Division of Stem Cell Regulation, Center for Molecular Medicine, Jichi Medical University, Tochigi, Japan.
Division of Pathophysiology, The Research Center for GLOBAL and LOCAL Infectious Diseases (RCGLID), Oita University, Oita, Japan.
Clin Transl Med. 2023 Aug;13(8):e1364. doi: 10.1002/ctm2.1364.
The immunomodulatory drug lenalidomide, which is now widely used for the treatment of multiple myeloma (MM), exerts pharmacological action through the ubiquitin-dependent degradation of IKZF1 and subsequent down-regulation of interferon regulatory factor 4 (IRF4), a critical factor for the survival of MM cells. IKZF1 acts principally as a tumour suppressor via transcriptional repression of oncogenes in normal lymphoid lineages. In contrast, IKZF1 activates IRF4 and other oncogenes in MM cells, suggesting the involvement of unknown co-factors in switching the IKZF1 complex from a transcriptional repressor to an activator. The transactivating components of the IKZF1 complex might promote lenalidomide resistance by residing on regulatory regions of the IRF4 gene to maintain its transcription after IKZF1 degradation.
To identify unknown components of the IKZF1 complex, we analyzed the genome-wide binding of IKZF1 in MM cells using chromatin immunoprecipitation-sequencing (ChIP-seq) and screened for the co-occupancy of IKZF1 with other DNA-binding factors on the myeloma genome using the ChIP-Atlas platform.
We found that c-FOS, a member of the activator protein-1 (AP-1) family, is an integral component of the IKZF1 complex and is primarily responsible for the activator function of the complex in MM cells. The genome-wide screening revealed the co-occupancy of c-FOS with IKZF1 on the regulatory regions of IKZF1-target genes, including IRF4 and SLAMF7, in MM cells but not normal bone marrow progenitors, pre-B cells or mature T-lymphocytes. c-FOS and IKZF1 bound to the same consensus sequence as the IKZF1 complex through direct protein-protein interactions. The complex also includes c-JUN and IKZF3 but not IRF4. Treatment of MM cells with short-hairpin RNA against FOS or a selective AP-1 inhibitor significantly enhanced the anti-MM activity of lenalidomide in vitro and in two murine MM models. Furthermore, an AP-1 inhibitor mitigated the lenalidomide resistance of MM cells.
C-FOS determines lenalidomide sensitivity and mediates drug resistance in MM cells as a co-factor of IKZF1 and thus, could be a novel therapeutic target for further improvement of the prognosis of MM patients.
免疫调节药物来那度胺目前广泛用于多发性骨髓瘤（MM）的治疗，它通过泛素依赖性降解 IKZF1 和随后下调干扰素调节因子 4（IRF4）发挥药理作用，IRF4 是 MM 细胞存活的关键因素。IKZF1 主要通过抑制正常淋巴谱系中的癌基因的转录来作为肿瘤抑制因子发挥作用。相比之下，IKZF1 在 MM 细胞中激活 IRF4 和其他癌基因，这表明在将 IKZF1 复合物从转录抑制剂转换为激活剂的过程中存在未知的共同因子。IKZF1 复合物的反式激活成分可能通过驻留在 IRF4 基因的调节区域上，在 IKZF1 降解后维持其转录，从而促进来那度胺耐药。
为了鉴定 IKZF1 复合物的未知成分，我们使用染色质免疫沉淀测序（ChIP-seq）分析了 MM 细胞中 IKZF1 的全基因组结合，并使用 ChIP-Atlas 平台筛选了 IKZF1 与骨髓瘤基因组上其他 DNA 结合因子的共同占据。
我们发现，激活蛋白-1（AP-1）家族的成员 c-FOS 是 IKZF1 复合物的一个组成部分，主要负责该复合物在 MM 细胞中的激活功能。全基因组筛选显示，c-FOS 与 IKZF1 在 MM 细胞中 IKZF1 靶基因的调节区域上共同占据，包括 IRF4 和 SLAMF7，但在正常骨髓祖细胞、前 B 细胞或成熟 T 淋巴细胞中则没有。c-FOS 和 IKZF1 通过直接的蛋白质-蛋白质相互作用与 IKZF1 复合物结合到相同的共有序列上。该复合物还包括 c-JUN 和 IKZF3，但不包括 IRF4。用针对 FOS 的短发夹 RNA 或选择性 AP-1 抑制剂处理 MM 细胞，可显著增强来那度胺在体外和两种 MM 小鼠模型中的抗 MM 活性。此外，AP-1 抑制剂减轻了 MM 细胞对来那度胺的耐药性。
c-FOS 作为 IKZF1 的共同因子，决定了来那度胺的敏感性和介导 MM 细胞的耐药性，因此可能成为改善 MM 患者预后的新的治疗靶点。
