The Immunoregulatory Mediator Macrophage Migration Inhibitory Factor (MIF) Catalyzes a Tautomerization Reaction

At The Interface: Small-Molecule Inhibitors of Soluble Cytokines

Cytokines are crucial regulators of the immune system that orchestrate interactions between cells and, when dysregulated, contribute to the progression of chronic inflammation, cancer, and autoimmunity. Numerous biologic-based clinical agents, mostly monoclonal antibodies, have validated cytokines as important clinical targets and are now part of the standard of care for a number of diseases. These agents, while impactful, still suffer from limitations including a lack of oral bioavailability, high cost of production, and immunogenicity. Small-molecule cytokine inhibitors are attractive alternatives that can address these limitations. Although targeting cytokine-cytokine receptor complexes with small molecules has been a challenging research endeavor, multiple small-molecule inhibitors have now been identified, with a number of them undergoing clinical evaluation. In this review, we highlight the recent advancements in the discovery and development of small-molecule inhibitors targeting soluble cytokines. The strategies for identifying these novel ligands as well as the structural and mechanistic insights into their activity represent important milestones in tackling these challenging and clinically important protein-protein interactions.

Inhibition of MIF with an Allosteric Inhibitor Triggers Cell Cycle Arrest in Acute Myeloid Leukemia

Macrophage migration inhibitory factor (MIF) is a key modulator of innate and adaptive immunity that has been extensively reported to promote tumor cell survival, proliferation, and metastasis. A recent study focusing on the microenvironment of acute myeloid leukemia (AML) showed that pharmacological inhibition of MIF signaling, in vitro as well as in vivo, reduces AML cell survival. Such data highlights the crucial role of MIF in AML pathogenesis and support the efforts for developing selective MIF modulators. Here, we report the identification and crystallographic characterization of a MIF inhibitor (compound 1) with an allosteric binding motif. Single point screening of 1 against a panel of National Cancer Institute (NCI) 60 human tumor cell lines revealed a selective antitumor activity for the AML cell line HL-60. After confirming the protein's expression in multiple AML cell lines, we utilized 1 to extract mechanistic insights into MIF action. Our findings demonstrate that AML cells utilize an MIF-dependent proliferation mechanism, which upon inhibition triggers a G0/G1 cell cycle arrest of the malignant cells. Complementary analysis of the MIF receptors utilizing neutralizing antibodies and selective small molecule antagonists associates this effect with inhibition of CD74 activation. The collection of data presented herein highlights the important role of MIF in proliferation of AML cells and points to the need of developing small molecule anticancer therapeutics that target MIF signaling.

Progress in the development of macrophage migration inhibitory factor small-molecule inhibitors

Macrophage migration inhibitory factor (MIF) functions as a critical cytokine regulating inflammatory and immune responses. Extensive research has demonstrated its involvement in the progression of various cancers, autoimmune diseases, and inflammatory disorders, establishing it as a pivotal target for anti-inflammatory and anticancer interventions. Therapeutic strategies aimed at MIF primarily focus on suppressing its activity through small molecule inhibitors and natural compounds. This review synthesizes current knowledge on MIF, encompassing its structural characteristics, enzymatic functions, signaling pathways, and roles in disease pathogenesis. Additionally, it provides an in-depth analysis of recent advancements in MIF inhibitor development, including design methodologies, structure-activity relationships, advanced eutectic analysis techniques, and key experimental findings. The discussion aims to support the development of safer, more effective, and highly selective small molecule inhibitors targeting MIF.

The distinct functions of MIF in inflammatory cardiomyopathy

The immune system plays a crucial role in cardiac homeostasis and disease, and the innate and adaptive immune systems can be beneficial or detrimental in cardiac injury. The pleiotropic proinflammatory cytokine macrophage migration inhibitory factor (MIF) is involved in the pathogenesis of many human disease conditions, including heart diseases and inflammatory cardiomyopathies. Inflammatory cardiomyopathies are frequently observed after microbial infection but can also be caused by systemic immune-mediated diseases, drugs, and toxic substances. Immune cells and MIF are implicated in many of these conditions and may affect progression of inflammatory cardiomyopathy (ICM) to myocardial remodeling and dilated cardiomyopathy (DCM). The potential for targeting MIF therapeutically in patients with inflammatory diseases is an active area of investigation. Here we review the current literature supporting the role(s) of MIF in ICM and cardiac dysfunction. We posit that future research to further elucidate the underlying functions of MIF in cardiac pathologies is warranted.

The macrophage migration inhibitory factor/CD74 axis in traumatic spinal cord injury: lessons learned from animal and human studies

Traumatic spinal cord injury (SCI) is a severe condition leading to long-term impairment of motor, sensory, and autonomic functions. Following the initial injury, a series of additional events is initiated further damaging the spinal cord. During this secondary injury phase, both an inflammatory and immune modulatory response are triggered that have damaging and anti-inflammatory properties, respectively. The proinflammatory cytokine macrophage migration inhibitory factor (MIF) and its receptor CD74 have been extensively studied in traumatic SCI. MIF expression is increased in spinal cord tissue after experimental SCI, mainly in astrocytes and microglia, as well as in the plasma of SCI patients. Functionally, MIF and CD74 were shown to regulate astrocyte viability, proliferation and cholesterol metabolism, microglia migration, and neuronal viability. Moreover, inhibition of the MIF/CD74 axis improved the functional recovery of SCI animals. We provide a detailed overview of studies analyzing the role of MIF and CD74 in traumatic SCI. We describe results from animal studies, using rat and mouse models for SCI, and human studies. Furthermore, we propose a new path for investigation, focused on B cells, that might lead to a better understanding of how MIF and CD74 contribute to the secondary injury cascade following traumatic SCI.

Covalent Isothiocyanate Inhibitors of Macrophage Migration Inhibitory Factor as Potential Colorectal Cancer Treatments

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that has roles in innate and adaptive human immune responses, as well as inflammation. MIF exerts its biological activity by binding to the cell surface receptor CD74 as well as intracellular signalling proteins. MIF also possesses keto-enol tautomerase activity. Inhibition of the tautomerase activity has been associated with loss of biological activity of MIF and a potential anticancer target. Isothiocyanates (ITCs) are a class of compounds present in cruciferous vegetables that inhibit the MIF tautomerase activity via covalent modification of the N-terminal proline. A range of substituted ITCs featuring benzyl, phenethyl and phenyl propyl isothiocyanates were designed, synthesised and tested to determine any structure activity relationship for inhibiting MIF. Crystal structures of covalent compounds 8 and 9 in complex with rhMIF revealed key hydrogen bonding and edge-to-face π stacking interactions. Compound 9 and 11 with sub micromolar activity were tested in the NCI60 cancer cell lines panel. Both compounds showed tissue-specific reduced growth in colon and renal cancer cell lines, while one of these showed potent, dose-dependent inhibition of growth against all seven colon cancer cell lines (GI50<2.5 μM) and all eight renal cancer cell lines (GI50<2.2 μM).

The role of macrophage migration inhibitory factor family and CD74 in the pathogenesis of melanoma

Melanoma is an aggressive tumour with poor prognosis that arises from the malignant transformation of melanocytes. Over the past few decades, intense research into the pathogenesis of melanoma has led to the development of BRAF and immune checkpoint inhibitors, including antibodies against programmed cell death protein 1 (PD-1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4), which have shown clinically significant efficacy. However, some tumours do not respond to these therapies initially or become treatment resistant. Most melanoma tissues appear to possess biological characteristics that allow them to evade these treatments, and identifying these characteristics is one of the major challenges facing cancer researchers. One such characteristic that has recently gained attention is the role of macrophage migration inhibitory factor (MIF) and its receptor CD74. This review outlines the cellular and molecular functions of CD74, MIF and their family of proteins. We then review their roles in tumours based on previous reports, highlight their pathological significance in melanoma and discuss their potential as therapeutic targets.

Targeting low levels of MIF expression as a potential therapeutic strategy for ALS

Mutations in SOD1 cause amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by motor neuron (MN) loss. We previously discovered that macrophage migration inhibitory factor (MIF), whose levels are extremely low in spinal MNs, inhibits mutant SOD1 misfolding and toxicity. In this study, we show that a single peripheral injection of adeno-associated virus (AAV) delivering MIF into adult SOD1G37R mice significantly improves their motor function, delays disease progression, and extends survival. Moreover, MIF treatment reduces neuroinflammation and misfolded SOD1 accumulation, rescues MNs, and corrects dysregulated pathways as observed by proteomics and transcriptomics. Furthermore, we reveal low MIF levels in human induced pluripotent stem cell-derived MNs from familial ALS patients with different genetic mutations, as well as in post mortem tissues of sporadic ALS patients. Our findings indicate that peripheral MIF administration may provide a potential therapeutic mechanism for modulating misfolded SOD1 in vivo and disease outcome in ALS patients.

Blocking the Self-Destruct Program of Dopamine Neurons through Macrophage Migration Inhibitory Factor Nuclease Inhibition

Parkinson's disease (PD) is a progressive neurodegenerative condition that pathognomonically involves the death of dopaminergic neurons in the substantia nigra pars compacta, resulting in a myriad of motor and non-motor symptoms. Given the insurmountable burden of this disease on the population and healthcare system, significant efforts have been put forth toward generating disease modifying therapies. This class of treatments characteristically alters disease course, as opposed to current strategies that focus on managing symptoms. Previous literature has implicated the cell death pathway known as parthanatos in PD progression. Inhibition of this pathway by targeting poly (ADP)-ribose polymerase 1 (PARP1) prevents neurodegeneration in a model of idiopathic PD. However, PARP1 has a vast repertoire of functions within the body, increasing the probability of side effects with the long-term treatment likely necessary for clinically significant neuroprotection. Recent work culminated in the development of a novel agent targeting the macrophage migration inhibitory factor (MIF) nuclease domain, also named parthanatos-associated apoptosis-inducing factor nuclease (PAAN). This nuclease activity specifically executes the terminal step in parthanatos. Parthanatos-associated apoptosis-inducing factor nuclease inhibitor-1 was neuroprotective in multiple preclinical mouse models of PD. This piece will focus on contextualizing this discovery, emphasizing its significance, and discussing its potential implications for parthanatos-directed treatment. © 2024 International Parkinson and Movement Disorder Society.

The role of MIF in periodontitis: A potential pathogenic driver, biomarker, and therapeutic target

OBJECTIVE

Periodontitis is an inflammatory disease that involves an imbalance in the oral microbiota, activation of inflammatory and immune responses, and alveolar bone destruction. Macrophage migration inhibitory factor (MIF) is a versatile cytokine involved in several pathological reactions, including inflammatory processes and bone destruction, both of which are characteristics of periodontitis. While the roles of MIF in cancer and other immune diseases have been extensively characterized, its role in periodontitis remains inconclusive.

RESULTS

In this review, we describe a comprehensive analysis of the potential roles of MIF in periodontitis from the perspective of immune response and bone regulation at the cellular and molecular levels. Moreover, we discuss its potential reliability as a novel diagnostic and therapeutic target for periodontitis.

CONCLUSION

This review can aid dental researchers and clinicians in understanding the current state of MIF-related pathogenesis, diagnosis, and treatment of periodontitis.

WISP1 induces the expression of macrophage migration inhibitory factor in human lung fibroblasts through Src kinases and EGFR-activated signaling pathways

Wnt1-inducible signaling protein 1 (WISP1/CCN4) is a secreted matricellular protein that is implicated in lung and airway remodeling. The macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that has been associated with chronic lung diseases. In this study, we aimed to investigate the WISP1 signaling pathway and its ability to induce the expression of MIF in primary cultures of fibroblasts from normal human lungs (HLFs). Our results showed that WISP1 significantly stimulated the expression of MIF in a concentration- and time-dependent fashion. In WISP1-induced expression of MIF, αvβ5-integrin and chondroitin sulfate proteoglycans as well as Src tyrosine kinases, MAP kinases, phosphatidylinositol 3-kinase/Akt, PKC, and NF-κB were involved. WISP1-induced expression of MIF was attenuated in the presence of the Src kinase inhibitor PP2 or the MIF tautomerase activity inhibitor ISO-1. Moreover, WISP1 significantly increased the phosphorylation and activation of EGF receptor (EGFR) through transactivation by Src kinases. WISP1 also induced the expression of MIF receptor CD74 and coreceptor CD44, through which MIF exerts its effects on HLFs. In addition, it was found that MIF induced its own expression, as well as its receptors CD74/CD44, acting in an autocrine manner. Finally, WISP1-induced MIF promoted the expression of cyclooxygenase 2, prostaglandin E2, IL-6, and matrix metalloproteinase-2 demonstrating the regulatory role of WISP1-MIF axis in lung inflammation and remodeling involving mainly integrin αvβ5, Src kinases, PKC, NF-κB, and EGFR. The specific signaling pathways involved in WISP1-induced expression of MIF may prove to be excellent candidates for novel targets to control inflammation in chronic lung diseases.NEW & NOTEWORTHY The present study demonstrates for the first time that Wnt1-inducible signaling protein 1 (WISP1) regulates migration inhibitory factor (MIF) expression and activity and identifies the main signaling pathways involved. The newly discovered WISP1-MIF axis may drive lung inflammation and could result in the design of novel targeted therapies in inflammatory lung diseases.

5-HMF attenuates inflammation and demyelination in experimental autoimmune encephalomyelitis mice by inhibiting the MIF-CD74 interaction

The neuroprotective role of 5-hydroxymethyl-2-furfural (5-HMF) has been demonstrated in a variety of neurological diseases. The aim of this study is to investigate the effect of 5-HMF on multiple sclerosis (MS). IFN-γ-stimulated murine microglia (BV2 cells) are considered a cell model of MS. With 5-HMF treatment, microglial M1/2 polarization and cytokine levels are detected. The interaction of 5-HMF with migration inhibitory factor (MIF) is predicted using online databases. The experimental autoimmune encephalomyelitis (EAE) mouse model is established, followed by a 5-HMF injection. The results show that 5-HMF facilitates IFN-γ-stimulated microglial M2 polarization and attenuates the inflammatory response. According to the network pharmacology and molecular docking results, 5-HMF has a binding site for MIF. Further results show that blocking MIF activity or silencing CD74 enhances microglial M2 polarization, reduces inflammatory activity, and prevents ERK1/2 phosphorylation. 5-HMF inhibits the MIF-CD74 interaction by binding to MIF, thereby inhibiting microglial M1 polarization and enhancing the anti-inflammatory response. 5-HMF ameliorates EAE, inflammation, and demyelination in vivo. In conclusion, our research indicates that 5-HMF promotes microglial M2 polarization by inhibiting the MIF-CD74 interaction, thereby attenuating inflammation and demyelination in EAE mice.

Moonlighting enzymes: when cellular context defines specificity

It is not often realized that the absolute protein specificity is an exception rather than a rule. Two major kinds of protein multi-specificities are promiscuity and moonlighting. This review discusses the idea of enzyme specificity and then focusses on moonlighting. Some important examples of protein moonlighting, such as crystallins, ceruloplasmin, metallothioniens, macrophage migration inhibitory factor, and enzymes of carbohydrate metabolism are discussed. How protein plasticity and intrinsic disorder enable the removing the distinction between enzymes and other biologically active proteins are outlined. Finally, information on important roles of moonlighting in human diseases is updated.

Underrepresented Impurities in 4-Hydroxyphenylpyruvate Affect the Catalytic Activity of Multiple Enzymes

Macrophage migration inhibitory factor (MIF) is a key immunostimulatory protein with regulatory properties in several disorders, including inflammation and cancer. All the reported inhibitors that target the biological activities of MIF have been discovered by testing against its keto/enol tautomerase activity. While the natural substrate is still unknown, model MIF substrates are used for kinetic experiments. The most extensively used model substrate is 4-hydroxyphenyl pyruvate (4-HPP), a naturally occurring intermediate of tyrosine metabolism. Here, we examine the impact of 4-HPP impurities in the precise and reproducible determination of MIF kinetic data. To provide unbiased evaluation, we utilized 4-HPP powders from five different manufacturers. Biochemical and biophysical analyses showed that the enzymatic activity of MIF is highly influenced by underrepresented impurities found in 4-HPP. Besides providing inconsistent turnover results, the 4-HPP impurities also influence the accurate calculation of ISO-1's inhibition constant, an MIF inhibitor that is broadly used for in vitro and in vivo studies. The macromolecular NMR data show that 4-HPP samples from different manufacturers result in differential chemical shift perturbations of amino acids in MIF's active site. Our MIF-based conclusions were independently evaluated and confirmed by 4-hydroxyphenylpyruvate dioxygenase (HPPD) and D-dopachrome tautomerase (D-DT); two additional enzymes that utilize 4-HPP as a substrate. Collectively, these results explain inconsistencies in previously reported inhibition values, highlight the effect of impurities on the accurate determination of kinetic parameters, and serve as a tool for designing error-free in vitro and in vivo experiments.

2,5-Pyridinedicarboxylic acid is a bioactive and highly selective inhibitor of D-dopachrome tautomerase

Macrophage migration inhibitory factor (MIF) and D-dopachrome tautomerase (D-DT) are two pleotropic cytokines, which are coexpressed in various cell types to activate the cell surface receptor CD74. Via the MIF/CD74 and D-DT/CD74 axes, the two proteins exhibit either beneficial or deleterious effect on human diseases. In this study, we report the identification of 2,5-pyridinedicarboxylic acid (a.k.a. 1) that effectively blocks the D-DT-induced activation of CD74 and demonstrates an impressive 79-fold selectivity for D-DT over MIF. Crystallographic characterization of D-DT-1 elucidates the binding features of 1 and reveals previously unrecognized differences between the MIF and D-DT active sites that explain the ligand's functional selectivity. The commercial availability, low cost, and high selectivity make 1 the ideal tool for studying the pathophysiological functionality of D-DT in disease models. At the same time, our comprehensive biochemical, computational, and crystallographic analyses serve as a guide for generating highly potent and selective D-DT inhibitors.

Synthesis and evaluation of a new class of MIF-inhibitors in activated macrophage cells and in experimental septic shock in mice

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine with enzymatic activities. Anti-inflammatory effects of MIF enzyme inhibitors indicate a link between its cytokine- and catalytic activities. Herein the synthesis, docking, and bioactivity of substituted benzylidene-1-indanone and -1-tetralone derivatives as MIF-tautomerase inhibitors is reported. Many of these substituted benzylidene-1-tetralones and -indan-1-ones were potent MIF-tautomerase inhibitors (IC₅₀ < 10 μmol/L), and the most potent inhibitors were the 1-indanone derivatives 16 and 20. Some of these compounds acted as selective enolase or ketonase inhibitors. In addition, compounds 16, 20, 26, 37 and 61 efficiently inhibited NO, TNFα and IL-6 production in lipopolysaccharide-induced macrophages. Compound 20, 37 and 61 also inhibited ROS generation, and compound 26 and 37 abolished activation of NF-κB. Compound 37 significantly augmented hypothermia induced by high dose of lipopolysaccharide in mice. The possible mechanisms of action were explored using molecular modelling and docking, as well as molecular dynamics simulations.

Macrophage migration inhibitory factor is vital for inflammatory properties and survival of peripheral blood leukocytes via enhancing mitochondrial function in Ctenopharyngodon idellus

Macrophage migration inhibitory factor (MIF) is a pleiotropic protein implicated in a broad spectrum of inflammatory and proliferative disorders. The gene sequence of grass carp (Ctenopharyngodon idella) was identified and the expression level of it was regulated by cadmium exposure in our previous study. To further clarify the immune-regulatory activity of grass carp MIF, MIF was over-expressed and interfered in grass carp peripheral blood leukocytes via transfection of plasmids pcDNA3.1-MIF-EGFP and pLKO.1-shRNA-EGFP-puro, respectively. Subsequently, survival, phagocytic capacity, mitochondrial function and cytokine production of the transfected leukocytes were assayed. The results shown that grass carp MIF was necessary for leukocyte survival, because it enhanced leukocyte viability and inhibited cell apoptosis, while MIF interference disrupted the cell viability and induced leukocyte apoptosis. The effect might benefit from improved mitochondrial function as evidenced by increased ATP production, which was due to maintained mitochondrial trans-membrane potential. In addition, MIF is essential for neutral red uptake into leukocyte, and it provoked chemokine monocyte chemotactic protein-1 (MCP-1), pro-inflammatory cytokine tumor necrosis factor-alpha (TNFα), interleukin 1β (IL1β), interleukin 6 (IL6), interleukin 8 (IL8), and suppressed anti-inflammatory cytokine interleukin 10 (IL10) production. These results indicated that grass carp MIF played a vital role in regulating inflammatory properties and survival of peripheral blood leukocytes.

D-dopachrome tautomerase in cardiovascular and inflammatory diseases-A new kid on the block or just another MIF?

Macrophage migration inhibitory factor (MIF) as well as its more recently described structural homolog D-dopachrome tautomerase (D-DT), now also termed MIF-2, are atypical cytokines and chemokines with key roles in host immunity. They also have an important pathogenic role in acute and chronic inflammatory conditions, cardiovascular diseases, lung diseases, adipose tissue inflammation, and cancer. Although our mechanistic understanding of MIF-2 is relatively limited compared to the extensive body of evidence available for MIF, emerging data suggests that MIF-2 is not only a functional phenocopy of MIF, but may have differential or even oppositional activities, depending on the disease and context. In this review, we summarize and discuss the similarities and differences between MIF and MIF-2, with a focus on their structures, receptors, signaling pathways, and their roles in diseases. While mainly covering the roles of the MIF homologs in cardiovascular, inflammatory, autoimmune, and metabolic diseases, we also discuss their involvement in cancer, sepsis, and chronic obstructive lung disease (COPD). A particular emphasis is laid upon potential mechanistic explanations for synergistic or cooperative activities of the MIF homologs in cancer, myocardial diseases, and COPD as opposed to emerging disparate or antagonistic activities in adipose tissue inflammation, metabolic diseases, and atherosclerosis. Lastly, we discuss potential future opportunities of jointly targeting MIF and MIF-2 in certain diseases, whereas precision targeting of only one homolog might be preferable in other conditions. Together, this article provides an update of the mechanisms and future therapeutic avenues of human MIF proteins with a focus on their emerging, surprisingly disparate activities, suggesting that MIF-2 displays a variety of activities that are distinct from those of MIF.

MIF homolog d-dopachrome tautomerase (D-DT/MIF-2) does not inhibit accumulation and toxicity of misfolded SOD1

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by loss of upper and lower motor neurons. About 20% of familial ALS cases are caused by dominant mutations in SOD1. It has been suggested that toxicity of mutant SOD1 results from its misfolding, however, it is unclear why misfolded SOD1 accumulates within specific tissues. We have demonstrated that macrophage migration inhibitory factor (MIF), a multifunctional protein with cytokine/chemokine and chaperone-like activity, inhibits the accumulation and aggregation of misfolded SOD1. Although MIF homolog, D-dopachrome tautomerase (D-DT/MIF-2), shares structural and genetic similarities with MIF, its biological function is not well understood. In the current study, we investigated, for the first time, the mechanism of action of D-DT in a model of ALS. We show that D-DT inhibits mutant SOD1 amyloid aggregation in vitro, promoting the formation of amorphous aggregates. Moreover, we report that D-DT interacts with mutant SOD1, but does not inhibit misfolded mutant SOD1 accumulation and toxicity in neuronal cells. Finally, we show that D-DT is expressed mainly in liver and kidney, with extremely low expression in brain and spinal cord of adult mice. Our findings contribute to better understanding of D-DT versus MIF function in the context of ALS.

PAAN/MIF nuclease inhibition prevents neurodegeneration in Parkinson's disease

Parthanatos-associated apoptosis-inducing factor (AIF) nuclease (PAAN), also known as macrophage migration inhibitor factor (MIF), is a member of the PD-D/E(X)K nucleases that acts as a final executioner in parthanatos. PAAN's role in Parkinson's disease (PD) and whether it is amenable to chemical inhibition is not known. Here, we show that neurodegeneration induced by pathologic α-synuclein (α-syn) occurs via PAAN/MIF nuclease activity. Genetic depletion of PAAN/MIF and a mutant lacking nuclease activity prevent the loss of dopaminergic neurons and behavioral deficits in the α-syn preformed fibril (PFF) mouse model of sporadic PD. Compound screening led to the identification of PAANIB-1, a brain-penetrant PAAN/MIF nuclease inhibitor that prevents neurodegeneration induced by α-syn PFF, AAV-α-syn overexpression, or MPTP intoxication in vivo. Our findings could have broad relevance in human pathologies where parthanatos plays a role in the development of cell death inhibitors targeting the druggable PAAN/MIF nuclease.

A Cysteine Variant at an Allosteric Site Alters MIF Dynamics and Biological Function in Homo- and Heterotrimeric Assemblies

Macrophage migration inhibitory factor (MIF) is an inflammatory protein with various non-overlapping functions. It is not only conserved in mammals, but it is found in parasites, fish, and plants. Human MIF is a homotrimer with an enzymatic cavity between two subunits with Pro1 as a catalytic base, activates the receptors CD74, CXCR2, and CXCR4, has functional interactions in the cytosol, and is reported to be a nuclease. There is a solvent channel down its 3-fold axis with a recently identified gating residue as an allosteric site important for regulating, to different extents, the enzymatic activity and CD74 binding and signaling. In this study we explore the consequence of converting the allosteric residue Tyr99 to cysteine (Y99C) and characterize its crystallographic structure, NMR dynamics, stability, CD74 function, and enzymatic activity. In addition to the homotrimeric variant, we develop strategies for expressing and purifying a heterotrimeric variant consisting of mixed wild type and Y99C for characterization of the allosteric site to provide more insight.

Tetralone derivatives are MIF tautomerase inhibitors and attenuate macrophage activation and amplify the hypothermic response in endotoxemic mice

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine playing crucial role in immunity. MIF exerts a unique tautomerase enzymatic activity that has relevance concerning its multiple functions and its small molecule inhibitors have been proven to block its pro-inflammatory effects. Here we demonstrate that some of the E-2-arylmethylene-1-tetralones and their heteroanalogues efficiently bind to MIF's active site and inhibit MIF tautomeric (enolase, ketolase activity) functions. A small set of the synthesised derivatives, namely compounds (4), (23), (24), (26) and (32), reduced inflammatory macrophage activation. Two of the selected compounds (24) and (26), however, markedly inhibited ROS and nitrite production, NF-κB activation, TNF-α, IL-6 and CCL-2 cytokine expression. Pre-treatment of mice with compound (24) exaggerated the hypothermic response to high dose of bacterial endotoxin. Our experiments suggest that tetralones and their derivatives inhibit MIF's tautomeric functions and regulate macrophage activation and thermal changes in severe forms of systemic inflammation.

Inhibition of macrophage migration inhibitory factor alleviates LPS-induced inflammation response of HEI-OC1 cells via suppressing NF-κB signaling

BACKGROUND

Sudden sensorineural hearing loss (SSNHL) is acute and unexplained. Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine in several inflammatory diseases. However, its role in SSNHL remains elusive.

METHODS

Lipopolysaccharide (LPS) was used to induce the inflammatory response of murine auditory cells, HEI-OC1. Silencing of MIF in HEI-OC1 cells was achieved by transfection of short hairpin RNA against MIF. 740Y-P and IMD0354 were used to stimulate the PI3K pathway and suppress the NF-κB pathway, respectively. RT-qPCR and western blotting were used to examine MIF and cyclooxygenase 2 (COX2) expression in LPS-treated HEI-OC1 cells. ELISA was employed to assess prostaglandin E2 (PGE2) concentrations.

RESULTS

MIF was upregulated in LPS-treated HEI-OC1 cells. MIF knockdown reduced PGE2 synthesis and COX2 expression in LPS-treated HEI-OC1 cells. Moreover, MIF knockdown suppressed activation of the PI3K/AKT and NF-κB pathway in LPS-treated HEI-OC1 cells. Additionally, inhibition of MIF decreased PGE2 production and COX2 expression via inactivation of the NF-κB pathway.

CONCLUSION

Inhibition of MIF alleviated LPS-induced inflammation in HEI-OC1 cells via inactivating the NF-κB signaling, which might provide a better understanding for SSNHL development.

Chemokine-like MDL proteins modulate flowering time and innate immunity in plants

Human macrophage migration inhibitory factor (MIF) is an atypical chemokine implicated in intercellular signaling and innate immunity. MIF orthologs (MIF/D-DT-like proteins, MDLs) are present throughout the plant kingdom, but remain experimentally unexplored in these organisms. Here, we provide an in planta characterization and functional analysis of the three-member gene/protein MDL family in Arabidopsis thaliana. Subcellular localization experiments indicated a nucleo-cytoplasmic distribution of MDL1 and MDL2, while MDL3 is localized to peroxisomes. Protein–protein interaction assays revealed the in vivo formation of MDL1, MDL2, and MDL3 homo-oligomers, as well as the formation of MDL1-MDL2 hetero-oligomers. Functionally, Arabidopsismdl mutants exhibited a delayed transition from vegetative to reproductive growth (flowering) under long-day conditions, but not in a short-day environment. In addition, mdl mutants were more resistant to colonization by the bacterial pathogen Pseudomonas syringae pv. maculicola. The latter phenotype was compromised by the additional mutation of SALICYLIC ACID INDUCTION DEFICIENT 2 (SID2), a gene implicated in the defense-induced biosynthesis of the key signaling molecule salicylic acid. However, the enhanced antibacterial immunity was not associated with any constitutive or pathogen-induced alterations in the levels of characteristic phytohormones or defense-associated metabolites. Interestingly, bacterial infection triggered relocalization and accumulation of MDL1 and MDL2 at the peripheral lobes of leaf epidermal cells. Collectively, our data indicate redundant functionality and a complex interplay between the three chemokine-like Arabidopsis MDL proteins in the regulation of both developmental and immune-related processes. These insights expand the comparative cross-kingdom analysis of MIF/MDL signaling in human and plant systems.

Targeting Macrophage Migration Inhibitory Factor in Acute Pancreatitis and Pancreatic Cancer

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine implicated in the pathogenesis of inflammation and cancer. It is produced by various cells and circulating MIF has been identified as a biomarker for a range of diseases. Extracellular MIF mainly binds to the cluster of differentiation 74 (CD74)/CD44 to activate downstream signaling pathways. These in turn activate immune responses, enhance inflammation and can promote cancer cell proliferation and invasion. Extracellular MIF also binds to the C-X-C chemokine receptors cooperating with or without CD74 to activate chemokine response. Intracellular MIF is involved in Toll-like receptor and inflammasome-mediated inflammatory response. Pharmacological inhibition of MIF has been shown to hold great promise in treating inflammatory diseases and cancer, including small molecule MIF inhibitors targeting the tautomerase active site of MIF and antibodies that neutralize MIF. In the current review, we discuss the role of MIF signaling pathways in inflammation and cancer and summarize the recent advances of the role of MIF in experimental and clinical exocrine pancreatic diseases. We expect to provide insights into clinical translation of MIF antagonism as a strategy for treating acute pancreatitis and pancreatic cancer.

The effects of genetic deletion of Macrophage migration inhibitory factor on the chronically hypoxic pulmonary circulation

While it is well established that the haemodynamic cause of hypoxic pulmonary hypertension is increased pulmonary vascular resistance, the molecular pathogenesis of the increased resistance remains incompletely understood. Macrophage migration inhibitory factor is a pleiotropic cytokine with endogenous tautomerase enzymatic activity as well as both intracellular and extracellular signalling functions. In several diseases, macrophage migration inhibitory factor has pro-inflammatory roles that are dependent upon signalling through the cell surface receptors CD74, CXCR2 and CXCR4. Macrophage migration inhibitory factor expression is increased in animal models of hypoxic pulmonary hypertension and macrophage migration inhibitory factor tautomerase inhibitors, which block some of the functions of macrophage migration inhibitory factor, and have been shown to attenuate hypoxic pulmonary hypertension in mice and monocrotaline-induced pulmonary hypertension in rats. However, because of the multiple pathways through which it acts, the integrated actions of macrophage migration inhibitory factor during the development of hypoxic pulmonary hypertension were unclear. We report here that isolated lungs from adult macrophage migration inhibitory factor knockout (MIF^-/- ) mice maintained in normoxic conditions showed greater acute hypoxic vasoconstriction than the lungs of wild type mice (MIF^+/+ ). Following exposure to hypoxia for three weeks, isolated lungs from MIF^-/- mice had significantly higher pulmonary vascular resistance than those from MIF^+/+ mice. The major mechanism underlying the greater increase in pulmonary vascular resistance in the hypoxic MIF^-/- mice was reduction of the pulmonary vascular bed due to an impairment of the normal hypoxia-induced expansion of the alveolar capillary network. Taken together, these results demonstrate that macrophage migration inhibitory factor plays a central role in the development of the pulmonary vascular responses to chronic alveolar hypoxia.

Macrophage migration inhibitory factor modulates cytokine expression in the trophoblast cell line HTR-8/SVneo

Extravillous trophoblasts are specific placental cells that invade the uterine stroma and spiral arteries modifying and adjusting them to pregnancy. Many pregnancy pathologies are associated with impairment of this process, including preeclampsia and intrauterine growth restriction, among others. Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that is abundant at the fetomaternal interface. Previous results from our group showed that MIF participates in trophoblast invasion and modulates the expression of molecules known to mediate stromal and endovascular trophoblast invasion. In this study we investigated the possibility that MIF could act as a regulator of cytokines known to modulate trophoblast invasion using the normal extravillous trophoblast-derived cell line HTR-8/SVneo. Expression of trophoblast MIF was attenuated by MIF mRNA-specific small interfering RNAs. Cytokine expression was assessed at the mRNA and protein levels using real-time quantitative polymerase chain reaction and flow cytometry respectively. Knockdown of MIF led to a significant decrease in mRNA for IL-1β (IL1B) and IL-8 (CXCL8) and interleukin (IL)-8 protein. The addition of recombinant human MIF to cell culture medium increased IL-6 after 24h treatment and IL-6 and IL-8 after 72h treatment. Cell viability was not affected by MIF silencing or rhMIF treatment. The results of this study imply that at least some of the effects of MIF on trophoblast invasion could be mediated through autocrine or paracrine modulation of trophoblast cytokine production.

Aerosolized drug-loaded nanoparticles targeting migration inhibitory factors inhibit Pseudomonas aeruginosa-induced inflammation and biofilm formation

Aim: Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine, which has been shown to promote disease severity in cystic fibrosis. Methods: In this study, aerosolized drug-loaded nanoparticles containing SCD-19, an inhibitor of MIF's tautomerase enzymatic activity, were developed and characterized. Results: The aerosolized nanoparticles had an optimal droplet size distribution for deep lung deposition, with a high degree of biocompatibility and significant cellular uptake. Conclusion: For the first time, we have developed an aerosolized nano-formulation against MIF's enzymatic activity that achieved a significant reduction in the inflammatory response of macrophages, and inhibited Pseudomonas aeruginosa biofilm formation on airway epithelial cells. This represents a potential novel adjunctive therapy for the treatment of P. aeruginosa infection in cystic fibrosis.

MIF-Dependent Control of Tumor Immunity

Initially identified as a T lymphocyte-elicited inhibitor of macrophage motility, macrophage migration inhibitory factor (MIF) has since been found to be expressed by nearly every immune cell type examined and overexpressed in most solid and hematogenous malignant cancers. It is localized to both extracellular and intracellular compartments and physically interacts with more than a dozen different cell surface and intracellular proteins. Although classically associated with and characterized as a mediator of pro-inflammatory innate immune responses, more recent studies demonstrate that, in malignant disease settings, MIF contributes to anti-inflammatory, immune evasive, and immune tolerant phenotypes in both innate and adaptive immune cell types. This review will summarize the studies describing MIF in tumor-specific innate and adaptive immune responses and attempt to reconcile these various pleiotropic functions in normal physiology.

Parthanatos and its associated components: Promising therapeutic targets for cancer

Parthanatos is a PARP1-dependent, caspase-independent, cell-death pathway that is distinct from apoptosis, necrosis, or other known forms of cell death. Parthanatos is a multistep pathway that plays a pivotal role in tumorigenesis. There are many molecules in the parthanatos cascade that can be exploited to create therapeutic interventions for cancer management, including PARP1, PARG, ARH3, AIF, and MIF. These critical molecules are involved in tumor cell proliferation, progression, invasion, and metastasis. Therefore, these molecular signals in the parthanatos cascade represent promising therapeutic targets for cancer therapy. In addition, intimate interactions occur between parthanatos and other forms of cancer cell death, such as apoptosis and autophagy. Thus, co-targeting a combination of parthanatos and other death pathways may further provide a new avenue for cancer precision treatment. In this review, we elaborate on the signaling pathways of canonical parthanatos and briefly introduce the non-canonical parthanatos. We also shed light on the role parthanatos and its associated components play in tumorigenesis, particularly with respect to the aforementioned five molecules, and discuss the promise targeted therapy of parthanatos and its associated components holds for cancer therapy.

Inhibition of Macrophage Migration Inhibitory Factor by a Chimera of Two Allosteric Binders

Human Macrophage Migration Inhibitory Factor (MIF) is a trimeric cytokine implicated in a number of inflammatory and autoimmune diseases and cancer. We previously reported that the dye p425 (Chicago Sky Blue), which bound MIF at the interface of two MIF trimers covering the tautomerase and allosteric pockets, revealed a unique strategy to block MIF's pro-inflammatory activities. Structural liabilities, including the large size, precluded p425 as a medicinal chemistry lead for drug development. We report here a rational design strategy linking only the fragment of p425 that binds over the tautomerase pocket to the core of ibudilast, a known MIF allosteric site-specific inhibitor. The chimeric compound, termed L2-4048, was shown by X-ray crystallography to bind at the allosteric and tautomerase sites as anticipated. L2-4048 retained target binding and blocked MIF's tautomerase CD74 receptor binding, and pro-inflammatory activities. Our studies lay the foundation for the design and synthesis of smaller and more drug-like compounds that retain the MIF inhibitory properties of this chimera.

Structural and functional insights into macrophage migration inhibitory factor from Oncomelania hupensis, the intermediate host of Schistosoma japonicum

Oncomelania hupensis is the unique intermediate host of Schistosoma japonicum. As an irreplaceable prerequisite in the transmission and prevalence of schistosomiasis japonica, an in-depth study of this obligate host-parasite interaction can provide glimpse into the molecular events in the competition between schistosome infectivity and snail immune resistance. In previous studies, we identified a macrophage migration inhibitory factor (MIF) from O. hupensis (OhMIF), and showed that it was involved in the snail host immune response to the parasite S. japonicum. Here, we determined the crystal structure of OhMIF and revealed that there were distinct structural differences between the mammalian and O. hupensis MIFs. Noticeably, there was a projecting and structured C-terminus in OhMIF, which not only regulated the MIF's thermostability but was also critical in the activation of its tautomerase activity. Comparative studies between OhMIF and human MIF (hMIF) by analyzing the tautomerase activity, oxidoreductase activity, thermostability, interaction with the receptor CD74 and activation of the ERK signaling pathway demonstrated the functional differences between hMIF and OhMIF. Our data shed a species-specific light on structural, functional, and immunological characteristics of OhMIF and enrich the knowledge on the MIF family.

Immune modulation by the macrophage migration inhibitory factor (MIF) family: D-dopachrome tautomerase (DDT) is not (always) a backup system

Human macrophage migration inhibition factor (MIF) is a protein with cytokine and chemokine properties that regulates a diverse range of physiological functions related to innate immunity and inflammation. Most research has focused on the role of MIF in different inflammatory diseases. D-dopachrome tautomerase (DDT), a different molecule with structural similarities to MIF, which shares receptors and biological functions, has recently been reported, but little is known about its roles and mechanisms. In this review, we sought to understand the similarities and differences between these molecules by summarizing what is known about their different structures, receptors and mechanisms regulating their expression and biological activities with an emphasis on immunological aspects.

Macrophage migration inhibitory factor and its binding partner HTRA1 are expressed by olfactory ensheathing cells

Macrophage migration inhibitory factor (MIF) is an important regulator of innate immunity with key roles in neural regeneration and responses to pathogens, amongst a multitude of other functions. The expression of MIF and its binding partners has been characterised throughout the nervous system, with one key exception: the primary olfactory nervous system. Here, we showed in young mice (postnatal day 10) that MIF is expressed in the olfactory nerve by olfactory ensheathing glial cells (OECs) and by olfactory nerve fibroblasts. We also examined the expression of potential binding partners for MIF, and found that the serine protease HTRA1, known to be inhibited by MIF, was also expressed at high levels by OECs and olfactory fibroblasts in vivo and in vitro. We also demonstrated that MIF mediated segregation between OECs and J774a.1 cells (a monocyte/macrophage cell line) in co-culture, which suggests that MIF contributes to the fact that macrophages are largely absent from olfactory nerve fascicles. Phagocytosis assays of axonal debris demonstrated that MIF strongly stimulates phagocytosis by OECs, which indicates that MIF may play a role in the response of OECs to the continual turnover of olfactory axons that occurs throughout life.

A selective small-molecule inhibitor of macrophage migration inhibitory factor-2 (MIF-2), a MIF cytokine superfamily member, inhibits MIF-2 biological activity

Cytokine macrophage migration inhibitory factor-2 (MIF-2 or D-dopachrome tautomerase) is a recently characterized second member of the MIF cytokine superfamily in mammalian genomes. MIF-2 shares pro-inflammatory and tumorigenic properties with the clinical target MIF (MIF-1), but the precise contribution of MIF-2 to immune physiology or pathology is unclear. Like MIF-1, MIF-2 has intrinsic keto-enol tautomerase activity and mediates biological functions by engaging the cognate, common MIF family receptor CD74. Evidence that the catalytic site of MIF family cytokines has a structural role in receptor binding has prompted exploration of tautomerase inhibitors as potential biological antagonists and therapeutic agents, although few catalytic inhibitors inhibit receptor activation. Here we describe the discovery and biochemical characterization of a selective small-molecule inhibitor of MIF-2. An in silico screen of 1.6 million compounds targeting the MIF-2 tautomerase site yielded several hits for potential catalytic inhibitors of MIF-2 and identified 4-(3-carboxyphenyl)-2,5-pyridinedicarboxylic acid (4-CPPC) as the most functionally potent compound. We found that 4-CPPC has an enzymatic IC₅₀ of 27 μm and 17-fold selectivity for MIF-2 versus MIF-1. An in vitro binding assay for MIF-1/MIF-2 to the CD74 ectodomain (sCD74) indicated that 4-CPPC inhibits MIF-2-CD74 binding in a dose-dependent manner (0.01-10 μm) without influencing MIF-1-CD74 binding. Notably, 4-CPPC inhibited MIF-2-mediated activation of CD74 and reduced CD74-dependent signal transduction. These results open opportunities for development of more potent and pharmacologically auspicious MIF-2 inhibitors to investigate the distinct functions of this MIF family member in vivo.

Macrophage migration inhibitory factor (MIF) as a therapeutic target for rheumatoid arthritis and systemic lupus erythematosus

Introduction. Macrophage migration inhibitory factor (MIF) is a pleiotropic inflammatory cytokine with upstream regulatory roles in innate and adaptive immunity and is implicated in the pathogenesis of autoimmune diseases including rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Several classes of MIF inhibitors such as small molecule inhibitors and peptide inhibitors are in clinical development. Areas covered. The role of MIF in the pathogenesis of RA and SLE is examined; the authors review the structure, physiology and signaling characteristics of MIF and the related cytokine D-DT/MIF-2. The preclinical and clinical trial data for MIF inhibitors are also reviewed; information was retrieved from PubMed and ClinicalTrials.gov using the keywords MIF, D-DT/MIF-2, CD74, CD44, CXCR2, CXCR4, Jab-1, rheumatoid arthritis, systemic lupus erythematosus, MIF inhibitor, small molecule, anti-MIF, anti-CD74, and peptide inhibitor. Expert opinion. Studies in mice and in humans demonstrate the therapeutic potential of MIF inhibition for RA and SLE. MIF- directed approaches could be particularly efficacious in patients with high expression MIF genetic polymorphisms. In patients with RA and SLE and high expression MIF alleles, targeted MIF inhibition could be a precision medicine approach to treatment. Anti-MIF pharmacotherapies could also be steroid-sparing in patients with chronic glucocorticoid dependence or refractory autoimmune disease.

Human Pleural Fluid Elicits Pyruvate and Phenylalanine Metabolism in Acinetobacter baumannii to Enhance Cytotoxicity and Immune Evasion

Acinetobacter baumannii (Ab) is one of the most treacherous pathogens among those causing hospital-acquired pneumonia (HAP). A. baumannii possesses an adaptable physiology, seen not only in its antibiotic resistance and virulence phenotypes but also in its metabolic versatility. In this study, we observed that A. baumannii undergoes global transcriptional changes in response to human pleural fluid (PF), a key host-derived environmental signal. Differential gene expression analyses combined with experimental approaches revealed changes in A. baumannii metabolism, affecting cytotoxicity, persistence, bacterial killing, and chemotaxis. Over 1,220 genes representing 55% of the differentially expressed transcriptomic data corresponded to metabolic processes, including the upregulation of glutamate, short chain fatty acid, and styrene metabolism. We observed an upregulation by 1.83- and 2.61-fold of the pyruvate dehydrogenase complex subunits E3 and E2, respectively. We also found that pyruvate (PYR), in conjunction with PF, triggers an A. baumannii pathogenic behavior that adversely impacts human epithelial cell viability. Interestingly, PF also amplified A. baumannii cytotoxicity against murine macrophages, suggesting an immune evasion strategy implemented by A. baumannii. Moreover, we uncovered opposing metabolic strategies dependent on the degree of pathogenicity of the strains, where less pathogenic strains demonstrated greater utilization of PYR to promote persister formation in the presence of PF. Additionally, our transcriptomic analysis and growth studies of A. baumannii suggest the existence of an alternative phenylalanine (PA) catabolic route independent of the phenylacetic acid pathway, which converts PA to phenylpyruvate (PP) and shuttles intermediates into styrene metabolism. This alternative route promoted a neutrophil-evasive state, as PF-induced degradation of PP significantly reduced overall human neutrophil chemotaxis in ex vivo chemotactic assays. Taken together, these data highlight A. baumannii pathoadaptabililty in response to host signals and provide further insight into the role of bacterial metabolism in virulence traits, antibiotic persistence strategies, and host innate immune evasion.

An Evolutionary Perspective of Dopachrome Tautomerase Enzymes in Metazoans

Melanin plays a pivotal role in the cellular processes of several metazoans. The final step of the enzymically-regulated melanin biogenesis is the conversion of dopachrome into dihydroxyindoles, a reaction catalyzed by a class of enzymes called dopachrome tautomerases. We traced dopachrome tautomerase (DCT) and dopachrome converting enzyme (DCE) genes throughout metazoans and we could show that only one class is present in most of the phyla. While DCTs are typically found in deuterostomes, DCEs are present in several protostome phyla, including arthropods and mollusks. The respective DCEs belong to the yellow gene family, previously reported to be taxonomically restricted to insects, bacteria and fungi. Mining genomic and transcriptomic data of metazoans, we updated the distribution of DCE/yellow genes, demonstrating their presence and active expression in most of the lophotrochozoan phyla as well as in copepods (Crustacea). We have traced one intronless DCE/yellow gene through most of the analyzed lophotrochozoan genomes and we could show that it was subjected to genomic diversification in some species, while it is conserved in other species. DCE/yellow was expressed in most phyla, although it showed tissue specific expression patterns. In the parasitic copepod Mytilicola intestinalis DCE/yellow even belonged to the 100 most expressed genes. Both tissue specificity and high expression suggests that diverse functions of this gene family also evolved in other phyla apart from insects.

Role of MIF and D-DT in immune-inflammatory, autoimmune, and chronic respiratory diseases: from pathogenic factors to therapeutic targets

Macrophage migration inhibitory factor (MIF) is a protein that acts as a cytokine-, enzyme-, endocrine- and chaperon-like molecule. It binds to the cell-surface receptor CD74 in association with CD44, which activates the downstream signal transduction pathway. In addition, MIF acts also as a noncognate ligand for C-X-C chemokine receptor type 2 (CXCR2), type 4 (CXCR4), and type 7 (CXCR7). Recently, D-dopachrome tautomerase (D-DT), a second member of the MIF superfamily, was identified. From a pharmacological and clinical point of view, the nonredundant biological properties of MIF and D-DT anticipate potential synergisms from their simultaneous inhibition. Here, we focus on the role of MIF and D-DT in human immune-inflammatory, autoimmune, and chronic respiratory diseases, providing an update on the progress made in the identification of specific small-molecule inhibitors of these proteins.

Phenotyping of circulating extracellular vesicles (EVs) in obesity identifies large EVs as functional conveyors of Macrophage Migration Inhibitory Factor

Objective

Obesity-associated metabolic dysfunctions are linked to dysregulated production of adipokines. Accumulating evidence suggests a role for fat-derived extracellular vesicles (EVs) in obesity-metabolic disturbances. Since EVs convey numerous proteins we aimed to evaluate their contribution in adipokine secretion.

Methods

Plasma collected from metabolic syndrome patients were used to isolate EV subtypes, namely microvesicles (MVs) and exosomes (EXOs). Numerous soluble factor concentrations were measured successively on total, MV- and EXO-depleted plasma by multiplexed immunoassays.

Results

Circulating MVs and EXOs were significantly increased with BMI, supporting a role of EVs as metabolic relays in obesity. Obesity was associated with dysregulated soluble factor production. Sequential depletion of plasma MVs and EXOs did not modify plasma levels of these molecules, with the exception of Macrophage Migration Inhibitory Factor (MIF). Half of plasma MIF circulated within MVs, and this MV secretory pathway was conserved over different MIF-producing cells. Although MV-associated MIF triggered rapid ERK1/2 activation in macrophages, these functional MV-MIF effects specifically relied on MIF tautomerase activity.

Conclusion

Our results emphasize the importance of reconsidering MIF-metabolic actions with regard to its MV-associated form and opening new EV-based strategies for therapeutic MIF approaches.

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Plasma EV subtypes are significantly increased with obesity.

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Plasma EV subtypes carry adipokines.

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MV (large EV subtype) constitute a major secretory pathway for MIF.

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MV-associated MIF transduces metabolic responses through its tautomerase activity.

Advances and Insights for Small Molecule Inhibition of Macrophage Migration Inhibitory Factor

Macrophage migration inhibitory factor (MIF) is an upstream regulator of the immune response whose dysregulation is tied to a broad spectrum of inflammatory and proliferative disorders. As its complex signaling pathways and pleiotropic nature have been elucidated, it has become an attractive target for drug discovery. Remarkably, MIF is both a cytokine and an enzyme that functions as a keto-enol tautomerase. Strategies including in silico modeling, virtual screening, high-throughput screening, and screening of anti-inflammatory natural products have led to a large and diverse catalogue of MIF inhibitors as well as some understanding of the structure-activity relationships for compounds binding MIF's tautomerase active site. With possible clinical trials of some MIF inhibitors on the horizon, it is an opportune time to review the literature to seek trends, address inconsistencies, and identify promising new avenues of research.

Inhibitors of Melanogenesis: An Updated Review

Melanins are pigment molecules that determine the skin, eye, and hair color of the human subject to its amount, quality, and distribution. Melanocytes synthesize melanin and provide epidermal protection from various stimuli, such as harmful ultraviolet radiation, through the complex process called melanogenesis. However, serious dermatological problems occur when there is excessive production of melanin in different parts of the human body. These include freckles, melasma, senile lentigo, pigmented acne scars, and cancer. Therefore, controlling the production of melanin is an important approach for the treatment of pigmentation related disorderes. In this Perspective, we focus on the inhibitors of melanogenesis that directly/indirectly target a key enzyme tyrosinase as well as its associated signaling pathways.

Characterization of a secreted macrophage migration inhibitory factor homologue of the parasitic nematode Haemonchus Contortus acting at the parasite-host cell interface

Modulation and suppression of the immune response of the host by nematode parasites have been reported extensively and the migration inhibitory factor (MIF) is identified as one of the major immunomodulator. In the present study, we cloned and produced recombinant MIF protein from the small ruminant’s nematode parasite Haemonchus contortus (rHCMIF-1), and investigated its immunomodulatory effects on goat monocyte. Enzymatic assays indicated that rHCMIF-1 possessed tautomerase activity. Immunohistochemical test demonstrated that the native HCMIF-1 protein was predominantly localized at the body surface and internal surface of the worm’s gut. We demonstrated that rHCMIF-1 could be distinguished by antisera from goats experimentally infected with H. contortus and could bind by goat monocytes. The immunomodulatory effects of HCMIF-1 on cytokine secretion, MHC molecule expression, NO production and phagocytosis were observed by co-incubation of rHCMIF-1 with goat monocytes. The results showed that the interaction of rHCMIF-1 decreased the production of TNF-α, IL-1β and IL-12p40, where as, it significantly increased the secretion of IL-10 and TGF β in goat monocytes. After rHCMIF-1 exposure, the expression of MHC-II on goat monocytes was inhibited. Moreover, rHCMIF-1 could down-regulate the LPS induced NO production of goat monocytes. Phagocytotic assay by FITC-dextran internalization showed that rHCMIF-1 could inhibit the phagocytosis of goat monocytes. Our findings provided potential targetas immunoregulator, and will be helpful to elucidate the molecular basis of host–parasite interactions and search for new potential protein as vaccine and drug target candidate.

Identification of CPE and GAIT elements in 3'UTR of macrophage migration inhibitory factor (MIF) involved in inflammatory response induced by LPS in Ciona robusta

Innate immune responses face infectious microorganisms by inducing inflammatory responses. Multiple genes within distinct functional categories are coordinately and temporally regulated by transcriptional 'on' and 'off' switches that account for the specificity of gene expression in response to external stimuli. Mechanisms that control transcriptional and post-transcriptional regulation are important in coordinating the initiation and resolution of inflammation. Macrophage migration inhibitory factor (MIF) is an important cytokine that, in Ciona robusta, is related to inflammatory response. It is well known that in C. robusta, formerly known as Ciona intestinalis, the pharynx is involved in the inflammatory reaction induced by lipopolysaccharide (LPS) injection in the body wall. Using this biological system, we describe the identification of two C. robusta MIFs (CrMIF1 and CrMIF2). The phylogenetic tree and modeling support a close relationship with vertebrate MIF family members. CrMIF1 and CrMIF2 possess two evolutionally conserved catalytic sites: a tautomerase and an oxidoreductase site with a conserved CXXC motif. Real-time PCR analysis shows a prompt expression induced by LPS inoculation in CrMIF1 and a late upregulation of CrMIF2 and in silico analyses of 3'UTR show a cis-acting GAIT element and a CPE element in 3'-UTR, which are not present in the 3'-UTR of CrMIF1, suggesting that different transcriptional and post-transcriptional control mechanisms are involved in the regulation of gene expression of MIF during inflammatory response in C. robusta.

Biological activities and functional analysis of macrophage migration inhibitory factor in Oncomelania hupensis, the intermediate host of Schistosoma japonicum

Schistosomiasis is a destructive parasitic zoonosis caused by agents of the genus Schistosoma, which afflicts more than 250 million people worldwide. The freshwater amphibious snail Oncomelania hupensis serves as the obligate intermediate host of Schistosoma japonicum. Macrophage migration inhibitory factor (MIF) has been demonstrated to be a pleiotropic immunoregulatory cytokine and a key signaling molecule involved in adaptive and innate immunity. In the present study, we obtained the full-length cDNA of OhMIF and analyzed the characteristics of the ORF and the peptide sequence in O. hupensis. Next we have successfully expressed and purified the recombinant OhMIF protein (rOhMIF) together with a site-directed mutant rOhMIFP2G, in which the N-terminal Proline (Pro2) was substituted by a Gly. Our results indicated that rOhMIF displayed the conserved D-dopachrome tautomerase activity which is dependent on Pro2, and this enzymatic activity can be significantly inhibited by the MIF antagonist ISO-1. Moreover, we also measured and compared the steady state kinetic values for D-dopachrome tautomerase activity of rOhMIF and rHsMIF, and the results showed that the reaction rate, catalytic efficiency and substrate affinity of rOhMIF are significantly lower than those of rHsMIF. Additionally, we also showed that rOhMIF had the oxidoreductase activity which can utilize DTT as reductant to reduce insulin. Furthermore, the results obtained from the in vitro injection assay demonstrated that rOhMIF and its mutant rOhMIFP2G can also induce the phosphorylation and activation of ERK1/2 pathway in O. hupensis circulating hemocytes, indicating that the tautomerase activity is not required for this biological function. These results are expected to produce a better understanding of the internal immune defense system in O. hupensis, and help to further explore the interaction between O. hupensis and its natural parasite S. japoniucm.

A global view of structure-function relationships in the tautomerase superfamily

The tautomerase superfamily (TSF) consists of more than 11,000 nonredundant sequences present throughout the biosphere. Characterized members have attracted much attention because of the unusual and key catalytic role of an N-terminal proline. These few characterized members catalyze a diverse range of chemical reactions, but the full scale of their chemical capabilities and biological functions remains unknown. To gain new insight into TSF structure-function relationships, we performed a global analysis of similarities across the entire superfamily and computed a sequence similarity network to guide classification into distinct subgroups. Our results indicate that TSF members are found in all domains of life, with most being present in bacteria. The eukaryotic members of the cis-3-chloroacrylic acid dehalogenase subgroup are limited to fungal species, whereas the macrophage migration inhibitory factor subgroup has wide eukaryotic representation (including mammals). Unexpectedly, we found that 346 TSF sequences lack Pro-1, of which 85% are present in the malonate semialdehyde decarboxylase subgroup. The computed network also enabled the identification of similarity paths, namely sequences that link functionally diverse subgroups and exhibit transitional structural features that may help explain reaction divergence. A structure-guided comparison of these linker proteins identified conserved transitions between them, and kinetic analysis paralleled these observations. Phylogenetic reconstruction of the linker set was consistent with these findings. Our results also suggest that contemporary TSF members may have evolved from a short 4-oxalocrotonate tautomerase-like ancestor followed by gene duplication and fusion. Our new linker-guided strategy can be used to enrich the discovery of sequence/structure/function transitions in other enzyme superfamilies.

Role of the Cysteine 81 Residue of Macrophage Migration Inhibitory Factor as a Molecular Redox Switch

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory and tumor-promoting cytokine that occurs in two redox-dependent immunologically distinct conformational isoforms. The disease-related structural isoform of MIF (oxMIF) can be specifically and predominantly detected in the circulation of patients with inflammatory diseases and in tumor tissue, whereas the ubiquitously expressed isoform of MIF (redMIF) is abundantly expressed in healthy and diseased subjects. In this article, we report that cysteine 81 within MIF serves as a "switch cysteine" for the conversion of redMIF to oxMIF. Modulating cysteine 81 by thiol reactive agents leads to significant structural rearrangements of the protein, resulting in a decreased β-sheet content and an increased random coil content, but maintaining the trimeric quaternary structure. This conformational change in the MIF molecule enables binding of oxMIF-specific antibodies BaxB01 and BaxM159, which showed beneficial activity in animal models of inflammation and cancer. Crystal structure analysis of the MIF-derived EPCALCS peptide, bound in its oxMIF-like conformation by the Fab fragment of BaxB01, revealed that this peptide adopts a curved conformation, making the central thiol protein oxidoreductase motif competent to undergo disulfide shuffling. We conclude that redMIF might reflect a latent zymogenic form of MIF, and formation of oxMIF leads to a physiologically relevant, i.e., enzymatically active, state.