Abstract B51: Tumor ER stress transmission to infiltrating myeloid cells in vivo require IRE1alpha and TLR4

Abstract

Abstract The unfolded protein response (UPR) facilitates tumor outgrowth through evoking a variety of cell intrinsic processes that promote cancer survival, angiogenesis, and chemoresistance. The UPR can be transmitted from stressed cancer cells to receiver myeloid cells in vitro through a process termed transmissible endoplasmic reticulum stress (TERS) in which receiver cells undergo a UPR and acquire tumor promoting pro-inflammatory (IL-6, TNF-alpha, IL-23) and immune-suppressive (Arg1) characteristics. Here, we confirmed that CD11b+ myeloid cells isolated from subcutaneous murine melanoma tumors in C57BL/6 mice display the TERS signature. In light of the fact that TERS signaling in myeloid receiver cells is partly TLR4-dependent, we interrogated subcutaneous tumors in TLR4 mice. We found that these tumors had delayed onset, reduced growth kinetics, and improved survival over tumors growing in wildtype mice. Most significantly, isolated CD11b+ cells from TLR4-/- tumors did not undergo a UPR nor upregulate inflammatory genes when compared to splenic controls, though, interestingly, still upregulated Arg1. Next, we probed individual signaling arms of the UPR in relation to TERS production. We utilized a panel of novel transgenic cell lines in which specific arms of the UPR can be conditionally activated and found that activated inositol requiring enzyme-1alpha (IRE1alpha) transmitted stress to myeloid cells. The remaining two UPR arms (PERK and ATF6) had little transmitting potential, if any. Bone marrow derived myeloid cells treated with TERS generated from IRE1alpha KO mouse embryonic fibroblasts (MEFs) had a markedly reduced UPR than those treated to wildtype MEF TERS. Subcutaneous tumors consisting of IRE1alpha KO TERS-conditioned myeloid dendritic cells and melanoma cancer cells had delayed onset and grew at reduced rate compared to tumor mixtures in which wildtype MEF TERS was used. Based on these data, we probed a patient melanoma for its co-localization of stress, myeloid infiltrate, and inflammation. Together, these data identify a novel signaling mechanism dependent on IRE1alpha and TLR4 used by stressed tumor cells to co-opt infiltrating myeloid cells to become tumor promoting. Citation Format: Jeffrey J. Rodvold, Nobuhiko Hiramatsu, Kevin T. Chiu, Navin R. Mahadevan, Jonathan Lin, Maurizio Zanetti. Tumor ER stress transmission to infiltrating myeloid cells in vivo require IRE1alpha and TLR4. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr B51.