ADAM17 Mediates Proteolytic Maturation of Voltage-Gated Calcium Channel Auxiliary α₂δ Subunits, and Enables Calcium...

The auxiliary α₂δ subunits of voltage-gated calcium (Ca_V) channels are key to augmenting expression and function of Ca_V1 and Ca_V2 channels, and are also important drug targets in several therapeutic areas, including neuropathic pain. The α₂δ proteins are translated as preproteins encoding both α₂ and δ, and post-translationally proteolyzed into α₂ and δ subunits, which remain associated as a complex. In this study, we have identified ADAM17 as a key protease involved in proteolytic processing of pro-α₂δ-1 and α₂δ-3 subunits. We provide three lines of evidence: First, proteolytic cleavage is inhibited by chemical inhibitors of particular metalloproteases, including ADAM17. Second, proteolytic cleavage of both α₂δ-1 and α₂δ-3 is markedly reduced in cell lines by knockout of ADAM17 but not ADAM10. Third, proteolytic cleavage is reduced by the N-terminal active domain of TIMP-3 (N-TIMP-3), which selectively inhibits ADAM17. We have found previously that proteolytic cleavage into mature α₂δ is essential for the enhancement of Ca_V function, and in agreement, knockout of ADAM17 inhibited the ability of α₂δ-1 to enhance both Ca_V2.2 and Ca_V1.2 calcium currents. Finally, our data also indicate that the main site of proteolytic cleavage of α₂δ-1 is the Golgi apparatus, although cleavage may also occur at the plasma membrane. Thus, our study identifies ADAM17 as a key protease required for proteolytic maturation of α₂δ-1 and α₂δ-3, and thus a potential drug target in neuropathic pain.