Essential roles for Dok2 and RasGAP in CD200 receptor-mediated regulation of human myeloid cells

Area of Science:

• Immunology
• Cell Biology
• Molecular Signaling

Background:

• The CD200 receptor (CD200R) is a known negative regulator of myeloid cells, interacting with its ligand CD200.
• Previous studies suggested roles for adaptor proteins Dok1 and Dok2 in CD200R signaling, primarily in murine models.

Purpose of the Study:

• To elucidate the specific molecular mechanisms by which CD200R inhibits human myeloid cell activation.
• To identify the key intracellular signaling molecules involved in CD200R-mediated negative regulation.

Main Methods:

• Utilized U937 cells expressing CD200R mutants to investigate signaling pathways.
• Employed biochemical assays to determine binding affinities between CD200R motifs and adaptor proteins.
• Performed RNA interference (RNAi) to knock down specific proteins (Dok2, RasGAP, Dok1, SHIP) and assess their impact on CD200R signaling.

Main Results:

• The NPLY motif in the CD200R cytoplasmic region is crucial for mediating inhibition.
• Downstream of tyrosine kinase 2 (Dok2) bound the phosphorylated NPLY motif with high affinity, outcompeting Dok1.
• CD200R engagement phosphorylated Dok2, leading to the recruitment of RAS p21 protein activator 1 (RasGAP).
• Knockdown of Dok2 and RasGAP, but not Dok1 or SHIP, abrogated CD200R-mediated inhibition.

Conclusions:

• CD200R inhibits human myeloid cell activation via direct recruitment of Dok2 and subsequent RasGAP activation.
• This signaling pathway differs from typical inhibitory receptors that rely on ITIMs and phosphatases.