ARMC6

ARMC6 is an armadillo repeat-containing protein that binds G-quadruplex-forming DNA and RNA structures in vitro, with preferential affinity for RNA G-quadruplexes including the telomeric repeat-containing RNA TERRA and G-quadruplex sequences from cancer gene promoters (EGFR, VEGF, c-MYC) (PMID:39029558). ARMC6 co-precipitates telomerase activity and interacts with the shelterin component TRF2, placing it at the interface of telomere biology (PMID:29948659). ARMC6 is a substrate of the protein histidine methyltransferase METTL9, which generates 1-methylhistidine at HxH motifs within ARMC6, establishing it as a defined target of this post-translational modification (PMID:40451431).

1. 2018 Low

   The first indication that ARMC6 participates in telomere biology came from its co-precipitation with telomerase activity and physical interaction with the shelterin protein TRF2, suggesting it operates in telomere-associated pathways.

   Evidence Co-immunoprecipitation of telomerase activity and in vitro protein–protein interaction assay with human ARMC6 and TRF2

   PMID:29948659

   Open questions at the time

   • Single in vitro pulldown without reciprocal validation or in-cell confirmation
   • No evidence that ARMC6 localizes to telomeres in cells
   • Functional consequence of ARMC6–TRF2 interaction undefined
2. 2024 Medium

   Identification of ARMC6 as a G-quadruplex recognition protein explained a potential molecular basis for its telomeric and gene-regulatory associations, showing it preferentially binds RNA over DNA G-quadruplex structures including TERRA and cancer gene promoter sequences.

   Evidence Electrophoretic mobility shift assays and biochemical binding experiments with recombinant ARMC6 and defined G-quadruplex substrates; overexpression in human cell lines with downstream gene expression analysis

   PMID:39029558

   Open questions at the time

   • In vivo binding targets not mapped (e.g., no CLIP or ChIP-seq)
   • Whether G-quadruplex binding is mediated by the armadillo repeats or another domain is unresolved
   • Physiological consequences of G-quadruplex binding on gene expression or telomere maintenance not established in loss-of-function studies
3. 2025 High

   Demonstration that ARMC6 is methylated at HxH motifs by METTL9 established it as a bona fide substrate of protein histidine methylation, raising the question of whether this modification regulates its G-quadruplex binding or protein interactions.

   Evidence In vitro methyltransferase assay with recombinant METTL9 and ARMC6, mass spectrometric identification of 1-methylhistidine, mutagenesis of HxH motifs

   PMID:40451431

   Open questions at the time

   • Whether ARMC6 is methylated by METTL9 in cells has not been shown
   • Functional impact of histidine methylation on ARMC6 activity, stability, or binding is unknown
   • Stoichiometry of modification in vivo is undefined

• The cellular function of ARMC6 remains poorly defined: it is unclear whether its G-quadruplex binding and telomere-associated interactions reflect a single unified role or distinct activities, and no loss-of-function phenotype has been reported.
• No knockout or knockdown phenotypic data available
• No genome-wide binding profile (ChIP-seq, CLIP) to define in vivo targets
• Relationship between METTL9-mediated methylation and G-quadruplex/telomere functions untested