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.
Highlights
Macrophage migration inhibitory factor (MIF) is expressed at high levels in various inflammatory diseases and cancer [1]
MIF activates the expression of p110c and p101 subunits of the Class IB phosphoinositide 3-kinases (PI3Ks)
We evaluated the expression levels of Class I PI3K catalytic subunits, p110a, b and c, after MIF treatment of THP-1 monocytes and HL60 neutrophil-like cells
Summary
Macrophage migration inhibitory factor (MIF) is expressed at high levels in various inflammatory diseases and cancer [1]. The mechanism underlying chemotaxis entails MIF activation of phosphoinositide 3-kinases (PI3Ks) that are upstream activators of the pleckstrin homology domain-containing protein kinase B (AKT) pathway [5]. Macrophage migration inhibitory factor triggers the PI3K/AKT signalling pathway by binding to its cell surface receptor CD74 in complex with CD44 as well as recently identified C-X-C chemokine receptors, CXCR2, CXCR4 and CXCR7 [6, 7]. Class I PI3K is composed of a heterodimer of a regulatory subunit (p85 or p101) and a catalytic subunit (p110a, b, d or c). Chemokines can activate all these catalytic subunits [5, 13]. It is controversial as to whether Class IA or Class IB is the major isoform involved in the production of phosphatidylinositol (3,4,5)-trisphosphate and the activation of downstream signalling pathways [21, 22]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
