PROSER1

PROSER1 is a chromatin-associated scaffold protein that bridges O-linked N-acetylglucosamine transferase (OGT) and TET family DNA dioxygenases (TET1/2/3), promoting TET O-GlcNAcylation and stabilization within chromatin-bound TET-OGT-PROSER1-DBHS (TOPD) complexes at enhancers and CpG islands to facilitate DNA demethylation and target gene activation (PMID:34667079, PMID:39562138). Beyond promoting TET-dependent demethylation, PROSER1 sequesters TET enzymes to prevent aberrant genome-wide demethylation and transposable element derepression, revealing a dual positive and negative regulatory role essential for mammalian neurodevelopment (PMID:39562138). In the hematopoietic system, PROSER1 loss partially phenocopies TET2 deficiency at enhancer methylation but causes progressive hematopoietic stem cell exhaustion without recapitulating TET2's tumor-suppressive function (PMID:40554416).

1. 2021 High

   Identifying how TET2 is recruited and stabilized at enhancers was an open question; the discovery that PROSER1 scaffolds the OGT–TET2 interaction established PROSER1 as the missing link coupling O-GlcNAcylation to DNA demethylation at enhancers and CpG islands.

   Evidence Reciprocal co-IP, ChIP-seq/ATAC-seq, PROSER1-KO DNA methylation profiling, and O-GlcNAcylation assays in cell lines

   PMID:34667079

   Open questions at the time

   • Whether PROSER1 interacts with TET family members beyond TET2 was not tested
   • Structural basis of PROSER1 scaffolding between OGT and TET2 is unresolved
   • In vivo organismal consequences of PROSER1 loss were not assessed
2. 2024 High

   Extending the interaction beyond TET2, this work showed PROSER1 engages all three TET enzymes and additionally revealed an unexpected sequestration function—preventing runaway demethylation and transposable element reactivation—thereby reframing PROSER1 as a bidirectional regulator of DNA methylation critical for neurodevelopment.

   Evidence Reciprocal co-IP with TET1/2/3, Proser1-knockout mouse models with DNA methylation profiling, transposable element expression analysis, and developmental phenotyping

   PMID:39562138

   Open questions at the time

   • Molecular determinants that switch PROSER1 from activating to sequestering TET are unknown
   • Whether the neurodevelopmental phenotype maps to specific TET paralogs has not been dissected
   • The role of the DBHS component within TOPD complexes is mechanistically unresolved
3. 2025 Medium

   Testing whether PROSER1's regulatory role extends to adult tissue homeostasis, this study demonstrated that PROSER1 loss causes progressive HSC exhaustion—partially phenocopying TET2-deficient enhancer hypermethylation but without TET2's leukemia-suppressive function—establishing a tissue-specific, non-redundant role for PROSER1.

   Evidence Serial HSC transplantation assays and conditional knockout mouse models with enhancer DNA methylation profiling

   PMID:40554416

   Open questions at the time

   • Single-lab study; independent replication of the HSC exhaustion phenotype is awaited
   • Whether PROSER1 modulates TET1/3 in hematopoietic cells was not addressed
   • Mechanism by which PROSER1 loss leads to HSC exhaustion (beyond methylation) is unexplored

• Key unresolved questions include the structural basis of PROSER1's scaffolding function, the molecular switch governing its dual activating versus sequestering modes, and whether PROSER1 mutations cause a human neurodevelopmental syndrome.
• No structural or biophysical data on PROSER1 or the TOPD complex exist
• Human genetic evidence linking PROSER1 variants to neurodevelopmental disease is lacking in the primary literature
• Whether PROSER1's broader regulation of OGT substrates has phenotypic consequences independent of TET enzymes is untested