MIF as a glucocorticoid-induced modulator of cytokine production

Pituitary cytokine and growth factor expression and action

The complex range of pituitary regulatory mechanisms reviewed here underlies the critical function of the pituitary in sustaining all higher life forms. Thus, the ultimate net secretion of pituitary hormones is determined by signal integration from all three tiers of pituitary control. It is clear from our current knowledge that the trophic hormone cells of the anterior pituitary are uniquely specialized to respond to these signals. Unravelling their diversity and complexity will shed light upon the normal function of the master gland. Understanding these control mechanisms will lead to novel diagnosis and therapy of disordered pituitary function (357).

Regulatory role for macrophage migration inhibitory factor in acute respiratory distress syndrome

Migration inhibitory factor (MIF) is known to exert significant pro-inflammatory effects and has the potential to override the anti-inflammatory action of glucocorticoids. In this study we have identified significant quantities of MIF in the alveolar airspaces of patients with acute respiratory distress syndrome (ARDS). We show in alveolar cells from patients with ARDS that MIF augments pro-inflammatory cytokine secretion (TNF alpha and IL-8), anti-MIF significantly attenuates TNF alpha and IL-8 secretion and MIF overrides, in a concentration-related fashion, the anti-inflammatory effects of glucocorticoids. These findings suggest that MIF may act as a mediator sustaining the pulmonary inflammatory response in ARDS and that an anti-MIF strategy may represent a novel therapeutic approach in inflammatory diseases such as ARDS.

Stabilized expression of mRNA is associated with mycobacterial resistance controlled by Nramp1

Control of innate resistance to the growth of mycobacteria is mediated by a gene termed Nramp1. Although the role of the protein product of Nramp1 in mediating resistance to mycobacterial growth is not known, the effect of the gene is pleiotropic and it has been suggested that the gene controls macrophage priming for activation. We have found that the functional capacity of macrophages from Mycobacterium bovis BCG-susceptible mice can be suppressed by corticosterone, while the function of macrophages from BCG-resistant mice remains unaffected. In this study, we show that corticosterone differentially affects the stability of mRNAs of several recombinant gamma interferon (rIFN-gamma)-induced genes. Treatment of macrophages from BCG-susceptible mice with corticosterone accelerates the decay of Nramp1 mRNA. The mRNA of IFN-gamma-induced genes of macrophages from BCG-resistant mice was more stable than the mRNA of macrophages from BCG-susceptible mice in the presence or absence of corticosterone. The results of this investigation suggest that Nramp1 acts by stabilizing the mRNA of genes associated with macrophage activation, thus accounting for the functional differences that have been attributed to these macrophage populations.

Effect of dexamethasone on invasion of human squamous cell carcinoma cells into collagen gel

The effect of dexamethasone (Dex) on the ability to invade type I collagen gel was investigated in two cell lines of oral squamous cell carcinoma (SCC). At concentrations higher than 10(-8) M, Dex significantly suppressed the invasive growth of SCC cells into the gel. The same concentrations of Dex led to a decrease in urokinase type plasminogen activator (u-PA) synthesis and an increase in plasminogen activator inhibitor type 1 (PAI-1) synthesis by SCC cells. These findings suggest that Dex inhibits the invasiveness of SCC cells by decreasing their proteolytic activity.

Identification of macrophage migration inhibitory factor in murine neonatal calvariae and osteoblasts

Bone resorption and formation are dynamic processes that occur in both normal and injured bone tissues. Regulation of these processes is mediated at the local level by cytokines and growth factors. Macrophage migration inhibitory factor (MIF) is one of the proinflammatory cytokines that activates macrophages and regulates production of other cytokines, such as tumour necrosis factor-alpha and interleukin-1. We here demonstrate, by reverse transcription-polymerase chain reaction, high expression of MIF mRNA in murine osteoblasts obtained from mouse neonatal calvariae and murine osteoblastic MC3T3-E1 cells. The presence of MIF protein in the osteoblasts was confirmed by Western blot analysis using anti-rat MIF antibody. Moreover, the immunohistochemical study revealed that MIF was localized largely in the cytoplasm. The pathophysiological function of MIF remains undefined; however, the present results suggest that MIF takes part in the osseous metabolism as well as in immunological events.

NMR characterization of structure, backbone dynamics, and glutathione binding of the human macrophage migration inhibitory factor (MIF)

Human macrophage migration inhibitory factor is a 114 amino acid protein that belongs to the family of immunologic cytokines. Assignments of 1H, 15N, and 13C resonances have enabled the determination of the secondary structure of the protein, which consists of two alpha-helices (residues 18-31 and 89-72) and a central four-stranded beta-sheet. In the beta-sheet, two parallel beta-sheets are connected in an antiparallel sense. From the total of three cysteines present in the primary structure of MIF, none was found to form disulfide bridges. 1H-15N heteronuclear T1, T2, and steady-state NOE measurements indicate that the backbone of MIF exists in a rigid structure of limited conformational flexibility (on the nanosecond to picosecond time scale). Several residues located in the loop regions and at the N termini of two helices exhibit internal motions on the 1-3 ns time scale. The capacity to bind glutathione was investigated by titration of a uniform 15N-labeled sample and led us to conclude that MIF has, at best, very low affinity for glutathione.

Detection and immunolocalization of macrophage migration inhibitory factor in rat iris and ciliary epithelium

To elucidate the role of macrophage migration inhibitory factor (MIF) in ocular inflammation, we examined the localization of MIF in the normal anterior uveal tract of rats. Immunohistochemistry using an anti-MIF antibody revealed that MIF was present in non-pigment epithelial cells of the ciliary body and the epithelial cells of the iris. Western blot analysis of these tissues showed a single band specific for MIF protein. The expression of MIF mRNA in these tissues was further confirmed by reverse transcription-polymerase chain reaction. Since MIF is known to be a potent proinflammatory cytokine, identification of the protein in iris and ciliary epithelial cells suggests the possibility that it may play an important role in ocular inflammation.

An essential regulatory role for macrophage migration inhibitory factor in T-cell activation

The protein known as macrophage migration inhibitory factor (MIF) was one of the first cytokines to be discovered and was described 30 years ago to be a T-cell-derived factor that inhibited the random migration of macrophages in vitro. A much broader role for MIF has emerged recently as a result of studies that have demonstrated it to be released from the anterior pituitary gland in vivo. MIF also is the first protein that has been identified to be secreted from monocytes/macrophages upon glucocorticoid stimulation. Once released, MIF acts to "override" or counter-regulate the suppressive effects of glucocorticoids on macrophage cytokine production. We report herein that MIF plays an important regulatory role in the activation of T cells induced by mitogenic or antigenic stimuli. Activated T cells produce MIF and neutralizing anti-MIF antibodies inhibit T-cell proliferation and interleukin 2 production in vitro, and suppress antigen-driven T-cell activation and antibody production in vivo. T cells also release MIF in response to glucocorticoid stimulation and MIF acts to override glucocorticoid inhibition of T-cell proliferation and interleukin 2 and interferon gamma production. These studies indicate that MIF acts in concert with glucocorticoids to control T-cell activation and assign a previously unsuspected but critical role for MIF in antigen-specific immune responses.

Crystal structure of macrophage migration inhibitory factor from human lymphocyte at 2.1 A resolution

The three-dimensional structure of the macrophage migration inhibitory factor (MIF) from human lymphocytes has been determined by X-ray crystallography at 2.1 A resolution. The structure was solved by a molecular replacement technique using the coordinates of rat MIF. The molecule forms a trimer structure similar to the rat MIF. However, unlike the rat MIF whose C-terminal tail (residues 104-114) is disordered in the crystal, human MIF has a definite main-chain conformation up to the C-terminal end. These eleven residues create two more beta-strands and join to the inter-subunit beta-sheet, which contribute to forming a trimer structure. Thus, the trimer structure consists of three seven-stranded beta-sheets surrounded by six alpha-helices. Each beta-sheet is comprised of beta-strands from each of the three monomers. This architecture is almost identical to 5-carboxymethyl-2-hydroxymuconate isomerase (CHMI) and is related to the E. coli signal transducing protein PII.

Evidence for the presence of macrophage migration inhibitory factor in murine reproductive organs and early embryos

Cytokines appear to play a critical role in the establishment of early pregnancy. In this study, we examined the mRNA expression of murine macrophage migration inhibitory factor (MIF), one of the cytokines activating macrophages, in the murine reproductive system by Northern blot analysis. It revealed that MIF mRNA was expressed in the ovary, the oviduct and the uterus during the pre-implantation period and all stages of the estrus cycle. The histological localization of MIF in the uterus was examined by an immunohistochemical method, which revealed that MIF was mostly present in the tunica muscularis. It was, moreover, demonstrated by reverse transcription-polymerase chain reaction (RT-PCR) that MIF mRNA was expressed in the ovulated oocytes, zygotes, 2-cell embryos, 8-cell embryos and blastocysts. MIF is known to be present in T-lymphocytes and monocytes/macrophages; however, it was revealed by the present study that MIF mRNA is expressed in the reproductive organs and the early stages of embryos. Considering these results, it s suggested that MIF plays an important role in the establishment of pregnancy.

MIF re-discovered: pituitary hormone and glucocorticoid-induced regulator of cytokine production

The protein mediator known as macrophage migration inhibitory factor (MIF) was one of the first cytokine activities to be discovered and was described 30 years ago to be a T cell-derived factor that inhibited the random migration of macrophages. Despite the long-standing association of MIF with activated lymphocytes, the precise role of MIF in host responses remained undefined. Recent studies however, have led to the description of a pituitary mediator that appears to act as the natural, counter-regulatory hormone for glucocorticoid action within the immune system. Isolated as a product of an anterior pituitary cell line, this protein was sequenced and found to have the same structure as MIF. The major role of MIF appears to be to act at an inflammatory site or lymph node to counter-balance the inhibitory effects of steroids on the primary immune response, which must necessarily be mounted to eliminate the source of infection or tissue invasion.

Crystal structure at 2.6-A resolution of human macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) was the first cytokine to be described, but for 30 years its role in the immune response remained enigmatic. In recent studies, MIF has been found to be a novel pituitary hormone and the first protein identified to be released from immune cells on glucocorticoid stimulation. Once secreted, MIF counterregulates the immunosuppressive effects of steroids and thus acts as a critical component of the immune system to control both local and systemic immune responses. We report herein the x-ray crystal structure of human MIF to 2.6 angstrom resolution. The protein is a trimer of identical subunits. Each monomer contains two antiparallel alpha-helices that pack against a four-stranded beta-sheet. The monomer has an additional two beta-strands that interact with the beta-sheets of adjacent subunits to form the interface between monomers. The three beta-sheets are arranged to form a barrel containing a solvent-accessible channel that runs through the center of the protein along a molecular 3-fold axis. Electrostatic potential maps reveal that the channel has a positive potential, suggesting that it binds negatively charged molecules. The elucidated structure for MIF is unique among cytokines or hormonal mediators, and suggests that this counterregulator of glucocorticoid action participates in novel ligand-receptor interactions.

Identification and immunohistochemical localization of macrophage migration inhibitory factor in human cornea

We identified macrophage migration inhibitory factor (MIF) mRNA expression in human cornea, and demonstrated its immunohistological localization. Reverse transcription-polymerase chain reaction analysis revealed that MIF mRNA was expressed in both the corneal epithelial and endothelial cells. Immunohistochemical study using the polyclonal antibody prepared from immunizing a rabbit with human recombinant MIF showed that MIF was present in the basal cells of corneal epithelium and endothelial cells. The fact that MIF exists in those cells of the cornea indicates that MIF may play an important role in corneal cell immunity and cellular differentiation.

Identification of macrophage migration inhibitory factor (MIF) in human skin and its immmunohistochemical localization

The presence and tissue localization of macrophage migration inhibitory factor (MIF) in human skin were examined. Reverse transcription-polymerase chain reaction analysis revealed that MIF mRNA was expressed in both surgically obtained normal human epidermis and primary cultured human keratinocytes. The expression of MIF was further confirmed by Western blot analysis, which demonstrated a single band at about 12.5 kDa using a polyclonal antibody against human recombinant MIF. Immunohistochemical studies showed that MIF existed in human epidermis, especially in the basal layer. The pathophysiological role of MIF in human skin remains undefined; however, the present results indicate that MIF may play an important role in immunity, inflammation and cellular differentiation of epidermal cells.

Crystal structure of the macrophage migration inhibitory factor from rat liver

The tertiary structure of the macrophage migration inhibitory factor (MIF) from rat liver (12,300 Mr) is presented at 2.2 A resolution. Each monomer consists of two beta/alpha/beta motifs aligned in quasi two-fold symmetry, comprising a domain consisting of a four-stranded mixed beta-sheet and two antiparallel alpha-helices. The protein exists as a trimer in the crystal. An extra beta-strand that is almost perpendicular to the other beta-strands joins to the beta-sheet of the neighbouring monomer in the trimer. Unexpected similarities were detected between MIF and two kinds of isomerase.

An essential role for macrophage migration inhibitory factor in the tuberculin delayed-type hypersensitivity reaction

30 years ago, investigations into the molecular basis of the delayed-type hypersensitivity reaction (DTH) provided evidence for the first lymphokine activity: a lymphocyte-derived mediator called macrophage migration inhibitory factor (MIF), which inhibited the random migration of peritoneal macrophages. Despite the long-standing association of MIF with the DTH reaction and the cloning of a human protein with macrophage migration inhibitory activity, the precise role of MIF in this classic cell-mediated immune response has remained undefined. This situation has been further complicated by the fact that two other cytokines, interferon gamma and IL-4, similarly inhibit macrophage migration and by the identification of mitogenic contaminants in some preparations of cloned human MIF. Using recently developed molecular probes for mouse MIF, we have examined the role of this protein in a classical model of DTH, the tuberculin reaction in mice. Both MIF messenger RNA and protein were expressed prominently in DTH lesions, as assessed by reverse transcription polymerase chain reaction, in situ hybridization, and immunostaining with anti-MIF antibody. The predominant cellular origin of MIF appeared to be the monocyte/macrophage, a cell type identified recently to be a major source of MIF release in vivo. The administration of neutralizing anti-MIF antibodies to mice inhibited significantly the development of DTH, thus affirming the central role of MIF in this classic immunological response.