Degradation Mechanism And Effect Of Cdc20 - Mediated Sp100 Protein

Cdc20is a co-activator of the anaphase-promoting complex/cyclosome (APC/C complex), which recruits substrates with a D-box at particular phases of the cell cycle and mediates their degradation. Sp100is a PML-NB scaffold protein, which localizes to nuclear particles during interphase and disperses from them during mitosis, participates in viral resistance, transcriptional regulation, and apoptosis. However, its metabolism during the cell cycle has not yet been completely characterized. We found a putative D-box in Sp100using the Eukaryotic Linear Motif (ELM) predictor. Overexpression of Cdc20resulted in decreased levels of overexpressed Sp100. Cdc20knockdown by cdc20specific siRNA resulted in increased Sp100protein levels in cells. Furthermore, we discovered that the Cdc20mediated degradation of Sp100is diminished by the proteasome inhibitor MG132, which suggests that the ubiquitination pathway is involved in this process. However, unlike the other Cdc20substrates, which display oscillating protein levels, the level of Sp100protein remains constant throughout the cell cycle. Additionally, both overexpression and knockdown of endogenous Sp100had no effect on the cell cycle. Our results suggested that Sp100is a novel substrate of Cdc20and it is degraded by the ubiquitination pathway. The intact D-box of Sp100was necessary for this process. We found that some proteins with D-box but could not be degraded by Cdc20, such as PML and Daxx. We constructed a series truncated body of Sp100and found that the D-box might be not suffient.