Tu139 - Human Naïve CD4+ T Cell Survival Is Maintained by a Novel CD46-KLF/SP Axis

Luopin Wang – Purdue University; Nicolas Merle – National Heart, Lung, and Blood Institute (NHLBI); Jack Bibby – National Heart, Lung, and Blood Institute (NHLBI); Natalia Kunz – National Heart, Lung, and Blood Institute (NHLBI); Gaelle Le Friec – King’s College London; Jubayer Rahman – National Heart, Lung, and Blood Institute (NHLBI); Paul Lavender – King’s College London; Henrik Hasle – Aarhus University; Majid Kazemian – Purdue University; Claudia Kemper – National Heart, Lung, and Blood Institute (NHLBI)

Abstract Text: Signals mediated by autocrine activation of the human-specific complement receptor CD46 during T cell receptor (TCR) stimulation are vital to Th1 induction in human CD4+ T cells. However, how exactly CD46 mediates this role at a molecular level is currently undefined. CD46 is expressed in different isoforms that can bear either one of two distinct cytoplasmic tails: CYT-1 or CYT-2. Nuclear translocation of CYT-1 is a critical requirement for the expression of genes coding for nutrient-influx-channels and mTORC1 activity that mediate metabolic adaptations needed for Th1 responses. The lack of a DNA binding domain in CD46-CYT-1 precludes it from acting directly as a transcription factor (TF) and we hence hypothesized that CYT-1 regulates gene expression via direct interaction with specific TF activator and/or repressor complexes. Indeed, CUT&RUN experiments in conjunction with ELISA and microscale thermophoresis experiments identified key members of the KLF/SP TFs family as central interacting partners of CD46-CYT-1 in human CD4+ T cells, with CYT-1 largely fostering KLF/SP TFs binding to the target DNA motifs. Unexpectedly, CYT-1-assisted KLF/SP binding shapes dominantly the transcriptional output of naïve CD4+ T cells and governs their survival via negative regulation, specifically, ‘death caspase machinery’ (caspases 2, 3, 8, and 9). Aligning with these findings, naïve CD4+ T from patients with a germline frameshift mutation in the CYT-1-binding region of KLF/SP TF displayed survival defects ex vivo. These data define a novel and critical human-specific pathway of gene regulation and further underpin the vital role of intracellular/autocrine complement in regulating normal cellular activity.