Calcineurin

File:Protein PPP3CA PDB 1aui.png

Crystallographic structure of calcineurin heterodimer composed of the catalytic (PPP3CA and regulatory (PPP3R1) subunits.

Calcineurin (CN) is a calcium and calmodulin dependent serine/threonine protein phosphatase (also known as protein phosphatase 3, and calcium-dependent serine-threonine phosphatase). It activates the T cells of the immune system and can be blocked by drugs. Calcineurin activates nuclear factor of activated T cell, cytoplasmic (NFATc), a transcription factor, by dephosphorylating it. The activated NFATc is then translocated into the nucleus, where it upregulates the expression of interleukin 2 (IL-2), which, in turn, stimulates the growth and differentiation of T cell response. Calcineurin is the target of a class of drugs called calcineurin inhibitors, which includes cyclosporine, pimecrolimus and tacrolimus.

Structure

Calcineurin is a heterodimer of a 61-kD calmodulin-binding catalytic subunit, calcineurin A and a 19-kD Ca²⁺-binding regulatory subunit, calcineurin B. There are three isozymes of the catalytic subunit, each encoded by a separate gene (PPP3CA, PPP3CB, and PPP3CC) and two isoforms of the regulatory, also encoded by separate genes (PPP3R1, PPP3R2).

protein phosphatase 3, catalytic subunit, alpha isozyme Identifiers Symbol PPP3CA Alt. symbols CALN, CALNA Entrez 5530 HUGO 9314 OMIM 114105 RefSeq NM_000944 UniProt Q08209 Other data EC number 3.1.3.16 Locus Chr. 4 q24

protein phosphatase 3, catalytic subunit, beta isozyme Identifiers Symbol PPP3CB Alt. symbols CALNB Entrez 5532 HUGO 9315 OMIM 114106 RefSeq NM_021132 UniProt P16298 Other data EC number 3.1.3.16 Locus Chr. 10 q22.2

protein phosphatase 3, catalytic subunit, gamma isozyme Identifiers Symbol PPP3CC Entrez 5533 HUGO 9316 OMIM 114107 RefSeq NM_005605 UniProt P48454 Other data EC number 3.1.3.16 Locus Chr. 8 p21.3

protein phosphatase 3, regulatory subunit B, alpha Identifiers Symbol PPP3R1 Entrez 5534 HUGO 9317 OMIM 601302 RefSeq NM_000945 UniProt P63098 Other data EC number 3.1.3.16 Locus Chr. 2 p14

protein phosphatase 3, regulatory subunit B, beta Identifiers Symbol PPP3R2 Entrez 5535 HUGO 9318 OMIM 613821 RefSeq NM_147180 UniProt Q96LZ3 Other data EC number 3.1.3.16 Locus Chr. 9 q31

Mechanism of action

When an antigen-presenting cell interacts with a T cell receptor on T cells, there is an increase in the cytoplasmic level of calcium, which activates calcineurin, by binding a regulatory subunit and activating calmodulin binding. Calcineurin induces different transcription factors (NFATs) that are important in the transcription of IL-2 genes. IL-2 activates T-helper lymphocytes and induces the production of other cytokines. In this way, it governs the action of cytotoxic lymphocytes. The amount of IL-2 being produced by the T-helper cells is believed to influence the extent of the immune response significantly.

Clinical relevance

Rheumatic diseases

Calcineurin inhibitors are prescribed for adult rheumatoid arthritis (RA) as a single drug or in combination with methotrexate. The microemulsion formulation is approved by the Federal Drug Administration of the United States for treatment of severely active RA. It is also prescribed for: psoriatic arthritis, psoriasis, acute ocular Behçet’s disease, juvenile idiopathic arthritis, adult and juvenile polymyositis and dermatomyositis, adult and juvenile systemic lupus erythematosus, adult lupus membranous nephritis, systemic sclerosis, aplastic anemia, steroid-resistant nephrotic syndrome, atopic dermatitis, severe corticosteroid-dependent asthma, severe ulcerative colitis, pemphigus vulgaris, myasthenia gravis, and dry eye disease, with or without Sjögren's syndrome (administered as ophthalmic emulsion).

Schizophrenia

Calcineurin is linked to receptors for several brain chemicals including NMDA, dopamine and GABA. An experiment with genetically-altered mice that could not produce calcineurin showed similar symptoms as in humans with schizophrenia: impairment in working memory, attention deficits, aberrant social behavior, and several other abnormalities characteristic of schizophrenia.

Diabetes

Calcineurin along with NFAT, may improve the function of diabetics' pancreatic beta cells. Thus tacrolimus contributes to the frequent development of new diabetes following renal transplantation.

Calcineurin/NFAT signaling is required for perinatal lung maturation and function.

Interactions

Calcineurin has been shown to interact with DSCR1 and AKAP5.

External links

• Calcineurin at the US National Library of Medicine Medical Subject Headings (MeSH)