Tyrosine phosphatase activity is required for response to Src kinase inhibition in cholangiocarcinoma

Background: Cancer of the biliary tract, cholangiocarcinoma (CCA), is increasing in incidence and has limited treatment options. In an attempt to further understand signaling pathways driving oncogenesis and impacting response to therapy we, and others, have identified altered activation of the transcriptional co-activator, Yes- associated protein (YAP) in CCA. Canonical regulatory pathways impacting YAP consist of serine kinases; however, more recently we have demonstrated a central role for tyrosine phosphorylation in regulating YAP function in CCA. Herein we explore the role of tyrosine phosphatases in regulating YAP tyrosine phosphorylation. Methods: In silico analysis of the TCGA cholangiocarcinoma dataset was undertaken specifically evaluating tyrosine phosphatase levels. Molecular studies utilized the human CCA cell lines HuCCT-1 and KMCH as well as the murine CCA cell line SB1 (expressing a flag-tagged YAP). Baseline tyrosine phosphatase levels were assessed by RT-PCR and immunoblot. YAP-interacting phosphatases were identified by co-immunoprecipitation. Tyrosine phosphorylation was inhibited utilizing the multi-kinase inhibitor dasatinib. The pan-tyrosine phosphatase inhibitor sodium orthovanadate (Na3VO4) and the selective SHP1/2 inhibitor NSC87877 were utilized. Tyrosine phosphorylation was assessed by immunoblot. YAP transcriptional activity was evaluated by RT-PCR. Apoptosis was evaluated by caspase 3/7 assay. Results: Multiple tyrosine phosphatases were noted to be expressed at lower levels in tumor versus normal adjacent liver in the TCGA RNAseq dataset. YAP-interacting tyrosine phosphatases identified by co-IP included PTPN1, 11, 23, and PTPRK. Profiling of tyrosine phosphatase levels by RT-PCR and immunoblot demonstrated higher levels in KMCH cells compared to HuCCT-1; notably the YAP-interacting phosphatase PTPN11 (SHP2) was elevated. Consistent with the anticipated function of the phosphatases, immunoblot demonstrated lower levels of tyrosine phosphorylated YAP (p-YAPY357) in KMCH cells compared to HuCCT-1. The role of SHP2 was further probed by incubation of KMCH and HuCCT-1 cells with NSC87877 which was associated with an increase in p-YAPY357 levels and YAP co-transcriptional activity. Conversely, incubation of HuCCT-1 cells with dasatinib rapidly decreased p-YAPY357 levels; and this effect was diminished by pre-incubation with either Na3VO4or NSC87877. The effect on YAP tyrosine phosphorylation paralleled effects on apoptosis; incubation of HuCCT-1 cells with dasatinib lead to an apoptotic response as measured by caspase 3/7 assay, which was eliminated by pre-incubation with Na3VO4 or NSC87877. Conclusions: Inhibition of the tyrosine phosphatase SHP2 is associated with elevated p-YAPY357 levels, elevated YAP co-transcriptional activity, and a blunted therapeutic response to dasatinib in cholangiocarcinoma cell lines. Citation Format: EeeLN Buckarma, Nathan Werneburg, Ayano Niibe, Gregory Gores, Rory Smoot. Tyrosine phosphatase activity is required for response to Src kinase inhibition in cholangiocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3449.