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Cholangiocyte Ciliary Defects Induce Sustained Epidermal Growth Factor Receptor Signaling

ABSTRACT: Background & Aims: The primary cilium, an organelle that protrudes from cell surfaces, is essential for sensing extracellular signals. With disturbed cellular communication and chronic liver pathologies, this organelle's dysfunctions have been linked to disorders, including polycystic liver disease (PLD) and Cholangiocarcinoma (CCA). This study aimed to clarify the interaction between primary cilia and the critical regulator of cellular proliferation known as the epidermal growth factor receptor (EGFR) signaling pathway, which has been linked to several clinical conditions. Approach & Results: The study identified abnormal EGFR signaling pathways inside cholangiocytes lacking functioning primary cilia using liver-specific IFT88 knockout mice, a Pkhd1 mutant rat model, and human cell lines with ciliary deficiencies. Cilia-deficient cholangiocytes showed persistent EGFR activation because of impaired receptor degradation, in contrast to their normal counterparts where EGFR localization to cilia promotes appropriate signaling. By using HDAC6 inhibitors to restore primary cilia, EGFR degradation was accelerated, which in turn reduced the maladaptive signaling. Importantly, EGFR was moved to cilia because of experimental intervention with the HDAC6 inhibitor tubastatin A in an orthotopic rat model, along with a reduction in the phosphorylation of ERK. In cholangiocarcinoma and polycystic liver disease cells, concurrent administration of EGFR and HDAC6 inhibitors displayed synergistic anti-proliferative effects that were related to the restoration of functioning primary cilia. Conclusion: The findings of this study shed light on defective ciliary function and robust EGFR signaling with slower receptor turnover. A potential method for treating EGFR-driven pathologies in PLD and CCA is the pharmacological restoration of primary cilia function.

ORGANISM(S): Homo sapiens

PROVIDER: GSE276560 | GEO | 2024/09/11

REPOSITORIES: GEO

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Project description:Polycystic liver disease (PLD) is a group of genetic disorders characterized by bile duct dilatation and/or progressive development of multiple intrahepatic fluid-filled biliary cysts (>10), which are the main cause of morbidity. Current surgical and/or pharmacological therapies exert short-term and modest benefits, and thus liver transplantation represents the only curative option. Recently, novel PLD-causative genes, encoding for endoplasmic reticulum (ER)-resident proteins involved in protein biogenesis and transport, were identified. Here, we hypothesized that aberrant proteostasis contributes to PLD pathogenesis, representing a potential therapeutic target. In this regard, ER stress was assessed at transcriptional (qPCR), proteomic (mass spectrometry), morphological (transmission electron microscopy; TEM) and functional (20S proteasome activity) levels in different models of PLD (i.e., human and rat). Moreover, PCK rat (animal model of PLD) was employed to determine the effects of ER stress inhibitors [4-phenylbutyric acid (4-PBA)] and/or inducers [tunicamycin (TM)] in hepatic cytogenesis and, consequently, in the progression of the disease. Likewise, the impact of the aforementioned ER stress modulators was also analyzed on the expression of unfolded protein response (UPR) factors, the 20S proteasome activity, the mechanisms involved in the maintenance of ER proteostasis and the cell fate decisions (i.e., survival/apoptosis). Interestingly, the expression levels of the UPR factors were markedly upregulated in liver tissue from PLD patients and PCK rats, as well as in primary cultures of human and rat cystic cholangiocytes, compared to normal controls. Additionally, cystic cholangiocytes showed altered proteomic profiles, mainly related to proteostasis (i.e., synthesis, folding, trafficking and degradation of nascent proteins), marked enlargement of the ER lumen (by TEM), and hyperactivation of the 20S proteasome. Notably, chronic treatment of PCK rats with 4-PBA decreased liver weight, as well as both liver and cystic volumes, of animals under baseline or TM administration compared to control groups. In vitro, 4-PBA downregulated the expression (mRNA) of UPR effectors, normalized, at least in part, proteomic profiles related to protein synthesis, folding, trafficking and degradation, and reduced the proteasome hyperactivity in cystic cholangiocytes, reducing their hyperproliferation and apoptosis. Conclusion: Restoration of proteostasis in cystic cholangiocytes with 4-PBA halts hepatic cystogenesis, emerging as a novel and promising therapeutic strategy.

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Cholangiocyte Ciliary Defects Induce Sustained Epidermal Growth Factor Receptor Signaling

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