Long Interleukin-22 Binding Protein Isoform-1 Is an Intracellular Activator of the Unfolded Protein Response

Targeted splicing therapy: new strategies for colorectal cancer

RNA splicing is the process of forming mature mRNA, which is an essential phase necessary for gene expression and controls many aspects of cell proliferation, survival, and differentiation. Abnormal gene-splicing events are closely related to the development of tumors, and the generation of oncogenic isoform in splicing can promote tumor progression. As a main process of tumor-specific splicing variants, alternative splicing (AS) can promote tumor progression by increasing the production of oncogenic splicing isoforms and/or reducing the production of normal splicing isoforms. This is the focus of current research on the regulation of aberrant tumor splicing. So far, AS has been found to be associated with various aspects of tumor biology, including cell proliferation and invasion, resistance to apoptosis, and sensitivity to different chemotherapeutic drugs. This article will review the abnormal splicing events in colorectal cancer (CRC), especially the tumor-associated splicing variants arising from AS, aiming to offer an insight into CRC-targeted splicing therapy.

IL-22BP production is heterogeneously distributed in Crohn’s disease

Crohn’s disease (CD), a form of inflammatory bowel disease (IBD), is characterized by impaired epithelial barrier functions and dysregulated mucosal immune responses. IL-22 binding protein (IL-22BP) is a soluble inhibitor regulating IL-22 bioactivity, a cytokine proposed to play protective roles during CD. We and others have shown that IL-22BP is produced in IBD inflamed tissues, hence suggesting a role in CD. In this work, we extended the characterization of IL-22BP production and distribution in CD tissues by applying enzyme-linked immunosorbent assays to supernatants obtained from the culture of endoscopic biopsies of patients, and reverse transcription-quantitative polymerase chain reaction on sorted immune cell subsets. We reveal that IL-22BP levels are higher in inflamed ileums than colons. We observe that in a cell-intrinsic fashion, populations of mononuclear phagocytes and eosinophils express IL-22BP at the highest levels in comparison to other sources of T cells. We suggest the enrichment of intestinal eosinophils could explain higher IL-22BP levels in the ileum. In inflamed colon, we reveal the presence of increased IL-22/IL22BP ratios compared to controls, and a strong correlation between IL-22BP and CCL24. We identify monocyte-derived dendritic cells (moDC) as a cellular subtype co-expressing both cytokines and validate our finding using in vitro culture systems. We also show that retinoic acid induces the secretion of both IL-22BP and CCL24 by moDC. Finally, we report on higher IL-22BP levels in active smokers. In conclusion, our work provides new information relevant to therapeutic strategies modulating IL-22 bioactivity in CD, especially in the context of disease location.

Genomic Multiple Sclerosis Risk Variants Modulate the Expression of the ANKRD55-IL6ST Gene Region in Immature Dendritic Cells

Intronic single-nucleotide polymorphisms (SNPs) in the ANKRD55 gene are associated with the risk for multiple sclerosis (MS) and rheumatoid arthritis by genome-wide association studies (GWAS). The risk alleles have been linked to higher expression levels of ANKRD55 and the neighboring IL6ST (gp130) gene in CD4+ T lymphocytes of healthy controls. The biological function of ANKRD55, its role in the immune system, and cellular sources of expression other than lymphocytes remain uncharacterized. Here, we show that monocytes gain capacity to express ANKRD55 during differentiation in immature monocyte-derived dendritic cells (moDCs) in the presence of interleukin (IL)-4/granulocyte-macrophage colony-stimulating factor (GM-CSF). ANKRD55 expression levels are further enhanced by retinoic acid agonist AM580 but downregulated following maturation with interferon (IFN)-γ and lipopolysaccharide (LPS). ANKRD55 was detected in the nucleus of moDC in nuclear speckles. We also analyzed the adjacent IL6ST, IL31RA, and SLC38A9 genes. Of note, in healthy controls, MS risk SNP genotype influenced ANKRD55 and IL6ST expression in immature moDC in opposite directions to that in CD4+ T cells. This effect was stronger for a partially correlated SNP, rs13186299, that is located, similar to the main MS risk SNPs, in an ANKRD55 intron. Upon analysis in MS patients, the main GWAS MS risk SNP rs7731626 was associated with ANKRD55 expression levels in CD4+ T cells. MoDC-specific ANKRD55 and IL6ST mRNA levels showed significant differences according to the clinical form of the disease, but, in contrast to healthy controls, were not influenced by genotype. We also measured serum sgp130 levels, which were found to be higher in homozygotes of the protective allele of rs7731626. Our study characterizes ANKRD55 expression in moDC and indicates monocyte-to-dendritic cell (Mo-DC) differentiation as a process potentially influenced by MS risk SNPs.

Procyanidin B2 Alleviates Palmitic Acid-Induced Injury in HepG2 Cells via Endoplasmic Reticulum Stress Pathway

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome featuring ectopic lipid accumulation in hepatocytes. NAFLD has been a severe threat to humans with a global prevalence of over 25% yet no approved drugs for the treatment to date. Previous studies showed that procyanidin B2 (PCB2), an active ingredient from herbal cinnamon, has an excellent hepatoprotective effect; however, the mechanism remains inconclusive. The present study aimed to investigate the protective effect and underlying mechanism of PCB2 on PA-induced cellular injury in human hepatoma HepG2 cells. Our results showed that PA-induced oxidative stress, calcium disequilibrium, and subsequent endoplasmic reticulum stress (ERS) mediated cellular injury, with elevated protein levels of GRP78, GRP94, CHOP, and hyperphosphorylation of PERK and IRE1α as well as the increased ratio of Bax/Bcl-2, which was restored by PCB2 in a concentration-dependent manner, proving the excellent antiapoptosis effect. In addition, 4-phenylbutyric acid (4-PBA), the ER stress inhibitor, increased cell viability and decreased protein levels of GRP78 and CHOP, which is similar to PCB2, and thapsigargin (TG), the ER stress agonist, exhibited conversely meanwhile partly counteracted the hepatic protection of PCB2. What is more, upregulated protein expression of p-IKKα/β, p-NF-κB p65, NLRP3, cleaved caspase 1, and mature IL-1β occurred in HepG2 cells in response to PA stress while rescued with the PCB2 intervention. In conclusion, our study demonstrated that PA induces ERS in HepG2 cells and subsequently activates downstream NLRP3 inflammasome-mediated cellular injury, while PCB2 inhibits NLRP3/caspase 1/IL-1β pathway, inflammation, and apoptosis with the presence of ERS, thereby promoting cell survival, which may provide pharmacological evidence for clinical approaches on NAFLD.

The Pathogenic Roles of IL-22 in Colitis: Its Transcription Regulation by Musculin in T Helper Subsets and Innate Lymphoid Cells

IL-22 plays a crucial role in promoting inflammation, antimicrobial immunity and tissue repair at barrier surfaces. The role of IL-22 in colitis is still controversial: while IL-22 has a protective effect on gut epithelium in acute injuries, it also enhances colitis in a context-dependent manner. Here, we summarize the Yin and Yang of IL-22 in colitis. Particularly, we emphasize the role of innate lymphoid cells (ILCs) in IL-22 production and regulation. A previously underappreciated transcription factor, Musculin (MSC), has been recently identified to be expressed in not only Th17 cells, but also RORγt+/Id2+ IL-22-producing group 3 ILCs in the gut of naïve mice. We hypothesize that the co-expression and interaction of MSC with the key transcription repressor Id2 in developing lymphoid cells (e.g., in LTi cells) and ILC precursors might fine tune the developmental programs or regulate the plasticity of adaptive Th subset and innate ILCs. The much-elevated expression of IL-22 in MSC-/- ILC3s suggests that MSC may function as: 1) a transcription suppressor for cytokines, particularly for IL-22, and/or 2) a gatekeeper for specific lineages of Th cells and innate ILCs as well. Amelioration of colitis symptoms in MSC-/- mice by IL-22-blocking agent IL-22BP-Fc suggests a counterintuitive pathogenic role of IL-22 in the absence of MSC as a checkpoint. The theory that exuberant production of IL-22 under pathological conditions (e.g., in human inflammatory bowel disease, IBD) may cause epithelial inflammation due to endoplasmic reticulum (ER) stress response is worth further investigation. Rheostatic regulation of IL-22 may be of therapeutic value to restore homeostatic balance and promote intestinal health in human colitis.

IL-22 Binding Protein (IL-22BP) in the Regulation of IL-22 Biology

Cytokines are powerful mediators of inflammation. Consequently, their potency is regulated in many ways to protect the host. Several cytokines, including IL-22, have coordinating binding proteins or soluble receptors that bind to the cytokine, block the interaction with the cellular receptor, and thus prevent cellular signaling. IL-22 is a critical cytokine in the modulation of tissue responses during inflammation and is highly upregulated in many chronic inflammatory disease patients, including those with psoriasis, rheumatoid arthritis, and inflammatory bowel disease (IBD). In healthy individuals, low levels of IL-22 are secreted by immune cells, mainly in the gastrointestinal (GI) tract. However, much of this IL-22 is likely not biologically active due to the high levels of IL-22 binding protein (IL-22BP) produced by intestinal dendritic cells (DCs). IL-22BP is a soluble receptor homolog that binds to IL-22 with greater affinity than the membrane spanning receptor. Much is known regarding the regulation and function of IL-22 in health and disease. However, less is known about IL-22BP. In this review, we will focus on IL-22BP, including its regulation, role in IL-22 biology and inflammation, and promise as a therapeutic. IL-22 can be protective or pathogenic, depending on the context of inflammation. IL-22BP also has divergent roles. Ongoing and forthcoming studies will expand our knowledge of IL-22BP and IL-22 biology, and suggest that IL-22BP holds promise as a way to regulate IL-22 biology in patients with chronic inflammatory disease.

The Rare IL22RA2 Signal Peptide Coding Variant rs28385692 Decreases Secretion of IL-22BP Isoform-1, -2 and -3 and Is Associated with Risk for Multiple Sclerosis

The IL22RA2 locus is associated with risk for multiple sclerosis (MS) but causative variants are yet to be determined. In a single nucleotide polymorphism (SNP) screen of this locus in a Basque population, rs28385692, a rare coding variant substituting Leu for Pro at position 16 emerged significantly (p = 0.02). This variant is located in the signal peptide (SP) shared by the three secreted protein isoforms produced by IL22RA2 (IL-22 binding protein-1(IL-22BPi1), IL-22BPi2 and IL-22BPi3). Genotyping was extended to a Europe-wide case-control dataset and yielded high significance in the full dataset (p = 3.17 × 10^-4). Importantly, logistic regression analyses conditioning on the main known MS-associated SNP at this locus, rs17066096, revealed that this association was independent from the primary association signal in the full case-control dataset. In silico analysis predicted both disruption of the alpha helix of the H-region of the SP and decreased hydrophobicity of this region, ultimately affecting the SP cleavage site. We tested the effect of the p.Leu16Pro variant on the secretion of IL-22BPi1, IL-22BPi2 and IL-22BPi3 and observed that the Pro16 risk allele significantly lowers secretion levels of each of the isoforms to around 50%-60% in comparison to the Leu16 reference allele. Thus, our study suggests that genetically coded decreased levels of IL-22BP isoforms are associated with augmented risk for MS.

Targeting the IL-22/IL-22BP axis enhances tight junctions and reduces inflammation during influenza infection

The seasonal burden of influenza coupled with the pandemic outbreaks of more pathogenic strains underscore a critical need to understand the pathophysiology of influenza injury in the lung. Interleukin-22 (IL-22) is a promising cytokine that is critical in protecting the lung during infection. This cytokine is strongly regulated by the soluble receptor IL-22-binding protein (IL-22BP), which is constitutively expressed in the lungs where it inhibits IL-22 activity. The IL-22/IL-22BP axis is thought to prevent chronic exposure of epithelial cells to IL-22. However, the importance of this axis is not understood during an infection such as influenza. Here we demonstrate through the use of IL-22BP-knockout mice (il-22ra2-/-) that a pro-IL-22 environment reduces pulmonary inflammation during H1N1 (PR8/34 H1N1) infection and protects the lung by promoting tight junction formation. We confirmed these results in normal human bronchial epithelial cells in vitro demonstrating improved membrane resistance and induction of the tight junction proteins Cldn4, Tjp1, and Tjp2. Importantly, we show that administering recombinant IL-22 in vivo reduces inflammation and fluid leak into the lung. Taken together, our results demonstrate the IL-22/IL-22BP axis is a potential targetable pathway for reducing influenza-induced pneumonia.

IL-18/IL-18BP and IL-22/IL-22BP: Two interrelated couples with therapeutic potential

Interleukin (IL)-18 and IL-22 are key components of cytokine networks that play a decisive role in (pathological) inflammation, host defense, and tissue regeneration. Tight regulation of cytokine-driven signaling, inflammation, and immunoactivation is supposed to enable nullification of a given deleterious trigger without mediating overwhelming collateral tissue damage or even activating a cancerous face of regeneration. In fact, feedback regulation by specific cytokine opponents is regarded as a major means by which the immune system is kept in balance. Herein, we shine a light on the interplay between IL-18 and IL-22 and their opponents IL-18 binding protein (IL-18BP) and IL-22BP in order to provide integrated information on their biology, pathophysiological significance, and prospect as targets and/or instruments of therapeutic intervention.

Pharmacological Targeting of the ER-Resident Chaperones GRP94 or Cyclophilin B Induces Secretion of IL-22 Binding Protein Isoform-1 (IL-22BPi1)

Of the three interleukin-22 binding protein (IL-22BP) isoforms produced by the human IL22RA2 gene, IL-22BPi2 and IL-22BPi3 are capable of neutralizing IL-22. The longest isoform, IL-22BPi1, does not bind IL-22, is poorly secreted, and its retention within the endoplasmic reticulum (ER) is associated with induction of an unfolded protein response (UPR). Therapeutic modulation of IL-22BPi2 and IL-22BPi3 production may be beneficial in IL-22-dependent disorders. Recently, we identified the ER chaperones GRP94 and cyclophilin B in the interactomes of both IL-22BPi1 and IL-22BPi2. In this study, we investigated whether secretion of the IL-22BP isoforms could be modulated by pharmacological targeting of GRP94 and cyclophilin B, either by means of geldanamycin, that binds to the ADP/ATP pocket shared by HSP90 paralogs, or by cyclosporin A, which causes depletion of ER cyclophilin B levels through secretion. We found that geldanamycin and its analogs did not influence secretion of IL-22BPi2 or IL-22BPi3, but significantly enhanced intracellular and secreted levels of IL-22BPi1. The secreted protein was heterogeneously glycosylated, with both high-mannose and complex-type glycoforms present. In addition, cyclosporine A augmented the secretion of IL-22BPi1 and reduced that of IL-22BPi2 and IL-22BPi3. Our data indicate that the ATPase activity of GRP94 and cyclophilin B are instrumental in ER sequestration and degradation of IL-22BPi1, and that blocking these factors mobilizes IL-22BPi1 toward the secretory route.