Toll like receptors serve as sentinels to the innate immune system by binding common pathological antigens and initiating host responses. These responses can be deleterious to the host if unchecked leading to chronic diseases including autoimmunity. DNAX-activating protein 12 (DAP12) is an adaptor protein containing an immunoreceptor tyrosine-based activation motif expressed in myeloid cells, NK cells, osteoclasts and microglia. In macrophages, DAP12 can couple with immunoreceptor triggering receptor expressed on myeloid cells 2 (TREM2) to negatively regulate TLR signaling through an as yet undefined mechanism. We have shown that downstream of kinase 3 (DOK3), through its phosphotyrosine domain, associates with DAP12 after low down LPS stimulation of bone marrow macrophages (BMM). DOK3-/- BMMs stimulated with LPS show increased phospoERK signaling at 20 and 40 minutes indicative of enhanced activation. Supernatants taken from these cells show significantly increased levels of proinflammatory cytokines TNFα, IL-6, and IL-12p40 compared to wild type cells. Upon LPS stimulation, DOK3 is phosphorylated in a DAP12- and Src kinase- dependent manner leading to DOK3 translocation to the plasma membrane. Despite the recruitment of SHIP1 to DOK3 and DAP12 after LPS stimulation; SHIP1 is not required for DAP12-dependent inhibition of LPS-induced ERK activation. These results reveal a new mechanism underlying DAP12 and TREM2 inhibition of TLR responses in macrophages.
- Copyright © 2013 by The American Association of Immunologists, Inc.