P2X7 receptor activation regulates rapid unconventional export of transglutaminase-2

Abstract

Transglutaminases (TG) are externalized from cells via an unknown unconventional secretory pathway. We show for the first time that purinergic signaling regulates active secretion of TG2, an enzyme with a pivotal role in stabilizing extracellular matrices and modulating cell-matrix interactions in tissue repair. Extracellular ATP promotes TG2 secretion by macrophages, and this can be blocked by a purinergic receptor P2X7 (P2X7R)-selective antagonist. Introduction of functional P2X7R into HEK293 cells is sufficient to confer rapid, regulated TG2 export. By employing pharmacological agents, TG2 release could be separated from P2X7R-mediated microvesicle shedding. Neither, Ca2+ signaling alone nor membrane depolarization triggered TG2 secretion which occurred only upon receptor membrane pore formation and without pannexin channel involvement. A gain-of-function mutation in P2X7R associated with autoimmune disease caused enhanced TG2 externalization from cells, and this correlated with increased pore activity. These results provide a mechanistic explanation for a link between active TG2 secretion and inflammatory responses, and aberrant enhanced TG2 activity in certain autoimmune conditions.