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BRD4 isoforms have distinct roles in tumor progression and metastasis in embryonal rhabdomyosarcoma

Taneja, R.; Das, D.; Leung, J. Y.; Tergaonkar, V.; Loh, A. H. P.; Chiang, C.-M.

2023-07-27 cancer biology
10.1101/2023.07.26.550665 bioRxiv
Show abstract

BRD4, a bromodomain and extraterminal (BET) protein, is deregulated in multiple cancers and has emerged as a promising drug target. However, the function of the two main BRD4 isoforms (BRD4-L and BRD4-S) has not been analyzed in parallel in most cancers. This complicates determining therapeutic efficacy of pan-BET inhibitors. In this study, using functional and transcriptomic analysis, we show that BRD-L and BRD4-S isoforms play distinct roles in embryonal rhabdomyosarcoma. BRD4-L has an oncogenic role and inhibits myogenic differentiation, at least in part, by activating myostatin expression. Depletion of BRD4-L in vivo impairs tumor progression but does not impact metastasis. On the other hand, depletion of BRD4-S has no significant impact on tumor growth, but strikingly promotes metastasis in vivo. Interestingly, BRD4-S loss results in the enrichment of BRD4-L and RNA Polymerase II at integrin gene promoters resulting in their activation. Our work unveils isoform-specific functions of BRD4 and demonstrates that BRD4-S functions as a gatekeeper to constrain the full oncogenic potential of BRD4-L.

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