Gαᵢ₁ and Gαᵢ₃ regulate macrophage polarization by forming a complex containing CD14 and Gab1

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 15; pp. 4731 - 4736
• Main Authors: Li, Xianjing, Wang, Duowei, Chen, Zhen, Lu, Ermei, Wang, Zhuo, Duan, Jingjing, Tian, Wei, Wang, Yun, You, Linjun, Zou, Yulian, Cheng, Yan, Zhu, Qingyi, Wan, Xiaojian, Xi, Tao, Jiang, Meisheng, Han, Yuyuan, Cao, Cong, Birnbaumer, Lutz, Chu, Wen-Ming, Yang, Yong
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 14.04.2015; National Acad Sciences
• Subjects: Adaptor Proteins, Signal Transducing; Animals; Biological Sciences; Blotting, Western; Cell Line, Tumor; Cells, Cultured; endocytosis; Endocytosis - drug effects; G-proteins; GTP-Binding Protein alpha Subunits, Gi-Go - genetics; GTP-Binding Protein alpha Subunits, Gi-Go - metabolism; Humans; inflammation; Interleukin-12 - metabolism; Interleukin-6 - metabolism; Lipopolysaccharide Receptors - genetics; Lipopolysaccharide Receptors - metabolism; Lipopolysaccharides - pharmacology; macrophages; Macrophages - drug effects; Macrophages - metabolism; Macrophages, Peritoneal - drug effects; Macrophages, Peritoneal - metabolism; Mice, 129 Strain; Mice, Knockout; Microscopy, Confocal; Mitogen-Activated Protein Kinases - metabolism; Phosphoproteins - genetics; Phosphoproteins - metabolism; plasma membrane; Protein Binding - drug effects; Protein Subunits - genetics; Protein Subunits - metabolism; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; signal transduction; Survival Analysis; Toll-like receptor 4; Toll-Like Receptor 4 - metabolism; transcription factor NF-kappa B; Tumor Necrosis Factor-alpha - metabolism; macrophage polarization; endosome; Gαi3; Gαi1; Toll-like receptor 4
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1503779112

Significance In this study, we demonstrate that guanine nucleotide-binding protein G(i) subunit alpha-1 and alpha-3 (Gα ᵢ₁/₃) regulate the downstream signaling pathways of Toll-like receptor 4 (TLR4). We show that Gα ᵢ₁/₃ form complexes containing the pattern recognition receptor (PRR) CD14 and growth factor receptor binding 2 (Grb2)-associated binding protein (Gab1), which are required for activation of PI3K-Akt signaling and NF-κB activation. Besides, Gα ᵢ₁/₃ act at both the plasma membrane and the endosome levels and are involved in TLR4 endocytosis. Furthermore, Gα ᵢ₁/₃ participated in the induction of M1 polarization of macrophages, and their decreased expression contributed to LPS tolerance. Thus, Gα ᵢ₁/₃ are important in controlling inflammation. Heterotrimeric G proteins have been implicated in Toll-like receptor 4 (TLR4) signaling in macrophages and endothelial cells. However, whether guanine nucleotide-binding protein G(i) subunit alpha-1 and alpha-3 (Gα ᵢ₁/₃) are required for LPS responses remains unclear, and if so, the underlying mechanisms need to be studied. In this study, we demonstrated that, in response to LPS, Gα ᵢ₁/₃ form complexes containing the pattern recognition receptor (PRR) CD14 and growth factor receptor binding 2 (Grb2)-associated binding protein (Gab1), which are required for activation of PI3K-Akt signaling. Gα ᵢ₁/₃ deficiency decreased LPS-induced TLR4 endocytosis, which was associated with decreased phosphorylation of IFN regulatory factor 3 (IRF3). Gα ᵢ₁/₃ knockdown in bone marrow-derived macrophage cells (Gα ᵢ₁/₃ KD BMDMs) exhibited an M2-like phenotype with significantly suppressed production of TNF-α, IL-6, IL-12, and NO in response to LPS. The altered polarization coincided with decreased Akt activation. Further, Gα ᵢ₁/₃ deficiency caused LPS tolerance in mice. In vitro studies revealed that, in LPS-tolerant macrophages, Gα ᵢ₁/₃ were down-regulated partially by the proteasome pathway. Collectively, the present findings demonstrated that Gα ᵢ₁/₃ can interact with CD14/Gab1, which modulates macrophage polarization in vitro and in vivo.