Systematic genetic mapping of necroptosis identifies SLC39A7 as modulator of death receptor trafficking

Regulation of cell and tissue homeostasis by programmed cell death is a fundamental process with wide physiological and pathological implications. The advent of scalable somatic cell genetic technologies creates the opportunity to functionally map these essential pathways, thereby identifying potential disease-relevant components. We investigated the genetic basis underlying necroptotic cell death by performing a complementary set of loss- and gain-of-function genetic screens. To this end, we established FADD-deficient haploid human KBM7 cells, which specifically and efficiently undergo necroptosis after a single treatment with either TNF or the SMAC mimetic compound birinapant. A series of unbiased gene-trap screens identified key signaling mediators, such as TNFR1, RIPK1, RIPK3, and MLKL. Among the novel components, we focused on the zinc transporter SLC39A7, whose knock-out led to necroptosis resistance by affecting TNF receptor trafficking and ER homeostasis. Orthogonal, solute carrier (SLC)-focused CRISPR/Cas9-based genetic screens revealed the exquisite specificity of SLC39A7, among ~ 400 SLC genes, for TNFR1- and FAS-but not TRAIL-R1-mediated responses. The newly established cellular model also allowed genome-wide gain-of-function screening for genes conferring resistance to necroptosis via the CRISPR/Cas9 synergistic activation mediator approach. Among these, we found cIAP1 and cIAP2, and characterized the role of TNIP1 (TNFAIP3-interacting protein 1), which prevented pathway activation in a ubiquitin-binding dependent manner. Altogether, the gain- and loss-of-function screens described here provide a global genetic chart of the molecular factors involved in necroptosis and death receptor signaling, prompting investigation of their individual contribution and potential role in pathological conditions.