PROSER1

PROSER1 is a chromatin-associated scaffolding protein that couples O-GlcNAc signaling to TET-mediated DNA demethylation at regulatory elements (PMID:34667079, PMID:39562138). It physically bridges OGT to TET2, mediating TET2 O-GlcNAcylation and stabilizing TET2 protein, and more broadly regulates OGT-dependent O-GlcNAcylation of chromatin-associated proteins (PMID:34667079). PROSER1 interacts with all three TET enzymes and with UTX (a component of the MLL3/4 enhancer-associated complexes), assembling chromatin-bound TET-OGT-PROSER1-DBHS (TOPD) complexes (PMID:34667079, PMID:39562138); its loss reduces recruitment of UTX, TET1/2, and OGT to enhancers and CpG islands, causing DNA hypermethylation and transcriptional downregulation of target genes (PMID:34667079). PROSER1 acts as a dual regulator of demethylation, both supporting TET activity and sequestering TET enzymes to restrain widespread demethylation and transposable element derepression (PMID:39562138). In hematopoiesis, PROSER1 loss partially phenocopies the enhancer hypermethylation of TET2 knockout and drives progressive exhaustion of hematopoietic stem cell self-renewal, yet TET2's leukemia-suppressive function is preserved without PROSER1, marking cooperative but separable roles (PMID:40554416).

1. 2021 High

   Establishing that PROSER1 is a physical scaffold linking the O-GlcNAc machinery to TET and MLL3/4 demethylation/activation activities answered how these enzymes are co-recruited to chromatin.

   Evidence Reciprocal co-immunoprecipitation identifying TET2, OGT, and UTX as interactors

   PMID:34667079

   Open questions at the time

   • Stoichiometry and architecture of the complex not resolved
   • Direct vs. indirect nature of each contact not fully dissected
2. 2021 High

   Defining PROSER1 as the bridge that delivers OGT to TET2 explained how TET2 is O-GlcNAcylated and stabilized, linking PROSER1 to TET2 protein homeostasis.

   Evidence PROSER1 knockout with western-blot readout of TET2 O-GlcNAcylation and protein levels

   PMID:34667079

   Open questions at the time

   • O-GlcNAc site(s) on TET2 not mapped
   • Whether stabilization is solely O-GlcNAc-dependent unclear
3. 2021 High

   Genome-wide profiling showed PROSER1 is required for enhancer/CpG-island recruitment of the demethylation machinery, establishing its functional consequence for DNA methylation and gene expression.

   Evidence ChIP-seq and genome-wide DNA methylation analysis in knockout cells

   PMID:34667079

   Open questions at the time

   • Direct vs. secondary effects on individual loci not separated
4. 2021 Medium

   Profiling chromatin O-GlcNAcylation beyond TET2 positioned PROSER1 as a broader regulator of OGT activity on chromatin proteins.

   Evidence O-GlcNAcylation profiling of chromatin proteins in PROSER1 knockout

   PMID:34667079

   Open questions at the time

   • Single lab, single method; broader claim not independently replicated
   • Specific additional substrates not enumerated
5. 2024 High

   Demonstrating interaction with all three TET enzymes and defining the chromatin-bound TOPD complex generalized PROSER1's role across the TET family.

   Evidence Co-immunoprecipitation, chromatin fractionation, and complex characterization

   PMID:39562138

   Open questions at the time

   • Whether TET1/TET3 are O-GlcNAcylated like TET2 not established
   • DBHS subunit contribution to complex function unclear
6. 2024 High

   In vivo loss-of-function revealed PROSER1 is a dual regulator that both promotes and restrains demethylation, resolving how excess demethylation and transposable element derepression are prevented.

   Evidence Loss-of-function mouse models with genome-wide methylation sequencing and transposable element expression assays

   PMID:39562138

   Open questions at the time

   • Molecular switch between positive and negative modes not defined
   • Locus determinants of sequestration vs. activation unknown
7. 2025 Medium

   Comparing PROSER1 and TET2 knockouts in hematopoietic cells placed PROSER1 in the TET2 demethylation pathway while revealing non-overlapping functions.

   Evidence PROSER1 knockout mouse with enhancer DNA methylation profiling compared to TET2 knockout

   PMID:40554416

   Open questions at the time

   • Single lab, not independently replicated
   • Basis of distinct (non-shared) methylation effects not defined
8. 2025 Medium

   Serial transplantation defined a physiological requirement for PROSER1 in hematopoietic stem cell self-renewal.

   Evidence Serial HSC transplantation assays in PROSER1 knockout mice

   PMID:40554416

   Open questions at the time

   • Molecular link between methylation changes and HSC exhaustion not established
   • Single lab, no independent replication
9. 2025 Medium

   Showing TET2's tumor-suppressive role persists without PROSER1 separated PROSER1's self-renewal function from TET2-mediated leukemia suppression.

   Evidence PROSER1 knockout mouse assessed for hematological malignancy (negative result)

   PMID:40554416

   Open questions at the time

   • Which TET2 functions are PROSER1-independent not mechanistically dissected
   • Negative result from single model

• The molecular determinants that toggle PROSER1 between promoting TET recruitment and sequestering TET to limit demethylation, and how this connects to HSC self-renewal, remain unresolved.
• No structural model of the TOPD complex
• Switch mechanism between activating and sequestering modes undefined
• Causal chain from methylation defects to stem cell exhaustion not established