Ki-1/57 is a nuclear and cytoplasmic regulatory protein first identified in malignant cells from Hodgkin's lymphoma. It is involved in gene expression regulation on both transcriptional and mRNA metabolism levels. Ki-1/57 belongs to the family of intrinsically unstructured proteins, undergoes phosphorylation by PKC and methylation by PRMT1. Previous characterization of its protein interaction profile by yeast two-hybrid screening showed that Ki- 1/57 interacts with proteins of the SUMOylation machinery: the SUMO E2 conjugating enzyme UBC9 and the SUMO E3 ligase PIAS3, which suggested that Ki-1/57 could be involved with this process. Herewe identified seven potential SUMO target sites (lysine residues) on K... More
Ki-1/57 is a nuclear and cytoplasmic regulatory protein first identified in malignant cells from Hodgkin's lymphoma. It is involved in gene expression regulation on both transcriptional and mRNA metabolism levels. Ki-1/57 belongs to the family of intrinsically unstructured proteins, undergoes phosphorylation by PKC and methylation by PRMT1. Previous characterization of its protein interaction profile by yeast two-hybrid screening showed that Ki- 1/57 interacts with proteins of the SUMOylation machinery: the SUMO E2 conjugating enzyme UBC9 and the SUMO E3 ligase PIAS3, which suggested that Ki-1/57 could be involved with this process. Herewe identified seven potential SUMO target sites (lysine residues) on Ki-1/57 sequenceand observed that Ki-1/57 is modified by SUMO proteinsin vitro and in vivo. We showed that SUMOylation of Ki-1/57 occurred on lysines 213, 276 and 336. In transfected cells expressingFLAG-Ki-1/57 wild-type,its paralog FLAG-CGI-55 wild-type or their nonSUMOylated triple-mutants, the number ofPML-nuclear bodies (PML-NBs) is reduced compared to the control cells not expressing the constructs. More interestingly, after treating cells with arsenic trioxide (As2O3) the number of PML-NBs is no longer reduced when the nonSUMOylated triple-mutant Ki-1/57 is expressed, suggesting that the SUMOylation of Ki-1/57 has a role in the control of As2O3-induced PML-NBs formation. A proteome-wide analysis of Ki-1/57 partners in the presence of either SUMO-1 or SUMO-2 suggests that the involvement of Ki-1/57 with the regulation of gene expression is independentofthe presence of either SUMO-1 or SUMO-2;however the presence of SUMO-1 strongly influences the interaction of Ki-1/57 with proteins associated to cellular metabolism, maintenance and cell cycle.
