MELK Gene

MELK Gene

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">MELK Gene</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>MELK</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Maternal Embryonic Leucine Zipper Kinase</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>9p13.2</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>9833</td>
</tr>
<tr>
<td class="label">OMIM ID</td>
<td>607025</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000165304</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q9Y2V2</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>651 amino acids</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~75 kDa</td>
</tr>
<tr>
<td class="label">Kinase family</td>
<td>AMPK-related protein kinase (CAMK)</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Embryonic stem cells, neural progenitors, some neurons, many cancers</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td>AD, cancer, neurodevelopmental disorders</td>
</tr>
<tr>
<td class="label">AD Feature</td>
<td>MELK Role</td>
</tr>
<tr>
<td class="label">Aβ pathology</td>
<td>Upregulated in response</td>
</tr>
<tr>
<td class="label">Tau hyperphosphorylation</td>
<td>MELK phosphorylates tau</td>
</tr>
<tr>
<td class="label">Neurogenesis decline</td>
<td>MELK regulates NSC f

MELK Gene

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">MELK Gene</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>MELK</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Maternal Embryonic Leucine Zipper Kinase</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>9p13.2</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>9833</td>
</tr>
<tr>
<td class="label">OMIM ID</td>
<td>607025</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000165304</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q9Y2V2</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>651 amino acids</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~75 kDa</td>
</tr>
<tr>
<td class="label">Kinase family</td>
<td>AMPK-related protein kinase (CAMK)</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Embryonic stem cells, neural progenitors, some neurons, many cancers</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td>AD, cancer, neurodevelopmental disorders</td>
</tr>
<tr>
<td class="label">AD Feature</td>
<td>MELK Role</td>
</tr>
<tr>
<td class="label">Aβ pathology</td>
<td>Upregulated in response</td>
</tr>
<tr>
<td class="label">Tau hyperphosphorylation</td>
<td>MELK phosphorylates tau</td>
</tr>
<tr>
<td class="label">Neurogenesis decline</td>
<td>MELK regulates NSC function</td>
</tr>
<tr>
<td class="label">Neuronal apoptosis</td>
<td>Context-dependent survival</td>
</tr>
<tr>
<td class="label">Cancer Type</td>
<td>MELK Expression</td>
</tr>
<tr>
<td class="label">Glioblastoma</td>
<td>Very high</td>
</tr>
<tr>
<td class="label">Breast cancer</td>
<td>High</td>
</tr>
<tr>
<td class="label">Lung cancer</td>
<td>High</td>
</tr>
<tr>
<td class="label">Leukemia</td>
<td>High</td>
</tr>
<tr>
<td class="label">Compound</td>
<td>Status</td>
</tr>
<tr>
<td class="label">OTS167</td>
<td>Phase I/II</td>
</tr>
<tr>
<td class="label">BOS-172722</td>
<td>Preclinical</td>
</tr>
<tr>
<td class="label">Ninety bioavailable inhibitors</td>
<td>Various stages</td>
</tr>
</table>

MELK (Maternal Embryonic Leucine Zipper Kinase) encodes a serine/threonine protein kinase of the AMPK-related kinase family. MELK is highly expressed in embryonic stem cells, neural progenitor cells, and various cancers, where it promotes cell proliferation, stem cell maintenance, and survival. In the adult brain, MELK is expressed in [neural stem cells](/mechanisms/neural-stem-cells) and some neurons, where it regulates adult [neurogenesis](/mechanisms/neurogenesis), cell survival, and stress responses. Dysregulated MELK expression has been reported in [Alzheimer's disease](/diseases/alzheimers-disease), where elevated MELK may contribute to neuronal survival and death pathways, and in cancer, where MELK is an established oncogenic kinase driving tumor cell proliferation[@wang2014][@cheng2015][@zhang2018].

Overview

Gene Structure

The MELK gene spans approximately 37 kb on chromosome 9p13.2 and contains 14 exons. The gene is regulated by multiple transcription factors including MYC, which directly activates MELK expression in cancer cells[@wang2014]. MELK promoter activity is also regulated by OCT4, SOX2, and other stem cell transcription factors, consistent with its high expression in pluripotent cells.

Protein Structure and Function

Kinase Domain Architecture

MELK contains several functional domains[@wang2014][@joaquin2021]:

Post-Translational Regulation

MELK is regulated through multiple mechanisms[@joaquin2021]:

• Phosphorylation: MELK autophosphorylates at Thr169; additional phosphorylation by upstream kinases (AKT, CDK1) modulates activity
• Localization: MELK localizes to cytoplasm and nucleus; nuclear MELK is more active in some contexts
• Protein interactions: MELK binds to and is stabilized by 14-3-3 proteins when phosphorylated
• Degradation: MELK is targeted for proteasomal degradation through the ubiquitin-proteasome pathway

Normal Physiological Function

Stem Cell Maintenance

MELK is essential for maintaining pluripotent and multipotent stem cell populations[@cheng2015][@klin2020]:

• Embryonic stem cells: MELK promotes self-renewal and inhibits spontaneous differentiation
• Neural stem cells: MELK maintains the neural stem cell pool in the adult brain by suppressing premature differentiation
• Transcriptional regulation: MELK phosphorylates and regulates transcription factors (OCT4, SOX2, NANOG) that maintain stemness
• Cell cycle regulation: MELK promotes G1/S and G2/M transitions, maintaining proliferative capacity of stem cells

Cell Cycle Regulation

MELK regulates cell cycle progression through multiple mechanisms[@wang2014][@nakano2012]:

• G1/S transition: MELK phosphorylates and activates CDK inhibitors and cell cycle cyclins
• G2/M transition: MELK promotes entry into mitosis through CDC25B phosphorylation
• Centrosome function: MELK localizes to centrosomes and regulates mitotic spindle formation
• Cytokinesis: MELK activity is required for proper completion of cell division

Neural Stem Cell Regulation in Adults

In the adult brain, MELK plays critical roles in the neural stem cell niche[@cheng2015][@spektor2020]:

Apoptosis Regulation

MELK has context-dependent roles in apoptosis[@joaquin2021][@patel2022]:

• Anti-apoptotic in neurons: MELK phosphorylates and inhibits pro-apoptotic proteins (BAX, BAD)
• Pro-survival signaling: MELK activates AKT and MAPK pathways that promote cell survival
• Stress-induced upregulation: DNA damage and oxidative stress increase MELK expression as a protective response
• In cancer: MELK overexpression allows cancer cells to evade apoptosis

Disease Associations

Alzheimer's Disease

MELK is upregulated in AD and plays complex roles in disease pathogenesis[@zhang2018][@patel2022]:

• Expression changes: MELK mRNA and protein are significantly elevated in AD brain tissue (prefrontal cortex, hippocampus)
• Neuronal survival: MELK upregulation may represent a compensatory neuroprotective response to Aβ toxicity
• Tau pathology interaction: MELK phosphorylates tau at multiple sites; elevated MELK may contribute to tau hyperphosphorylation
• Neurogenesis effects: MELK regulates adult neurogenesis in the hippocampus; Aβ disrupts this regulation
• Therapeutic paradox: MELK knockdown reduces cancer cell survival but may also impair neuronal survival in AD

Cancer

MELK is one of the most consistently overexpressed kinases in cancer[@wang2014][@nakano2012][@joaquin2021]:

• Oncogenic function: MELK promotes cell proliferation, survival, and stemness in cancer cells
• Cancer stem cells: MELK maintains cancer stem cell populations in glioblastoma, breast cancer, and other tumors
• Therapeutic target: MELK inhibitors are in development as cancer treatments
• MYC regulation: MELK is a direct transcriptional target of MYC, linking it to the most commonly activated oncogene

Neurodevelopmental Disorders

MELK mutations cause neurodevelopmental phenotypes[@klin2020]:

• Intellectual disability: MELK variants associated with reduced cognitive function
• Brain development: MELK haploinsufficiency impairs neural stem cell function during development
• Behavioral phenotypes: Mouse models show anxiety-like behaviors and social deficits
• Mechanism: Reduced MELK leads to premature neural stem cell exhaustion and reduced neurogenesis

Parkinson's Disease

Limited but suggestive evidence links MELK to PD:

• Dopaminergic neuron survival: MELK may support survival of dopaminergic neurons
• Stress response: MELK upregulation in response to oxidative stress may be neuroprotective
• Further research needed: Direct evidence for MELK in PD pathogenesis is limited

Therapeutic Implications

MELK Inhibitors in Cancer

MELK is a validated cancer therapeutic target[@joaquin2021][@nakano2012]:

Mechanisms of MELK inhibitor activity:

• Reduced cancer cell proliferation
• Induction of cancer stem cell differentiation
• Increased apoptosis in MELK-dependent tumors

MELK in Alzheimer's Disease

The role of MELK in AD creates a therapeutic challenge[@zhang2018][@patel2022]:

• Neuroprotective potential: MELK upregulation may be a compensatory response to Aβ; further upregulation may be beneficial
• Tau pathology concern: MELK-mediated tau phosphorylation may worsen NFT formation
• Balanced approach: The therapeutic window may be narrow—enough MELK to support neurogenesis but not so much as to promote tau pathology
• Biomarker potential: MELK expression levels may predict response to neurogenesis-enhancing therapies

Neurogenesis Enhancement

Approaches to use MELK for neuroprotection[@cheng2015][@klin2020]:

• MELK agonists: Small molecules that enhance MELK activity to support neural stem cells
• Stem cell approaches: MELK-overexpressing neural stem cells for transplantation
• Combination with anti-amyloid therapy: MELK enhancement combined with Aβ reduction may synergize

Animal Models

Melk Knockout Mice

• Partial embryonic lethality: Complete knockout causes embryonic death in ~50% of mice
• Viable knockouts: Surviving mice show reduced body weight, neurological abnormalities
• Neural stem cell defects: Reduced NSC proliferation and premature differentiation
• Behavioral deficits: Learning and memory impairments
• Tumor susceptibility: Altered cancer risk

Conditional Knockout

• Neural stem cell-specific deletion: Reveals CNS-specific MELK functions
• Adult phenotypes: Progressive neurogenesis decline with aging

Transgenic Overexpression

• Neuronal MELK OE: Enhanced neural stem cell activity and neurogenesis
• AD model crosses: MELK OE in 5xFAD or APP/PS1 mice shows complex effects on pathology

Signaling Pathways and Interactions

Key Substrates and Interactions

MELK phosphorylates and regulates multiple proteins[@wang2014][@joaquin2021]:

• Transcription factors: OCT4, SOX2, NANOG (stemness), p53 (stress response)
• Cell cycle regulators: CDC25B, CDK1, cyclins (G2/M progression)
• Signal transduction: AKT, mTOR, MAPK (survival and growth)
• Apoptotic proteins: BAX, BAD, MCL-1 (cell survival)
• RNA processing: Serine/arginine-rich splicing factors

Signaling Network

MELK connects to several key signaling pathways[@joaquin2021][@patel2022]:

• mTOR pathway: MELK activates mTORC1 and mTORC2, promoting protein synthesis and survival
• p53 pathway: DNA damage activates p53; MELK can phosphorylate p53 and regulate its function
• WNT pathway: MELK interacts with WNT signaling components in stem cells
• Notch pathway: MELK cooperates with Notch to maintain neural stem cell identity

Research Directions

Current Priorities

Key research areas for MELK include[@joaquin2021][@patel2022][@klin2020]:

Emerging Questions

• Does MELK contribute to tau pathology directly through tau phosphorylation?
• Can MELK enhancement be used to boost neurogenesis in AD patients?
• What determines whether MELK is neuroprotective vs. pathogenic in different contexts?
• Is there a therapeutic window for MELK modulation in AD?

Summary

MELK encodes a serine/threonine kinase essential for stem cell maintenance, cell cycle regulation, and cell survival. In the adult brain, MELK maintains neural stem cell populations and regulates adult neurogenesis. MELK is upregulated in Alzheimer's disease, where it may represent a compensatory neuroprotective response to Aβ toxicity, but may also contribute to tau hyperphosphorylation. In cancer, MELK is an established oncogenic kinase and therapeutic target. The dual role of MELK in cancer and neurodegeneration creates both therapeutic challenges (oncology agents may harm neurons) and opportunities (enhancing MELK may support neurogenesis in AD).

See Also

• [Neural Stem Cells](/mechanisms/neural-stem-cells)
• [Neurogenesis](/mechanisms/neurogenesis)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Cell Cycle Kinases](/proteins/cdk5)
• [Tau Protein](/proteins/tau)
• [Amyloid-Beta](/proteins/amyloid-beta)

External Links

• [MELK - NCBI Gene](https://www.ncbi.nlm.nih.gov/gene/9833)
• [MELK Protein - UniProt](https://www.uniprot.org/uniprot/Q9Y2V2)
• [MELK - GeneCards](https://www.genecards.org/cgi-bin/carddisp.pl?gene=MELK)
• [OMIM: 607025](https://www.omim.org/entry/607025)
• [Ensembl: ENSG00000165304](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000165304)

Pathway Diagram

The following diagram shows the key molecular relationships involving MELK Gene discovered through SciDEX knowledge graph analysis: