Non-canonical activating roles of RCoR2 sustain transcription in adrenergic neuroblastoma [ATAC-seq]
CoREST complexes, composed of LSD1, HDAC1/2, and RCoR1/2/3, are pivotal in neurodevelopment and have long been recognized as transcriptional repressors across various cancers. However, distinct roles of the three RCoR factors remain underexplored. Here, we unveil non-canonical functions of RCoR2 in MYCN-amplified neuroblastoma (NB), underscoring its unique significance compared to its paralogues. This novel insight shifts the paradigm, highlighting RCoR2 as a key determinant of NB chromatin landscape.NB cell growth and tumorigenesis critically depend on RCoR1 and 2, with the RCOR2 gene exhibiting high histone acetylation levels and selective increased expression in NB. Unlike the well-known repressive roles of RCoR1, RNA-seq analyses demonstrate RCoR2 as a positive regulator of gene expression. RCoR2 predominantly occupies active promoters and regions of open chromatin marked by H3K27ac and Pol2, defining its distinct binding pattern compared to RCoR1, which primarily targets enhancers. Surprisingly, CoREST complexes co-occupy chromatin with NB core regulatory transcription factors (CRTFs), which positively drive NB-specific signatures. RCoR2, and not RCoR1, interacts with CRTFs, regulates their expression and its transcription is activated through a strong Super-enhancer. Collectively, these data indicate RCoR2 as a new component of the adrenergic NB core regulatory circuitry (CRC). Mechanistically, H3K27ac and H3K4me2 levels are not drastically altered upon RCoR2 reduction, suggesting RCoR2 is not the primary driver of CoREST complexes' catalytic activity. Instead, HiChIP data indicate that RCoR2 mediates chromatin looping, facilitating enhancer-promoter interactions and maintaining 3D chromatin architecture to sustain oncogenic transcriptional programs. Taken together, our data underscore RCoR2 as a key oncogenic determinant in neuroblastoma due to its role in chromatin landscape. We propose a model in which RCoR2 facilitates interactions between CRTF-bound enhancers and their associated transcription start sites, thereby sustaining the expression of genes essential for neuroblastoma survival. Consequently, we reveal RCoR2 as a novel critical vulnerability in high-risk neuroblastoma and a promising target for cancer therapeutics. Overall design: ATAC-seq in Kelly neuroblastoma cells conditionally (dox-on) expressing shRNA targeting RCOR1 or RCOR2.