Onco-mRNA Translational Specificity Mechanisms in Pancreatic Cancer

Abstract public domain (NIH RePORTER)

Project Summary/Abstract: The Myc oncogene is a critical driver of tumorigenesis and is difficult to drug. In particular, ~42% of pancreatic ductal adenocarcinomas (PDAC) have high levels of Myc protein, which correlates with the poorest prognosis. While many cancer studies rely solely on transcriptomic analyses, RNA levels often do not correlate with protein abundance, highlighting the centrality of translational control to clinical outcomes. Oncogene translation is tightly controlled through regulatory sequences and structures in the onco-mRNA 5’ untranslated region (UTR), enabling cancer cells to adapt, proliferate, and resist anti-cancer therapies, yet how this occurs at the molecular level remains elusive. Myc is a key paradigm of post-transcriptional regulation, but it is unknown how PDAC cells selectively modulate translation efficiency to maintain Myc protein dosage. Using a new transcript-specific translational reporter and genome-wide CRISPRi screening, I identified the first regulatory network that orchestrates MYC mRNA translation in PDAC, which prominently includes RNA binding proteins (RBPs). My strong preliminary data show that a top hit from the screen, a poorly understood RBP, RBM42, promotes MYC translation to maintain Myc protein levels and sustain PDAC cell growth. I hypothesize that select RBPs, including RBM42, mediate PDAC cell survival, growth in vivo, and response to anti-cancer treatment by regulating Myc protein expression. Aim I is designed to establish the role of RBM42 in PDAC tumorigenesis in vivo and mechanistically dissect how RBM42 contributes to PDAC initiation and maintenance, using tumor xenograft and genetically engineered mouse models. Aim II seeks to elucidate how RBM42 interacts with the MYC 5’UTR RNA structure and helps maintain Myc protein dosage for PDAC cells to resist chemotherapies. Aim III is intended to uncover the selective repressors of MYC translation in PDAC, identifying new post-transcriptional tumor suppressive mechanisms. My innovative approach combines functional CRISPRi screening, in vivo models, and multi-omic analyses to unveil previously unknown layers of post-transcriptional control of Myc. The overall goal of this project is to decipher novel selective regulators of Myc to impact the therapeutic targeting of PDAC. My long-term career goal is to run an independent lab studying the post- transcriptional regulation of onco-mRNAs to identify new mechanisms and treatment strategies for PDAC. The translational control code cannot be solely discovered by conventional genomic and transcriptomic analyses of cancer. Therefore, I will combine unbiased screening strategies and innovative RNA biology techniques to understand the functional mechanisms controlling the protein expression of PDAC drivers such as Myc. UCSF’s exceptional research environment, career development activities, and facilities will be key to the success of the proposed research and training. Together with vital professional development, this research proposal will help me obtain an independent faculty position and secure future grant support. Ultimately, these studies will generate new clinical opportunities to meaningfully impact the therapeutic targeting of PDAC and improve outcomes.

Public health relevance public domain (NIH RePORTER)

Project Narrative: The Myc oncogene is a critical driver of cancer that is highly expressed in about half of pancreatic ductal adenocarcinomas (PDAC), where it correlates with poor prognosis and is difficult to drug. To uncover how Myc protein dosage is established to drive PDAC, we will interrogate our novel network of selective regulators of MYC RNA translation to illuminate how RNA binding proteins modulate Myc expression to promote PDAC tumorigenesis in vivo, resist chemotherapies, and function as tumor suppressors. The findings of this proposal will be instrumental in revealing novel post-transcriptional mechanisms regulating Myc expression and provide new therapeutic opportunities for PDAC.