Proprotein convertase furin interacts with and cleaves pro-ADAMTS4 (aggrecanase-1) in the trans-Golgi network

A member of the A disintegrin and metalloproteinase domain with thrombospondin type-1 motifs (ADAMTS-4) protease family can efficiently cleave aggrecan at several sites detected in joints of osteoarthritic patients. Although recent studies have shown that removal of the prodomain of ADAMTS4 is critical for its ability to degrade aggrecan, the cellular mechanisms for its processing and trafficking remain unclear. In this study, by using both furin-specific inhibitor and RNA interference technique, we demonstrate that furin plays an important role in the intracellular removal of ADAMTS4 prodomain. Further, we demonstrate that proADAMTS4 can be processed by means of multiple furin recognition sites: (RPRR209)-R-206, (209)RAKR(212), or (KR212)-K-211. The processing of proADAMTS4 was completely blocked by brefeldin A treatment, suggesting that processing occurs in the trans-Golgi network. Indeed, ADAMTS4 is co-localized with furin in trans-Golgi network. Interestingly, the pro form of ADAMTS4, not its mature one, co-precipitates with furin, suggesting that furin physically interacts with the prodomain of ADAMTS-4. In addition, our evidence suggests that a furin-independent pathway may also contribute to the activation of ADAMTS4. These results indicate that the activation mechanism for ADAMTS4 can be targeted for therapeutical intervention against this enzyme.