Induction of DAP12 phosphorylation, calcium mobilization, and cytokine secretion by Ly49H

The ability of several Ly49 family members to inhibit natural killer (NK) c ell functions through recruitment of SHP-1 phosphatase has been reported. I n contrast, the mechanisms underlying the activating signal generated by Ly 49D are poorly understood. A homodimeric phosphoprotein (pp16) that physica lly and functionally associates with Ly49D has been described. In this stud y, a rabbit anti-mouse pp16 antiserum,vas generated and used to demonstrate that pp16 corresponds to the recently described DAP12 molecule. In additio n, we show chat a second Ly49 family member that lacks an immunoreceptor ty rosine-based inhibitory motif and contains a charged residue in the transme mbrane domain, Ly49H, also associates with DAP12, Furthermore, we show that engagement of the Ly49H/DAP12 complex results in phosphorylation of DAP12, intracellular calcium mobilization, and tumor necrosis factor secretion in transfected cells. These results thus provide evidence that Ly49H is an ac tivating receptor that associates with. DAP12, previously described as a pp 16 component of the Ly49D receptor complex.