Lewandowska, O. | Search bioRxiv

bioRxiv2024

The EIF4EBP1 gene encoding 4EBP1 is transcriptionally upregulated by MYC and linked to shorter survival in medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumor in childhood and is stratified into four molecular groups - WNT, SHH, Group 3 and Group 4. Group 3 MB patients exhibit the poorest prognosis, with a 5-year overall survival of <60%, followed by Group 4 MB patients. Apart from MYC amplification in a subset of Group 3 MBs, the molecular pathomechanisms driving aggressiveness of these tumors remain incompletely characterized. The gene encoding the mTOR substrate and mRNA translation inhibitor eukaryotic translation initiation factor 4E-binding protein 1 (EIF4EBP1) represents a possible MYC target gene whose corresponding protein, 4EBP1, was shown to be more active in Group 3 versus Group 4 MBs. However, the prognostic role of 4EBP1 in MB and the mechanisms supporting 4EBP1 overexpression in Group 3 MB are still elusive. We analyzed EIF4EBP1 mRNA expression in publicly available data sets and found an upregulation in MB as compared to non-neoblastic brain. EIF4EBP1 mRNA expression levels were higher in Group 3 compared to Group 4 MBs. EIF4EBP1 mRNA expression was correlated with MYC expression, most prominently in Group 3 MBs. Survival analyses highlighted that high EIF4EBP1 mRNA expression was associated with reduced overall and event-free survival across all MB patients and in Group 3/Group 4 MB patients. Immunohistochemical evaluation of 4EBP1 protein expression in MB tissues confirmed that high levels of 4EBP1 are associated with poor outcome. Functional analyses revealed that MYC directly regulates EIF4EBP1 promoter activity, providing a mechanism for increased EIF4EBP1 mRNA levels in Group 3 MBs. Finally, we observed that 4EBP1 may support colony formation of in vitro cultured MB cells. Our data highlight that transcriptional upregulation of EIF4EBP1 by MYC promotes in vitro tumorigenicity of MB cells and associates with shorter survival of MB patients.

cancer biology↗

bioRxiv2024

Oncogenic RAS signaling suppresses ferroptosis via transcriptional upregulation of GCH1

Ferroptosis is an iron-dependent form of regulated cell death arising from excessive lipid peroxidation. The role of oncogenic RAS signaling in modulating the cellular response to ferroptosis is controversial. While seminal studies described that oncogenic RAS transformation drives a synthetic lethal vulnerability to archetypal ferroptosis inducers including erastin (eradicator of RAS and ST-expressing cells) and RSL3 (Ras selective lethal 3), more recent work suggest that oncogenic RAS signaling may confer ferroptosis resistance. Thus, the impact of oncogenic RAS expression on ferroptosis sensitivity is still poorly understood. Here, using orthogonal cellular systems across multiple classes of ferroptosis- inducing agents, as well as in silico therapeutic drug-response analyses, we provide unifying evidence that oncogenic RAS signaling suppresses ferroptosis. Integrated proteo- and transcriptomic analyses in oncogenic RAS-transformed cells further uncovered that RAS signaling upregulates the ferroptosis suppressor GTP cyclohydrolase I (GCH1) via transcriptional induction by the transcription factor ETS1 downstream of the RAS-MAPK signaling cascade. Targeted repression of Gch1 or of Gch1-controlled tetrahydrobiopterin (BH4) synthesis pathway is sufficient to sensitize RAS-mutant cell lines to ferroptosis in 2D and 3D cell models, as well as in tumor organoids and tumor xenografts, highlighting a mechanism through which RAS promotes resistance to ferroptosis induction. Furthermore, we found that GCH1 expression is clinically relevant and correlates with RAS signaling activation in human cancers. Overall, this study redefines oncogenic RAS signaling to be a ferroptosis suppressor, and identifies GCH1 as a mediator of this effect and a potential clinical target for the sensitization of RAS-driven cancers to ferroptosis-inducing agents. Significance StatementAlthough it is commonly accepted that ferroptosis induction is a mutant RAS-selective lethality, accumulating evidence suggests that oncogenic RAS protects cells against this form of cell death. However, a systematic survey establishing the relationship between RAS and ferroptosis sensitivity is lacking, and the molecular mechanisms this entails are still poorly understood. Here, we report across RAS-mutant isoforms, in diverse cellular models, and using multiple ferroptosis-inducing compounds that oncogenic RAS consistently suppresses ferroptosis. Further, we show that oncogenic RAS-mediated ferroptosis suppression is attributed to the upregulation of GCH1 and its downstream metabolite, tetrahydrobiopterin. Our study delivers a shift towards a new paradigm in which oncogenic RAS confers ferroptosis resistance, and a potential clinical strategy to re-engage ferroptosis sensitivity in RAS-driven cancers.

cancer biology↗