Sorafenib inhibits signal transducer and activator of transcription-3 signaling in cholangiocarcinoma cells by activating the phosphatase shatterproof 2

Abstract

The Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway is one of the key signaling cascades in cholangiocarcinoma (CCA) cells, mediating their resistance to apoptosis. Our aim was to ascertain if sorafenib, a multikinase inhibitor, may also inhibit JAK/STAT signaling and, therefore, be efficacious for CCA. Sorafenib treatment of three human CCA cell lines resulted in Tyr⁷⁰⁵ phospho‐STAT3 dephosphorylation. Similar results were obtained with the Raf‐kinase inhibitor ZM336372, suggesting sorafenib promotes Tyr⁷⁰⁵ phospho‐STAT3 dephosphorylation by inhibiting Raf‐kinase activity. Sorafenib treatment enhanced an activating phosphorylation of the phosphatase SHP2. Consistent with this observation, small interfering RNA–mediated knockdown of phosphatase shatterproof 2 (SHP2) inhibited sorafenib‐induced Tyr⁷⁰⁵ phospho‐STAT3 dephosphorylation. Sorafenib treatment also decreased the expression of Mcl‐1 messenger RNA and protein, a STAT3 transcriptional target, as well as sensitizing CCA cells to tumor necrosis factor–related apoptosis‐inducing ligand (TRAIL)‐mediated apoptosis. In an orthotopic, syngeneic CCA model in rats, sorafenib displayed significant tumor suppression resulting in a survival benefit for treated animals. In this in vivo model, sorafenib also decreased tumor Tyr⁷⁰⁵ STAT3 phosphorylation and increased tumor cell apoptosis. Conclusion: Sorafenib accelerates STAT3 dephosphorylation by stimulating phosphatase SHP2 activity, sensitizes CCA cells to TRAIL‐mediated apoptosis, and is therapeutic in a syngeneic rat, orthotopic CCA model that mimics human disease. (HEPATOLOGY 2009.)