2-pyridone mycotoxins act as novel actin depolymerizing agents and function endogenously to regulate cytoskeleton dynamics

2-pyridones, e.g., the mycotoxins tenellin and fumosorinone, are a class of fungal secondary metabolites with a wide range of attributed activities but whose mechanisms of action and biological functions remain obscure. Here, we show that tenellin and fumosorinone disrupt cytoskeleton dynamics via direct actin binding at the ATP binding site, inducing F-actin disassembly. Tenellin could block proliferation of embryonic fibroblast NIH/3T3 cells, inducing apoptosis, and inhibit actin-cytoskeleton assembly in plant cells. A set of conserved actin amino acid residues within the ATP binding pocket was identified as critical for modulating tenellin-actin interactions, with both pyridones active against purified actins derived from across the Kingdoms, from plant to animal. Loss of tenellin induced alterations in fungal actin cytoskeletal dynamics, enhancing fungal polarized growth but reducing conidial yield and tolerance to abiotic stresses. Tenellin production was affected by environmental conditions and regulated by secondary metabolite regulators (LaeA methyltransferase), light/circadian rhythm (White Collar-1), and nutrient sensing/target of rapamycin (TOR) pathways. These data provide a mechanistic basis for the reported activities of 2-pyridones and the biological functioning of these compounds as fungal environmental adaptations linking secondary metabolite synthesis to regulation of actin dynamics, and hence hyphal growth and morphogenesis. The ability of tenellin and other 2-pyridones to target the cytoskeleton opens new avenues for drug discovery and development of tools for studying actin assembly dynamics in a wide range of systems.