Fig. 8: Proposed model of the molecular pathways whereby mMIC and sMIC differentially regulate NK cell function.

Engagement of the receptor NKG2D to the two forms of MIC ligand, mMIC, and sMIC leads to distinct signaling cascades resulting in activation of NK cell cytotoxicity and inflammatory cytokine/chemokine production, respectively. mMIC-NKG2D interaction delivers a regulated stimulation through canonical immune synapse formation and selectively activates PLCγ2/SLP-76/Vav-1 and ERK/JNK signaling axis for NK cell cytotoxicity and upregulation of T-bet for IFNγ secretion. Conversely, the lack of canonical immune synapse formation upon sMIC-NKG2D interaction delivers a chronic and deregulated stimulation that results in activation of CBM-signalosome-mediated pro-inflammatory pathways. The activation of CBM-signalosome pathways is associated with persistent activation of Fyn/ADAP and PKC-θ pathways. The ITAM immediate downstream molecule Lck is required for both mMIC- and sMIC-stimulated events.