ACTR1A

ACTR1A (alpha-centractin) is a subunit of the dynactin complex that additionally participates in innate immune signaling and is subject to post-translational regulation (PMID:31221720, PMID:41142317). ACTR1A physically associates with TLR2 and is required for TLR2-mediated pro-inflammatory cytokine induction, since its knockdown reduces cytokine output downstream of the receptor (PMID:31221720). ACTR1A is also an in vitro substrate of the SETD3 protein histidine methyltransferase, which methylates recombinant ACTR1A and contacts it in cells, extending SETD3's substrate repertoire beyond beta-actin to this dynactin subunit (PMID:41142317). Beyond these findings, the structural basis of these interactions, the in-cell methylation site, and the link between ACTR1A modification and dynactin function have not been characterized in the available corpus.

1. 2019 Medium

   Established that the dynactin subunit ACTR1A has a role in innate immune signaling by physically engaging TLR2 and being required for downstream cytokine induction, a function not predicted by its cytoskeletal role.

   Evidence Cross-linking co-immunoprecipitation proteomics with biochemical validation and RNAi knockdown read out by pro-inflammatory cytokine induction

   PMID:31221720

   Open questions at the time

   • Reciprocal interaction validated in a single lab; direct vs. indirect binding to TLR2 not resolved
   • Mechanism by which ACTR1A promotes TLR2 signaling (receptor trafficking, scaffolding) not defined
   • No structural or domain-mapping data for the ACTR1A-TLR2 association
2. 2025 Medium

   Identified ACTR1A as a post-translationally modified target by showing it is methylated in vitro by SETD3, raising the possibility that dynactin function is regulated by histidine methylation.

   Evidence TurboID proximity labeling and mass spectrometry, radiochemical in vitro methylation with recombinant SETD3, and CRISPR/Cas9 SETD3 knockout cell lines

   PMID:41142317

   Open questions at the time

   • In vitro methylation only; no in-cell confirmation of the modification or its site
   • Functional consequence of ACTR1A methylation for dynactin or dynein-mediated transport not tested
   • Single-lab finding without independent replication

• How ACTR1A's dynactin/cytoskeletal role, its TLR2-associated signaling function, and its SETD3-dependent methylation are mechanistically connected remains unknown.
• No in-cell methylation site identified
• No structural model of ACTR1A interactions
• No demonstrated effect of methylation on transport or immune signaling