Loss of LDOC1 by chromatin compaction in mesenchymal tumor cells is required for PFA1 ependymoma growth [CUT&RUN]

Posterior fossa molecular subtype A (PFA) ependymoma occurs in young children and is the deadliest subtype of pediatric ependymoma. High-risk subtypes with chromosome 1q+ and/or 6q- exhibit significantly poorer outcome compared to wild-type PFA. However, 50% of wild-type PFA patients relapse and there is a high risk of gaining chromosome 1q at recurrence. We previously found constitutively active NF-kB, through loss of LDOC1, led to chronic IL-6 secretion and an overall immunosuppressive tumor microenvironment in the higher risk wild-type PFA ependymoma subset (PFA1). In this study, we delineate the mechanistic consequences of LDOC1 loss in PFA1, using our PFA ependymoma in vitro and in vivo models under normoxia and hypoxia conditions. We noted chromatin compaction by H3K27me3 at the LDOC1 loci results in loss of LDOC1 gene expression. Restoration of LDOC1 was sufficient to reduce proliferation, NF-kB signaling and significant decrease in IL-6 secretion. Furthermore, tumors implanted with LDOC1- transduced cells in vivo were out competed by non-transduced cells, suggesting loss of LDOC1 is required for PFA tumor growth. These findings shed further light on the biology of PFA1 ependymoma and the role LDOC1 loss has on the tumor and immunobiology of high risk pediatric ependymoma.