Combined Proteomic and In Silico Target Identification Reveal a Role for 5-Lipoxygenase in Developmental Signaling Pathways

Identification and validation of the targets of bioactive small molecules identified in cell-based screening is challenging and often meets with failure, calling for the development of new methodology. We demonstrate that a combination of chemical proteomics with in silico target prediction employing the SPiDER method may provide efficient guidance for target candidate selection and prioritization for experimental in-depth evaluation. We identify 5-lip-oxygenase (5-LO) as the target of the Wnt pathway inhibitor Lipoxygenin. Lipoxygenin is a non-redox 5-LO inhibitor, modulates the beta-catenin-5-LO complex and induces reduction of both beta-catenin and 5-LO levels in the nucleus. Lipoxygenin and the structurally unrelated 5-LO inhibitor CJ-13,610 promote cardiac differentiation of human induced pluripotent stem cells and inhibit Hedgehog, TGF-beta, BMP, and Activin A signaling, suggesting an unexpected and yet unknown role of 5-LO in these developmental pathways.