Identification of USP13 and FBXL14 as c-Myc–interacting proteins in glioma cells. (A and B) Identification of USP13 peptide (A) and FBXL14 peptide (B) in the c-Myc–interacting proteins by mass spectrometry analysis. c-Myc–interacting proteins were immunoprecipitated from partially differentiated GSCs (T387) that were induced by serum for a short time (2 d). Protein complexes were digested with trypsin before analysis by LC-MS. Ubiquitin-specific protease 13 (USP13) and the F-box/LRP-repeat protein 14 (FBXL14) were identified in LC-MS analysis by the peptides covering the protein sequence. The mass spectrometry spectra for the USP13 peptide DLGYMoYFYR (A) and the FBXL14 peptide VLNLGLWQMTDSEK (B) are shown. (C and D) Co-IP analyses of protein interaction between endogenous c-Myc and USP13 (C) or FBXL14 (D) in partially differentiated GSCs (T387) induced by serum for a short time (2 d). Cell lysates were immunoprecipitated with specific antibodies against c-Myc, USP13, or FBXL14. The co-IP complexes and total cell lysates were analyzed by IB with antibodies against c-Myc and USP13 or FBXL14. TCL, total cell lysate.