Pin1-mediated Sp1 phosphorylation by CDK1 increases Sp1 stability and decreases its DNA-binding activity during mitosis

Abstract

We have shown that Sp1 phosphorylation at Thr739 decreases its DNA-binding activity. In this study, we found that phosphorylation of Sp1 at Thr739 alone is necessary, but not sufficient for the inhibition of its DNA-binding activity during mitosis. We demonstrated that Pin1 could be recruited to the Thr739(p)-Pro motif of Sp1 to modulate the interaction between phospho-Sp1 and CDK1, thereby facilitating CDK1-mediated phosphorylation of Sp1 at Ser720, Thr723 and Thr737 during mitosis. Loss of the C-terminal end of Sp1 (amino acids 741-785) significantly increased Sp1 phosphorylation, implying that the C-terminus inhibits CDK1-mediated Sp1 phosphorylation. Binding analysis of Sp1 peptides to Pin1 by isothermal titration calorimetry indicated that Pin1 interacts with Thr739(p)-Sp1 peptide but not with Thr739-Sp1 peptide. X-ray crystallography data showed that the Thr739(p)-Sp1 peptide occupies the active site of Pin1. Increased Sp1 phosphorylation by CDK1 during mitosis not only stabilized Sp1 levels by decreasing interaction with ubiquitin E3-ligase RNF4 but also caused Sp1 to move out of the chromosomes completely by decreasing its DNA-binding activity, thereby facilitating cell cycle progression. Thus, Pin1-mediated conformational changes in the C-terminal region of Sp1 are critical for increased CDK1-mediated Sp1 phosphorylation to facilitate cell cycle progression during mitosis.

Sp1 transcription factor: A long-standing target in cancer chemotherapy

“…Interestingly, Sp1 is phosphorylated specifically in mid-late G1-phase (Black, et al, 1999). Pin1, a peptidyl-prolyl isomerase, which is highly expressed in several cancers, including prostate, breast, lung and colon cancers, mediates Sp1 phosphorylation by CDK1 and increases Sp1 stability and decreases its DNA-binding activity during mitosis (Yang, et al, 2014a). Besides, Sp1 and Sp3 levels are kept constant during mitosis, which would indicate a significant recovery of the pre-existing levels in newly formed nuclei (He & Davie, 2006).…”

Pinning Down the Transcription: A Role for Peptidyl-Prolyl cis-trans Isomerase Pin1 in Gene Expression

“…Other transcription factors regulated by Pin1 at the level of protein stability include RelA (Ryo et al, 2003), β-catenin (Ryo et al, 2001), IRF3 (Saitoh et al, 2006), Naong (Moretto-Zita et al, 2010), Oct4 (Nishi et al, 2011), MEF2C (Magli et al, 2010), SP1 (Yang et al, 2014), Osterix (Lee et al, 2015), ATF1 (Huang et al, 2016), TR3 (Chen et al, 2012), FoxM1 (Kruiswijk et al, 2016;Wang et al, 2016), Smad3 (Nakano et al, 2009), RAR (Gianni et al, 2009), FoxO3 (Shimizu et al, 2016), PPARγ (Fujimoto et al, 2010;, and HIF-1a (Han H. J. et al, 2016) (Table 1). The detailed mechanisms for how Pin1 regulates their stability might be different for each factor, it appears that changing the accessibility of E3 ligases to the Pin1 substrates due to Pin1-medaited protein conformational change via isomerization might represent a general mechanism for the regulation of protein stability by Pin1.…”

“…The detailed mechanisms for how Pin1 regulates their stability might be different for each factor, it appears that changing the accessibility of E3 ligases to the Pin1 substrates due to Pin1-medaited protein conformational change via isomerization might represent a general mechanism for the regulation of protein stability by Pin1. In this regard, Pin1 prevents the binding of E3 ligase RNF4 to SP1 and SPOP for Naong, respectively (Yang et al, 2014;Zhang et al, 2019). By changing the stability of these transcription factors and their transcriptional activities, Pin1 regulates diverse biological processes, including inflammatory response, cell proliferation, stem cell reprogramming, myogenesis, and bone formation ( Table 1) (Liou et al, 2011).…”

“…It has to be noted that Pin1 can also decrease the DNA binding activity of transcription factors. Binding of Pin1 to phosphorylated Thr739 of Sp1 has been reported to cause Sp1 to move out of the chromosome completely by decreasing its DNA binding activity during mitosis (Yang et al, 2014).…”

Betulinic acid increases radiosensitization of oral squamous cell carcinoma through inducing Sp1 sumoylation and PTEN expression

“…Sp1 is overexpressed in many types of tumors, such as in breast cancers, pancreatic tumors, thyroid tumors, gastric tumors, liver cancers and gliomas (23)(24)(25), and is a negative prognostic factor for survival. The transcriptional activity of Sp1 is modulated by several post-translational modifications, such as acetylation (26), phosphorylation (27), sumoylation (28), and O-GlcNAcylation (29). Post-translational modification can regulate protein level, transactivation activity, or DNA binding affinity of Sp1 (30).…”