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The immunological and neuroendocrine properties of macrophage migration inhibitory factor (MIF) are diverse. In this article we review the known cellular, molecular and genetic properties of MIF that place it as a key regulatory cytokine, acting within both the innate and adaptive immune responses.The unexpected and paradoxical induction of MIF secretion by low concentrations of glucocorticoids is explored. The role of MIF as a locally acting modulator of glucocorticoid sensitivity within foci of inflammation is also discussed. MIF has no homology with any other pro-inflammatory cytokine and until recently lacked a recognised transmembrane receptor. MIF has also been shown to be directly taken up into target cells and to interact with intracellular signalling molecules, including the Jun activation domain-binding protein Jab-1.Comprehensive analysis of the MIF gene has identified important functional polymorphisms and a series of genetic studies has revealed both association and linkage of MIF with inflammatory diseases. Altered MIF regulation may therefore be pivotal to acquiring chronic inflammation following an innate immune response.

The development of methods for engineering proteins with novel properties opens the way to manipulating intracellular processes in a therapeutically useful way. Glucocorticoids, acting via glucocorticoid receptors (GR), are potent anti-inflammatory agents, acting to oppose nuclear factor kappa B (NF kappa B) function. The herpes viral protein, VP22, has been reported to confer intercellular trafficking activity on 'cargo' proteins, potentially facilitating gene therapy with intracellular proteins. VP22GR, resulting from the addition of VP22 to the N terminal of GR, was equipotent with the wild-type GR in opposing NF kappa B p65-driven expression of an NF kappa B reporter gene. Surprisingly, VP22GR was incapable of inducing transactivation of positive glucocorticoid reporter genes (MMTV-luc and TAT3-luc). Furthermore, the VP22GR had powerful dominant negative activity on both endogenous and exogenous GR transactivation. VP22GR was cytoplasmic in quiescent cells, and after hormone addition underwent nuclear translocation to share the same distribution as the GR. The ability of the VP22GR to selectively confer and enhance glucocorticoid-dependent transrepression of NF kappa B may be of use therapeutically in e.g. transplant rejection, inflammatory arthritis or asthma.

We have previously described a panel of human small cell lung carcinoma (SCLC) cell lines that have profound glucocorticoid resistance, resulting from various molecular defects in glucocorticoid signalling. However, in one SCLC cell line, CORL103, the cause of the resistance is unknown. These cells are refractory to dexamethasone stimulation of MMTV even when exogenous wild-type glucocorticoid receptor (GR) is co-transfected. This is in contrast to cell lines DMS79 and CORL24 where resistance is overcome by transfection of the wild-type receptor. Sequencing of the GR from CORL103 cells revealed two point mutations, but neither of these induced dominant negative activity. Steroid hormone resistance extended to mineralocorticoid and progesterone receptor (MR, PR) activation of MMTV-luc, whereas oestrogen and thyroid hormone receptor transactivation were normal. A simpler reporter, TAT3-luc, containing three copies of the tyrosine aminotransferase glucocorticoid response element (GRE), was responsive when transfected into CORL103 cells with GR, MR and PR expression vectors and activated with their respective ligands. Similarly, pHH-luc and pAH-luc (truncated MMTV variants containing the GRE region, both derived from a different strain of MMTV), were effectively transactivated with dexamethasone. This suggests that the minor changes in the flanking sequence of the MMTV promoter are critically important in determining steroid responsiveness in CORL103 cells. We propose that minor differences in MMTV may determine recruitment of co-factors, which destabilise GR binding to the MMTV GREs. These findings represent a new, selective, model of glucocorticoid resistance that may explain specific cell and target gene differences in glucocorticoid sensitivity.