Regulation of mRNA homeostasis by PD-L1

St. John'S University, Queens NY

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Abstract

Abstract The goal of this project is to identify mechanisms by which immune checkpoint programmed death ligand 1 (PD-L1) regulates mRNA homeostasis of anti-apoptotic genes. As a cell surface protein, PD-L1 inhibits T cell responses, resulting in immune escape. However, PD-L1 also has important non-immune intracellular functions that are much less understood. Our recent studies show that IFNγ induces the nuclear translocation and accumulation of PD-L1 in ovarian and prostate cancer cells. In addition, our preliminary data indicate that suppression of the IFNγ-induced PD-L1 expression increases apoptosis and decreases mRNA levels of NFκB-dependent anti-apoptotic genes. Based on those findings, we will test the central hypothesis that the intracellular PD-L1 serves as a regulator of anti-apoptotic gene mRNA homeostasis. In Aim 1, we will determine whether PD-L1 increases the levels of anti-apoptotic genes by promoting their transcription, and/or whether it increases stability of their mRNAs in ovarian and prostate cancer cells. In Aim 2, we will determine whether PD-L1 directly binds to the anti-apoptotic gene promoters and facilitates their acetylation, and we will investigate whether PD-L1 binds the anti-apoptotic mRNAs and affects their subcellular localization. Although the project focuses on the NFκB-dependent anti-apoptotic genes, the results will likely reveal general mechanisms by which PD-L1 regulates synthesis and/or stability of other mRNAs. Immunotherapies targeting cell surface PD-L1 have shown impressive clinical outcomes in many cancers; however, only a fraction of patients achieves durable responses, highlighting our incomplete understanding of the mechanisms of PD-L1 functions. Findings from this study will provide the first data on the mechanisms of how PD-L1 regulates mRNA homeostasis of anti- apoptotic genes. This information will advance our understanding of the intracellular, immune-independent functions of PD-L1, and may lead to the development of novel therapies that target PD-L1 anti-apoptotic functions in cancer cells.