Dynamic interplay of BRD4 isoforms in embryonal rhabdomyosarcoma

In this study, we show that long and short isoform of the epigenetic regulator BRD4 is overexpressed in ERMS patient-derived cell lines and patient tumour specimens. Functionally, knockdown of long isoform of BRD4 reduced proliferation and promotes differentiation. Knockdown of the short isoform on the other hand promotes migration and invasion. The functional observations were confirmed in vitro and in vivo. Through RNA Sequencing analysis, we identified Myostatin (MSTN) and Integrins (ITGs) as important downstream target of long and short isoform of BRD4 respectively. We thus conclude from this study that long isoform functions as an oncogenic driver and can only promote metastasis only when the short isoform that functions as a blocker of tumor spread is removed. The interplay of the isoform identifies the long form as a therapeutic target and the short form as a predictive biomarker for metastasis in ERMS. RD cells were treated with control siRNA (BRD4WT), BRD4 Long siRNA (siBRD4L) or BRD4 Short siRNA (siBRD4S) for 48 hours, after which total RNA was collected with TRIzol reagent. RNA was purified and quality of purified RNA was checked using Nanodrop and gel electrophoresis. Three samples of each were used for sequencing analysis, done by Novogene.