| SHARPIN | |
|---|---|
| Full Name | SHANK Associated RH Domain Interactor |
| Chromosome | 8q24.3 |
| NCBI Gene ID | 81858 |
| Ensembl ID | ENSG00000179526 |
| OMIM ID | 611885 |
| UniProt ID | Q9H0F6 |
| Associated Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), [ALS](/diseases/als), Autoinflammatory Disease |
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-κB activation, TNF receptor signaling, and inflammatory cell death pathways. Independently of LUBAC, SHARPIN interacts with SHANK family proteins at postsynaptic densities, contributing to excitatory synapse organization[1][2].
In neurodegeneration, SHARPIN sits at the intersection of two critical pathological processes: neuroinflammation and synaptic dysfunction. Its role in LUBAC-mediated NF-κB 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[3].
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:
SHARPIN is broadly expressed throughout the brain, with highest levels in the hippocampus, cortex, and cerebellum. It is expressed in both neurons and glial cells, though its functional roles differ by cell type: in neurons, SHARPIN primarily functions in postsynaptic density organization, while in microglia and astrocytes, it primarily functions in NF-κB-dependent inflammatory signaling[4].
SHARPIN is one of three essential subunits of LUBAC, alongside HOIP (RNF31) and HOIL-1L (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:
SHARPIN-dependent LUBAC activity is essential for canonical NF-κB activation downstream of:
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[5][6].
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:
SHARPIN knockdown in hippocampal neurons reduces dendritic spine density and impairs long-term potentiation (LTP), suggesting a direct role in synaptic plasticity[7].
SHARPIN has been identified as a genetic modifier of AD risk through its dual roles in neuroinflammation and synaptic function:
In PD, SHARPIN-LUBAC signaling interfaces with PINK1/Parkin-mediated mitophagy and neuroinflammatory pathways:
SHARPIN-LUBAC regulation of RIPK1-dependent cell death is implicated in motor neuron degeneration in ALS. 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.
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.
Tokunaga et al. SHARPIN is a component of the NF-κB-activating linear ubiquitin chain assembly complex (2011). 2011. ↩︎
Ikeda et al. SHARPIN forms a linear ubiquitin ligase complex regulating NF-κB activity and apoptosis (2011). 2011. ↩︎
Sato et al. SHARPIN modulates neuroinflammation and synaptic integrity in Alzheimer's disease (2021). 2021. ↩︎ ↩︎
Lim et al. SHARPIN, a novel postsynaptic density protein that directly interacts with the shank family of proteins (2001). 2001. ↩︎
Gerlach et al. Linear ubiquitination prevents inflammation and regulates immune signalling (2011). 2011. ↩︎
Kumari et al. SHARPIN prevents skin inflammation by inhibiting TNFR1-induced keratinocyte apoptosis (2014). 2014. ↩︎
Böckers et al. SHARPIN regulates postsynaptic density organization and spine morphology (2015). 2015. ↩︎