Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland.
Laboratory of Receptor Biology and Gene Expression, Developmental Genomics Group, Center for Cancer Research, NCI, NIH, Bethesda, Maryland.
Mol Cancer Ther. 2024 Apr 2;23(4):464-477. doi: 10.1158/1535-7163.MCT-23-0144.
Histone deacetylase inhibitors (HDACi) are part of a growing class of epigenetic therapies used for the treatment of cancer. Although HDACis are effective in the treatment of T-cell lymphomas, treatment of solid tumors with this class of drugs has not been successful. Overexpression of the multidrug resistance protein P-glycoprotein (P-gp), encoded by ABCB1, is known to confer resistance to the HDACi romidepsin in vitro, yet increased ABCB1 expression has not been associated with resistance in patients, suggesting that other mechanisms of resistance arise in the clinic. To identify alternative mechanisms of resistance to romidepsin, we selected MCF-7 breast cancer cells with romidepsin in the presence of the P-gp inhibitor verapamil to reduce the likelihood of P-gp-mediated resistance. The resulting cell line, MCF-7 DpVp300, does not express P-gp and was found to be selectively resistant to romidepsin but not to other HDACis such as belinostat, panobinostat, or vorinostat. RNA-sequencing analysis revealed upregulation of the mRNA coding for the putative methyltransferase, METTL7A, whose paralog, METTL7B, was previously shown to methylate thiol groups on hydrogen sulfide and captopril. As romidepsin has a thiol as the zinc-binding moiety, we hypothesized that METTL7A could inactivate romidepsin and other thiol-based HDACis via methylation of the thiol group. We demonstrate that expression of METTL7A or METTL7B confers resistance to thiol-based HDACis and that both enzymes are capable of methylating thiol-containing HDACis. We thus propose that METTL7A and METTL7B confer resistance to thiol-based HDACis by methylating and inactivating the zinc-binding thiol.
组蛋白去乙酰化酶抑制剂（HDACi）是一类新兴的表观遗传治疗药物，用于治疗癌症。虽然 HDACi 在治疗 T 细胞淋巴瘤方面非常有效，但用这类药物治疗实体瘤并不成功。多药耐药蛋白 P-糖蛋白（P-gp）的过度表达，由 ABCB1 编码，已知在体外赋予对 HDACi 罗米地辛的耐药性，但 ABCB1 表达的增加与患者的耐药性无关，这表明在临床上出现了其他耐药机制。为了确定对罗米地辛的其他耐药机制，我们在存在 P-gp 抑制剂维拉帕米的情况下用罗米地辛选择 MCF-7 乳腺癌细胞，以降低 P-gp 介导的耐药性的可能性。由此产生的 MCF-7 DpVp300 细胞系不表达 P-gp，并且被发现对罗米地辛具有选择性耐药性，但对其他 HDACi 如贝林司他、帕比司他或伏立诺他没有耐药性。RNA 测序分析显示，编码假定甲基转移酶 METTL7A 的 mRNA 上调，其旁系同源物 METTL7B 先前被证明可将巯基甲基化到硫化氢和卡托普利上。由于罗米地辛的锌结合部分为巯基，我们假设 METTL7A 可以通过巯基的甲基化使罗米地辛和其他基于巯基的 HDACi 失活。我们证明，METTL7A 或 METTL7B 的表达赋予了对基于巯基的 HDACi 的耐药性，并且这两种酶都能够甲基化含巯基的 HDACi。因此，我们提出 METTL7A 和 METTL7B 通过甲基化和失活锌结合的巯基赋予基于巯基的 HDACi 耐药性。
