Scaffolding of the H4K5ac chromatin remodeling complex by lncRNA <i>MAHAC</i> mediates epithelial-mesenchymal transition

Anchoring of a chromatin remodeler complex by long non-coding RNAs (lncRNAs) is a frequently utilized mechanism for lncRNAs to regulate gene expression. Hypoxia is a microenvironmental condition that plays a crucial role in promoting tumor progression. We previously identified a hypoxia-inducible lncRNA, RP11-390F4.3, that regulates epithelial-mesenchymal transition (EMT) without a delineated mechanism. Here, we show that the lncRNA RP11-390F4.3 (renamed MAHAC: MAintenance of Histone ACetylation) specifically induces histone H4 lysine 5 acetylation (H4K5ac) mark and promotes the deposition of H4K5ac mark on the promoters of EMT transcription factors. MAHAC scaffolds the ILF3/NF90-ILF2-CBP complex, which is co-localized with the members of the complex inside the nucleus under hypoxia. The minimal MAHAC region (nt 686-741) required for scaffolding the complex was mapped, and it induces allosteric activation of H4K5ac in in vitro histone acetyltransferase assay. This minimal MAHAC region is essential for hypoxia-induced EMT, migration, invasion, and H4K5ac activation. These findings demonstrate that hypoxia-induced MAHAC represents an unexplored allosteric regulator of H4K5ac that activates EMT and induces tumor progression.