ABSTRACT
The response of the skin to harmful environmental agents is shaped decisively by the status of the immune system. Keratinocytes constitutively express and secrete the chemokine-like mediator, macrophage migration inhibitory factor (MIF), more strongly than dermal fibroblasts, thereby creating a MIF gradient in skin. By using global and epidermis-restricted Mif-knockout (Mif-/- and K14-Cre+/tg; Miffl/fl) mice, we found that MIF both recruits and maintains antigen-presenting cells in the dermis/epidermis. The reduced presence of antigen-presenting cells in the absence of MIF was associated with accelerated and increased formation of nonmelanoma skin tumors during chemical carcinogenesis. Our results demonstrate that MIF is essential for maintaining innate immunity in skin. Loss of keratinocyte-derived MIF leads to a loss of control of epithelial skin tumor formation in chemical skin carcinogenesis, which highlights an unexpected tumor-suppressive activity of MIF in murine skin.-Brocks, T., Fedorchenko, O., Schliermann, N., Stein, A., Moll, U. M., Seegobin, S., Dewor, M., Hallek, M., Marquardt, Y., Fietkau, K., Heise, R., Huth, S., Pfister, H., Bernhagen, J., Bucala, R., Baron, J. M., Fingerle-Rowson, G. Macrophage migration inhibitory factor protects from nonmelanoma epidermal tumors by regulating the number of antigen-presenting cells in skin.
Subject(s)
Macrophage Migration-Inhibitory Factors/metabolism , Skin Neoplasms/chemically induced , Skin/cytology , Skin/immunology , Animals , Anthracenes/toxicity , Antigens, CD/genetics , Antigens, CD/metabolism , Carcinogenesis , Gene Expression Regulation/physiology , Inflammation/metabolism , Keratinocytes/metabolism , Macrophage Migration-Inhibitory Factors/genetics , Mice , Mice, Inbred BALB C , Mice, Knockout , Mice, Transgenic , Piperidines/toxicity , Pyridines/toxicity , Receptors, CXCR/genetics , Receptors, CXCR/metabolismABSTRACT
Macrophage migration-inhibitory factor (MIF) is an upstream regulator of innate immunity and a potential molecular link between inflammation and cancer. The unusual structural homology between MIF and certain tautomerases, which includes both a conserved substrate-binding pocket and a catalytic N-terminal proline (Pro1), has fueled speculation that an enzymatic reaction underlies MIF's biologic function. To address the functional role of the MIF tautomerase activity in vivo, we created a knock-in mouse in which the endogenous mif gene was replaced by one encoding a tautomerase-null, Pro1-->Gly1 MIF protein (P1G-MIF). While P1G-MIF is completely inactive catalytically, it maintains significant, albeit reduced, binding to its cell surface receptor (CD74) and to the intracellular binding protein JAB1/CSN5. P1G-MIF knock-in mice (mif(P1G/P1G)) and cells derived from these mice show a phenotype in assays of growth control and tumor induction that is intermediate between those of the wild type (mif(+/+)) and complete MIF deficiency (mif(-)(/)(-)). These data provide genetic evidence that MIF's intrinsic tautomerase activity is dispensable for this cytokine's growth-regulatory properties and support a role for the N-terminal region in protein-protein interactions.
