Regulation of NK cell maturation by the intramembrane protease SPPL3 (HEM5P.224)

Abstract

Abstract Natural killer (NK) cells play an essential role in tumor surveillance through direct tumor cell lysis. Signal peptide peptidase-like 3 (SPPL3) is a highly conserved intramembrane aspartyl protease, but very little is known about its functions in vivo. We developed an SPPL3 conditional knockout mouse and found that deletion of SPPL3 within the hematopoietic system using Vav1-iCre resulted in a peripheral defect in NK cell number. The reduced NK cell population was hypofunctional in tumor clearance in vivo and direct tumor lysis in vitro. Analysis of SPPL3-deficient NK cells revealed a substantial block in terminal maturation, at the CD27+CD11b- stage. Deletion of SPPL3 in NK cells by NKp46-iCre confirmed a cell-autonomous requirement for SPPL3 in NK development and function. CRISPR/Cas9 genome editing was used to create a knockin mouse expressing a protease-dead SPPL3 knockin allele, D271A. NK cells expressing SPPL3 D271A exhibited the same block in terminal differentiation as SPPL3-deficient NK cells. Our results reveal that the proteolytic function of the SPPL3 intramembrane protease is critical for normal NK cell maturation at a checkpoint that regulates the transition from CD11b- to CD11b+ cells.