THE ROLE OF TRAF6 PHOSPHORYLATION IN Src/TRAF6-MEDIATED IKK, JNK, Akt ACTIVATION AND TUMORIGENESIS
Date of Graduation
Genes and Development
Doctor of Philosophy (PhD)
Hui-Kuan Lin, Ph.D.
Xin Lin, Ph.D.
Mong-Hong Lee, Ph.D.
Angabin Matin, Ph.D.
Dos Sarbassov, Ph.D.
TRAF6 E3 ligase regulates numerous essential biological processes such as innate immune response, cell survival and osteoclast differentiation. Upon activation, it mediates activation of IKK/NF-κB and JNK signaling in response to engagement of toll-like receptor 4 (TLR4), interleukin-1 receptor (IL-1R), and receptor activator of NF-κB (RANK) to their cognate ligands, including lipopolysaccharide (LPS), IL-1, and RANK ligand (RANKL). Recently, TRAF6 has also been shown to be involved in Akt signaling activation upon activation of insulin-like growth factor-1 receptor (IGF-1R), in turn orchestrating cell survival and tumorigenesis. Therefore, TRAF6 is a key player for the activation of IKK, JNK and Akt by diverse receptor signaling. Although TRAF6 activity is induced by these receptors, the mechanism by which TRAF6 is activated under these stimulating conditions remains largely unclear.
Here, we show that TRAF6 Y473 phosphorylation is commonly induced and serves as an essential mode for TRAF6 activation by multiple signaling stimuli including IGF-1, IL-1, LPS, and RANKL. We identify Src tyrosine kinase as a direct kinase for TRAF6 and a mediator of TRAF6 Y473 phosphorylation. Notably, we find that Src or Traf6 deficiency impairs IKK, Akt, and JNK activation, which can be rescued by phosphomimetic TRAF6, but not by phosphorylation-dead TRAF6 mutant. Mechanistically, we show that TRAF6 phosphorylation is imperative for TRAF6 dimerization/oligomerization and its binding to E2 enzyme, UBC13. Significantly, we find that TRAF6 phosphorylation is critical for TRAF6-mediated cancer progression and represents a biomarker for poor survival outcome. Our study therefore resolves the long-standing puzzle of achievement of TRAF6 activation and elucidates TRAF6 phosphorylation as a central mode for Src/TRAF6-mediated downstream kinase activation and tumorigenesis
TRAF6 E3 ligase, Src tyrosine kinase, Ubiquitination, IKK, JNK, Akt, Tumorigenesis