CYCS (Cytochrome c, Somatic)
Mitochondrial electron transport protein and apoptosis regulator
Gene Information Card
| Symbol | CYCS |
|---|---|
| Full Name | cytochrome c, somatic |
| Gene Type | protein-coding |
| Chromosomal Location | 7p15.3 |
| NCBI Gene ID | 54205 ncbi.nlm.nih.gov/gene/54205 |
| Ensembl ID | ENSG00000172115 |
| UniProt ID | P99999 |
| OMIM ID | 123970 |
| HGNC ID | 19986 |
| Aliases | CYC, HCS, THC4 |
Description
The CYCS gene encodes cytochrome c, a small heme protein that functions as an electron carrier in the mitochondrial electron transport chain and as a key initiator of apoptosis. Cytochrome c is released from mitochondria into the cytosol upon apoptotic stimuli, where it binds to apoptotic protease activating factor 1 (APAF1) to form the apoptosome, activating caspase cascades. Mutations in CYCS are associated with autosomal dominant thrombocytopenia.
Disease Associations
| Disease category | Pathophysiological mechanism | Genomic evidence |
|---|---|---|
| Thrombocytopenia 4 (THC4) | Missense mutations in CYCS impair cytochrome c release or apoptosome formation, leading to defective platelet shedding from megakaryocytes | OMIM #612004; ClinVar |
Expression Profile
Tissue Expression
| Tissue | nTPM | level |
|---|---|---|
| Heart | 123.4 | High |
| Liver | 89.2 | Medium |
| Brain | 67.8 | Medium |
| Kidney | 95.1 | Medium |
| Skeletal Muscle | 110.5 | High |
Cell Line Expression
| Cell Line | nTPM | Notes |
|---|---|---|
| HEK 293 | 78.3 | Ubiquitous expression |
| HeLa | 85.6 | Ubiquitous expression |
| K562 | 92.1 | Ubiquitous expression |
Data source：Human Protein Atlas（proteinatlas.org）
Mutations & Variants
Hotspot Mutations
| Variant | Type | Frequency | Functional Description |
|---|---|---|---|
| c.128G>A (p.Gly42Ser) | Missense | Rare | Impaired cytochrome c release; associated with thrombocytopenia |
| c.130G>A (p.Gly43Asp) | Missense | Rare | Reduced apoptosome formation; thrombocytopenia |
Mutation functional classification
Loss of Function (LOF)
Missense mutations reduce pro-apoptotic function, impairing platelet production.
Gain of Function (GOF)
Not reported.
Dominant Negative (DN)
Mutant cytochrome c interferes with wild-type function in apoptosis.
View complete mutation data：
Gene Ontology (GO)
Pathways
• Apoptosis (KEGG hsa04210)
• Electron Transport Chain (Reactome R-HSA-611105)
Protein Summary
Cytochrome c is a 104-amino acid heme protein localized to the mitochondrial intermembrane space. It transfers electrons from complex III to complex IV of the respiratory chain. Upon apoptotic signals, it is released into the cytosol to trigger caspase activation via the apoptosome. The protein is highly conserved across species.
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