A prodigiosin analogue inactivates NADPH oxidase in macrophage cells by inhibiting assembly of p47phox and Rac

Prodigiosins are natural red pigments that have multi-biological activities. Recently, we discovered a marine bacterial strain, which produces a red pigment. Extensive two-dimensional nuclear magnetic resonance and mass spectrometry analysis showed that the pigment is a prodigiosin analogue (PG-L-1). Here, we investigated the effect of PG-L-1 on NADPH oxidase activity in macrophage cells. PG-L-1 significantly inhibited superoxide anion (O ₂^-) production by phorbol 12-myristate 13-acetate (PMA)-stimulated RAW 264.7 cells, a mouse macrophage cell line. The ED ₅₀ value was estimated to be ∼0.3 μM. PG-L-1 had no direct scavenging effect on O₂^- generated by hypoxanthine/ xanthine oxidase system in electron spin resonance-spin trapping determinations, suggesting that this compound directly acts on the O₂^- production system, NADPH oxidase, in macrophage cells. We further investigated the effect of PG-L-1 on the behaviour of the cytosolic components of the NADPH oxidase, p67^phox, p47^phox, p40^phox, Rac and protein kinase C (PKC), in PMA-stimulated RAW 264.7 cells. Although PG-L-1 showed no effect on the activation of PKC, the immunoblotting analysis using specific antibodies showed that PG-L-1 strongly inhibits the association of p47^phox and Rac in the plasma membrane of PMA-stimulated RAW 264.7 cells. These results suggest that PG-L-1 inactivates NADPH oxidase through the inhibition of the binding of p47^phox and Rac to the membrane components of NADPH oxidase.