This file contains the characterization of M2 (Supplementary Fig.S1) and M1 (Supplementary Fig.S2) type polarization in both Lgr4 knockdown and overexpression cells; the expression and immune regulation of Lgr4 in tumor tissues (Supplementary Fig.S3); the toxicity of LGR4 ECD, Rspo1 antibody and BLZ945 on tumor cells and macrophages (Supplementary Fig.S4); the immune regulation of Rspo/Lgr4 blockade in B16F10 melanoma mouse model (Supplementary Fig.S5).
Funding
National Key R&D Program of China
National Natural Science Foundation of China
Science and Technology Commission of Shanghai Municipality
Shanghai Municipal Education Commission
CPRIT
ARTICLE ABSTRACT
Therapies targeting immune checkpoints have shown great clinical potential in a subset of patients with cancer but may be hampered by a failure to reverse the immunosuppressive tumor microenvironment (TME). As the most abundant immune cells in TME, tumor-associated macrophages (TAM) play nonredundant roles in restricting antitumor immunity. The leucine-rich repeat-containing G-protein–coupled receptor 4 (Lgr4, also known as Gpr48) has been associated with multiple physiologic and pathologic functions. Lgr4 and its ligands R-spondin 1–4 have been shown to promote the growth and metastasis of tumor cells. However, whether Lgr4 can promote tumor progression by regulating the function of immune cells in the tumor microenvironment remains largely unknown. Here, we demonstrate that Lgr4 promotes macrophage M2 polarization through Rspo/Lgr4/Erk/Stat3 signaling. Notably, urethane-induced lung carcinogenesis, Lewis lung carcinoma (LLC), and B16F10 melanoma tumors were all markedly reduced in Lgr4fl/flLyz2cre/+ mice, characterized by fewer protumoral M2 TAMs and increased CD8+ T lymphocyte infiltration in the TME. Furthermore, LLC tumor growth was greatly depressed when Rspo/Lgr4/Erk/Stat3 signaling was blocked with either the LGR4 extracellular domain or an anti-Rspo1 antibody. Importantly, blocking Rspo-Lgr4 signaling overcame LLC resistance to anti-PD-1 therapy and improved the efficacy of PD-1 immunotherapy against B16F10 melanoma, indicating vital roles of Rspo-Lgr4 in host antitumor immunity and a potential therapeutic target in cancer immunotherapy.Significance: This study identifies a novel receptor as a critical switch in TAM polarization whose inhibition sensitizes checkpoint therapy–resistant lung cancer to anti-PD-1 therapy.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/17/4929/F1.large.jpg. Cancer Res; 78(17); 4929–42. ©2018 AACR.
