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Updated: Apr 24, 2026
Characterization of MLKL-mediated Plasma Membrane Rupture in Necroptosis
Published on: August 7, 2018
RIPK1 can function as an inhibitor rather than an initiator of RIPK3-dependent necroptosis
Conor J Kearney1, Sean P Cullen, Danielle Clancy
1Molecular Cell Biology Laboratory, Department of Genetics, The Smurfit Institute, Trinity College, Dublin, Ireland.
Abstract:
Tumour necrosis factor and lipopolysaccharide can promote a regulated form of necrosis, called necroptosis, upon inhibition of caspase activity in cells expressing receptor-interacting serine/threonine kinase (RIPK)3. Because inhibitors of RIPK1 kinase activity such as necrostatin-1 block necroptosis in many settings, RIPK1 is thought to be required for activation of RIPK3, leading to necroptosis. However, here we show that, although necrostatin potently inhibited tumour necrosis factor-induced, lipopolysaccharide-induced and polyIC-induced necroptosis, RIPK1 knockdown unexpectedly potentiated this process. In contrast, RIPK3 knockdown potently suppressed necroptosis under the same conditions. Significantly, necrostatin failed to block necroptosis in the absence of RIPK1, indicating that its ability to suppress necroptosis was indeed RIPK1-dependent. These data argue that RIPK1 is dispensable for necroptosis and can act as an inhibitor of this process. Our observations also suggest that necrostatin enhances the inhibitory effects of RIPK1 on necroptosis, as opposed to blocking its participation in this process.
Insights
Receptor-interacting serine/threonine kinase 1 (RIPK1) does not activate necroptosis, contrary to prior belief. Instead, RIPK1 acts as an inhibitor of necroptosis, and necrostatin enhances this inhibitory role.
Area of Science:
- Cellular biology
- Molecular mechanisms of cell death
- Immunology
Background:
- Necroptosis is a regulated form of necrosis triggered by TNF and LPS when caspases are inhibited.
- Receptor-interacting serine/threonine kinase 1 (RIPK1) inhibitors like necrostatin-1 are thought to block necroptosis by inhibiting RIPK1 activation of RIPK3.
- The precise role of RIPK1 in necroptosis activation remains incompletely understood.
Purpose of the Study:
- To investigate the role of RIPK1 in necroptosis signaling pathways.
- To determine whether RIPK1 is required for necroptosis activation or acts as an inhibitor.
- To elucidate the mechanism by which necrostatin-1 inhibits necroptosis.
Main Methods:
- Utilized knockdown of RIPK1 and RIPK3 in cells.
- Administered necrostatin-1 to inhibit RIPK1 kinase activity.
- Induced necroptosis using tumor necrosis factor (TNF), lipopolysaccharide (LPS), and polyinosinic:polycytidylic acid (polyIC).
Main Results:
- RIPK1 knockdown potentiated TNF-, LPS-, and polyIC-induced necroptosis.
- RIPK3 knockdown suppressed necroptosis under the same conditions.
- Necrostatin-1 failed to inhibit necroptosis in the absence of RIPK1, confirming RIPK1's role in necrostatin's inhibitory function.
- RIPK1 was dispensable for necroptosis induction and appeared to function as an inhibitor.
Conclusions:
- RIPK1 is not required for necroptosis and may act as an inhibitor of this cell death pathway.
- Necrostatin-1's inhibitory effect on necroptosis is dependent on the presence of RIPK1.
- Necrostatin-1 appears to enhance RIPK1's inhibitory function rather than blocking its participation in necroptosis.
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