Abstract A098: SLC12A2 as a novel “brake” on immunogenic apoptotic cell clearance

Phagocytes face a key challenge during efferocytosis – they must engulf an apoptotic cell, often similar in size, while maintaining their own cell integrity, shape, and volume. Yet little is known about phagocyte volume homeostasis during apoptotic cell clearance. To this end, we performed an unbiased transcriptomics screen designed to reveal alterations of phagocyte gene expression after engulfment of apoptotic Jurkat lymphoma cells and identified several transcriptional programs distinctly modified in engulfing phagocytes. We identified a program involving cell volume regulation and potassium/chloride flux, the latter of which is thought to underlie immunogenic responses. Disruption of one member of this cell volume program, SLC12A2, resulted in “overeating” of apoptotic JurkaT-cells by individual phagocytes and a significant increase in cell size. Importantly, we demonstrate that SLC12A2-deficient phagocytes actively engulfing apoptotic JurkaT-cells led to a downregulation of the hallmark antiinflammatory efferocytosis program and robust upregulation of a proinflammatory program. In particular, we observed robust upregulation of immunogenic programs, including a type I interferon signature, in SLC12A2-deficient engulfing phagocytes that were not observed in phagocytes over-expressing the phosphatidylserine receptor TIM4, Mechanistically, we found that the chloride-sensing kinase WNK1 and downstream kinases OSR1 and SPAK function to regulate chloride flux into engulfing phagocytes via SLC12A2, and that this pathway regulates the apoptotic JurkaT-cell “overeating” observed in SLC12A2-deficient phagocytes. Collectively, these data elucidate a novel mechanism by which phagocytes protect themselves from potentially dangerous apoptotic cell-derived inflammatory ligands and suggest that SLC12A2 serves to actively suppress immunogenic responses by phagocytes and limits the rate of corpse uptake during efferocytosis. Citation Format: Justin Shaun Arnold Perry, Sho Morioka, Christopher Medina, Michael Raymond, Kodi Ravichandran. SLC12A2 as a novel “brake” on immunogenic apoptotic cell clearance [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A098.