Acetylation of CCAR2 Establishes a BET/BRD9 Acetyl Switch in Response to Combined Deacetylase and Bromodomain Inhibition

Abstract

There continues to be interest in targeting epigenetic "readers, writers, and erasers" for the treatment of cancer and other pathologies. However, a mechanistic understanding is frequently lacking for the synergy observed when combining deacetylase and bromodomain inhibitors. Here we identify cell cycle and apoptosis regulator 2 (CCAR2) as an early target for acetylation in colon cancer cells treated with sulforaphane. N-terminal acetylation of CCAR2 diminished its interactions with histone deacetylase 3 and b-catenin, interfering with Wnt coactivator functions of CCAR2, including in cells harboring genetically encoded CCAR2 acetylation. Protein domain arrays and pull-down assays identified acetyl "reader" proteins that recognized CCAR2 acetylation sites, including BRD9 and members of the bromodomain and extraterminal domain (BET) family. Treatment with the BET inhibitor JQ1 synergized with sulforaphane in colon cancer cells and suppressed tumor development effectively in a preclinical model of colorectal cancer. Studies with sulforaphaneþJQ1 in combination implicated a BET/BRD9 acetyl switch and a shift in the pool of acetyl "reader" proteins in favor of BRD9-regulated target genes. Significance: These results highlight the competition that exists among the "readers" of acetylated histone and nonhistone proteins and provide a mechanistic basis for potential new therapeutic avenues involving epigenetic combination treatments.

Acetylation and Deacetylation of DNA Repair Proteins in Cancers

“…Acetylation of CCAR2 on Lys54/97 induced by HDACI sulforaphane (SFN) diminished its interactions with HDAC3 and β-catenin. Treatment with the BET (acetyl-lysine reading proteins) inhibitor JQ1 synergized with SFN suppressed tumor development effectively in a preclinical model of colorectal cancer (79). Another study identified that once Lys112 and Lys215 on CCAR2 were acetylated by MYST family HAT hMOF, the interaction of CCAR2-SIRT1 was suppressed, resulting in an increased activity of SIRT1, which further deacetylated CCAR2 to stabilize the SIRT1-CCAR2 complex.…”

Epigenetic treatment combinations to effectively target cisplatin‐resistant germ cell tumors: past, present, and future considerations

“…They are the only domains, which bind specifically to histone acetylation marks (Jain & Barton, 2017). Even though combined treatment with HDAC and BET inhibitors (BETi) revealed additive or synergistic effects in several cancer entities, such as cutaneous T-cell lymphoma, neuroblastoma, glioblastoma, non-small cell lung cancer, adenocarcinoma, and colon cancer (Mazur et al, 2015;Shahbazi et al, 2016;Adeegbe et al, 2017;Meng et al, 2018;Rajendran et al, 2019;Zhao et al, 2019), so far only few studies described the mono-and combined treatment options with BETis in GCTs. Even though combined treatment with HDAC and BET inhibitors (BETi) revealed additive or synergistic effects in several cancer entities, such as cutaneous T-cell lymphoma, neuroblastoma, glioblastoma, non-small cell lung cancer, adenocarcinoma, and colon cancer (Mazur et al, 2015;Shahbazi et al, 2016;Adeegbe et al, 2017;Meng et al, 2018;Rajendran et al, 2019;Zhao et al, 2019), so far only few studies described the mono-and combined treatment options with BETis in GCTs.…”

“…Recently, the anti-cancer efficacy of inhibitors against the bromodomain and extra-terminal domain-containing (BET) protein family have been evaluated in several cancers, such as prostate, breast, colon, intestine, pancreas, liver, lung, brain, oral squamous cell carcinoma, and leukemias (Sahai et al, 2016;Saenz et al, 2017;Xu & Vakoc, 2017;Sahni & Keri, 2018;Zhang et al, 2018;Baldan et al, 2019). Even though combined treatment with HDAC and BET inhibitors (BETi) revealed additive or synergistic effects in several cancer entities, such as cutaneous T-cell lymphoma, neuroblastoma, glioblastoma, non-small cell lung cancer, adenocarcinoma, and colon cancer (Mazur et al, 2015;Shahbazi et al, 2016;Adeegbe et al, 2017;Meng et al, 2018;Rajendran et al, 2019;Zhao et al, 2019), so far only few studies described the mono-and combined treatment options with BETis in GCTs. The amount of transcripts of bromodomain-containing genes increases the higher the GCT stage is (Gashaw et al, 2005), indicating bromodomains being an interesting target for GCT treatment.…”

Epigenetic Regulation of NRF2/KEAP1 by Phytochemicals

“…Thus, Nrf2 exerted an apparent oncogenic role in the gut, and Nrf2 status dictated Hdac inhibitory responses to sulforaphane and the extent of tumor growth suppression [164]. Another interesting avenue is the synergistic combination of sulforaphane with the BET inhibitor JQ1 in colon cancer models, targeting the non-histone protein Cell cycle and apoptosis regulator 2 (CCAR2) for acetylation and altered Wnt coactivator functionality [165]. As BET proteins are reported to interact with and inhibit NRF2 [44], the prospect of combined deacetylase and bromodomain inhibition affecting NRF2 regulation is worthy of further mechanistic investigation.…”