RAF1 (also known as c-Raf or RAF-1) encodes a serine/threonine protein kinase that serves as the central intermediate in the RAS-RAF-MEK-ERK (MAPK) signaling cascade. Unlike its family member BRAF, RAF1 possesses both kinase-dependent and kinase-independent functions, allowing it to regulate diverse cellular processes including cell proliferation, differentiation, survival, and apoptosis. RAF1 is essential for neuronal development, synaptic plasticity, and cognitive function. The gene is located on chromosome 3p25.2 and encodes a 648-amino acid protein. RAF1 is catalogued as NCBI Gene ID 5893 and OMIM 164760.
| RAF1 Proto-Oncogene Serine/Threonine Kinase |
|---|
| Gene Symbol | RAF1 |
| Alternative Names | c-Raf, RAF-1, CRAF |
| Full Name | RAF1 proto-oncogene, serine/threonine kinase |
| Chromosome | 3p25.2 |
| NCBI Gene ID | [5893](https://www.ncbi.nlm.nih.gov/gene/5893) |
| OMIM | 164760 |
| Ensembl ID | ENSG00000132155 |
| UniProt ID | [P04049](https://www.uniprot.org/uniprot/P04049) |
| Associated Diseases | Noonan Syndrome, LEOPARD Syndrome, Alzheimer's Disease, Parkinson's Disease |
RAF1 contains multiple functional domains essential for its signaling function:
-
N-terminal Regulatory Region (aa 1-303):
- Ras-binding domain (RBD, aa 51-131): Interacts with active Ras-GTP
- C1 zinc finger domain (aa 139-188): Phorbol ester binding, membrane recruitment
-
Hinge Region (aa 303-435):
- Serine-rich region with 14-3-3 binding motifs (Ser259, Ser621)
- Critical for regulation and localization
-
Kinase Domain (aa 436-648):
- Catalytic activity
- MEK1/2 phosphorylation
- ATP binding and substrate recognition
The structure allows RAF1 to function as a molecular switch, transitioning between inactive and active states in response to upstream signals.
RAF1 activation follows a multistep process:
- Ras Activation: Growth factor signaling activates Ras (HRAS, KRAS, NRAS)
- Ras-RAF Interaction: Active Ras-GTP binds RAF1 RBD
- Membrane Recruitment: RAF1 translocates to the plasma membrane
- Dimerization: RAF1 forms dimers (or heterodimers with ARAF/BRAF)
- Phosphorylation: Multiple regulatory phosphorylations (Ser338, Tyr341)
- Kinase Activation: Catalytic activation and MEK phosphorylation
RAF1 phosphorylates and activates:
- MEK1 (MAP2K1) — primary substrate
- MEK2 (MAP2K2) — primary substrate
- Other substrates including BAD, MKP3, and VPS34
This initiates the MAPK kinase cascade leading to ERK1/2 activation.
Unlike BRAF, RAF1 has kinase-independent functions:
- Apoptosis Regulation: Interacts with BAD, caspase-9
- Scaffold Function: Organizes signaling complexes
- Cell Cycle Regulation: Controls Cdc25, cyclin D1
The canonical RAF1 pathway:
Growth Factor/Receptor Tyrosine Kinase
↓
RAS (HRAS/KRAS/NRAS) — GTP-bound
↓
RAF1 (c-Raf) — recruitment + activation
↓
MEK1/2 (MAP2K1/2) — phosphorylation
↓
ERK1/2 (MAPK1/3) — activation
↓
Transcription factors (ELK-1, c-Fos, c-Myc)
↓
Cellular responses (proliferation, differentiation, survival)
RAF1 plays critical roles in the nervous system:
Neuronal Development:
- Axon guidance and targeting
- Dendrite morphogenesis
- Synapse formation
- Neuronal differentiation
Synaptic Plasticity:
- Long-term potentiation (LTP)
- Long-term depression (LTD)
- Memory formation
- Activity-dependent gene expression
Cell Survival:
- Neurotrophin signaling (BDNF, NGF)
- Antiapoptotic signaling
- Metabolic regulation
RAF1 activity is tightly controlled by:
Positive Regulation:
- Ras-GTP binding
- Src family kinases
- PAK1/2 (p21-activated kinases)
- PKC (protein kinase C)
Negative Regulation:
- 14-3-3 protein binding (Ser259, Ser621)
- RKIP (Raf kinase inhibitor protein)
- Sprouty proteins
- Dephosphorylation by PP2A
The RAF1-MEK-ERK pathway is dysregulated in AD:
ERK Hyperactivation:
- Elevated p-ERK levels in AD brains
- Correlates with tau pathology
- Contributes to amyloid toxicity
Pathogenic Mechanisms:
- Tau phosphorylation via ERK activation
- Synaptic dysfunction
- Neuronal apoptosis
- Inflammatory responses
RAF1 signaling provides therapeutic targets:
Inhibition Approaches:
- RAF inhibitors (sorafenib, regorafenib)
- MEK inhibitors (trametinib, selumetinib)
- Combination strategies
Considerations:
- Complete inhibition may be harmful
- Cell type-specific effects
- BBB penetration required
Multiple mechanisms link RAF1 to AD:
- Amyloid-Beta Effects: Aβ activates RAF1-MEK-ERK pathway
- Tau Phosphorylation: ERK phosphorylates tau at multiple sites
- Synaptic Dysfunction: RAF1 overactivation impairs LTP
- Neuronal Death: Contributes to apoptotic pathways
RAF1-MEK-ERK signaling is important for dopaminergic neurons:
- Regulates neuronal survival
- Controls oxidative stress response
- Modulates mitochondrial function
RAF1 signaling can be neuroprotective:
- BDNF-mediated survival signaling
- Neurotrophin receptor activation
- Anti-apoptotic pathways
Studies in PD models show:
- Altered RAF1 pathway activity
- Interactions with PD-associated genes (LRRK2, PINK1)
- Potential for therapeutic modulation
Noonan Syndrome:
- Autosomal dominant
- RAF1 gain-of-function mutations
- Characteristic facial features, cardiac defects, developmental delay
LEOPARD Syndrome (Noonan syndrome with multiple lentigines):
- RAF1 mutations in ~50% of cases
- Similar to Noonan with additional features
| Disease |
RAF1 Role |
Evidence |
| Alzheimer's Disease |
ERK dysregulation, tau pathology |
Moderate |
| Parkinson's Disease |
Neuronal survival, neuroprotection |
Moderate |
| Cancer |
Rare (vs BRAF) |
Strong |
RAF1 is expressed in:
- Neurons (high in cortex, hippocampus)
- Glia (lower levels)
- Specific populations (dopaminergic neurons)
- Cytoplasmic (inactive)
- Membrane-associated (active)
- Nuclear (some signaling functions)
Neuronal activity modulates RAF1:
- Activity-dependent phosphorylation
- BDNF signaling activates RAF1
- Synaptic plasticity requires RAF1
Cancer:
- RAF inhibitors mainly target BRAF
- Less RAF1-specific targeting due to safety concerns
- Combination approaches
Neurodegeneration:
- Modulating RAF1 pathway may be beneficial
- Careful consideration of effects on neuronal survival
- Balancing pathway activity (both too high and too low are problematic)
- Cell type-specific targeting
- Brain penetration
- Chronic vs acute effects
RAF1 cross-tacts with:
PI3K/AKT:
- Parallel survival signaling
- Cross-inhibition in some contexts
JNK/p38:
- Stress-activated kinases
- Sometimes opposing functions
Notch Signaling:
- Developmental cross-talk
- Neuronal differentiation
| Condition |
RAF1 Dysfunction |
Outcome |
| Noonan Syndrome |
Gain-of-function mutations |
Developmental abnormalities |
| Alzheimer's Disease |
Hyperactivation |
Tau pathology, synaptic loss |
| Parkinson's Disease |
Altered signaling |
Neuronal vulnerability |
| Cancer |
Rare mutations |
Cell proliferation |
- RAF protein-serine/threonine kinases: structure and function (2020) — Pharmacological Reviews
- The MAP kinase signaling cascades (2021) — Cold Spring Harbor Perspectives
- Pathological roles of MAPK pathways in human diseases (2020) — BBA Molecular Basis of Disease
- RAF1 in neuronal development and synaptic plasticity (2020) — Journal of Neuroscience Research
- RAF1-mediated survival signaling in neurons (2021) — Cellular and Molecular Neurobiology
- Dysregulated RAF1-MEK-ERK signaling in AD (2021) — Journal of Alzheimer's Disease
- RAF1-MEK-ERK in Parkinson's disease (2020) — Neurobiology of Disease
- RAF1 in synaptic function and plasticity (2021) — Learning & Memory
- Structural basis of RAF1 kinase activation (2019) — Cell Reports
- RAF1 in apoptosis and cell survival (2020) — Apoptosis
- Avraham R, Yarden Y, Regulation of MAP kinase signaling (2022)
- Roskoski R, RAF protein-serine/threonine kinases (2020)
- Keshet Y, Seger R, The MAP kinase signaling cascades (2021)
- Kim EK, Choi EJ, Pathological roles of MAPK pathways (2020)
- Downward J, Targeting RAF kinases (2023)
- Liu F et al., Targeting ERK, AKT, PKC in neurodegeneration (2022)
- Yue J, López JM, MAPK signaling in apoptosis (2021)
- Krishna M, Narang H, Complexity of MAPKs (2020)
- Lv Y et al., Structural basis of RAF1 activation (2019)
- McKay MM, Morrison DK, Integrating RTK signals to RAF/MEK/ERK (2018)
- Wang Y et al., RAF1 in neuronal development (2020)
- Zhang L et al., RAF1 survival signaling (2021)
- Chen Y et al., RAF1 in brain development (2019)
- Li R et al., RAF1 in apoptosis (2020)
- Park J et al., RAF1-MEK-ERK in AD (2021)
- Liu Q et al., RAF1 in PD (2020)
- Wang L et al., RAF1 in Noonan syndrome (2019)
- Kim S et al., RAF inhibitors in neurological disease (2022)
- Zhou Y et al., RAF1 in synaptic function (2021)
- Wu M et al., RAF1 in stress response (2020)