Selective inhibition of HDAC6 regulates expression of the oncogenic driver EWSR1-FLI1 through the EWSR1 promoter in Ewing sarcoma

Daniel J García-Domínguez,Antonio Llombart-Bosch,Ángel M Carcaboso,Laura Carmen Terrón-Camero,Rocío Flores-Campos,Jaume Mora,Elisabet Figuerola-Bou,Giovanna Magagnoli,Isidro Machado,Eduardo Andrés-León,Ana M Espinosa-Oliva,Rocío M De Pablos,Nabil Hajji,Enrique De Álava,Sara Sánchez-Molina,Lourdes Hontecillas-Prieto,María José Robles,Katia Scotlandi,Guillem Pascual-Pasto

doi:10.1038/s41388-021-01974-4

Abstract

Ewing sarcoma (EWS) is an aggressive bone and soft tissue tumor of children and young adults in which the principal driver is a fusion gene, EWSR1-FLI1. Although the essential role of EWSR1-FLI1 protein in the regulation of oncogenesis, survival, and tumor progression processes has been described in-depth, little is known about the regulation of chimeric fusion-gene expression. Here, we demonstrate that the active nuclear HDAC6 in EWS modulates the acetylation status of specificity protein 1 (SP1), consequently regulating the SP1/P300 activator complex binding to EWSR1 and EWSR1-FLI1 promoters. Selective inhibition of HDAC6 impairs binding of the activator complex SP1/P300, thereby inducing EWSR1-FLI1 downregulation and significantly reducing its oncogenic functions. In addition, sensitivity of EWS cell lines to HDAC6 inhibition is higher than other tumor or non-tumor cell lines. High expression of HDAC6 in primary EWS tumor samples from patients correlates with a poor prognosis in two independent series accounting 279 patients. Notably, a combination treatment of a selective HDAC6 and doxorubicin (a DNA damage agent used as a standard therapy of EWS patients) dramatically inhibits tumor growth in two EWS murine xenograft models. These results could lead to suitable and promising therapeutic alternatives for patients with EWS.

Highlights

Ewing sarcoma (EWS) is a highly aggressive tumor that affects children and young adults [1], showing gene fusions involving one member of the FET family of genes and a member of the ETS family of transcription factors, with EWSR1-FLI1 being the most common [1]
The analysis revealed that only trichostatin A and BML-281 had an IC50 value below 1.5 μM for all seven EWS cell lines (Supplementary Fig. 1B)
Due to pan-HDACis effects on nonspecific targets [11], we hypothesized that it would be more appropriate to evaluate the effects of selective HDACis, which could maintain the effectiveness on EWSR1-FLI1 depletion while simultaneously reducing treatment toxicity [9, 11, 36, 37]

Summary

Introduction

Ewing sarcoma (EWS) is a highly aggressive tumor that affects children and young adults [1], showing gene fusions involving one member of the FET family of genes (usually EWSR1) and a member of the ETS family of transcription factors, with EWSR1-FLI1 being the most common [1]. Little is known about the molecular mechanisms regulating the expression of the chimeric fusion, it is well known it is an aberrant transcription factor that can recruit transcription regulator proteins, such as lysine-specific histone demethylase 1A (LSD1) and histone deacetylases (HDACs) [5]. We have shown that the pan-HDAC inhibitor SAHA inhibits EWSR1-FLI1 expression [10]. It remains to be determined which HDAC (s) are involved in the regulation of EWSR1-FLI1 expression. The identification of specific HDAC(s) involved in the regulation of EWSR1-FLI1, and the use of selective inhibitors, may improve efficacy and avoid toxicity of treatments, and enhance our understanding about the regulatory mechanisms of EWSR1-FLI1

Methods

Results

Conclusion