The Study Of Transcriptional Pattern Of UHRF1 In Neoplasm And Its Ubiquitin Ligase Function

UHRF1 is a ubiquitin ligase and hemi-methylated DNA binding protein important for DNA methylation. It recruits DNMT1 during DNA replication in order to methylate the hemi-methylated DNA newly formed in S phase, regulates cell cycle, and stimulates cell proliferation. Although UHRF1 is highly expressed in cancer cells, clinical study on its pattern of expression is very limited. Although UHRF1 catalyzes the ubiquitination of substrates such as histone H3, relatively little is known on the function and regulation of this ubiquitin ligase. Analysis of differential expression of UHRF1 in TCGA database shows that it is highly expressed in twelve types of cancers at transcriptional level, indicating potential link between UHRF1 and the development of neoplasm. This characteristic could be used as a potential dianostic marker. Furthermore, this study indicates that UHRF1 catalyzes intermolecular self-ubiquitination, and is neddylated by Nedd8 and sumoylated by Sumo1. The SRA domain of UHRF1 is known to bind hemi-methylated DNA, but herein is not required for UHRF1 to ubiquitinate itself and substrates including H3, DNMT3Aand SET8. The binding to hemi-methylated DNA of various length and methylation does not inhibit this function. Full length UHRF1 and truncated UHRF1 lacking SRA domain catalyze mono- and poly-ubiquitination of DNMT3A, and UHRF1 catalyzes poly-ubiquitination of the DNMT3A isoform DNMT3A2 in vitro. Moreover, UHRF1 ubiquitinates SET8 in vitro rather than in vivo. Consistent with ubiquitination-mediated degradation of DNMT3A induced by UHRF1, DNMT3 A inhibits the catalytic function of UHRF1 and its truncated version lacking SRA domain. However, DNMT3A2 does not inhibit the catalytic ability of UHRF1. In consistence, in vitro pull down experiment shows that DNMT3A directly interacts with UHRF1. This interaction does not rely on the RING and SRA domains of UHRF1, but could depend on its N-terminal UBL domain. In addition, the UHRF1 homolog UHRF2 also ubiquitinates DNMT3A and DNMT3A2. However, DNMT3A rather than DNMT3A2 inhibits UHRF2. These observations should be clinically relevant and facilitate the understanding of the function and regulation of UHRFl.