Notch signaling is aberrantly activated in approximately 30% of hepatocellular carcinoma (HCC), significantly contributing to tumorigenesis and disease progression. Expression of the major Notch receptor, NOTCH1, is upregulated in HCC cells and correlates with advanced disease stages, although the molecular mechanisms underlying its overexpression remain unclear. Here, we report that expression of the intracellular domain of NOTCH1 (NICD1) is upregulated in HCC cells due to antagonism between the E3-ubiquitin ligase F-box/WD repeat-containing protein 7 (FBXW7) and the large scaffold protein abnormal spindle-like microcephaly-associated protein (ASPM) isoform 1 (ASPM-i1). Mechanistically, FBXW7-mediated polyubiquitination and the subsequent proteasomal degradation of NICD1 are hampered by the interaction of NICD1 with ASPM-i1, thereby stabilizing NICD1 and rendering HCC cells responsive to stimulation by Notch ligands. Consistently, downregulating ASPM-i1 expression reduced the protein abundance of NICD1 but not its FBXW7-binding-deficient mutant. Reinforcing the oncogenic function of this regulatory module, the forced expression of NICD1 significantly restored the tumorigenic potential of ASPM-i1-deficient HCC cells. Echoing these findings, NICD1 was found to be strongly co-expressed with ASPM-i1 in cancer cells in human HCC tissues (P < 0.001). In conclusion, our study identifies a novel Notch signaling regulatory mechanism mediated by protein–protein interaction between NICD1, FBXW7, and ASPM-i1 in HCC cells, representing a targetable vulnerability in human HCC.

中文翻译：

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ASPM 通过阻断肝细胞癌细胞中的 FBXW7 结合来稳定 NOTCH 胞内结构域 1 并促进肿瘤发生

Notch 信号传导在约 30% 的肝细胞癌 (HCC) 中异常激活，对肿瘤发生和疾病进展有显着影响。主要Notch受体NOTCH1的表达在HCC细胞中上调，并与晚期疾病阶段相关，尽管其过度表达的分子机制仍不清楚。在这里，我们报道了由于 E3-泛素连接酶 F-box/WD 重复含有蛋白 7 (FBXW7) 和大支架蛋白异常纺锤体之间的拮抗作用，NOTCH1 (NICD1) 的胞内结构域的表达在 HCC 细胞中上调。如小头畸形相关蛋白 (ASPM) 同工型 1 (ASPM-i1)。从机制上讲，NICD1 与 ASPM-i1 的相互作用阻碍了 FBXW7 介导的多泛素化和随后的 NICD1 蛋白酶体降解，从而稳定了 NICD1 并使 HCC 细胞对 Notch 配体的刺激做出反应。一致地，下调 ASPM-i1 表达会降低 NICD1 的蛋白质丰度，但不会降低其 FBXW7 结合缺陷突变体的蛋白质丰度。NICD1 的强制表达增强了该调节模块的致癌功能，显着恢复了 ASPM-i1 缺陷的 HCC 细胞的致瘤潜力。与这些发现相呼应的是，NICD1 在人类 HCC 组织的癌细胞中与 ASPM-i1 强烈共表达（P  < 0.001）。总之，我们的研究确定了 HCC 细胞中由 NICD1、FBXW7 和 ASPM-i1 之间的蛋白质相互作用介导的新型 Notch 信号传导调节机制，代表了人类 HCC 中的可靶向脆弱性。