title: Sp1 phosphorylation by cyclin-dependent kinase 1/cyclin B1 represses its DNA-binding activity during mitosis in cancer cells.
abstract: Sp1 is important for the transcription of many genes. Our previous studies have shown that Sp1 is degraded in normal cell, but it is preserved in cancer cells during mitosis and exists a priori in the daughter cells, ready to engage in gene transcription and thereby contributes to the proliferation and survival of cancer cells. The mechanism by which Sp1 is preserved in cancer cells during mitosis remains unknown. In this study, we observed that Sp1 strongly colocalized with cyclin-dependent kinase 1 (CDK1)/cyclin B1 during mitosis. Moreover, we showed that Sp1 is a novel mitotic substrate of CDK1/cyclin B1 and is phosphorylated by it at Thr 739 before the onset of mitosis. Phospho-Sp1 reduced its DNA-binding ability and facilitated the chromatin condensation process during mitosis. Mutation of Thr739 to alanine resulted in Sp1 remaining in the chromosomes, delayed cell-cycle progression, and eventually led to apoptosis. Screening of Sp1-associated proteins during mitosis by using liquid chromatography/mass spectrometry indicated the tethering of Sp1 to myosin/F-actin. Furthermore, phospho-Sp1 and myosin/F-actin appeared to exist as a congregated ring at the periphery of the chromosome. However, at the end of mitosis and the beginning of interphase, Sp1 was dephosphorylated by PP2A and returned to the chromatin. These results indicate that cancer cells use CDK1 and PP2A to regulate the movement of Sp1 in and out of the chromosomes during cell-cycle progression, which may benefit cancer-cell proliferation.
authors.affiliation: Institute of Bioinformatics and Biosignal Transduction, College of Bioscience and Biotechnology, Tainan, Taiwan.
authors.forename: J-Y
authors.initials: JY
authors.lastname: Chuang
authors.forename: S-A
authors.initials: SA
authors.lastname: Wang
authors.forename: W-B
authors.initials: WB
authors.lastname: Yang
authors.forename: H-C
authors.initials: HC
authors.lastname: Yang
authors.forename: C-Y
authors.initials: CY
authors.lastname: Hung
authors.forename: T-P
authors.initials: TP
authors.lastname: Su
authors.forename: W-C
authors.initials: WC
authors.lastname: Chang
authors.forename: J-J
authors.initials: JJ
authors.lastname: Hung
mesh_terms: D000199:Actins / Q000378:metabolism; D000230:Adenocarcinoma / Q000139:chemically induced / Q000378:metabolism; D020816:Amino Acid Motifs; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D042002:Chromatin Assembly and Disassembly; D056744:Cyclin B1 / Q000378:metabolism*; D004789:Enzyme Activation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006367:HeLa Cells; D006801:Humans; D007399:Interphase; D015674:Mammary Neoplasms, Animal / Q000139:chemically induced / Q000378:metabolism; D008770:Methylnitrosourea; D008938:Mitosis; D009218:Myosins / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D054648:Protein Phosphatase 2 / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism
chemical_list: D000199:Actins; C534699:CCNB1 protein, human; D056744:Cyclin B1; D016329:Sp1 Transcription Factor; D013912:Threonine; D008770:Methylnitrosourea; D016203:CDC2 Protein Kinase; D054648:Protein Phosphatase 2; D009218:Myosins