RNASEH2C

RNASEH2C is a non-catalytic subunit of the heterotrimeric RNase H2 ribonuclease, where it partners with RNASEH2B to form a soluble B/C sub-complex that nucleates assembly of the active trimer upon addition of the catalytic RNASEH2A subunit (PMID:19015152). Although it lacks catalytic activity itself, RNASEH2C contributes to enzymatic function, as the Aicardi-Goutières syndrome (AGS3)-associated R69W mutation significantly reduces RNase H2 specific activity (PMID:19015152), and the AGS3-causing p.Arg145Leu variant destabilizes the protein and drives its degradation, defining a loss-of-function disease mechanism (PMID:36585007). Independent of its role in the RNase H2 complex, RNASEH2C functions as a regulator of macrophage biology and tumor immunity: in macrophages it promotes lysosomal degradation of the scaffold protein RAI14 via enhanced TRAF3IP1 expression and mTOR suppression, restraining MHC II-mediated antigen presentation and Th1 activation (PMID:41361104), and it acts as a non-enzymatic chromatin-associated factor that binds cyclin-dependent kinase promoters (CDK1/CDK9) to drive macrophage proliferation while fostering an immunosuppressive microenvironment (PMID:41986071). Consistent with an immune-modulatory role, loss of Rnaseh2c reduces breast cancer metastasis through engagement of T cell-mediated adaptive immunity rather than cGAS-STING signaling (PMID:31125342).

1. 2008 High

   Established the architecture of human RNase H2 and defined RNASEH2C's role as a scaffolding subunit, answering how the active enzyme assembles and why RNASEH2C matters despite lacking catalysis.

   Evidence Biochemical reconstitution of the heterotrimer and in vitro activity assays with AGS-associated mutant proteins

   PMID:19015152

   Open questions at the time

   • Structural basis of how RNASEH2C contributes to catalytic activity not resolved
   • Why R69W reduces activity while other AGS mutations are near-normal unexplained
2. 2019 Medium

   Revealed an enzyme-independent role for RNASEH2C in cancer, showing it acts as a metastasis susceptibility factor through adaptive immunity rather than its nuclease function.

   Evidence shRNA knockdown in mouse breast cancer metastasis models with immunophenotyping and RNA-seq

   PMID:31125342

   Open questions at the time

   • Enzymatic independence inferred, not directly tested by reconstitution
   • Molecular target/mechanism linking RNASEH2C to T cell response not identified
3. 2023 Low

   Defined the molecular consequence of a specific AGS3-causing variant, showing it acts by protein destabilization and degradation.

   Evidence In vitro expression of the p.Arg145Leu variant and crystal structure simulation

   PMID:36585007

   Open questions at the time

   • No functional rescue or reconstitution to confirm loss-of-function
   • Computational structural modeling not validated experimentally
4. 2025 Medium

   Connected RNASEH2C to a defined signaling axis in macrophages, showing it suppresses antigen presentation by promoting RAI14 degradation via TRAF3IP1/mTOR.

   Evidence In vitro cell models, mouse tumor models, reciprocal co-IP, immunoblotting, flow cytometry, scRNA-seq

   PMID:41361104

   Open questions at the time

   • Functional rescue not reported
   • Direct physical interaction map among RNASEH2C, TRAF3IP1, and RAI14 incompletely defined
5. 2026 Low

   Proposed a chromatin-associated, non-enzymatic role in which RNASEH2C binds CDK promoters to drive macrophage proliferation and shape an immunosuppressive microenvironment.

   Evidence Single-cell RNA-seq, CUT&Tag, bulk RNA-seq, multiparametric immunofluorescence, flow cytometry, molecular dynamics simulation

   PMID:41986071

   Open questions at the time

   • Chromatin binding claim from CUT&Tag lacks reconstitution or mutagenesis
   • Direct DNA-binding capacity of RNASEH2C not biochemically demonstrated
   • No rescue experiments described

• How RNASEH2C's canonical scaffolding role in the RNase H2 nuclease relates mechanistically to its enzyme-independent functions in macrophage proliferation, chromatin binding, and tumor immunity remains unresolved.
• No structural or biochemical link between the nuclear nuclease role and the immune-regulatory roles
• Whether chromatin/promoter binding is direct and sequence-specific is undetermined
• No reconstitution distinguishing enzymatic from non-enzymatic functions in immune cells