NKG2D triggering hampers DNAM-1-mediated signaling in human NK cells

Caterina Marangio¹Nadia Domenica Milito¹Erisa Putro¹Alessia Carnevale¹Cristina Capuano²Alessandra Zingoni¹Marco Cippitelli¹Angela Santoni^1,3Rossella Paolini^1*Rosa Molfetta^1*

• ¹Laboratory Affiliated to Istituto Pasteur Italia-Fondazione Cenci Bolognetti, Department of Molecular Medicine, Sapienza University of Rome, Rome, Lazio, Italy
• ²Departmental Faculty of Medicine and Surgery, UniCamillus-Saint Camillus International University of Health and Medical Sciences,, Rome, Italy
• ³Mediterranean Neurological Institute Neuromed (IRCCS), Pozzilli, Italy

Natural Killer (NK) cells are cytotoxic innate lymphocytes able to detect transformed cells through the balanced action of inhibitory and activating receptors. NKG2D is one of the main activating receptors involved in tumor surveillance thanks to its ability to recognize stress-induced ligands. Of note, the prolonged exposure to NKG2D ligands promotes receptor down-modulation that results in defective activation of NKG2D and other unrelated activating receptors, including DNAM-1 that is also involved in tumor clearance. However, further investigations are necessary to characterize how the NKG2D/DNAM-1 interplay affects NK cell anti-tumor function. Here, we showed that NKG2D crosslinking mediated by the natural ligand MICA or an agonist antibody had different consequences on primary cultured human NK cells. Indeed, MICA stimulation increases the expression of the checkpoint receptor TIGIT that is able to counteract DNAM-1 activation. Stimulation with the agonist antibody, without altering TIGIT expression, directly inhibits DNAM-1-mediated signal transduction and cytotoxic function with a mechanism that required NKG2D endocytosis. Understanding the molecular mechanisms responsible for suppression of NK cell activation may help the development of therapeutic anti-cancer strategies aimed to prevent NK cell dysfunction or to reinvigorate an impaired cytotoxic activity.