RIPK1 dephosphorylation and kinase activation by PPP1R3G/PP1γ promote apoptosis and necroptosis

Area of Science:

• Molecular Biology
• Immunology
• Cell Biology

Background:

• Receptor-interacting protein kinase 1 (RIPK1) regulates inflammation and cell death pathways.
• Phosphorylation of RIPK1, particularly at serine 25, inhibits its kinase activity and downstream cell death.
• The mechanisms of dephosphorylation for inhibitory RIPK1 sites remain largely unknown.

Purpose of the Study:

• To identify regulators of RIPK1 inhibitory phosphorylation.
• To elucidate the role of Protein Phosphatase 1 regulatory subunit 3G (PPP1R3G) in RIPK1-mediated cell death.
• To investigate the in vivo function of PPP1R3G in inflammatory responses.

Main Methods:

• Utilized a sensitized CRISPR whole-genome knockout screen to identify genes involved in RIPK1-dependent cell death.
• Investigated the interaction between PPP1R3G and its catalytic subunit, protein phosphatase 1 gamma (PP1γ).
• Assessed RIPK1 phosphorylation and cell death in wild-type and knockout cells, including in Ppp1r3g knockout mice.

Main Results:

• Discovered PPP1R3G as essential for RIPK1-dependent apoptosis and necroptosis.
• Demonstrated that PPP1R3G recruits PP1γ to complex I to dephosphorylate RIPK1 at inhibitory sites.
• Showed that PPP1R3G knockout mice are protected from TNF-induced systemic inflammatory response syndrome.

Conclusions:

• PPP1R3G plays a critical role in regulating RIPK1 activity and downstream inflammatory and cell death processes.
• PPP1R3G-mediated dephosphorylation of RIPK1 is a key mechanism controlling apoptosis and necroptosis.
• Targeting PPP1R3G could offer therapeutic strategies for inflammatory diseases.