CLK1 Activates YAP to Promote Intrahepatic Cholangiocarcinogenesis

Abstract Cdc2-like kinase 1 (CLK1) has dual-specificity kinase ability to phosphorylate tyrosine and serine/threonine protein residues. CLK1 regulates many physiological processes and has been shown to contribute to multiple types of cancer. Here, we investigated the functional role of CLK1 during intrahepatic cholangiocarcinoma (ICC) development. The expression of CLK1 was elevated in ICC tumors, and patients with high expression of CLK1 demonstrated poor prognosis. In hydrodynamically transfected mouse models, CLK1 alone was insufficient to induce ICC, whereas CLK1 cooperated with AKT (AKT/CLK1) to trigger ICC initiation. In addition, overexpression of CLK1 in ICC cells facilitated proliferation in vitro and tumor growth in vivo, while loss of CLK1 elicited the opposite effects. Moreover, RNAseq analysis indicated that high levels of CLK1 corresponded with activation of the Hippo-YAP signaling pathway. Consistently, the AKT/CLK1 murine tumors displayed upregulation of YAP as well as its downstream targets. Furthermore, loss or pharmacological inhibition YAP in ICC cells inhibited CLK1-induced growth, and deletion of Yap completely retarded the induction of AKT/CLK1 tumors. Mechanistically, 4D-label free mass spectrometry and co-immunoprecipitation assays revealed WWC2 as a potential mediator of CLK1-YAP cascade. Collectively, the current findings identify a critical role for CLK1 in promoting ICC development and indicate that inhibiting YAP might be an effective approach for perturbing CLK1-mediated tumorigenesis.