USP1 stabilized PLK1 via its deubiquitination. (A) GSEA plots showing the enrichment of gene signatures associated with PLK1 pathway in the USP1-depledted vs sh-control group. (B-C) Cell lysates of Jurkat and MOLT4 cells were precipitated with anti-PLK1 or anti-USP1 antibodies, and the precipitates were examined by immunoblotting. Immunoblot analysis of USP1 and PLK1 expression in Jurkat (D) and MOLT4 (E) cells infected with sh-control or USP1-shRNA. (F) Immunoblot analysis of USP1 and PLK1 expression in Jurkat cells with or without overexpression of USP1-flag. (G) Jurkat cells infected with control or USP1 shRNA were treated with dimethyl sulfoxide (DMSO) or MG132 for 12 hours. The expression of PLK1 and USP1 was assessed. (H) Jurkat cells were treated with DMSO or ML323. The lysates were immunoprecipitated with anti-PLK1 antibody. UB-PLK1 was analyzed by anti-ubiquitin antibody. The expression of GAPDH in whole cell lysates was analyzed as a control. (I) The expression of USP1 and PLK1 in primary pediatric T-ALL samples was measured. The representative immunoblotting image of USP1 and PLK1 expression (left) is shown. The correlation between USP1 and PLK1 expression in T-ALL samples is shown (right) (by the Pearson correlation test, n = 11). IgG, immunoglobulin G; IP, immunoprecipitation.