CDKN1A and thyroid gland carcinoma: To explore the potential mechanism by which USP44 acts as a tumor suppressor in thyroid cancer, we performed co-immunoprecipitation (co-IP) assays followed by identification of co-precipitating proteins using liquid chromatography tandem mass spectrometry (LC-MS/MS), showing that p21 was detected in the Flag-tagged USP44 immunoprecipitates (Fig. 5A and B).