Thapsigargin and cyclopiazonic acid initiate rapid and dramatic increases of IL-6 mRNA expression and IL-6 secretion in murine peritoneal macrophages.

Two different inhibitors of endosomal calcium ATPase activity, cyclopiazonic acid and thapsigargin, were shown to release a common intracellular calcium pool in normal, murine macrophages. Furthermore, the release of this pool was accompanied by increased calcium uptake from the extracellular medium. The activity of these inhibitors was linked to an important biologic response, because both cyclopiazonic acid and thapsigargin induced rapid and dramatic increases in IL-6 mRNA expression and secretion. Compared with control cultures, macrophages treated with these inhibitors increased IL-6 mRNA expression approximately 10-fold by 15 min and approximately 20-fold by 2 h, as determined using quantitative competitive-reverse transcribed-PCRs. The increased mRNA expression was coupled to translation and secretion of this monokine since cyclopiazonic acid and thapsigargin induced significant increases in IL-6 secretion as early as 2 h, and up to approximately 70-fold increases by 20 h, when compared with control cultures. Taken together, these results demonstrate that both cyclopiazonic acid and thapsigargin generate potent intracellular signals that initiate rapid and dramatic production of IL-6. Both thapsigargin and cyclopiazonic acid increased IL-6 mRNA expression at 15 min in the absence of Ca2+ influx from the extracellular medium. These results suggest that events associated with endosomal Ca(2+)-ATPase inhibition contribute to the activation of normal macrophages as defined by increased monokine secretion.