The adaptor 3BP2 activates CD244-mediated cytotoxicity in PKC- and SAP-dependent mechanisms

Natural killer (NK) cell cytotoxicity requires triggering of activation receptors over inhibitory receptors. CD244, a member of CD150 receptor family, positively regulates NK-mediated lyses by activating an intracellular multiproteic signaling network that involves the adaptors X-linked lymphoproliferative gene product SAP and 3BP2. However, the exact mechanisms used by 3BP2 to enhance CD244-mediated cytotoxicity are still not fully understood. Here using the human NK cell line YT-overexpressing 3BP2, we found that the adaptor increases CD244, PI3K, and Vav phosphorylation upon CD244 engagement. The use of enzymatic inhibitors revealed that 3BP2-dependent cytolysis enhancement was PKC-dependent and PI3K-ERK independent. Furthermore, 3BP2 overexpression enhanced PKC delta phosphorylation. SAP knockdown expression inhibited PKC delta activation, indicating that the activating role played by 3BP2 depends upon the presence of SAP. In conclusion, our data show that 3BP2 acts downstream of SAP, increases CD244 phosphorylation and links the receptor with PI3K, Vav, PLC gamma, and PKC downstream events in order to achieve maximum NK killing function.