Enzymatically Inactive Macrophage Migration Inhibitory Factor Inhibits Monocyte Chemotaxis and Random Migration

Abstract

Macrophage migration inhibitory factor (MIF) is a cytokine that was first described as an inhibitor of the random migration of monocytes and macrophages and has since been proposed to have a number of immune and catalytic functions. One of the functions assigned to MIF is that of a tautomerase that interconverts the enol and keto forms of phenylpyruvate and (p-hydroxyphenyl)pyruvate and converts D-dopachrome, a stereoisomer of naturally occurring L-dopachrome, to 5,6-dihydroxyindole-2-carboxylic acid. The physiological significance of the MIF enzymatic activity is unclear. The three-dimensional structure of MIF is strikingly similar to that of two microbial enzymes (4-oxalocrotonate tautomerase and 5-carboxymethyl-2-hydroxymuconate isomerase) that otherwise share little sequence identity with MIF. MIF and these two enzymes have an invariant N-terminal proline that serves as a catalytic base. Here we report a new biological function for MIF, as an inhibitor of monocyte chemoattractant protein 1- (MCP-1-) induced chemotaxis of human peripheral blood monocytes. We find that MIF inhibition of chemotaxis does not occur at the level of the CC chemokine receptor for MCP-1, CCR2, since MIF does not alter the binding of (125)I-MCP-1 to monocytes. The role of MIF enzymatic activity in inhibition of monocyte chemotaxis and random migration was studied with two MIF mutants in which the N-terminal proline was replaced with either a serine or a phenylalanine. Both mutants remain capable of inhibiting monocyte chemotaxis and random migration despite significantly reduced or no phenylpyruvate tautomerase activity. These data suggest that this enzymatic activity of MIF does not play a role in its migration inhibiting properties.

Human Pancreatic Islets Produce and Secrete MCP-1/CCL2: Relevance in Human Islet Transplantation

“…It might be that its presence with ␤-cells encompasses also the limitation of infiltrating monocytes. It is worth noting that some studies recently demonstrated that MIF also inhibited the MCP-1-induced migration of monocytes (56,57). In addition, we do not know which is the amount of MCP-1 released by islet in vivo and if in physiological condition is sufficient to induce monocyte recruitment.…”

Trichomonas vaginalis homolog of macrophage migration inhibitory factor induces prostate cell growth, invasiveness, and inflammatory responses

“…Catalytically inactive HuMIF is greatly impaired in its ability to stimulate generation of superoxide in activated neutrophils (37); thus, the reduced tautomerase activity of TvMIF could decrease the molecule's priming of host neutrophils. Enzymatic tautomerase activity is not necessary for biological functions, such as macrophage migration, countering the effects of glucocorticoids, or growth regulatory and invasion-promoting properties (38)(39)(40). Thus, our further analyses have focused on characterizing possible biological functions of TvMIF that could contribute to prostate cancer.…”

“…A standard biological activity of HuMIF is the ability to inhibit random migration of macrophages or monocytes (38,41). To determine whether TvMIF exerts this activity, we examined its effect on monocyte migration using a Boyden chamber assay.…”

Direct Modification of the Proinflammatory Cytokine Macrophage Migration Inhibitory Factor by Dietary Isothiocyanates

“…Because of the lack of an identified physiological substrate, whether tautomerase activity is a biologically relevant function of MIF is a matter of debate. On the negative side, P2 mutants retain MIF-like activity in assays of its proinflammatory action (52). However, others argue that the tautomerase active site may be critical for permitting and regulating interactions of MIF with receptors or binding proteins, including CD74 (41).…”