Marked cell-type-specific differences in glycosylation of human interleukin-6

Targeting IL-6 by engineered Lactococcus lactis via surface-displayed affibody

BACKGROUND

Dysregulated production of interleukin (IL)-6 is implicated in the pathology of inflammatory bowel disease (IBD). Neutralization of IL-6 in the gut by safe probiotic bacteria may help alleviate intestinal inflammation. Here, we developed Lactococcus lactis with potent and selective IL-6 binding activity by displaying IL-6-specific affibody on its surface.

RESULTS

Anti-IL-6 affibody (designated as ZIL) was expressed in fusion with lactococcal secretion peptide Usp45 and anchoring protein AcmA. A high amount of ZIL fusion protein was detected on bacterial surface, and its functionality was validated by confocal microscopy and flow cytometry. Removal of IL-6 from the surrounding medium by the engineered L. lactis was evaluated using enzyme-linked immunosorbent assay. ZIL-displaying L. lactis sequestered recombinant human IL-6 from the solution in a concentration-dependent manner by up to 99% and showed no binding to other pro-inflammatory cytokines, thus proving to be highly specific for IL-6. The removal was equally efficient across different IL-6 concentrations (150-1200 pg/mL) that were found to be clinically relevant in IBD patients. The ability of engineered bacteria to capture IL-6 from cell culture supernatant was assessed using immunostimulated human monocytic cell lines (THP-1 and U-937) differentiated into macrophage-like cells. ZIL-displaying L. lactis reduced the content of IL-6 in the supernatants of both cell lines in a concentration-dependent manner by up to 94%. Dose response analysis showed that bacterial cell concentrations of 10⁷ and 10⁹ CFU/mL (colony forming units per mL) were required for half-maximal removal of recombinant and macrophage-derived IL-6, respectively.

CONCLUSION

The ability of ZIL-displaying L. lactis to bind pathological concentrations of IL-6 at common bacterial doses suggests physiological significance.

Glycosylation as a key parameter in the design of nucleic acid vaccines

Vaccine-induced immunity is expected to target the native antigens expressed by the pathogens. Therefore, it is highly important to generate vaccine antigens that are immunologically indistinguishable from the native antigens. Nucleic acid vaccines, comprised of DNA, mRNA, or recombinant viral vector vaccines, introduce the genetic material encoding the antigenic protein for the host to express. Because these proteins will undergo host posttranslational modifications, host glycosylation can potentially alter the structure and immunological efficacy of the antigen. In this review, we discuss the potential impact of host protein glycosylation on the immune responses generated by nucleic acid vaccines against bacterial and viral pathogens.

Interleukin-6 at the Host-Tumor Interface: STAT3 in Biomolecular Condensates in Cancer Cells

It was recognized over 30 years ago that the polyfunctional cytokine interleukin-6 (IL-6) was an almost invariant presence at the host-tumor interface. The IL-6 in the tumor microenvironment was produced either by the cancer cell or by host stromal cells, or by tumor-infiltrating immune cells, or all of them. IL-6 effects in this context included local changes in tumor cell-cell and cell-substrate adhesion, enhanced motility, epithelial to mesenchymal transformation (EMT), and changes in cell proliferation rates in both solid tumors as well as hematologic dyscrasias. Locally produced IL-6 enhanced cancer-targeting functions of tumor-infiltrating macrophages and immune cells. Additionally, the sex-biased phenotype of certain cancers [e.g., hepatocellular carcinoma (HCC) which is 3-5-fold more common in men] was related to the inhibition of macrophage-derived IL-6 production by estradiol-17β (E2). In many circumstances, locally produced IL-6 reached the peripheral circulation and elicited systemic effects such as cachexia and paraneoplastic syndrome (including fever, increased erythrocyte sedimentation rate, increased levels of C-reactive protein in serum, hypoalbuminemia). This review highlights the EMT produced by IL-6 in cancer cells, as well as mechanisms underlying sex bias in HCC, enhanced IL-6 expression in cancer cells resulting from mutations in p53, consequent alterations in STAT3 transcriptional signaling, and the newer understanding of STAT3 nuclear bodies in the cancer cell as phase-separated biomolecular condensates and membraneless organelles (MLOs). Moreover, the perplexing issue of discrepant measurements of IL-6 in human circulation using different assays, especially in patients undergoing immunotherapy, is discussed. Additionally, the paradoxical chaperone (enhancing) effect of anti-IL-6 “neutralizing” antibodies on IL-6 in vivo and consequent limitations of immunotherapy using anti-IL-6 mAb is considered.

Hidden Relationships between N-Glycosylation and Disulfide Bonds in Individual Proteins

N-Glycosylation (NG) and disulfide bonds (DBs) are two prevalent co/post-translational modifications (PTMs) that are often conserved and coexist in membrane and secreted proteins involved in a large number of diseases. Both in the past and in recent times, the enzymes and chaperones regulating these PTMs have been constantly discovered to directly interact with each other or colocalize in the ER. However, beyond a few model proteins, how such cooperation affects N-glycan modification and disulfide bonding at selective sites in individual proteins is largely unknown. Here, we reviewed the literature to discover the current status in understanding the relationships between NG and DBs in individual proteins. Our results showed that more than 2700 human proteins carry both PTMs, and fewer than 2% of them have been investigated in the associations between NG and DBs. We summarized both these proteins with the reported relationships in the two PTMs and the tools used to discover the relationships. We hope that, by exposing this largely understudied field, more investigations can be encouraged to unveil the hidden relationships of NG and DBs in the majority of membranes and secreted proteins for pathophysiological understanding and biotherapeutic development.

Elucidating Proteoform Dynamics Underlying the Senescence Associated Secretory Phenotype

Primary diploid cells exit the cell cycle in response to exogenous stress or oncogene activation through a process known as cellular senescence. This cell-autonomous tumor-suppressive mechanism is also a major mechanism operative in organismal aging. To date, temporal aspects of senescence remain understudied. Therefore, we use quantitative proteomics to investigate changes following forced HRAS^G12V expression and induction of senescence across 1 week in normal diploid fibroblasts. We demonstrate that global intracellular proteomic changes correlate with the emergence of the senescence-associated secretory phenotype and the switch to robust cell cycle exit. The senescence secretome reinforces cell cycle exit, yet is largely detrimental to tissue homeostasis. Previous studies of secretomes rely on ELISA, bottom-up proteomics or RNA-seq. To date, no study to date has examined the proteoform complexity of secretomes to elucidate isoform-specific, post-translational modifications or regulated cleavage of signal peptides. Therefore, we use a quantitative top-down proteomics approach to define the molecular complexity of secreted proteins <30 kDa. We identify multiple forms of immune regulators with known activities and affinities such as distinct forms of interleukin-8, as well as GROα and HMGA1, and temporally resolve secreted proteoform dynamics. Together, our work demonstrates the complexity of the secretome past individual protein accessions and provides motivation for further proteoform-resolved measurements of the secretome.

Mice lacking liver-specific β-catenin develop steatohepatitis and fibrosis after iron overload

BACKGROUND & AIMS

Iron overload disorders such as hereditary hemochromatosis and iron loading anemias are a common cause of morbidity from liver diseases and increase risk of hepatic fibrosis and hepatocellular carcinoma (HCC). Treatment options for iron-induced damage are limited, partly because there is lack of animal models of human disease. Therefore, we investigated the effect of iron overload in liver-specific β-catenin knockout mice (KO), which are susceptible to injury, fibrosis and tumorigenesis following chemical carcinogen exposure.

METHODS

Iron overload diet was administered to KO and littermate control (CON) mice for various times. To ameliorate an oxidant-mediated component of tissue injury, N-Acetyl-L-(+)-cysteine (NAC) was added to drinking water of mice on iron overload diet.

RESULTS

KO on iron diet (KO +Fe) exhibited remarkable inflammation, followed by steatosis, oxidative stress, fibrosis, regenerating nodules and occurrence of occasional HCC. Increased injury in KO +Fe was associated with activated protein kinase B (AKT), ERK, and NF-κB, along with reappearance of β-catenin and target gene Cyp2e1, which promoted lipid peroxidation and hepatic damage. Addition of NAC to drinking water protected KO +Fe from hepatic steatosis, injury and fibrosis, and prevented activation of AKT, ERK, NF-κB and reappearance of β-catenin.

CONCLUSIONS

The absence of hepatic β-catenin predisposes mice to hepatic injury and fibrosis following iron overload, which was reminiscent of hemochromatosis and associated with enhanced steatohepatitis and fibrosis. Disease progression was notably alleviated by antioxidant therapy, which supports its chemopreventive role in the management of chronic iron overload disorders.

LAY SUMMARY

Lack of animal models for iron overload disorders makes it hard to study the disease process for improving therapies. Feeding high iron diet to mice that lack the β-catenin gene in liver cells led to increased inflammation followed by fat accumulation, cell death and wound healing that mimicked human disease. Administration of an antioxidant prevented hepatic injury in this model.

Probing binding mechanism of interleukin-6 and olokizumab: in silico design of potential lead antibodies for autoimmune and inflammatory diseases

Computer-aided antibody engineering has been successful in the design of new biologics for disease diagnosis and therapeutic interventions. Interleukin-6 (IL-6), a well-recognized drug target for various autoimmune and inflammatory diseases such as rheumatoid arthritis, multiple sclerosis, and psoriasis, was investigated in silico to design potential lead antibodies. Here, crystal structure of IL-6 along with monoclonal antibody olokizumab was explored to predict antigen-antibody (Ag - Ab)-interacting residues using DiscoTope, Paratome, and PyMOL. Tyr56, Tyr103 in heavy chain and Gly30, Ile31 in light chain of olokizumab were mutated with residues Ser, Thr, Tyr, Trp, and Phe. A set of 899 mutant macromolecules were designed, and binding affinity of these macromolecules to IL-6 was evaluated through Ag - Ab docking (ZDOCK, ClusPro, and Rosetta server), binding free-energy calculations using Molecular Mechanics/Poisson Boltzman Surface Area (MM/PBSA) method, and interaction energy estimation. In comparison to olokizumab, eight newly designed theoretical antibodies demonstrated better result in all assessments. Therefore, these newly designed macromolecules were proposed as potential lead antibodies to serve as a therapeutics option for IL-6-mediated diseases.

The human rhabdomyosarcoma cell line TE671--Towards an innovative production platform for glycosylated biopharmaceuticals

The market of therapeutic glycoproteins (including coagulation factors, antibodies, cytokines and hormones) is one of the profitable, fast-growing and challenging sectors of the biopharmaceutical industry. Although mammalian cell culture is still expensive and technically complex, the ability to produce desired post-translational modifications, in particular glycosylation, is a major issue. Glycans can influence ligand binding, serum half-life as well as biological activity or product immunogenicity. Aiming to establish a novel production platform for recombinant glycoproteins, the human TE671 cell line was investigated. Since the initial analysis of cell membrane proteins showed a promising glycosylation of TE671 cells for biotechnological purposes, we focused on the recombinant expression of two model glycoproteins of therapeutical relevance. The optimization of the cell transfection procedure and serum-free expression succeeded for the human serine protease inhibitor alpha-1-antitrypsin (A1AT) and the hematopoietic cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF). N-glycan analyses of both purified proteins by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry provided first fundamental insights into the TE671 glycosylation potential. Besides protein specific pattern, strong distinctions - in particular for N-glycan fucosylation and sialylation - were observed depending on the medium conditions of the respective TE671 cell cultivations. The cell line's ability to synthesize complex and highly sialylated N-glycan structures has been shown. Our results demonstrate the TE671 cell line as a serious alternative to other existing human expression systems.

Genetic ablation of N-linked glycosylation reveals two key folding pathways for R345W fibulin-3, a secreted protein associated with retinal degeneration

An R345W mutation in the N-glycoprotein, fibulin-3 (F3), results in inefficient F3 folding/secretion and higher intracellular F3 levels. Inheritance of this mutation causes the retinal dystrophy malattia leventinese. N-Linked glycosylation is a common cotranslational protein modification that can regulate protein folding efficiency and energetics. Therefore, we explored how N-glycosylation alters the protein homeostasis or proteostasis of wild-type (WT) and R345W F3 in ARPE-19 cells. Enzymatic and lectin binding assays confirmed that WT and R345W F3 are both primarily N-glycosylated at Asn249. Tunicamycin treatment selectively reduced R345W F3 secretion by 87% (vs. WT F3). Genetic elimination of F3 N-glycosylation (via an N249Q mutation) caused R345W F3 to aggregate intracellularly and adopt an altered secreted conformation. The endoplasmic reticulum (ER) chaperones GRP78 (glucose-regulated protein 78) and GRP94 (glucose-regulated protein 94), and the ER lectins calnexin and calreticulin were identified as F3 binding partners by immunoprecipitation. Significantly more N249Q and N249Q/R345W F3 interacted with GRP94, while substantially less N249Q and N249Q/R345W interacted with the ER lectins than their N-glycosylated counterparts. Inhibition of GRP94 ATPase activity reduced only N249Q/R345W F3 secretion (by 62%), demonstrating this variant's unique reliance on GRP94 for secretion. These observations suggest that R345W F3, but not WT F3, requires N-glycosylation to acquire a stable, native-like structure.

Establishment of a novel cell-based assay for screening small molecule antagonists of human interleukin-6 receptor

AIM

Blockade of interleukin-6 (IL-6) or its receptor (IL-6R) is effective in preventing the progression of autoimmune diseases, such as systemic lupus erythematosus and rheumatoid arthritis. In the present study, we established a novel cell-based assay for identifying small molecule IL-6R antagonists.

METHODS

HEK293A cells were transfected with recombinant plasmids pTaglite-SNAP-IL6R and pABhFc-IL6 to obtain membrane-bound IL-6R and recombinant human IL-6 coupled with human Fc fragment (rhIL-6), respectively. A novel screening assay based on the interaction between IL-6R and rhIL-6 was established, optimized and validated. The stability of the assay was also assessed by calculating the Z'-factor.

RESULTS

RhIL-6 dose-dependently bound to IL-6R expressed at HEK293A cell surface. The IC50 value of the known antagonist ab47215 was 0.38±0.08 μg/mL, which was consistent with that obtained using the traditional method (0.36±0.14 μg/mL). The value of Z'-factor was 0.68, suggesting that the novel assay was stable for high throughput screening. A total of 474 compounds were screened using the novel screening assay, and 3 compounds exhibited antagonistic activities (IC50=8.73±0.28, 32.32±9.08, 57.83±4.24 μg/mL). Furthermore, the active compounds dose-dependently inhibited IL-6-induced proliferation of 7TD1 cells, and reduced IL-6-induced STAT3 phosphorylation in U937 cells.

CONCLUSION

A novel cell-based screening assay for identifying small molecule IL-6R antagonists was established, which simplifies the procedures in traditional cellular ELISA screening and profiling and reduces the costs.

Semisynthesis of biologically active glycoforms of the human cytokine interleukin 6

Human interleukin 6 (IL-6) is a potent cytokine with immunomodulatory properties. As the influence of N-glycosylation on the in vivo activities of IL-6 could not be elucidated so far, a semisynthesis of homogeneous glycoforms of IL-6 was established by sequential native chemical ligation. The four cysteines of IL-6 are convenient for ligations and require only the short synthetic glycopeptide 43-48. The Cys-peptide 49-183 could be obtained recombinantly by cleavage of a SUMO tag. The fragment 1-42 was accessible by the simultaneous cleavage of two inteins, leading to the 1-42 thioester with the native N-terminus. Ligation and refolding studies showed that the inherently labile Asp-Pro bond 139-140 was detrimental for the sequential C- to N-terminal ligation. A reversed ligation sequence using glycopeptide hydrazides gave full-length IL-6 glycoproteins, which showed full bioactivity after efficient refolding and purification.

IL-23 is pro-proliferative, epigenetically regulated and modulated by chemotherapy in non-small cell lung cancer

BACKGROUND

IL-23 is a member of the IL-6 super-family and plays key roles in cancer. Very little is currently known about the role of IL-23 in non-small cell lung cancer (NSCLC).

METHODS

RT-PCR and chromatin immunopreciptiation (ChIP) were used to examine the levels, epigenetic regulation and effects of various drugs (DNA methyltransferase inhibitors, Histone Deacetylase inhibitors and Gemcitabine) on IL-23 expression in NSCLC cells and macrophages. The effects of recombinant IL-23 protein on cellular proliferation were examined by MTT assay. Statistical analysis consisted of Student's t-test or one way analysis of variance (ANOVA) where groups in the experiment were three or more.

RESULTS

In a cohort of primary non-small cell lung cancer (NSCLC) tumours, IL-23A expression was significantly elevated in patient tumour samples (p < 0.05). IL-23A expression is epigenetically regulated through histone post-translational modifications and DNA CpG methylation. Gemcitabine, a chemotherapy drug indicated for first-line treatment of NSCLC also induced IL-23A expression. Recombinant IL-23 significantly increased cellular proliferation in NSCLC cell lines.

CONCLUSIONS

These results may therefore have important implications for treating NSCLC patients with either epigenetic targeted therapies or Gemcitabine.

Combined inhibition of aromatase activity and dihydrotestosterone supplementation attenuates renal injury in male streptozotocin (STZ)-induced diabetic rats

Our previous studies showed that streptozotocin (STZ)-induced diabetic male rats have increased estradiol and decreased testosterone levels that correlate with renal injury (Xu Q, Wells CC, Garman GH, Asico L, Escano CS, Maric C. Hypertension 51: 1218-1224, 2008). We further showed that either supplementing dihydrotestosterone (DHT) or inhibiting estradiol biosynthesis in these diabetic rats was only partially renoprotective (Manigrasso MB, Sawyer RT, Marbury DC, Flynn ER, Maric C. Am J Physiol Renal Physiol 301: F634-F640, 2011; Xu Q, Prabhu A, Xu S, Manigrassso MB, Maric C. Am J Physiol 297: F307-F315, 2009). The aim of this study was to test the hypothesis that the combined therapy of DHT supplementation and inhibition of estradiol synthesis would afford better renoprotection than either treatment alone. The study was performed in 12-wk-old male nondiabetic (ND), STZ-induced diabetic (D), and STZ-induced diabetic rats that received the combined therapy of 0.75 mg/day of DHT along with 0.15 mg · kg(-1) · day(-1) of an aromatase inhibitor, anastrozole (Dta), for 12 wk. Treatment with the combined therapy resulted in attenuation of albuminuria by 84%, glomerulosclerosis by 55%, and tubulointerstitial fibrosis by 62%. In addition, the combined treatment decreased the density of renal cortical CD68-positive cells by 70% and decreased protein expression of transforming growth factor-β protein expression by 60%, collagen type IV by 65%, TNF-α by 55%, and IL-6 by 60%. We conclude that the combined treatment of DHT and blocking aromatase activity in diabetic male STZ-induced diabetic rats provides superior treatment than either treatment alone in the prevention of diabetic renal disease.

Inhibition of estradiol synthesis attenuates renal injury in male streptozotocin-induced diabetic rats

We previously showed that the male streptozotocin (STZ)-induced diabetic rat exhibits decreased circulating testosterone and increased estradiol levels. While supplementation with dihydrotestosterone is partially renoprotective, the aim of the present study was to examine whether inhibition of estradiol synthesis, by blocking the aromatization of testosterone to estradiol using an aromatase inhibitor, can also prevent diabetes-associated renal injury. The study was performed on male Sprague-Dawley nondiabetic, STZ-induced diabetic, and STZ-induced diabetic rats treated with 0.15 mg/kg of anastrozole, an aromatase inhibitor (Da) for 12 wk. Treatment with anastrozole reduced diabetes-associated increases in plasma estradiol by 39% and increased plasma testosterone levels by 187%. Anastrozole treatment also attenuated urine albumin excretion by 42%, glomerulosclerosis by 30%, tubulointerstitial fibrosis by 32%, along with a decrease in the density of renal cortical CD68-positive cells by 50%, and protein expression of transforming growth factor-β by 20%, collagen type IV by 29%, tumor necrosis factor-α by 28%, and interleukin-6 by 25%. Anastrozole also increased podocin protein expression by 18%. We conclude that blocking estradiol synthesis in male STZ-induced diabetic rats is renoprotective.

The role of interleukin-6 in insulin resistance, body fat distribution and energy balance

Interleukin-6 (IL-6) is a central player in the regulation of inflammation, haematopoiesis, immune response and host defense mechanisms. During the last decade, an accumulating amount of data suggested a pivotal role for IL-6 in metabolic processes, thus fortifying the picture of IL-6 as a multifaceted, pleiotropic cytokine. Because of its secretion by adipose tissue and contracting skeletal muscle and its broad action on central and peripheral organs, IL-6 has been termed an adipokine and a myokine. Its quantitative release from adipose tissue results in a subclinical, systemic elevation of IL-6 plasma levels with increasing body fat content, which may be implicated in the proinflammatory state leading to insulin resistance. On the other hand, IL-6 produced in the working muscle during physical activity could act as an energy sensor by activating AMP-activated kinase and enhancing glucose disposal, lipolysis and fat oxidation. In addition, both impaired IL-6 secretion and action are risk factors for weight gain. Thus, IL-6 clearly has lipolytic effects and anti-obesity potential. However, the application of IL-6 itself is at least limited by a narrow therapeutic range and its important function for a balanced inflammatory response. Further studies on the molecular basis of the metabolic effects of IL-6 could elucidate novel therapeutic strategies for custom-designed, IL-6-related substances.

Essential role of IL-6 signaling pathway in keloid pathogenesis

Cytokines are pleiotropic substances that are known to participate in inflammatory and immune responses as well as cell differentiation and proliferation. Interleukin-6 (IL-6) is a key cytokine with pro-inflammatory function. Wound healing is a complex cascade of physiologic events comprising inflammation, proliferation and remodeling, and proceeds with the integrated actions of different cells, cytokines, and the extracellular matrix. Aberrant wound healing results in keloid formation which causes disfigured appearance, discomfort, psychological stress, and patient frustration. In this review, the role of IL-6 signaling pathway in the pathogenesis of keloid is assessed and its potential as a therapeutic target is addressed. The existing data suggest that IL-6 mediated inflammation is a key player and may be considered as a common causative factor for development of keloid. Furthermore, in a recent comprehensive study, we confirmed the functional role of IL-6 signaling in keloid pathogenesis. Accordingly, inhibitory strategies of IL-6 signaling pathway by targeting the IL-6 receptors, its downstream effecters, or other molecules influencing this pathway appear to have considerable potential as new therapeutic or preventive challenges for keloid. Hopefully, several IL-6 blocking agents including a humanized antibody to IL-6 receptor have been developed and successfully used in clinical trials of inflammatory diseases. It is likely that these agents may prove worthy in the treatment or prevention of keloid as well. Future in-depth exploration of such challenges will shed light on their efficacy and safety for clinical application in keloid.

Leptin gene expression and systemic levels in healthy men: effect of exercise, carbohydrate, interleukin-6, and epinephrine

Leptin, an adipose tissue-derived cytokine, is correlated with adipose mass as obese persons have increased levels of leptin that decrease with weight loss. Previous studies demonstrate that high-energy-expenditure exercise decreases circulating leptin levels, whereas low-energy-expenditure exercise has no effect. We aimed to test the hypothesis that acute exercise reduced leptin mRNA levels in human adipose tissue and that this effect would be ameliorated by carbohydrate supplementation. Because exercise markedly increases circulating IL-6 and epinephrine, we investigated whether the changes in leptin seen with acute exercise could be mediated by IL-6 or epinephrine infusion. Abdominal subcutaneous adipose tissue mRNA and plasma levels of leptin were measured in healthy men in response to 3-h ergometer exercise with or without carbohydrate (CHO) ingestion ( n = 8) and in response to infusion with recombinant human (rh)IL-6 ( n = 11) or epinephrine ( n = 8) or saline. Plasma leptin declined in response to exercise ( P < 0.05) compared with rest, whereas mRNA expression in adipose tissue was unaffected. The exercise-induced decrease in plasma leptin was attenuated by CHO ingestion ( P < 0.001). A 3-h epinephrine infusion decreased plasma leptin ( P < 0.001) to the same level seen with 3 h of exercise, whereas leptin levels were unaffected by rhIL-6 infusion. In conclusion, both acute exercise and epinephrine infusion decreased plasma leptin to a similar extent, whereas there was no effect with rhIL-6 infusion. Acute exercise solely affected leptin plasma levels, as mRNA levels were unchanged. The exercise-induced decrease in circulating leptin was counteracted by CHO ingestion, suggesting a posttranscriptional regulatory mechanism of leptin involving substrate availability.

Kaposi's Sarcoma-associated Herpesvirus-encoded Viral Interleukin-6 Is Secreted and Modified Differently Than Human Interleukin-6

Viral interleukin-6 (vIL-6) is a homolog of cellular IL-6 that is encoded by the Kaposi's sarcoma-associated herpesvirus (KSHV) genome. vIL-6 binds to the IL-6 signal transducer gp130 without the cooperation of the IL-6 high affinity receptor to induce STAT3 DNA binding and cell proliferation. Although vIL-6 is believed to be important in the pathogenesis of KSHV-induced diseases, its secretion and post-translational modifications have not previously been characterized. Pulse-chase analysis revealed that the half-time of vIL-6 secretion is approximately 8-fold longer than that of human IL-6. Yet, the vIL-6 signal sequence targets human IL-6 secretion to nearly wild-type levels. Surprisingly, vIL-6 was not secreted from a cell line that does not express gp130 but expression of human gp130 in these cells enabled the secretion of vIL-6. Consistent with this observation, complete maturation of gp130 N-glycans is inhibited by vIL-6 coexpression, suggesting that the binding of the receptor to vIL-6 occurs intracellularly in early or pre-Golgi compartments. Furthermore, a vIL-6 mutant containing an endoplasmic reticulum retention signal is not secreted but does still induce receptor activation and signaling. Secreted vIL-6 is completely glycosylated at both possible N-glycosylaton sites and contains a large proportion of immature high-mannose glycans that is not typical of cytokines. These findings suggest that vIL-6 may induce gp130 signaling by an exclusively autocrine mechanism that relies on intracellular binding to its receptor. During KSHV infection, vIL-6 may only induce signaling in KSHV-infected cells to benefit the viral life cycle and promote oncogenic transformation.

The protein product of the tumor suppressor gene, melanoma differentiation-associated gene 7, exhibits immunostimulatory activity and is designated IL-24

The melanoma differentiation-associated gene 7 (mda-7) has been studied primarily in the context of its tumor suppressor activity. Although mda-7 has been designated as IL-24 based on its gene location in the IL-10 locus and its mRNA expression in leukocytes, no functional evidence supporting this cytokine designation exists. To further characterize MDA-7/IL-24 expression patterns in the human immune system, MDA-7/IL-24 protein levels were examined in human PBMC. MDA-7/IL-24 was detected in PHA- and LPS-stimulated whole PBMC lysate by Western blot and in PHA-activated CD56 and CD19 subsets by immunohistochemistry. The biological function of MDA-7/IL-24, secreted from Ad-MDA7-transfected HEK 293 cells, was assessed by examining the effect of MDA-7/IL-24 on the cytokine secretion profile of PBMC. Within 48 h MDA-7/IL-24 induced secretion of high levels of IL-6, TNF-alpha, and IFN-gamma and low levels of IL-1beta, IL-12, and GM-CSF from human PBMC as measured by ELISA. The MDA-7/IL-24-mediated induction of these Th1-type cytokines was inhibited by the addition of IL-10 to the PBMC cultures, suggesting that these two related protein family members may provide antagonistic functions. Therefore, because human blood leukocytes can be stimulated to produce MDA-7/IL-24, as well as respond to MDA-7/IL-24 by expressing secondary cytokines, MDA-7/IL-24 has the expression profile and major functional attributes that justify its designation as an IL.

C-terminal peptides of interleukin-6 modulate the expression of junB protooncogene and the production of fibrinogen by HepG2 cells

Interleukin-6 (IL-6) is a 185 amino acid residue helical cytokine with various biological activities (e. g. B cell development, acute phase reaction). We have investigated the role of the 168-185 C-terminal region of IL-6 in the induction of fibrinogen synthesis and expression of junB mRNA using synthetic peptides corresponding to this region. Circular dichroism spectroscopy data suggest that even truncated peptides have a strong tendency to adopt an ordered conformation. Peptides were tested alone or in combination with recombinant hIL-6 on an IL-6 responsive human hepatoma HepG2 cell line. The expression of the protooncogene junB monitored by competitive RT-PCR represents an early, while the fibrinogen production detected by sandwich ELISA a late, marker of IL-6 initiated events. We found that peptides--depending on their structure--modulate spontaneous as well as IL-6 induced fibrinogen production and/or mRNA expression of junB by exhibiting inhibition (in the presence of IL-6) or stimulation (in the absence of IL-6).

Reversal of EBV immortalization precedes apoptosis in IL-6-induced human B cell terminal differentiation

Cell death in B cell terminal differentiation rapidly follows cell cycle arrest in IL-6 differentiation of EBV-immortalized, IgG-bearing human lymphoblastoid cells in vitro. G1 arrest is now found to coincide with repression of EBNA2 and LMP1, two EBV genes essential for B cell transformation, without activation of the viral lytic cycle. IL-6-differentiated B cells die by apoptosis, as evidenced by increases in Annexin V binding activity, PARP cleavage, and chromatin disorganization. Expression of Mcl-1, a Bcl-2 family member, was specifically induced during IL-6 differentiation and down-regulated during apoptosis. Thus, IL-6 reverses EBV immortalization and activates the terminal differentiation program in IgG-bearing human B lymphoblastoid cells, including regulation of an anti-apoptotic gene to coordinate differentiation, cell cycle arrest, and cell death.

Interleukin-6: structure-function relationships

Interleukin-6 (IL-6) is a multifunctional cytokine that plays a central role in host defense due to its wide range of immune and hematopoietic activities and its potent ability to induce the acute phase response. Overexpression of IL-6 has been implicated in the pathology of a number of diseases including multiple myeloma, rheumatoid arthritis, Castleman's disease, psoriasis, and post-menopausal osteoporosis. Hence, selective antagonists of IL-6 action may offer therapeutic benefits. IL-6 is a member of the family of cytokines that includes interleukin-11, leukemia inhibitory factor, oncostatin M, cardiotrophin-1, and ciliary neurotrophic factor. Like the other members of this family, IL-6 induces growth or differentiation via a receptor-system that involves a specific receptor and the use of a shared signaling subunit, gp130. Identification of the regions of IL-6 that are involved in the interactions with the IL-6 receptor, and gp130 is an important first step in the rational manipulation of the effects of this cytokine for therapeutic benefit. In this review, we focus on the sites on IL-6 which interact with its low-affinity specific receptor, the IL-6 receptor, and the high-affinity converter gp130. A tentative model for the IL-6 hexameric receptor ligand complex is presented and discussed with respect to the mechanism of action of the other members of the IL-6 family of cytokines.

Induction of cell cycle arrest and B cell terminal differentiation by CDK inhibitor p18(INK4c) and IL-6

Cell cycle arrest and cell death are tightly coupled to terminal differentiation of B cells to plasma cells in vivo. This process was recapitulated in vitro by stimulation of IgG-bearing human B lymphoblastoid cells with interleukin-6 (IL-6), which led to orderly cell cycle arrest, differentiation, and apoptosis. In terminally differentiated plasmacytoid cells, phosphorylation of pRb was suppressed, correlating with the activation of the D-type cyclin-dependent kinase (CDK) inhibitors p18(INK4c) and p21(WAF1/CIP1). The expression of CDK6, however, remained unchanged. Activation of p18 by IL-6 was rapid, concomitant with marked enhancement of its association with CDK6 and cell cycle arrest. Overexpression of p18 in IgM-bearing lymphoblastoid cells, which differentiated in response to IL-6 but did not exit the cell cycle, reconstituted coupled differentiation and cell cycle arrest. Thus, CDK inhibitors, in particular p18, are likely to play a pivotal role in controlling cell cycle arrest and cell death in terminal differentiation of late-stage B cells to plasma cells via inhibition of pRb phosphorylation by CDK6.

Cell-adhesion-disrupting action of interleukin 6 in human ductal breast carcinoma cells

Recombinant baculovirus-derived interleukin 6 (IL-6) disrupts the attachment of human ductal breast carcinoma subline ZR-75-1-Tx cells to neighbors and the substratum in culture without inhibiting the proliferation of the cells. The nonadherent cells lack pseudopodia and do not translocate directionally. These findings stand in contrast to the earlier observations in the Ro subline of ZR-75-1 cells in which IL-6 induces cell-cell separation without detachment of the cells from the substratum, with the cells displaying pseudopodia, increased motility, and decreased proliferation. The IL-6-induced ZR-75-1-Tx cell detachment and rounding are reversible by incubation of the treated cells in IL-6-free medium for several days. The distinctive changes induced by IL-6 in ZR-75-1-Ro cells are similarly reversible. Either acidic fibroblast growth factor or phorbol 12-myristate 13-acetate can replace serum as a cofactor in IL-6-induced ZR-75-1-Tx cell detachment. Our findings indicate that genetic changes can occur in breast carcinoma cells that through cytokine action markedly affect cell structure, adhesiveness, and motility.

Fib420: a normal human variant of fibrinogen with two extended alpha chains

In fibrinogen, alpha E chains form a subpopulation of alpha subunits that are distinguished by a carboxyl extension homologous to the C termini of the other two constituent chains: beta and gamma. The molecular mass of alpha E is > 50% greater than that of the common alpha subunit, due in part to an extra 236 amino acids. These residues are encoded by exon VI, a recently discovered extension of the fibrinogen alpha gene. Additional mass is contributed by posttranslational processing, including N-glycosylation, which, based on experiments with the inhibitor tunicamycin, was found to account in large measure for alpha E migration on SDS/PAGE at approximately 110 kDa rather than at its calculated mass of 92,843 Da. An antibody specific for the exon VI-encoded domain of alpha E (anti-VI) and capable of recognizing alpha E-containing fibrinogen in both native and denatured form was generated using a recombinant protein as immunogen. Its use in Western blot analysis of fractions of normal human blood (plasma and preparations of fibrinogen) revealed a single, sharp, alpha E-containing band migrating behind the position of the broad, predominant fibrinogen band, (alpha beta gamma)2. Designation of the upper band as Fib420, an approximately 420-kDa homodimer of the formula (alpha E beta gamma)2, is based on the overwhelming proportion of alpha E subunits (> 80% of the total alpha chains) found in anti-VI-immunoprecipitable material from hepatoma cell medium. Several lines of evidence suggest that the alpha E subunit, alone or incorporated into fibrinogen, is more stable than the common alpha chain, a feature of potential clinical importance.

Carboxy-terminal-extended variant of the human fibrinogen alpha subunit: a novel exon conferring marked homology to beta and gamma subunits

Similarities between the N-terminal regions of the three subunits of the clotting protein fibrinogen--(alpha beta gamma)2--suggest that they evolved from a common progenitor. However, to date no human alpha chain has been found with the strong C-terminal homology shared by the beta and gamma chains. Here we examine the natural product of a novel fibrinogen alpha chain transcript bearing a separate open reading frame that supplies the missing C-terminal homology to the other chains. Additional splicing leads to the use of this extra sequence as a sixth exon elongating the alpha chain by 35%. Since the extended alpha chain (alpha E) is assembled into fibrinogen molecules and its synthesis is enhanced by interleukin-6, it suggests participation in both the acute phase response and normal physiology.

Phosphorylation of interleukin-6 at serine54: an early event in the secretory pathway in human fibroblasts

The cytokine interleukin-6 (IL-6) is the major phosphoprotein secreted by human fibroblasts induced with interleukin-1 alpha (IL-1 alpha). We have determined that Ser54 is the predominant site of phosphorylation on the fibroblast-derived IL-6 polypeptide; the amino acid motif surrounding this site is reminiscent of the target site for the Golgi-associated protein (casein) kinase. It has been shown earlier that the IL-6 polypeptide follows the classical secretory pathway where N-linked glycosylation is detectable within the first 15 minutes of labeling with [35S]-methionine and O-linked glycosylation occurs between 15-30 minutes after the start of polypeptide synthesis. Pulse-chase experiments using [32P]-orthophosphate or [35S]-methionine as tracers indicated that phosphorylation of IL-6 occurred prior to its O-glycosylation suggesting that the de novo synthesized IL-6 polypeptide is rapidly, perhaps even cotranslationally, phosphorylated at an intravesicular site (in the endoplasmic reticulum and/or Golgi). When IL-1 alpha-induced fibroblasts were exposed to cycloheximide there was enhancement of the net de novo synthesis and secretion of IL-6 as followed by [35S]-methionine labeling ("superinduction") but the secreted cytokine was no longer phosphorylated as monitored by [32P] labeling. Thus, phosphorylation of the IL-6 polypeptide is not an obligatory requirement for secretion of this cytokine. Furthermore, IL-6 phosphorylation is inhibited by cycloheximide through a mechanism different from the drug's effects on polypeptide synthesis per se.

Interleukin-6 enhances motility of breast carcinoma cells

Interleukin-6 (IL-6) is the major systemic mediator of the early host response to infection and injury (the "acute phase response"). Furthermore, IL-6 is often detected in the peripheral circulation and in the local neoplastic tissue in cancer patients. IL-6 has distinctive effect on epithelial cells depending upon the cell type examined. IL-6 enhances proliferation of normal human keratinocytes without affecting cell morphology. In contrast, IL-6 inhibits the proliferation of ductal breast carcinoma cell lines T-47D, ZR-71-1 and MCF-7. In addition to, but independent of, the inhibition of cell proliferation, IL-6 induces a cellular phenotype in the typically epitheliod T-47D and ZR-75-1 cells, which is characterized by fibroblastoid morphology, increased cell-cell separation even within preformed colonies, decreased adherens type junction formation (desmosomes and focal adhesions), and enhanced motility. Time-lapse cinemicrography of T-47D and wild-type ZR-75-1 cells reveals increased local movement of IL-6-treated cells and also movement of these cells over considerable distances. The effects of IL-6 on breast cancer cell proliferation and motility are reversible by removal of IL-6 from the culture medium. Time-lapse cinemicrography reveals that in clone B ZR-75-1 cells, which are not sensitive to the DNA synthesis-inhibitory effect of IL-6 or to its cell-separating effect on preformed colonies, IL-6 can still block rapid readherence of post-mitotic cells to their neighbors and to the substratum leading to enhanced dispersal of cancer cells into the culture medium. In wild-type ZR-75-1 cells, 12-O-tetradecanoyl phorbol ester (TPA) exerts a cell-scattering effect on breast cancer cells without inhibiting cell proliferation. Combined treatment with IL-6 and TPA produces a cell-scattering effect that greatly exceeds in magnitude and speed the phenotypic change elicited by either reagent alone. Staurosporine blocks cell-scattering caused by TPA but not that caused by IL-6 suggesting that IL-6 and TPA elicit similar phenotypic changes in breast cancer cells via different pathways. Taken together, these findings identify a previously unrecognized property of IL-6, that of enhancing cell motility.