PRC1.6 molecule L3MBTL2 protects MYCN-amplified neuroblastoma cells via epigenetic gene suppression

Polycomb-group complexes are evolutionarily conserved epigenetic machineries that regulate stem cell fate decisions/development and are also implicated in tumorigenesis mainly by histone modification. PRC1 complexes mediates ubiquitylation of histone H2A on lysine 119 and consists of PRC1.1 to PRC1.6 complexes. Here, we studied the functional roles of a PRC1.6 molecule L3MBTL2 in neuroblastoma (NB) cells. L3MBTL2 knockout- and knockdown-experiments elucidated that L3MBTL2 depletion suppressed NB cell proliferation according with cell cycle arrest and gamma-H2A up-regulation. L3MBTL2 knockout profoundly suppressed xenograft tumor formation. Transcriptome analysis detected the suppressed cell cycle-related pathways and the activated the differentiation-related pathways. The remarkable de-repressed genes by the L3MBTL2 knockout were BRME1 and NRIP3. ChIP experiments showed co-localization of the PRC1.6 components PCGF6/E2F6/L3MBTL2 and MYCN at the transcription start sites (TSS) of these genes. L3MBTL2 knockout reduced H2AK119ub marks at the TSS regions but PCGF6 binding was heterogeneously changed. This study clarified the significance of PRC1.6 molecule L3MBTL2 in NB cell homeostasis and the epigenetic mechanism of the L3MBTL2-mediated gene suppression in NB that regulates the PRC1.6 complex localization and H2AK119 mono-ubiquitination in a gene locus-specific manner. Total RNA was extracted from L3MBTL2 KO NB cells, and a microarray analysis was performed using the Agilent platform of 8 × 60 K design ID G4851B (Agilent Single Color. 39494, Agilent Technologies, Santa Clara, CA, USA). Total RNA 200 ng was labeled with Cyanine3 using a Low Input Quick-Amp Labeling Kit (one color, Agilent Technologies) according to the manufacturer’s manuals.