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Phosphorylation by CDK1 and JNK1 regulate the DNA binding activity of transcription factor Sp1 during mitosis

The transcription factor Sp1 is ubiquitously expressed in different cells and thereby regulates the expression of genes involved in many cellular processes. This study reveals that Sp1 was phosphorylated at threonine 739 by JNK and CDK1 and not co‐localized with the chromatin at the beginning of mitotic stage. EMSA, DNA affinity precipitation assay, and ChIP assay were performed and revealed that during mitosis the DNA‐binding ability of phosphorylated Sp1was decrease as well as dephosphorylation of Sp1 by phosphatase restored the DNA binding affinity. In addition, the phosphorylation of Sp1 during mitotic stage also suppressed Sp1 to interact with p300, Brg1, and RNA polII and reduced the transcriptional activity of Sp1 target genes. Moreover, in late mitosis, the Pin1 interacted with the high phosphorylation of Sp1 and recruited the PP2A to dephosphorylate Sp1. In Pin1 knockout MEF cells, there was a delay in the relocalization of Sp1 to the nucleus during telophase. Taken together, our results indicated that Sp1 interacts with JNK and CDK1, followed by phosphorylation of Sp1 at early mitosis. Sp1, then, is disassociated from DNA and loses interaction with co‐activator. In late mitosis, Pin1 and PP2A are recruited by phosphorylation of Sp1, leading to the enhancement of the DNA binding‐ability and protein interactional function of Sp1.