Deciphering the role of NELFE in modulating MYC signaling in HCC - ABSTRACT Hepatocellular carcinoma (HCC) is an aggressive tumor type with poor prognosis due to the diverse etiology, tumor heterogeneity, and the frequent late stage diagnosis. HCC is the fourth cause of cancer-related deaths in the world and is seen at higher rates among Hispanics, Blacks, and Asian Pacific Islanders compared with non- Hispanic whites. In the U.S, the rate of death from liver cancer has increased >40%. The proto-oncogene MYC is deregulated in ~80% of HCC. Yet, MYC remains to be an undruggable target. Although, the most common alteration is gene amplification (~30%), a significant proportion of MYC-driven HCCs have deregulated MYC signaling without concomitant MYC gene amplification. How MYC signaling is deregulated in HCC without concomitant MYC gene amplification is not understood. Our long-term goal is to understand the molecular basis for this phenotype to develop therapies to indirectly target MYC as a therapeutic strategy in HCC. The specific objective of this proposal is to confirm Negative Elongation Factor E (NELFE) as a central regulator of MYC signaling to promote HCC. The central hypothesis is deregulated NELFE modulates MYC signaling to promote HCC regardless of MYC status. We recently discovered the NELFE is over-expressed in 48% of HCC and is required for MYC-induced hepatocarcinogenesis. Preliminary data indicate NELFE alters nucleosome accessibility to modulate MYC-signaling. Moreover, we found NELFE localizes in the nucleus as biomolecular condensates, membraneless organelles that modulate transcription. Perturbation of NELFE condensates alters protein-protein interactions important for MYC signaling, suggesting NELFE condensation as a novel mechanism for MYC-induced HCC. We discovered a novel truncated NELFE isoform with anti-tumorigenic effects in advanced HCC. Isoform switching from FL NELFE to the truncated form via antisense oligonucleotides significantly reduced tumorigenic phenotypes and condensates. Here, we will use biophysical, biochemical, in vitro and in vivo assays to elucidate the role of NELFE on chromatin accessibility and biomolecular condensates as promoters of HCC through MYC signaling. Furthermore, we will use our established genetic models and antisense oligonucleotides to test the critical anti-tumorigenic function of the truncated NELFE isoform in HCC. Together, our proposed studies will define the novel role NELFE as a regulator of MYC as an essential player in the pathophysiological mechanisms of hepatocarcinogenesis and establish the function of the novel truncated NELFE protein.
