Tumor-secreted Pros1 inhibits macrophage M1 polarization to reduce antitumor immune response
Eric Ubil, Laura Caskey, Alisha Holtzhausen, Debra Hunter, Charlotte Story, H. Shelton Earp
Eric Ubil, Laura Caskey, Alisha Holtzhausen, Debra Hunter, Charlotte Story, H. Shelton Earp
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Research Article Cell biology Immunology

Tumor-secreted Pros1 inhibits macrophage M1 polarization to reduce antitumor immune response

Abstract

Tyro3, Axl, Mer (TAM) receptor tyrosine kinases reduce inflammatory, innate immune responses. We demonstrate that tumor-secreted protein S (Pros1), a Mer/Tyro3 ligand, decreased macrophage M1 cytokine expression in vitro and in vivo. In contrast, tumor cells with CRISPR-based deletion of Pros1 failed to inhibit M1 polarization. Tumor cell–associated Pros1 action was abrogated in macrophages from Mer- and Tyro3- but not Axl-KO mice. In addition, several other murine and human tumor cell lines suppressed macrophage M1 cytokine expression induced by IFN-γ and LPS. Investigation of the suppressive pathway demonstrated a role for PTP1b complexing with Mer. Substantiating the role of PTP1b, M1 cytokine suppression was also lost in macrophages from PTP1b-KO mice. Mice bearing Pros1-deficient tumors showed increased innate and adaptive immune infiltration, as well as increased median survival. TAM activation can also inhibit TLR-mediated M1 polarization. Treatment with resiquimod, a TLR7/8 agonist, did not improve survival in mice bearing Pros1-secreting tumors but doubled survival for Pros1-deleted tumors. The tumor-derived Pros1 immune suppressive system, like PD-L1, was cytokine responsive, with IFN-γ inducing Pros1 transcription and secretion. Inhibition of Pros1/TAM interaction represents a potential novel strategy to block tumor-derived immune suppression.

Authors

Eric Ubil, Laura Caskey, Alisha Holtzhausen, Debra Hunter, Charlotte Story, H. Shelton Earp

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Figure 4

Mer complexes with PTP1b and inhibits p38-mediated M1 gene expression.

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Mer complexes with PTP1b and inhibits p38-mediated M1 gene expression. (...
(A) Coimmunoprecipitation of p38α and p-p38α with Mer after stimulation of M1-induced macrophages with Pros1. n = 3, *P < 0.05 relative to macrophage-only IFN-γ+LPS treatment, 3 independent replicates. (B) Coimmunoprecipitation of Mer and p38α with PTP1b after stimulation of M1-induced macrophages with Pros1 and/or BVT948. n = 3, *P < 0.05 relative to macrophage-only IFN-γ+LPS treatment, †P < 0.05 relative to IFN-γ+LPS–treated B16F10 cocultured macrophages, 3 independent replicates. (C) Expression of M1-associated genes in M1-induced macrophages cocultured with B16F10 in the presence or absence of PTP inhibitors BVT948, PTP inhibitor III, and NSC87877. n = 8, *P < 0.05 relative to M1-induced macrophages, †P < 0.05 relative to M1-induced macrophages cocultured with B16F10 cells. (D) M1-induced PTP1b-KO macrophages cultured in the presence of Pros1 or cocultured with B16F10 cells. n = 4, *P < 0.05 relative to M1-induced macrophages. Data are mean ± SEM; P values calculated by 2-tailed Student’s t test.