In vivo disruption of nuclear HSATII RNA biomolecular condensates

Emerging studies have begun highlighting the significance of cellular regulation in the context of biomolecular condensates. These membraneless entities, formed by liquid-liquid phase separation (LLPS), compartmentalize regulatory elements that include proteins and long non-coding RNAs (lncRNAs). Biogenesis of these condensates includes molecular scaffolds called architectural lncRNAs (arcRNAs); which have the ability to nucleate regulatory elements. Tandemly repeating satellite sequences account for 3% of the human genome. One of them, Human Satellite II (HSATII), has a loosely defined monomer sequence and is located near centromeres of several human chromosomes. HSATII lncRNAs have growing evidence of important regulatory functions in epithelial cancer cells. Pericentromeric HSATII DNA is transcriptionally repressed in normal cells, however misregulation of these heterochromatic sequences in cancer cells allows for its aberrant transcription. The repetitive HSATII lncRNAs aggregate into large foci that remain in cis at their sites of transcription, and recruit regulatory proteins. Using NEAT1 and paraspeckles as models we present evidence that HSATII assembles into LLPS biomolecular condensates in vivo, that can be dispersed by doxorubicin into the nucleus and cytoplasm. Treatment with doxorubicin and 1,6-Hexanediol, drugs known to disrupt other condensates, resulted in significant redistribution of HSATII RNA. While this study serves to demonstrate that HSATII foci are condensates, it may also have broader implications for drug mechanisms in cancer therapeutics.