STK4 — Serine/Threonine Kinase 4
<div class="infobox infobox-gene">
<h3>STK4</h3>
<table>
<tr><td><strong>Gene Symbol</strong></td><td>STK4 (MST1)</td></tr>
<tr><td><strong>Full Name</strong></td><td>Serine/Threonine Kinase 4</td></tr>
<tr><td><strong>Chromosomal Location</strong></td><td>20q13.12</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>6789</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000101109</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>Q13043</td></tr>
<tr><td><strong>OMIM ID</strong></td><td>604472</td></tr>
<tr><td><strong>Protein Family</strong></td><td>STE20 family, Hippo pathway</td></tr>
<tr><td><strong>Aliases</strong></td><td>MST1, KRS2</td></tr>
<tr><td><strong>Protein Length</strong></td><td>491 amino acids</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Parkinson's Disease, Alzheimer's Disease, ALS, Cancer, Neurodevelopmental Disorders</td></tr>
</table>
</div>
Overview
flowchart TD
STK4["STK4"] -->|"activates"| Anxiety["Anxiety"]
STK4["STK4"] -->|"regulates"| Ms["Ms"]
STK4["STK4"] -->|"activates"| Depression["Depression"]
DNAJB12["DNAJB12"] -->|"regulates"| STK4["STK4"]
RB1CC1["RB1CC1"] -->|"regulates"| STK4["STK4"]
SCN4B["SCN4B"] -->|"regulates"| STK4["STK4"]
style STK4 fill:#4fc3f7,stroke:#333,color:#000
...STK4 — Serine/Threonine Kinase 4
<div class="infobox infobox-gene">
<h3>STK4</h3>
<table>
<tr><td><strong>Gene Symbol</strong></td><td>STK4 (MST1)</td></tr>
<tr><td><strong>Full Name</strong></td><td>Serine/Threonine Kinase 4</td></tr>
<tr><td><strong>Chromosomal Location</strong></td><td>20q13.12</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>6789</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000101109</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>Q13043</td></tr>
<tr><td><strong>OMIM ID</strong></td><td>604472</td></tr>
<tr><td><strong>Protein Family</strong></td><td>STE20 family, Hippo pathway</td></tr>
<tr><td><strong>Aliases</strong></td><td>MST1, KRS2</td></tr>
<tr><td><strong>Protein Length</strong></td><td>491 amino acids</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Parkinson's Disease, Alzheimer's Disease, ALS, Cancer, Neurodevelopmental Disorders</td></tr>
</table>
</div>
Overview
Mermaid diagram (expand to render)
STK4 (Serine/Threonine Kinase 4), also known as MST1 (Mammalian Ste20-like Kinase 1), is a critical component of the Hippo signaling pathway. Located on chromosome 20q13.12, this gene encodes a serine/threonine kinase that plays essential roles in organ size control, cell proliferation, [apoptosis](/mechanisms/apoptosis-pathways), stem cell self-renewal, and neuronal survival. STK4 has emerged as a significant player in neurodegeneration, with dysregulated activity implicated in Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS). The kinase functions as both a tumor suppressor in peripheral tissues and a pro-apoptotic regulator in the nervous system [@stk4_hippo_pathway][@stk4_mst1_function].
Protein Structure and Function
Domain Architecture
STK4 contains several functional domains [@stk4_hippo_pathway]:
- N-terminal kinase domain: Catalytic serine/threonine kinase activity (~300 amino acids)
- C-terminal regulatory domain: Contains autoinhibitory sequences
- Scaffold interaction region: Bins to SAV1 and other pathway components
Hippo Signaling Pathway
STK4 (MST1) is the founding member of the MST1/2 (STE20-like kinases 1 and 2) family. Within the Hippo pathway, STK4 functions as the upstream kinase that initiates the cascade [@stk4_hippo_yap_taz]:
Activation — STK4 is activated by autophosphorylation and phosphorylation by upstream kinases
Complex formation — STK4 forms a heterodimer with STK3 (MST2) and associates with SAV1 (Salvador)
Downstream phosphorylation — Activated STK4 phosphorylates LATS1/2 kinases
YAP/TAZ inhibition — LATS1/2 phosphorylate YAP/TAZ, preventing their nuclear translocationPro-Apoptotic Functions
Beyond its role in the Hippo pathway, STK4 has direct pro-apoptotic functions [@stk4_apoptosis_caspase][@stk4_foxo_neurons]:
- Caspase activation: Direct phosphorylation of caspase-3 and caspase-9
- FOXO transcription factors: Phosphorylates FOXO1/FOXO3a, promoting nuclear translocation and transcriptional activation of pro-apoptotic genes
- BIM activation: Upregulates pro-apoptotic BIM protein
- Mitochondrial pathway: Promotes cytochrome c release
Expression Pattern
Brain Expression
STK4 is expressed throughout the central nervous system [@stk4_hippo_brain]:
- Hippocampus: High expression in CA1-CA3 regions and dentate gyrus
- Cortex: Pyramidal neurons in layers II-VI
- Cerebellum: Purkinje cells and granule cells
- Substantia nigra: Moderate expression in dopaminergic neurons
- Subventricular zone: Neural stem cells
- Cell types: Neurons, [astrocytes](/cell-types/astrocytes), and neural progenitor cells
Tissue Distribution
| Region | Expression Level | Cell Types |
|--------|-----------------|-------------|
| [Hippocampus](/brain-regions/hippocampus) | High | Pyramidal neurons, granule cells |
| [Cortex](/brain-regions/cortex) | High | Pyramidal neurons, interneurons |
| Cerebellum | High | Purkinje cells |
| [Substantia nigra](/brain-regions/substantia-nigra) | Moderate | Dopaminergic neurons |
| Spinal cord | Moderate | Motor neurons |
Beyond the brain, STK4 is expressed in:
- Heart: High cardiac expression
- Liver: Hepatocytes
- Immune system: T lymphocytes and other immune cells
Role in Neurodegeneration
Alzheimer's Disease
STK4 activation contributes to AD pathogenesis through multiple mechanisms [@chow2017][@ardestani2019]:
Apoptotic neuron loss: STK4 promotes apoptosis in hippocampal neurons
Tau pathology: STK4 affects tau phosphorylation through cross-talk with other kinases
Synaptic dysfunction: STK4 activation leads to synaptic loss
Amyloid toxicity: Aβ-induced STK4 activation amplifies neuronal deathThe kinase is activated in AD brain tissue, and inhibition of STK4 has shown neuroprotective effects in cellular models.
Parkinson's Disease
In PD, STK4 plays several roles [@yuan2018][@ma2020][@stk4_parkinson]:
Dopaminergic neuron survival: STK4 promotes apoptosis of [dopamine](/entities/dopamine) neurons
Alpha-synuclein toxicity: STK4 is activated by α-synuclein aggregates
Mitochondrial dysfunction: STK4 contributes to mitochondrial apoptosis
Neuroinflammation: STK4 activation in glial cells promotes inflammationSTK4 inhibition has demonstrated protective effects in PD models, suggesting therapeutic potential.
Amyotrophic Lateral Sclerosis (ALS)
STK4 dysregulation in ALS includes [@pantovic2018]:
Motor neuron apoptosis: Accelerated STK4-mediated cell death
TDP-43 pathology: Interaction between STK4 and TDP-43 aggregates
Axonal degeneration: STK4 promotes axonal retraction and degeneration
Glial involvement: Activated STK4 in astrocytes and microgliaMolecular Mechanisms
STK4 Activation in Neurodegeneration
│
├──► Stress Signals
│ ├──► Oxidative stress
│ ├──► ER stress
│ ├──► Mitochondrial dysfunction
│ └──► Protein aggregates
│
├──► Apoptotic Cascade
│ ├──► Caspase activation
│ ├──► FOXO phosphorylation
│ ├──► Mitochondrial permeabilization
│ └──► Cell death
│
└──► Synaptic Dysfunction
├──► Synaptic protein loss
├──► Dendritic spine reduction
└──► Neural connectivity impairment
Disease Associations
Cancer
STK4 functions as a tumor suppressor [@stk4_therapeutic]:
- Loss of STK4 promotes uncontrolled cell growth and tumor formation
- STK4 mutations are found in various cancers
- YAP/TAZ overactivation due to Hippo pathway inactivation promotes oncogenesis
Neurodevelopmental Disorders
Biallelic STK4 mutations cause:
- Autosomal recessive immunodeficiency 38 — combined immunodeficiency
- Neurodevelopmental abnormalities — developmental delay, intellectual disability
- Growth retardation — impaired somatic growth
Other Neurodegenerative Conditions
- Stroke — MST1 mediates ischemic neuronal injury [@huang2020]
Therapeutic Implications
Small Molecule Inhibitors
- STK4 inhibitors: Pharmacological inhibition of kinase activity
- Caspase inhibitors: Downstream blockade of apoptotic pathway
- FOXO modulators: Prevent nuclear translocation of pro-apoptotic factors
Gene Therapy Approaches
- RNAi knockdown: Reduce STK4 expression
- ASO therapy: Antisense oligonucleotides targeting STK4
- CRISPR inhibition: CRISPRa to suppress STK4 transcription
Neuroprotective Strategies
- Antioxidants: Counteract oxidative stress that activates STK4
- Autophagy enhancers: Clear protein aggregates reducing STK4 activation
- Neurotrophic factors: Promote neuronal survival independent of STK4
Interactions and Pathways
Protein Interactions
STK4 interacts with several key proteins:
- SAV1: Scaffold protein, forms functional complex
- STK3 (MST2): Kinase partner, forms heterodimer
- LATS1/2: Downstream kinases, phosphorylation targets
- FOXO1/3: Transcription factors, phosphorylation substrates
- Caspase-3/9: Executioner caspases, direct targets
Signaling Cross-talk
STK4 activity is modulated by multiple pathways:
- PI3K/AKT: AKT phosphorylates and inhibits STK4
- MAPK pathways: Cross-talk with stress-activated kinases
- Wnt/β-catenin: Interaction with developmental pathways
- Notch signaling: Coordinate regulation of neural stem cells
Animal Models
Mouse Models
- Stk4 knockout: Viable but with increased tumor susceptibility
- Conditional knockouts: Brain-specific deletion for neurodegeneration studies
- Transgenic models: Overexpression of activated STK4
Research Applications
- Kinase inhibitor testing
- Pathway validation in vivo
- Therapeutic intervention studies
Biomarkers
STK4 activation (phosphorylated MST1) serves as a biomarker for:
- Neurodegenerative disease progression
- Cancer prognosis
- Treatment response to neuroprotective agents
STK4 in Neuroinflammation
STK4 plays a significant role in neuroinflammatory processes:
Glial Cell Activation
- Microglia: STK4 activation promotes microglial activation and pro-inflammatory cytokine release
- Astrocytes: STK4 modulates astrocyte reactivity in neurodegenerative conditions
- Inflammatory response: STK4 contributes to chronic neuroinflammation
Cytokine Regulation
STK4 affects production of:
- TNF-α
- IL-1β
- IL-6
- Chemokines
Therapeutic Implications
Targeting STK4 in neuroinflammation:
- Reduces glial activation
- Decreases cytokine production
- May slow disease progression
STK4 in Synaptic Plasticity
STK4 regulates synaptic function and plasticity:
Dendritic Spine Dynamics
- STK4 activation reduces spine density
- Affects synaptic stability
- Impairs learning and memory
Long-term Potentiation
- STK4 interferes with LTP formation
- Affects AMPA receptor trafficking
- Impairs synaptic strengthening
- STK4 activation in hippocampus impairs memory
- Inhibits CREB activation
- Affects immediate early gene expression
STK4 and Mitochondrial Dynamics
STK4 directly impacts mitochondrial function:
Mitophagy Regulation
- STK4 promotes PINK1/Parkin-independent mitophagy
- Affects mitochondrial quality control
- Contributes to neuronal energy deficits
Mitochondrial Apoptosis
- STK4 promotes mitochondrial outer membrane permeabilization
- Enhances cytochrome c release
- Activates intrinsic apoptotic pathway
Bioenergetics
- STK4 reduces ATP production
- Impairs mitochondrial membrane potential
- Contributes to metabolic dysfunction
Research Techniques
Kinase Activity Assays
- In vitro kinase assays with recombinant STK4
- Phospho-antibody detection of p-STK4
- ATP-based activity measurements
Interaction Studies
- Co-immunoprecipitation
- Yeast two-hybrid screening
- Mass spectrometry proteomics
Animal Models
- Stk4 knockout mice
- Conditional brain-specific knockouts
- Transgenic overexpression models
STK4 in Brain Development
During development, STK4 plays important roles:
Neural Progenitor Cells
- Regulates proliferation of neural stem cells
- Controls cell cycle exit
- Affects differentiation decisions
Neuronal Migration
- Modulates neuronal positioning
- Affects cortical layering
- Contributes to proper brain architecture
Axon Guidance
- STK4 influences axon pathfinding
- Regulates growth cone dynamics
- Affects circuit formation
Cross-Links
- [STK3](/genes/stk3) — MST2, paralog
- [YAP1](/genes/yap1) — Downstream effector
- [LATS1](/genes/lats1) — Downstream kinase
- [TAZ](/genes/taz) — YAP partner
- [Hippo Signaling Pathway](/mechanisms/hippo-signaling-pathway)
- [Apoptosis Pathways](/mechanisms/apoptosis-pathways)
- [FoxO Transcription Factors](/mechanisms/foxo-transcription-factors)
- [Neuroinflammation](/mechanisms/neuroinflammation)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
See Also
- [Hippo Signaling Pathway](/mechanisms/hippo-signaling-pathway)
- [YAP1](/genes/yap1)
- [LATS1](/genes/lats1)
- [STK3](/genes/stk3)
- [Apoptosis Pathways](/mechanisms/apoptosis-pathways)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [FoxO Transcription Factors](/mechanisms/foxo-transcription-factors)
- [Dopaminergic Neurons](/cell-types/dopamine-neurons-drd)
External Links
- [NCBI Gene: STK4](https://www.ncbi.nlm.nih.gov/gene/6789)
- [OMIM: STK4](https://www.omim.org/entry/604472)
- [Ensembl: STK4](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000101109)
- [UniProt: STK4](https://www.uniprot.org/uniprot/Q13043)
- [GeneCards: STK4](https://www.genecards.org/cgi-bin/carddisp.pl?gene=STK4)
References
[The Hippo pathway in organ size control and cancer (2013)](https://pubmed.ncbi.nlm.nih.gov/23376971/)
[MST1/STK4 functions in cell proliferation and apoptosis (2006)](https://pubmed.ncbi.nlm.nih.gov/16452207/)
[MST1 promotes neuronal apoptosis through FoxO1 phosphorylation (2009)](https://pubmed.ncbi.nlm.nih.gov/19513069/)
[Hippo pathway regulation of YAP/TAZ in cancer (2013)](https://pubmed.ncbi.nlm.nih.gov/23273996/)
[MST1/2 in stem cell biology and organ size control (2013)](https://pubmed.ncbi.nlm.nih.gov/23527165/)
[Hippo pathway regulates autophagy in cancer (2015)](https://pubmed.ncbi.nlm.nih.gov/26027639/)
[MST1 activation of caspase-dependent apoptosis (2007)](https://pubmed.ncbi.nlm.nih.gov/17446862/)
[FoxO transcription factors in neuronal health and disease (2009)](https://pubmed.ncbi.nlm.nih.gov/19240134/)
[Control of organ size by the Hippo pathway (2006)](https://pubmed.ncbi.nlm.nih.gov/16510871/)
[Cross-talk between Hippo and Wnt signaling pathways (2014)](https://pubmed.ncbi.nlm.nih.gov/24439957/)
[Hippo pathway in neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/31346942/)
[MST1 activation in dopaminergic neurons in Parkinson's disease models (2018)](https://pubmed.ncbi.nlm.nih.gov/29507046/)
[Hippo signaling in neural development and disease (2017)](https://pubmed.ncbi.nlm.nih.gov/28958679/)
[SAV1 forms a complex with MST1 to regulate Hippo signaling (2007)](https://pubmed.ncbi.nlm.nih.gov/17277771/)
[Targeting the Hippo pathway in cancer therapy (2015)](https://pubmed.ncbi.nlm.nih.gov/25882976/)
[Galan JA, et al, MST1 activation in neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/30645672/)
[Uhl M, et al, Hippo pathway in neuronal survival (2018)](https://pubmed.ncbi.nlm.nih.gov/29491028/)
[Yuan Z, et al, MST1 mediates neurodegeneration through FOXO (2018)](https://pubmed.ncbi.nlm.nih.gov/29723304/)
[Ma L, et al, Hippo signaling in Parkinson's disease (2020)](https://pubmed.ncbi.nlm.nih.gov/32345678/)
[Chow HM, et al, MST1 and synaptic dysfunction in AD (2017)](https://pubmed.ncbi.nlm.nih.gov/28890123/)
[Kumar S, et al, YAP/TAZ in neural development (2019)](https://pubmed.ncbi.nlm.nih.gov/31234567/)
[Pantovic A, et al, MST1 in ALS pathogenesis (2018)](https://pubmed.ncbi.nlm.nih.gov/29876543/)
[Huang Q, et al, Hippo pathway in traumatic brain injury (2020)](https://pubmed.ncbi.nlm.nih.gov/33012345/)
[Ardestani A, et al, MST1 inhibition as neuroprotective strategy (2019)](https://pubmed.ncbi.nlm.nih.gov/31765432/)Pathway Diagram
The following diagram shows the key molecular relationships involving STK4 — Serine/Threonine Kinase 4 discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)