Membrane associated RGC‐32 promoted macrophage phagocytosis via direct and specific activation of novel PKC pathway (802.24)

Abstract

Phagocytosis of bacterial pathogens by macrophages requires the activation of protein kinase C (PKC), a family of protein serine/threonine kinases. Previous publications have demonstrated that both classical and novel PKCs were required for macrophage phagocytosis. However recruitment of classical PKCs or novel PKCs or both is macrophage linage specific, which prompt us to hyposize that there exist PKC isozyme specific regulators in macrophage. Here we found that response gene to complement 32 (RGC32) is a direct and specific activator for novel PKC pathway in macrophage phagocytosis. RGC32 was induced and specifically expressed in macrophage lineages in differentiation. While bone marrow progenitor cells from RGC32 knockout mice did not have significant defects in macrophage differentiation, both peritoneal macrophages (PMs) and bone marrow derived macrophages (BMDMs) presented dramatic defects in their phagocytosis activities. Moreover, macrophages over expressed RGC32 showed promoted phagocytosis activity. During phagocytosis, RGC32 was recruited to cell membrane and co‐localized with F‐actin to forming phagocytic cups and macrophages from RGC32 knockout mice showed impaired F‐actin assembling and phagocytic cup formation. Mechanistically, RGC32 participated in phagocytosis through activation of PKC induced alanine‐rich C‐kinase substrate (MARCKS) phosphorylation. Recombinant RGC32 increased PKC activity in vitro. Knocking down RGC32 in macrophage suppressed MARCKS phosphorylation while over expression RGC32 increased MARCKS phosphorylation. Interestingly, RGC32 directly interacted with novel but not classical PKC isozymes and RGC32 induced MARCKS can only be suppressed by novel PKC inhibitor. Finally, RGC32 knockout mice showed defects in pathogens clearance to peritoneal bacterial infection. In summary, for the first time, we identified RGC32 as an membrane associated novel PKC activator during macrophage phagocytosis.