Structural and functional consequences of switching carboxy terminal domains in mouse CD200 receptors

Abstract

CD200:CD200R interactions regulate immune responses. Since CD200Rs show extensive homology in their extracellular region, generating anti-CD200R specific antibodies is a challenge. We report below on the generation of mAbs specific for murine (m)R1/R2 and evidence that mR2 is expressed on the cell surface in the absence of the adaptor protein Dap12. Despite homology between mR1 and mR4, the unexpected reduction in the molecular mass ( i.e. 90kDa vs 48kDa) between the two receptors suggested that the TM and cytoplasmic region of mR4 regulated glycosylation. Substitution of the TM and cytoplasmic region of mR1 and mR2 with that of mR4 reduced glycosylation of the chimeric receptors mR 1 r 4 and mR 2 r 4 implying that these regions regulated the glycosylation of mCD200Rs. In activation experiments, phosphorylation of Dap12 following interaction with CD200 occurred on cells expressing mR2V5 but not mR4V5. Similar experiments with the chimeric receptors mR 1 r 2 and mR 1 r 4 also produced phosphorylation of Dap12. Our data suggest that the TM and cytoplasmic region of mCD200Rs dictate their state of glycosylation and provide further evidence that both mCD200R1 and mCD200R2 bind CD200 as ligand with functional consequences for down- stream signaling.