COX6C

COX6C encodes a subunit of mitochondrial Complex IV whose depletion impairs oxidative phosphorylation, lowers ATP and mitochondrial membrane potential, and produces structural mitochondrial defects, thereby constraining cell proliferation (PMID:41502258). Loss of COX6C further impairs mitochondrial fusion and drives ROS accumulation and AMPK pathway activation, which disrupts spindle formation and chromosome segregation, engages the spindle assembly checkpoint, and ultimately causes mitotic arrest and apoptosis in lung adenocarcinoma cells (PMID:38242874). COX6C protein levels are post-transcriptionally restrained by the RNA-binding protein DAZAP1, which loads onto cox6c pre-mRNA in an intron-dependent manner and negatively regulates its splicing; both DAZAP1 knockdown and COX6C overexpression retard cell growth (PMID:29505834). COX6C was also identified as the fusion partner of HMGIC at a 12q15/8q22-23 translocation breakpoint in uterine leiomyoma (PMID:10679920). Beyond these findings, the structural basis of COX6C incorporation into Complex IV has not been characterized in the available corpus.

1. 2000 Medium

   Establishing COX6C as a recurrent rearrangement partner located the gene at a defined chromosomal breakpoint and linked it to a benign tumor through gene fusion rather than through its enzymatic role.

   Evidence 3' RACE and fusion cDNA cloning/sequencing from uterine leiomyoma tissue identifying an HMGIC-COX6C fusion transcript

   PMID:10679920

   Open questions at the time

   • Does not establish whether the fusion alters COX6C function or expression
   • No functional consequence of the fusion protein tested
2. 2018 Medium

   Identifying DAZAP1 as a negative regulator answered how COX6C protein output is controlled post-transcriptionally, revealing intron-dependent splicing suppression as a tuning mechanism with growth consequences.

   Evidence RNA-binding assays comparing genomic vs intronless vectors, DAZAP1 knockdown/overexpression, RT-PCR for pre-mRNA accumulation, and cell growth assays

   PMID:29505834

   Open questions at the time

   • Mechanism by which intron loading impedes splicing not resolved
   • Not independently replicated
   • Physiological contexts where DAZAP1 regulates COX6C unknown
3. 2024 Medium

   Functional depletion studies connected COX6C loss to a defined cascade from mitochondrial dysfunction to mitotic arrest, establishing it as a determinant of cell viability beyond simple bioenergetics.

   Evidence siRNA knockdown in lung adenocarcinoma cells with ROS, AMPK western blot, mitochondrial fusion/morphology, spindle microscopy, cell cycle and apoptosis assays; and siRNA knockdown in multiple myeloma cells with ATP, membrane potential, TEM and proliferation readouts

   PMID:38242874 PMID:41502258

   Open questions at the time

   • Causal ordering of ROS-AMPK-spindle steps relies on correlative pathway readouts
   • Direct demonstration of Complex IV activity loss not provided
   • Single-lab findings per cancer type
4. 2024 Low

   Proteomic and pathway-positioning studies placed COX6C downstream of regulatory signals in disease contexts, framing it as an effector of OXPHOS-dependent phenotypes.

   Evidence siRNA rescue in cardiomyocyte/MI model placing COX6C downstream of methylprotodioscin; and overexpression/knockdown plus xenograft and ChIP placing COX6C downstream of an NHE7-OXPHOS-ER stress axis

   PMID:39321507 PMID:41575611

   Open questions at the time

   • COX6C placement is correlative western-blot/proteomics evidence without reconstitution of its mechanism
   • Direct molecular link between upstream regulators and COX6C activity not demonstrated

• How COX6C assembles into and modulates Complex IV at the structural and biochemical level remains unresolved in the available corpus.
• No structural model of COX6C within Complex IV
• No direct measurement of holoenzyme activity attributable to COX6C
• Regulatory inputs beyond DAZAP1 uncharacterized