ADAM17 Mediates Proteolytic Maturation of Voltage-Gated Calcium Channel Auxiliary α(2)δ Subunits, and Enables Calcium Current Enhancement

The auxiliary α(2)δ subunits of voltage-gated calcium (Ca(V)) channels are key to augmenting expression and function of Ca(V)1 and Ca(V)2 channels, and are also important drug targets in several therapeutic areas, including neuropathic pain. The α(2)δ proteins are translated as preproteins encoding both α(2) and δ, and post-translationally proteolyzed into α(2) 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-α(2)δ-1 and α(2)δ-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 α(2)δ-1 and α(2)δ-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 α(2)δ is essential for the enhancement of Ca(V) function, and in agreement, knockout of ADAM17 inhibited the ability of α(2)δ-1 to enhance both Ca(V)2.2 and Ca(V)1.2 calcium currents. Finally, our data also indicate that the main site of proteolytic cleavage of α(2)δ-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 α(2)δ-1 and α(2)δ-3, and thus a potential drug target in neuropathic pain.