Necroptosis is a programmed form of cell death mediated by the formation of a detergent-insoluble protein complex called necrosome. Receptor Interacting Protein Kinases (RIPK) 1 and 3 have been identified as the key components of the necrosome. Phosphorylation and ubiquitination of several RIPK1/3 residues have been implicated to play important roles in regulating apoptosis and necroptosis.

As the main mechanism for cellular protein degradation, ubiquitin-proteasome system (UPS) has been associated with a myriad of cellular pathways, including apoptosis. However, the mechanism and function of UPS under apoptotic or necroptotic conditions are poorly understood.

Here we report that proteasome inhibitor bortezomib and Valosin-Containing Protein (VCP) inhibitor NMS-873 inhibit necroptosis in human colorectal cancer HT-29 cells. VCP inhibition clearly changes the ubiquitination profile of RIPK1 and RIPK3 in the necrosome. RIPK1 interacts with VCP upon TNFalpha stimulation in a complex separate from the necrosome or TNF Receptor 1 signaling complex.