Differential effects of mucosal adjuvant cholera toxin (CT) on macrophage cyclooxygenase-2 (COX-2) and endoplasmic reticulum (ER) stress (39.44)

Abstract

Abstract CT is known to induce enhanced COX-2 activity and increased release of prostaglandin E2 (PGE2) in macrophages (MØ) and mucosal cells; CT also induces ER stress and unfolded protein responses. Since CT alone does not induce COX-2 transcription in MØ, post-transcriptional mechanisms up-regulating COX-2 appear essential, but remain elusive. To determine whether CT-induced ER stress is associated with regulation of MØ COX-2, RAW 264.7 MØ were treated overnight with CT (0.2 and 1 µg/ml) followed by 6 h treatment with heat-killed Mycobacterium bovis bacillus Calmette-Guérin (BCG, 5, 50, and 100 µg/ml). We found that pre-treatment with CT caused dose-dependent inhibition of BCG-induced COX-2 expression and marked elevation of growth arrest- and DNA damage-inducible gene 153 (GADD153), suggesting increased ER stress. Expression of glucose-regulated protein 78 (GRP78), an ER chaperone, was unchanged. In sharp contrast, if MØ had been pre-treated with BCG overnight before 6 h CT treatment, COX-2 expression was enhanced, GADD153 was not induced, and GRP78 expression was unchanged. Either pre- or post-treatment with CT resulted in inhibition of BCG-induced TNFα production. Our results indicate that the differential COX-2 regulation by CT is dependent on an ER stress/GADD153 pathway. Further studies will be conducted to assess whether the ER stress-dependent biphasic COX-2 expression is also observed in mucosal MØ and epithelial cells in CT-treated animals. (Supported by NIH HL71711, DOD DAMD 17-03-1-0004, BCCRP 06BS-04-9615)