Project 4

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PROJECT 4 SUMMARY: METABOLIC AND FUNCTIONAL REPROGRAMMING OF IMMUNOSUPPRESSIVE MYELOPOIESIS IN LUNG TUMORS Lung cancer cells and tumor-infiltrating immune subsets activate an integrated signaling network known as the unfolded protein response (UPR) as a reaction to the sustained and pronounced endoplasmic reticulum (ER) expansion and stress induced by the precarious conditions of the tumor microenvironment (TME). The UPR promotes cellular adaptation processes in the TME that initially drive the survival of ER stressed cells. However, the role of the intrinsic activation of UPR drivers in immune cells in the modulation of anti-tumor immunity remains unclear. Expansion of myeloid-derived suppressor cells (MDSC) in tumor-bearing hosts has emerged as a primary mechanism to block protective anti-tumor immunity and a major obstacle to the success of lung cancer immunotherapy. To date, however, the approaches to therapeutically block MDSC are limited to myelosuppressive inhibitors that are only partially effective and cause rebound in MDSC numbers as the bone marrow recovers. The primary goal of this study is to dissect the intrinsic mechanistic interplay between the sustained over-activation of UPR-related PKR-like ER kinase (PERK) and the metabolic events that polarize MDSC into highly immunoinhibitory myeloid cells in lung tumors. In cooperation with Projects #1-3, we hypothesize that the intrinsic elimination of PERK functionally and metabolically transforms MDSC into immunostimulatory cells that restore protective anti-tumor immunity. Mechanistically, we argue that the ablation of PERK impairs NRF2 signaling, which alters the expression of the cystine transporter, xCT, and promotes the accumulation of reactive oxygen species (ROS) that disrupt mitochondrial homeostasis and trigger the TP53 ↔ STING-dependent production of type I interferons. Thus, therapeutic inhibition of PERK in tumor beds will overcome MDSC-linked T cell suppression and boost the effects of several forms of immunotherapy in lung cancer. We propose the following Aims: In Aim 1, we will evaluate the role of blunted NRF2-related cystine metabolism in the mitochondrial dysfunction observed in PERK-deficient MDSC from lung tumors. In Aim 2, we will elucidate the impact of the TP53 ↔ cGAS ↔ STING axis in the functional transformation of PERK-null MDSC into myeloid cells with the ability to promote anti-tumor T cell responses. In Aim 3, we will test whether therapeutic modulation or detection of active PERK, or its down-stream targets, serve as effective strategies to enhance and monitor the activities of immunotherapy in lung cancer. The development of these Aims will have a profound impact on the field by substantiating a primary signal whereby tumors regulate myeloid cell function through activation of key ER stress mediators. This will provide a mechanistic rationale for the development of novel therapeutic approaches to effectively reprogram MDSC into myeloid cells that induce anti-tumor immunity, and to enhance the efficacy of lung cancer immunotherapy.