·CCK-8 method, flow cytometry, Swiss Giemsa staining, and Western blotting were used to detect the proliferation, cell cycle and apoptosis of Jurkat cells and the expression of mitosis-related protein kinases after oridonin treatment. Western blotting was used to detect the phosphorylation level of PLK1 downstream proteins in Jurkat cells after oridonin treatment. Computer simulation, immunoprecipitation, Western blotting and Celluar Thermal Shift Assay were used to study the binding mode and binding site of oridonin and PLK1. Student's-t test was performed for comparison between each two groups. Statistical significance was accepted at a value of P<0.05.

·Oridonin could induce G₂/M phase arrest in Jurkat cells by up-regulating the content of PLK1 protein and promoting its kinase activity. Oridonin could directly bind to PLK1 protein to inhibit its degradation through the ubiquitin proteasome pathway. The mutation of Cys67 or Cys133 amino acid residues of PLK1 protein inhibited its direct binding to oridonin. And the mutation inhibited the stabilizing effect of oridonin on PLK1 protein.

·Oridonin inhibits PLK1 protein ubiquitination modification and degradation by directly binding to its protein. Oridonin can also promote PLK1 protein kinase activity and induce G₂/M phase arrest in Jurkat cells. The Cys67 and Cys133 sites of the PLK1 protein are the key sites for the protein to bind to oridonin.