Brefeldin A

The lactone antibiotic brefeldin A has been shown to attenuate the secretion and production of chemical mediators involved in inflammation and immune responses (Hoermannsperger et al. 2009; Netschetal. 2006; Ouyang et al. 2013). Brefeldin A attenuates the TNF-α-inducedsecretionofcytokineIL-15inHeLacells (Ouyang et al. 2013). Brefeldin A inhibits the secretion and production of the T cell chemokine interferon-inducible protein (IP-10) in small intestinal epithelial cell line Mode-K cells treated with TNF-α (Hoermannsperger et al. 2009). Brefeldin A inhibits IL-1β-induced chemokine IL-8 secretion in the human epithelial colorectal adenocarcinoma cells Caco-2 (Netsch et al. 2006). Brefeldin A inhibits secretion of eosinophil cationic proteins from IFN-γ- and eotaxin-stimulated eosinophil granules (Neves et al. 2008). Brefeldin A has demonstrated to inhibit the PGE2-induced decrease in the production of chemokine (C-C motif) ligand 3 in Leishmania donovani (Saha et al. 2014). Brefeldin A inhibits the effect of Aralia cordate lectin on the expression and production of IL-8 in Caco-2 cells (Koyama et al. 2005). Brefeldin A suppresses the expression of IL-8 mRNA and production of IL-8 induced by Shiga toxin, ricin, and modeccin in Caco-2 cells (Yamasaki et al. 2004). Thus, brefeldin A appears to suppress production of chemical mediators involved in inflammation and immune responses.

The mediators of brefeldin A-induced apoptosis have not been well characterized. Evidence obtained so far indicates involvement of pRB dephosphorylation, p53-independent p21 activation, activation of caspase-3, caspase-7-mediated caspase-12 activation, activation of glycogen synthase kinase-3b and caspase-9, and activation of caspase-2, caspase-3, and caspase-9 via phosphorylation of c-Jun N-terminal kinase. We have studied the mechanism of action of brefeldin A using RT-PCR and promoter-luciferase reporter assay. We herein report that brefeldin A up-regulates CHOP expression via the activation of AARE1, ERSE, and AP-1 elements.

In summary, the present work identifies an important role of BIG1 in the cell regulation of surface expression of GABA_AR as well as a potential role for mediating synaptic inhibition by governing GABA_AR intracellular trafficking. This novel function of BIG1 is dependent on its GEF activity. BIG2, another member of the brefeldin A-inhibited ARF-GEFs, has been reported to be a GABA_AR β subunit-interacting protein. To further explore the involvement of BIG2 or the reciprocity of BIG1 and BIG2 in regulating GABA_ARs, trafficking in neurons will be investigated in future research.

Figure 1A shows the time course of changes in Isc after terbutaline (10 µM, a β₂-specific adrenergic agonist) was added to the basolateral surface in the absence and presence of amiloride (10 µM) in the apical solution. Most of the terbutaline-induced Isc was sensitive to amiloride with a small component being sensitive to bumetanide. As shown in Figures 1A and B, terbuatline increased the amiloride-sensitive Isc about 2.5-fold at 50 min after its application. The effect of terbutaline was completely abolished when brefeldin A (1 µg/ml), an inhibitor of intracellular protein trafficking, had been added 30 minutes earlier into both the apical and basolateral solutions (total application time of brefeldin A = 80 min). Brefeldin A also decreased the amiloride-sensitive Isc of FDLE under basal conditions (Fig. 1B). In contrast to its effects on the amiloride-sensitive Isc, brefeldin A did not alter either the basal or terbutaline-stimulated bumetanide-sensitive Isc (Fig. 1C).