Structural basis for decreased induction of class IB PI3‐kinases expression by MIF inhibitors

Abstract

Macrophage migration inhibitory factor (MIF) is a master regulator of proinflammatory cytokines and plays pathological roles when not properly regulated in rheumatoid arthritis, lupus, atherosclerosis, asthma and cancer. Unlike canonical cytokines, MIF has vestigial keto‐enol tautomerase activity. Most of the current MIF inhibitors were screened for the inhibition of this enzymatic activity. However, only some of the enzymatic inhibitors inhibit receptor‐mediated biological functions of MIF, such as cell recruitment, through an unknown molecular mechanism. The goal of this study was to understand the molecular basis underlying the pharmacological inhibition of biological functions of MIF. Here, we demonstrate how the structural changes caused upon inhibitor binding translate into the alteration of MIF‐induced downstream signalling. Macrophage migration inhibitory factor activates phosphoinositide 3‐kinases (PI3Ks) that play a pivotal role in immune cell recruitment in health and disease. There are several different PI3K isoforms, but little is known about how they respond to MIF. We demonstrate that MIF up‐regulates the expression of Class IB PI3Ks in leucocytes. We also demonstrate that MIF tautomerase active site inhibitors down‐regulate the expression of Class IB PI3Ks as well as leucocyte recruitment in vitro and in vivo. Finally, based on our MIF:inhibitor complex crystal structures, we hypothesize that the reduction in Class IB PI3K expression occurs because of the displacement of Pro1 towards the second loop of MIF upon inhibitor binding, which results in increased flexibility of the loop 2 and sub‐optimal MIF binding to its receptors. These results will provide molecular insights for fine‐tuning the biological functions of MIF.

Roles of phosphatidyl inositol 3 kinase gamma (PI3Kγ) in respiratory diseases

“…MIF participates as a proinflammatory cytokine in both innate and adaptive immune responses, contributing to the pathogenesis of inflammatory, metabolic, autoimmune, and allergic diseases. Of note, MIF plays a pivotal role in activating the expression of PI3Kγ regulatory (p101) and catalytic subunits (p110) [ 59 ]. In turn, increased PI3Kγ activity is responsible for IL-13-mediated contraction of airway smooth muscle (ASM) cells, the underlying mechanism of AHR induced by allergen sensitization or cytokines in asthma [ 59 – 63 ].…”

“…Of note, MIF plays a pivotal role in activating the expression of PI3Kγ regulatory (p101) and catalytic subunits (p110) [ 59 ]. In turn, increased PI3Kγ activity is responsible for IL-13-mediated contraction of airway smooth muscle (ASM) cells, the underlying mechanism of AHR induced by allergen sensitization or cytokines in asthma [ 59 – 63 ]. IL-13 receptor and PI3Kγ are both expressed in ASM cells, in which they control contractility by regulating Ca 2+ oscillations [ 64 ].…”

Function, Regulation and Biological Roles of PI3Kγ Variants

“…Interestingly, reports suggest a temporal diverse expression of the regulatory subunits with an induced upregulation of p101 in immune cells and heart tissues while p87 protein levels remained unchanged [33,112]. Most recently, it was demonstrated that macrophage migration inhibitory factor (MIF) up-regulates the expression of p101 in THP-1 monocytes and HL60 neutrophil-like cells [113]. Hence, it is tempting to consider p101 as part of an inducible PI3Kγ but further work needs to explore this possibility.…”

Structural Plasticity in the C-Terminal Region of Macrophage Migration Inhibitory Factor-2 Is Associated with an Induced Fit Mechanism for a Selective Inhibitor

“…11,12 Chemical modifications, site-directed mutagenesis, and recent structural modeling studies indicate that CD74 activation is dependent on residues at the interface between two subunits, outside the catalytic cavity of the MIF proteins. 9,11–13 Recent mechanistic insights into the MIF-1-induced activation of CD74 showed that the activation process is dynamically controlled by an allosteric site that is found on one side of the solvent channel. 14 Whether a similar allosteric site exists for MIF-2 has yet to be explored.…”