Sen Santara and Lee et al. identified ecto-CRT, a product of ER stress, as an activating ligand of NKp46 that contributed to increased NK cell-mediated killing of stressed and senescent cells. The NKp46 receptor specifically bound to D237 and D258 in the P domain of ecto-CRT, triggering NK cell signaling and NKp46 caps with ecto-CRT in NK immune synapses. This mechanism was identified in both human and mouse cells. NK cells also controlled tumors in mouse models bearing tumors expressing ecto-CRT, dependent on NKp46. This effect appeared to be due to increased NK cell recognition, degranulation, and cytokine secretion, rather than increased infiltration.
ABSTRACT: Natural killer (NK) cell kill infected, transformed and stressed cells when an activating NK cell receptor is triggered(1). Most NK cells and some innate lymphoid cells express the activating receptor NKp46, encoded by NCR1, the most evolutionarily ancient NK cell receptor(2,3). Blockage of NKp46 inhibits NK killing of many cancer targets(4). Although a few infectious NKp46 ligands have been identified, the endogenous NKp46 cell surface ligand is unknown. Here we show that NKp46 recognizes externalized calreticulin (ecto-CRT), which translocates from the endoplasmic reticulum (ER) to the cell membrane during ER stress. ER stress and ecto-CRT are hallmarks of chemotherapy-induced immunogenic cell death(5,6), flavivirus infection and senescence. NKp46 recognition of the P_domain of ecto-CRT triggers NK_ cell signalling and NKp46 caps with ecto-CRT in NK immune synapses. NKp46-mediated killing is inhibited by knockout or knockdown of CALR, the gene encoding CRT, or CRT antibodies, and is enhanced by ectopic expression of glycosylphosphatidylinositol-anchored CRT. NCR1)-deficient human (and Nrc1-deficient mouse) NK cells are impaired in the killing of ZIKV-infected, ER-stressed and senescent cells and ecto-CRT-expressing cancer cells. Importantly, NKp46 recognition of ecto-CRT controls mouse B16 melanoma and RAS-driven lung cancers and enhances tumour-infiltrating NK_ cell degranulation and cytokine secretion. Thus, NKp46 recognition of ecto-CRT as a danger-associated molecular pattern eliminates ER-stressed cells.
Author Info: (1) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. Department of Biolog
Author Info: (1) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, India. (2) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. (3) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. (4) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA. (5) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA. (6) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. (7) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. (8) Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA. (9) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. Laboratorio de Neuroinmunobiologa, Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnologa, Universidad Nacional Autnoma de Mxico, Cuernavaca, Mexico. (10) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. (11) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. (12) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. (13) Center for Nanoscale Systems, Faculty of Arts and Sciences, Harvard University, Cambridge, MA, USA. (14) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA. (15) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. caroline.junqueira@childrens.harvard.edu. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. caroline.junqueira@childrens.harvard.edu. Instituto Ren Rachou, Fundao Oswaldo Cruz, Belo Horizonte, Brazil. caroline.junqueira@childrens.harvard.edu. (16) Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. judy.lieberman@childrens.harvard.edu. Department of Pediatrics, Harvard Medical School, Boston, MA, USA. judy.lieberman@childrens.harvard.edu.
