BRD4-S Drives Colorectal Cancer Progression via DDX27-Regulated Splicing and MAPK Signaling Activation

Background: As a major contributor to cancer-associated deaths, advanced colorectal cancer (CRC) has a constrained range of effective treatment options. The short isoform of bromodomain-containing protein 4 (BRD4-S) has recently been implicated as a potential oncogenic driver; however, its regulatory mechanisms and functional role in CRC remain incompletely understood. Methods: BRD4-S expression, regulation, and function in CRC were investigated through bioinformatics analyses of the Cancer Genome Atlas (TCGA) datasets, in vitro studies using CRC cell lines (HT29, SW620), and in vivo xenograft models in nude mice. Experimental approaches included quantitative real-time PCR (qRT-PCR), Western blotting, co-immunoprecipitation, RNA immunoprecipitation, immunofluorescence, colony formation, Cell Counting Kit-8 (CCK-8), and scratch assays. Gene enrichment and interaction analyses were performed to identify relevant pathways and molecular partners. Results: BRD4-S was markedly upregulated in CRC tissues and cell lines, and elevated BRD4-S expression correlated with poorer patient survival. Silencing BRD4-S, but not BRD4-L, significantly impaired CRC cell proliferation, migration, and tumor growth in vivo. Mechanistically, the RNA helicase DEAD-box helicase 27 (DDX27) interacted with Serine and Arginine Rich Splicing Factor 6 (SRSF6) to promote alternative splicing of BRD4 pre-mRNA toward the BRD4-S isoform. Inhibition of SRSF6 phosphorylation suppressed BRD4-S production and blocked activation of the mitogen-activated protein kinase (MAPK)/extracellular regulated protein kinases ERK signaling pathway, identified as a key downstream effector of BRD4-S. Conclusions: This study defines a novel DDX27–SRSF6–BRD4-S–MAPK/ERK signaling axis that drives CRC progression. These findings underscore the therapeutic potential of targeting BRD4 isoform switching and its regulatory splicing machinery in CRC.