NLR family pyrin domain containing 3 (NLRP3) (previously known as NACHT, LRR and PYD domains-containing protein 3 ALP3and cryopyrin), is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

that in humans is encoded by the ''NLRP3''

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

located on the long arm of

chromosome 1 Chromosome 1 is the designation for the largest human chromosome. Humans have two copies of chromosome 1, as they do with all of the autosomes, which are the non- sex chromosomes. Chromosome 1 spans about 249 million nucleotide base pairs, which ...

. NLRP3 is expressed predominantly in macrophages and as a component of the

inflammasome Inflammasomes are cytosolic multiprotein oligomers of the innate immune system responsible for the activation of inflammatory responses. Activation and assembly of the inflammasome promotes proteolytic cleavage, maturation and secretion of pro-in ...

, detects products of damaged cells such as extracellular ATP and crystalline

uric acid Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the metabolic breakdown ...

. Activated NLRP3 in turn triggers an immune response. Mutations in the NLRP3 gene are associated with a number of organ specific autoimmune diseases.

Nomenclature

NACHT, LRR, and PYD are respectively acronyms for: * NACHT – NAIP (neuronal apoptosis inhibitor protein), C2TA MHC,_HET-E_(Podospora_anserina#Heterokaryon_incompatibility.html" ;"title="Major_histocompatibility_complex.html" ;"title="lass 2 transcription activator, of the MHC,_HET-E_(Podospora_anserina#Heterokaryon_incompatibility">heterokaryon_incompatibility)_and_TP1_(telomerase-associated_protein_1) *_ MHC,_HET-E_(Podospora_anserina#Heterokaryon_incompatibility">heterokaryon_incompatibility)_and_TP1_(telomerase-associated_protein_1) *_Leucine-rich_repeat">LRR_–_"leucine-rich_repeat"__and_is_synonymous_with_NLR,_for_''_or_''nucleotide-binding_domain,_leucine-rich_repeat" *_Pyrin_domain.html" ;"title="Leucine-rich_repeat.html" ;"title="Major histocompatibility complex">MHC, HET-E (Podospora anserina#Heterokaryon incompatibility">heterokaryon incompatibility) and TP1 (telomerase-associated protein 1) * Leucine-rich repeat">LRR – "leucine-rich repeat" and is synonymous with NLR, for '' or ''nucleotide-binding domain, leucine-rich repeat" * Pyrin domain">PYD – "PYRIN domain," after the ''pyrin'' proteins The ''NLRP3'' gene name abbreviates "NLR family, pyrin domain containing 3," where NLR refers to "nucleotide-binding domain, leucine-rich repeat." The NACHT, LRR and PYD domains-containing protein 3 is also called: * cold induced autoinflammatory syndrome 1 (CIAS1), * caterpiller-like receptor 1.1 (CLR1.1), and * PYRIN-containing APAF1-like protein 1 (PYPAF1).

Structure

This gene encodes a pyrin-like protein which contains a pyrin domain, a nucleotide-binding site (NBS) domain, and a leucine-rich repeat (LRR) motif. This protein interacts with pyrin domain (PYD) of apoptosis-associated speck-like protein containing a CARD (ASC). Proteins which contain the

caspase recruitment domain Caspase recruitment domains, or caspase activation and recruitment domains (CARDs), are interaction motifs found in a wide array of proteins, typically those involved in processes relating to inflammation and apoptosis. These domains mediate th ...

, CARD, have been shown to be involved in inflammation and immune response.

Function

NLRP3 is a component of the innate immune system that functions as a

pattern recognition receptor Pattern recognition receptors (PRRs) play a crucial role in the proper function of the innate immune system. PRRs are germline-encoded host sensors, which detect molecules typical for the pathogens. They are proteins expressed, mainly, by cells of ...

(PRR) that recognizes

pathogen-associated molecular pattern Pathogen-associated molecular patterns (PAMPs) are small molecular motifs conserved within a class of microbes. They are recognized by toll-like receptors (TLRs) and other pattern recognition receptors (PRRs) in both plants and animals. A vast arra ...

s (PAMPs). NLRP3 belongs to the

NOD-like receptor The nucleotide-binding oligomerization domain-like receptors, or NOD-like receptors (NLRs) (also known as nucleotide-binding leucine-rich repeat receptors), are intracellular sensors of pathogen-associated molecular patterns (PAMPs) that enter the ...

(NLR) subfamily of PRRs and NLRP3 together with the adaptor ASC protein

PYCARD PYCARD, often referred to as ASC (Apoptosis-associated speck-like protein containing a CARD), is a protein that in humans is encoded by the ''PYCARD'' gene. It is localized mainly in the nucleus of monocytes and macrophages. In case of pathogen in ...

forms a

caspase-1 Caspase-1/Interleukin-1 converting enzyme (ICE) is an evolutionarily conserved enzyme that proteolysis, proteolytically cleaves other proteins, such as the Protein precursor, precursors of the inflammatory cytokines Interleukin 1 beta, interleuki ...

activating complex known as the NLRP3

. NLRP3 in the absence of activating signal is kept in an inactive state complexed with

HSP90 Hsp90 (heat shock protein 90) is a chaperone protein that assists other proteins to fold properly, stabilizes proteins against heat stress, and aids in protein degradation. It also stabilizes a number of proteins required for tumor growth, ...

and SGT1 in the

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

. NLRP3 inflammasome detects danger signals such as crystalline

and extracellular ATP released by damaged cells. These signals release HSP90 and SGT1 from and recruit ASC protein and caspase-1 to the inflammasome complex. Caspase-1 within the activated NLRP3 inflammasome complex in turn activates the inflammatory cytokine,

IL-1β Interleukin-1 beta (IL-1β) also known as leukocytic pyrogen, leukocytic endogenous mediator, mononuclear cell factor, lymphocyte activating factor and other names, is a cytokine protein that in humans is encoded by the ''IL1B'' gene."Catabolin" ...

. The NLRP3 inflammasome appears to be activated by changes in intracellular potassium caused by potassium efflux from

mechanosensitive ion channel Mechanosensitive channels, mechanosensitive ion channels or stretch-gated ion channels (not to be confused with mechanoreceptors). They are present in the membranes of organisms from the three domains of life: bacteria, archaea, and eukarya. They a ...

s located in the cell membrane. It appears that NLRP3 is also regulated by

reactive oxygen species In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen () p ...

(ROS), though the precise mechanisms of such regulation has not been determined. It is suggested that NLRP3 provides protection against ''

Streptococcus pneumoniae ''Streptococcus pneumoniae'', or pneumococcus, is a Gram-positive, spherical bacteria, alpha-hemolytic (under aerobic conditions) or beta-hemolytic (under anaerobic conditions), aerotolerant anaerobic member of the genus Streptococcus. They ar ...

'' infections by activating

STAT6 Signal transducer and activator of transcription 6 (STAT6) is a transcription factor that belongs to the Signal Transducer and Activator of Transcription (STAT) family of proteins. The proteins of STAT family transmit signals from a receptor com ...

and

SPDEF SAM pointed domain-containing Ets transcription factor is a protein that in humans is encoded by the ''SPDEF'' gene. PDEF is an ETS transcription factor expressed in prostate epithelial cells. It acts as an androgen-independent transactivator of P ...

Pathology

Mutations in the NLRP3 gene have been associated with a spectrum of dominantly inherited autoinflammatory diseases called

cryopyrin-associated periodic syndrome Cryopyrin-associated periodic syndrome (CAPS) is a group of rare, heterogeneous autoinflammatory disease characterized by interleukin 1β-mediated systemic inflammation and clinical symptoms involving skin, joints, central nervous system, and eyes ...

(CAPS). This includes

familial cold autoinflammatory syndrome Cold urticaria (essentially meaning cold hives) is a disorder in large red welts called hives (''urticaria'') form on the skin after exposure to a cold stimulus. The hives are usually itchy and often the hands and feet will become itchy and swoll ...

(FCAS),

Muckle–Wells syndrome Muckle–Wells syndrome (MWS) is a rare autosomal dominant disease which causes sensorineural deafness and recurrent hives, and can lead to amyloidosis. Individuals with MWS often have episodic fever, chills, and joint pain. As a result, MWS is ...

(MWS), chronic infantile neurological cutaneous and articular ( CINCA) syndrome, neonatal onset multisystem inflammatory disease (NOMID), and keratoendotheliitis fugax hereditaria. Defects in this gene have also been linked to

familial Mediterranean fever Familial Mediterranean fever (FMF) is a hereditary inflammatory disorder. FMF is an autoinflammatory disease caused by mutations in Mediterranean fever gene, which encodes a 781–amino acid protein called pyrin. While all ethnic groups are sus ...

. In addition, the NLRP3 inflammasome has a role in the

pathogenesis Pathogenesis is the process by which a disease or disorder develops. It can include factors which contribute not only to the onset of the disease or disorder, but also to its progression and maintenance. The word comes from Greek πάθος ''pat ...

gout Gout ( ) is a form of inflammatory arthritis characterized by recurrent attacks of a red, tender, hot and swollen joint, caused by deposition of monosodium urate monohydrate crystals. Pain typically comes on rapidly, reaching maximal intens ...

, hemorrhagic stroke and

neuroinflammation Neuroinflammation is inflammation of the nervous tissue. It may be initiated in response to a variety of cues, including infection, traumatic brain injury,Ebert SE, Jensen P, Ozenne B, Armand S, Svarer C, Stenbaek DS ''et al.'' Molecular imaging of ...

occurring in protein-misfolding diseases, such as Alzheimer's,

Parkinson's Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms becom ...

, and

prion disease Prions are misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals. It i ...

s. Amelioration of mouse models of many diseases has been shown to occur by deletion of the NLRP3 inflammasome, including

type 2 diabetes Type 2 diabetes, formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance, and relative lack of insulin. Common symptoms include increased thirst, frequent urinatio ...

, multiple sclerosis, Alzheimer's disease, and

atherosclerosis Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually no s ...

. The compound

β-Hydroxybutyrate β-Hydroxybutyric acid, also known as 3-hydroxybutyric acid or BHB, is an organic compound and a beta hydroxy acid with the chemical formula CH3CH(OH)CH2CO2H; its conjugate base is β-hydroxybutyrate, also known as 3-hydroxybutyrate. β-Hydroxyb ...

has been shown to block NLRP3 activation, and thus may be of benefit for many of these diseases. Deregulation of NLRP3 has been connected with

carcinogenesis Carcinogenesis, also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cells are transformed into cancer cells. The process is characterized by changes at the cellular, genetic, and epigenetic levels and abno ...

. For example, all the components of the NLRP3 inflammasome are downregulated or completely lost in human hepatocellular carcinoma.

Inhibition

The NLRP3 inflammasome has garnered attention as a potential drug target for a variety of diseases underpinned by inflammation. The diarylsulfonylurea MCC-950 has been identified as a potent and selective NLRP3 inhibitor. Nodthera and Inflazome, have entered phase I clinical trials with NLRP3 inhibitors. Another NLRP3 antagonist is Dapansutrile (OLT1177). This β-sulfonyl nitrile molecule compound was developed by Olactec Therapeutics, and is a selective NLRP3 inhibitor. Dapansutrile, been used in clinical trials as a remedy for heart failure, osteoarthritis and gouty arthritis.

References and notes

External links

* {{DEFAULTSORT:Nalp3 LRR proteins Human proteins NOD-like receptors