Die another way: necroptosis as alternative route to cell death

Introduction:

The deregulation of pro- and anti-survival signalling pathways leads to escape from cell death and contributes to a poor response to chemotherapy and relapse in malignancies. Exploiting recently identified novel cell death mechanisms such as necroptosis represents an attractive strategy to eradicate such resistant tumor cells. Necroptosis occurs without caspase activation and relies on distinct protein-protein interactions regulated by receptor-interacting protein kinase 1, RIP1. RIP1 is held in check by the inhibitor of apoptosis proteins (IAPs). Depletion of IAPs using small-molecule SMAC mimetics (SM) can potently induce a switch from RIP1-controlled survival to cell death.

Methods:

We use a combination of CRIPSR/Cas9-based genome editing methodologies, cell death assays, correlative gene expression analyses and xenograft models.

Results:

We have recently found that a subgroup of acute lymphoblastic leukemia (ALL) samples including refractory cases responds to SM with simultaneous activation of apoptosis and necroptosis. Using a multicolor lentiCRISPR-based functional genomic approach, we identified RIP1 as key regulator of both cell death mechanisms upon cIAP depletion. Accordingly, deletion of both apopotic and necroptotic genes is required to rescue cell viability after SM treatment. Comparative gene expression analyses combined with functional CRISPR-based genome editing approaches suggest that upstream of RIP1, TNF receptor 2 is required for the composition of a RIP1/TNF receptor 1 containing death signalling complex.

Conclusion:

Thus, our data indicate that necroptosis is a relevant stress management pathway that specifies a targetable vulnerability in resistant disease.