Defining the necroptotic transcriptional signaling pathway

Abstract

Neurons are post-mitotic, non-regenerative cells that have evolved fine-tuned immunological responses to maintain life-long cellular integrity; this includes resistance to common programmed cell death (PCD) pathways, including apoptosis and necroptosis. We have previously demonstrated a necroptosis-independent role for the key necroptotic kinase RIPK3 in host defense against neurotropic flavivirus infection. While this work showed that neuronal RIPK3 expression is essential for chemokine production and recruitment of peripheral immune cells to the infected CNS, the full RIPK3-dependent transcriptional signature and molecular mechanism underlying RIPK3-dependent transcription in neurons are incompletely understood. It also remains unclear what factors govern differential RIPK3 effector functions in different cell types. Here, we show that RIPK3 activation has distinct outcomes in primary cortical neurons and mouse embryonic fibroblasts (MEFs) during Zika virus (ZIKV) infection and sterile activation. We found that RIPK3 activation does not induce death in neurons; in these cells, RIPK3 is the dominant driver of antiviral gene transcription following ZIKV infection. While RIPK3 activation in MEF cells induces cell death, ablation of downstream cell death effectors unveils a RIPK3-dependent transcriptional program which largely overlaps with that observed in ZIKV-infected neurons. Using death resistant MEFs as a model to study RIPK3 signaling revealed that RIPK3 transcription relied on interactions with the RHIM domain-containing proteins RIPK1 and TRIF, effects mirrored in the RIPK3-dependent antiviral transcriptional signature observed in ZIKV-infected neurons. These findings suggest the pleotropic functions of RIPK3 are largely context dependent and that in cells that are resistant to cell death, RIPK3 acts as a mediator of inflammatory transcription.