Modulation of RUNX1-BRD4 cooperation by post-translational modification of a histone-like motif in the Runt domain

The RUNX1 transcription factor is strongly influenced by post-translational modifications. Here, we investigate a post-translational modification hotspot within a short peptide region in the evolutionarily conserved DNA-binding Runt domain. Cancer-specific mutations have been found clustered in this region, which also partially resembled the N-terminal tail of histone H4. We found that lysine acetylation of this histone-like motif promoted RUNX1 interaction with the BET-domain transcription co-activator BRD4,resulting in enhanced RUNX1 phosphorylation and transcriptional activity. Flanking post-translational modifications, such as arginine methylation and threonine phosphorylation, strongly inhibited the RUNX1-BRD4 complex formation. RNA sequencing revealed that knockdown of RUNX1 and BRD4 resulted in downregulation of genes associated with cell proliferation, suggesting that RUNX1 and BRD4 cooperated in driving cell cycle progression in gastric cancer. We identified AMIGO2 – known for its roles in invasion, proliferation and survival in cancer – as a common transcriptional target of RUNX1 and BRD4. Depletion of RUNX1 and BRD4 impaired cell proliferation and invasion in gastric cancer cells. Our work therefore indicates an oncogenic function for RUNX1-BRD4 interaction. Post-translational modification is reversible and can be pharmacologically targeted. We provide a basis for future design of drugs to specifically target the RUNX1-BRD4 interaction. Overall design: Analysing transcriptome changes after RUNX1 or BRD4 depletion. AGS gastric adenocarcinoma cells were treated with control siRNA, siRNA targeting RUNX1 or BRD4 for 48 h. RNA samples were subjected to transcriptome sequencing. RNA libraries were prepared and sequenced by the MGISEQ-2000 (DNBSEQ) platform - Paired-end 100bp Sequencing / 40M Paired-end reads or 8Gb clean data per sample.