Tryptophan Metabolic Enzyme IL4I1 Inhibits Ferroptosis by Decreasing Ubiquitination of Nrf2 via I3P in Glioblastoma

Glioblastoma multiforme (GBM) is the deadliest brain tumour with an extremely poor prognosis. Tryptophan catabolism could enhance an array of protumour-genic signals and promoted tumour progression in GBM. However, the mechanisms of oncogenic signalling under tryptophan catabolism and potential therapy targeting this pathway have not been completely understood. Interleukin 4-induced 1 (IL4I1) is newly defined as a tryptophan metabolic enzyme and the potential function in GBM cells still remains unclear. In our study, we found IL4I1 was upregulated in GBM patients and predicted poor prognosis. Upregulation of IL4I1 inhibited GBM ferroptosis in vitro and in vivo. Further, we found that indole-3-pyruvic acid (I3P) from tryptophan mediated by IL4I1 could scavenge free radical and had an impressive role in inhibiting ferroptosis. To clarify the potential mechanism of I3P in GBM ferroptosis, we performed transcriptomic analyses of GBM cells treated with I3P and found that Nrf2 related genes was upregulated. Further, we found that the ubiquitination of Nrf2 could be attenuate by I3P binding with Nrf2 directly. Knockdown of Nrf2 attenuated the induction of anti-ferroptosis by IL4I1, pointing to Nrf2 as a key mediator of this process. In vivo, overexpression of IL4I1 with ML385 in GBM xenografts promoted ferroptosis. Collectively, this study emphasises the crucial roles of IL4I1 in anti-ferroptosis through Nrf2 signalling pathway but not AHR pathway by catabolism tryptophan, suggesting IL4I1 and tryptophan reprogramming as potential therapeutic targets for GBM.