Histone variant H3.3 promotes metastasis in alveolar rhabdomyosarcoma

• Published in: The Journal of pathology Vol. 259; no. 3; pp. 342 - 356
• Main Authors: Karthik, Nandini, Lee, Jane Jia Hui, Soon, Joshua Ling Jun, Chiu, Hsin Yao, Loh, Amos Hong Pheng, Ong, Derrick Sek Tong, Tam, Wai Leong, Taneja, Reshma
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-03-2023; Wiley Subscription Services, Inc
• Subjects: adhesion; Alveoli; Cell adhesion molecules; Cell Line, Tumor; Cell migration; Epigenetics; Gene expression; Histocompatibility Antigens - genetics; Histocompatibility Antigens - metabolism; histone variant; Histone-Lysine N-Methyltransferase - genetics; Histones; Histones - genetics; Histones - metabolism; Humans; Lysine; Melanoma; Metastases; Metastasis; Methyltransferase; motility; Promoter Regions, Genetic; Rhabdomyosarcoma; Rhabdomyosarcoma, Alveolar - genetics; Rhabdomyosarcoma, Alveolar - pathology; Sarcoma; Therapeutic targets; Tumorigenesis; Tumors; histone variant; motility; sarcoma; adhesion; metastasis; epigenetics
• ISSN: 0022-3417; 1096-9896
• DOI: 10.1002/path.6048

The relatively quiet mutational landscape of rhabdomyosarcoma (RMS) suggests that epigenetic deregulation could be central to oncogenesis and tumour aggressiveness. Histone variants have long been recognised as important epigenetic regulators of gene expression. However, the role of histone variants in RMS has not been studied hitherto. In this study, we show that histone variant H3.3 is overexpressed in alveolar RMS (ARMS), an aggressive subtype of RMS. Functionally, knockdown of H3F3A, which encodes for H3.3, significantly impairs the ability of ARMS cells to undertake migration and invasion and reduces Rho activation. In addition, a striking reduction in metastatic tumour burden and improved survival is apparent in vivo. Using RNA‐sequencing and ChIP‐sequencing analyses, we identified melanoma cell adhesion molecule (MCAM/CD146) as a direct downstream target of H3.3. Loss of H3.3 resulted in a reduction in the presence of active marks and an increase in the occupancy of H1 at the MCAM promoter. Cell migration and invasion were rescued in H3F3A‐depleted cells through MCAM overexpression. Moreover, we identified G9a, a lysine methyltransferase encoded by EHMT2, as an upstream regulator of H3F3A. Therefore, this study identifies a novel H3.3 dependent axis involved in ARMS metastasis. These findings establish the potential of MCAM as a therapeutic target for high‐risk ARMS patients. © 2022 The Pathological Society of Great Britain and Ireland.