IRE1α regulates macrophage polarization, PD-L1 expression, and tumor survival.

Alyssa Batista,Hannah Carter,T Cameron Waller,Gonzalo Almanza,Kristen Jepsen,Jonathan Lin,Jeffrey J Rodvold,Su Xian,Takao Iwawaki,Maurizio Zanetti,Alyssa Lew,Stephen C Searles,Thomas C Freeman

doi:10.1371/journal.pbio.3000687

Abstract

In the tumor microenvironment, local immune dysregulation is driven in part by macrophages and dendritic cells that are polarized to a mixed proinflammatory/immune-suppressive phenotype. The unfolded protein response (UPR) is emerging as the possible origin of these events. Here we report that the inositol-requiring enzyme 1 (IRE1α) branch of the UPR is directly involved in the polarization of macrophages in vitro and in vivo, including the up-regulation of interleukin 6 (IL-6), IL-23, Arginase1, as well as surface expression of CD86 and programmed death ligand 1 (PD-L1). Macrophages in which the IRE1α/X-box binding protein 1 (Xbp1) axis is blocked pharmacologically or deleted genetically have significantly reduced polarization and CD86 and PD-L1 expression, which was induced independent of IFNγ signaling, suggesting a novel mechanism in PD-L1 regulation in macrophages. Mice with IRE1α- but not Xbp1-deficient macrophages showed greater survival than controls when implanted with B16.F10 melanoma cells. Remarkably, we found a significant association between the IRE1α gene signature and CD274 gene expression in tumor-infiltrating macrophages in humans. RNA sequencing (RNASeq) analysis showed that bone marrow-derived macrophages with IRE1α deletion lose the integrity of the gene connectivity characteristic of regulated IRE1α-dependent decay (RIDD) and the ability to activate CD274 gene expression. Thus, the IRE1α/Xbp1 axis drives the polarization of macrophages in the tumor microenvironment initiating a complex immune dysregulation leading to failure of local immune surveillance.

Highlights

Myeloid cells in the tumor microenvironment (TME) are of central relevance to understand the dynamics of tumor progression [1]
Previous in vitro studies indicated that bone marrow–derived dendritic cell (BMDC) and bone marrow–derived macrophage (BMDM) respond to a cell-nonautonomous unfolded protein response (UPR) developing a complex phenotype characterized by a UPR activation and a mixed proinflammatory/immune suppressive (IIS) phenotype [26,28]
We implanted B16.F10 murine melanoma cells into C57BL/6 mice that carry the Xbp1-Venus fusion transgene under the control of the cytomegalovirus (CMV)-β actin promoter, known as the endoplasmic reticulum (ER) stress-activated indicator (ERAI) [41], which reports inositolrequiring enzyme 1 (IRE1α)-mediated X-box binding protein 1 (XBP1) splicing through the expression of the fluorescent Venus protein

Summary

Introduction

Myeloid cells in the tumor microenvironment (TME) are of central relevance to understand the dynamics of tumor progression [1]. Bone marrow–derived macrophages (BMDMs) and bone marrow–derived dendritic cells (BMDCs) cultured in conditioned media (CM) of ER stressed cancer cells develop a de novo UPR and acquire a mixed IIS phenotype [26,28] characterized by the transcriptional up-regulation of the tumorigenic proinflammatory cytokines IL-6, tumor necrosis factor α (TNFα), and IL-23 [32,33,34], and contextually of the immune-suppressive enzyme Arginase (Arg1) [35] Under these conditions, cross-priming of naïve CD8+ T cells by BMDC is greatly compromised [28]. We discovered that IRE1α signaling regulates programmed death ligand 1 (PD-L1) expression in murine and in tumor-infiltrating macrophages in humans

Results

Discussion

Materials and methods