CBX8 Together with SET Facilitates Ovarian Carcinoma Growth and Metastasis by Suppressing the Transcription of SUSD2

Polycomb group proteins are often dysregulated in cancer, leading to disruption of epigenetic landscapes and acquisition of cancer hallmarks. Chromobox 8 (CBX8) is a core component of canonical polycomb repressive complex 1; however, its role in transcriptional regulation and in ovarian carcinoma progression has not been extensively investigated. In this study, we find that CBX8 is upregulated in ovarian cancer. Overexpression and knock-down approaches show that CBX8 facilitates the growth and migration of CAOV3, A2780, and SKOV3 cells in vitro. Consis-tently, depletion of CBX8 suppresses the growth and metastasis of ovarian carcinoma in vivo. Mechanistically, RNA-sequencing assays together with functional rescue experiments identify a tumor suppressor, SUSD2, as the functional target of CBX8 in ovarian carcinoma cells. Significantly, FLAG affinity coupled with mass spectrometry discovers that CBX8 interacts with a subunit of inhibitor of acetyltransferases (INHAT), SET, which also promotes the growth and migration of A2780 cells. CBX8 and SET cobind to the promoter of SUSD2 to establish H2AK119ub1 and prevent the acetylation of histone H3, resulting in transcriptional suppression of SUSD2. Implications: Our study uncovers a novel mechanism CBX8 explores to execute gene repression, and provides new therapeutic targets for ovarian carcinoma.