TRAF6, a member of the tumour necrosis factor receptor-associated factor family, was first identified as a transducer of CD40 and interleukin-1 receptor (IL-1R) signals based on the interaction of TRAF6 with the cytoplasmic tail of CD40 and with the IL-1R associated kinase in vitro. However, the functions of TRAF6 in vivo remain unidentified.
We show that TRAF6−/− mice exhibit severe osteopetrosis and are defective in osteoclast formation. In vitro culture experiments revealed that osteoclast precursor cells derived from TRAF6−/− mice are unable to differentiate to functional osteoclasts in response to osteoclast differentiation factor (ODF). In bone marrow of TRAF6−/− mice, the number of sIgM+B220+ immature B cells is markedly reduced while the ratio of proB to preB cells is not affected. In contrast, development of thymocytes is not affected. Furthermore, TRAF6−/− mice are defective in lymph node organogenesis and IL-1 signalling in thymocytes.
The results identify TRAF6 as an essential component of ODF signalling pathway, and also show that TRAF6 plays pivotal roles in immune and inflammatory systems in vivo.