Interferon-inducible Protein 16 Expression Research Articles

Post-transcriptional regulation of IFI16 promotes inflammatory endothelial pathophenotypes observed in pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a progressive disease driven by endothelial cell inflammation and dysfunction, resulting in the pathological remodeling of the pulmonary vasculature. Innate immune activation has been linked to PAH development; however, the regulation, propagation, and reversibility of the induction of inflammation in PAH is poorly understood. Here, we demonstrate a role for interferon inducible protein 16 (IFI16), an innate immune sensor, as a modulator of endothelial inflammation in pulmonary hypertension, utilizing human pulmonary artery endothelial cells (PAECs). Inflammatory stimulus of PAECs with IL-1β up-regulates IFI16 expression, inducing proinflammatory cytokine up-regulation and cellular apoptosis. IFI16 mRNA stability is regulated by post-transcriptional m6A modification, mediated by Wilms' tumor 1-associated protein (WTAP), a structural stabilizer of the methyltransferase complex, via regulation of m6A methylation of IFI16. Additionally, m6A levels are increased in the peripheral blood mononuclear cells of PAH patients compared to control, indicating that quantifying this epigenetic change in patients may hold potential as a biomarker for disease identification. In summary, our study demonstrates IFI16 mediates inflammatory endothelial pathophenotypes seen in pulmonary arterial hypertension.

IFI16 Induced by Direct Interaction between Esophageal Squamous Cell Carcinomas and Macrophages Promotes Tumor Progression via Secretion of IL-1α.

Tumor-associated macrophages (TAMs), one of the major components of the tumor microenvironment, contribute to the progression of esophageal squamous cell carcinoma (ESCC). We previously established a direct co-culture system of human ESCC cells and macrophages and reported the promotion of malignant phenotypes, such as survival, growth, and migration, in ESCC cells. These findings suggested that direct interactions between cancer cells and macrophages contribute to the malignancy of ESCC, but its underlying mechanisms remain unclear. In this study, we compared the expression levels of the interferon-induced genes between mono- and co-cultured ESCC cells using a cDNA microarray and found that interferon-inducible protein 16 (IFI16) was most significantly upregulated in co-cultured ESCC cells. IFI16 knockdown suppressed malignant phenotypes and also decreased the secretion of interleukin-1α (IL-1α) from ESCC cells. Additionally, recombinant IL-1α enhanced malignant phenotypes of ESCC cells through the Erk and NF-κB signaling. Immunohistochemistry revealed that high IFI16 expression in human ESCC tissues tended to be associated with disease-free survival and was significantly associated with tumor depth, lymph node metastasis, and macrophage infiltration. The results of this study reveal that IFI16 is involved in ESCC progression via IL-1α and imply the potential of IFI16 as a novel prognostic factor for ESCC.

The Nuclear DNA Sensor IFI16 Indiscriminately Binds to and Diminishes Accessibility of the HSV-1 Genome to Suppress Infection.

ABSTRACTHuman cells identify invading pathogens and activate immune signaling pathways through a wide array of pattern recognition receptors, including DNA sensors. The interferon-inducible protein 16 (IFI16) is a nuclear DNA sensor that recognizes double-stranded DNA from a number of viral sources, including genomes of nuclear-replicating viruses. Among these is the prevalent human pathogen herpes simplex virus 1 (HSV-1). Upon binding to the HSV-1 DNA genome, IFI16 both induces antiviral cytokine expression and suppresses virus gene expression. Here, we used a multiomics approach of DNA sequencing techniques paired with targeted mass spectrometry to obtain an extensive view of the interaction between IFI16 and the HSV-1 genome and how this binding affects the viral DNA structure and protein expression. Through chromatin immunoaffinity purification coupled with next-generation DNA sequencing (ChIP-seq), we found that IFI16 binds to the HSV-1 genome in a sequence-independent manner while simultaneously exhibiting broad enrichment at two loci: UL30, the viral DNA polymerase gene, and US1 to US7. The assay for transposase-accessible chromatin with sequencing (ATAC-seq) revealed that these two regions are among the most accessible stretches of DNA on the genome, thereby facilitating IFI16 binding. Accessibility of the entire HSV-1 genome is elevated upon IFI16 knockout, indicating that expression of IFI16 globally induces chromatinization of viral DNA. Deletion of IFI16 also results in a global increase in the expression of HSV-1 proteins, as measured by parallel reaction monitoring-mass spectrometry of viral proteins representing 80% of the HSV-1 genome. Altogether, we demonstrate that IFI16 interacts with the HSV-1 genome in a sequence-independent manner, coordinating epigenetic silencing of the viral genome and decreasing protein expression and virus replication.IMPORTANCE Mammalian host defense against viral infection includes broad-acting cellular restriction factors, as well as effectors of intrinsic and innate immunity. IFI16 is a critical nuclear host defense factor and intrinsic immune protein involved in binding viral DNA genomes, thereby repressing the replication of nucleus-replicating viruses, including the human herpes simplex virus 1. What has remained unclear is where on the viral genome IFI16 binds and how binding affects both viral DNA structural accessibility and viral protein expression. Our study provides a global view of where and how a nuclear restriction factor of DNA viruses associates with viral genomes to exert antiviral functions during early stages of an acute virus infection. Our study can additionally serve as a systems-level model to evaluate nuclear DNA sensor interactions with viral genomes, as well as the antiviral outcomes of transcriptionally silencing pathogen-derived DNA.

Aligned Expression of IFI16 and STING Genes in RRMS Patients' Blood.

Multiple sclerosis (MS) is a chronic neurodegenerative disease of the central nervous system. The most common disease phenotype is Relapsing-Remitting MS (RRMS). Beta interferons are the first line of RRMS patients' treatment. Interferon-inducible protein 16 (IFI16) as a DNA sensing molecule and its downstream complex stimulator of interferon genes (STING) play a critical role in the activation of type I interferons. Hence we aimed to evaluate the expression rate of IFI16 and STING in RRMS patients' blood under a different type of IFNβ treatment. In the present study, 99 individuals participated. The participants were divided into 4 groups: 28 control subjects, 25 new cases of RRMS patients, 25 RRMS patients treated with IFNβ-1a (B1a), 21 RRMS patients treated with IFNβ-1b (B1b). The EDTA-treated blood samples were taken and transferred at standard conditions to the Cellular and Molecular Research Center of Shahrekord University of Medical Sciences, RNA was extracted and converted into cDNA. To evaluate the expression of IFI16 and STING, the Real-Time PCR method using SYBR Green/ROX qPCR master mix was performed done. The level of genes expression was measured using 2-ΔΔCt method. The obtained data were analyzed using SPSS v22 software. Comparison of the IFI and STING mRNA expression in blood samples in association with gender and age showed no significant differences (p>0.05). Also, the evaluation of IFI16 mRNA level revealed that the IFI16 genes' expressions were remarkably higher in the new case group compared to the control group, however, STING expression did not show any significant difference. The mRNA levels of IFI16 and STING in IFNβ-treated groups were significantly lower than the new case group (p<0.001). Also, the genes' expressions in both the IFNβ-treated groups were significantly lower compared to the control group (p<0.001). In the assessment of the correlation of IFI16 and STING expressions with age and sex in different research groups, no statistically significant differences were seen (p>0.05). Perhaps the IFNβ therapy decreases the IFI16 and STING expression in a STINGdependent pathway as a negative feedback mechanism for regulation of the immune system and suppression of pro-inflammatory cytokines production. The important role of DNA sensing molecules and STING-dependent pathway in MS gives a new insight into future treatment based on STING-direct therapies.

Elevated cell-free fetal DNA contributes to placental inflammation and antiangiogenesis via AIM2 and IFI16 during pre-eclampsia.

Accumulated evidence has shown that pre-eclampsia (PE) is related to both maternal and utero-placental antiangiogenesis and inflammation. Remarkably, an elevated cell-free fetal DNA (cffDNA) level has been found in maternal circulation; however, it remains unclear whether this DNA can induce activation of cytosolic DNA sensor signaling pathways and lead to the development of PE. In this study, we found that trophoblast cells constitutively expressed the cytosolic DNA sensors, absent in melanoma 2 (AIM2) and interferon-inducible protein 16 (IFI16). The cffDNA and pro-inflammatory and antiangiogenic factors were present at higher concentrations in PE compared with the control group and correlated with the severity of PE. DNA stimulation significantly increased the AIM2 and IFI16 levels, consistent with the elevated AIM2 and IFI16 expression in women with PE, and elicited increased production of AIM2-mediatedinterleukin IL-8 (IL-8), IL-6 and CC chemokine ligand 2 (CCL2) and IFI16-mediated sEndoglin, sFlt-1 and CXCL10. Furthermore, enhancement of the inflammatory response was found to be induced by DNA exposure, but DNA exposure did not induce PE-like symptoms in pregnant mice. It is possible that elevated cffDNA could reflect the degree of placental damage and trigger cytosolic DNA sensoractivation, which disrupts the immunity balance and, consequently, contributes to inflammatory and antiangiogenic responses. In conclusion, the results of this study suggest that circulating cffDNA levels are increased in preeclamptic women and act through AIM2 and IFI16 activation to promote the production of pro-inflammatory and antiangiogenic factors, which correlate with the severity of the disease, and may offer insights into the etiology and pathogenesis of PE.

PYHIN Proteins and HPV: Role in the Pathogenesis of Head and Neck Squamous Cell Carcinoma.

In the last decades, the human papillomavirus (HPV) emerged as an etiological cause of head and neck squamous cell carcinoma (HNSCC), especially in the oropharynx. The role of two intracellular DNA sensors, which belong to the PYHIN family (interferon-inducible protein 16 (IFI16) and absent in melanoma 2 protein (AIM2)), has been analyzed in relation to HPV infection and head and neck carcinogenesis. In particular, IFI16 and AIM2 expression depends on HPV infection in HNSCC. They represent viral restriction factors and are key components of the intrinsic immunity activated against different viruses, including HPV. This review analyzed and summarized the recent findings about the role of PYHIN proteins in HPV+ and HPV− HNSCC.

Nucleosomal dsDNA Stimulates APOL1 Expression in Human Cultured Podocytes by Activating the cGAS/IFI16-STING Signaling Pathway

APOL1 alleles G1 and G2 are associated with faster progression to lupus nephritis (LN)-associated end-stage renal disease (LN-ESRD) in African Americans. Increased levels of type I interferons (IFNs) and nucleosome-associated double-stranded DNA (dsDNA) fragments (nsDNA) are the hallmark of this disease. Here, we identify cyclic GMP-AMP synthase (cGAS) and interferon-inducible protein 16 (IFI16) as the major DNA sensors in human immortalized podocytes. We also show that nsDNA triggers the expression of APOL1 and IFNβ via IRF3 activation through the cGAS/IFI16-STING pathway. We demonstrate that maximal APOL1 expression also requires the activation of type I IFN receptor (IFNAR) and STAT1 signaling triggered by IFNβ produced in response to nsDNA, or by exogenous IFNβ. Finally, we show that STAT1 activation is sufficient to upregulate IFI16, subsequently boosting APOL1 expression through a positive feedback mechanism. Collectively, we find that nsDNA-induced APOL1 expression is mediated by both IFNβ-independent and dependent signaling pathways triggered by activation of the cGAS/IFI16-STING pathway. We propose that simultaneous inhibition of STING and the IFNAR-STAT1 pathway may attenuate IFI16 expression, reduce IFI16-cGAS cross-talk, and prevent excessive APOL1 expression in human podocytes in response to nsDNA.

Effects of interferon inducible protein 16 (IFI16) on viral protein and pro-inflammatory cytokine expression in human T-cell leukemia virus type 1 (HTLV-1)-positive T cells

Objective To investigate the effects of interferon inducible protein 16 (IFI16), a cytosolic DNA sensor, on the expression of human T-cell leukemia virus type 1 (HTLV-1) proteins and pro-inflammatory cytokines in adult HTLV-1-positive T cells. Methods IFI16 expression in different HTLV-1-positive T cell lines was detected by immunoblot assay. Specific siRNA targeting the IFI16 gene was constructed and the gene silencing efficiency was detected by immunoblot assay. Expression of HTLV-1 Tax protein at mRNA and protein levels was respectively detected by real-time PCR and immunoblot assay after knocking down the expression of IFI16 in HTLV-1-positive T cells with siRNA. Expression of interferon (IFN)-α, IFN-γ, tumor necrosis factor (TNF)-α, Tax and Env were detected by real-time PCR. Results Compared with the HTLV-1-negative T cell line Jurkat, IFI16 expression was enhanced in the HTLV-1-positive T cell lines MT2, MT4 and C8166. Tax expression was increased, while that of IFN-α, IFN-γ and TNF-α was decreased in MT2 and MT4 cells after silencing the expression of IFI16 with siRNA. Conclusions IFI16 expression was increased in HTLV-1-positive MT2 and MT4 cells. Meanwhile, IFI16 promoted the production of interferon and pro-inflammatory cytokines and inhibited the expression of HTLV-1 proteins. Key words: Interferon inducible protein 16 (IFI16); Human T-cell leukemia lymphoma virus type 1 (HTLV-1); Interferon; T lymphocyte; TNF-α

Differential neutrophil gene expression in blood and milk during pre-implantation pregnancy in Karan Fries cattle

ABSTRACT The blood leucocytes, neutrophils being the first line of defense, detect the implanting embryo, which is semi-allogenic, and show changes in their gene expression. It is possible to diagnose cattle as non-pregnant around 21–24 days post insemination by progesterone (P4) assay. Concentration of progesterone level in the inseminated animals may not be an accurate method for early pregnancy diagnosis. Identification of suitable methods that allow pregnancy diagnosis around or before day 20 after artificial insemination (AI) will be of considerable value. The present study has been carried out to understand the differential gene expression of IFI16 (interferon-inducible protein 16), MX1 (Myxovirus resistance 1), OAS1 (2'-5'-Oligoadenylate Synthetase 1) and TNFα (tumor necrosis factor alpha) genes on 0, 4, 8, 12, 15, 18 and 21 days post AI, respectively, from Karan Fries cattle as a tool for early pregnancy diagnosis in neutrophil cells isolated from blood and milk. Statistical analysis between pregnant and non-pregnant animals in both blood and milk samples revealed that IFI16 gene was upregulated in the milk samples of pregnant animals on 8th day post-AI and found to be significantly different (P < 0.05) between pregnant and non-pregnant cattle and may be used as a biomarker for early pregnancy detection in cattle.

IFI16 is involved in HBV-associated acute-on-chronic liver failure inflammation

BackgroundHepatitis B virus (HBV) is a hepatotropic DNA virus, and its DNA may be a potent inflammatory molecule. Interferon-inducible protein 16 (IFI16), a newly discovered DNA sensor, plays an important role in the process of inflammation in viral infections. Our study sought to identify a correlation between IFI16 expression and inflammation in patients with chronic hepatitis B (CHB) and HBV-associated acute-on-chronic liver failure (HBV-ACLF).MethodsWe performed flow cytometry to measure IFI16 levels in peripheral blood mononuclear cells (PBMC) and used immunohistochemistry and western blotting to measure IFI16 protein levels in liver tissues. The cellular source of IFI16 was detected using double immunofluorescence. All datum were analyzed using SPSS 13.0 and GraphPad Prism 6.ResultsThe number of IFI16+ cells was significantly associated with the degree of inflammation. In detail, the number of IFI16+ cells was higher in livers but lower in PBMCs in HBV-ACLF patients than those in CHB patients and healthy controls. There was no significant difference between CHB patients and healthy controls in numbers of IFI6+ cells in livers and PBMCs. There was no significant relationship between IFI16 expression levels and HBV parameters. Furthermore, IFI16 was expressed in the nucleus of Kupffer cells (KCs), endothelial cells, natural killer cells, dendritic cells, and hepatic stellate cells in healthy donors and CHB patients, but only in the cytoplasm of KCs in the livers of HBV-ACLF patients.ConclusionsIFI16 was closely related to the degree of inflammation in CHB and HBV-ACLF patients and may serve as a vital contributor to the pathogeneses of liver damage in HBV-ACLF.

Association of Antibodies to Interferon-Inducible Protein-16 With Markers of More Severe Disease in Primary Sjögren's Syndrome.

Interferon-inducible protein-16 (IFI16) is an intracellular DNA receptor involved in innate immunity. We evaluated the frequency, phenotypic characteristics, and clinical associations of anti-IFI16 antibodies in patients with primary Sjögren's syndrome (SS), and quantitated expression levels of IFI16 in SS and control salivary gland lysates. Anti-IFI16 antibodies were assayed by enzyme-linked immunosorbent assay using sera from patients with primary SS (n = 133) and from healthy controls (n = 47). Sera from systemic lupus erythematosus (SLE) patients (n = 132) were included as disease controls. Immunoprecipitation of in vitro transcription-translated IFI16 was used to determine which portion of IFI16 the antibodies recognized. Expression of IFI16 in salivary gland lysates was quantitated by immunoblotting. Anti-IFI16 antibodies were present in the sera of 38 of 133 SS patients (29%) compared to 1 of 47 healthy controls (2.1%) (SS versus controls; P < 0.0002) and in 31 of 132 SLE controls (24%). In SS, anti-IFI16 antibodies were associated with an abnormal Schirmer's test (P = 0.003), hyperglobulinemia (P = 0.02), antinuclear antibody ≥1:320 (P = 0.01), germinal center-like structures in labial salivary gland lymphoid infiltrates (P = 0.01), and higher focus scores (3.4 versus 2.4; P = 0.005). High-titer IFI16 antibodies were directed against an epitope outside the N-terminus in 9 of 13 SS patients (69%). IFI16 was expressed in 4 of 5 (80%) of SS and 1 of 6 (17%) of control labial salivary glands. Anti-IFI16 antibodies are a prominent specificity in primary SS and are associated with markers of severe disease. IFI16 is expressed at higher levels in SS salivary glands compared to controls. These high levels in disease target tissue may contribute to the ongoing anti-IFI16 immune response.

MPTH-28STUDY OF THE ROLE OF IFI-16 EXPRESSION IN GLIOMAS

Interferon inducible protein 16 (IFI-16) is a member of the p200 human family proteins, having two domains: C-terminus binding dsDNA and N-terminus as a typical protein-protein interaction domain. IFI-16 gene is located at 1q23.1 chromosome, its functions ranging from transcriptional regulation, apoptosis, proliferation and differentiation. IFI-16 is mostly expressed in epithelial, endothelial and hematopoietic tissues, with nuclear localization signal: in the nucleolus it is able to activate and fine-tune the transcription, when in the nucleoplasm probably it is inactivated. In the nucleoli a physical and functional link of IFI-16 to p53 has been reported, as negative regulator of the cell cycle. We have studied IFI-16 expression in 40 low grade and 40 anaplastic gliomas (half of them analysed with their relapse) and 40 glioblastomas using immunohistochemical and molecular techniques, using two antibodies against the C- and N-terminus of IFI-16. Nuclear accumulation of p53, IDH1(R132H), MGMT methylation status and LOH of chromosomes 1p, 19q, 9p, 17p and 10q were also evaluated. We mainly found a nucleolar expression of IFI-16 in astrocytic lower grade gliomas, related to p53: this physical and functional binding was also demonstrated by co-immunoprecipitation and Protein Ligation Assay analysis. In anaplastic gliomas and glioblastomas, IFI-16 is largely expressed in the nucleoplasm, unrelated to p53 expression. This shift of localization suggests a possible loss of its role as protective factor in lower grade astrocytic gliomas. In oligodendrogliomas IFI-16 expression was completely absent and it is strictly related to 1p/19q co-deletion. Our results, related to clinical data, identify IFI-16 as a possible prognostic marker in glioma patients and of interest to define new molecular profiles for their therapy. This is the first study of IFI-16 in gliomas, suggesting an early role of this molecule in proliferation and malignant progression of these tumours.

Innate DNA sensing is impaired in HIV patients and IFI16 expression correlates with chronic immune activation

The innate immune system has been recognized to play a role in the pathogenesis of HIV infection, both by stimulating protective activities and through a contribution to chronic immune activation, the development of immunodeficiency and progression to AIDS. A role for DNA sensors in HIV recognition has been suggested recently, and the aim of the present study was to describe the influence of HIV infection on expression and function of intracellular DNA sensing. Here we demonstrate impaired expression of interferon-stimulated genes in responses to DNA in peripheral blood monuclear cells from HIV-positive individuals, irrespective of whether patients receive anti-retroviral treatment. Furthermore, we show that expression levels of the DNA sensors interferon-inducible protein 16 (IFI16) and cyclic guanosine monophosphate-adenosine monophosphate synthase were increased in treatment-naive patients, and for IFI16 expression was correlated with high viral load and low CD4 cell count. Finally, our data demonstrate a correlation between IFI16 and CD38 expression, a marker of immune activation, in CD4(+) central and effector memory T cells, which may indicate that IFI16-mediated DNA sensing and signalling contributes to chronic immune activation. Altogether, the present study demonstrates abnormal expression and function of cytosolic DNA sensors in HIV patients, which may have implications for control of opportunistic infections, chronic immune activation and T cell death.

Interferon-Inducible Protein 16 (IFI-16) Is Upregulated In Chronic Myeloid Leukemia (CML) and Is Involved In Oncogene-Induced Senescence

IFI-16 is a transcriptional factor induced by IFN-γ and α in human cells and is involved in several cellular processes including cell cycle regulation, telomere length control and cellular senescence. Recently it has been shown that, similar to other oncogenes such as RAS and BRAF in solid tumors, acute expression of BCR-ABL in hematopoietic cells can induce senescence (Wajapayee et al, Blood 2010). This oncogene-induced senescence (OIS) which is a barrier for tumor development, is obviously bypassed by secondary events leading to malignant transformation. The molecular basis of the BCR-ABL-induced senescence in CML cells is not determined. In the UT7 cell line model expressing native (unmutated) BCR-ABL and its T315I-mutated counterpart, we identified by a gene profiling, a major increase of the expression IFI-16 (42-fold and 18-fold increase, respectively) as compared to parental UT7 cells. This major increase of IFI-16 expression in UT7 cells expressing native BCR-ABL was confirmed in western blots, whereas there was no detectable IFI-16 protein in parental UT7 cells. To determine if IFI-16 protein levels were dependent on BCR-ABL expression, we have used doxycycline-inducible BCR-ABL UT7 model. In this TET-Off system, the addition of doxycycline to cultures inhibits the expression of BCR-ABL by day7 and this was accompanied by a concomittant inhibition of IFI-16 expression. As expected, IFN-α (1000 U/ml) induced IFI-16 expression in parental UT7 cells and to a much higher degree in UT-7 BCR-ABL cells. In the UT7-T315I cells, IFN- α showed also a synergistic effect for IFI-16 expression which was less prominent. As IFI-16 expression can be modulated by oxidative stress, we have performed experiments in the presence of N-acetyl-cysteine which did not modify IFI-16 protein levels. To further study the role of IFI-16 in this model, we have transfected UT7 cells and their BCR-ABL expressing counterparts using shRNA-IFI-16 lentiviral vectors allowing silencing of IFI-16 expression. UT7 clones resistant to puromycin were amplified and the clones with reduced or absent expression of IFI-16 were selected for further analyses. In senescence-induction experiments, we have found that native BCR-ABL expressing UT7 silenced for IFI-16 expression, had reduced beta-galactosidase activity suggesting an inhibition of senescence phenotype. We have then checked the localization of IFI-16 in BCR-ABL and BCR-ABL T315I-expressing UT7 cells. In BCR-ABL-UT7 cells. IFI-16 was mainly in the cytoplasm and was relocated to nucleus upon IFN-α treatment. On the other hand, in UT7-T135I cells, IFI-16 was distributed between cytoplasm and nucleus and IFN-α had no effect on IFI-16 localisation. To determine the potential involvement of IFI-16 in human CML, we have analyzed IFI-16 expression by Q-RT-PCR. In a cohort of 40 Chronic Phase (CP) CML patients at diagnosis, the expression of IFI-16 was found to be significantly increased (2-Fold) as compared to controls (n=30). Thus, our results suggest strongly that IFI-16 induction could be one of the mechanisms of OIS in in BCR-ABL expressing cells. We also demonstrate for the first time that this mechanism is operational in primary CML cells. Further exploitation of this senescence pathway could be of therapeutic interest with the goal of enhancing this phenomenon especially at the level of the most primitive, TKI-resistant CML stem cells. Current experiments are underway to study the role of IFI-16 in the most primitive leukemic stem cell compartments. Disclosures:Guilhot:Novartis, BMS, Ariad, Pfizer: Honoraria. Turhan:BMS, Novartis: Honoraria, Research Funding.

Redistribution of the nuclear protein IFI16 into the cytoplasm of ultraviolet B-exposed keratinocytes as a mechanism of autoantigen processing

The skin has long been recognized as a prominent target tissue in systemic lupus erythematosus (SLE) which plays a crucial role in the initiation and perpetuation of the autoimmune reaction cascade as a consequence of ultraviolet (UV)-induced keratinocyte apoptosis. Antibodies against IFI16 (interferon-inducible protein 16) have been detected in the sera of patients with SLE. To verify whether the induction of autoimmunity against IFI16 involves redistribution of this nuclear protein in keratinocytes during UVB-induced cell death. An in vitro epidermal model was developed to investigate the fate of the IFI16 protein in keratinocytes after irradiation with UVB; both keratinocyte monolayers and human skin explants were used. IFI16 expression and localization were also analysed in diseased skin sections of patients with SLE. We demonstrated that IFI16, normally restricted to the nucleus, can be induced to appear in the cytoplasm under conditions of UVB-induced cell injury. This nucleus to cytoplasm translocation was also observed in skin explants exposed to UVB and in the diseased skin sections from patients with SLE. In addition, IFI16 was found in the supernatants of UVB-exposed keratinocytes. The finding that IFI16 is present in the cytoplasm of diseased skin cells from patients with SLE and the demonstration of IFI16 in the supernatants of UVB-exposed keratinocytes, suggest that UVB irradiation or other stimuli may favour an abnormal IFI16 presentation to the afferent limb of the immune system and potentially an autoimmune response against the protein itself.