Abstract A078: Functional screen for mediators of onco-mRNA translation specificity in pancreatic cancer

Abstract Oncogenic protein dosage is tightly regulated to enable cancer cells to adapt and survive. In healthy cells, translation initiation of onco-mRNA transcripts encoding oncogenes and growth factors is tightly regulated to maintain accurate protein expression levels. However, this process is broken in cancer cells, which rely on the maintenance of high dosage of oncogenic proteins for their survival and to drive cancer development. Whether this is regulated at the level of translational control and the key factors in cis and trans remain unknown. The Myc oncogene is a central paradigm of an exquisitely regulated oncogene and a major driver of pancreatic ductal adenocarcinoma (PDAC). While there has been a tremendous effort to target Myc in cancer, clinically relevant Myc inhibition remains a challenge. Therefore, identifying selective promoters of MYC translation may present a novel therapeutic opportunity. Employing a genome-wide CRISPRi screen for modulators of MYC mRNA translation initiation in PDAC cells, we identified regulators of selective MYC translation and validated four RNA binding proteins (RBPs), including epitranscriptome modifiers. We focused on a top hit, a little studied RBP, RBM42, which is highly expressed in PDAC and predicts poor patient survival. We found that RBM42 binds and selectively regulates the translation of MYC and a precise, yet vital suite of pro-oncogenic transcripts, including JUN and EGFR. Mechanistically, employing immunoprecipitation-mass spectrometry analysis, we found that RMB42 is a novel ribosome-associated protein (RAP). Through RNA structure determination and mutagenesis analysis, we showed that RBM42 directly binds and remodels the MYC 5’UTR RNA structure, facilitating the formation of the translation pre-initiation complex and increasing MYC translation. Importantly, we demonstrated that RBM42 is necessary for human PDAC cell growth and fitness and PDAC tumorigenesis in xenograft mouse models in a Myc-dependent manner in vivo. In PDAC patient samples, RBM42 expression is correlated with Myc protein levels and transcriptional activity. This work transforms our understanding of the translational code in cancer and offers a new therapeutic opening to target the expression of oncogenes. Citation Format: Joanna R Kovalski, Goksu Sarioglu, Vishvak Subramanyam, Grace Hernandez, Gilles Rademaker, Juan A Oses-Prieto, Macey Slota, Kwun Wah Wen, Grace E Kim, Alma L Burlingame, Hani Goodarzi, Rushika M Perera, Davide Ruggero. Functional screen for mediators of onco-mRNA translation specificity in pancreatic cancer abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84 (17 Suppl₂): Abstract nr A078.