IAPs, regulators of innate immunity and inflammation

E3 ubiquitin ligase gene BIRC3 modulates TNF-induced cell death pathways and promotes aberrant proliferation in rheumatoid arthritis fibroblast-like synoviocytes

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease characterized by synovitis, degradation of articular cartilage, and bone destruction. Fibroblast-like synoviocytes (FLS) play a central role in RA, producing a significant amount of inflammatory mediators such as tumor necrosis factor(TNF)-α and IL-6, which promote inflammatory responses within the joints. Moreover, FLS exhibit tumor-like behavior, including aggressive proliferation and enhanced anti-apoptotic capabilities, which collectively drive chronic inflammation and joint damage in RA. TNF is a major pro-inflammatory cytokine that mediates a series of signaling pathways through its receptor TNFR1, including NF-κB and MAPK pathways, which are crucial for inflammation and cell survival in RA. The abnormal proliferation and anti-apoptotic characteristics of FLS in RA may result from dysregulation in TNF-mediated cell death pathways such as apoptosis and necroptosis. Ubiquitination is a critical post-translational modification regulating these signaling pathways. E3 ubiquitin ligases, such as cIAP1/2, promote the ubiquitination and degradation of target proteins within the TNF receptor complex, modulating the signaling proteins. The high expression of the BIRC3 gene and its encoded protein, cIAP2, in RA regulates various cellular processes, including apoptosis, inflammatory signaling, immune response, MAPK signaling, and cell proliferation, thereby promoting FLS survival and inflammatory responses. Inhibiting BIRC3 expression can reduce the secretion of inflammatory cytokines by RA-FLS under both basal and inflammatory conditions and inhibit their proliferation. Although BIRC3 inhibitors show potential in RA treatment, their possible side effects must be carefully considered. Further research into the specific mechanisms of BIRC3, including its roles in cell signaling, apoptosis regulation, and immune evasion, is crucial for identifying new therapeutic targets and strategies.

Exploration of Molecular Mechanisms of Immunity in the Pacific Oyster (Crassostrea gigas) in Response to Vibrio alginolyticus Invasion

Over the years, oysters have faced recurring mass mortality issues during the summer breeding season, with Vibrio infection emerging as a significant contributing factor. Tubules of gill filaments were confirmed to be in the hematopoietic position in Crassostrea gigas, which produce hemocytes with immune defense capabilities. Additionally, the epithelial cells of oyster gills produce immune effectors to defend against pathogens. In light of this, we performed a transcriptome analysis of gill tissues obtained from C. gigas infected with Vibrio alginolyticus for 12 h and 48 h. Through this analysis, we identified 1024 differentially expressed genes (DEGs) at 12 h post-injection and 1079 DEGs at 48 h post-injection. Enrichment analysis of these DEGs revealed a significant association with immune-related Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. To further investigate the immune response, we constructed a protein-protein interaction (PPI) network using the DEGs enriched in immune-associated KEGG pathways. This network provided insights into the interactions and relationships among these genes, shedding light on the underlying mechanisms of the innate immune defense mechanism in oyster gills. To ensure the accuracy of our findings, we validated 16 key genes using quantitative RT-PCR. Overall, this study represents the first exploration of the innate immune defense mechanism in oyster gills using a PPI network approach. The findings provide valuable insights for future research on oyster pathogen control and the development of oysters with enhanced antimicrobial resistance.

Airway epithelial cells mount an early response to mycobacterial infection

Lung epithelial cells represent the first line of host defence against foreign inhaled components, including respiratory pathogens. Their responses to these exposures may direct subsequent immune activation to these pathogens. The epithelial response to mycobacterial infections is not well characterized and may provide clues to why some mycobacterial infections are cleared, while others are persistent and pathogenic. We have utilized an air-liquid interface model of human primary bronchial epithelial cells (ALI-PBEC) to investigate the epithelial response to infection with a variety of mycobacteria: Mycobacterium tuberculosis (Mtb), M. bovis (BCG), M. avium, and M. smegmatis. Airway epithelial cells were found to be infected by all four species, albeit at low frequencies. The proportion of infected epithelial cells was lowest for Mtb and highest for M. avium. Differential gene expression analysis revealed a common epithelial host response to mycobacteria, including upregulation of BIRC3, S100A8 and DEFB4, and downregulation of BPIFB1 at 48 h post infection. Apical secretions contained predominantly pro-inflammatory cytokines, while basal secretions contained tissue growth factors and chemokines. Finally, we show that neutrophils were attracted to both apical and basal secretions of infected ALI-PBEC. Neutrophils were attracted in high numbers to apical secretions from PBEC infected with all mycobacteria, with the exception of secretions from M. avium-infected ALI-PBEC. Taken together, our results show that airway epithelial cells are differentially infected by mycobacteria, and react rapidly by upregulation of antimicrobials, and increased secretion of inflammatory cytokines and chemokines which directly attract neutrophils. Thus, the airway epithelium may be an important immunological component in controlling and regulating mycobacterial infections.

Molecular basis for nuclear accumulation and targeting of the inhibitor of apoptosis BIRC2

The inhibitor of apoptosis protein BIRC2 regulates fundamental cell death and survival signaling pathways. Here we show that BIRC2 accumulates in the nucleus via binding of its second and third BIR domains, BIRC2BIR2 and BIRC2BIR3, to the histone H3 tail and report the structure of the BIRC2BIR3-H3 complex. RNA-seq analysis reveals that the genes involved in interferon and defense response signaling and cell-cycle regulation are most affected by depletion of BIRC2. Overexpression of BIRC2 delays DNA damage repair and recovery of the cell-cycle progression. We describe the structural mechanism for targeting of BIRC2BIR3 by a potent but biochemically uncharacterized small molecule inhibitor LCL161 and demonstrate that LCL161 disrupts the association of endogenous BIRC2 with H3 and stimulates cell death in cancer cells. We further show that LCL161 mediates degradation of BIRC2 in human immunodeficiency virus type 1-infected human CD4+ T cells. Our findings provide mechanistic insights into the nuclear accumulation of and blocking BIRC2.

Differential regulation of BIRC2 and BIRC3 expression by inflammatory cytokines and glucocorticoids in pulmonary epithelial cells

Roles for the baculoviral inhibitor of apoptosis repeat-containing (BIRC) genes, BIRC2 and BIRC3, may include signaling to the inflammatory transcription factor, nuclear factor-κB (NF-κB) and protection from cell death. However, distinct functions for each BIRC are not well-delineated. Given roles for the epithelium in barrier function and host defence, BIRC2 and BIRC3 expression was characterized in pulmonary epithelial cell lines and primary human bronchial epithelial cells (pHBECs) grown as undifferentiated cells in submersion culture (SC) or as highly differentiated cells at air-liquid interface (ALI). In A549 cells, interleukin-1β (IL1B) and tumor necrosis factor α (TNF) induced BIRC3 mRNA (~20-50-fold), with maximal protein expression from 6-24 h. Similar effects occurred in BEAS-2B and Calu-3 cells, as well as SC and ALI pHBECs. BIRC2 protein was readily detected in unstimulated cells, but was not markedly modulated by IL1B or TNF. Glucocorticoids (dexamethasone, budesonide) modestly increased BIRC3 mRNA and protein, but showed little effect on BIRC2 expression. In A549 cells, BIRC3 mRNA induced by IL1B was unchanged by glucocorticoids and showed supra-additivity with TNF-plus-glucocorticoid. Supra-additivity was also evident for IL1B-plus-budesonide induced-BIRC3 in SC and ALI pHBECs. Using A549 cells, IL1B- and TNF-induced BIRC3 expression, and to a lesser extent, BIRC2, was prevented by NF-κB inhibition. Glucocorticoid-induced BIRC3 expression was prevented by silencing and antagonism of the glucocorticoid receptor. Whereas TNF, but not IL1B, induced degradation of basal BIRC2 and BIRC3 protein, IL1B- and TNF-induced BIRC3 protein remained stable. Differential regulation by cytokines and glucocorticoids shows BIRC2 protein expression to be consistent with roles in rapid signaling events, whereas cytokine-induced BIRC3 may be more important in later effects. While TNF-induced degradation of both BIRCs may restrict their activity, cytokine-enhanced BIRC3 expression could prime for its function. Finally, shielding from glucocorticoid repression, or further enhancement by glucocorticoid, may indicate a key protective role for BIRC3.

Identification of mitophagy-related biomarkers and immune infiltration in major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is a life-threatening and debilitating mental health condition. Mitophagy, a form of selective autophagy that eliminates dysfunctional mitochondria, is associated with depression. However, studies on the relationship between mitophagy-related genes (MRGs) and MDD are scarce. This study aimed to identify potential mitophagy-related biomarkers for MDD and characterize the underlying molecular mechanisms.

METHODS

The gene expression profiles of 144 MDD samples and 72 normal controls were retrieved from the Gene Expression Omnibus database, and the MRGs were extracted from the GeneCards database. Consensus clustering was used to determine MDD clusters. Immune cell infiltration was evaluated using CIBERSORT. Functional enrichment analyses were performed to determine the biological significance of mitophagy-related differentially expressed genes (MR-DEGs). Weighted gene co-expression network analysis, along with a network of protein-protein interactions (PPI), was used to identify key modules and hub genes. Based on the least absolute shrinkage and selection operator analysis and univariate Cox regression analysis, a diagnostic model was constructed and evaluated using receiver operating characteristic curves and validated with training data and external validation data. We reclassified MDD into two molecular subtypes according to biomarkers and evaluated their expression levels.

RESULTS

In total, 315 MDD-related MR-DEGs were identified. Functional enrichment analyses revealed that MR-DEGs were mainly enriched in mitophagy-related biological processes and multiple neurodegenerative disease pathways. Two distinct clusters with diverse immune infiltration characteristics were identified in the 144 MDD samples. MATR3, ACTL6A, FUS, BIRC2, and RIPK1 have been identified as potential biomarkers of MDD. All biomarkers showed varying degrees of correlation with immune cells. In addition, two molecular subtypes with distinct mitophagy gene signatures were identified.

CONCLUSIONS

We identified a novel five-MRG gene signature that has excellent diagnostic performance and identified an association between MRGs and the immune microenvironment in MDD.

The Functions of TRIM56 in Antiviral Innate Immunity and Tumorigenesis

As a member of the TRIM (tripartite motif) protein family, TRIM56 can function as an E3 ubiquitin ligase. In addition, TRIM56 has been shown to possess deubiquitinase activity and the ability to bind RNA. This adds to the complexity of the regulatory mechanism of TRIM56. TRIM56 was initially found to be able to regulate the innate immune response. In recent years, its role in direct antiviral and tumor development has also attracted the interest of researchers, but there is no systematic review on TRIM56. Here, we first summarize the structural features and expression of TRIM56. Then, we review the functions of TRIM56 in TLR and cGAS-STING pathways of innate immune response, the mechanisms and structural specificity of TRIM56 against different types of viruses, and the dual roles of TRIM56 in tumorigenesis. Finally, we discuss the future research directions regarding TRIM56.

Phenotypic screening platform identifies statins as enhancers of immune cell-induced cancer cell death

BACKGROUND

High-throughput screening (HTS) of small molecule drug libraries has greatly facilitated the discovery of new cancer drugs. However, most phenotypic screening platforms used in the field of oncology are based solely on cancer cell populations and do not allow for the identification of immunomodulatory agents.

METHODS

We developed a phenotypic screening platform based on a miniaturized co-culture system with human colorectal cancer- and immune cells, providing a model that recapitulates part of the tumor immune microenvironment (TIME) complexity while simultaneously being compatible with a simple image-based readout. Using this platform, we screened 1,280 small molecule drugs, all approved by the Food and Drug Administration (FDA), and identified statins as enhancers of immune cell-induced cancer cell death.

RESULTS

The lipophilic statin pitavastatin had the most potent anti-cancer effect. Further analysis demonstrated that pitavastatin treatment induced a pro-inflammatory cytokine profile as well as an overall pro-inflammatory gene expression profile in our tumor-immune model.

CONCLUSION

Our study provides an in vitro phenotypic screening approach for the identification of immunomodulatory agents and thus addresses a critical gap in the field of immuno-oncology. Our pilot screen identified statins, a drug family gaining increasing interest as repurposing candidates for cancer treatment, as enhancers of immune cell-induced cancer cell death. We speculate that the clinical benefits described for cancer patients receiving statins are not simply caused by a direct effect on the cancer cells but rather are dependent on the combined effect exerted on both cancer and immune cells.

TRIM56 promotes malignant progression of glioblastoma by stabilizing cIAP1 protein

BACKGROUND

The tripartite motif (TRIM) family of proteins plays a key role in the developmental growth and therapeutic resistance of many tumors. However, the regulatory mechanisms and biological functions of TRIM proteins in human glioblastoma (GBM) are not yet fully understood. In this study, we focused on TRIM56, which emerged as the most differentially expressed TRIM family member with increased expression in GBM.

METHODS

Western blot, real-time quantitative PCR (qRT-PCR), immunofluorescence (IF) and immunohistochemistry (IHC) were used to study the expression levels of TRIM56 and cIAP1 in GBM cell lines. Co-immunoprecipitation (co-IP) was used to explore the specific binding between target proteins and TRIM56. A xenograft animal model was used to verify the tumor promoting effect of TRIM56 on glioma in vivo.

RESULTS

We observed elevated expression of TRIM56 in malignant gliomas and revealed that TRIM56 promoted glioma progression in vitro and in a GBM xenograft model in nude mice. Analysis of the Human Ubiquitin Array and co-IPs showed that cIAP1 is a protein downstream of TRIM56. TRIM56 deubiquitinated cIAP1, mainly through the zinc finger domain (amino acids 21-205) of TRIM56, thereby reducing the degradation of cIAP1 and thus increasing its expression. TRIM56 also showed prognostic significance in overall survival of glioma patients.

CONCLUSIONS

TRIM56-regulated post-translational modifications may contribute to glioma development through stabilization of cIAP1. Furthermore, TRIM56 may serve as a novel prognostic indicator and therapeutic molecular target for GBM.

Progress in Anticancer Drug Development Targeting Ubiquitination-Related Factors

Ubiquitination is extensively involved in critical signaling pathways through monitoring protein stability, subcellular localization, and activity. Dysregulation of this process results in severe diseases including malignant cancers. To develop drugs targeting ubiquitination-related factors is a hotspot in research to realize better therapy of human diseases. Ubiquitination comprises three successive reactions mediated by Ub-activating enzyme E1, Ub-conjugating enzyme E2, and Ub ligase E3. As expected, multiple ubiquitination enzymes have been highlighted as targets for anticancer drug development due to their dominant effect on tumorigenesis and cancer progression. In this review, we discuss recent progresses in anticancer drug development targeting enzymatic machinery components.

The conservation of IAP-like proteins in fungi, and their potential role in fungal programmed cell death

Programmed cell death (PCD) is a tightly regulated process which is required for survival and proper development of all cellular life. Despite this ubiquity, the precise molecular underpinnings of PCD have been primarily characterized in animals. Attempts to expand our understanding of this process in fungi have proven difficult as core regulators of animal PCD are apparently absent in fungal genomes, with the notable exception of a class of proteins referred to as inhibitors of apoptosis proteins (IAPs). These proteins are characterized by the conservation of a distinct Baculovirus IAP Repeat (BIR) domain and animal IAPs are known to regulate a number of processes, including cellular death, development, organogenesis, immune system maturation, host-pathogen interactions and more. IAP homologs are broadly conserved throughout the fungal kingdom, but our understanding of both their mechanism and role in fungal development/virulence is still unclear. In this review, we provide a broad and comparative overview of IAP function across taxa, with a particular focus on fungal processes regulated by IAPs. Furthermore, their putative modes of action in the absence of canonical interactors will be discussed.

Functional analyses of inhibitor of apoptosis protein 1 (IAP1) of Antheraea pernyi multinucleocapsid nucleopolyhedrovirus (AnpeNPV) in viral replication and occlusion body production

Inhibitor of apoptosis protein 1 (IAP1) of Antheraea pernyi multinucleocapsid nucleopolyhedrovirus (AnpeNPV) belongs to the baculovirus IAP1 type. The function of AnpeNPV-IAP1 in viral replication and occlusion body (OB) production remains unknown. In this study, we demonstrated that AnpeNPV-iap1 is a late gene. AnpeNPV-IAP1 mainly localizes to the nuclear ring zone and exhibits dynamic distribution in the cytoplasm and the virogenic stroma during AnpeNPV infection. AnpeNPV-IAP1 impacted the expression of a variety of viral genes at the very late phase of infection in Tn-Hi5 cells. The deletion of AnpeNPV-iap1 caused decreased expression levels of polyhedrin, morphological changes to OBs and reduced OB production in A. pernyi pupae, along with a lengthening of the lethal time of A. pernyi larvae. These results suggest that AnpeNPV-iap1 is involved in regulating viral gene expression, OB production and morphogenesis in A. pernyi.

The NLRP3 inflammasome: molecular activation and regulation in spermatogenesis and male infertility; a systematic review

Background

Infertility related to varicocele, infections, metabolic dysfunctions, oxidative stress and environmental toxicants is also associated with inflammatory processes that ultimately lead to the activation of the inflammasome pathway (IP). IP is classically activated by DAMPs, MAMPs or LAMPs, which stand for Damage-, Microbe- or Lifestyle-Associated Molecular Patterns, respectively. The most important player in IP activation is the NLRP3 (NOD[Nuclear oligomerization domain]-, LRR[Leucine rich repeat]- and pyrin domain-containing protein 3) which functions as an intracellular sensor of D/M/L-AMPs resulting in activation of caspase-1, promotion of apoptosis, pyroptosis and generation of inflammatory cytokines. This review addresses the question of whether IP activation might be associated with male infertility situations.

Results & conclusions

We conducted a systematic review of articles published in the Google Scholar, and PubMed databases through October 2021. It turns out that inflammasome activation and its consequences including cytokine storms, apoptosis and pyroptosis could be associated with the reduced sperm count as well as the structural and functional sperm defects recorded in several situations associated with male infertility suggesting that anti-inflammatory therapeutic strategies could be possibly considered to restore male fertility in future research.

Perkinsus marinus suppresses in vitro eastern oyster apoptosis via IAP-dependent and caspase-independent pathways involving TNFR, NF-kB, and oxidative pathway crosstalk

The protozoan parasite Perkinsus marinus causes Dermo disease in eastern oysters, Crassostrea virginica, and can suppress apoptosis of infected hemocytes using incompletely understood mechanisms. This study challenged hemocytes in vitro with P. marinus for 1 h in the presence or absence of caspase inhibitor Z-VAD-FMK or Inhibitor of Apoptosis protein (IAP) inhibitor GDC-0152. Hemocytes exposure to P. marinus significantly reduced granulocyte apoptosis, and pre-incubation with Z-VAD-FMK did not affect P. marinus-induced apoptosis suppression. Hemocyte pre-incubation with GDC-0152 prior to P. marinus challenge further reduced apoptosis of granulocytes with engulfed parasite, but not mitochondrial permeabilization. This suggests P. marinus-induced apoptosis suppression may be caspase-independent, affect an IAP-involved pathway, and occur downstream of mitochondrial permeabilization. P. marinus challenge stimulated hemocyte differential expression of oxidation-reduction, TNFR, and NF-kB pathways. WGCNA analysis of P. marinus expression in response to hemocyte exposure revealed correlated protease, kinase, and hydrolase expression that could contribute to P. marinus-induced apoptosis suppression.

The expanded inhibitor of apoptosis gene family in oysters possesses novel domain architectures and may play diverse roles in apoptosis following immune challenge

Background

Apoptosis plays important roles in a variety of functions, including immunity and response to environmental stress. The Inhibitor of Apoptosis (IAP) gene family of apoptosis regulators is expanded in molluscs, including eastern, Crassostrea virginica, and Pacific, Crassostrea gigas, oysters. The functional importance of IAP expansion in apoptosis and immunity in oysters remains unknown.

Results

Phylogenetic analysis of IAP genes in 10 molluscs identified lineage specific gene expansion in bivalve species. Greater IAP gene family expansion was observed in C. virginica than C. gigas (69 vs. 40), resulting mainly from tandem duplications. Functional domain analysis of oyster IAP proteins revealed 3 novel Baculoviral IAP Repeat (BIR) domain types and 14 domain architecture types across gene clusters, 4 of which are not present in model organisms. Phylogenetic analysis of bivalve IAPs suggests a complex history of domain loss and gain. Most IAP genes in oysters (76% of C. virginica and 82% of C. gigas), representing all domain architecture types, were expressed in response to immune challenge (Ostreid Herpesvirus OsHV-1, bacterial probionts Phaeobacter inhibens and Bacillus pumilus, several Vibrio spp., pathogenic Aliiroseovarius crassostreae, and protozoan parasite Perkinsus marinus). Patterns of IAP and apoptosis-related differential gene expression differed between the two oyster species, where C. virginica, in general, differentially expressed a unique set of IAP genes in each challenge, while C. gigas differentially expressed an overlapping set of IAP genes across challenges. Apoptosis gene expression patterns clustered mainly by resistance/susceptibility of the oyster host to immune challenge. Weighted Gene Correlation Network Analysis (WGCNA) revealed unique combinations of transcripts for 1 to 12 IAP domain architecture types, including novel types, were significantly co-expressed in response to immune challenge with transcripts in apoptosis-related pathways.

Conclusions

Unprecedented diversity characterized by novel BIR domains and protein domain architectures was observed in oyster IAPs. Complex patterns of gene expression of novel and conserved IAPs in response to a variety of ecologically-relevant immune challenges, combined with evidence of direct co-expression of IAP genes with apoptosis-related transcripts, suggests IAP expansion facilitates complex and nuanced regulation of apoptosis and other immune responses in oysters.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08233-6.

Confined migration promotes cancer metastasis through resistance to anoikis and increased invasiveness

Mechanical stress is known to fuel several hallmarks of cancer, ranging from genome instability to uncontrolled proliferation or invasion. Cancer cells are constantly challenged by mechanical stresses not only in the primary tumour but also during metastasis. However, this latter has seldom been studied with regards to mechanobiology, in particular resistance to anoikis, a cell death programme triggered by loss of cell adhesion. Here, we show in vitro that migrating breast cancer cells develop resistance to anoikis following their passage through microporous membranes mimicking confined migration (CM), a mechanical constriction that cancer cells encounter during metastasis. This CM-induced resistance was mediated by Inhibitory of Apoptosis Proteins, and sensitivity to anoikis could be restored after their inhibition using second mitochondria-derived activator of caspase (SMAC) mimetics. Anoikis-resistant mechanically stressed cancer cells displayed enhanced cell motility and evasion from natural killer cell-mediated immune surveillance, as well as a marked advantage to form lung metastatic lesions in mice. Our findings reveal that CM increases the metastatic potential of breast cancer cells.

Sexual dimorphism in neurological function after SCI is associated with disrupted neuroinflammation in both injured spinal cord and brain

Whereas human spinal cord injury (SCI) is more common in men, the prevalence is growing in women. However, little is known about the effect of biological sex on brain dysfunction and injury mechanisms. To model the highest per capita rate of injury (ages between 16 and 30 years old) in humans, in the present study, young adult or a young/middle-aged male and female C57BL/6 mice were subjected to moderate contusion SCI. When mice were injured at 10-12-week-old, transcriptomic analysis of inflammation-related genes and flow cytometry revealed a more aggressive neuroinflammatory profile in male than females following 3 d SCI, ostensibly driven by sex-specific changes myeloid cell function rather than cell number. Female mice were generally more active at baseline, as evidenced by greater distance traveled in the open field. After SCI, female mice had more favorable locomotor function than male animals. At 13 weeks post-injury, male mice showed poor performance in cognitive and depressive-like behavioral tests, while injured female mice showed fewer deficits in these tasks. However, when injured at 6 months old followed by 8 months post-injury, male mice had considerably less inflammatory activation compared with female animals despite having similar or worse outcomes in affective, cognitive, and motor tasks. Collectively, these findings indicate that sex differences in functional outcome after SCI are associated with the age at onset of injury, as well as disrupted neuroinflammation not only at the site of injury but also in remote brain regions. Thus, biological sex should be considered when designing new therapeutic agents.

Cytoplasmic and Nuclear Functions of cIAP1

Cellular inhibitor of apoptosis 1 (cIAP1) is a cell signaling regulator of the IAP family. Through its E3-ubiquitine ligase activity, it has the ability to activate intracellular signaling pathways, modify signal transduction pathways by changing protein-protein interaction networks, and stop signal transduction by promoting the degradation of critical components of signaling pathways. Thus, cIAP1 appears to be a potent determinant of the response of cells, enabling their rapid adaptation to changing environmental conditions or intra- or extracellular stresses. It is expressed in almost all tissues, found in the cytoplasm, membrane and/or nucleus of cells. cIAP1 regulates innate immunity by controlling signaling pathways mediated by tumor necrosis factor receptor superfamily (TNFRs), some cytokine receptors and pattern recognition-receptors (PRRs). Although less documented, cIAP1 has also been involved in the regulation of cell migration and in the control of transcriptional programs.

Advances in new antivirals for chronic hepatitis B

Chronic hepatitis B virus (HBV) infection remains a global health burden. Timely and effective antiviral therapy is beneficial for patients with HBV infection. With existing antiviral drugs, including nucleos(t)ide analogs and interferon-alfa, patients can achieve viral suppression with improved prognosis. However, the rate of hepatitis B surface antigen loss is low. To achieve a functional cure and even complete cure in chronic hepatitis B patients, new antivirals need to be developed. In this review, we summarized the advantages and disadvantages of existing antiviral drugs and focused on new antivirals including direct-acting antiviral drugs and immunotherapeutic approaches.

Expression levels of cellular inhibitor of apoptosis proteins and colitogenic cytokines are inversely correlated with the activation of interferon regulatory factor 4

Cellular inhibitors of apoptosis proteins 1 (cIAP1) and 2 (cIAP2) are involved in signaling pathways mediated by Toll-like receptors (TLRs) and tumor necrosis factor (TNF)-α. Excessive activation of TLRs and TNF-α underlies the immunopathogenesis of Crohn's disease (CD) and ulcerative colitis (UC). However, the roles played by cIAP1 and cIAP2 in the development of CD and UC remain poorly understood. In this study, we attempted to clarify the molecular link between cIAP1/cIAP2 and colonic inflammation. Human monocyte-derived dendritic cells (DCs) treated with siRNAs specific for cIAP1 or cIAP2 exhibited reduced pro-inflammatory cytokine responses upon stimulation with TLR ligands. Expression of cIAP1 and cIAP2 in human DCs was suppressed in the presence of interferon regulatory factor 4 (IRF4). This effect was associated with inhibition of cIAP1 and cIAP2 polyubiquitination. To verify these in vitro findings, we created mice overexpressing IRF4 in DCs and showed that these mice were resistant to trinitrobenzene sulfonic acid-induced colitis as compared with wild-type mice; these effects were accompanied by reduced expression levels of cIAP1 and cIAP2. Pro-inflammatory cytokine production by mesenteric lymph node cells upon stimulation with TLR ligands was reduced in mice with DC-specific IRF4 overexpression as compared with that in wild-type mice. Finally, in clinical samples of the colonic mucosa from patients with CD, there was a negative relationship between the percentage of IRF4+ DCs and percentages of cIAP1+ or cIAP2+ lamina propria mononuclear cells. These data suggest that the colitogenic roles of cIAP1 and cIAP2 are negatively regulated by IRF4.

Viral manipulation of host cell necroptosis and pyroptosis

Cell death forms an essential component of the antiviral immune response. Viral infection elicits different forms of host cell death, including the lytic and inflammatory cell death modes necroptosis or pyroptosis. The induction of both types of cell death not only eliminates virus-infected cells but also contributes to the development of innate and adaptive immunity through the release of inflammatory mediators. The importance of necroptosis and pyroptosis in host defence is evident from the numerous viral evasion mechanisms that suppress these cell death pathways. Here, we review the emerging principles by which viruses antagonise host cell necroptosis and pyroptosis to promote their spread and block host immunity.

SMAC Mimetics as Therapeutic Agents in HIV Infection

Although combination antiretroviral therapy is extremely effective in lowering HIV RNA to undetectable levels in the blood, HIV persists in latently infected CD4⁺ T-cells and persistently infected macrophages. In latently/persistently infected cells, HIV proteins have shown to affect the expression of proteins involved in the apoptosis pathway, notably the inhibitors of apoptosis proteins (IAPs), and thereby influence cell survival. IAPs, which are inhibited by endogenous second mitochondrial-derived activators of caspases (SMAC), can serve as targets for SMAC mimetics, synthetic compounds capable of inducing apoptosis. There is increasing evidence that SMAC mimetics can be used to reverse HIV latency and/or kill cells that are latently/persistently infected with HIV. Here, we review the current state of knowledge of SMAC mimetics as an approach to eliminate HIV infected cells and discuss the potential future use of SMAC mimetics as part of an HIV cure strategy.

The Zebrafish Antiapoptotic Protein BIRC2 Promotes Edwardsiella piscicida Infection by Inhibiting Caspases and Accumulating p53 in a p53 Transcription-Dependent and -Independent Manner

IAPs (inhibitors of apoptosis) are endogenous caspase inhibitors with multiple biological activities. In the present study, we show functional characteristics of antiapoptotic protein BIRC2 (cIAP1) in response to Edwardsiella piscicida infection. Overexpression of BIRC2 in zebrafish larvae promoted the proliferation of E. piscicida, leading to a decreased larvae survival. The expression levels of caspases including casp3, casp8, and casp9 were significantly inhibited by BIRC2 overexpression in the case of E. piscicida infection. Treatment of zebrafish larvae microinjected with BIRC2 with the caspase activator PAC-1 completely blocked the negative regulation of BIRC2 on the E. piscicida infection, with the reduced inhibition on the casp3 and without inhibition on casp8 and casp9. In contrast to the regulation of BIRC2 on the caspases, BIRC2 overexpression significantly induced the expression of p53, especially at 24 hpi. In addition to the cytoplasmic p53 expression, BIRC2 overexpression also induced the expression of the nuclear p53 protein. Further analysis demonstrated that BIRC2 could interact and colocalize with p53 in the cytoplasm. The numbers of E. piscicida in larvae overexpressed with BIRC2 and treated with pifithrin-μ (an inhibitor of mitochondrial p53) or pifithrin-α (an inhibitor of p53 transactivation) were lower than those of larvae without pifithrin-μ or pifithrin-α treatment. Critically, the p53 inactivators pifithrin-μ and pifithrin-α had no significant effect on larval survival, but completely rescued larval survival for zebrafish microinjected with BIRC2 in the case of E. piscicida infection. Collectively, the present study suggest that piscine BIRC2 is a negative regulator for antibacterial immune response in response to the E. piscicida infection via inhibiting caspases, and accumulating p53 in a p53 transcription-dependent and -independent manner.

Therapeutic perspective of thiosemicarbazones derivatives in inflammatory pathologies: A summary of in vitro/in vivo studies

Following induction of inflammation, the nuclear factor kappa B (NF-κB) in activated macrophages induces the transcription of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and cyclooxygenase (COX), an inflammatory enzyme implicated in the synthesis of prostaglandins (PGs). The latter are involved in the transition and the maintenance of chronic inflammation underling various chronic disorders that require treatment. Concerning this, many anti-inflammatory drugs are available to treat the inflammatory disorders, but their therapeutic use is associated with a variety of side effects. Therefore, the discovery of new safer and potential anti-inflammatory drugs is necessary. In this regard, thiosemicarbazones (TSC) compounds and their metals complexes attracted high interest due to their wide range of biological activities, interestingly, the anti-inflammatory activity. They are formed by the action of thiosemicarbazide on an aldehyde or ketone, and contain a sulfur atom in place of the oxygen atom. Their ability to form a stable complex with transition metal is known to enhances the biological activity and reduces the side effects of the parent compound. Thus, this review article describes the inflammatory response mediated by NF-κB-COX-PGs and summarizes the anti-inflammatory activity of different thiosemicarbazones derivatives synthesized in research area.

Lipopolysaccharide- TLR-4 Axis regulates Osteoclastogenesis independent of RANKL/RANK signaling

BACKGROUND

Lipopolysaccharide (LPS) is an endotoxin and a vital component of gram-negative bacteria's outer membrane. During gram-negative bacterial sepsis, LPS regulates osteoclast differentiation and activity, in addition to increasing inflammation. This study aimed to investigate how LPS regulates osteoclast differentiation of RAW 264.7 cells in vitro.

RESULTS

Herein, we revealed that RAW cells failed to differentiate into mature osteoclasts in vitro in the presence of LPS. However, differentiation occurred in cells primed with receptor activator of nuclear factor-kappa-Β ligand (RANKL) for 24 h and then treated with LPS for 48 h (henceforth, denoted as LPS-treated cells). In cells treated with either RANKL or LPS, an increase in membrane levels of toll-like receptor 4 (TLR4) receptor was observed. Mechanistically, an inhibitor of TLR4 (TAK-242) reduced the number of osteoclasts as well as the secretion of tumor necrosis factor (TNF)-α in LPS-treated cells. RANKL-induced RAW cells secreted a very basal level TNF-α. TAK-242 did not affect RANKL-induced osteoclastogenesis. Increased osteoclast differentiation in LPS-treated osteoclasts was not associated with the RANKL/RANK/OPG axis but connected with the LPS/TLR4/TNF-α tumor necrosis factor receptor (TNFR)-2 axis. We postulate that this is because TAK-242 and a TNF-α antibody suppress osteoclast differentiation. Furthermore, an antibody against TNF-α reduced membrane levels of TNFR-2. Secreted TNF-α appears to function as an autocrine/ paracrine factor in the induction of osteoclastogenesis independent of RANKL.

CONCLUSION

TNF-α secreted via LPS/TLR4 signaling regulates osteoclastogenesis in macrophages primed with RANKL and then treated with LPS. Our findings suggest that TLR4/TNF-α might be a potential target to suppress bone loss associated with inflammatory bone diseases, including periodontitis, rheumatoid arthritis, and osteoporosis.

The BIRC Family Genes Expression in Patients with Triple Negative Breast Cancer

The BIRC (baculoviral IAP repeat-containing; BIRC) family genes encode for Inhibitor of Apoptosis (IAP) proteins. The dysregulation of the expression levels of the genes in question in cancer tissue as compared to normal tissue suggests that the apoptosis process in cancer cells was disturbed, which may be associated with the development and chemoresistance of triple negative breast cancer (TNBC). In our study, we determined the expression level of eight genes from the BIRC family using the Real-Time PCR method in patients with TNBC and compared the obtained results with clinical data. Additionally, using bioinformatics tools (Ualcan and The Breast Cancer Gene-Expression Miner v4.5 (bc-GenExMiner v4.5)), we compared our data with the data in the Cancer Genome Atlas (TCGA) database. We observed diverse expression pattern among the studied genes in breast cancer tissue. Comparing the expression level of the studied genes with the clinical data, we found that in patients diagnosed with breast cancer under the age of 50, the expression levels of all studied genes were higher compared to patients diagnosed after the age of 50. We observed that in patients with invasion of neoplastic cells into lymphatic vessels and fat tissue, the expression levels of BIRC family genes were lower compared to patients in whom these features were not noted. Statistically significant differences in gene expression were also noted in patients classified into three groups depending on the basis of the Scarff-Bloom and Richardson (SBR) Grading System.

The Multiple Roles of the IAP Super-family in cancer

The Inhibitor of Apoptosis proteins (IAPs) are a family of proteins that are mainly known for their anti-apoptotic activity and ability to directly bind and inhibit caspases. Recent research has however revealed that they have extensive roles in governing numerous other cellular processes. IAPs are known to modulate ubiquitin (Ub)-dependent signaling pathways through their E3 ligase activity and influence activation of nuclear factor κB (NF-κB). In this review, we discuss the involvement of IAPs in individual hallmarks of cancer and the current status of therapies targeting these critical proteins.

Increased Expression of BIRC2, BIRC3, and BIRC5 from the IAP Family in Mesenchymal Stem Cells of the Umbilical Cord Wharton's Jelly (WJSC) in Younger Women Giving Birth Naturally

The knowledge of factors affecting the viability as well as proliferation and therapeutic potential of perinatal stem cells is of great importance for the decisions concerning their collection, multiplication, and storing. The aim of this work is to evaluate the expression of the BIRC2, BIRC3, and BIRC5 genes at the level of transcription in mesenchymal stem cells derived from the umbilical cord Wharton's jelly. The study examined the relationship between the expression level of the studied genes and selected biophysical parameters of umbilical blood: pH, pCO₂, pO₂, and cHCO₃. Moreover, the relationship between the pregnant age, the type of delivery (natural delivery or cesarean section), and the level of expression of the BIRC2, BIRC3, and BIRC5 genes was assessed. The research was carried out on mesenchymal stem cells derived from the umbilical cord Wharton's jelly (WJSC) taken from 55 women immediately after delivery. Expression of the examined genes was assessed with the qPCR method using commercially available reagent kits. On the basis of the conducted research, it was demonstrated that WJSCs collected from younger women giving birth naturally, and in the acidic environment of the umbilical cord blood, are characterized by a higher expression of the BIRC2, BIRC3, and BIRC5 genes. It was shown that the expression of the BIRC2 and BIRC3 genes in Wharton's jelly mesenchymal stem cells declines with the mother's age. Our research suggests that stem cells collected from younger women giving birth naturally can be more resistant to apoptosis and show a more stem cell-like character, which can increase their therapeutic potential and clinical utility, but this conclusion needs to be approved in the next studies.

Osteoclastogenesis in periodontal diseases: Possible mediators and mechanisms

BACKGROUND

Periodontitis is the inflammation of the tooth-supporting structures and is one of the most common diseases of the oral cavity. The outcome of periodontal infections is tooth loss due to a lack of alveolar bone support. Osteoclasts are giant, multi-nucleated, and bone-resorbing cells that are central for many osteolytic diseases, including periodontitis. Receptor activator of nuclear factor-kB ligand (RANKL) is the principal factor involved in osteoclast differentiation, activation, and survival. However, under pathological conditions, a variety of pro-inflammatory cytokines secreted by activated immune cells also contribute to osteoclast differentiation and activity. Lipopolysaccharide (LPS) is a vital component of the outer membrane of the Gram-negative bacteria. It binds to the Toll-like receptors (TLRs) expressed in many cells and elicits an immune response.

HIGHLIGHTS

The presence of bacterial LPS in the periodontal area stimulates the secretion of RANKL as well as other inflammatory mediators, activating the process of osteoclastogenesis. RANKL, either independently or synergistically with LPS, can regulate osteoclastogenesis, while LPS alone cannot. MicroRNA, IL-22, M1/M2 macrophages, and memory B cells have recently been shown to modulate osteoclastogenesis in periodontal diseases.

CONCLUSION

In this review, we summarize the mechanism of osteoclastogenesis accompanying periodontal diseases at the cellular level. We discuss a) the effects of LPS/TLR signaling and other cytokines on RANKL-dependent and -independent mechanisms involved in osteoclastogenesis; b) the recently identified role of several endogenous factors such as miRNA, IL-22, M1/M2 macrophages, and memory B cells in regulating osteoclastogenesis during periodontal pathogenesis.

Toward Curative Immunomodulation Strategies for Chronic Hepatitis B Virus Infection

Chronic hepatitis B virus (HBV) infection remains a major cause of morbidity and mortality worldwide. HBV surface antigen loss is considered a functional cure and is an ideal goal for antiviral therapy. However, current treatment regimens, including nucleos(t)ide analogues or interferons monotherapy and combination therapy, rarely achieve this goal in chronic hepatitis B patients. Nucleos(t)ide analogues (NAs), as well as many direct antiviral drugs in ongoing development, are able to inhibit HBV replication and gene expression, but it is hard to achieve immune control and prevent recurrence after therapy cessation. Host immunity, especially HBV-specific T cell response, is proven to play a critical role in control or clearance of HBV infection. Considering HBV chronically infected patients display varying degrees of dysfunction regarding their immune system, novel approaches to enhancing antiviral immune responses are necessary in order to combine with current antiviral agents. In this Review, we focus on the role of innate and adaptive immune responses in HBV immunopathogenesis and discuss attractive strategies or drugs that aim to activate or rebuild antiviral immunity to achieve the goal of an HBV functional cure.

The IAP antagonist birinapant potentiates bortezomib anti-myeloma activity in vitro and in vivo

Background

Mechanisms by which Smac mimetics (SMs) interact with proteasome inhibitors (e.g., bortezomib) are largely unknown, particularly in multiple myeloma (MM), a disease in which bortezomib represents a mainstay of therapy.

Methods

Interactions between the clinically relevant IAP (inhibitor of apoptosis protein) antagonist birinapant (TL32711) and the proteasome inhibitor bortezomib were investigated in multiple myeloma (MM) cell lines and primary cells, as well as in vivo models. Induction of apoptosis and changes in gene and protein expression were monitored using MM cell lines and confirmed in primary MM cell populations. Genetically modified cells (e.g., exhibiting shRNA knockdown or ectopic expression) were employed to evaluate the functional significance of birinapant/bortezomib-induced changes in protein levels. A MM xenograft model was used to evaluate the in vivo activity of the birinapant/bortezomib regimen.

Results

Birinapant and bortezomib synergistically induced apoptosis in diverse cell lines, including bortezomib-resistant cells (PS-R). The regimen robustly downregulated cIAP1/2 but not the canonical NF-κB pathway, reflected by p65 phosphorylation and nuclear accumulation. In contrast, the bortezomib/birinapant regimen upregulated TRAF3, downregulated TRAF2, and diminished p52 processing and BCL-X_L expression, consistent with disruption of the non-canonical NF-κB pathway. TRAF3 knockdown, ectopic TRAF2, or BCL-X_L expression significantly diminished birinapant/bortezomib toxicity. The regimen sharply increased extrinsic apoptotic pathway activation, and cells expressing dominant-negative FADD or caspase-8 displayed markedly reduced birinapant/bortezomib sensitivity. Primary CD138⁺ (n = 43) and primitive MM populations (CD138⁻/19⁺/20⁺/27⁺; n = 31) but not normal CD34⁺ cells exhibited significantly enhanced toxicity with combined treatment (P < 0.0001). The regimen was also fully active in the presence of HS-5 stromal cells or growth factors (e.g., IL-6 and VEGF). Finally, the regimen was well tolerated and significantly increased survival (P < 0.05 and P < 0.001) compared to single agents in a MM xenograft model. Combined treatment also downregulated cIAP1/2 and p52 while increasing PARP cleavage in MM cells in vivo.

Conclusions

Our data suggest that birinapant and bortezomib interact synergistically in MM cells, including those resistant to bortezomib, through inactivation of the non-canonical NF-κB and activation of the extrinsic apoptotic pathway both in vitro and in vivo. They also argue that a strategy combining cIAP antagonists and proteasome inhibitors warrants attention in MM.

Electronic supplementary material

The online version of this article (10.1186/s13045-019-0713-x) contains supplementary material, which is available to authorized users.

Targeting the BIR Domains of Inhibitor of Apoptosis (IAP) Proteins in Cancer Treatment

Inhibitor of apoptosis (IAP) proteins are characterized by the presence of the conserved baculoviral IAP repeat (BIR) domain that is involved in protein-protein interactions. IAPs were initially thought to be mainly responsible for caspase inhibition, acting as negative regulators of apoptosis, but later works have shown that IAPs also control a plethora of other different cellular pathways. As X-linked IAP (XIAP), and other IAP, levels are often deregulated in cancer cells and have been shown to correlate with patients' prognosis, several approaches have been pursued to inhibit their activity in order to restore apoptosis. Many small molecules have been designed to target the BIR domains, the vast majority being inspired by the N-terminal tetrapeptide of Second Mitochondria-derived Activator of Caspases/Direct IAp Binding with Low pI (Smac/Diablo), which is the natural XIAP antagonist. These compounds are therefore usually referred to as Smac mimetics (SMs). Despite the fact that SMs were intended to specifically target XIAP, it has been shown that they also interact with cellular IAP-1 (cIAP1) and cIAP2, promoting their proteasome-dependent degradation. SMs have been tested in combination with several cytotoxic compounds and are now considered promising immune modulators which can be exploited in cancer therapy, especially in combination with immune checkpoint inhibitors. In this review, we give an overview of the structural hot-spots of BIRs, focusing on their fold and on the peculiar structural patches which characterize the diverse BIRs. These structures are exploited/exploitable for the development of specific and active IAP inhibitors.

HTiP: High-Throughput Immunomodulator Phenotypic Screening Platform to Reveal IAP Antagonists as Anti-cancer Immune Enhancers

Protein- and cell-based immunotherapeutic agents have revolutionized cancer treatment. However, small-molecule immunomodulators with favorable pharmacological properties for reaching intracellular targets remain to be developed. To explore the vast chemical space, a robust method that recapitulates the complex cancer-immune microenvironment in a high-throughput format is essential. To address this critical gap, we developed a high-throughput immunomodulator phenotypic screening platform, HTiP, which integrates the immune and cancer cell co-culture system with imaging- and biochemical-based multiplexed readouts. Using the HTiP platform, we have demonstrated its capability in modeling an oncogenic KRAS mutation-driven immunosuppressive phenotype. From a bioactive chemical library, multiple structurally distinct compounds were identified, all of which target the same class of proteins, inhibitor of apoptosis protein (IAP). IAP has demonstrated roles in cancer immunity. Identification of IAP antagonists as potent anti-tumor immune enhancers provides strong validating evidence for the use of the HTiP platform to discover small-molecule immunomodulators.

The SMAC Mimetic APG-1387 Sensitizes Immune-Mediated Cell Apoptosis in Hepatocellular Carcinoma

The inhibitor of apoptosis protein (IAP) genes are frequently overexpressed in malignancies. Second mitochondria-derived activator of caspase (SMAC) mimetics, which target IAPs, have potential to trigger cancer cell death and sensitize tumor cells to cytotoxic therapy. The aim of this study was to investigate the anti-tumor potential of a novel bivalent SMAC mimetic, APG-1387, in hepatocellular carcinoma (HCC). The mRNA and protein expressions of IAPs, including cellular IAPs (cIAP1 and cIAP2) and X chromosome-linked IAP (XIAP), were increased in HCC tumors compared with normal liver tissue. APG-1387 treatment alone significantly reduced the protein levels of IAPs, but had only a modest effect on the viability and apoptosis of HCC cells in vitro. However, APG-1387 in combination with tumor necrosis factor-alpha (TNF-α) or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) significantly reduced cell viability and proliferation, and induced apoptosis in HepG2 cells, as well as in HCCLM3 cells that harbors cancer stem cell-like properties. These synergistic killing effects were caspase-dependent and partially dependent on RIPK1 kinase activity. Furthermore, APG-1387 also promoted the killing effect of Natural Killer cells on HCC cells in vitro and the combination therapy significantly inhibited tumor growth by inducing cell apoptosis in xenograft mice model. In conclusion, our study clarified that APG-1387 could sensitize HCC cells to cytokines or immune cells mediated cell killing and implied that potential of SMAC mimetic based combination immunotherapy for HCC treatment.

IAP genes partake weighty roles in the astogeny and whole body regeneration in the colonial urochordate Botryllus schlosseri

Inhibitors of Apoptosis Protein (IAP) genes participate in processes like apoptosis, proliferation, innate immunity, inflammation, cell motility, differentiation and in malignancies. Here we reveal 25 IAP genes in the tunicate Botryllus schlosseri's genome and their functions in two developmental biology phenomena, a new mode of whole body regeneration (WBR) induced by budectomy, and blastogenesis, the four-staged cycles of botryllid ascidian astogeny. IAP genes that were specifically upregulated during these developmental phenomena were identified, and protein expression patterns of one of these genes, IAP28, were followed. Most of the IAP genes upregulation recorded at blastogenetic stages C/D was in concert with the upregulation at 100 μM H₂O₂ apoptotic-induced treatment and in parallel to expressions of AIF1, Bax, Mcl1, caspase 2 and two orthologues of caspase 7. Wnt agonist altered the takeover duration along with reduced IAP expressions, and displacement of IAP28⁺ phagocytes. WBR was initiated solely at blastogenetic stage D, where zooidal absorption was attenuated and regeneration centers were formed either from remains of partially absorbed zooids or from deformed ampullae. Subsequently, bud-bearing zooids developed, in concert with a massive IAP28-dependent phagocytic wave that eliminated the old zooids, then proceeded with the establishment of morphologically normal-looking colonies. IAP4, IAP14 and IAP28 were also involved in WBR, in conjunction with the expression of the pro-survival PI3K-Akt pathway. IAPs function deregulation by Smac mimetics resulted in severe morphological damages, attenuation in bud growth and differentiation, and in destabilization of colonial coordination. Longtime knockdown of IAP functions prior to the budectomy, resulted in colonial death.

E2F1 binds to the peptide-binding groove within the BIR3 domain of cIAP1 and requires cIAP1 for chromatin binding

The cellular inhibitor of apoptosis 1 (cIAP1) is an E3-ubiquitin ligase that regulates cell signaling pathways involved in fundamental cellular processes including cell death, cell proliferation, cell differentiation and inflammation. It recruits ubiquitination substrates thanks to the presence of three baculoviral IAP repeat (BIR) domains at its N-terminal extremity. We previously demonstrated that cIAP1 promoted the ubiquitination of the E2 factor 1 (E2F1) transcription factor. Moreover, we showed that cIAP1 was required for E2F1 stabilization during the S phase of cell cycle and in response to DNA damage. Here, we report that E2F1 binds within the cIAP1 BIR3 domain. The BIR3 contains a surface hydrophobic groove that specifically anchors a conserved IAP binding motif (IBM) found in a number of intracellular proteins including Smac. The Smac N-7 peptide that includes the IBM, as well as a Smac mimetic, competed with E2F1 for interaction with cIAP1 demonstrating the importance of the BIR surface hydrophobic groove. We demonstrated that the first alpha-helix of BIR3 was required for E2F1 binding, as well as for the binding of Smac and Smac mimetics. Overexpression of cIAP1 modified the ubiquitination profile of E2F1, increasing the ratio of E2F1 conjugated with K11- and K63-linked ubiquitin chains, and decreasing the proportion of E2F1 modified by K48-linked ubiquitin chains. ChIP-seq analysis demonstrated that cIAP1 was required for the recruitment of E2F1 onto chromatin. Lastly, we identified an E2F-binding site on the cIAP1-encoding birc2 gene promoter, suggesting a retro-control regulation loop.

Getting the "Kill" into "Shock and Kill": Strategies to Eliminate Latent HIV

Despite the success of antiretroviral therapy (ART), there is currently no HIV cure and treatment is life long. HIV persists during ART due to long-lived and proliferating latently infected CD4+ T cells. One strategy to eliminate latency is to activate virus production using latency reversing agents (LRAs) with the goal of triggering cell death through virus-induced cytolysis or immune-mediated clearance. However, multiple studies have demonstrated that activation of viral transcription alone is insufficient to induce cell death and some LRAs may counteract cell death by promoting cell survival. Here, we review new approaches to induce death of latently infected cells through apoptosis and inhibition of pathways critical for cell survival, which are often hijacked by HIV proteins. Given advances in the commercial development of compounds that induce apoptosis in cancer chemotherapy, these agents could move rapidly into clinical trials, either alone or in combination with LRAs, to eliminate latent HIV infection.

Inhibitors of apoptosis: clinical implications in cancer

Inhibitor of apoptosis (IAP) family comprises a group of endogenous proteins that function as main regulators of caspase activity and cell death. They are considered the main culprits in evasion of apoptosis, which is a fundamental hallmark of carcinogenesis. Overexpression of IAP proteins has been documented in various solid and hematological malignancies, rendering them resistant to standard chemotherapeutics and radiation therapy and conferring poor prognosis. This observation has urged their exploitation as therapeutic targets in cancer with promising pre-clinical outcomes. This review describes the structural and functional features of IAP proteins to elucidate the mechanism of their anti-apoptotic activity. We also provide an update on patterns of IAP expression in different tumors, their impact on treatment response and prognosis, as well as the emerging investigational drugs targeting them. This aims at shedding the light on the advances in IAP targeting achieved to date, and encourage further development of clinically applicable therapeutic approaches.

cIAP1 regulates the EGFR/Snai2 axis in triple-negative breast cancer cells

Inhibitor of apoptosis (IAP) proteins constitute a family of conserved molecules that regulate both apoptosis and receptor signaling. They are often deregulated in cancer cells and represent potential targets for therapy. In our work, we investigated the effect of IAP inhibition in vivo to identify novel downstream genes expressed in an IAP-dependent manner that could contribute to cancer aggressiveness. To this end, immunocompromised mice engrafted subcutaneously with the triple-negative breast cancer MDA-MB231 cell line were treated with SM83, a Smac mimetic that acts as a pan-IAP inhibitor, and tumor nodules were profiled for gene expression. SM83 reduced the expression of Snai2, an epithelial-to-mesenchymal transition factor often associated with increased stem-like properties and metastatic potential especially in breast cancer cells. By testing several breast cancer cell lines, we demonstrated that Snai2 downregulation prevents cell motility and that its expression is promoted by cIAP1. In fact, the chemical or genetic inhibition of cIAP1 blocked epidermal growth factor receptor (EGFR)-dependent activation of the mitogen-activated protein kinase (MAPK) pathway and caused the reduction of Snai2 transcription levels. In a number of breast cancer cell lines, cIAP1 depletion also resulted in a reduction of EGFR protein levels which derived from the decrease of its gene transcription, though, paradoxically, the silencing of cIAP1 promoted EGFR protein stability rather than its degradation. Finally, we provided evidence that IAP inhibition displays an anti-tumor and anti-metastasis effect in vivo. In conclusion, our work indicates that IAP-targeted therapy could contribute to EGFR inhibition and to the reduction of its downstream mediators. This approach could be particularly effective in tumors characterized by high levels of EGFR and Snai2, such as triple-negative breast cancer.

Negative correlation between X-linked inhibitors of apoptosis and second mitochondria-derived activator of caspase expression levels in cervical carcinoma and cervical intraepithelial neoplasia

X-linked inhibitors of apoptosis (XIAP) and second mitochondria-derived activator of caspase (Smac) have been widely reported to serve roles in the development of cervical carcinoma. The present study analyzed the associations between the expression levels of XIAP and Smac in normal cervical epithelium, cervical intraepithelial neoplasia (CIN) and cervical carcinoma. Immunohistochemistry staining of formalin-fixed, paraffin-embedded tissue sections was performed in order to analyze the expression levels of XIAP and Smac in 15 cases of normal cervical tissues, 69 cases of CIN and 76 cases of cervical carcinoma. All the tissue samples were confirmed by pathological diagnosis. The association of XIAP and Smac expression levels was analyzed using one-way analysis of variance, χ² tests and Spearman's ρ for the nonparametric bi-variant correlation analysis. Overall survival was determined using the log-rank test and Kaplan-Meier survival curves. The expression level of XIAP was increased in CIN and cervical carcinoma tissues compared with normal cervical tissues, whereas Smac demonstrated a converse expression pattern to XIAP in these tissues. The positive staining level of XIAP protein was increased in grade 3 CIN compared with that in grade 1–2 CIN, and was significantly higher in the less-differentiated tissue of cervical carcinoma compared with the well- or medium-differentiated tissues (P<0.05). The staining level was also significantly increased in cervical carcinoma with stage 2b-3 compared with tissues from stage 1–2a carcinoma (P<0.05). The expression levels of Smac were in opposition to these results. XIAP was associated with pelvic lymph node metastasis, whereas no association was identified with Smac expression. The expression level of XIAP was significantly and negatively associated with cell survival time in cervical carcinoma, whereas the expression level of Smac was significantly and positively associated with cell survival time in cervical carcinoma. Therefore, XIAP and Smac may participate in the development of cervical cancer. The expression levels of XIAP and Smac were significantly and inversely associated. This may be useful in early diagnosis, evaluation of surgery and chemotherapy and the prognosis of cervical carcinoma.

Cancer therapies in HIV cure research

PURPOSE OF REVIEW

This article provides an overview of anticancer therapies in various stages of clinical development as potential interventions to target HIV persistence.

RECENT FINDINGS

Epigenetic drugs developed for cancer have been investigated in vitro, ex vivo and in clinical trials as interventions aimed at reversing HIV latency and depleting the amount of virus that persists on antiretroviral therapy. Treatment with histone deacetylase inhibitors induced HIV expression in patients on antiretroviral therapy but did not reduce the frequency of infected cells. Other interventions that may accelerate the decay of latently infected cells, in the presence or absence of latency-reversing therapy, are now being explored. These include apoptosis-promoting agents, nonhistone deacetylase inhibitor compounds to reverse HIV latency and immunotherapy interventions to enhance antiviral immunity such as immune checkpoint inhibitors and Toll-like receptor agonists.

SUMMARY

A curative strategy in HIV will likely need to both reduce the amount of virus that persists on antiretroviral therapy and improve anti-HIV immune surveillance. Although we continue to explore advances in the field of oncology including cancer immunotherapy, there are major differences in the risk-benefit assessment between HIV-infected individuals and patients with malignancies. Drug development specifically targeting HIV persistence will be the key to developing effective interventions with an appropriate safety profile.

DNA damage and S phase-dependent E2F1 stabilization requires the cIAP1 E3-ubiquitin ligase and is associated with K63-poly-ubiquitination on lysine 161/164 residues

The E2F transcription factor 1 is subtly regulated along the cell cycle progression and in response to DNA damage by post-translational modifications. Here, we demonstrated that the E3-ubiquitin ligase cellular inhibitor of apoptosis 1 (cIAP1) increases E2F1 K63-poly-ubiquitination on the lysine residue 161/164 cluster, which is associated with the transcriptional factor stability and activity. Mutation of these lysine residues completely abrogates the binding of E2F1 to CCNE, TP73 and APAF1 promoters, thus inhibiting transcriptional activation of these genes and E2F1-mediated cell proliferation control. Importantly, E2F1 stabilization in response to etoposide-induced DNA damage or during the S phase of cell cycle, as revealed by cyclin A silencing, is associated with K63-poly-ubiquitinylation of E2F1 on lysine 161/164 residues and involves cIAP1. Our results reveal an additional level of regulation of the stability and the activity of E2F1 by a non-degradative K63-poly-ubiquitination and uncover a novel function for the E3-ubiquitin ligase cIAP1.

Exome Analysis of Rare and Common Variants within the NOD Signaling Pathway

Pediatric inflammatory bowel disease (pIBD) is a chronic heterogeneous disorder. This study looks at the burden of common and rare coding mutations within 41 genes comprising the NOD signaling pathway in pIBD patients. 136 pIBD and 106 control samples underwent whole-exome sequencing. We compared the burden of common, rare and private mutation between these two groups using the SKAT-O test. An independent replication cohort of 33 cases and 111 controls was used to validate significant findings. We observed variation in 40 of 41 genes comprising the NOD signaling pathway. Four genes were significantly associated with disease in the discovery cohort (BIRC2 p = 0.004, NFKB1 p =  0.005, NOD2 p = 0.029 and SUGT1 p = 0.047). Statistical significance was replicated for BIRC2 (p = 0.041) and NOD2 (p = 0.045) in an independent validation cohort. A gene based test on the combined discovery and replication cohort confirmed association for BIRC2 (p = 0.030). We successfully applied burden of mutation testing that jointly assesses common and rare variants, identifying two previously implicated genes (NFKB1 and NOD2) and confirmed a possible role in disease risk in a previously unreported gene (BIRC2). The identification of this novel gene provides a wider role for the inhibitor of apoptosis gene family in IBD pathogenesis.

Survivin and NAIP in Human Benign Prostatic Hyperplasia: Protective Role of the Association of Serenoa repens, Lycopene and Selenium from the Randomized Clinical Study

Benign prostatic hyperplasia (BPH) treatment includes the apoptosis machinery modulation through the direct inhibition of caspase cascade. We previously demonstrated that Serenoa repens (Ser) with lycopene (Ly) and selenium (Se) reawakened apoptosis by reducing survivin and neuronal apoptosis inhibitory protein (NAIP) levels in rats. The aim of this study was to evaluate the effectiveness of Ser-Se-Ly association on survivin and NAIP expression in BPH patients. Ninety patients with lower urinary tract symptoms (LUTS) due to clinical BPH were included in this randomized, double-blind, placebo-controlled trial. Participants were randomly assigned to receive placebo (Group BPH + placebo, n = 45) or Ser-Se-Ly association (Group BPH + Ser-Se-Ly; n = 45) for 3 months. At time 0, all patients underwent prostatic biopsies. After 3 months of treatment, they underwent prostatic re-biopsy and specimens were collected for molecular, morphological, and immunohistochemical analysis. After 3 months, survivin and NAIP were significantly decreased, while caspase-3 was significantly increased in BPH patients treated with Ser-Se-Ly when compared with the other group. In BPH patients treated with Ser-Se-Ly for 3 months, the glandular epithelium was formed by a single layer of cuboidal cells. PSA showed high immunoexpression in all BPH patients and a focal positivity in Ser-Se-Ly treated patients after 3 months. Evident prostate specific membrane antigen (PSMA) immunoexpression was shown in all BPH patients, while no positivity was present after Ser-Se-Ly administration. Ser-Se-Ly proved to be effective in promoting apoptosis in BPH patients.

The functional interplay between the HIF pathway and the ubiquitin system - more than a one-way road

The hypoxia inducible factor (HIF) pathway and the ubiquitin system represent major cellular processes that are involved in the regulation of a plethora of cellular signaling pathways and tissue functions. The ubiquitin system controls the ubiquitination of proteins, which is the covalent linkage of one or several ubiquitin molecules to specific targets. This ubiquitination is catalyzed by approximately 1000 different E3 ubiquitin ligases and can lead to different effects, depending on the type of internal ubiquitin chain linkage. The best-studied function is the targeting of proteins for proteasomal degradation. The activity of E3 ligases is antagonized by proteins called deubiquitinases (or deubiquitinating enzymes), which negatively regulate ubiquitin chains. This is performed in most cases by the catalytic removal of these chains from the targeted protein. The HIF pathway is regulated in an oxygen-dependent manner by oxygen-sensing hydroxylases. Covalent modification of HIFα subunits leads to the recruitment of an E3 ligase complex via the von Hippel-Lindau (VHL) protein and the subsequent polyubiquitination and proteasomal degradation of HIFα subunits, demonstrating the regulation of the HIF pathway by the ubiquitin system. This unidirectional effect of an E3 ligase on the HIF pathway is the best-studied example for the interplay between these two important cellular processes. However, additional regulatory mechanisms of the HIF pathway through the ubiquitin system are emerging and, more recently, also the reciprocal regulation of the ubiquitin system through components of the HIF pathway. Understanding these mechanisms and their relevance for the activity of each other is of major importance for the comprehensive elucidation of the oxygen-dependent regulation of cellular processes. This review describes the current knowledge of the functional bidirectional interplay between the HIF pathway and the ubiquitin system on the protein level.

The Smac Mimetic BV6 Improves NK Cell-Mediated Killing of Rhabdomyosarcoma Cells by Simultaneously Targeting Tumor and Effector Cells

Rhabdomyosarcoma (RMS), the most common cancer of connective tissues in pediatrics, is often resistant to conventional therapies. One underlying mechanism of this resistance is the overexpression of Inhibitor of Apoptosis (IAP) proteins, leading to a dysfunctional cell death program within tumor cells. Smac mimetics (SM) are small molecules that can reactivate the cell death program by antagonizing IAP proteins and thereby compensating their overexpression. Here, we report that SM sensitize two RMS cell lines (RD and RH30) toward natural killer (NK) cell-mediated killing on the one hand, and increase the cytotoxic potential of NK cells on the other. The SM-induced sensitization of RH30 cells toward NK cell-mediated killing is significantly reduced through blocking tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on NK cells prior to coculture. In addition, the presence of zVAD.fmk, a pancaspase inhibitor, rescues tumor cells from the increase in killing, indicating an apoptosis-dependent cell death. On the NK cell side, the presence of SM in addition to IL-2 during the ex vivo expansion leads to an increase in their cytotoxic activity against RH30 cells. This effect is mainly TNFα-dependent and partially mediated by NK cell activation, which is associated with transcriptional upregulation of NF-κB target genes such as IκBα and RelB. Taken together, our findings implicate that SM represent a novel double-hit strategy, sensitizing tumor and activating NK cells with one single drug.

Apoptosis, Toll-like, RIG-I-like and NOD-like Receptors Are Pathways Jointly Induced by Diverse Respiratory Bacterial and Viral Pathogens

Lower respiratory tract infections are among the top five leading causes of human death. Fighting these infections is therefore a world health priority. Searching for induced alterations in host gene expression shared by several relevant respiratory pathogens represents an alternative to identify new targets for wide-range host-oriented therapeutics. With this aim, alveolar macrophages were independently infected with three unrelated bacterial (Streptococcus pneumoniae, Klebsiella pneumoniae, and Staphylococcus aureus) and two dissimilar viral (respiratory syncytial virus and influenza A virus) respiratory pathogens, all of them highly relevant for human health. Cells were also activated with bacterial lipopolysaccharide (LPS) as a prototypical pathogen-associated molecular pattern. Patterns of differentially expressed cellular genes shared by the indicated pathogens were searched by microarray analysis. Most of the commonly up-regulated host genes were related to the innate immune response and/or apoptosis, with Toll-like, RIG-I-like and NOD-like receptors among the top 10 signaling pathways with over-expressed genes. These results identify new potential broad-spectrum targets to fight the important human infections caused by the bacteria and viruses studied here.