Macrophage Migration Inhibitory Factor-CXCR4 Receptor Interactions: EVIDENCE FOR PARTIAL ALLOSTERIC AGONISM IN COMPARISON WITH CXCL12 CHEMOKINE.

An emerging number of non-chemokine mediators are found to bind to classical chemokine receptors and to elicit critical biological responses. Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine that exhibits chemokine-like activities through non-cognate interactions with the chemokine receptors CXCR2 and CXCR4, in addition to activating the type II receptor CD74. Activation of the MIF-CXCR2 and -CXCR4 axes promotes leukocyte recruitment, mediating the exacerbating role of MIF in atherosclerosis and contributing to the wealth of other MIF biological activities. Although the structural basis of the MIF-CXCR2 interaction has been well studied and was found to engage a pseudo-ELR and an N-like loop motif, nothing is known about the regions of CXCR4 and MIF that are involved in binding to each other. Using a genetic strain of Saccharomyces cerevisiae that expresses a functional CXCR4 receptor, site-specific mutagenesis, hybrid CXCR3/CXCR4 receptors, pharmacological reagents, peptide array analysis, chemotaxis, fluorescence spectroscopy, and circular dichroism, we provide novel molecular information about the structural elements that govern the interaction between MIF and CXCR4. The data identify similarities with classical chemokine-receptor interactions but also provide evidence for a partial allosteric agonist compared with CXCL12 that is possible due to the two binding sites of CXCR4.

Comparing immobilized kinase inhibitors and covalent ATP probes for proteomic profiling of kinase expression and drug selectivity.

Kinases are involved in the regulation of many cellular processes and aberrant kinase signaling has been implicated in human disease. As a consequence, kinases are attractive drug targets. Assessing kinase function and drug selectivity in a more physiological context is challenging and often hampered by the generally low expression level of kinases and the extensive post-translation modification in vivo. Kinase drug selectivity screens by chemical proteomics have gained attention because they allow the profiling of hundreds of kinases against one drug at the same time. Here, we directly compared two such methods, notably, immobilized broad spectrum kinase inhibitors (kinobeads) and active site labeling using desthiobiotin-ATP and -ADP probes. Affinity purification of ∼ 100 kinases by either kinobeads or ATP/ADP probes was readily achieved using 1 mg of cellular protein. Bioinformatic analysis revealed a high degree of complementarity of the two techniques. Kinobeads covered the Tyrosine Kinase family particularly well and ATP probes enriched higher numbers of STE family kinases. A consecutive combination of both enrichment strategies therefore allowed for the coverage of a larger part of the kinome than any one technique alone. While kinobeads are very selective for kinases, the ATP/ADP probes also enriched a large number of other nucleotide binding proteins. Both methods were applied to the selectivity profiling of the small molecular Aurora kinase inhibitor tozasertib in K562 cells. Our data confirmed Aurora A, B, and BCR-ABL as the main targets of tozasertib and identified TNK1, STK2, RPS6KA1, and RPS6KA3 as submicromolar off targets.