USP22 and cholangiocarcinoma: To determine the physical interactions in CCA, we performed Co-IP by immunoprecipitating the endogenous SIRT1 or USP22 proteins and showed the reciprocal immunoprecipitation of them by the respective antibodies from RBE-shUSP22 or RBE-shControl cell lysates, but not by the IgG control (Fig. 4D).