| Summary: | 博士 === 國立成功大學 === 生物資訊與訊息傳遞研究所 === 104 === Our previous study found that Sp1 phosphorylation at Threonine739 decreased DNA-binding activity of Sp1 during mitosis. Here, we demonstrated that Sp1 Thr739 phosphorylation alone is necessary, but not sufficient for the decrease of DNA-binding activity in mitosis stage. Further study showed that Pin1 could be recruited to phospho-Thr739-Pro740 motif of Sp1 and then regulate the interaction between phospho-Thr739-Sp1 and CDK1 during mitosis, thereby Sp1 could be further highly phosphorylated by CDK1 at Ser720, Thr723, and Thr737. The Pin1-mediated Sp1 highly phosphorylation by CDK1 can decrease DNA-binding affinity of Sp1. Loss of C-terminus (amino acid 741-785) significantly increased the phosphorylation by CDK1 without Pin1, suggesting that C-terminus of Sp1 inhibits highly phosphorylation by CDK1. The structure study by X-ray crystallography indicated that Pin1 increased the cis signal and showed that the phospho-Thr739-Sp1 peptide located in the active site of Pin1, suggesting that Pin1 alters the conformation of C-terminal Sp1. During mitosis, Sp1 highly phosphorylation by CDK1 not only stabilized protein level of Sp1 by reducing the interaction between Sp1 and its ubiquitin E3-ligase RNF4 but also made Sp1 completely leave the chromosomes by decreasing the DNA-binding activity of Sp1. This regulation of Sp1 by CDK1 phosphorylation can facilitate the cell cycle progression. Thus, Pin1-mediated conformational alteration of C-terminal Sp1 is critical for the Sp1 highly phosphorylation by CDK1 in mitosis, leading cell cycle progression. In addition to the cell cycle regulation in cancer cells, highly phosphorylation can preserve Sp1 during cell cycle and then Sp1 can rapidly start to regulate gene transcription in cancer cells after cell division. So we investigated the genes Sp1 regulated in cancer cells to clarify the function of preserved Sp1 during cell cycle. Our ChIP-seq and small RNA-seq data suggested that Sp1 can regulate lots of microRNAs in cancer cells and may affect tumor progression via miRNA regulation. Our data showed that Sp1 can exhibit positive and negative control on miRNA, so we chose the Sp1-positive regulated miR-22 and Sp1-negative regulated miR-103 for our study. In this study, we found that Sp1 can activate the promoter of miR-22 by Sp1 binding site, and Sp1 can repress miR-103 through non-canonical intronic microRNA regulation. Instead of regulating miR-103 host gene promoter, Sp1 can directly regulate miR-103 promoter. Although there is not any Sp1 binding site on miR-103 promoter, we found that Sp1 can repress miR-103 transcription by forming a repression complex with YY1 and HADC1. This study showed that Sp1 can exhibit positive and negative control on miRNA transcription in cancer cells, suggesting that Sp1 might play an important role in tumorigenesis by regulating miRNA.
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