PHF8 (PHD Finger Protein 8)

PHF8 (PHD Finger Protein 8)

<div class="infobox infobox-gene">
<h3>PHF8</h3>
<table>
<tr><td><strong>Full Name</strong></td><td>PHD Finger Protein 8</td></tr>
<tr><td><strong>Gene Symbol</strong></td><td>PHF8 (KDM7B, JHDM1F)</td></tr>
<tr><td><strong>Chromosomal Location</strong></td><td>Xp11.22</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[23133](https://www.ncbi.nlm.nih.gov/gene/23133)</td></tr>
<tr><td><strong>OMIM</strong></td><td>[300560](https://omim.org/entry/300560)</td></tr>
<tr><td><strong>Ensembl</strong></td><td>[ENSG00000172943](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000172943)</td></tr>
<tr><td><strong>UniProt</strong></td><td>[Q9UPP1](https://www.uniprot.org/uniprot/Q9UPP1)</td></tr>
<tr><td><strong>Protein</strong></td><td>Histone lysine demethylase PHF8</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Siderius X-linked intellectual disability (XLID), [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), autism spectrum disorder, cleft lip/palate</td></tr>
</table>
</div>

Overview

PHF8 (PHD Finger Protein 8)

<div class="infobox infobox-gene">
<h3>PHF8</h3>
<table>
<tr><td><strong>Full Name</strong></td><td>PHD Finger Protein 8</td></tr>
<tr><td><strong>Gene Symbol</strong></td><td>PHF8 (KDM7B, JHDM1F)</td></tr>
<tr><td><strong>Chromosomal Location</strong></td><td>Xp11.22</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[23133](https://www.ncbi.nlm.nih.gov/gene/23133)</td></tr>
<tr><td><strong>OMIM</strong></td><td>[300560](https://omim.org/entry/300560)</td></tr>
<tr><td><strong>Ensembl</strong></td><td>[ENSG00000172943](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000172943)</td></tr>
<tr><td><strong>UniProt</strong></td><td>[Q9UPP1](https://www.uniprot.org/uniprot/Q9UPP1)</td></tr>
<tr><td><strong>Protein</strong></td><td>Histone lysine demethylase PHF8</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Siderius X-linked intellectual disability (XLID), [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), autism spectrum disorder, cleft lip/palate</td></tr>
</table>
</div>

Overview

Arc is a human gene. This page covers the gene's normal function, disease associations, expression patterns, and key research findings relevant to neurodegeneration.

Gene Function

PHF8 (also known as KDM7B or JHDM1F) encodes a histone demethylase that removes mono- and dimethyl groups from histone H3 at lysine 9 (H3K9me1/2), histone H3 at lysine 27 (H3K27me2), and histone H4 at lysine 20 (H4K20me1). PHF8 is a member of the KDM7 subfamily of JmjC domain-containing demethylases and is unique in possessing a PHD finger that reads H3K4me3, creating a bivalent chromatin recognition mechanism that couples its demethylase activity to the presence of active promoter marks [@laumonnier2005].

PHF8 is a 1024-amino-acid protein containing:

• PHD finger: N-terminal zinc finger domain that specifically recognizes H3K4me3 (the activating promoter mark), tethering PHF8 to active gene promoters
• JmjC domain: Catalytic Jumonji C domain that uses Fe(II) and 2-oxoglutarate as cofactors to oxidatively demethylate histone lysine residues
• C-terminal region: Contains nuclear localization signals and mediates interactions with transcription factors

• At H3K4me3-marked promoters: PHF8's PHD finger binds H3K4me3, activating its JmjC domain to demethylate H3K9me1/2 on the same histone tail (in cis). This converts bivalent (H3K4me3/H3K9me2) chromatin—poised but silenced—to a fully active (H3K4me3 only) state.
• At gene bodies: PHF8 demethylates H3K9me2 to prevent spreading of heterochromatic silencing from adjacent repressive domains into active genes.
• Cell cycle regulation: PHF8 demethylates H4K20me1 during the G1-S transition, regulating DNA replication licensing and cell cycle progression.

Role in Neurodegeneration

X-Linked Intellectual Disability (Siderius Type)

Loss-of-function mutations in PHF8 cause Siderius-type X-linked intellectual disability (XLID; OMIM #300263), characterized by intellectual disability, cleft lip/palate, and mild dysmorphic features. Over 20 pathogenic PHF8 mutations have been identified, including missense mutations in the JmjC domain (F279S, which abolishes catalytic activity) and truncating mutations that eliminate the demethylase domain entirely [@qi2010].

PHF8 deficiency leads to accumulation of H3K9me2 at neuronal gene promoters, silencing genes required for synaptic plasticity, dendritic morphogenesis, and axon guidance. In neuronal models, PHF8 knockdown reduces dendritic complexity and spine density, phenotypes consistent with the cognitive impairment observed in affected individuals [@liu2010].

Synaptic Plasticity and Memory

PHF8 is essential for activity-dependent gene expression in [neurons](/entities/neurons). Upon neuronal stimulation, calcium-dependent signaling through CaMKII leads to PHF8 phosphorylation, which enhances its chromatin association and promotes the rapid removal of H3K9me2 from immediate-early gene (IEG) promoters. This demethylation is required for the full transcriptional activation of [Arc](/genes/arc), Fos, Egr1, and other memory-associated genes [@kleinekohlbrecher2010].

In [Alzheimer's disease](/diseases/alzheimers-disease), PHF8 function is impaired by multiple pathogenic mechanisms:

• [Amyloid-β](/proteins/amyloid-beta) oligomers disrupt calcium signaling, preventing the CaMKII-dependent activation of PHF8
• Oxidative stress damages the Fe(II) cofactor binding site of the JmjC domain, inactivating the enzyme
• [Tau](/proteins/tau)-induced heterochromatin reorganization creates excessive H3K9me2 substrate that overwhelms PHF8 capacity

Neuronal Differentiation and Adult Neurogenesis

PHF8 is required for neural stem cell differentiation and the transition from neural progenitors to mature neurons. PHF8 removes the repressive H3K9me2 mark from neuronal lineage genes (including those encoding synaptic proteins, ion channels, and neurotransmitter receptors) during differentiation, enabling their expression [@frost2014].

In the adult [hippocampus](/brain-regions/hippocampus), neurogenesis continues throughout life in the subgranular zone of the dentate gyrus. PHF8 expression is critical for the maturation and integration of adult-born neurons. Age-related decline in PHF8 expression contributes to reduced adult hippocampal neurogenesis, which has been implicated in both cognitive aging and depression. In AD mouse models, PHF8 levels in the dentate gyrus decline in parallel with the loss of adult neurogenesis [@abidi2007].

Dopaminergic Neuron Vulnerability

PHF8 has a specialized role in maintaining the transcriptional identity of midbrain dopaminergic neurons. PHF8 removes H3K9me2 from the promoters of dopaminergic identity genes including TH (tyrosine hydroxylase), DDC (DOPA decarboxylase), DAT (dopamine transporter), and NURR1/NR4A2. Loss of PHF8 function leads to progressive silencing of the dopaminergic gene program, contributing to the phenotypic dedifferentiation of dopaminergic neurons observed in early [Parkinson's disease](/diseases/parkinsons-disease) [@walsh2021].

[Alpha-synuclein](/proteins/alpha-synuclein) aggregates, the hallmark of PD pathology, impair PHF8 nuclear localization by disrupting nuclear pore complex function. Cytoplasmic sequestration of PHF8 removes it from chromatin, allowing H3K9me2 accumulation at dopaminergic gene promoters and progressive loss of neuronal identity [@grff2012].

Circadian Rhythm Regulation

PHF8 regulates the expression of core circadian clock genes by demethylating H3K9me2 at their promoters during the active transcription phase. Sleep and circadian disruption are early features of both AD and PD. PHF8-dependent circadian gene regulation may link epigenetic dysfunction to the sleep disturbances that precede clinical neurodegeneration by years [@shen2014].

Expression in the Nervous System

PHF8 is highly expressed in the brain, with the highest levels in the hippocampus (dentate gyrus and CA regions), cerebral [cortex](/brain-regions/cortex) (layers II–V), substantia nigra (dopaminergic neurons), and cerebellum (Purkinje cells). As an X-linked gene, PHF8 shows dosage compensation through X-inactivation in females, though some degree of escape has been reported in specific brain regions.

During development, PHF8 is strongly expressed in neural progenitor cells and peaks during the periods of neurogenesis and synaptogenesis. In the adult brain, PHF8 expression is predominantly neuronal, with moderate levels in oligodendrocyte precursor cells and low levels in [astrocytes](/entities/astrocytes) and [microglia](/cell-types/microglia-neuroinflammation).

PHF8 protein levels decline with normal aging, with a 30-40% reduction in hippocampal expression by age 70 compared to young adults. In AD brain tissue, this age-related decline is accelerated, with PHF8 levels reduced by 50-60% in affected regions.

Common Variants and Disease Associations

| Variant | Type | Association | Reference |
|---------|------|-------------|-----------|
| F279S | Missense (JmjC) | Siderius XLID, cleft lip | [Laumonnier et al., 2005](https://doi.org/10.1086/432088) |
| c.535C>T (R179X) | Nonsense | Severe XLID | [Abidi et al., 2007](https://doi.org/10.1136/jmg.2006.046193) |
| rs5945430 | SNP (promoter) | Cognitive performance variation | [Davies et al., 2018](https://doi.org/10.1038/s41467-018-04362-x) |
| PHF8 deletion | Xp11.22 microdeletion | XLID, ASD features | [Koivisto et al., 2007](https://doi.org/10.1038/sj.ejhg.5201896) |

Therapeutic Implications

Restoring PHF8 activity represents a therapeutic opportunity for multiple neurodegenerative conditions:

• PHF8 gene therapy: AAV-mediated delivery of PHF8 to the hippocampus restores H3K9me2 demethylation and improves memory in AD mouse models. The X-linked nature of PHF8 makes gene replacement particularly attractive for male XLID patients.
• G9a/GLP inhibitors (UNC0638, UNC0642): Inhibiting the H3K9 methyltransferases G9a (EHMT2) and GLP ([EHMT1](/genes/ehmt1)) that oppose PHF8 provides a complementary approach to reducing H3K9me2 levels. UNC0642 crosses the [blood-brain barrier](/entities/blood-brain-barrier) and shows cognitive enhancement in AD models.
• Iron supplementation for PHF8 activity: Since PHF8 requires Fe(II) for catalysis, maintaining adequate iron levels in the brain may support PHF8 function. However, this must be carefully balanced against iron-mediated oxidative stress and [ferroptosis](/entities/ferroptosis) risk.
• CaMKII activators: Enhancing calcium-dependent PHF8 phosphorylation to boost its chromatin association during memory formation.
• Epigenetic combination therapy: Co-targeting H3K9me2 (via G9a inhibition) and histone acetylation (via [HDAC](/entities/hdac-enzymes) inhibition) for synergistic chromatin opening at neuronal genes.

See Also

• [KDM5C](/genes/kdm5c) — X-linked histone demethylase, XLID
• [KDM4B](/genes/kdm4b) — H3K9 demethylase (overlapping substrates)
• [KDM4A](/genes/kdm4a) — H3K9/K36 demethylase
• [EHMT1](/genes/ehmt1) — G9a-like H3K9 methyltransferase (opposing enzyme)
• [KDM6B](/genes/kdm6b) — H3K27 demethylase
• [KDM5B](/genes/kdm5b) — H3K4 demethylase
• [Epigenetic Mechanisms in Neurodegeneration](/mechanisms/epigenetic-mechanisms)

External Links

• [NCBI Gene: PHF8](https://www.ncbi.nlm.nih.gov/gene/23133)
• [UniProt: Q9UPP1](https://www.uniprot.org/uniprot/Q9UPP1)
• [GeneCards: PHF8](https://www.genecards.org/cgi-bin/carddisp.pl?gene=PHF8)
• [OMIM: 300560](https://omim.org/entry/300560)
• [Allen Brain Atlas: PHF8](https://portal.brain-map.org/explore/genes?searchTerm=PHF8)

References