PP2A Inhibitors Arrest G2/M Transition Through JNK/Sp1-Dependent Down-Regulation Of CDK1

Objective:Protein phosphatase 2A(PP2A) plays an important role in the control of the cell cycle.We previously reported that the PP2 A inhibitors, cantharidin and okadaic acid(OA),efficiently repressed the growth of cancer cells. In the present study, we found that PP2 A inhibitors arrested the cell cycle at the G2 phase through a mechanism that was dependent on the JNK pathway.Methods:1. Cell proliferation was evaluated by using MTT assay.2. Cell cycle distribution was assayed by flow cytometry.3. Microarray and real-time PCR were used to determine mRNA expression level.Protein expression was evaluated by western blot.4. Small inhibitors or siRNA were used to verify the mechanisms involved in cell signaling transduction.5. Luciferase reporter gene assay was used to evaluate transcriptional activity.6. Chromatin Immunoprecipitation(ChIP) assay was used to evaluate binding between transcription factor and target DNA.Results:1. PP2 A inhibitors repressed G2/M cell cycle transition and cell growth through JNK pathway dependent manner.2. PP2 A inhibitors repressed CDK1 expression through JNK pathway dependent manner, leading to G2/M cell cycle arrest and cell growth inhibition.3. PP2 A inhibitors repressed CDK1 transcription through activation of Sp1 transcript factor. The CDK1 promoter region responding to JNK/Sp1 pathway located at-382bp~-372 bp upstream of transcriptionsl start site.Conclusion:PP2A inhibitors induced G2/M cell cycle arrest and growth inhibiton through PP2A/JNK/Sp1/CDK1 pathway dependent manner.