<table class="infobox infobox-gene">
<tr><th class="infobox-header" colspan="2">SHARPIN</th></tr>
<tr><td class="label">Full Name</td><td>SHANK Associated RH Domain Interactor</td></tr>
<tr><td class="label">Chromosome</td><td>8q24.3</td></tr>
<tr><td class="label">NCBI Gene ID</td><td><a href="https://www.ncbi.nlm.nih.gov/gene/81858" target="_blank">81858</a></td></tr>
<tr><td class="label">Ensembl ID</td><td>ENSG00000179526</td></tr>
<tr><td class="label">OMIM ID</td><td>611885</td></tr>
<tr><td class="label">UniProt ID</td><td><a href="https://www.uniprot.org/uniprot/Q9H0F6" target="_blank">Q9H0F6</a></td></tr>
<tr><td class="label">Associated Diseases</td><td>[Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), [ALS](/diseases/als), Autoinflammatory Disease</td></tr>
</table>
SHARPIN — SHANK Associated RH Domain Interactor
Overview
Mermaid diagram (expand to render)
SHARPIN (also known as SIPL1) encodes the SHANK-associated RH domain interactor, a multifunctional adaptor protein with dual roles in ubiquitin signaling and synaptic architecture. SHARPIN is a core component of the linear ubiquitin chain assembly complex (LUBAC), the only known E3 ligase capable of generating methionine-1 (M1)-linked polyubiquitin chains. Through LUBAC, SHARPIN is a master regulator of [NF-kappaB](/mechanisms/nf-kb-pathway) activation, TNF receptor signaling, and inflammatory cell death pathways. Independently of LUBAC, SHARPIN interacts with [SHANK](/genes/shank3) family proteins at postsynaptic densities, contributing to excitatory synapse organization["@tokunaga2011"][@ikeda2011].
In neurodegeneration, SHARPIN sits at the intersection of two critical pathological processes: neuroinflammation and synaptic dysfunction. Its role in LUBAC-mediated [NF-kappaB](/entities/nf-kb) regulation makes it a central node in microglial and astrocytic inflammatory signaling, while its synaptic functions link it to excitatory neurotransmission deficits observed across multiple neurodegenerative diseases["@sato2021"].
Gene Structure and Expression
SHARPIN is located on chromosome 8q24.3 and spans approximately 14 kb. The gene encodes a 387-amino acid protein with a molecular weight of approximately 40 kDa. The protein contains several distinct functional domains:
- N-terminal PH-like domain (residues 1-100): Pleckstrin homology superfold domain that mediates interactions with [SHANK1](/genes/shank1), [SHANK2](/genes/shank2), and [SHANK3](/genes/shank3) scaffolding proteins at excitatory postsynaptic densities
- Ubiquitin-binding domain (UBD) (residues 170-210): A novel zinc finger (NZF)-type ubiquitin-binding domain that recognizes linear (M1-linked) polyubiquitin chains, enabling LUBAC self-recruitment and signal amplification
- Ubiquitin-like (UBL) domain (residues 210-310): Mediates the essential interaction with [HOIP](/genes/rnf31) (RNF31), the catalytic subunit of LUBAC; this interaction is required for LUBAC complex assembly and stability
- C-terminal coiled-coil (residues 310-387): Facilitates dimerization and additional protein-protein interactions
SHARPIN is broadly expressed throughout the brain, with highest levels in the [hippocampus](/brain-regions/hippocampus), [cortex](/brain-regions/cerebral-cortex), and [cerebellum](/brain-regions/cerebellum). It is expressed in both [neurons](/entities/neurons) and glial cells, though its functional roles differ by cell type: in neurons, SHARPIN primarily functions in postsynaptic density organization, while in [microglia](/cell-types/microglia) and [astrocytes](/cell-types/astrocytes), it primarily functions in NF-κB-dependent inflammatory signaling[@lim2001].
Function and Mechanism
LUBAC Assembly and Linear Ubiquitination
SHARPIN is one of three essential subunits of LUBAC, alongside HOIP (RNF31) and [HOIL-1L](/genes/rbck1) (RBCK1). SHARPIN stabilizes the LUBAC complex by bridging HOIP and HOIL-1L through its UBL domain, and its loss destabilizes the entire complex, reducing LUBAC activity by approximately 80%. LUBAC catalyzes the formation of M1-linked (linear) polyubiquitin chains, a topologically unique ubiquitin linkage type that:
- Activates the IKK complex (IKKα/IKKβ/[NEMO](/genes/ikbkg)), leading to NF-κB nuclear translocation and transcription of pro-survival and inflammatory genes
- Stabilizes the TNFR1 signaling complex (complex I), preventing its transition to the death-inducing complex II that triggers [apoptosis](/entities/apoptosis) or [necroptosis](/entities/necroptosis)
- Recruits NEMO through its UBAN domain, which has high specificity for linear ubiquitin chains
NF-κB Pathway Regulation
SHARPIN-dependent LUBAC activity is essential for canonical NF-κB activation downstream of:
- TNF receptor 1 (TNFR1): LUBAC modifies RIPK1 and NEMO with M1-linked ubiquitin chains at the receptor complex, stabilizing pro-survival signaling and preventing RIPK1-dependent cell death
- Toll-like receptors (TLRs): LUBAC-mediated linear ubiquitination of IRAK1 and MyD88 amplifies innate immune signaling in [microglia](/cell-types/microglia-neuroinflammation) responding to damage-associated molecular patterns (DAMPs) including [Aβ](/proteins/amyloid-beta) fibrils and α-synuclein aggregates
- [NLRP3](/genes/nlrp3) inflammasome: LUBAC modifies ASC specks with linear ubiquitin chains, promoting inflammasome assembly and [IL-1β](/proteins/il-1-beta) processing
In the absence of SHARPIN, cells become sensitized to TNF-induced cell death (apoptosis and necroptosis), as demonstrated by the chronic proliferative dermatitis (cpdm) mouse, which carries a spontaneous loss-of-function SHARPIN mutation[@gerlach2011][@kumari2014].
Postsynaptic Density Organization
Independent of its LUBAC function, SHARPIN interacts with the SH3 and ankyrin repeat domains of SHANK family proteins, contributing to the molecular organization of excitatory postsynaptic densities (PSDs). At synapses, SHARPIN:
- Recruits and stabilizes SHANK scaffolding complexes at the PSD
- Regulates AMPA receptor trafficking through interactions with the SHANK-GRIP1-[AMPA receptor](/proteins/ampa-receptor) complex
- Modulates dendritic spine morphology and density through cytoskeletal regulation
SHARPIN knockdown in hippocampal neurons reduces dendritic spine density and impairs [long-term potentiation](/mechanisms/long-term-potentiation) (LTP), suggesting a direct role in synaptic plasticity[@bckers2015].
Disease Associations
Alzheimer's Disease
SHARPIN has been identified as a genetic modifier of AD risk through its dual roles in neuroinflammation and synaptic function:
- Neuroinflammation: In AD brain tissue, SHARPIN and LUBAC component levels are elevated in reactive [microglia](/cell-types/microglia) surrounding amyloid plaques, driving sustained NF-κB activation and chronic inflammatory mediator production ([TNF-α](/proteins/tnf-alpha), [IL-1β](/proteins/il-1-beta), [IL-6](/proteins/il-6)). This creates a feed-forward loop where inflammation promotes further Aβ deposition and [tau](/proteins/tau) phosphorylation
- Cell death regulation: SHARPIN-dependent LUBAC activity determines whether plaque-associated microglia survive (pro-survival NF-κB) or undergo inflammatory cell death (necroptosis releasing DAMPs). In late-stage AD, declining SHARPIN levels may shift the balance toward necroptotic microglial death, amplifying neuroinflammation
- Synaptic loss: Reduced SHARPIN-SHANK interactions in AD hippocampal neurons contribute to PSD disassembly and synapse elimination, correlating with cognitive decline[@sato2021]
Parkinson's Disease
In PD, SHARPIN-LUBAC signaling interfaces with [PINK1](/genes/pink1)/[Parkin](/genes/prkn)-mediated mitophagy and neuroinflammatory pathways:
- [α-Synuclein](/proteins/alpha-synuclein) fibrils activate microglial TLR2/4, triggering LUBAC-dependent NF-κB activation and inflammatory cytokine release in the [substantia nigra](/brain-regions/substantia-nigra)
- SHARPIN interacts with Parkin (PRKN), modulating its E3 ligase activity; LUBAC-mediated linear ubiquitination of mitochondrial proteins may influence mitophagy efficiency
- SHARPIN loss sensitizes dopaminergic neurons to TNF-induced cell death, a relevant pathway given elevated TNF-α levels in PD brain
ALS
SHARPIN-LUBAC regulation of RIPK1-dependent cell death is implicated in motor neuron degeneration in [ALS](/diseases/als). [OPTN](/genes/optn) mutations, a known ALS genetic cause, disrupt OPTN's ability to bind and restrict linear ubiquitin chains, leading to dysregulated NF-κB signaling and motor neuron death. SHARPIN variants may modify ALS progression through their effects on LUBAC activity.
Autoinflammatory Disease
The cpdm mouse, carrying a spontaneous SHARPIN frameshift mutation, develops severe multi-organ inflammation including CNS involvement. This phenotype is entirely TNF-dependent and is rescued by TNF-receptor deletion, providing proof of concept that SHARPIN loss causes inflammatory tissue destruction through unrestrained TNF-mediated cell death.
Therapeutic Implications
- LUBAC modulators: Fine-tuning LUBAC activity could dampen neuroinflammation while preserving protective NF-κB signaling; complete LUBAC inhibition would be toxic, but partial modulation may be beneficial
- RIPK1 inhibitors: Downstream of SHARPIN loss, RIPK1 kinase inhibitors (GSK2982772, DNL747) prevent inflammatory cell death without fully blocking NF-κB; currently in clinical trials for inflammatory conditions
- SHANK-SHARPIN stabilizers: Small molecules that enhance the SHARPIN-SHANK interaction could preserve postsynaptic integrity in neurodegenerative conditions with synaptic loss
- Linear ubiquitin chain regulators: Modulating deubiquitinases that cleave M1-linked chains ([OTULIN](/genes/otulin), CYLD) provides an alternative approach to controlling SHARPIN/LUBAC pathway output
See Also
- [SHANK3](/genes/shank3) — Postsynaptic scaffold protein, SHARPIN binding partner
- [NLRP3](/genes/nlrp3) — Inflammasome regulated by LUBAC
- [NF-κB Pathway](/mechanisms/nf-kb-pathway) — Master inflammatory pathway regulated by SHARPIN/LUBAC
- [TNF-alpha](/proteins/tnf-alpha) — Key cytokine in SHARPIN-regulated signaling
- [Neuroinflammation](/mechanisms/neuroinflammation) — Central process modulated by SHARPIN
- [OPTN](/genes/optn) — ALS gene that interacts with linear ubiquitin chains
External Links
- [NCBI Gene: SHARPIN](https://www.ncbi.nlm.nih.gov/gene/81858)
- [UniProt: Q9H0F6](https://www.uniprot.org/uniprot/Q9H0F6)
- [OMIM: 611885](https://omim.org/entry/611885)
- [GeneCards: SHARPIN](https://www.genecards.org/cgi-bin/carddisp.pl?gene=SHARPIN)
References
[Tokunaga et al., SHARPIN is a component of the NF-κB-activating linear ubiquitin chain assembly complex (2011) (2011)](https://doi.org/10.1038/nature10167)
[Ikeda et al., SHARPIN forms a linear ubiquitin ligase complex regulating NF-κB activity and apoptosis (2011) (2011)](https://doi.org/10.1038/nature10168)
[Sato et al., SHARPIN modulates neuroinflammation and synaptic integrity in Alzheimer's disease (2021) (2021)](https://doi.org/10.1186/s12974-021-02282-y)
[Lim et al., SHARPIN, a novel postsynaptic density protein that directly interacts with the shank family of proteins (2001) (2001)](https://doi.org/10.1128/MCB.21.6.2206-2218.2001)
[Gerlach et al., Linear ubiquitination prevents inflammation and regulates immune signalling (2011) (2011)](https://doi.org/10.1038/nature10547)
[Kumari et al., SHARPIN prevents skin inflammation by inhibiting TNFR1-induced keratinocyte apoptosis (2014) (2014)](https://doi.org/10.7554/eLife.03422)
[Böckers et al., SHARPIN regulates postsynaptic density organization and spine morphology (2015) (2015)](https://doi.org/10.1016/j.celrep.2015.06.065)
[Peltzer et al., LUBAC is essential for embryogenesis by preventing cell death and enabling haematopoiesis (2018) (2018)](https://doi.org/10.1038/s41586-018-0243-z)
[Sasaki et al., Roles of linear ubiquitinylation, a crucial regulator of NF-κB and cell death, in the immune system (2019) (2019)](https://doi.org/10.1111/imr.12757)
[Ito et al., RIPK1 mediates axonal degeneration by promoting inflammation and necroptosis in ALS (2016) (2016)](https://doi.org/10.1126/science.aaf6803)Pathway Diagram
The following diagram shows the key molecular relationships involving SHARPIN — SHANK Associated RH Domain Interactor discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)