The proline and serine rich protein PROSER1 mediates O-GlcNAcylation of TET2 to regulate DNA demethylation on UTX-dependent enhancers and CpG islands [ChIP-seq]

DNA methylation at enhancers and CpG islands usually leads to gene repression, which is counteracted by DNA demethylation through the TET protein family. However, how TET enzymes are recruited and regulated at these genomic loci is not fully understood. Here, we identify TET2 and a previously undescribed proline and serine rich protein, PROSER1 as interactors of UTX, a component of the enhancer-associated MLL3/4 complexes. Affinity purification of PROSER1 resulted in the identification of OGT and TET1-3. We find that PROSER1 mediates the interaction between OGT and TET2, thus promoting TET2 O-GlcNAcylation and protein stability. Additionally, PROSER1, UTX, OGT, and TET1/2 colocalize on many genomic elements genome-wide. Loss of PROSER1 results in lower enrichment of UTX, and TET1/2 at enhancers and CpG islands, with a concomitant increase in DNA methylation and transcriptional downregulation of associated target genes and increased DNA hypermethylation encroachment at H3K4me1-predisposed CpG islands. Taken together, this study describes for the first time a regulator of TET2 O-GlcNAcylation and its implications in mediating DNA demethylation at UTX-dependent enhancers and CpG islands. Identify if loss of PROSER1 would affect the localization of UTX, TET proteins, OGT, H3K4 mono, di, tri-methylation, and H3K27ac at enhancers and CpG islands

增强子（enhancer）与CpG岛（CpG islands）处的DNA甲基化（DNA methylation）通常会导致基因阻遏，而这一过程会被TET蛋白家族（TET protein family）介导的DNA去甲基化所拮抗。然而，TET酶如何被招募至这些基因组位点（genomic loci）并受到调控，目前尚未完全阐明。本研究中，我们鉴定出TET2以及一种此前未被报道的富脯氨酸富丝氨酸蛋白PROSER1，其为增强子相关MLL3/4复合物（MLL3/4 complexes）组分之一UTX的互作蛋白。对PROSER1进行亲和纯化（affinity purification）后，我们成功鉴定出OGT以及TET1-3。我们发现PROSER1可介导OGT与TET2之间的相互作用，进而促进TET2的O-连接N-乙酰葡糖胺糖基化（O-GlcNAcylation）与蛋白质稳定性。此外，PROSER1、UTX、OGT与TET1/2可在全基因组（genome-wide）范围内的众多基因组元件（genomic elements）上共定位（colocalize）。PROSER1缺失会导致UTX与TET1/2在增强子和CpG岛处的富集水平降低，同时伴随DNA甲基化水平升高、相关靶基因的转录下调，以及H3K4单甲基化预倾向的CpG岛上DNA超甲基化侵袭范围扩大。综上，本研究首次报道了一种TET2的O-连接N-乙酰葡糖胺糖基化调控因子，并揭示了其在介导UTX依赖型增强子和CpG岛处DNA去甲基化中的作用。
本研究旨在探究PROSER1缺失是否会影响UTX、TET蛋白、OGT、H3K4单/双/三甲基化以及H3K27乙酰化（H3K27ac）在增强子和CpG岛处的定位情况。