Macrocyclic θ-defensins suppress tumor necrosis factor-α (TNF-α) shedding by inhibition of TNF-α-converting enzyme

Theta-defensins (θ-defensins) are macrocyclic peptides expressed exclusively in granulocytes and selected epithelia of Old World monkeys. They contribute to anti-pathogen host defense responses by directly killing a diverse range of microbes. Of note, θ-defensins also modulate microbe-induced inflammation by affecting the production of soluble tumor necrosis factor (sTNF) and other proinflammatory cytokines. Here, we report that natural rhesus macaque θ-defensin (RTD) isoforms regulate sTNF cellular release by inhibiting TNF-α-converting enzyme (TACE; also known as adisintegrin and metalloprotease 17; ADAM17), the primary pro-TNF sheddase. Dose-dependent inhibition of cellular TACE activity by RTDs occurred when leukocytes were stimulated with live Escherichia coli cells as well as numerous Toll-like receptor agonists. Moreover, the relative inhibitory potencies of the RTD isoforms strongly correlated with their suppression of TNF release by stimulated blood leukocytes and THP-1 monocytes. RTD isoforms also inhibited ADAM10, a sheddase closely related to TACE. TACE inhibition was abrogated by introducing a single opening in the RTD-1 backbone, demonstrating that the intact macrocycle is required for enzyme inhibition. Enzymologic analyses showed that RTD-1 is a fast binding, reversible, non-competitive inhibitor of TACE. We conclude that θ-defensin-mediated inhibition of pro-TNF proteolysis by TACE represents a rapid mechanism for the regulation of sTNF and TNF-dependent inflammatory pathways. Molecules with structural and functional features mimicking those of θ-defensins may have clinical utility as TACE inhibitors for managing TNF-driven diseases.