Phosphatidylinositol 3-kinase, phosphoinositide-specific phospholipase-Cγ and protein kinase-C signal myelin phagocytosis mediated by complement receptor-3 alone and combined with scavenger receptor-AI/II in macrophages

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Abstract

Complement-receptor-3 (CR3/MAC-1), scavenger-receptor-AI/II (SRAI/II) and Fcγ-receptor (FcγR) can mediate phagocytosis of degenerated myelin in macrophages and microglia. However, CR3/MAC-1 and SRAI/II, but not FcγR, mediate phagocytosis after axonal injury. We tested for phosphatidylinositol 3-kinase (PI3K), phosphoinositide-specific phospholipase-Cγ (PLCγ) and protein kinase-C (PKC) signaling in myelin phagocytosis mediated by CR3/MAC-1 alone and by CR3/MAC-1 combined with SRAI/II. Phagocytosis was inhibited by PI3K inhibitors wortmannin and LY-294002, PLCγ inhibitor U-73122, classical PKC (cPKC) inhibitor Go-6976, general PKC inhibitors Ro-318220 and calphostin-C, and BAPTA/AM which chelates intracellular Ca2+ required for cPKC activation. PKC activator PMA augmented phagocytosis and further alleviated inhibitions induced by PI3K and PLCγ inhibitors. Overall, altering PKC activity modulated phagocytosis 4- to 6-fold between inhibition and augmentation. PLCγ activation did not require tyrosine phosphorylation. Thus, signaling of myelin phagocytosis mediated by CR3/MAC-1 alone and by CR3/MAC-1 combined with SRAI/II involves PI3K, PLCγ and cPKC, the cascade PI3K→PLCγ→cPKC, and wide-range modulation by PKC. This pathway may thus be targeted for in vivo modulation, which may explain differences in the efficiency of CR3/MAC-1-mediated myelin phagocytosis in different pathological conditions. © 2004 Elsevier Inc. All rights reserved.

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Makranz, C., Cohen, G., Baron, A., Levidor, L., Kodama, T., Reichert, F., & Rotshenker, S. (2004). Phosphatidylinositol 3-kinase, phosphoinositide-specific phospholipase-Cγ and protein kinase-C signal myelin phagocytosis mediated by complement receptor-3 alone and combined with scavenger receptor-AI/II in macrophages. Neurobiology of Disease, 15(2), 279–286. https://doi.org/10.1016/j.nbd.2003.11.007

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