Transforming Growth Factor (TGF)-β-activated Kinase 1 (TAK1) Activation Requires Phosphorylation of Serine 412 by Protein Kinase A Catalytic Subunit α (PKACα) and X-linked Protein Kinase (PRKX)

Background: Understanding of molecular mechanism of TAK1 activation is incomplete. Results: PKAC and PRKX phosphorylate TAK1 at serine 412 to regulate TAK1 activation in the IL-1 receptor (IL-1R) and Toll-like receptor (TLR) signaling pathways. Conclusion: TAK1 activation requires phosphorylation by PKAC and PRKX. Significance: This study advanced our understanding of the molecular mechanism of TAK1 activation.TGF--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 Thr-184 and Thr-187 residues at the activation loop, the molecular mechanism underlying the complete activation of TAK1 remains elusive. In this work, we show that the Thr-187 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 Ser-412, which is critical for TAK1 response to proinflammatory stimuli, such as TNF-, LPS, and IL-1. In vitro kinase and shRNA-based knockdown assays reveal that TAK1 Ser-412 phosphorylation is regulated by cAMP-dependent protein kinase catalytic subunit (PKAC) 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 Ser-391 in zebrafish TAK1 plays a conserved role in NF-B activation. Collectively, our data unravel a previously unknown mechanism involving TAK1 phosphorylation mediated by PKAC and PRKX that contributes to innate immune signaling.