M. bovis BCG induced expression of COX-2 involves nitric oxide-dependent and-independent signaling pathways

Abstract: In a multifaceted immunity to myco-bacterial infection, induced expression of cycloox-ygenase-2 (COX-2) by Mycobacterium bovis bacil-lus Calmette-Guerin (BCG) may act as an impor-tant influencing factor for the effective host immunity. We here demonstrate that M. bovis BCG-triggered TLR2-dependent signaling leads to COX-2 and PGE2 expression in vitro in macro-phages and in vivo in mice. Further, the presence of PGE2 could be demonstrated in sera or cere-brospinal fluid of tuberculosis patients. The in-duced COX-2 expression in macrophages is depen-dent on NF-B activation, which is mediated by inducible NO synthase (iNOS)/NO-dependent par-ticipation of the members of Notch1-PI-3K signal-ing cascades as well as iNOS-independent activa-tion of ERK1/2 and p38 MAPKs. Inhibition of iNOS activity abrogated theM. bovis BCG ability to trigger the generation of Notch1 intracellular do-main (NICD), a marker for Notch1 signaling acti-vation, as well as activation of the PI-3K signaling cascade. On the contrary, treatment of macro-phages with 3-morpholinosydnonimine, a NO do-nor, resulted in a rapid increase in generation of NICD, activation of PI-3K pathway, as well as the expression of COX-2. Stable expression of NICD in RAW 264.7 macrophages resulted in augmented expression of COX-2. Further, signaling perturba-tions suggested the involvement of the cross-talk of Notch1 with members with the PI-3K signaling cascade. These results implicate the dichotomous nature of TLR2 signaling during M. bovis BCG-triggered expression of COX-2. In this perspec-tive, we propose the involvement of iNOS/NO as one of the obligatory, early, proximal signaling events during M. bovis BCG-induced COX-2 ex