RCCD1

RCCD1 is a multifunctional protein that operates as a substrate and stable partner of the 2-oxoglutarate-dependent oxygenase JMJD5, contributing to genome maintenance, mitochondrial physiology, and cancer cell behavior [PMID:29563586, PMID:bio_10.1101_2025.11.22.689938]. JMJD5 catalyzes stereoselective C-3 hydroxylation of arginine residues within RCCD1-derived sequences, an assignment supported by in vitro reconstitution and high-resolution crystal structures of the enzyme active site (PMID:29563586, PMID:36450832). The two proteins form a hydroxylase complex required to suppress replication stress and genome instability; this complex engages RAD51 paralogues to enable normal replication fork restart, and cancer-associated JMJD5 missense mutations disrupt the JMJD5:RCCD1 interaction while impairing hydroxylase activity [PMID:bio_10.1101_2025.11.22.689938]. Beyond the nucleus, RCCD1 localizes to the mitochondrial matrix, where it associates with the MICOS complex and mtDNA to regulate mtDNA transcription, oxidative phosphorylation, and reactive oxygen species, and is upregulated under hypoxia to limit ROS and apoptosis (PMID:37903896). In the cytoplasm, RCCD1 destabilizes microtubules through its interaction with JMJD5, reducing acetylated alpha-tubulin and promoting TGF-beta-induced EMT and cell migration (PMID:28455245). RCCD1 transcription is driven by E2F1 binding to its promoter, and its expression promotes proliferation, migration, and invasion across breast, colorectal, and colon cancer models, including a cancer-associated-fibroblast program in which RCCD1 activates AMPK/mTOR/ULK1 autophagy to drive WNT5A secretion (PMID:37903896, PMID:39024731, PMID:41798776).

1. 2017 Medium

   Established the first cellular function for RCCD1, showing it controls microtubule dynamics and TGF-beta-driven EMT through a physical link to JMJD5.

   Evidence siRNA knockdown in NSCLC cells with Western blot for acetylated alpha-tubulin and EMT markers, migration assays, and RCCD1-JMJD5 co-immunoprecipitation

   PMID:28455245

   Open questions at the time

   • Does not establish whether the JMJD5-RCCD1 interaction acts via hydroxylation in this context
   • Direct molecular link between RCCD1 and tubulin acetylation enzymes not defined
   • Single lab, single cell-type context
2. 2018 High

   Defined RCCD1 biochemically as a substrate of JMJD5, reassigning JMJD5 as an arginine C-3 hydroxylase rather than a histone demethylase.

   Evidence In vitro peptide hydroxylation assays with JMJD5 and high-resolution crystallography of the JMJD5 active site with substrate peptides

   PMID:29563586

   Open questions at the time

   • Hydroxylation demonstrated on peptides, not full-length RCCD1 in cells
   • Functional consequence of RCCD1 arginine hydroxylation not determined
   • Identity of the modified arginine residue's downstream role unknown
3. 2022 High

   Reinforced the protein-hydroxylase model by detailing the JMJD5 cofactor-binding pocket acting on RCCD1-derived sequences.

   Evidence X-ray crystallography of JMJD5 with 2-oxoglutarate analogues

   PMID:36450832

   Open questions at the time

   • Structural work centers on JMJD5; no structure of the RCCD1 complex
   • Does not address cellular regulation of the hydroxylation reaction
4. 2023 Medium

   Revealed an unexpected mitochondrial role for RCCD1, placing it in the matrix in association with MICOS and mtDNA to regulate respiration and ROS under hypoxia.

   Evidence Subcellular fractionation, co-IP with MICOS components, mtDNA transcription and ROS/apoptosis assays, and breast cancer proliferation/xenograft models

   PMID:37903896

   Open questions at the time

   • Mechanism by which RCCD1 enters and acts in the matrix is undefined
   • Whether JMJD5 hydroxylation governs mitochondrial RCCD1 function unknown
   • Single lab
5. 2024 Medium

   Identified the upstream transcriptional control of RCCD1, showing E2F1 directly drives its expression to promote EMT and tumor cell aggressiveness.

   Evidence DNA pull-down and dual-luciferase promoter assays, plus proliferation, wound-healing, and invasion assays in colorectal cancer cells

   PMID:39024731

   Open questions at the time

   • Does not connect E2F1-driven expression to any specific RCCD1 molecular activity
   • Single lab
6. 2025 Medium

   Demonstrated that the JMJD5:RCCD1 complex safeguards genome stability by enabling replication fork restart via RAD51 paralogues, and that cancer mutations in JMJD5 break this complex.

   Evidence Structural analysis of cancer missense mutations, in vitro hydroxylase assays, co-IP of JMJD5:RCCD1 and RAD51 paralogues, and DNA fiber replication fork restart assays (preprint)

   PMID:bio_10.1101_2025.11.22.689938

   Open questions at the time

   • Preprint, not yet peer-reviewed
   • Whether RAD51 paralogue interaction is direct or hydroxylation-dependent unresolved
   • Mechanistic role of RCCD1 hydroxylation in fork restart not isolated
7. 2026 Medium

   Extended RCCD1's tumor-promoting role to the stroma, showing it drives autophagy-dependent WNT5A secretion from cancer-associated fibroblasts to activate Wnt signaling in tumor cells.

   Evidence CAF/tumor coculture, single-cell RNA-seq, AMPK/mTOR/ULK1 pathway Western blots, autophagy inhibition and WNT5A neutralization rescue, and clinical sample validation

   PMID:41798776

   Open questions at the time

   • How RCCD1 engages AMPK/mTOR/ULK1 mechanistically is undefined
   • Relationship to RCCD1's nuclear and mitochondrial functions unclear
   • Single study

• It remains unknown how RCCD1's distinct nuclear (replication/genome stability), mitochondrial (OXPHOS/ROS), and cytoplasmic (microtubule/EMT) activities are coordinated, and whether JMJD5-mediated arginine hydroxylation regulates each of these roles.
• No demonstrated functional consequence of RCCD1 arginine hydroxylation in cells
• No unified model linking the three subcellular localizations
• No structural model of the full-length JMJD5:RCCD1 complex