cIAPs control RIPK1 kinase activity-dependent and -independent cell death and tissue inflammation

Cellular inhibitor of apoptosis proteins (cIAPs) are RING-containing E3 ubiquitin ligases that ubiquitylate receptor-interacting protein kinase 1 (RIPK1) to regulate TNF signalling. Here, we established mice simultaneously expressing enzymatically inactive cIAP1/2 variants, bearing mutations in the RING domains of cIAP1/2 (cIAP1/2 mutant RING, cIAP1/2MutR ). cIap1/2MutR/MutR mice died during embryonic development due to RIPK1-mediated apoptosis. While expression of kinase-inactive RIPK1D138N rescued embryonic development, Ripk1D138N/D138N /cIap1/2MutR/MutR mice developed systemic inflammation and died postweaning. Cells expressing cIAP1/2MutR and RIPK1D138N were still susceptible to TNF-induced apoptosis and necroptosis, implying additional kinase-independent RIPK1 activities in regulating TNF signalling. Although further ablation of Ripk3 did not lead to any phenotypic improvement, Tnfr1 gene knock-out prevented early onset of systemic inflammation and premature mortality, indicating that cIAPs control TNFR1-mediated toxicity independent of RIPK1 and RIPK3. Beyond providing novel molecular insights into TNF-signalling, the mouse model established in this study can serve as a useful tool to further evaluate ongoing therapeutic protocols using inhibitors of TNF, cIAPs and RIPK1.

LRP8-mediated selenocysteine uptake is a targetable vulnerability in MYCN-amplified neuroblastoma

Ferroptosis has emerged as an attractive strategy in cancer therapy. Understanding the operational networks regulating ferroptosis may unravel vulnerabilities that could be harnessed for therapeutic benefit. Using CRISPR-activation screens in ferroptosis hypersensitive cells, we identify the selenoprotein P (SELENOP) receptor, LRP8, as a key determinant protecting MYCN-amplified neuroblastoma cells from ferroptosis. Genetic deletion of LRP8 leads to ferroptosis as a result of an insufficient supply of selenocysteine, which is required for the translation of the antiferroptotic selenoprotein GPX4. This dependency is caused by low expression of alternative selenium uptake pathways such as system Xc- . The identification of LRP8 as a specific vulnerability of MYCN-amplified neuroblastoma cells was confirmed in constitutive and inducible LRP8 knockout orthotopic xenografts. These findings disclose a yet-unaccounted mechanism of selective ferroptosis induction that might be explored as a therapeutic strategy for high-risk neuroblastoma and potentially other MYCN-amplified entities.

Identification of treatment-induced vulnerabilities in pancreatic cancer patients using functional model systems

Despite the advance and success of precision oncology in gastrointestinal cancers, the frequency of molecular-informed therapy decisions in pancreatic ductal adenocarcinoma (PDAC) is currently neglectable. We present a longitudinal precision oncology platform based on functional model systems, including patient-derived organoids, to identify chemotherapy-induced vulnerabilities. We demonstrate that treatment-induced tumor cell plasticity in vivo distinctly changes responsiveness to targeted therapies, without the presence of a selectable genetic marker, indicating that tumor cell plasticity can be functionalized. By adding a mechanistic layer to precision oncology, adaptive processes of tumors under therapy can be exploited, particularly in highly plastic tumors, such as pancreatic cancer.