J Biol Chem. 2014 July 15.doi: 10.1074/jbc.M114.559963
Chuan Ouyang, Li Nie, Meidi Gu, Ailing Wu, Xu Han, Xiaojian Wang, Jianzhong Shao*, Zongping Xia*
Abstract
TGF-β-activated kinase 1 (TAK1) is a key kinase in mediating toll-like receptors (TLRs) and interleukin-1 receptor (IL-1R) signaling. Although TAK1 activation involves the phosphorylation of Thr184 and Thr187 residues at the activation loop, the molecular mechanism underlying the complete activation of TAK1 remains elusive. In this work, we show that the Thr187 phosphorylation of TAK1 is regulated by its C-terminal coiled-coil domain mediated dimerization in an autophosphorylation manner. Importantly, we find that TAK1 activation in mediating downstream signaling requires an additional phosphorylation at serine 412 (Ser412), which is critical for TAK1 response to proinflammatory stimuli, such as tumor necrosis factor (TNF)-α, lipopolysaccharide(LPS), and IL-1β. In vitro kinase and short hairpin RNA-based knockdown assays reveal that TAK1 Ser412 phosphorylation is regulated by cAMP-dependent protein kinase catalytic subunit α (PKACα) and X-linked protein kinase (PRKX), which is essential for proper signaling and proinflammatory cytokine induction by TLR/IL-1R activation. Morpholino-based in vivo knockdown and rescue studies show that the corresponding site Ser391 in zebrafish TAK1 plays a conserved role in nuclear factor-κB activation. Collectively, our data unravel a previously unknown mechanism involving TAK1 phosphorylation mediated by PKACα and PRKX that contributes to innate immune signaling.
