The interferon-inducible IFI16 gene inhibits tube morphogenesis and proliferation of primary, but not HPV16 E6/E7-immortalized human endothelial cells

Cytosolic DNA sensor IFI16 proteins: Potential molecular integrators of interactions among the aging hallmarks

Cellular changes that are linked to aging in humans include genomic instability, telomere attrition, epigenetic alterations, mitochondrial dysfunction, cellular senescence, and altered intercellular communications. The extent of the changes in these aging hallmarks and their interactions with each other are part of the human aging. However, the molecular mechanisms through which the aging hallmarks interact with each other remain unclear. Studies have indicated a potential role for the type I interferon (IFN) and p53-inducible IFI16 proteins in interactions with the aging hallmarks. The IFI16 proteins are members of the PYHIN protein family. Proteins in the family share a DNA-binding domain (the HIN domain) and a protein-protein interaction pyrin domain (PYD). IFI16 proteins are needed for cytosolic DNA-induced activation of the cGAS-STING pathway for type I IFN (IFN-β) expression. The pathway plays an important role in aging-related inflammation (inflammaging). Further, increased levels of the IFI16 proteins potentiate the cell growth inhibitory functions of the p53 and pRb tumor suppressors proteins. Moreover, IFI16 proteins are needed for most aging hallmarks. Therefore, here we discuss how an improved understanding of the role of the IFI16 proteins in integration of the aging hallmarks has potential to improve the human health and lifespan.

STAT signaling as a target for intervention: from cancer inflammation and angiogenesis to non-coding RNAs modulation

As a landmark, scientific investigation in cytokine signaling and interferon-related anti-viral activity, signal transducer and activator of transcription (STAT) family of proteins was first discovered in the 1990s. Today, we know that the STAT family consists of several transcription factors which regulate various molecular and cellular processes, including proliferation, angiogenesis, and differentiation in human carcinoma. STAT family members play an active role in transducing signals from cell membrane to nucleus through intracellular signaling and thus activating gene transcription. Additionally, they are also associated with the development and progression of human cancer by facilitating inflammation, cell survival, and resistance to therapeutic responses. Accumulating evidence suggests that not all STAT proteins are associated with the progression of human malignancy; however, STAT3/5 are constitutively activated in various cancers, including multiple myeloma, lymphoma, breast cancer, prostate hepatocellular carcinoma, and non-small cell lung cancer. The present review highlights how STAT-associated events are implicated in cancer inflammation, angiogenesis and non-coding RNA (ncRNA) modulation to highlight potential intervention into carcinogenesis-related cellular processes.

Functions and roles of IFIX, a member of the human HIN-200 family, in human diseases

Pyrin and hematopoietic expression, interferon-inducible nature, and nuclear localization (HIN) domain family member 1 (PYHIN1), also known as IFIX, belongs to the family of pyrin proteins. This family includes structurally and functionally related mouse (e.g., p202, p203, and p204 proteins) and human (e.g., the interferon-inducible protein 16, absent in melanoma 2 protein, myeloid cell nuclear differentiation antigen, and pyrin and HIN domain family 1 or IFIX) proteins. The IFIX protein belongs to the HIN-200 family of interferon-inducible proteins that have a 200-amino acid signature motif at their C-termini. The increased expression of pyrin proteins in most cell types inhibits cell cycle control and modulates cell survival. Consistent with this role for pyrin proteins, IFIX is a potential antiviral DNA sensor that is essential for immune responses, the detection of viral DNA in the nucleus and cytoplasm, and the binding of foreign DNA via its HIN domain in a sequence non-specific manner. By promoting the ubiquitination and subsequent degradation of MDM2, IFIX acts as a tumor suppressor, thereby leading to p53/TP53 stabilization, HDAC1 regulation via the ubiquitin-proteasome pathway, and tumor-cell-specific silencing of the maspin gene. These data demonstrate that the potential molecular mechanism(s) underlying the action of the IFIX protein might be associated with the development of human diseases, such as viral infections, malignant tumors, and autoimmune diseases. This review summarizes the current insights into IFIX functions and how its regulation affects the outcomes of various human diseases.

Interferon-induced protein 16 expression in colorectal cancer and its correlation with proliferation and immune signature markers

Interferon-induced protein 16 (IFI16) is important for innate immune recognition of foreign/damaged DNA. Abnormal IFI16 expression is closely related to the occurrence of multiple malignant tumours, but its expression pattern in colorectal cancer (CRC) remains unclear. The present study aimed to investigated IFI16 expression and association with cell proliferation in CRC tissues and adjacent normal tissues. A multiplex immunofluorescence panel of antibodies against IFI16, Ki-67 and phosphorylated (p)-ERK1/2 was applied to assess a tissue microarray (TMA). The TMA included 77 CRC samples and 74 normal adjacent tissue samples which were collected from The First People's Hospital of Yunnan Province (Kunming, China) (3 paracancerous tissues were lost because of repeated cutting). Immunohistochemistry was used to detect CD8⁺ tumour-infiltrating lymphocyte (TIL) abundance and programmed death-ligand 1 (PD-L1) expression in cancer tissues. The present study demonstrated that IFI16 localized to the nucleus of CRC cells. Although IFI16 was weakly expressed in normal mucosal epithelial cells, absent to strong expression was detectable in different patients with CRC. Typically, IFI16 was not co-localized with Ki-67 within CRC cells. The multiplex immunofluorescence data demonstrated that the proportion of IFI16^-/Ki-67⁺ cells from CRC tissues was 57.13%; however, that of IFI16⁺/Ki-67⁺ cells was 1.50%. The IFI16^-/Ki-67⁺ phenotype was significantly positively associated with the tumor-node-metastasis stage and was marginally significantly correlated with lymph node metastasis. p-ERK1/2 protein was primarily localized to the cytoplasm and cell membrane of CRC cells and sometimes to the nucleus. Although, IFI16 demonstrated a strong correlation with p-ERK1/2, IFI16 did not co-localize with p-ERK1/2 and the proportion of IFI16 and p-ERK1/2 double-negative CRC cells was 84.95%. IFI16 expression displayed no significant association with CD8⁺ TILs or PD-L1. However, a strong positive correlation between CD8⁺ TILs and PD-L1 was observed. High CD8⁺ TIL infiltration in CRC tissue was associated with lower lymph node metastasis and tumor-node-metastasis stage. In summary, the results of the present study provided a novel insight for the role of IFI16 in CRC occurrence via the regulation of cancer cell proliferation.

Interferons α and β in cancer: therapeutic opportunities from new insights

Over the past decade, preclinical and clinical research have confirmed the essential role of interferons for effective host immunological responses to malignant cells. Type I interferons (IFNα and IFNβ) directly regulate transcription of >100 downstream genes, which results in a myriad of direct (on cancer cells) and indirect (through immune effector cells and vasculature) effects on the tumour. New insights into endogenous and exogenous activation of type I interferons in the tumour and its microenvironment have given impetus to drug discovery and patient evaluation of interferon-directed strategies. When combined with prior observations or with other effective modalities for cancer treatment, modulation of the interferon system could contribute to further reductions in cancer morbidity and mortality. This Review discusses new interferon-directed therapeutic opportunities, ranging from cyclic dinucleotides to genome methylation inhibitors, angiogenesis inhibitors, chemoradiation, complexes with neoantigen-targeted monoclonal antibodies, combinations with other emerging therapeutic interventions and associations of interferon-stimulated gene expression with patient prognosis - all of which are strategies that have or will soon enter translational clinical evaluation.

IFI16, an amplifier of DNA-damage response: Role in cellular senescence and aging-associated inflammatory diseases

DNA-damage induces a DNA-damage response (DDR) in mammalian cells. The response, depending upon the cell-type and the extent of DNA-damage, ultimately results in cell death or cellular senescence. DDR-induced signaling in cells activates the ATM-p53 and ATM-IKKα/β-interferon (IFN)-β signaling pathways, thus leading to an induction of the p53 and IFN-inducible IFI16 gene. Further, upon DNA-damage, DNA accumulates in the cytoplasm, thereby inducing the IFI16 protein and STING-dependent IFN-β production and activation of the IFI16 inflammasome, resulting in the production of proinflammatory cytokines (e.g., IL-1β and IL-18). Increased expression of IFI16 protein in a variety of cell-types promotes cellular senescence. However, reduced expression of IFI16 in cells promotes cell proliferation. Because expression of the IFI16 gene is induced by activation of DNA-damage response in cells and increased levels of IFI16 protein in cells potentiate the p53-mediated transcriptional activation of genes and p53 and pRb-mediated cell cycle arrest, we discuss how an improved understanding of the role of IFI16 protein in cellular senescence and associated inflammatory secretory phenotype is likely to identify the molecular mechanisms that contribute to the development of aging-associated human inflammatory diseases and a failure to cancer therapy.

IFI16 mediates soluble Flt-1 and endoglin production by trophoblast cells

OBJECTIVES

Preeclampsia is a serious pregnancy-specific hypertensive syndrome that is characterized by widespread maternal endothelial dysfunction. Previous studies have shown that increased levels of circulating cell-free fetal DNA in women with preeclampsia correspond to the degree of disease severity; however, it is unknown whether this DNA is a key signal that contributes to the development of preeclampsia. The detection of DNA is critical to appropriate innate immune responses. The interferon-inducible protein 16 (IFI16) - a member of the HIN-200 family - is an innate immune receptor for intracellular DNA, which is implicated in the control of cell growth, apoptosis, angiogenesis, and immunomodulation; however, its role in preeclampsia remains unresolved. Here, we tested the hypothesis that this DNA can activate IFI16 in the placentas of women with preeclampsia and is sufficient to induce soluble fms-like tyrosine kinase 1 (sFlt-1) and soluble endoglin (sEng) production.

METHODS

We characterized IFI16 in severe preeclamptic placentas and assessed whether DNA increased the release of sFlt-1 and sEng from trophoblast cells and placental explants. Furthermore, we determined whether IFI16 was involved in DNA-induced sFlt-1 and sEng production.

RESULTS

Placental immunoreactivity and protein levels of IFI16 were significantly increased in women with preeclampsia compared to matched control women. Treatment of human trophoblasts with the IFI16 agonist poly(dA:dT) significantly increased IFI16 levels. Furthermore, poly(dA:dT) induced sFlt-1 and sEng production by human trophoblasts in an IFI16-dependent manner.

CONCLUSIONS

We conclude that trophoblast cells respond to cell-free fetal DNA through the IFI16 receptor, resulting in the production of the preeclampsia-related antiangiogenic factors sFlt-1 and sEng.

IFI16 Expression Is Related to Selected Transcription Factors during B-Cell Differentiation

The interferon-inducible DNA sensor IFI16 is involved in the modulation of cellular survival, proliferation, and differentiation. In the hematopoietic system, IFI16 is consistently expressed in the CD34+ stem cells and in peripheral blood lymphocytes; however, little is known regarding its regulation during maturation of B- and T-cells. We explored the role of IFI16 in normal B-cell subsets by analysing its expression and relationship with the major transcription factors involved in germinal center (GC) development and plasma-cell (PC) maturation. IFI16 mRNA was differentially expressed in B-cell subsets with significant decrease in IFI16 mRNA in GC and PCs with respect to naïve and memory subsets. IFI16 mRNA expression is inversely correlated with a few master regulators of B-cell differentiation such as BCL6, XBP1, POU2AF1, and BLIMP1. In contrast, IFI16 expression positively correlated with STAT3, REL, SPIB, RELA, RELB, IRF4, STAT5B, and STAT5A. ARACNE algorithm indicated a direct regulation of IFI16 by BCL6, STAT5B, and RELB, whereas the relationship between IFI16 and the other factors is modulated by intermediate factors. In addition, analysis of the CD40 signaling pathway showed that IFI16 gene expression directly correlated with NF-κB activation, indicating that IFI16 could be considered an upstream modulator of NF-κB in human B-cells.

Interferons and their stimulated genes in the tumor microenvironment

Constitutive expression of interferons (IFNs) and activation of their signaling pathways have pivotal roles in host responses to malignant cells in the tumor microenvironment. IFNs are induced by the innate immune system and in tumors through stimulation of Toll-like receptors (TLRs) and through other signaling pathways in response to specific cytokines. Although in the oncologic context IFNs have been thought of more as exogenous pharmaceuticals, the autocrine and paracrine actions of endogenous IFNs probably have even more critical effects on neoplastic disease outcomes. Through high-affinity cell surface receptors, IFNs modulate transcriptional signaling, leading to regulation of more than 2,000 genes with varying patterns of temporal expression. Induction of the gene products by both unphosphorylated and phosphorylated STAT1 after ligand binding results in alterations in tumor cell survival, inhibition of angiogenesis, and augmentation of actions of T, natural killer (NK), and dendritic cells. The interferon-stimulated gene (ISG) signature can be a favorable biomarker of immune response but, in a seemingly paradoxical finding, a specific subset of the full ISG signature indicates an unfavorable response to DNA-damaging interventions such as radiation. IFNs in the tumor microenvironment thus can alter the emergence, progression, and regression of malignancies.

Embryonic stem cell-specific signature in cervical cancer

The wide range of invasive and noninvasive lesion phenotypes associated with high-risk human papillomavirus (HR-HPV) infection in cervical cancer (CC) indicates that not only the virus but also specific cervical epithelial cells in the transformation zone (TZ), such as stem cells (SCs), play an important part in the development of cervical neoplasia. In this review, we focused in an expression signature that is specific to embryonic SCs and to poorly differentiated cervical malignant tumors and we hypothesize that this expression signature may play an important role to promote cell growth, survival, colony formation, lack of adhesion, as well as cell invasion and migration in CC.

Interferon Inducible IFI16 Expression in p16 Positive Squamous Cell Carcinoma of the Oropharynx

Human-papillomavirus- (HPV-) positive oropharyngeal squamous cell carcinomas (OPSCC) are reported to be more responsive to treatment and to be related to a favorable prognosis compared with non-HPV carcinomas. However, the molecular basis of the responsiveness is unclear. Interferon inducible IFI16, which is implicated in the control of cell growth, apoptosis, angiogenesis, and immunomodulation in various types of cancers, is reported to be frequently expressed in the HPV-positive head and neck SCC and to correlate with a better prognosis. In this study, we hypothesized that HPV related OPSCC expresses IFI16 resulting in favorable prognosis. To clarify the relationship between the prognosis of HPV related OPSCC patients and IFI16 status, we examined immunohistologically the pretreatment specimens of OPSCC for the expression of p16 as a surrogate marker of HPV infection and IFI16. We could not show that the expression of IFI16 is associated with that of p16. There was no significant difference in the survival rate between IFI16 positive and negative groups. Patients with p16 negative tumor exhibited worse survival rate regardless of IFI16 status. In this limited case series, we could not conclude that IFI16 expression is altered in p16 positive OPSCC and that it would be a new predictive marker or a useful therapeutic tool.

The Asian-American E6 variant protein of human papillomavirus 16 alone is sufficient to promote immortalization, transformation, and migration of primary human foreskin keratinocytes

We examined how well the human papillomavirus (HPV) E6 oncogene can function in the absence of the E7 oncogene during the carcinogenic process in human keratinocytes using a common HPV variant strongly associated with cervical cancer: the Asian-American E6 variant (AAE6). This E6 variant is 20 times more frequently detected in cervical cancer than the prototype European E6 variant, as evidenced by independent epidemiological data. Using cell culture and cell-based functional assays, we assessed how this variant can perform crucial carcinogenesis steps compared to the prototype E6 variant. The ability to immortalize and transform primary human foreskin keratinocytes (PHFKs) to acquire resilient phenotypes and the ability to promote cell migration were evaluated. The immortalization capability was assayed based on population doublings, number of passages, surpassing mortality stages 1 and 2, human telomerase reverse transcriptase (hTERT) expression, and the ability to overcome G(1) arrest via p53 degradation. Transformation and migration efficiency were analyzed using a combination of functional cell-based assays. We observed that either AAE6 or prototype E6 proteins alone were sufficient to immortalize PHFKs, although AAE6 was more potent in doing so. The AAE6 variant protein alone pushed PHFKs through transformation and significantly increased their migration ability over that of the E6 prototype. Our findings are in line with epidemiological data that the AA variant of HPV16 confers an increased risk over the European prototype for cervical cancer, as evidenced by a superior immortalization, transformation, and metastatic potential.

Interferon-inducible protein 16: insight into the interaction with tumor suppressor p53

IFI16 is a member of the interferon-inducible HIN-200 family of nuclear proteins. It has been implicated in transcriptional regulation by modulating protein-protein interactions with p53 tumor suppressor protein and other transcription factors. However, the mechanisms of interaction remain unknown. Here, we report the crystal structures of both HIN-A and HIN-B domains of IFI16 determined at 2.0 and 2.35 Å resolution, respectively. Each HIN domain comprises a pair of tightly packed OB-fold subdomains that appear to act as a single unit. We show that both HIN domains of IFI16 are capable of enhancing p53-DNA complex formation and transcriptional activation via distinctive means. HIN-A domain binds to the basic C terminus of p53, whereas the HIN-B domain binds to the core DNA-binding region of p53. Both interactions are compatible with the DNA-bound state of p53 and together contribute to the effect of full-length IFI16 on p53-DNA complex formation and transcriptional activation.

The multifaceted interferon-inducible p200 family proteins: from cell biology to human pathology

The interferon-inducible p200 family proteins consist of a group of homologous human and mouse proteins that have an N-terminal Pyrin domain and 1 or 2 partially conserved 200 amino acid long C-terminal domains (designated the HIN domain or p200 X domain). These proteins display multifaceted activity due to their ability to bind to various target proteins (eg, transcription factors, signaling proteins, and tumor suppressor proteins) and modulate different cell functions. In addition to a role in interferon biology, increasing evidence supports a role for these proteins as regulators of various cell functions, including proliferation, differentiation, apoptosis, senescence, inflammasome assembly, and control of organ transplants. As a consequence, alterations in their expression and function may be of relevance in the pathogenesis of human diseases, such as systemic autoimmune syndromes, tumors, and degenerative diseases. This review summarizes the literature describing these data, highlights some of the important findings derived from recent studies, and speculates about future perspectives.

HSV as a vector in vaccine development and gene therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), major human pathogen whose lifestyle is based on a long-term dual interaction with the infected host characterized by the existence of lytic and latent infections, has allowed the development of potential vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous system, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases and targeted infection of specific tissues or organs. Three different classes of vectors can be derived from HSV-1: replication-competent attenuated vectors, replication-incompetent recombinant vectors and defective helper-dependent vectors known as amplicons. This chapter highlights the current knowledge concerning design, construction and recent applications, as well as the potential and current limitations of the three different classes of HSV-1-based vectors.

The interferon-inducible HIN-200 gene family in apoptosis and inflammation: implication for autoimmunity

The Ifi-200/HIN-200 gene family encodes highly homologous human (IFI16, myeloid cell nuclear differentiation antigen, absent in melanoma 2, and IFIX) and murine proteins (Ifi202a, Ifi202b, Ifi203, Ifi204, Ifi205, and Ifi206), which are induced by type I and II interferons (IFN). These proteins have been described as regulators of cell proliferation and differentiation and, more recently, several reports have suggested their involvement in both apoptotic and inflammatory processes. The relevance of HIN-200 proteins in human disease is beginning to be clarified, and emerging experimental data indicate their role in autoimmunity. Autoimmune disorders are sustained by perpetual activation of inflammatory process and a link between autoimmunity and apoptosis has been clearly established. Moreover, the interferon system is now considered as a key player in autoimmune disorders such as systemic lupus erythemathosus, systemic sclerosis, and Sjögren's syndrome, and it is therefore conceivable to hypothesize that HIN-200 may be among the pivotal mediators of IFN activity in autoimmune disease. In particular, the participation of HIN-200 proteins in apoptosis and inflammation could support their potential role in autoimmunity.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

Expression of the interferon-inducible proteins MxA and IFI16 in liver allografts

AIMS

To test the hypothesis that the activation of the interferon (IFN) system pathways might link hepatitis C virus (HCV) recurrence in the liver allograft with acute cellular rejection.

METHODS AND RESULTS

In this retrospective study, allograft biopsy specimens from 28 adult patients (14 HCV+ and 14 HCV-) who had undergone their first liver transplantation were analysed. Eleven biopsy specimens showed acute cellular rejection (Banff rejection activity index score > or =3). Specimens were immunostained for two IFN-inducible proteins, MxA and IFI16, and for CD45. The predominant MxA reactivity pattern was hepatocytic, whereas IFI16 was expressed in both the hepatocellular and inflammatory compartments. Moderate to strong MxA expression in hepatocytes was associated positively with rejection score (P < 0.01), donor's age < or =45 years (P < 0.05) and aspartate aminotransferase levels >40 U/l on the day of biopsy (P < 0.05), and inversely with infiltration of portal triads by IFI16+/CD45+ cells (P < 0.005) and time to progression beyond Ishak stage 2 of recurrent hepatitis C (P < 0.01). On multivariate analysis, MxA expression in hepatocytes was independently associated with allograft rejection and donor's age.

CONCLUSIONS

Acute allograft rejection and recurrence of HCV infection in the liver allograft appear to intersect in the IFN system pathways.

Activation and modulation of antiviral and apoptotic genes in pigs infected with classical swine fever viruses of high, moderate or low virulence

The immune response to CSFV and the strategies of this virus to evade and suppress the pigs’ immune system are still poorly understood. Therefore, we investigated the transcriptional response in the tonsils, median retropharyngeal lymph node (MRLN), and spleen of pigs infected with CSFV strains of similar origin with high, moderate, and low virulence. Using a porcine spleen/intestinal cDNA microarray, expression levels in RNA pools prepared from infected tissue at 3 dpi (three pigs per virus strain) were compared to levels in pools prepared from uninfected homologue tissues (nine pigs). A total of 44 genes were found to be differentially expressed. The genes were functionally clustered in six groups: innate and adaptive immune response, interferon-regulated genes, apoptosis, ubiquitin-mediated proteolysis, oxidative phosphorylation and cytoskeleton. Significant up-regulation of three IFN-γ-induced genes in the MRLNs of pigs infected with the low virulence strain was the only clear qualitative difference in gene expression observed between the strains with high, moderate and low virulence. Real-time PCR analysis of four response genes in all individual samples largely confirmed the microarray data at 3 dpi. Additional PCR analysis of infected tonsil, MRLN, and spleen samples collected at 7 and 10 dpi indicated that the strong induction of expression of the antiviral response genes chemokine CXCL10 and 2′–5′ oligoadenylate synthetase 2, and of the TNF-related apoptosis-inducing ligand (TRAIL) gene at 3 dpi, decreased to lower levels at 7 and 10 dpi. For the highly and moderately virulent strains, this decrease in antiviral and apoptotic gene expression coincided with higher levels of virus in these immune tissues.

Notch induces cell cycle arrest and apoptosis in human erythroleukaemic TF-1 cells

OBJECTIVE

Notch signalling is known to promote hematopoietic stem cell self-renewal and to influence the lineage commitment decisions of progenitor cells. The purpose of this study was to investigate the mechanism of Notch-induced apoptosis in the erythroleukaemic cell line TF-1, and in primary cord blood CD34+ cells.

METHODS

Retroviral constructs containing constitutively active forms of Notch as well as components of the Notch signalling pathway were used to transduce cells and their effect on cell cycle kinetics and apoptosis assayed by immunostaining for the S-phase marker Ki67 and Annexin V.

RESULTS

We found that TF-1 cells undergo cell cycle arrest followed by apoptosis in a cytokine-independent manner in response to active Notch. Transduction of TF-1 cells with known targets of Notch signalling, Deltex1, HES1 and HERP2, showed that Notch-induced cell cycle arrest was not mediated by these proteins. However, analysis of cell cycle gene expression revealed that Notch signalling was associated with an up-regulation of IFI16 expression in TF-1 cells and in primary cord blood CD34+ cells.

CONCLUSION

These data demonstrate that, in the context of TF-1 cells, Notch signalling can induce cell cycle arrest and apoptosis.

Cloning and characterisation of Ifi206: a new murine HIN-200 family member

HIN-200 proteins are interferon-inducible proteins capable of regulating cell growth, senescence, differentiation and death. Using a combination of in silico analysis of NCBI EST databases and screening of murine C57BL/6 cDNA libraries we isolated novel murine HIN-200 cDNAs designated Ifi206S and Ifi206L encoding two putative mRNA splice variants. The p206S and p206L protein isoforms have a modular domain structure consisting of an N-terminal PAAD/DAPIN/Pyrin domain, a region rich in serine, threonine and proline residues and a C-terminal 200 B domain characteristic of other HIN-200 proteins. Ifi206 mRNA was detected only in the spleen and lung of BALB/c and C57BL/6 mice and expression was up-regulated by both types I and II IFN subtypes. p206 protein was predominantly expressed in the cytoplasm and addition of LMB, a CRM1 dependent nuclear export inhibitor, caused p206 to accumulate in the nucleus. Unlike other human and mouse HIN-200 proteins that contain only a single 200 amino acid domain, overexpression of p206 impaired the clonogenic growth of tumour cell lines. Thus, p206 represents the newest HIN-200 family member discovered. It has distinct and restricted pattern of expression however maintains many of the hallmarks of HIN-200 proteins including the presence of a characteristic 200 X domain, induction by interferon and an ability to suppress tumour cell growth.

Effects of IFI16 overexpression on the growth and doxorubicin sensitivity of head and neck squamous cell carcinoma–derived cell lines

BACKGROUND

In a previous analysis of head and neck squamous cell carcinomas (HNSCCs), we showed that the levels of the interferon-inducible protein IFI16 inversely correlate with cancer grade. In this study, we further evaluate the molecular role of IFI16 in the development of HNSCCs.

METHODS

The effect of IFI16 expression was evaluated by its retroviral restoration in an IFI16-negative HNSCC-derived cell line, HNO136. Growth rate and soft agar colony formation were evaluated. The effect of IFI16 restoration in cells exposed to doxorubicin was also analyzed.

RESULTS

IFI16 restoration resulted in the inhibition of both cell growth and in vitro transforming activity and increased doxorubicin-induced cell death by accumulating the cells at the G2/M phase.

CONCLUSION

In agreement with our previous in vivo data, IFI16 appears to be involved in maintaining the normal growth of epithelial cells, whereas its downregulation may contribute to uncontrolled cell proliferation and tumorigenesis.

Role of the Interferon-Inducible Gene IFI16 in the Etiopathogenesis of Systemic Autoimmune Disorders

Interferons (IFNs) are now known to exert a multitude of immunological functions on both the innate and adaptive immunity. Given their pleiotropic effects on the immune system, it is conceivable that excess type I IFN or aberrant regulation of its signaling could contribute to autoimmunity. Several lines of evidence link IFNs to autoimmune disorders, in particular to systemic lupus erythematosus (SLE) and systemic sclerosis (SSc). Expression of a spectrum of genes that constitutes an "IFN signature" is the most significant observation indicating that IFNs may be dominant among the pathogenic mediators involved in some autoimmune diseases. A family of IFN-inducible genes, designated HIN-200 in the human and IFI-200 in the murine species, encodes evolutionary related human (IFI16, MNDA, AIM2, IFIX) and murine proteins (Ifi202 a, Ifi202b, Ifi203, Ifi204, Ifi205/D3). Physiological IFI16 expression was found in cells of the immune system, in endothelial cells, and in stratified squamous epithelia, such as skin. The presence of anti-IFI16 antibodies was reported in SLE and primary/secondary Sjögren's syndrome. More recently, we reported that anti-IFI16 autoantibodies differentiate limited cutaneous systemic sclerosis (lcSSc) from diffuse systemic sclerosis (dcSSc). Molecular studies performed in primary endothelial cells overexpressing IFI16 demonstrated that it may be involved in the early steps of inflammation by modulating endothelial cell function, such as expression of adhesion molecules and chemokine production, cell growth, and apoptosis. Moreover, here we report that IFI16 expression is induced by proinflammatory cytokines. In this article the role of the IFI16 protein and its corresponding autoantibodies in the etiopathogenesis of systemic autoimmune diseases, in which chronic inflammation is involved, are discussed.

A novel role of the interferon-inducible protein IFI16 as inducer of proinflammatory molecules in endothelial cells

The human IFI16 gene is an interferon-inducible gene implicated in the regulation of endothelial cell proliferation and tube morphogenesis. Immunohistochemical analysis has demonstrated that this gene is highly expressed in endothelial cells in addition to hematopoietic tissues. In this study, gene array analysis of human umbilical vein endothelial cells overexpressing IFI16 revealed an increased expression of genes involved in immunomodulation, cell growth, and apoptosis. Consistent with these observations, IFI16 triggered expression of adhesion molecules such as ICAM-1 and E-selectin or chemokines such as interleukin-8 or MCP-1. Treatment of cells with short hairpin RNA targeting IFI16 significantly inhibited ICAM-1 induction by interferon (IFN)-gamma demonstrating that IFI16 is required for proinflammatory gene stimulation. Moreover, functional analysis of the ICAM-1 promoter by deletion- or site-specific mutation demonstrated that NF-kappaB is the main mediator of IFI16-driven gene induction. NF-kappaB activation appears to be triggered by IFI16 through a novel mechanism involving suppression of IkappaBalpha mRNA and protein expression. Support for this finding comes from the observation that IFI16 targeting with specific short hairpin RNA down-regulates NF-kappaB binding activity to its cognate DNA and inhibits ICAM-1 expression induced by IFN-gamma. Using transient transfection and luciferase assay, electrophoretic mobility shift assay, and chromatin immunoprecipitation, we demonstrate indeed that activation of the NF-kappaB response is mediated by IFI16-induced block of Sp1-like factor recruitment to the promoter of the IkappaBalpha gene, encoding the main NF-kappaB inhibitor. Activation of NF-kappaB accompanied by induction of proinflammatory molecules was also observed when IkappaBalpha expression was down-regulated by specific small interfering RNA, resulting in an outcome similar to that observed with IFI16 overexpression. Taken together, these data implicate IFI16 as a novel regulator of endothelial proinflammatory activity and provide new insights into the physiological functions of the IFN-inducible gene IFI16.

Antitumor effects of non-replicative herpes simplex vectors expressing antiangiogenic proteins and thymidine kinase on Lewis lung carcinoma establishment and growth

There is growing evidence that combinations of antiangiogenic proteins with other antineoplastic treatments such as chemo- or radiotherapy and suicide genes-mediated tumor cytotoxicity lead to synergistic effects. In the present work, we tested the activity of two non-replicative herpes simplex virus (HSV)-1-based vectors, encoding human endostatin::angiostatin or endostatin::kringle5 fusion proteins in combination with HSV-1 thymidine kinase (TK) molecule, on endothelial cells (ECs) and Lewis lung carcinoma (LLC) cells. We observed a significant reduction of the in vitro growth, migration and tube formation by primary ECs upon direct infection with the two recombinant vectors or cultivation with conditioned media obtained from the vector-infected LLC cells. Moreover, direct cytotoxic effect of HSV-1 TK on both LLC and ECs was demonstrated. We then tested the vectors in vivo in two experimental settings, that is, LLC tumor growth or establishment, in C57BL/6 mice. The treatment of pre-established subcutaneous tumors with the recombinant vectors with ganciclovir (GCV) induced a significant reduction of tumor growth rate, while the in vitro infection of LLC cells with the antiangiogenic vectors before their implantation in mice flanks, either in presence or absence of GCV, completely abolished the tumor establishment.

Involvement of RB gene family in tumor angiogenesis

Angiogenesis, the development of new blood vessels from pre-existing vessels, represents a fundamental step in tumor progression and metastatization. The induction of vasculature is required for growth of the tumor mass, to ensure an adequate supply of oxygen and metabolites to the tumor beyond a critical size. Tumor angiogenesis is a highly regulated process that is controlled physiologically by the tumor microenvironment and genetically by alteration of several oncogenes or tumor suppressor genes. We will focus on recent demonstrations regarding the involvement of the retinoblastoma family proteins (phosphorylated retinoblastoma (pRb), p107 and pRb2/p130) at different levels of the angiogenic process. pRb and its homologs can regulate the expression of pro- and antiangiogenic factors, such as the vascular endothelial growth factor, through an E2F-dependent mechanism. Moreover, pRb is able to modulate also the transcriptional activity of several angiogenesis-related factors like HIF-1, Id2 and Oct-1. pRb2/p130 is required for both differentiation and mobilization of bone marrow-derived endothelial cell precursors and endothelial sprouting from neighboring vessels. The involvement of the pRb pathway in the angiogenesis process has also been demonstrated by different cellular models expressing viral oncoproteins, like human papilloma virus. Moreover, some natural and synthetic compounds demonstrate their antiangiogenetic activity with a mechanism of action involving pRb. Finally, the possible prognostic value of immunohistochemical evaluation of pRb and/or pRb2/p130 expression can represent a useful tool for the characterization of the angiogenic phenotype of specific tumor histotypes.

Signal transducer and activator of transcription 1 activation in endothelial cells is a negative regulator of angiogenesis

To determine the role of the transcription factor signal transducer and activator of transcription (STAT) 1 on endothelial cell function, human umbilical vein endothelial cells (HUVEC) were treated with IFN-gamma, a potent activator of STAT1. IFN-gamma inhibited cell growth and tube formation of HUVECs. Although the potent proangiogenic protein vascular endothelial growth factor (VEGF) stimulated cell growth and tube formation, IFN-gamma could suppress these effects of VEGF. Transfection of HUVECs with short interfering RNA targeting STAT1 abrogated IFN-gamma-induced inhibition of HUVEC growth and tube formation, and suppressed the inhibition of VEGF-induced tube formation by IFN-gamma, indicating that STAT1 is critical for this process. IFN-gamma blocks the biological activity of VEGF through inhibition of genes necessary for the VEGF response, including angiopoietin-2, urokinase plasminogen activator, tissue inhibitor of matrix metalloproteinase-1, cyclooxygenase-2, and VEGF receptor 2. To extend these findings in vivo, the role of STAT1 in angiogenesis was examined in STAT1-deficient mice using the Matrigel in vivo angiogenesis assay. Substantial cellular infiltration and formation of vascular structures occurred in STAT1-/- mice compared with wild-type controls. These data indicate that STAT1 plays a key role in the inhibition of angiogenesis through its action within endothelial cells, and exploiting this process may be useful in treating cancers and vascular tumors.

Current status and perspective of antiangiogenic therapy for cancer: urinary cancer

Angiogenesis is considered a prerequisite for solid tumor growth. Antiangiogenic therapy reduces tumor size and extends host survival in a number of preclinical animal models. However, in humans antiangiogenic therapy is a poor promoter of tumor regression and has shown minimal effect on patient survival. In urinary cancers, such as renal cell cancer, prostate cancer, and bladder cancer, advanced refractory disease is a good candidate for antiangiogenic therapy because of its resistance to ordinary chemotherapy, radiotherapy, and hormonal therapy. Unique characteristics of molecular mechanisms underlie the induction of angiogenesis in urinary cancers. In this review, we summarize these unique mechanisms and review the results of clinical trials of antiangiogenic therapy for these cancers, discussing prospects and problems relating to antiangiogenic therapy.

Interferon-inducible protein IFIXalpha1 functions as a negative regulator of HDM2

The 200-amino-acid repeat (HIN-200) gene family with the hematopoietic interferon (IFN)-inducible nuclear protein encodes highly homologous proteins involved in cell growth, differentiation, autoimmunity, and tumor suppression. IFIX is the newest member of the human HIN-200 family and is often downregulated in breast tumors and breast cancer cell lines. The expression of the longest isoform of IFIX gene products, IFIXalpha1, is associated with growth inhibition, suppression of transformation, and tumorigenesis. However, the mechanism underlying the tumor suppression activity of IFIXalpha1 is not well understood. Here, we show that IFIXalpha1 downregulates HDM2, a principal negative regulator of p53, at the posttranslational level. IFIXalpha1 destabilizes HDM2 protein and promotes its ubiquitination. The E3 ligase activity of HDM2 appears to be required for this IFIXalpha1 effect. Importantly, HDM2 downregulation is required for the IFIXalpha1-mediated increase of p53 protein levels, transcriptional activity, and nuclear localization, suggesting that IFIXalpha1 positively regulates p53 by acting as a negative regulator of HDM2. We found that IFIXalpha1 interacts with HDM2. Interestingly, the signature motif of the HIN-200 gene family, i.e., the 200-amino-acid HIN domain of IFIXalpha1, is sufficient not only for binding HDM2 but also for downregulating it, leading to p53 activation. Finally, we show that IFIX mediates HDM2 downregulation in an IFN-inducible system. Together, these results suggest that IFIXalpha1 functions as a tumor suppressor by repressing HDM2 function.

Development and application of replication-incompetent HSV-1-based vectors

The replication-incompetent HSV-1-based vectors are herpesviruses in which genes that are 'essential' for viral replication have been either mutated or deleted. These deletions have substantially reduced their cytotoxicity by preventing early and late viral gene expression and, together with other deletions involving 'nonessential' genes, have also created space to introduce distinct and independently regulated expression cassettes for different transgenes. Therapeutic effects in gene therapy applications requiring simultaneous and synergic expression of multiple gene products are easily achievable with these vectors. A number of different HSV-1-based nonreplicative vectors for specific gene therapy applications have been developed so far. They have been tested in different gene therapy animal models of neuropathies (Parkinson's disease, chronic pain, spinal cord injury pain) and lysosomal storage disorders. Many replication-incompetent HSV-1-based vectors have also been used either as potential anti-herpes vaccines, as well as vaccine vectors for other pathogens in murine and simian models. Anticancer gene therapy approaches have also been successfully set up; gene therapy to other targets by using these vectors is feasible.

A novel autoantigen to differentiate limited cutaneous systemic sclerosis from diffuse cutaneous systemic sclerosis: The interferon-inducible gene IFI16

OBJECTIVE

To investigate the presence and clinical significance of autoantibodies against the interferon-inducible gene IFI16 in systemic sclerosis (SSc), systemic lupus erythematosus (SLE), and other autoimmune diseases.

METHODS

Immunohistochemical analysis was used to evaluate the expression of IFI16 in skin biopsy specimens obtained from patients with SSc and patients with SLE. Levels of antibodies against IFI16 in sera from 82 patients with SSc and 100 patients with SLE were determined by enzyme-linked immunosorbent assay. Other autoimmune diseases such as primary Sjögren's syndrome (SS), rheumatoid arthritis (RA), chronic urticaria, and hepatitis C virus (HCV) infection were also examined.

RESULTS

Expression of IFI16 was greatly increased and was ubiquitous in all layers of the epidermis and in the dermal inflammatory infiltrates of lesional skin from both patients with SLE and patients with SSc. Patients with SLE, those with primary SS, and those with SSc exhibited significantly higher anti-IFI16 IgG antibody levels compared with normal controls (for SLE, P < 0.002; for primary SS, P < 0.001; for SSc, P < 0.0005). Anti-IFI16 titers above the ninety-fifth percentile for control subjects were observed in 26% of the patients with SLE, 50% of those with primary SS, and 21% of those with SSc (28% of patients with limited cutaneous SSc [lcSSc] versus 4% of patients with diffuse cutaneous SSc [dcSSc]). In contrast, the prevalence of anti-IFI16 was 4% in patients with RA, 5% in those with chronic urticaria, and 13% in those with HCV infection.

CONCLUSION

The results of this study provide evidence that an IFN-inducible gene, IFI16, may be involved in the pathophysiologic mechanisms of connective tissue disorders such as SSc. Moreover, a strict correlation with lcSSc was also demonstrated, thus providing a novel tool in the differential diagnosis of lcSSc from dcSSc.

The HIN domain of IFI-200 proteins consists of two OB folds

The interferon-inducible p200 (IFI-200/HIN-200) family of proteins regulates cell growth and differentiation, and confers resistance to the development of tumors and virus infections. IFI-200 family members are thought to exert their biological effects by modulation of the transcriptional activities of numerous factors and interaction with other proteins through the C-terminal HIN domains. However, the HIN domain structure and function have remained obscure. Therefore, we performed a comprehensive bioinformatics analysis and assembled a structure-based multiple sequence alignment of IFI-200 proteins. The application of fold recognition methods revealed that the HIN domain consists of two consecutive OB domains. Our structural models of DNA-binding HIN domains afford the long-sought interpretations for many previous experimental observations. Our results also raise the possibility of as yet unexplored functional roles of IFI-200 proteins as transcriptional regulators and as interaction partners of proteins involved in immunomodulatory and apoptotic processes.

Up-regulation of the interferon-inducible IFI16 gene by oxidative stress triggers p53 transcriptional activity in endothelial cells

Reactive oxygen species (ROS), including hydrogen peroxide (H2O2), induces injury of endothelium in a variety of pathophysiological conditions, such as inflammation, aging, and cancer. In our study, we characterized the signaling pathway linking oxidative stress induced by sublethal concentrations of H2O2 to p53 in primary human endothelial cells through the interferon (IFN)-inducible gene IFI16. Induction of IFI16 by H2O2 was concentration- and time-dependent (maximum at 50 microM, 6 h after treatment) and down-regulated by pretreatment with N-acetyl-L-cysteine, which acts as an antioxidant. This pathway is a general response to ROS and not specific to H2O2 treatment, as two other ROS-generating compounds, i.e., S-nitroso-N-acetylpenicillamine and tert-butyl hydroperoxide, were equally capable to induce IFI16. Moreover, IFI16 up-regulation is a result of protein accumulation, as expression of corresponding mRNA, assessed by real-time polymerase chain reaction, was not affected. To investigate the mechanism of IFI16 accumulation, cells were incubated for 6 h in the presence of H2O2 or IFN-beta, and then cycloheximide was added to inhibit further protein synthesis. The half-life of IFI16 protein was found to be significantly increased in H2O2-treated cells compared with IFN-beta-treated cells (t1/2 = 120 min vs. > 30 min in H2O2- vs. IFN-beta-treated cells, respectively). An increase of IFI16 was accompanied by interaction with p53 phosphorylated at its N terminus, as shown by immunoprecipitation experiments. Moreover, binding to IFI16 resulted in its transcriptional activation as shown by an increase in the activity of a reporter gene driven by p53-responsive sequences derived from the p21(WAF1) promoter, along with an increase in the p21 mRNA and protein levels. Altogether, these results demonstrate a novel role of IFI16 in the signal transduction pathway that leads to p53 activation by oxidative stress in endothelial cells.

IFI16 is an essential mediator of growth inhibition, but not differentiation, induced by the leukemia inhibitory factor/JAK/STAT pathway in medullary thyroid carcinoma cells

Activation of Ras or Raf in the human medullary thyroid carcinoma (MTC) cell line, TT, induces growth arrest and differentiation via two parallel, yet independent, pathways. One of these pathways is intracellular and the other is a cell-extrinsic, autocrine/paracrine pathway mediated by the leukemia inhibitory factor (LIF)/JAK/STAT pathway. Here, we show that IFI16 is a necessary and sufficient downstream effector for LIF effects in MTC cells, specifically required for the LIF/JAK/STAT pathway-induced growth inhibition in these cells. IFI16 was induced by Raf or LIF. Dominant-negative STAT3 could block the induction, indicating that Raf can induce IFI16 only via the cell-extrinsic pathway. Knock-down of IFI16 using siRNA abrogated LIF-induced changes in cellular levels of E2F1, cyclin D1, and p21WAF/CIP1, and cell cycle arrest. In addition, adenovirus-mediated overexpression of IFI16 was sufficient to induce growth arrest. In contrast to its essential role for LIF-mediated growth arrest, IFI16 was not required for differentiation induced by LIF. Knock-down of IFI16 could not block changes in differentiation markers of the MTC cells, including calcitonin, RET, and cell morphology. Our study identifies IFI16 as an essential growth-specific effector of the cell-extrinsic growth inhibitory pathway of Ras/Raf signaling in MTC cells.

Role of IFI 16 in cellular senescence of human fibroblasts

Defects in interferon (IFN) signaling that result in loss of expression of IFN-inducible proteins are associated with cellular immortalization, an important early event in the development of human cancer. Here we report that loss of IFN-inducible IFI 16 expression in human fibroblasts allows bypass of cellular senescence. We found that levels of IFI 16 mRNA and protein were higher in human old versus young fibroblasts and immortalization of fibroblasts with telomerase resulted in decreased expression of IFI 16. Moreover, overexpression of IFI 16 in immortalized fibroblasts strongly inhibited cell proliferation. Interestingly, knockdown of IFI 16 expression in fibroblasts inhibited p53-mediated transcription, downregulated p21(WAF1) expression, and extended the proliferation potential. Importantly, treatment of immortal cell lines with 5-aza-2'-deoxycytidine, an inhibitor of DNA methyltransferase, resulted in upregulation of IFI 16. Our observations support the idea that increased levels of IFI 16 in older populations of human fibroblasts contribute to cellular senescence.