Proteasomes are essential protease complexes that maintain cellular homeostasis, and aberrant proteasomal activity supports cancer development. The regulatory mechanisms and biological function of the ubiquitin-26S proteasome have been studied extensively, while those of the ubiquitin-independent 20S proteasome system remain obscure. Here, we show that the cap 'n' collar (CNC) family transcription factor NRF3 specifically enhances 20S proteasome assembly in cancer cells and that 20S proteasomes contribute to colorectal cancer development through ubiquitin-independent proteolysis of the tumor suppressor p53 and retinoblastoma (Rb) proteins. The NRF3 gene is highly expressed in many cancer tissues and cell lines and is important for cancer cell growth. In cancer cells, NRF3 upregulates the assembly of the 20S proteasome by directly inducing the gene expression of the 20S proteasome maturation protein POMP. Interestingly, NRF3 knockdown not only increases p53 and Rb protein levels but also increases p53 activities for tumor suppression, including cell cycle arrest and induction of apoptosis. Furthermore, protein stability and cell viability assays using two distinct proteasome inhibitor anticancer drugs, the 20S proteasome inhibitor bortezomib and the ubiquitin-activating enzyme E1 inhibitor TAK-243, show that the upregulation of the NRF3-POMP axis leads to ubiquitin-independent proteolysis of p53 and Rb and to impaired sensitivity to bortezomib but not TAK-243. More importantly, the NRF3-POMP axis supports tumorigenesis and metastasis, with higher NRF3/POMP expression levels correlating with poor prognoses in patients with colorectal or rectal adenocarcinoma. These results suggest that the NRF3-POMP-20S proteasome assembly axis is significant for cancer development via ubiquitin-independent proteolysis of tumor suppressor proteins.

中文翻译：

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NRF3-POMP-20S蛋白酶体组装轴通过不依赖泛素的p53和视网膜母细胞瘤蛋白进行蛋白水解来促进癌症的发展。

蛋白酶体是维持细胞动态平衡的必需蛋白酶复合物，蛋白酶体的异常活性支持癌症的发展。泛素26S蛋白酶体的调控机制和生物学功能已得到广泛研究，而与泛素无关的20S蛋白酶体系统的调控机制和生物学功能仍然不清楚。在这里，我们表明，'n'项圈（CNC）家族转录因子NRF3特异性增强癌细胞中的20S蛋白酶体组装，并且20S蛋白酶体通过肿瘤抑制因子p53和视网膜母细胞瘤（Rb）的泛素依赖性蛋白水解作用而促进了结直肠癌的发展。蛋白质。NRF3基因在许多癌症组织和细胞系中高度表达，对癌细胞的生长非常重要。在癌细胞中 NRF3通过直接诱导20S蛋白酶体成熟蛋白POMP的基因表达来上调20S蛋白酶体的装配。有趣的是，敲除NRF3不仅增加了p53和Rb蛋白的水平，而且还增加了p53抑制肿瘤的活性，包括细胞周期停滞和凋亡诱导。此外，使用两种不同的蛋白酶体抑制剂抗癌药，20S蛋白酶体抑制剂硼替佐米和泛素激活酶E1抑制剂TAK-243进行蛋白质稳定性和细胞生存力分析，结果表明NRF3-POMP轴的上调导致了蛋白的泛素依赖性蛋白水解p53和Rb对硼替佐米的敏感性下降，但对TAK-243的敏感性下降。更重要的是，NRF3-POMP轴支持肿瘤发生和转移，NRF3 / POMP表达水平较高与大肠或直肠腺癌患者预后不良相关。这些结果表明，NRF3-POMP-20S蛋白酶体组装轴通过不依赖泛素的肿瘤抑制蛋白蛋白水解对癌症发展具有重要意义。