Crystallization and preliminary X-ray analysis of human D-dopachrome tautomerase

Macrophage migration inhibitory factor MtMIF3 prevents the premature aging of Medicago truncatula nodules

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine involved in immune response in animals. However, the role of MIFs in plants such as Medicago truncatula, particularly in symbiotic nitrogen fixation, remains unclear. An investigation of M. truncatula-Sinorhizobium meliloti symbiosis revealed that MtMIF3 was mainly expressed in the nitrogen-fixing zone of the nodules. Silencing MtMIF3 using RNA interference (Ri) technology resulted in increased nodule numbers but higher levels of bacteroid degradation in the infected cells of the nitrogen-fixing zone, suggesting that premature aging was induced in MtMIF3-Ri nodules. In agreement with this conclusion, the activities of nitrogenase, superoxide dismutase and catalase were lower than those in controls, but cysteine proteinase activity was increased in nodulated roots at 28 days postinoculation. In contrast, the overexpression of MtMIF3 inhibited nodule senescence. MtMIF3 is localized in the plasma membrane, nucleus, and cytoplasm, where it interacts with methionine sulfoxide reductase B (MsrB), which is also localized in the chloroplasts of tobacco leaf cells. Taken together, these results suggest that MtMIF3 prevents premature nodule aging and protects against oxidation by interacting with MtMsrB.

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.

The Dichotomic Role of Macrophage Migration Inhibitory Factor in Neurodegeneration

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine expressed by different cell types and exerting multiple biological functions. It has been shown that MIF may be involved in several disorders, including neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS), Parkinson disease (PD), and Huntington disease (HD), that represent an unmet medical need. Therefore, further studies are needed to identify novel pathogenetic mechanisms that may translate into tailored therapeutic approaches so to improve patients’ survival and quality of life. Here, we reviewed the preclinical and clinical studies investigating the role of MIF in ALS, PD, and HD. The emerging results suggest that MIF might play a dichotomic role in these disorders, exerting a protective action in ALS, a pathogenetic action in HD, and a yet undefined and debated role in PD. The better understanding of the role of MIF in these diseases could allow its use as a novel diagnostic and therapeutic tool for the monitoring and treatment of the patients and for eventual biomarker-driven therapeutic approaches.

Emerging Role of the Macrophage Migration Inhibitory Factor Family of Cytokines in Neuroblastoma. Pathogenic Effectors and Novel Therapeutic Targets?

Neuroblastoma (NB) is the most frequent extracranial pediatric tumor. Despite the current available multiple therapeutic options, the prognosis for high-risk NB patients remains unsatisfactory and makes the disease a clear unmet medical need. Thus, more tailored therapeutic approaches are warranted to improve both the quality of life and the survival of the patients. Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that plays a key role in several diseases, including cancer. Preclinical and clinical studies in NB patients convergently indicate that MIF exerts pro-tumorigenic properties in NB. MIF is upregulated in NB tumor tissues and cell lines and it contributes to NB aggressiveness and immune-escape. To date, there are only a few data about the role of the second member of the MIF family, the MIF homolog d-dopachrome tautomerase (DDT), in NB. Here, we review the preclinical and clinical studies on the role of the MIF family of cytokines in NB and suggest that MIF and possibly DDT inhibitors may be promising novel prognostic and therapeutic targets in NB management.

Modeling of both shared and distinct interactions between MIF and its homologue D-DT with their common receptor CD74

D-dopachrome tautomerase (D-DT) shares amino acid sequence similarity, structural architecture and biological activity with the cytokine MIF. Recent studies show that the two protein homologs also bind to the same cell surface receptor, CD74, to activate the ERK1/2 pathway that ultimately leads to pro-inflammatory and pro-survival gene expression. We recently showed that RTL1000 and DRa1-MOG-35-55, two biological drugs with potent anti-inflammatory properties that treat experimental autoimmune encephalomyelitis (EAE) in mice, bind to the cell surface receptor CD74 with high affinity and compete with MIF for binding to the same regions of CD74. Computational modeling of MIF and RTL1000 binding interactions with CD74 predicted the presence of three CD74 binding regions for each MIF homotrimer. Through a similar approach we have now expanded our work to study the D-DT (MIF-2) interaction with CD74 that is mainly defined by three elements scattered throughout the disordered regions of the interacting molecules. The model predicted: (a) a hydrophobic cradle between CD74 and D-DT consisting of N-terminal tyrosine residues of three CD74 monomers arranged in a planar alignment interacts with aromatic amino acid residues located in the disordered D-DT C-terminus; (b) a triad consisting of the E103 residue on one D-DT monomer in close contact with R179 and S181 on one chain of the CD74 trimer forms an intermolecular salt bridge; and (c) amino acid residues on the C-terminus random coil of CD74 chain C form a long interacting area of ∼500Å2 with a disordered region of D-DT chain B. These three binding elements were also present in MIF/CD74 binding interactions, with involvement of identical or highly similar amino acid residues in each MIF homotrimer that partner with the exact same residues in CD74. Topologically, however, the location of the three CD74 binding regions of the D-DT homotrimer differs substantially from that of the three MIF binding regions. This key difference in orientation appears to derive from a sequence insertion in D-DT that topologically limits binding to only one CD74 molecule per D-DT homotrimer, in contrast to predicted binding of up to three CD74 molecules per MIF homotrimer. These results have implications for the manner in which D-DT and MIF compete with each other for binding to the CD74 receptor and for the relative potency of DRa1-MOG-35-55 and RTL1000 for competitive inhibition of D-DT and MIF binding and activation through CD74.

D-dopachrome tautomerase is over-expressed in pancreatic ductal adenocarcinoma and acts cooperatively with macrophage migration inhibitory factor to promote cancer growth

Previous studies have established the important role of MIF in the development of pancreatic ductal adenocarcinoma (PDAC) for both therapeutic and diagnostic perspectives, but little is known about the expression and function of D-dopachrome tautomerase (DDT), a functional homolog of MIF, in PDAC. In the present study, we demonstrated that DDT was over-expressed in PDAC tissues in a pattern correlated with MIF. In the pancreatic cancer cell lines, PANC-1, BXPC-3 and ASPC-1, both DDT and MIF were expressed and co-localized with each other in the endosomal compartments and plasma membrane. Knockdown of DDT and MIF in PANC-1 cells cooperatively inhibited ERK1/2 and AKT phosphorylation, increased p53 expression, and reduced cell proliferation, invasion and tumor formation. These effects were rescued by the re-expression of MIF or DDT, but not by the forced expression of the tautomerase-deficient mutants of DDT and MIF, P1G-DDT and P1G-MIF. Finally, we observed that 4-iodo-6-phenylpyrimidine (4-IPP), a covalent tautomerase inhibitor of both DDT and MIF, attenuated PANC-1 cell proliferation and colony formation in vitro and tumor growth in vivo. Thus, targeting the tautomerase sites of both MIF and DDT may offer more efficient therapeutic benefits to PDAC patients.

Brain miffed by macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a cytokine which also exhibits enzymatic properties like oxidoreductase and tautomerase. MIF plays a pivotal role in innate and acquired immunity as well as in the neuroendocrine axis. Since it is involved in the pathogenesis of acute and chronic inflammation, neoangiogenesis, and cancer, MIF and its signaling components are considered suitable targets for therapeutic intervention in several fields of medicine. In neurodegenerative and neurooncological diseases, MIF is a highly relevant, but still a hardly investigated mediator. MIF operates via intracellular protein-protein interaction as well as in CD74/CXCR2/CXCR4 receptor-mediated pathways to regulate essential cellular systems such as redox balance, HIF-1, and p53-mediated senescence and apoptosis as well as multiple signaling pathways. Acting as an endogenous glucocorticoid antagonist, MIF thus represents a relevant resistance gene in brain tumor therapies. Alongside this dual action, a functional homolog-annotated D-dopachrome tautomerase/MIF-2 has been uncovered utilizing the same cell surface receptor signaling cascade as MIF. Here we review MIF actions with respect to redox regulation in apoptosis and in tumor growth as well as its extracellular function with a focus on its potential role in brain diseases. We consider the possibility of MIF targeting in neurodegenerative processes and brain tumors by novel MIF-neutralizing approaches.

Characterization of catalytic centre mutants of macrophage migration inhibitory factor (MIF) and comparison to Cys81Ser MIF

Macrophage migration inhibitory factor (MIF) displays both cytokine and enzyme activities, but its molecular mode of action is still unclear. MIF contains three cysteine residues and we showed recently that the conserved Cys57-Ala-Leu-Cys60 (CALC) motif is critical for the oxidoreductase and macrophage-activating activities of MIF. Here we probed further the role of this catalytic centre by expression, purification, and characterization of the cysteine-->serine mutants Cys60Ser, Cys57Ser/Cys60Ser, and Cys81Ser of human MIF and of mutants Ala58Gly/Leu59Pro and Ala58Gly/Leu59His, containing a thioredoxin (Trx)-like and protein disulphide isomerase (PDI)-like dipeptide, respectively. The catalytic centre mutants formed inclusion bodies and the resultant mutant proteins Cys57Ser/Cys60Ser, Ala58Gly/Leu59Pro, and Als58Gly/Leu59His were only soluble in organic solvent or 6 m GdmHCl when reconstituted at concentrations above 1 microgram.mL-1. This made it necessary to devise new purification methods. By contrast, mutant Cys81Ser was soluble. Effects of pH, solvent, and ionic strength conditions on the conformation of the mutants were analysed by far-UV CD spectropolarimetry and mutant stability was examined by denaturant-induced unfolding. The mutants, except for mutant Cys81Ser, showed a close conformational similarity to wild-type (wt) MIF, and stabilization of the mutants was due mainly to acid pH conditions. Intramolecular disulphide bond formation at the CALC region was confirmed by near-UV CD of mutant Cys60Ser. Mutant Cys81Ser was not involved in disulphide bond formation, yet had decreased stability. Analysis in the oxidoreductase and a MIF-specific cytokine assay revealed that only substitution of the active site residues led to inactivation of MIF. Mutant Cys60Ser had no enzyme and markedly reduced cytokine activity, whereas mutant Cys81Ser was active in both tests. The Trx-like variant showed significant enzyme activity but was less active than wtMIF; PDI-like MIF was enzymatically inactive. However, both variants had full cytokine activity. Together with the low but nonzero cytokine activity of mutant Cys60Ser, this indicated that the cytokine activity of MIF may not be tightly regulated by redox effects or that a distinguishable receptor mechanism exists. This study provides evidence for a role of the CALC motif in the oxidoreductase and cytokine activities of MIF, and suggests that Cys81 could mediate conformational effects. Availability and characterization of the mutants should greatly aid in the further elucidation of the mechanism of action of the unusual cytokine MIF.

Crystal structure of human D-dopachrome tautomerase, a homologue of macrophage migration inhibitory factor, at 1.54 A resolution

D-Dopachrome tautomerase shares a low homologous amino acid sequence (33% homology) with the macrophage migration inhibitory factor (MIF) and possesses similar tautomerase activity as well. MIF is a cytokine involved in inflammatory reactions and immune responses. Whereas recent studies have identified MIF as a pituitary hormone and immunoregulator, much less is known about the structural basis of these physiological functions and the real significance of tautomerase activity. Therefore, interest in the structure-function relationship between D-dopachrome tautomerase and MIF has increased, especially with regard to inflammation and immune responses. We have determined the X-ray crystal structure of human D-dopachrome tautomerase at 1.54 A resolution. D-Dopachrome tautomerase folds to form a homotrimer that has extensive contact between subunits by intersubunit beta-sheets. Its overall topology and trimeric formations are similar to those of human MIF. The N-terminal proline is located at the bottom of a positively charged pocket in which the conformations of Lys32 and Ser63 are highly conserved. These positively charged properties are also seen in the active site pocket of human MIF, bacterial 5-(carboxymethyl)-2-hydroxymuconate isomerase (CHMI), and 4-oxalocrotonate tautomerase (4-OT). A detailed comparison of these structures revealed significant differences in the environment around the potential active site, the intersubunit contacts, and charge distribution on the molecular surface. It can be concluded that these features are related to the physiological role and tautomerase activity of MIF and D-dopachrome tautomerase. The present structural study could be helpful for designing effective inhibitors that modulate immunoregulatory and hormone-like effects.

Physical mapping of the evolutionary boundary between human chromosomes 21 and 22 on mouse chromosome 10

Adjacent regions of mouse Chromosome 10 (MMU10) show conserved synteny with human chromosome 22 (HSA22) and the telomeric region of HSA21. Physical mapping on MMU10 using YAC fragmentation and PAC contig analyses demonstrates that Prmt2 has a position consistent with its human homolog, HRMT1L1, being telomeric to S100B on HSA21. This result establishes Prmt2 as the new proximal boundary of the region of conserved synteny between MMU10 and HSA21 and predicts that it is the most telomeric gene known on HSA21. Physical mapping refines the positions and order of HSA22 homologs Mmp11, Mif, and Ddt, demonstrates the orientation of S100b on the mouse chromosome, and localizes the junction of conserved synteny between HSA21 and HSA22 on MMU10. Comparative mapping in this region is important for defining gene structure and dosage imbalance in Down syndrome (DS), for developing animal models of DS, and for understanding processes of chromosome evolution.

Molecular cloning of human D-dopachrome tautomerase cDNA: N-terminal proline is essential for enzyme activation

D-Dopachrome tautomerase converts 2-carboxy-2,3-dihydroindole-5,6-quinone (D-dopachrome) into 5,6-dihydroxyindole. This protein has an amino acid sequence that is highly homologous with that of macrophage migration inhibitory factor (MIF), which has the potential to catalyze D-dopachrome to 5,6-dihydroxyindole-2-carboxylic acid and is an important cytokine for T-lymphocyte activation. We isolated and sequenced a 566 bp-long cDNA encoding human D-dopachrome tautomerase. The cDNA contains an open reading frame encoding 118 amino acids, including the initiator methionine. The amino acid sequence of the protein shares 80% homology with that of the rat enzyme. Northern blot analysis demonstrated that mRNA of D-dopachrome tautomerase is expressed in a large amount in the liver, and to lesser extent in other organs, including the heart, lung and pancreas. After purification of D-dopachrome tautomerase expressed in E. coli, we confirmed that the recombinant protein catalyzes the conversion of D-dopachrome to 5,6-dihydroxyindole. Its catalytic mechanism is not well understood. We found that the protein completely lost the enzyme activity when the N-terminal proline residue was replaced with alanine by site-directed mutagenesis. This fact suggests that the N-terminal proline is essential for the catalytic mechanism. Although the precise pathophysiological function of D-dopachrome tautomerase remains to be elucidated, the present results could contribute to further understanding of isomerase activity in relation to the immune response.