A Truncated Human NKG2D Splice Isoform Negatively Regulates NKG2D-Mediated Function

Abstract

Natural killer group 2, member D (NKG2D) is a stimulatory receptor expressed by NK cells and a subset of T cells. NKG2D is crucial in diverse aspects of innate and adaptive immune functions. In this study, we characterize a novel splice variant of human NKG2D that encodes a truncated receptor lacking the ligand-binding ectodomain. This truncated NKG2D (NKG2DTR) isoform was detected in primary human NK and CD8+ T cells. Overexpression of NKG2DTR severely attenuated cell killing and IFN-γ release mediated by full-length NKG2D (NKG2DFL). In contrast, specific knockdown of endogenously expressed NKG2DTR enhanced NKG2D-mediated cytotoxicity, suggesting that NKG2DTR is a negative regulator of NKG2DFL. Biochemical studies demonstrated that NKG2DTR was bound to DNAX-activated protein of 10 kDa (DAP10) and interfered with the interaction of DAP10 with NKG2DFL. In addition, NKG2DTR associated with NKG2DFL, which led to forced intracellular retention, resulting in decreased surface NKG2D expression. Taken together, these data suggest that competitive interference of NKG2D/DAP10 complexes by NKG2DTR constitutes a novel mechanism for regulation of NKG2D-mediated function in human CD8+ T cells and NK cells.