N-terminal domain of nuclear IL-1α shows structural similarity to the C-terminal domain of Snf1 and binds to the HAT/core module of the SAGA complex

ATM and IRAK1 orchestrate two distinct mechanisms of NF-κB activation in response to DNA damage

DNA damage in cells induces the expression of inflammatory genes. However, the mechanism by which cells initiate an innate immune response in the presence of DNA lesions blocking transcription remains unknown. Here we find that genotoxic stresses lead to an acute activation of the transcription factor NF-κB through two distinct pathways, each triggered by different types of DNA lesions and coordinated by either ataxia-telangiectasia mutated (ATM) or IRAK1 kinases. ATM stimulates NF-κB in cells with DNA double-strand breaks. By contrast, IRAK1-induced NF-κB signaling occurs in neighboring cells through IL-1α secretion from transcriptionally stressed cells caused by DNA lesions blocking RNA polymerases. Subsequently, both pathways stimulate TRAF6 and the IKK complex to promote NF-κB-mediated inflammatory gene expression. These findings provide an alternative mechanism for damaged cells with impaired transcription to initiate an inflammatory response without relying on their own gene expression, a necessary step that injured cells depend on during canonical innate immune responses.

Proximity labelling of pro-interleukin-1α reveals evolutionary conserved nuclear interactions

Interleukin-1α is a suggested dual-function cytokine that diverged from interleukin-1β in mammals potentially by acquiring additional biological roles that relate to highly conserved regions in the pro-domain of interleukin-1α, including a nuclear localisation sequence and histone acetyltransferase-binding domains. Why evolution modified pro-interleukin-1α's subcellular location and protein interactome, and how this shaped interleukin-1α's intracellular role, is unknown. Here we show that TurboID proximity labelling with pro-interleukin-1α suggests a nuclear role for pro-interleukin-1α that involves interaction with histone acetyltransferases, including EP300. We also identify and validate inactivating mutations in the pro-interleukin-1α nuclear localisation sequence of multiple mammalian species, including toothed whales, castorimorpha and marsupials. However, histone acetyltransferase-binding domains are conserved in those species that have lost pro-interleukin-1α nuclear localisation. Together, these data suggest that histone acetyltransferase binding and nuclear localisation occurred together, and that while some species lost the nuclear localisation sequence in their pro-interleukin-1α, histone acetyltransferase binding ability was maintained. The nuclear localisation sequence was lost from several distinct species at different evolutionary times, suggesting convergent evolution, and that the loss of the nuclear localisation sequence confers some important biological outcome.

Tumor Cell-Associated IL-1α Affects Breast Cancer Progression and Metastasis in Mice through Manipulation of the Tumor Immune Microenvironment

IL-1α is a dual function cytokine that affects inflammatory and immune responses and plays a pivotal role in cancer. The effects of intracellular IL-1α on the development of triple negative breast cancer (TNBC) in mice were assessed using the CRISPR/Cas9 system to suppress IL-1α expression in 4T1 breast cancer cells. Knockout of IL-1α in 4T1 cells modified expression of multiple genes, including downregulation of cytokines and chemokines involved in the recruitment of tumor-associated pro-inflammatory cells. Orthotopical injection of IL-1α knockout (KO) 4T1 cells into BALB/c mice led to a significant decrease in local tumor growth and lung metastases, compared to injection of wild-type 4T1 (4T1/WT) cells. Neutrophils and myeloid-derived suppressor cells were abundant in tumors developing after injection of 4T1/WT cells, whereas more antigen-presenting cells were observed in the tumor microenvironment after injection of IL-1α KO 4T1 cells. This switch correlated with increased infiltration of CD3+CD8+ and NKp46+cells. Engraftment of IL-1α knockout 4T1 cells into immunodeficient NOD.SCID mice resulted in more rapid tumor growth, with increased lung metastasis in comparison to engraftment of 4T1/WT cells. Our results suggest that tumor-associated IL-1α is involved in TNBC progression in mice by modulating the interplay between immunosuppressive pro-inflammatory cells vs. antigen-presenting and cytotoxic cells.

Analysis of the effects of importin α1 on the nuclear translocation of IL-1α in HeLa cells

Interleukin-1α (IL-1α), a cytokine released by necrotic cells, causes sterile inflammation. On the other hand, IL-1α is present in the nucleus and also regulates the expression of many proteins. A protein substrate containing a classical nuclear localization signal (cNLS) typically forms a substrate/importin α/β complex, which is subsequently transported to the nucleus. To the best of our knowledge, no study has directly investigated whether IL-1α-which includes cNLS-is imported into the nucleus in an importin α/β-dependent manner. In this study, we noted that all detected importin α subtypes interacted with IL-1α. In HeLa cells, importin α1-mediated nuclear translocation of IL-1α occurred at steady state and was independent of importin β1. Importin α1 not only was engaged in IL-1α nuclear transport but also concurrently functioned as a molecule that regulated IL-1α protein level in the cell. Furthermore, we discussed the underlying mechanism of IL-1α nuclear translocation by importin α1 based on our findings.

Gene deletion of Interleukin-1α reduces ER stress-induced CHOP expression in macrophages and attenuates the progression of atherosclerosis in apoE-deficient mice

The pathophysiology of atherosclerosis initiation and progression involves many inflammatory cytokines, one of them is interleukin (IL)-1α that has been shown to be secreted by activated macrophages. We have previously shown that IL-1α from bone marrow-derived cells is critical for early atherosclerosis development in mice. It is known that endoplasmic reticulum (ER) stress in macrophages is involved in progression to more advanced atherosclerosis, but it is still unknown whether this effect is mediated through cytokine activation or secretion. We previously demonstrated that IL-1α is required in ER stress-induced activation of inflammatory cytokines in hepatocytes and in the associated induction of steatohepatitis. In the current study, we aimed to examine the potential role of IL-1α in ER stress-induced activation of macrophages, which is relevant to progression of atherosclerosis. First, we demonstrated that IL-1α is required for atherosclerosis development and progression in the apoE knockout (KO) mouse model of atherosclerosis. Next, we showed that ER stress in mouse macrophages results in the protein production and secretion of IL-1α in a dose-dependent manner, and that IL-1α is required in ER stress-induced production of the C/EBP homologous protein (CHOP), a critical step in ER stress-mediated apoptosis. We further demonstrated that IL-1α-dependent CHOP production in macrophages is specifically mediated through the PERK-ATF4 signaling pathway. Altogether, these findings highlight IL-1α as a potential target for prevention and treatment of atherosclerotic cardiovascular disease.

The alarmin interleukin-1α causes preterm birth through the NLRP3 inflammasome

Sterile intra-amniotic inflammation is a clinical condition frequently observed in women with preterm labor and birth, the leading cause of neonatal morbidity and mortality worldwide. Growing evidence suggests that alarmins found in amniotic fluid, such as interleukin (IL)-1α, are central initiators of sterile intra-amniotic inflammation. However, the causal link between elevated intra-amniotic concentrations of IL-1α and preterm birth has yet to be established. Herein, using an animal model of ultrasound-guided intra-amniotic injection of IL-1α, we show that elevated concentrations of IL-1α cause preterm birth and neonatal mortality. Additionally, using immunoblotting techniques and a specific immunoassay, we report that the intra-amniotic administration of IL-1α induces activation of the NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome in the fetal membranes, but not in the decidua, as evidenced by a concomitant increase in the protein levels of NLRP3, active caspase-1, and IL-1β. Lastly, using Nlrp3-/- mice, we demonstrate that the deficiency of this inflammasome sensor molecule reduces the rates of preterm birth and neonatal mortality caused by the intra-amniotic injection of IL-1α. Collectively, these results demonstrate a causal link between elevated IL-1α concentrations in the amniotic cavity and preterm birth as well as adverse neonatal outcomes, a pathological process that is mediated by the NLRP3 inflammasome. These findings shed light on the mechanisms underlying sterile intra-amniotic inflammation and provide further evidence that this clinical condition can potentially be treated by targeting the NLRP3 inflammasome.

Interleukin-1 as Innate Mediator of T Cell Immunity

The three-signal paradigm tries to capture how the innate immune system instructs adaptive immune responses in three well-defined actions: (1) presentation of antigenic peptides in the context of MHC molecules, which allows for a specific T cell response; (2) T cell co-stimulation, which breaks T cell tolerance; and (3) secretion of polarizing cytokines in the priming environment, thereby specializing T cell immunity. The three-signal model provides an empirical framework for innate instruction of adaptive immunity, but mainly discusses STAT-dependent cytokines in T cell activation and differentiation, while the multi-faceted roles of type I IFNs and IL-1 cytokine superfamily members are often neglected. IL-1α and IL-1β are pro-inflammatory cytokines, produced following damage to the host (release of DAMPs) or upon innate recognition of PAMPs. IL-1 activity on both DCs and T cells can further shape the adaptive immune response with variable outcomes. IL-1 signaling in DCs promotes their ability to induce T cell activation, but also direct action of IL-1 on both CD4+ and CD8+ T cells, either alone or in synergy with prototypical polarizing cytokines, influences T cell differentiation under different conditions. The activities of IL-1 form a direct bridge between innate and adaptive immunity and could therefore be clinically translatable in the context of prophylactic and therapeutic strategies to empower the formation of T cell immunity. Understanding the modalities of IL-1 activity during T cell activation thus could hold major implications for rational development of the next generation of vaccine adjuvants.

Nuclear Alarmin Cytokines in Inflammation

Pathogen-associated molecular patterns (PAMPs) are some nonspecific and highly conserved molecular structures of exogenous specific microbial pathogens, whose products can be recognized by pattern recognition receptor (PRR) on innate immune cells and induce an inflammatory response. Under physiological stress, activated or damaged cells might release some endogenous proteins that can also bind to PRR and cause a harmful aseptic inflammatory response. These endogenous proteins were named damage-associated molecular patterns (DAMPs) or alarmins. Indeed, alarmins can also play a beneficial role in the tissue repair in certain environments. Besides, some alarmin cytokines have been reported to have both nuclear and extracellular effects. This group of proteins includes high-mobility group box-1 protein (HMGB1), interleukin (IL)-33, IL-1α, IL-1F7b, and IL-16. In this article, we review the involvement of nuclear alarmins such as HMGB1, IL-33, and IL-1α under physiological state or stress state and suggest a novel activity of these molecules as central initiators in the development of sterile inflammation.

The IL-1 family cytokines and receptors in autoimmune diseases

The role of the cytokines and receptors of the IL-1 family in inflammation is well known. Several cytokines of the family have a powerful inflammatory activity, with IL-1β being the best-characterized factor. The inflammatory activity of IL-1 cytokines is regulated by other factors of the family, including receptor antagonists, soluble receptors and anti-inflammatory cytokines. The causative role of IL-1β is well-established in autoinflammatory diseases, mainly due to gain-of-function mutations in genes encoding the IL-1β-maturing inflammasome. Exaggerated production of IL-1β and IL-18 correlates with disease and disease severity also in several autoimmune and chronic inflammatory and degenerative pathologies, although it is not clear whether they have a causative role or are only involved in the downstream disease symptoms. A better understanding of the pathological role of IL-1 family cytokines in autoimmunity involves a deeper evaluation, in the pathological situations, of the possible anomalies in the feed-back anti-inflammatory mechanisms that in physiological reactions control and dump IL-1-mediated inflammation. Thus, we expect that IL-1 cytokines may be pathogenic only when, in addition to enhanced production, there is a concomitant failure of their control mechanisms. In this review we will examine the current knowledge on the role of IL-1 family cytokines in autoimmune and chronic inflammatory and degenerative diseases, with a particular focus on their endogenous control mechanisms, mainly based on soluble receptors/inhibitors and receptor antagonists. This will allow us to formulate a knowledge-based hypothesis on the involvement of IL-1 cytokines in the pathogenesis vs. the clinical features of these diseases.

Interleukin-1α associates with the tumor suppressor p53 following DNA damage

Interleukin-1α (IL-1α) is a dual-function proinflammatory mediator. In addition to its role in the canonical IL-1 signaling pathway, which employs membrane-bound receptors, a growing body of evidence shows that IL-1α has some additional intracellular functions. We identified the interaction of IL-1α with the tumor suppressor p53 in the nuclei and cytoplasm of both malignant and noncancerous mammalian cell lines using immunoprecipitation and the in situ proximity ligation assay (PLA). This interaction was enhanced by treatment with the antineoplastic drug etoposide, which suggests a role for the IL-1α•p53 interaction in genotoxic stress.

Identifying the Translatome of Mouse NEBD-Stage Oocytes via SSP-Profiling; A Novel Polysome Fractionation Method

Meiotic maturation of oocyte relies on pre-synthesised maternal mRNA, the translation of which is highly coordinated in space and time. Here, we provide a detailed polysome profiling protocol that demonstrates a combination of the sucrose gradient ultracentrifugation in small SW55Ti tubes with the qRT-PCR-based quantification of 18S and 28S rRNAs in fractionated polysome profile. This newly optimised method, named Scarce Sample Polysome Profiling (SSP-profiling), is suitable for both scarce and conventional sample sizes and is compatible with downstream RNA-seq to identify polysome associated transcripts. Utilising SSP-profiling we have assayed the translatome of mouse oocytes at the onset of nuclear envelope breakdown (NEBD)—a developmental point, the study of which is important for furthering our understanding of the molecular mechanisms leading to oocyte aneuploidy. Our analyses identified 1847 transcripts with moderate to strong polysome occupancy, including abundantly represented mRNAs encoding mitochondrial and ribosomal proteins, proteasomal components, glycolytic and amino acids synthetic enzymes, proteins involved in cytoskeleton organization plus RNA-binding and translation initiation factors. In addition to transcripts encoding known players of meiotic progression, we also identified several mRNAs encoding proteins of unknown function. Polysome profiles generated using SSP-profiling were more than comparable to those developed using existing conventional approaches, being demonstrably superior in their resolution, reproducibility, versatility, speed of derivation and downstream protocol applicability.

Impact of Nuclear Interleukin-1 Alpha and EGFR Expression on Recurrence and Survival Outcomes in Oral Squamous Cell Carcinomas

Interleukin-1 alpha (IL-1α) is a pleiotropic cytokine involved in inflammation and immune response and is upregulated in many solid tumors including head and neck squamous cell carcinomas. Although IL-1α expression is generally associated with poor prognosis, the implications of the subcellular localization of IL-1α expression in patient outcomes are poorly understood. This study is aimed at investigating the prognostic value of nuclear and cytoplasmic immunohistochemical IL-1α expression in oral squamous cell carcinomas (OSCCs). Tissue microarrays containing 146 OSCCs were analyzed for IL-1α and epidermal growth factor receptor (EGFR) expression by immunohistochemistry. IL-1α and EGFR expression scores were correlated with clinicopathological parameters and survival outcomes. IL-1α expression was observed in the nuclear and/or cytoplasmic compartments in 98% of evaluable tumors and 78% of tumors expressed IL-1α in both compartments. There were no differences observed in overall survival or progression-free survival between high, moderate, or negative IL-1α nuclear/cytoplasmic expression scores. When IL-1α nuclear/cytoplasmic expression scores were stratified by positive or negative EGFR expression, tumors with a combined EGFR-positive and high nuclear IL-1α expression profile were significantly more likely to possess perineural invasion and were significantly associated with a high risk of tumor recurrence and worse progression-free survival compared to all other EGFR and combined IL-1α/EGFR expression profiles. Altogether, nuclear IL-1α expression may enhance the prognostic value of EGFR in OSCC and warrants further study as a prognostic biomarker for recurrence.

Uncoupling the Senescence-Associated Secretory Phenotype from Cell Cycle Exit via Interleukin-1 Inactivation Unveils Its Protumorigenic Role

Cellular senescence has emerged as a potent tumor suppressor mechanism in numerous human neoplasias. Senescent cells secrete a distinct set of factors, collectively termed the senescence-associated secretory phenotype (SASP), which has been postulated to carry both pro- and antitumorigenic properties depending on tissue context. However, the in vivo effect of the SASP is poorly understood due to the difficulty of studying the SASP independently of other senescence-associated phenotypes. Here, we report that disruption of the interleukin-1 (IL-1) pathway completely uncouples the SASP from other senescence-associated phenotypes such as cell cycle exit. Transcriptome profiling of IL-1 receptor (IL-1R)-depleted senescent cells indicates that IL-1 controls the late arm of the senescence secretome, which consists of proinflammatory cytokines induced by NF-κB. Our data suggest that both IL-1α and IL-1β signal through IL-1R to upregulate the SASP in a cooperative manner. Finally, we show that IL-1α inactivation impairs tumor progression and immune cell infiltration without affecting cell cycle arrest in a mouse model of pancreatic cancer, highlighting the protumorigenic property of the IL-1-dependent SASP in this context. These findings provide novel insight into the therapeutic potential of targeting the IL-1 pathway in inflammatory cancers.

Redefining the ancestral origins of the interleukin-1 superfamily

The interleukin-1 (IL-1) receptor and ligand families are components of the immune system. Knowledge of their evolutionary history is essential to understand their function. Using chromosomal anatomy and sequence similarity, we show that IL-1 receptor family members are related and nine members are likely formed from duplication and modification of a proto-IL-1R1 receptor. The IL-1 ligands have a different evolutionary history. The first proto-IL-1β gene coincided with proto-IL-1R1 and duplication events resulted in the majority of IL-1 ligand family members. However, large evolutionary distances are observed for IL-1α, IL-18 and IL-33 proteins. Further analysis show that IL-33 and IL-18 have poor sequence similarity and no chromosomal evidence of common ancestry with the IL-1β cluster and therefore should not be included in the IL-1 ligand ancestral family. IL-1α formed from the duplication of IL-1β, and moonlighting functions of pro-IL-1α acted as divergent selection pressures for the observed sequence dissimilarity.

Function and regulation of IL-1α in inflammatory diseases and cancer

The interleukin (IL)-1 family of cytokines is currently comprised of 11 members that have pleiotropic functions in inflammation and cancer. IL-1α and IL-1β were the first members of the IL-1 family to be described, and both signal via the same receptor, IL-1R. Over the last decade, much progress has been made in our understanding of biogenesis of IL-1β and its functions in human diseases. Studies from our laboratory and others have highlighted the critical role of nod-like receptors (NLRs) and multi-protein complexes known as inflammasomes in the regulation of IL-1β maturation. Recent studies have increased our appreciation of the role played by IL-1α in inflammatory diseases and cancer. However, the mechanisms that regulate the production of IL-1α and its bioavailability are relatively understudied. In this review, we summarize the distinctive roles played by IL-1α in inflammatory diseases and cancer. We also discuss our current knowledge about the mechanisms that control IL-1α biogenesis and activity, and the major unanswered questions in its biology.

Propiece IL-1α facilitates the growth of acute T-lymphocytic leukemia cells through the activation of NF-κB and SP1

Interleukin 1α (IL-1α) is a pro-inflammatory cytokine that possesses multiple immune-regulatory functions. It is mainly expressed as the cell-associated form and not actively secreted in healthy tissues. The intracellular IL-1α has been shown to be a chromatin-associated cytokine and can affect transcription. There are spontaneous expressions of IL-1α in acute lymphocytic leukemia (ALL) blasts. However, the role of nuclear-localized IL-1α in ALL is not clear. Here we showed that overexpression of the nuclear form of IL-1α (propiece IL-1α) could promote proliferation and reduce apoptosis of T-ALL cells. It also increased the ALL cells’ resistance to low serum concentration and cisplatin treatment. In vivo growth of the T-ALL cells overexpressing the propiece IL-1α were also enhanced compared to the control cells. Microarray analysis revealed many changes in gene expressions related to cell growth and stress, including a group of metallothionein genes. Moreover, the expressions of transcription factors, NFκB and specific protein 1 (SP1), were up-regulated by propiece IL-1α. Propiece IL-1α could bind to the promoter of SP1 and a binding sequence logo was identified. Therefore, nuclear expression of propiece IL-1α can facilitate the growth of T-ALL cells possibly through the activation of NFκB and SP1.

Distinct recruitment of human eIF4E isoforms to processing bodies and stress granules

BACKGROUND

Eukaryotic translation initiation factor 4E (eIF4E) plays a pivotal role in the control of cap-dependent translation initiation, modulates the fate of specific mRNAs, occurs in processing bodies (PBs) and is required for formation of stress granules (SGs). In this study, we focused on the subcellular localization of a representative compendium of eIF4E protein isoforms, particularly on the less studied members of the human eIF4E protein family, eIF4E2 and eIF4E3.

RESULTS

We showed that unlike eIF4E1, its less studied isoform eIF4E3_A, encoded by human chromosome 3, localized to stress granules but not PBs upon both heat shock and arsenite stress. Furthermore, we found that eIF4E3_A interacts with human translation initiation factors eIF4G1, eIF4G3 and PABP1 in vivo and sediments into the same fractions as canonical eIF4E1 during polysome analysis in sucrose gradients. Contrary to this finding, the truncated human eIF4E3 isoform, eIF4E3_B, showed no localization to SGs and no binding to eIF4G. We also highlighted that eIF4E2 may exhibit distinct functions under different stresses as it readily localizes to P-bodies during arsenite and heat stresses, whereas it is redirected to stress granules only upon heat shock. We extended our study to a number of protein variants, arising from alternative mRNA splicing, of each of the three eIF4E isoforms. Our results surprisingly uncovered differences in the ability of eIF4E1_1 and eIF4E1_3 to form stress granules in response to cellular stresses.

CONCLUSION

Our comparison of all three human eIF4E isoforms and their protein variants enriches the intriguing spectrum of roles attributed to the eukaryotic initiation translation factors of the 4E family, which exhibit a distinctive localization within different RNA granules under different stresses. The localization of eIF4E3_A to stress granules, but not to processing bodies, along with its binding to eIF4G and PABP1 suggests a role of human eIF4E3_A in translation initiation rather than its involvement in a translational repression and mRNA decay and turnover. The localization of eIF4E2 to stress granules under heat shock but not arsenite stress indicates its distinct function in cellular response to these stresses and points to the variable protein content of SGs as a consequence of different stress insults.

HMGB1, IL-1α, IL-33 and S100 proteins: dual-function alarmins

Our immune system is based on the close collaboration of the innate and adaptive immune systems for the rapid detection of any threats to the host. Recognition of pathogen-derived molecules is entrusted to specific germline-encoded signaling receptors. The same receptors have now also emerged as efficient detectors of misplaced or altered self-molecules that signal tissue damage and cell death following, for example, disruption of the blood supply and subsequent hypoxia. Many types of endogenous molecules have been shown to provoke such sterile inflammatory states when released from dying cells. However, a group of proteins referred to as alarmins have both intracellular and extracellular functions which have been the subject of intense research. Indeed, alarmins can either exert beneficial cell housekeeping functions, leading to tissue repair, or provoke deleterious uncontrolled inflammation. This group of proteins includes the high-mobility group box 1 protein (HMGB1), interleukin (IL)-1α, IL-33 and the Ca²⁺-binding S100 proteins. These dual-function proteins share conserved regulatory mechanisms, such as secretory routes, post-translational modifications and enzymatic processing, that govern their extracellular functions in time and space. Release of alarmins from mesenchymal cells is a highly relevant mechanism by which immune cells can be alerted of tissue damage, and alarmins play a key role in the development of acute or chronic inflammatory diseases and in cancer development.

Interleukin 1α and the inflammatory process

Inflammation occurs after disruption of tissue homeostasis by cell stress, injury or infection and ultimately involves the recruitment and retention of cells of hematopoietic origin, which arrive at the affected sites to resolve damage and initiate repair. Interleukin 1α (IL-1α) and IL-1β are equally potent inflammatory cytokines that activate the inflammatory process, and their deregulated signaling causes devastating diseases manifested by severe acute or chronic inflammation. Although much attention has been given to understanding the biogenesis of IL-1β, the biogenesis of IL-1α and its distinctive role in the inflammatory process remain poorly defined. In this review we examine key aspects of IL-1α biology and regulation and discuss its emerging importance in the initiation and maintenance of inflammation that underlie the pathology of many human diseases.

Interleukin-1α deficiency attenuates endoplasmic reticulum stress-induced liver damage and CHOP expression in mice

BACKGROUND & AIMS

ER stress promotes liver fat accumulation and induction of inflammatory cytokines, which contribute to the development of steatohepatitis. Unresolved ER stress upregulates the pro-apoptotic CHOP. IL-1α is localized to the nucleus in apoptotic cells, but is released when these cells become necrotic and induce sterile inflammation. We investigated whether IL-1α is involved in ER stress-induced apoptosis and steatohepatitis.

METHODS

We employed WT and IL-1α-deficient mice to study the role of IL-1α in ER stress-induced steatohepatitis.

RESULTS

Liver CHOP mRNA was induced in a time dependent fashion in the atherogenic diet-induced steatohepatitis model, and was twofold lower in IL-1α deficient compared to WT mice. In the ER stress-driven steatohepatitis model, IL-1α deficiency decreased the elevation in serum ALT levels, the number of apoptotic cells (measured as caspase-3-positive hepatocytes), and the expression of IL-1β, IL-6, TNFα, and CHOP, with no effect on the degree of fatty liver formation. IL-1α was upregulated in ER-stressed-macrophages and the protein was localized to the nucleus. IL-1β mRNA and CHOP mRNA and protein levels were lower in ER-stressed-macrophages from IL-1α deficient compared to WT mice. ER stress induced the expression of IL-1α and IL-1β also in mouse primary hepatocytes. Recombinant IL-1α treatment in hepatocytes did not affect CHOP expression but upregulated both IL-1α and IL-1β mRNA levels.

CONCLUSION

We show that IL-1α is upregulated in response to ER stress and IL-1α deficiency reduces ER stress-induced CHOP expression, apoptosis and steatohepatitis. As a dual function cytokine, IL-1α may contribute to the induction of CHOP intracellularly, while IL-1α released from necrotic cells accelerates steatohepatitis via induction of inflammatory cytokines by neighboring cells.

Interleukin-1α

Although the IL-1α molecule has long been recognized, information about its distinct role in various diseases is limited, since most clinical studies have focused on the role of IL-1β. Despite triggering the same IL-1 receptor as does IL-1β, there is, however, a distinct role for IL-1α in some inflammatory diseases. IL-1α is a unique cytokine since it is constitutively present intracellularly in nearly all resting non-hematopoietic cells in health as well as being up-regulated during hypoxia. During cell necrosis, IL-1α functions as an alarm molecule and thus plays a critical role early in inflammation. Following its release from damage tissue cells, IL-1α mediates neutrophil recruitment to the site of injury, inducing IL-1β, other cytokines and chemokines from surrounding resident cells. Another unique attribute of IL-1α is its nuclear localization sequence present in the N-terminal half of the precursor termed the propiece. The IL-1α propiece translocates into the nucleus and participates in the regulation of transcription. Therefore, IL-1α, like IL-1 family members IL-33 and IL-37, is a 'dual-function' cytokine binding to chromatin as well as to its cell surface receptor. Some cancer cells can express membrane IL-1α, which can increase immunogenicity of tumor cells and serve in anti-tumor immune surveillance and tumor regression. However, in the tumor microenvironment, precursor IL-1α released from dying tumor cells is inflammatory and, similar to IL-1β, increases tumor invasiveness and angiogenesis.