© BioMed Central Ltd 2005
Published: 27 June 2005
Cyclophilins (Enzyme Commission (EC) number 22.214.171.124) belong to a group of proteins that have peptidyl-prolyl cis-trans isomerase activity; such proteins are collectively known as immunophilins and also include the FK-506-binding proteins and the parvulins. Cyclophilins are found in all cells of all organisms studied, in both prokaryotes and eukaryotes; humans have a total of 16 cyclophilin proteins, Arabidopsis up to 29 and Saccharomyces 8. The first member of the cyclophilins to be identified in mammals, cyclophilin A, is the major cellular target for, and thus mediates the actions of, the immunosuppressive drug cyclosporin A. Cyclophilin A forms a ternary complex with cyclosporin A and the calcium-calmodulin-activated serine/threonine-specific protein phosphatase calcineurin; formation of this complex prevents calcineurin from regulating cytokine gene transcription. Recent studies have implicated a diverse array of additional cellular functions for cyclophilins, including roles as chaperones and in cell signaling.
Gene organization and evolutionary history
The terms 'cyclophilin' and 'peptidyl-prolyl isomerase' (PPIase) are almost synonymous today, but the identification of the first protein that showed PPIase activity over 20 years ago  was independent of the purification of cyclophilin A (CypA) from bovine thymocytes as an intracellular protein with a high affinity for the immunosuppressive drug cyclosporin A (CsA) . It was not until five years later that the 18 kDa protein with PPIase activity and CypA were found to be one and the same [3, 4]. Along with the discoveries of other PPIase proteins (immunophilins), such as the parvulins and the FK-506-binding proteins (FKBPs, which bind the immunosuppressant drug FK-506), additional cyclophilins have subsequently been identified and the cyclophilins were found to constitute a protein family. All cyclophilins share a common domain of approximately 109 amino acids, the cyclophilin-like domain (CLD), surrounded by domains unique to each member of the family that are associated with subcellular compartmentalization and functional specialization [5, 6].
Cyclophilins have been found in mammals, plants, insects, fungi, and bacteria; they are structurally conserved throughout evolution and all have PPIase activity. There are 7 major cyclophilins in humans - hCypA (also called hCyp-18a, 18 denotes molecular mass of 18 kDa), hCypB (also called hCyp-22/p, 22 kDa), hCypC, hCypD, hCypE, hCyp40 (40 kDa), and hCypNK (first identified from human natural killer cells) - and a total of 16 unique proteins [7, 8]. Drosophila has at least 9 cyclophilins  and the plant Arabidopsis thaliana has 29 putative cyclophilins , whereas 8 cyclophilins, Cpr1-Cpr8, have been found in Saccharomyces cerevisiae (reviewed in ). Little is known about the genomic structure of human cyclophilin genes; they are generally not linked to each other in the genome.
Cyclophilins also have varying degrees of affinity for the immunosuppressive drug CsA, a cyclic 11-amino-acid peptide produced by the fungus Tolypocladium inflatum. CypA, in particular, is the major intracellular receptor for CsA . In mammals, the CsA-CypA complex binds to and inhibits calcineurin, a calcium-calmodulin-activated serine/threonine-specific protein phosphatase. The inhibition of calcineurin blocks the translocation of nuclear factor of activated T cells (NF-AT) from the cytosol to the nucleus, thus preventing the transcription of genes encoding cytokines such as interleukin-2 [11, 12]. In the yeast S. cerevisiae, inhibition of the calcineurin homolog by the complex between CsA and the cyclophilin A homolog Cpr1 prevents recovery from pheromone-induced growth arrest . In the human-pathogenic fungus Cryptococcus neoformans, inhibition of the calcineurin homolog Cna1 by a complex of CsA with either of the cyclophilin A homologs Cpal or Cpa2 prevents growth at elevated temperatures [14, 15].
Characteristic structural features
Localization and function
Cyclophilins can be found in most cellular compartments of most tissues and encode unique functions. In mammals, CypA and Cyp40 are cytosolic whereas CypB and CypC have amino-terminal signal sequences that target them to the ER protein secretory pathway (reviewed in [7, 16]). CypD has a signal sequence that directs it to the mitochondria [22, 23]; CypE has an amino-terminal RNA-binding domain and is localized in the nucleus  and Cyp40 has TPRs and is located in the cytosol . Human CypNK is the largest cyclophilin, with a large, hydrophilic and positively charged carboxyl terminus, and is located in the cytosol [26, 27].
Functions of mammalian cyclophilins
The immunosuppressive action of CsA is exerted via a ternary complex between CsA, CypA and calcineurin. The crystal structure of the complex has recently been determined to a resolution of 2.8 Å (Figure 2) [36, 37]. Binding of the CsA-CypA complex to calcineurin increases the complex's stability, and the complexed proteins remain resistant to proteolytic cleavage . Upon binding of CsA to CypA, the charges and hydrophobic surfaces of the drug-protein complex become more congruent with the binding site on calcineurin. The CsA-CypA complex binds at the interface between the catalytic and regulatory subunits of calcineurin (Figure 2). Most importantly, CsA-CypA binding to calcineurin inhibits the phosphatase activity and biological function of calcineurin [11, 13, 39, 40].
Several protein-folding processes depend on the catalytic and/or chaperone-like activities of cyclophilins. For example, CypA promotes both the formation and the infectivity of virions of the human immunodeficiency virus (HIV)-1 [41–47]. CypA is incorporated into HIV-1 virions, where it interacts with HIV-1 Gag, the polyprotein precursor of virion structural proteins. A small region of the HIV-1 capsid protein containing four conserved prolines has been shown to be important for incorporation of CypA into virions [48, 49].
A retina-specific cyclophilin of the fruit fly Drosophila melanogaster, NinaA (an ortholog of mammal CypC), is crucial for the folding of rhodopsin isoforms [50, 51]. A mutation in the gene encoding NinaA results in improper folding of rhodopsin and subsequent abnormal expression of the protein . CypA is also important in the folding of neu-ronal receptors. Using CsA to probe the expression of homo-oligomeric receptors containing nicotinic acetylcholine receptor subunit α7, Helekar and colleagues  concluded that CypA might have a critical role in the maturation of homo-oligomeric receptors by acting directly or indirectly as a prolyl isomerase or as a molecular chaperone.
Cyclophilins can also act as modulators of protein function. The mammalian cyclophilin Cyp40 is part of the steroid-receptor complex and can form a dimeric complex with the heat-shock protein Hsp90, a process not affected by CsA [53, 54]. In yeast, the Cyp40 homologs Cpr6 and Cpr7 also associate with Hsp90 homologs and have analogous functions . A mammalian Cyp40 has been shown to regulate the activity of the transcription factor c-Myb , whereas CypA has been associated with YY1, a zinc-finger suppressor of gene transcription , and Zpr1, an essential zinc-finger protein . In addition, the ER-specific cyclophilin CypB can form a complex with the peptide hormone prolactin to induce transcription of a range of genes .
Functions of yeast cyclophilins
Contrary to the expectation that the highly conserved cyclophilins might be essential for protein folding, none of the eight individual cyclophilins was found to be essential in S. cerevisiae . In fact, we showed that an octuplet mutant lacking all eight cyclophilins was viable and that there was little or no evidence for functional redundancy . Recent studies also reveal that Cpr1 has a role in modulating the activity of two different histone-deacetylase complexes (Sin3-Rpd3 and Set3C) and is important in enabling the transcriptional events necessary during the switch from mitotic to meiotic cell division in budding yeast [29, 60, 61]. This is in accord with our recent finding that Cpr1 is enriched in the nucleus in yeast cells, and it reveals a clear selective pressure for maintaining this highly conserved enzyme .
The pathogenic yeast C. neoformans has two similar CypA-related proteins, Cpa1 and Cpa2. In contrast to the viable octuplet cyclophilin mutant strain of S. cerevisiae, Cpa1 is required for growth of C. neoformans at elevated temperatures and for full expression of fungal virulence, whereas Cpa2 is dispensable for these functions in the presence of Cpa1. Deletion of both the CPA1 and CPA2 genes leads to a conditional synthetic phenotype, resulting in a defect in growth and virulence . In our current models, this role of Cpa1 and Cpa2 is hypothesized to be independent of calcineurin function, suggesting a novel role for cyclophilin A homologs in the growth and virulence of this pathogen .
Recent studies have suggested a new role for cyclophilins in cell signaling. For example, mammalian CypA has been found to regulate the T-cell-specific interleukin-2 tyrosine kinase Itk, which contains conserved Src homology 2 (SH2), Src homology 3 (SH3), and kinase domains [63–65]. Itk is a non-receptor protein-tyrosine kinase that has a role in the maturation of thymocytes and is required for intracellular signaling events leading to T-cell activation. Binding of CypA to the SH2 domain of Itk results in conformational change within the SH2 domain that alters ligand specificity . Mutation of a proline residue in the SH2 domain disrupts the interaction between Itk and CypA and specifically increases the production of type 2 (Th2) cytokines (cytokines produced by Th2 helper cells) [65, 66].
In another example of a cyclophilin involved in cell signaling, human CypB has been found to govern the activation of interferon-regulatory factor-3 (IRF-3). IRF-3 is a member of the group of interferon regulatory factors that induce interferon-β once translocated into the nucleus. CypB interacts with IRF-3 in the yeast two-hybrid assay. An RNA-interference study of CypB indicates that the suppression of virus-induced IRF-3 phosphorylation and other related events can result in the inhibition of interferon-1β .
Finally, the mitochondrially targeted cyclophilin CypD has been found to play an important role in the mitochondrial permeability transition, in which mitochondrial pores open, leading to cell death [68–72]. By generating CypD-deficient mice, several research groups have discovered that CypD and the mitochondrial permeability transition are required to mediate the cell death induced by calcium and oxidative damage, but not to mediate conventional apoptosis involving Bcl-2 family proteins [70–72]. Further exploration of the role of CypD in mitochondrial function and its potential as a novel drug target has been also discussed recently .
We thank Hengming Ke for providing Figure 2 and J.A. King for careful reading of the manuscript. Research in the Wang and Heitman laboratories is supported by NIH grants A1054958 (P.W.), A103911I5, A1042159, A1050113, and A1050438 (J.H.). J.H. is a Burroughs-Wellcome Scholar in Molecular Pathogenic Mycology and an investigator of the Howard Hughes Medical Institute.
- Fischer G, Bang H, Mech C: Determination of enzymatic catalysis for the cis-trans-isomerization of peptide binding in proline-containing peptides. Biomed Biochim Acta. 1984, 43: 1101-1111. This paper reports the first identification of a PPIase.PubMed
- Handschumacher RE, Harding MW, Rice J, Drugge RJ, Speicher DW: Cyclophilin: a specific cytosolic binding protein for cyclosporin A. Science. 1984, 226: 544-547. The first report of cyclophilin A as the cellular receptor for cyclosporin A.PubMedView Article
- Fischer G, Wittmann-Liebold B, Lang K, Kiefhaber T, Schmid FX: Cyclophilin and peptidyl-prolyl cis-trans isomerase are probably identical proteins. Nature. 1989, 337: 476-478. 10.1038/337476a0. The report that cyclophilin A is a PPIase.PubMedView Article
- Takahashi N, Hayano T, Suzuki M: Peptidyl-prolyl cis-trans isomerase is the cyclosporin A-binding protein cyclophilin. Nature. 1989, 337: 473-475. 10.1038/337473a0. See .PubMedView Article
- Marks AR: Cellular functions of immunophilins. Physiol Rev. 1996, 76: 631-649. An excellent review on cyclophilin function.PubMed
- Arevalo-Rodriguez M, Wu X, Hanes SD, Heitman J: Prolyl isomerases in yeast. Front Biosci. 2004, 9: 2420-2446. A comprehensive review of the yeast PPIases.PubMedView Article
- Galat A: Peptidylprolyl cis/trans isomerases (immunophilins): biological diversity - targets - functions. Curr Top Med Chem. 2003, 3: 1315-1347. An excellent review of immunophilin functions.PubMedView Article
- Waldmeier PC, Zimmermann K, Qian T, Tintelnot-Blomley M, Lemasters JJ: Cyclophilin D as a drug target. Curr Med Chem. 2003, 10: 1485-1506. 10.2174/0929867033457160. A review exploring possibilities of mitochondrially localized CypD in therapeutic applications.PubMedView Article
- He Z, Li L, Luan S: Immunophilins and parvulins. Superfamily of peptidyl prolyl isomerases in Arabidopsis. Plant Physiol. 2004, 134: 1248-1267. 10.1104/pp.103.031005. A review of the plant PPIases.PubMedPubMed CentralView Article
- Gothel SF, Marahiel MA: Peptidyl-prolyl cis-trans isomerases, a superfamily of ubiquitous folding catalysts. Cell Mol Life Sci. 1999, 55: 423-436. 10.1007/s000180050299. An excellent review of PPIases.PubMedView Article
- Liu J, Farmer JD, Lane WS, Friedman J, Weissman I, Schreiber SL: Calcineurin is a common target of cyclophilin-cyclosporin A and FKBP-FK506 complexes. Cell. 1991, 66: 807-815. 10.1016/0092-8674(91)90124-H. The first report of calcineurin as the target for CypA-CsA and FK506-FKBP.PubMedView Article
- O'Keefe SJ, Tamura J, Kincaid RL, Tocci MJ, O'Neill EA: FK-506-and CsA-sensitive activation of the interleukin-2 promoter by calcineurin. Nature. 1992, 357: 692-694. 10.1038/357692a0. This paper describes calcineurin as a component of the T-cell receptor signal transduction pathway.PubMedView Article
- Foor F, Parent SA, Morin N, Dahl AM, Ramadan N, Chrebet G, Bostian KA, Nielsen JB: Calcineurin mediates inhibition by FK506 and cyclosporin of recovery from alpha-factor arrest in yeast. Nature. 1992, 360: 682-684. 10.1038/360682a0. This paper shows that the binding of FK506 to FKBP12 inhibits calcineurin function in yeast.PubMedView Article
- Odom A, Muir S, Lim E, Toffaletti DL, Perfect J, Heitman J: Calcineurin is required for virulence of Cryptococcus neoformans. EMBO J. 1997, 16: 2576-2589. 10.1093/emboj/16.10.2576. This is the first report of C. neoformans calcineurin function.PubMedPubMed CentralView Article
- Fox DS, Cruz MC, Sia RA, Ke H, Cox GM, Cardenas ME, Heitman J: Calcineurin regulatory subunit is essential for virulence and mediates interactions with FKBP12-FK506 in Cryptococcus neoformans. Mol Microbiol. 2001, 39: 835-849. 10.1046/j.1365-2958.2001.02295.x. See .PubMedView Article
- Dornan J, Taylor P, Walkinshaw MD: Structures of immunophilins and their ligand complexes. Curr Top Med Chem. 2003, 3: 1392-1409. This article and  review the structures of cyclophilins and FKBPs.PubMedView Article
- Kallen J, Spitzfaden C, Zurini MG, Wider G, Widmer H, Wuthrich K, Walkinshaw MD: Structure of human cyclophilin and its binding site for cyclosporin A determined by X-ray crystallography and NMR spectroscopy. Nature. 1991, 353: 276-279. 10.1038/353276a0. See .PubMedView Article
- Ke HM, Zydowsky LD, Liu J, Walsh CT: Crystal structure of recombinant human T-cell cyclophilin A at 2.5 A resolution. Proc Natl Acad Sci USA. 1991, 88: 9483-9487. A report of the crystal structure of CypA.PubMedPubMed CentralView Article
- Mikol V, Kallen J, Walkinshaw MD: X-ray structure of a cyclophilin B/cyclosporin complex: comparison with cyclophilin A and delineation of its calcineurin-binding domain. Proc Natl Acad Sci USA. 1994, 91: 5183-5186. A report of the crystal structure of CypB.PubMedPubMed CentralView Article
- Ke H, Zhao Y, Luo F, Weissman I, Friedman J: Crystal structure of murine cyclophilin C complexed with immunosuppressive drug cyclosporin A. Proc Natl Acad Sci USA. 1993, 90: 11850-11854. A report of the crystal structure of CypC.PubMedPubMed CentralView Article
- Taylor P, Dornan J, Carrello A, Minchin RF, Ratajczak T, Walkinshaw MD: Two structures of cyclophilin 40: folding and fidelity in the TPR domains. Structure. 2001, 9: 431-438. 10.1016/S0969-2126(01)00603-7. A report of the crystal structure of Cyp40.PubMedView Article
- Andreeva L, Heads R, Green CJ: Cyclophilins and their possible role in the stress response. Int J Exp Pathol. 1999, 80: 305-315. 10.1046/j.1365-2613.1999.00128.x. A review of the functions of cyclophilins in stress tolerance.PubMedPubMed CentralView Article
- Hamilton GS, Steiner JP: Immunophilins: beyond immunosuppression. J Med Chem. 1998, 41: 5119-5143. 10.1021/jm980307x. A review of immunophilins in pharmacological applications.PubMedView Article
- Mi H, Kops O, Zimmermann E, Jaschke A, Tropschug M: A nuclear RNA-binding cyclophilin in human T cells. FEBS Lett. 1996, 398: 201-205. 10.1016/S0014-5793(96)01248-3. This paper reports that CypE contains a RNA-binding domain.PubMedView Article
- Kieffer LJ, Seng TW, Li W, Osterman DG, Handschumacher RE, Bayney RM: Cyclophilin-40, a protein with homology to the P59 component of the steroid receptor complex. Cloning of the cDNA and further characterization. J Biol Chem. 1993, 268: 12303-12310. An article further characterizing Cyp40.PubMed
- Anderson SK, Gallinger S, Roder J, Frey J, Young HA, Ortaldo JR: A cyclophilin-related protein involved in the function of natural killer cells. Proc Natl Acad Sci USA. 1993, 90: 542-546. This paper and  are the first reports on CypNK.PubMedPubMed CentralView Article
- Rinfret A, Collins C, Menard R, Anderson SK: The N-terminal cyclophilin-homologous domain of a 150-kilodalton tumor recognition molecule exhibits both peptidylprolyl cis-trans-isomerase and chaperone activities. Biochemistry. 1994, 33: 1668-1673. 10.1021/bi00173a008. See .PubMedView Article
- Haendler B, Keller R, Hiestand PC, Kocher HP, Wegmann G, Movva NR: Yeast cyclophilin: isolation and characterization of the protein, cDNA and gene. Gene. 1989, 83: 39-46. 10.1016/0378-1119(89)90401-0. An early report of the yeast Cpr1.PubMedView Article
- Arevalo-Rodriguez M, Heitman J: Cyclophilin A is localized to the nucleus and controls meiosis in Saccharomyces cerevisiae. Eukaryot Cell. 2005, 4: 17-29. 10.1128/EC.4.1.17-29.2005. A report of the yeast Cpr1, which controls meiosis.PubMedPubMed CentralView Article
- Koser PL, Sylvester D, Livi GP, Bergsma DJ: A second cyclophilin-related gene in Saccharomyces cerevisiae. Nucleic Acids Res. 1990, 18: 1643-This paper and  report the identification of yeast Cpr2.PubMedPubMed CentralView Article
- Koser PL, Bergsma DJ, Cafferkey R, Eng WK, McLaughlin MM, Ferrara A, Silverman C, Kasyan K, Bossard MJ, Johnson RK, et al: The CYP2 gene of Saccharomyces cerevisiae encodes a cyclosporin A-sensitive peptidyl-prolyl cis-trans isomerase with an N-terminal signal sequence. Gene. 1991, 108: 73-80. 10.1016/0378-1119(91)90489-X. See .PubMedView Article
- McLaughlin MM, Bossard MJ, Koser PL, Cafferkey R, Morris RA, Miles LM, Strickler J, Bergsma DJ, Levy MA, Livi GP: The yeast cyclophilin multigene family: purification, cloning and characterization of a new isoform. Gene. 1992, 111: 85-92. 10.1016/0378-1119(92)90606-P. This paper and  report the identification of yeast Cpr3.PubMedView Article
- Frigerio G, Pelham HR: A Saccharomyces cerevisiae cyclophilin resident in the endoplasmic reticulum. J Mol Biol. 1993, 233: 183-188. 10.1006/jmbi.1993.1497. See .PubMedView Article
- Huh WK, Falvo JV, Gerke LC, Carroll AS, Howson RW, Weissman JS, O'Shea EK: Global analysis of protein localization in budding yeast. Nature. 2003, 425: 686-691. 10.1038/nature02026. An analysis of protein localization in yeast.PubMedView Article
- Duina AA, Marsh JA, Gaber RF: Identification of two CyP-40-like cyclophilins in Saccharomyces cerevisiae, one of which is required for normal growth. Yeast. 1996, 12: 943-952. 10.1002/(SICI)1097-0061(199608)12:10<943::AID-YEA997>3.0.CO;2-3. A report of the yeast Cpr6 and Cpr7.PubMedView Article
- Jin L, Harrison SC: Crystal structure of human calcineurin complexed with cyclosporin A and human cyclophilin. Proc Natl Acad Sci USA. 2002, 99: 13522-13526. 10.1073/pnas.212504399. This paper and  report the crystal structure of the cyclophilin-CsA-calcineurin complex.PubMedPubMed CentralView Article
- Huai Q, Kim HY, Liu Y, Zhao Y, Mondragon A, Liu JO, Ke H: Crystal structure of calcineurin-cyclophilin-cyclosporin shows common but distinct recognition of immunophilin-drug complexes. Proc Natl Acad Sci USA. 2002, 99: 12037-12042. 10.1073/pnas.192206699. See .PubMedPubMed CentralView Article
- Hornbogen T, Pieper R, Hoffmann K, Kleinkauf H, Zocher R: Two new cyclophilins from Fusarium sambucinum and Aspergillus niger: resistance of cyclophilin/cyclosporin A complexes against proteolysis. Biochem Biophys Res Commun. 1992, 187: 791-796. 10.1016/0006-291X(92)91265-R. A study showing that the binding of CsA to cyclophilin resists proteolytic cleavage.PubMedView Article
- Liu J, Albers MW, Wandless TJ, Luan S, Alberg DG, Belshaw PJ, Cohen P, MacKintosh C, Klee CB, Schreiber SL: Inhibition of T cell signaling by immunophilin-ligand complexes correlates with loss of calcineurin phosphatase activity. Biochemistry. 1992, 31: 3896-3901. 10.1021/bi00131a002. See  and . A report of calcineurin function in T-cell signaling.PubMedView Article
- Breuder T, Hemenway CS, Movva NR, Cardenas ME, Heitman J: Calcineurin is essential in cyclosporin A- and FK506-sensitive yeast strains. Proc Natl Acad Sci USA. 1994, 91: 5372-5376. A report of the function of calcineurin in yeast.PubMedPubMed CentralView Article
- Luban J, Bossolt KL, Franke EK, Kalpana GV, Goff SP: Human immunodeficiency virus type 1 Gag protein binds to cyclophilins A and B. Cell. 1993, 73: 1067-1078. 10.1016/0092-8674(93)90637-6. This reference and [42-49] are reports of the interaction between the HIV Gag protein and cyclophilins.PubMedView Article
- Luban J: Absconding with the chaperone: essential cyclophilin-Gag interaction in HIV-1 virions. Cell. 1996, 87: 1157-1159. 10.1016/S0092-8674(00)81811-5. See .PubMedView Article
- Bosco DA, Eisenmesser EZ, Pochapsky S, Sundquist WI, Kern D: Catalysis of cis/trans isomerization in native HIV-1 capsid by human cyclophilin A. Proc Natl Acad Sci USA. 2002, 99: 5247-5252. 10.1073/pnas.082100499. See .PubMedPubMed CentralView Article
- Braaten D, Aberham C, Franke EK, Yin L, Phares W, Luban J: Cyclosporine A-resistant human immunodeficiency virus type 1 mutants demonstrate that Gag encodes the functional target of cyclophilin A. J Virol. 1996, 70: 5170-5176. See .PubMedPubMed Central
- Braaten D, Franke EK, Luban J: Cyclophilin A is required for an early step in the life cycle of human immunodeficiency virus type 1 before the initiation of reverse transcription. J Virol. 1996, 70: 3551-3560. See .PubMedPubMed Central
- Braaten D, Luban J: Cyclophilin A regulates HIV-1 infectivity, as demonstrated by gene targeting in human T cells. EMBO J. 2001, 20: 1300-1309. 10.1093/emboj/20.6.1300. See .PubMedPubMed CentralView Article
- Sokolskaja E, Sayah DM, Luban J: Target cell cyclophilin A modulates human immunodeficiency virus type 1 infectivity. J Virol. 2004, 78: 12800-12808. 10.1128/JVI.78.23.12800-12808.2004. See .PubMedPubMed CentralView Article
- Franke EK, Yuan HE, Luban J: Specific incorporation of cyclophilin A into HIV-1 virions. Nature. 1994, 372: 359-362. 10.1038/372359a0. See .PubMedView Article
- Thali M, Bukovsky A, Kondo E, Rosenwirth B, Walsh CT, Sodroski J, Gottlinger HG: Functional association of cyclophilin A with HIV-1 virions. Nature. 1994, 372: 363-365. 10.1038/372363a0. See .PubMedView Article
- Stamnes MA, Shieh BH, Chuman L, Harris GL, Zuker CS: The cyclophilin homolog ninaA is a tissue-specific integral membrane protein required for the proper synthesis of a subset of Drosophila rhodopsins. Cell. 1991, 65: 219-227. 10.1016/0092-8674(91)90156-S. This paper and  report the role of NinaA in the synthesis of Drosophila rhodopsins.PubMedView Article
- Colley NJ, Baker EK, Stamnes MA, Zuker CS: The cyclophilin homolog ninaA is required in the secretory pathway. Cell. 1991, 67: 255-263. 10.1016/0092-8674(91)90177-Z. See .PubMedView Article
- Helekar SA, Char D, Neff S, Patrick J: Prolyl isomerase requirement for the expression of functional homo-oligomeric ligand-gated ion channels. Neuron. 1994, 12: 179-189. 10.1016/0896-6273(94)90162-7. This report suggests that cyclophilins may play a role in the maturation of homo-oligomeric receptors.PubMedView Article
- Ratajczak T, Carrello A, Mark PJ, Warner BJ, Simpson RJ, Moritz RL, House AK: The cyclophilin component of the unactivated estrogen receptor contains a tetratricopeptide repeat domain and shares identity with p59 (FKBP59). J Biol Chem. 1993, 268: 13187-13192. This paper and  show that Cyp40 is a part of the steroid-receptor complex.PubMed
- Chang HC, Lindquist S: Conservation of Hsp90 macromolecular complexes in Saccharomyces cerevisiae. J Biol Chem. 1994, 269: 24983-24988. See .PubMed
- Leverson JD, Ness SA: Point mutations in v-Myb disrupt a cyclophilin-catalyzed negative regulatory mechanism. Mol Cell. 1998, 1: 203-211. 10.1016/S1097-2765(00)80021-0. This study shows that Cyp40 inhibits the c-Myb DNA binding activity.PubMedView Article
- Yang WM, Inouye CJ, Seto E: Cyclophilin A and FKBP12 interact with YY1 and alter its transcriptional activity. J Biol Chem. 1995, 270: 15187-15193. 10.1074/jbc.270.25.15187. Immunophilins modulate the zinc-finger transcription factor YY1.PubMedView Article
- Ansari H, Greco G, Luban J: Cyclophilin A peptidyl-prolyl isomerase activity promotes ZPR1 nuclear export. Mol Cell Biol. 2002, 22: 6993-7003. 10.1128/MCB.22.20.6993-7003.2002. This report shows that the yeast Cpr1 modulates the function of the zinc-finger transcription factor Zpr1 by promoting its nuclear export.PubMedPubMed CentralView Article
- Rycyzyn MA, Clevenger CV: The intranuclear prolactin/cyclophilin B complex as a transcriptional inducer. Proc Natl Acad Sci USA. 2002, 99: 6790-6795. 10.1073/pnas.092160699. This study reports the interaction between CypB and the somatolactogenic hormone prolactin.PubMedPubMed CentralView Article
- Dolinski K, Muir S, Cardenas M, Heitman J: All cyclophilins and FK506 binding proteins are, individually and collectively, dispensable for viability in Saccharomyces cerevisiae. Proc Natl Acad Sci USA. 1997, 94: 13093-13098. 10.1073/pnas.94.24.13093. A report of a yeast dodecuplet mutant strain in which all 12 genes encoding 8 cyclophilins and 4 FKBPs were deleted.PubMedPubMed CentralView Article
- Arevalo-Rodriguez M, Cardenas ME, Wu X, Hanes SD, Heitman J: Cyclophilin A and Ess1 interact with and regulate silencing by the Sin3-Rpd3 histone deacetylase. EMBO J. 2000, 19: 3739-3749. 10.1093/emboj/19.14.3739. This study shows that the yeast Cpr1 and parvilin Ess1 function in parallel, both targeting the Sin3-Rpd3 histone-deacetylase complex.PubMedPubMed CentralView Article
- Pijnappel WW, Schaft D, Roguev A, Shevchenko A, Tekotte H, Wilm M, Rigaut G, Seraphin B, Aasland R, Stewart AF: The S. cerevisiae SET3 complex includes two histone deacetylases, Hos2 and Hst1, and is a meiotic-specific repressor of the sporulation gene program. Genes Dev. 2001, 15: 2991-3004. 10.1101/gad.207401. This study reports that the yeast Cpr1 is a part of the Set3 complex that maintains histone-deacetylase activities.PubMedPubMed CentralView Article
- Wang P, Cardenas ME, Cox GM, Perfect JR, Heitman J: Two cyclophilin A homologs with shared and distinct functions important for growth and virulence of Cryptococcus neoformans. EMBO Rep. 2001, 2: 511-518. 10.1093/embo-reports/kve135. A description of the function of two cyclophilin A homologs in the pathogenic fungus C. neoformans.PubMedPubMed CentralView Article
- Brazin KN, Mallis RJ, Fulton DB, Andreotti AH: Regulation of the tyrosine kinase Itk by the peptidyl-prolyl isomerase cyclophilin A. Proc Natl Acad Sci USA. 2002, 99: 1899-1904. 10.1073/pnas.042529199. This paper and  give evidence that CypA inhibits the catalytic activity of the tyrosine kinase Itk.PubMedPubMed CentralView Article
- Min L, Fulton DB, Andreotti AH: A case study of proline isomerization in cell signaling. Front Biosci. 2005, 10: 385-397. An overview of the role of CypA in the regulation of Itk.PubMedView Article
- Colgan J, Asmal M, Neagu M, Yu B, Schneidkraut J, Lee Y, Sokolskaja E, Andreotti A, Luban J: Cyclophilin A regulates TCR signal strength in CD4+ T cells via a proline-directed conformational switch in Itk. Immunity. 2004, 21: 189-201. 10.1016/j.immuni.2004.07.005. See .PubMedView Article
- Mallis RJ, Brazin KN, Fulton DB, Andreotti AH: Structural characterization of a proline-driven conformational switch within the Itk SH2 domain. Nat Struct Biol. 2002, 9: 900-905. 10.1038/nsb864. A further look at the interaction between cyclophilin A and Itk.PubMedView Article
- Obata Y, Yamamoto K, Miyazaki M, Shimotohno K, Kohno S, Matsuyama T: Role of cyclophilin B in activation of interferon regulatory factor-3. J Biol Chem. 2005, 280: 18355-18360. 10.1074/jbc.M501684200. In this study, CypB was shown to interact with IRF-3; it may play a role in IRF-3 activation.PubMedView Article
- Lin DT, Lechleiter JD: Mitochondrial targeted cyclophilin D protects cells from cell death by peptidyl prolyl isomerization. J Biol Chem. 2002, 277: 31134-31141. 10.1074/jbc.M112035200. This study and [70-72] link CypD to mitochondrial permeability transition pores, cell damage, and apoptotic cell death.PubMedView Article
- Capano M, Virji S, Crompton M: Cyclophilin-A is involved in excitotoxin-induced caspase activation in rat neuronal B50 cells. Biochem J. 2002, 363: 29-36. This study presents the evidence that CypA participates in the activation of the caspase cascade in neuronal cells.PubMedPubMed CentralView Article
- Nakagawa T, Shimizu S, Watanabe T, Yamaguchi O, Otsu K, Yamagata H, Inohara H, Kubo T, Tsujimoto Y: Cyclophilin D-dependent mitochondrial permeability transition regulates some necrotic but not apoptotic cell death. Nature. 2005, 434: 652-658. 10.1038/nature03317. See .PubMedView Article
- Baines CP, Kaiser RA, Purcell NH, Blair NS, Osinska H, Hambleton MA, Brunskill EW, Sayen MR, Gottlieb RA, Dorn GW, et al: Loss of cyclophilin D reveals a critical role for mitochondrial permeability transition in cell death. Nature. 2005, 434: 658-662. 10.1038/nature03434. See .PubMedView Article
- Basso E, Fante L, Fowlkes J, Petronilli V, Forte MA, Bernardi P: Properties of the permeability transition pore in mitochondria devoid of cyclophilin D. J Biol Chem. 2005, 280: 18558-18561. 10.1074/jbc.C500089200. See .PubMedView Article