Tyr1497 in the BRG1 Bromodomain of the SWI/SNF Complex is Critical for the Binding and Function of a Selective BRG1 Inhibitor.

in Journal of cellular and molecular medicine by Yinan Wang, Chuanhe Yang, Gustavo A Miranda-Carboni, Hannah Kelso, Jayaraman Seetharaman, Dong-Jin Hwang, Duane D Miller, Lawrence M Pfeffer

TLDR

  • The study found that IV-255, a selective BRD inhibitor, sensitizes GBM cells to TMZ-induced DNA double-strand breaks and apoptotic cell death by binding to the BRG1 BRD, specifically the Tyr1497 residue.

Abstract

BRG1 and BRM are subunits of the SWI/SNF chromatin remodelling complex, which has DNA-stimulated ATPase activity and can destabilise histone-DNA interactions. Targeting SWI/SNF is beneficial for treating various tumours, including glioblastoma (GBM). Our research focussed on BRG1 due to its overexpression in GBM. We developed IV-255, a selective bromodomain (BRD) inhibitor that binds to BRG1 but not BRM. IV-255 sensitised GBM cells to temozolomide (TMZ), the standard GBM treatment. We identified the binding site of IV-255 within the BRG1 BRD and found that the Tyr1497 residue is crucial for IV-255's effect on TMZ-induced GBM cell death, while Asn1540 is not. Structural analyses confirmed that Tyr1497 is involved in the IV-255 binding pocket. Mechanistically, IV-255 increases γH2AX staining in GBM cell nuclei in response to TMZ, indicating an impaired DNA double-strand break response dependent on Tyr1497. IV-255 also sensitised GBM cells to TMZ-induced apoptosis, as shown by PARP and caspase-3 cleavage, which also requires Tyr1497. In conclusion, Tyr1497 within the BRD of BRG1 is critical for its interaction with IV-255 and for sensitising GBM cells to TMZ-induced DNA double-strand breaks and apoptotic cell death.

Overview

  • The study focused on BRG1, a subunit of the SWI/SNF chromatin remodeling complex, which is overexpressed in glioblastoma (GBM) and can destabilize histone-DNA interactions.
  • The researchers developed a selective bromodomain (BRD) inhibitor, IV-255, which binds to BRG1 but not BRM, and sensitizes GBM cells to temozolomide (TMZ), the standard GBM treatment.
  • The study aimed to understand the binding site of IV-255 within the BRG1 BRD and its mechanism of action in sensitizing GBM cells to TMZ-induced DNA double-strand breaks and apoptotic cell death.

Comparative Analysis & Findings

  • The study found that the Tyr1497 residue within the BRG1 BRD is crucial for IV-255's effect on TMZ-induced GBM cell death, while Asn1540 is not.
  • Structural analysis confirmed that Tyr1497 is involved in the IV-255 binding pocket.
  • Mechanistically, IV-255 increased γH2AX staining in GBM cell nuclei in response to TMZ, indicating an impaired DNA double-strand break response dependent on Tyr1497.

Implications and Future Directions

  • The study highlights the importance of targeting BRG1 as a potential therapeutic strategy for treating GBM.
  • Future studies should investigate the potential of IV-255 as a therapeutic agent for GBM treatment, and its efficacy in combination with TMZ.
  • Additionally, further research is needed to determine the impact of IV-255 on other cancer types and its potential off-target effects.
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