Productive transcription of miR-124-3p by RelA and RNA polymerase II directs RIP1 ubiquitination-dependent apoptosis resistance during hypoxia

Abstract

The K63-linked ubiquitination of RIP1 coordinates survival/death homeostasis by driving transcription of genes downstream of RelA. Previously, we demonstrated that EGF-dependent RelA transactivation overcomes hypoxia-initiated apoptosis, yet the underlying mechanisms remain mysterious. We report here that UBXN1 deficiency empowers apoptosis resistance against hypoxia through triggering IκBα degradation, for which K63-linked ubiquitination of RIP1 is required. MiR-124-3p is a bona fide inhibitor upstream of UBXN1, thereby antagonizing the hypoxia-initiated apoptosis. UBXN1 repression by miR-124-3p restores the K63-linked ubiquitination of RIP1, IKKβ phosphorylation, IκBα-RelA disassembly, RelA nuclear localization and transactivation of EGF gene as well as EGF secretion under hypoxia. Reconstitution of wild-type UBXN1, but not a truncated UBXN1ΔUBA mutant, or pharmacological inhibition of RelA transactivation in miR-124-3p-replete cells compromises the apoptosis-resistant phenotypes of miR-124-3p. Hypoxia transcriptionally downregulates miR-124-3p by disassociating RelA and RNAP II from its promoter. EGFR activation renders the K63-linked ubiquitination of RIP1 and hypoxic tolerance in conjunction with miR-124-3p. Our findings identify a pivotal role of miR-124-3p in ubiquitin conjugation of RIP1 against hypoxic damage and underscore that productive transcription of miR-124-3p by RelA and RNAP II might be a switching mechanism for this process.