The human cathelicidin LL-37 modulates the activities of the P2X 7 receptor in a structure-dependent manner

Abstract

Extracellular ATP, released at sites of inflammation or tissue damage, activates the P2X7 receptor, which in turn triggers a range of responses also including cell proliferation. In this study the ability of the human cathelicidin LL-37 to stimulate fibroblast growth was inhibited by commonly used P2X7 blockers. We investigated the structural requirements of the growth-promoting activity of LL-37 and found that it did not depend on helix sense (the all-D analog was active) but did require a strong helix-forming propensity in aqueous solution (a scrambled analog and primate LL-37 orthologs devoid of this property were inactive). The involvement of P2X7 was analyzed using P2X7-expressing HEK293 cells. LL-37 induced proliferation of these cells, triggered Ca2+ influx, promoted ethidium bromide uptake, and synergized with benzoyl ATP to enhance the pore and channel functions of P2X7. The activity of LL-37 had an absolute requirement for P2X7 expression as it was blocked by the P2X7 inhibitor KN-62, was absent in cells lacking P2X7, and was restored by P2X7 transfection. Of particular interest, LL-37 led to pore-forming activity in cells expressing a truncated P2X7 receptor unable to generate the non-selective pore typical of the full-length receptor. Our results indicate that P2X7 is involved in the proliferative cell response to LL-37 and that the structural/ aggregational properties of LL-37 determine its capacity to modulate the activation state of P2X7. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc.