Serine/threonine protein phosphatase 5 is a potential therapeutic target in cholangiocarcinoma

摘要

Abstract Background & Aims Few molecules are currently verified to be actionable drug targets in cholangiocarcinoma ( CCA ). Serine/threonine protein phosphatase 5 ( PP 5) dysregulation is related to several malignancies. However, the role of PP 5 in CCA is poorly defined. Methods Colony and tumorsphere formation assays were conducted to establish the role of PP 5 in CCA tumorigenesis. Cantharidin ( CTD ) and norcantharidin ( NCTD ), both potent PP 5 inhibitors, were used in in vitro and in vivo experiments to validate the potential therapeutic role of PP 5. Results Increased cell growth, colony formation and tumorsphere formation were observed in PP 5‐overexpressing CCA cells , whereas PP 5 knockdown by sh RNA decreased cell growth and colony formation. Tumours from Hu CCT 1 xenograft‐bearing mice treated with PP 5‐sh RNA showed decreased growth and increased AMP ‐activated protein kinase ( AMPK ) phosphorylation. Furthermore, CTD treatment decreased cell viability, reduced PP 5 activity and enhanced AMPK phosphorylation in CCA cell lines. Overexpressing PP 5 or enhancing PP 5 activity suppressed AMPK phosphorylation and decreased CTD ‐induced cell death. Suppressing p‐ AMPK with si RNA or inhibitors also decreased CTD ‐induced cell death, suggesting a pivotal role for PP 5‐ AMPK cascades in CCA . Immunoprecipitation revealed that PP 5 interacted with AMPK . Importantly, treatment of Hu CCT 1 xenograft‐bearing mice with NCTD , a CTD analogue with a lower systemic toxicity in vivo , suppressed PP 5 activity, increased p‐ AMPK and reduced tumour volume. Conclusions Protein phosphatase 5 negatively regulates AMPK phosphorylation and contributes to CCA aggressiveness; thus, PP 5 may be a potential therapeutic target in CCA .