Background Hepatic progenitor cells serve not only as the origin of combined hepatocellular cholangiocarcinoma (cHCC-CCA) but are also responsible for malignancy recurrence after surgical resection. Nucleophosmin 1 (NPM1) has been implicated in cancer metastasis and poor prognosis. This study aimed to determine the expression of NPM1 by hepatic progenitor cells in cHCC-CCA and the effects of targeting NPM1 on hepatic progenitor cells and BEL-7402 cells with characteristics of both progenitor cells and cHCC-CCA. Methods First, NPM1 was detected by RT‒PCR, western blotting, and double-immunofluorescence staining in cHCC-CCA tissues. NPM1 expression was subsequently analysed in rat hepatic progenitor cells cultured in vitro and in interleukin 6 (IL6)-treated cells. The effects and mechanism of NPM1 on hepatic progenitor cells were determined by knocking down NPM1 and performing RNA sequencing analysis. Finally, NSC348884, a small-molecule inhibitor that disrupts NPM1 dimer formation, was used to confirm the function of NPM1 in BEL-7402 cells. Results Both human hepatic progenitor cells in cHCC-CCA tissues and rat in vitro cultured hepatic progenitor cells highly expressed NPM1. IL6, a cytokine involved in the malignant transformation of hepatic progenitor cells, dose-dependently increased NPM1 and PCNA expression. Knocking down NPM1 reduced IL6R transcription ( P < 0.0001) and inhibited the proliferation ( P = 0.0065) of hepatic progenitor cells by suppressing the mTOR signalling pathway and activating the apoptosis pathway. Furthermore, knocking down NPM1 in hepatic progenitor cells resulted in more apoptotic cells (7.33 ± 0.09% vs. 3.76 ± 0.13%, P < 0.0001) but fewer apoptotic cells in the presence of NSC348884 (47.57 ± 0.49% vs. 63.40 ± 0.05%, P = 0.0008) than in the control cells, suggesting that low-NPM1-expressing cells are more resistant to NSC348884. In addition, NSC348884 induced the apoptosis of BEL-7402 cells with an IC50 of 2.77 μmol/L via the downregulation of the IL-6R and mTOR signalling pathways and inhibited the growth of BEL-7402 cells in a subcutaneous xenograft tumour model ( P = 0.0457). Conclusions Targeting NPM1 inhibits proliferation and induces apoptosis in hepatic progenitor cells and BEL-7402 cells, thus serving as a potential therapy for cHCC-CCA.
Pancreatic ductal adenocarcinoma (PDAC) is a fatal cancer with poor prognosis. COP9 signalosome subunit 6 (CSN6), a key regulator of different E3 ubiquitin ligases, plays oncogenic roles in various cancers. However, its function in PDAC remains elusive. Here, this demonstrates that human PDAC tumors expressing high levels of CSN6 present with poor prognosis and gemcitabine resistance. Conditional knockout (KO) of CSN6 hinders tumor formation in a KPP spontaneous PDAC mouse model. Proteomic analysis indicates that CSN6 promotes ribosome biogenesis by activating rDNA transcription and protein synthesis. Mechanistically, CSN6 antagonizes DDB1-CUL4 associated factor 1 (DCAF1)-mediated ubiquitination of Nucleophosmin (NPM1), thereby promoting NPM1-orchestrated ribosome biogenesis. In line with CSN6-mediated gemcitabine resistance, CSN6-NPM1 axis enhances ribosome biogenesis, thereby promoting translation of gemcitabine resistance genes, including Cytidine deaminase (CDA), Ribonucleotide reductase subunit M1/2 (RRM1/2). Significantly, combining gemcitabine with NPM1 inhibitor NSC348884 synergistically suppresses CSN6-high pancreatic cancer xenografts. Clinically, CSN6 expression positively correlates with NPM1 in PDAC tissues, and their concurrent high expression is significantly associated with poor clinical outcomes. This study characterizes CSN6 as an oncogenic protein that promotes NPM1 stabilization by interacting with DCAF1, thereby enhancing ribosome biogenesis and cellular resistance to gemcitabine in PDAC. NPM1 may serve as a therapeutic target for CSN6 high PDAC that exhibits gemcitabine drug resistance.
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