Abstract P61: Distinct Roles of BRD4 Isoforms in Tumor Progression and Metastasis in Embryonal Rhabdomyosarcoma

Abstract

Abstract The deregulation of BRD4, a bromodomain and extraterminal (BET) protein, has been implicated in various cancers, positioning it as a promising target for drug development. Yet, the specific roles of the two primary BRD4 isoforms, BRD4-L and BRD4-S, remain poorly understood across most cancer types. This knowledge gap poses challenges in assessing the effectiveness of pan-BET inhibitors as potential therapies. This study seeks to address this gap by employing functional and transcriptomic analyses to elucidate the distinct contributions of BRD4 isoforms in embryonal rhabdomyosarcoma (ERMS). Through a comprehensive investigation, the research uncovers that BRD4-L and BRD4-S isoforms exert discrete functions in ERMS. Specifically, BRD4-L is found to exert an oncogenic role by inhibiting myogenic differentiation, partially through the activation of myostatin expression. Importantly, depletion of BRD4-L in vivo is shown to impede tumor progression without significantly affecting metastasis. In contrast, the absence of BRD4-S has an unexpected impact-while it has a minimal effect on tumor growth, it markedly enhances metastatic potential in vivo. Intriguingly, the depletion of BRD4-S leads to the heightened presence of BRD4-L and RNA Polymerase II at integrin gene promoters, consequently activating these genes. This novel insight underscores that BRD4-S acts as a gatekeeper, restraining the full scope of oncogenic activities driven by BRD4-L. Collectively, this study reveals distinctive roles for BRD4 isoforms and uncovers a delicate interplay in ERMS. Importantly, the findings indicate that pan-BRD4 inhibition might not be the optimal therapeutic strategy for ERMS due to the intricate interplay between isoforms. By illuminating the intricate functions of BRD4 isoforms, this research advances our understanding of the complex regulatory mechanisms underlying tumor progression and metastasis in ERMS. Citation Format: Dipanwita Das, Jia Yu Leung, Amos Hong Pheng Loh, Reshma Taneja. Distinct Roles of BRD4 Isoforms in Tumor Progression and Metastasis in Embryonal Rhabdomyosarcoma [abstract]. In: Proceedings of Frontiers in Cancer Science; 2023 Nov 6-8; Singapore. Philadelphia (PA): AACR; Cancer Res 2024;84(8_Suppl):Abstract nr P61.