells, OVCAR3. AIF translocates from the mitochondria to the nucleus and induces nuclear fragmentation and cell death. Both a small molecule Bid inhibitor (BI-6C9) or Bid-RNA interference (RNAi) preserved mitochondrial membrane potential, prevented nuclear translocation of AIF, and abrogated IFN-α2a-induced cell death. Cell death induced by tBid was inhibited by AIF-RNAi, indicating that caspase-independent AIF signaling is the main pathway through which Bid mediates cell death. This was further supported by experiments showing that BI-6C9 did not prevent the release of cytochrome c from mitochondria to cytosol, while the release of AIF was prevented. In conclusion, IFN-α2a-induced apoptosis is mediated via the mitochondria-associated pathway involving the cleavage of Bid followed by AIF release that involves Bak activation and translocation of AIF from the mitochondria to the nucleus in OVCAR3 cells.

The Cullin 3 substrate adaptor KLHL20 mediates DAPK ubiquitination to control interferon responses

Death-associated protein kinase (DAPK) was identified as a mediator of interferon (IFN)-induced cell death. How IFN controls DAPK activation remains largely unknown. Here, we identify the BTB-Kelch protein KLHL20 as a negative regulator of DAPK. KLHL20 binds DAPK and Cullin 3 (Cul3) via its Kelch-repeat domain and BTB domain, respectively. The KLHL20-Cul3-ROC1 E3 ligase complex promotes DAPK polyubiquitination, thereby inducing the proteasomal degradation of DAPK. Accordingly, depletion of KLHL20 diminishes DAPK ubiquitination and degradation. The KLHL20-mediated DAPK ubiquitination is suppressed in cells receiving IFN-alpha or IFN-gamma, which induces an enrichment/sequestration of KLHL20 in the PML nuclear bodies, thereby separating KLHL20 from DAPK. Consequently, IFN triggers the stabilization of DAPK. This mechanism of DAPK stabilization is crucial for determining IFN responsiveness of tumor cells and contributes to IFN-induced autophagy. This study identifies KLHL20-Cul3-ROC1 as an E3 ligase for DAPK ubiquitination and reveals a regulatory mechanism of DAPK, through blocking its accessibility to this E3 ligase, in IFN-induced apoptotic and autophagic death. Our findings may be relevant to the problem of IFN resistance in cancer therapy.

Interferon regulatory factor family of transcription factors and regulation of oncogenesis

A family of transcription factors, the interferon regulatory factors (IRF), was identified originally in the context of the regulation of the type I interferon (IFN)-alpha/beta system. The IRF family has now expanded to nine members, and gene-disruption studies have revealed the critical involvement of these members in multiple facets of host defense systems, such as innate and adaptive immune responses and tumor suppression. In the present review article, we aim at summarizing our current knowledge of the roles of IRF in host defense, with special emphasis on their involvement in the regulation of oncogenesis.

Interferon alpha induces nucleus-independent apoptosis by activating extracellular signal-regulated kinase 1/2 and c-Jun NH2-terminal kinase downstream of phosphatidylinositol 3-kinase and mammalian target of rapamycin

Interferon (IFN)alpha induces apoptosis via Bak and Bax and the mitochondrial pathway. Here, we investigated the role of known IFNalpha-induced signaling cascades upstream of Bak activation. By pharmacological and genetic inhibition of the kinases protein kinase C (PKC)delta, extracellular signal-regulated kinase (ERK), and c-Jun NH(2)-terminal kinase (JNK) in U266-1984 and RHEK-1 cells, we could demonstrate that all three enzymes are critical for the apoptosis-associated mitochondrial events and apoptotic cell death induced by IFNalpha, at a step downstream of phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR). Furthermore, the activation of JNK was found to occur in a PKCdelta/ERK-dependent manner. Inhibition of these kinases did not affect the canonical IFNalpha-stimulated Janus tyrosine kinase-signal transducer and activator of transcription signaling or expression of IFN-responsive genes. Therefore, enucleated cells (cytoplasts) were examined for IFNalpha-induced apoptosis, to test directly whether this process depends on gene transcription. Cytoplasts were found to undergo apoptosis after IFNalpha treatment, as analyzed by several apoptosis markers by using flow cytometry, live cell imaging, and biochemical analysis of flow-sorted cytoplasts. Furthermore, inhibition of mTOR, ERK, and JNK blocked IFNalpha-induced apoptosis in cytoplasts. In conclusion, IFNalpha-induced apoptosis requires activation of ERK1/2, PKCdelta, and JNK downstream of PI3K and mTOR, and it can occur in a nucleus-independent manner, thus demonstrating for the first time that IFNalpha induces apoptosis in the absence of de novo transcription.

Interferons and osteosarcoma

In 1970, we initiated studies at the Karolinska hospital to find out whether biologically meaningful doses of interferon (IFN) alpha preparations could be administered systemically to patients with viral and tumour diseases without causing unacceptable side effects. Antiviral and antitumour efficiency was demonstrated. Only a limited number of patients were injected due to shortage of high dose IFN preparations. Osteosarcoma patients participated in these early attempts. Due to clinical observations on one patient and due to lack of meaningful systemic standard treatment for osteosarcoma at the time, we decided to continue to give adjuvant IFN treatment to a consecutive series of osteosarcoma patients attending our hospital . We were encouraged by the preliminary follow up results of the series and continued to use this therapeutic principle up to 1990. The clinical results achieved are briefly summarized in this mini-review as are the results obtained in simultaneously ongoing model experiments in vitro and in vivo. A randomized large scale ongoing trial, involving the use of adjuvant IFN treatment of osteosarcoma patients, has been initiated by the European and American osteosarcoma study group 35 years after the first osteosarcoma patient received IFN. The trial is briefly outlined in this article.

Distinct functions of IRF-3 and IRF-7 in IFN-alpha gene regulation and control of anti-tumor activity in primary macrophages

Type I IFN (IFN-alpha/beta) have important biological functions ranging from immune cell development and activation, to tumor cell killing and most importantly inhibition of virus replication. Following viral infection or activation of Toll-like receptors (TLRs) via distinct ligands, IFN-alpha/beta are produced. Two members of the interferon regulatory factor (IRF) family - IRF-3 and IRF-7 - are the major modulators of IFN gene expression. Activation of IRF-3 and IRF-7 by TBK1/IKKvarepsilon mediated phosphorylation promotes IFN gene expression and potentiates the production of IFN responsive genes important to the development of an effective antiviral immune response. IFN treatment can augment anti-tumor properties and they are potentially key players in cancer therapy. For example, adoptive transfer of IFN-gamma-activated macrophages can mediate tumor cell killing via direct cell-cell contact, as well as release of soluble cytotoxic pro-inflammatory molecules. A recent study investigated whether IRF-3 and IRF-7 could mediate the acquisition of new anti-tumor effector functions in macrophages. Adenovirus mediated transduction of the active form of IRF-7 into primary macrophages resulted in the production of type I IFN, upregulation of target genes including TRAIL and increased tumoricidal activity of macrophages; in contrast, the active form of IRF-3 led to induction of cell death. These studies indicate that IRF-7 transduced macrophages may be an attractive candidate for in vivo adoptive therapy of cancer.

STAT1 mediates differentiation of chronic lymphocytic leukemia cells in response to Bryostatin 1

Bryostatin 1 is known to exhibit in vitro and in vivo activity against chronic lymphocytic leukemia (CLL) cells by inducing their further maturation into plasma-like cells. Signal transducer and activator of transcription (STAT) proteins play a central role in B-lymphocyte growth and function and are aberrantly phosphorylated on serine residues in CLL cells. To determine whether STAT transcription factors are important in Bryostatin 1-induced differentiation of CLL cells, primary CLL cells were examined for signaling events following exposure to Bryostatin 1 in vitro. Western analysis and electrophoretic mobility shift assays revealed that Bryostatin 1 induced tyrosine phosphorylation and DNA binding of STAT1, yet there was no effect on constitutive serine phosphorylation of STAT1. Bryostatin 1-induced STAT1 activation occurred in a manner that was dependent on protein kinase C (PKC), mitogen-activated protein kinase (MAPK), and Janus tyrosine kinase (JAK) activation. Evidence indicates that Bryostatin 1 induces STAT1 activation through an interferon gamma (IFN gamma) autocrine loop. However, STAT1 activation by IFN gamma stimulation alone was not sufficient to induce differentiation. This insufficiency is due to the broader effect on gene expression caused by Bryostatin 1 compared with IFN gamma, as demonstrated by microarray analysis. Both up-regulation of CD22 expression and immunoglobulin M (IgM) production, markers of CLL differentiation, were inhibited by a decoy oligonucleotide for STAT1, indicating that STAT1 is necessary for Bryostatin 1-induced differentiation of CLL cells. This study implicates STAT transcription factors as important mediators of Bryostatin 1-induced differentiation of CLL cells and could possibly lead to improved therapeutic approaches for the treatment of CLL.

Integration of interferon-alpha/beta signalling to p53 responses in tumour suppression and antiviral defence

Swift elimination of undesirable cells is an important feature in tumour suppression and immunity. The tumour suppressor p53 and interferon-alpha and -beta (IFN-alpha/beta) are essential for the induction of apoptosis in cancerous cells and in antiviral immune responses, respectively, but little is known about their interrelationship. Here we show that transcription of the p53 gene is induced by IFN-alpha/beta, accompanied by an increase in p53 protein level. IFN-alpha/beta signalling itself does not activate p53; rather, it contributes to boosting p53 responses to stress signals. We show examples in which p53 gene induction by IFN-alpha/beta contributes to tumour suppression. Furthermore, we show that p53 is activated in virally infected cells to evoke an apoptotic response and that p53 is critical for antiviral defence of the host. Our study reveals a hitherto unrecognized link between p53 and IFN-alpha/beta in tumour suppression and antiviral immunity, which may have therapeutic implications.

Interferon-alpha-induced apoptosis in U266 cells is associated with activation of the proapoptotic Bcl-2 family members Bak and Bax

We have recently reported that the cytokine interferon-alpha (IFNalpha), commonly used in the treatment of cancer, induced a caspase-dependent apoptosis in tumor cell lines. The signaling mechanisms involved have not been defined. Here, we show that both proapoptotic Bcl-2 family members Bak and Bax were activated by IFNalpha, strictly in correlation with the induction of apoptosis. Using double stainings, we demonstrated that Bak was activated prior to cytochrome c (cyt c) release and caspase-3 activation, whereas activated Bax was only found in cells with released cyt c, mitochondrial depolarization, as well as activated caspase-3. Furthermore, IFNalpha-induced activation of Bak, and to a large extent also of Bax, was dependent on caspase activity. With the use of a panel of specific caspase inhibitors we found, however, that none of caspases-1 to -10 were responsible for this activation. Neither was the Ca(2+)-dependent protease calpain nor the stress-activated p38 SAPK pathway significantly involved. Overexpression of Bcl-2 blocked apoptosis induced by IFNalpha totally abolished Bak activation, as well as decreased the amount of activated Bax. We conclude that IFNalpha induces Bak and Bax activation via distinct mechanisms involving an unknown protease, and that their activation is regulated by Bcl-2.

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.

New aspects of IFN-alpha/beta signalling in immunity, oncogenesis and bone metabolism

Although interferons (IFNs) were originally identified as humoral factors that confer an antiviral state upon cells, they have been demonstrated to be multifunctional in a variety of biological systems. The IFN-alpha/beta system modulates not only the cellular immune response to viral and bacterial infections, but also the oncogenic process and bone metabolism. Further studies have revealed additional unique facets of the IFN-alpha/beta system. A weak signal by constitutively produced IFN-alpha/beta is critical not only for the regulation of cellular amplification of IFN-alpha/beta production upon viral infection or the enhancement of signalling by other cytokines, but also for the regulation of adaptive immune responses, such as the enhancement of CD8()+ T cell activation. Furthermore, IFN-beta signalling is critical for the regulation of the bone-resorbing osteoclasts. In this review, we focus on the newly discovered roles of the IFN-alpha/beta system in host defense and bone remodeling, particularly on the functions of the weak IFN-alpha/beta signalling in the context of what we refer to as the "revving-up" model.

Strong inhibition of Ewing tumor xenograft growth by combination of human interferon-alpha or interferon-beta with ifosfamide

Ewing sarcoma is the second most common bone tumor in childhood. Despite aggressive chemotherapy and radiotherapy strategies, the prognosis of patients with metastatic disease remains poor. We have recently reported that Ewing tumor cell proliferation was strongly inhibited by IFN-beta and to a lesser degree by IFN-alpha. Moreover, under IFN-beta treatment, some cell lines undergo apoptosis. Since the possibility of using IFNs for Ewing tumor treatments may be of interest, we have evaluated the efficacy of Hu-IFNs in a nude mice model of Ewing tumor xenografts. The results reported here show that human type I IFNs, Hu-IFN-alpha and Hu-IFN-beta impaired tumor xenograft take and displayed an anti-growth effect toward established xenografts. Furthermore, we have also shown that combined therapy with Hu-IFNs and ifosfamide (IFO), an alkylating agent widely used in high-dose chemotherapy of Ewing tumors, results in a strong antitumor effect. Pathological analysis showed that Hu-IFN-alpha/IFO and Hu-IFN-beta/IFO were characterized by a dramatic decrease in the mitotic index and marked necrosis, as well as extensive fibrosis associated with numerous calcifications. To our knowledge, this is the first demonstration of a potential antitumor effect of human type I IFNs and IFO on Ewing tumors, providing a rational foundation for a promising therapeutic approach to Ewing sarcoma.

Production of matrix metalloproteinase-9 in early stage B-CLL: suppression by interferons

Besides vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), matrix metalloproteinases (MMPs) play critical roles in angiogenesis, tumor invasion and metastasis. Increased angiogenesis is observed in chronic B lymphocytic leukemia (B-CLL) and published data reported VEGF and bFGF production in this disease. The purpose of this study was to investigate MMP expression in early stage B-CLL. Elevated MMP-9 concentrations were detected by ELISA in the sera of B-CLL patients (median level 250 ng/ml) compared with healthy donors (67 ng/ml) (P < 0.0001), and immunostaining with antibodies against MMP-9 and B cell antigens (CD19, CD23) substantiated the presence of MMP-9 in tumoral B lymphocytes. By using RT-PCR, ELISA and zymography experiments, we confirmed that B-CLL cells expressed and released the pro-form of MMP-9 with Mr 92 kDa (158-1300 pg/ml/10(6) cells/48 h), p-aminophenylmercuric acetate generating a 82 kDa active form. In contrast, the production of MMP-9 by normal counterpart B cells was significantly low (28-169 pg/ml/10(6)cells/48 h). Moreover, B-CLL culture supernatants contained bFGF (median levels 17 pg/ml/10(6) cells/48 h), VEGF (1.4 pg/ml/10(6) cells/48 h) and TNF-alpha (0.2 pg/ml/10(6) cells/48 h). TNF-alpha and VEGF antibodies blocked MMP-9 at the mRNA and protein levels. Interferons (IFNs) type I or type II repressed MMP-9 gelatinolytic activity in a dose and time dependency, and this was reflected by a parallel inhibition of MMP-9 mRNA and protein. IFNs however did not affect the production of bFGF, VEGF and TNF-alpha. Together, our data show that B-CLL lymphocytes synthesize MMP-9 and emphasize the specific inhibitory actions of IFNs on its expression.

A fresh look at tumor immunosurveillance and immunotherapy

Despite major advances in our understanding of adaptive immunity and dendritic cells, consistent and durable responses to cancer vaccines remain elusive and active immunotherapy is still not an established treatment modality. The key to developing an effective anti-tumor response is understanding why, initially, the immune system is unable to detect transformed cells and is subsequently tolerant of tumor growth and metastasis. Ineffective antigen presentation limits the adaptive immune response; however, we are now learning that the host's innate immune system may first fail to recognize the tumor as posing a danger. Recent descriptions of stress-induced ligands on tumor cells recognized by innate effector cells, new subsets of T cells that regulate tumor tolerance and the development of spontaneous tumors in mice that lack immune effector molecules, beckon a reflection on our current perspectives on the interaction of transformed cells with the immune system and offer new hope of stimulating therapeutic immunity to cancer.

Biologic responses to IFN-alpha administration in humans

Although interferon-alpha (IFN-alpha) was discovered over 40 years ago, it was many years before it was registered as a therapeutic agent. Because of its unique qualities, it has been registered for both antiviral and antitumor indications. In addition to its therapeutic effects in viral diseases and cancer, IFN-alpha interferes with several important physiologic systems. It interacts with the immune system and affects several neuroendocrine and metabolic circuits. The specific mechanisms by which IFN-alpha exerts its therapeutic effects are complex, and it is very difficult to tie the biologic actions of IFN-alpha to specific clinical effects.

Immunostimulatory effects of human recombinant interleukin-12 on peripheral blood mononuclear cells from normal dogs

Interleukin-12 (IL-12) plays a pivotal role in regulating cellular immune responses involving autoimmunity, infectious disease, and cancer. Human recombinant (hr) IL-12 is being evaluated for therapy of human cancer. We investigated the potential of hrIL-12 to activate canine peripheral blood mononuclear cells (PBMC) using proliferation and cytotoxicity as readouts. Human rIL-12 caused increased proliferation of PBMC, and enhanced lysis of allogeneic canine tumor targets mediated by PBMC from normal dogs in vitro. In addition, antibody-dependent cellular cytotoxicity (ADCC) mediated by canine PBMC was enhanced by hrIL-12. These results indicate that hrIL-12 is recognized by canine immune cells, triggering a number of immune responses in canine PBMC, that may be important for immunotherapy of canine cancer. Information from this investigation provides impetus for evaluation of the effects of hrIL-12 on PBMC from tumor-bearing dogs and should be helpful in the development of hrIL-12 as an immune cell activator in vivo in the dog.