StIKKing it to a death kinase: IKKs prevent TNF-α-induced cell death by phosphorylating RIPK1

Area of Science:

• Cellular biology
• Molecular signaling
• Immunology

Background:

• Tumor Necrosis Factor-alpha (TNF-α) signaling pathways are crucial in mammalian biology, governing cell survival and death.
• The kinase RIPK1 is central to these pathways, with its poly-ubiquitylation previously thought to dictate its role in NF-κB activation (survival) versus cell death signaling.
• A simplified model posits TNF-α receptor signaling bifurcates into NF-κB-mediated survival and death-inducing signals.

Discussion:

• This study reveals that phosphorylation of RIPK1 by IKK-α and IKK-β acts as a critical switch in TNF-α receptor signaling.
• Phosphorylation by IKKs inhibits RIPK1's ability to form pro-apoptotic complexes with FADD and caspase 8, thereby preventing apoptosis.
• These IKKs also confer protection against RIPK1-dependent necroptosis, independent of NF-κB transcriptional activity.

Key Insights:

• Phosphorylation of RIPK1 by IKK-α/β is a novel mechanism regulating cell death downstream of TNF-α receptor.
• This phosphorylation event dampens RIPK1's kinase activity and its assembly into death-inducing complexes.
• RIPK1 kinase activity is regulated by both ubiquitylation and phosphorylation states.

Outlook:

• Further investigation into RIPK1 phosphorylation by IKKs could uncover new therapeutic targets for diseases involving aberrant cell death.
• Understanding this regulatory switch offers deeper insights into TNFR1-mediated cell fate decisions.
• This work expands the known mechanisms controlling apoptosis and necroptosis signaling pathways.