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  3. The CDK4/6-UCHL5-BRD4 axis confers resistance to BET inhibitors in MLL-rearranged leukemia cells by suppressing BRD4 protein degradation

The CDK4/6-UCHL5-BRD4 axis confers resistance to BET inhibitors in MLL-rearranged leukemia cells by suppressing BRD4 protein degradation

  • Biochem Biophys Res Commun. 2022 Jan 15:588:147-153. doi: 10.1016/j.bbrc.2021.12.063.
Keigo Amari 1,  Satoru Sasagawa 2,  Natsuki Imayoshi 3,  Yuki Toda 1,  Shigekuni Hosogi 1,  Toshihiko Imamura 4,  Eishi Ashihara 5
Affiliations

Affiliations

  • 1 Department of Clinical and Translational Physiology, Kyoto Pharmaceutical University, Kyoto, Japan.
  • 2 Molecular Biology Laboratory, Research Institute, Nozaki Tokushukai Hospital, Osaka, Japan.
  • 3 Department of Clinical and Translational Physiology, Kyoto Pharmaceutical University, Kyoto, Japan; DC1, Japan Society for the Promotion of Science, Tokyo, Japan.
  • 4 Department of Pediatrics, Kyoto Prefectural University of Medicine, Kyoto, Japan.
  • 5 Department of Clinical and Translational Physiology, Kyoto Pharmaceutical University, Kyoto, Japan. Electronic address: [email protected].
PMID: 34954522 DOI: 10.1016/j.bbrc.2021.12.063
Abstract

Among acute leukemias, mixed-lineage leukemia-rearranged (MLL-r) leukemia is associated with poor prognosis. Bromodomain and extra-terminal inhibitors (BETi) are promising agents for treatment of hematological malignancies; however, the mechanisms underlying sensitivity to BETi and biomarkers to predict sensitivity are yet to be clarified. Here, we established OTX015-resistant MLL-r cell lines (OTX015-R cells) and used them to explore therapeutic targets in BETi-resistant MLL-r leukemia. OTX015-R cells exhibited resistance to various BETi, and levels of bromodomain-containing protein 4 (BRD4) and BRD4-regulated molecules, such as c-Myc and B-cell/CLL lymphoma-2 (Bcl-2), were remarkably increased in OTX015-R cells relative to those in the parental cells; however, BRD4 mRNA transcript levels were not elevated. These results suggest that overexpression of BRD4 protein, through suppression of BRD4 degradation, may contribute to BETi-resistance. Notably, expression of ubiquitin carboxyl-terminal hydrolase isozyme L5 (UCHL5) was increased in OTX015-R cells. Further, a UCHL5 inhibitor, b-AP15, and UCHL5 knockdown had antitumor effects by degrading BRD4. In addition, sensitivity to OTX015 was partially recovered in OTX015-R cells pretreated with b-AP15. Furthermore, cyclin-dependent kinase 4/6 (CDK4/6) inhibition decreased UCHL5 expression, suppressed OTX015-R cell proliferation, and induced Apoptosis. These results indicate that the CDK4/6-UCHL5-BRD4 axis confers resistance to BETi by suppressing BRD4 degradation. We propose that this pathway is a potential novel therapeutic target in BETi-resistant MLL-r leukemia with BRD4 overexpression.

Keywords

BET inhibitor resistance; BRD4; CDK4/6; MLL-rearranged leukemia; UCHL5.

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