Tumor-Derived Endothelial Cells Evade Apoptotic Activity of the Interferon-Inducible IFI16 Gene

The role of IFI16 in regulating PANoptosis and implication in heart diseases

Interferon Gamma Inducible Protein 16 (IFI16) belongs to the HIN-200 protein family and is pivotal in immunological responses. Serving as a DNA sensor, IFI16 identifies viral and aberrant DNA, triggering immune and inflammatory responses. It is implicated in diverse cellular death mechanisms, such as pyroptosis, apoptosis, and necroptosis. Notably, these processes are integral to the emergent concept of PANoptosis, which encompasses cellular demise and inflammatory pathways. Current research implies a significant regulatory role for IFI16 in PANoptosis, particularly regarding cardiac pathologies. This review delves into the complex interplay between IFI16 and PANoptosis in heart diseases, including atherosclerosis, myocardial infarction, heart failure, and diabetic cardiomyopathy. It synthesizes evidence of IFI16's impact on PANoptosis, with the intention of providing novel insights for therapeutic strategies targeting heart diseases.

Comprehensive analysis identifies IFI16 as a novel signature associated with overall survival and immune infiltration of skin cutaneous melanoma

Background

Skin cutaneous melanoma (SKCM) is the most common skin tumor with high mortality. The unfavorable outcome of SKCM urges the discovery of prognostic biomarkers for accurate therapy. The present study aimed to explore novel prognosis-related signatures of SKCM and determine the significance of immune cell infiltration in this pathology.

Methods

Four gene expression profiles (GSE130244, GSE3189, GSE7553 and GSE46517) of SKCM and normal skin samples were retrieved from the GEO database. Differentially expressed genes (DEGs) were then screened, and the feature genes were identified by the LASSO regression and Boruta algorithm. Survival analysis was performed to filter the potential prognostic signature, and GEPIA was used for preliminary validation. The area under the receiver operating characteristic curve (AUC) was obtained to evaluate discriminatory ability. The Gene Set Variation Analysis (GSVA) was performed, and the composition of the immune cell infiltration in SKCM was estimated using CIBERSORT. At last, paraffin-embedded specimens of primary SKCM and normal skin tissues were collected, and the signature was validated by fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC).

Results

Totally 823 DEGs and 16 feature genes were screened. IFI16 was identified as the signature associated with overall survival of SKCM with a great discriminatory ability (AUC > 0.9 for all datasets). GSVA noticed that IFI16 might be involved in apoptosis and ultraviolet response in SKCM, and immune cell infiltration of IFI16 was evaluated. At last, FISH and IHC both validated the differential expression of IFI16 in SKCM.

Conclusions

In conclusion, our comprehensive analysis identified IFI16 as a signature associated with overall survival and immune infiltration of SKCM, which may play a critical role in the occurrence and development of SKCM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02409-6.

Biological relevance of Cytomegalovirus genetic variability in congenitally and postnatally infected children

BACKGROUND

Human cytomegalovirus (HCMV) is the leading cause of congenital infections resulting in severe morbidity and mortality among infected children. Although the virus is highly polymorphic, particularly in genes contributing to immune evasion, the mechanisms underlying its genetic variability and pathogenicity are only partially understood.

OBJECTIVES

We aimed to characterize different HCMV clinical strains isolated from 21 congenitally- or postnatally-infected children for in vitro growth properties and genetic polymorphisms.

STUDY DESIGN

The growth of various HCMV isolates was analyzed in different cell culture models. Genetic polymorphism was assessed by genetic and phylogenetic analysis of viral genes involved in virulence (UL144, US28, and UL18), latency (UL133-138), or drug resistance (UL54 and UL97).

RESULTS

Here, we report a high degree of genetic and phenotypic diversity in distinct HCMV clinical isolates, as shown by their in vitro growth properties. In particular, HCMV isolates displayed the highest degree of genetic variability in the UL144 gene, where we were able to define four distinct genotypes within the cohort based on UL144 heterogeneity. Lastly, among all isolates we were able to identify 36 mutations in UL54 and 2 in UL97.

CONCLUSIONS

Our findings indicate that surprisingly high levels of genetic HCMV variability correlate with a high degree of phenotypic polymorphism, which in turn might differentially influence the growth, fitness, and drug susceptibility of HCMV.

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.

Nuclear DNA sensor IFI16 as circulating protein in autoimmune diseases is a signal of damage that impairs endothelial cells through high-affinity membrane binding

IFI16, a nuclear pathogenic DNA sensor induced by several pro-inflammatory cytokines, is a multifaceted protein with various functions. It is also a target for autoantibodies as specific antibodies have been demonstrated in the sera of patients affected by systemic autoimmune diseases. Following transfection of virus-derived DNA, or treatment with UVB, IFI16 delocalizes from the nucleus to the cytoplasm and is then eventually released into the extracellular milieu. In this study, using an in-house capture enzyme-linked immunsorbent assay we demonstrate that significant levels of IFI16 protein can also exist as circulating form in the sera of autoimmune patients. We also show that the rIFI16 protein, when added in-vitro to endothelial cells, does not affect cell viability, but severely limits their tubulogenesis and transwell migration activities. These inhibitory effects are fully reversed in the presence of anti-IFI16 N-terminal antibodies, indicating that its extracellular activity resides within the N-terminus. It was further demonstrated that endogenous IFI16 released by apoptotic cells bind neighboring cells in a co-culture. Immunofluorescence assays revealed existence of high-affinity binding sites on the plasma membrane of endothelial cells. Free recombinant IFI16 binds these sites on HUVEC with dissociation constant of 2.7 nM, radioiodinated and unlabeled IFI16 compete for binding sites, with inhibition constant (K_i) of 14.43 nM and half maximal inhibitory concentration (IC₅₀) of 67.88 nM; these data allow us to estimate the presence of 250,000 to 450,000 specific binding sites per cell. Corroborating the results from functional assays, this binding could be completely inhibited using anti-IFI16 N-terminal antibody, but not with an antibody raised against the IFI16 C-terminal. Altogether, these data demonstrate that IFI16 may exist as circulating protein in the sera of autoimmune patients which binds endothelial cells causing damage, suggesting a new pathogenic and alarmin function through which this protein triggers the development of autoimmunity.