Department of Biomedical Sciences, City University of Hong Kong, Kowloon, Hong Kong SAR, China; Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA; Department of Pathology, The University of Hong Kong, Queen Mary Hospital, Pokfulam, Hong Kong SAR, China.
Department of Biomedical Sciences, City University of Hong Kong, Kowloon, Hong Kong SAR, China; Key Laboratory of Biochip Technology, Biotech and Health Centre, Shenzhen Research Institute of City University of Hong Kong, Shenzhen, 518057, China.
Exp Cell Res. 2020 Sep 1;394(1):111989. doi: 10.1016/j.yexcr.2020.111989. Epub 2020 Apr 10.
All-trans retinoic acid (ATRA) is an anti-cancer differentiation therapy agent effective for acute promyelocytic leukemia (APL) but not acute myeloid leukemia (AML) in general. Using the HL-60 human non-APL AML model where ATRA causes nuclear enrichment of c-Raf that drives differentiation and G1/G0 cell cycle arrest, we now observe that c-Raf in the nucleus showed novel interactions with several prominent regulators of the cell cycle and cell differentiation. One is cyclin-dependent kinase 2 (Cdk2). ATRA treatment caused c-Raf to dissociate from Cdk2. This was associated with enhanced binding of Cdk2 with retinoic acid receptor α (RARα). Consistent with this novel Raf/CDK2/RARα axis contributing to differentiation, CD38 expression per cell, which is transcriptionally regulated by a retinoic acid response element (RARE), is enhanced. The RB tumor suppressor, a fundamental regulator of G1 cell cycle progression or arrest, was also targeted by c-Raf in the nucleus. RB and specifically the S608 phosphorylated form (pS608RB) complexed with c-Raf. ATRA treatment induced S608RB-hypophosphorylation associated with G1/G0 cell cycle arrest and release of c-Raf from RB. We also found that nuclear c-Raf interacted with SMARCD1, a pioneering component of the SWI/SNF chromatin remodeling complex. ATRA treatment diminished the amount of this protein bound to c-Raf. The data suggest that ATRA treatment to HL-60 human cells re-directed c-Raf from its historically pro-proliferation functions in the cytoplasm to pro-differentiation functions in the nucleus.
全反式维甲酸（ATRA）是一种抗癌分化治疗药物，对急性早幼粒细胞白血病（APL）有效，但对一般急性髓细胞白血病（AML）无效。我们使用 HL-60 人非 APL AML 模型，其中 ATRA 导致 c-Raf 在核内富集，从而驱动分化和 G1/G0 细胞周期停滞，现在观察到核内的 c-Raf 与细胞周期和细胞分化的几个重要调节剂有新的相互作用。其中一个是细胞周期蛋白依赖性激酶 2（Cdk2）。ATRA 处理导致 c-Raf 与 Cdk2 解离。这与 Cdk2 与维甲酸受体 α（RARα）的结合增强有关。与该新型 Raf/CDK2/RARα 轴有助于分化一致，每个细胞的 CD38 表达增强，CD38 表达受维甲酸反应元件（RARE）转录调控。RB 肿瘤抑制因子是 G1 细胞周期进程或停滞的基本调节剂，也是核内 c-Raf 的靶标。RB 特别是 S608 磷酸化形式（pS608RB）与 c-Raf 结合。ATRA 处理诱导 S608RB 低磷酸化，与 G1/G0 细胞周期停滞和 c-Raf 从 RB 释放有关。我们还发现核内 c-Raf 与 SMARCD1 相互作用，SMARCD1 是 SWI/SNF 染色质重塑复合物的先驱成分。ATRA 处理减少了与 c-Raf 结合的这种蛋白质的量。数据表明，ATRA 处理 HL-60 人细胞将 c-Raf 从其在细胞质中的历史上的促增殖功能重新定向到细胞核中的促分化功能。
