Histone variant H3.3 promotes metastasis in alveolar rhabdomyosarcoma

Abstract

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.

The Role and Mechanism of the Histone Methyltransferase G9a in Tumors: Update

“…G9a is an upstream H3F3A regulator, whereas melanoma cell adhesion molecule (MCAM/CD146) is a direct downstream target of H3.3 and a potential therapeutic target. 69 …”

“…G9a is an upstream H3F3A regulator, whereas melanoma cell adhesion molecule (MCAM/CD146) is a direct downstream target of H3.3 and a potential therapeutic target. 69 In Ewing sarcoma (EWS) tumors, G9a overexpression is associated with poor prognosis. The expression of G9a is significantly higher in metastatic EWS tumors than in primary or recurrent tumors.…”

Involvement of the H3.3 Histone Variant in the Epigenetic Regulation of Gene Expression in the Nervous System, in Both Physiological and Pathological Conditions

“…In the alveolar rhabdomyosarcoma, H3.3 is overexpressed both in vivo and in cell lines: in this latter system, knockdown of the H3F3A gene reduces the ability of the cell to migrate, suggesting that the H3.3 variant regulates genes involved in motility, like melanoma cell adhesion molecule (MCAM, also known as CD146) [ 140 ].…”