Protein C inhibitor

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Protein C inhibitor (PCI, SERPINA5) is a serine protease inhibitor (serpin) which limits the activity of protein C (an anticoagulant).

An N-terminal fragment of PCI is a possible serum biomarker for prostate cancer.[1]

Protein C inhibitor is activated by heparin against thrombin.[2]

Protein C inhibitor (PCI) is serine protease inhibitor of serpin type that is found in most tissues and fluids, including blood plasma, seminal plasma and urine of human.[3] It is a 52kD glycoprotein and belongs to serine protease inhibitor ( Serpin) super family of protein.[3] In the beginning protein C Inhibitor (PCI) was identified as an inhibitor of activated protein C (APC), it is currently clear that this inhibitor has an expansive specificity, inhibiting several blood coagulation enzymes counting thrombin and factor Xa.[4][5]


In the beginning, protein C inhibitor(PCI) was originally identified in human plasma by Griffin and Marlar[6] and first isolation was performed by Suzuki et al.[7] Protein C inhibitor (PCI) can be isolated from human plasma using an ordinary chromatographic procedure consisting of barium citrate adsorption, polyethylene glycol fractionation, DEAE-Sepharose CL-6B treatment, ammonium sulfate fractionation, dextran sulfate-agarose chromatography, gel filtration on ACA-44, and DEAE-Sephacel chromatography.[7][8]


The structure (primary structure) of protein C inhibitor was deduced from its cDNA nucleotide sequence. The human Protein C inhibitor have 19 amino acid signal peptide.[9]

Gene organization

The study of genomic DNA by restriction mapping, polymerase chain reaction analysis and DNA sequencing showed the gene being 11.5 kilobases in length, consisting of five exons separated by four introns.[8] The genetic code of protein C inhibitor is similar to alpha 1-antitrypsin and alpha 1-antichymotrypsin.[8]


The in vivo half time degradation of Protein C inhibitor in plasma is found to be 23 hours, whereas the half time degradation of protein C inhibitor and protein C complex is 20 minutes.[10]

Binding with heparin

Protein C inhibitors have ability to inhibit protein C, thrombin and other enzymes that are stimulated by heparin. The heparin binding site of protein C inhibitor is from 264-283 region.[5] Heparin enhances the rate of inhibition leading to the conformational change in the structure of Protein C and other proteases. The binding site of heparin is different for protein C inhibitor and other proteases[10] Heparin regulates the protein C inhibitor (PCI) activity and furthermore its specificity in those system where there is presence of two or more target proteases.[11]

Clinical significance

As an antimicrobial agent

Protein C inhibitor interacts with lipid membrane subsequently leading to permeabilization of bacterial pathogen exerting the antimicrobial activity. Protein C inhibitor a potent antimicrobial agent that have ability to destroy the bacterial cell wall, causing death of the bacteria.[12]


Protein C inhibitor significantly reduces fertilization by inhibiting both the binding and penetration of zona free hamster oocytes by human sperm. This effect of PCI is dose dependent as 0.04MicroM PCI inhibited 50% binding and penetration ability.[13]

Inhibition of tumor growth

PCI communicated by malignant cells smothers tumor invasion by hindering urokinase-sort plasminogen activator, and restrains tumor development and metastasis which is independent of its protease inhibitory activity.[14]


Deficiency of protein C in inhibitor in human body may cause male infertility.Protein C inhibitor has a great role in reproduction as it has ability to inhibit the sperm protease acrosin.[15] Protein C inhibitor circulates in male reproductive organ as plasma protein in huge amount.[15] Either due to deficiency or due to the presence of inactive protein C inhibitor can lead to infertility of male reproductive organ.[16]


Protein C inhibitor has often been shown to interact with prostate specific antigen,[17][18] protein C[19][20] and PLAU.[19][21]

See also


  1. "Predicting Prostate Cancer Biochemical Recurrence Using a Panel of Serum Proteomic Biomarkers".
  2. Huntington JA (June 2013). "Thrombin inhibition by the serpins". Journal of Thrombosis and Haemostasis. 11 Suppl 1: 254–64. doi:10.1111/jth.12252. PMID 23809129.
  3. 3.0 3.1 Laurell M, Christensson A, Abrahamsson PA, Stenflo J, Lilja H (April 1992). "Protein C inhibitor in human body fluids. Seminal plasma is rich in inhibitor antigen deriving from cells throughout the male reproductive system". The Journal of Clinical Investigation. 89 (4): 1094–101. doi:10.1172/JCI115689. PMC 442965. PMID 1372913.
  4. Boulaftali Y, Adam F, Venisse L, Ollivier V, Richard B, Taieb S, Monard D, Favier R, Alessi MC, Bryckaert M, Arocas V, Jandrot-Perrus M, Bouton MC (January 2010). "Anticoagulant and antithrombotic properties of platelet protease nexin-1". Blood. 115 (1): 97–106. doi:10.1182/blood-2009-04-217240. PMID 19855083.
  5. 5.0 5.1 Pratt CW, Church FC (May 1992). "Heparin binding to protein C inhibitor" (PDF). The Journal of Biological Chemistry. 267 (13): 8789–94. PMID 1315738.
  6. Marlar RA, Griffin JH (1980). "Deficiency of protein C inhibitor in combined factor V/VIII deficiency disease". The Journal of Clinical Investigation. 66 (5): 1186–9. doi:10.1172/JCI109952. PMC 371561. PMID 6253526.
  7. 7.0 7.1 Suzuki K, Nishioka J, Hashimoto S (1983). "Protein C inhibitor. Purification from human plasma and characterization". The Journal of Biological Chemistry. 258 (1): 163–8. PMID 6294098.
  8. 8.0 8.1 8.2 Meijers JC, Chung DW (August 1991). "Organization of the gene coding for human protein C inhibitor (plasminogen activator inhibitor-3). Assignment of the gene to chromosome 14". The Journal of Biological Chemistry. 266 (23): 15028–34. PMID 1714450.
  9. Suzuki K, Deyashiki Y, Nishioka J, Kurachi K, Akira M, Yamamoto S, Hashimoto S (January 1987). "Characterization of a cDNA for human protein C inhibitor. A new member of the plasma serine protease inhibitor superfamily". The Journal of Biological Chemistry. 262 (2): 611–6. PMID 3027058.
  10. 10.0 10.1 Suzuki K (1 March 2000). "Protein C inhibitor (PAI-3): structure and multi-function". Fibrinolysis and Proteolysis. 14 (2): 133–145. doi:10.1054/fipr.2000.0063.
  11. Geiger M, Zechmeister-Machhart M, Uhrin P, Hufnagl P, Ecke S, Priglinger U, Xu J, Zheng X, Binder BR (1996). "Protein C inhibitor (PCI)". Immunopharmacology. 32 (1–3): 53–6. doi:10.1016/0162-3109(96)00013-6. PMID 8796266.
  12. Malmström E, Mörgelin M, Malmsten M, Johansson L, Norrby-Teglund A, Shannon O, Schmidtchen A, Meijers JC, Herwald H (December 2009). "Protein C inhibitor--a novel antimicrobial agent". PLoS Pathogens. 5 (12): e1000698. doi:10.1371/journal.ppat.1000698. PMC 2788422. PMID 20019810.
  13. España F, Navarro S, Medina P, Zorio E, Estellés A (February 2007). "The role of protein C inhibitor in human reproduction". Seminars in Thrombosis and Hemostasis. 33 (1): 41–5. doi:10.1055/s-2006-958460. PMID 17253188.
  14. Akita N, Ma N, Okamoto T, Asanuma K, Yoshida K, Nishioka J, Shimaoka M, Suzuki K, Hayashi T (June 2015). "Host protein C inhibitor inhibits tumor growth, but promotes tumor metastasis, which is closely correlated with hypercoagulability". Thrombosis Research. 135 (6): 1203–8. doi:10.1016/j.thromres.2015.03.026. PMID 25887633.
  15. 15.0 15.1 Uhrin P, Dewerchin M, Hilpert M, Chrenek P, Schöfer C, Zechmeister-Machhart M, Krönke G, Vales A, Carmeliet P, Binder BR, Geiger M (December 2000). "Disruption of the protein C inhibitor gene results in impaired spermatogenesis and male infertility". The Journal of Clinical Investigation. 106 (12): 1531–9. doi:10.1172/JCI10768. PMC 381472. PMID 11120760.
  16. He S, Lin YL, Liu YX (June 1999). "Functionally inactive protein C inhibitor in seminal plasma may be associated with infertility". Molecular Human Reproduction. 5 (6): 513–9. doi:10.1093/molehr/5.6.513. PMID 10340997.
  17. Christensson A, Lilja H (February 1994). "Complex formation between protein C inhibitor and prostate-specific antigen in vitro and in human semen". European Journal of Biochemistry / FEBS. 220 (1): 45–53. doi:10.1111/j.1432-1033.1994.tb18597.x. PMID 7509746.
  18. Kise H, Nishioka J, Kawamura J, Suzuki K (May 1996). "Characterization of semenogelin II and its molecular interaction with prostate-specific antigen and protein C inhibitor". European Journal of Biochemistry / FEBS. 238 (1): 88–96. doi:10.1111/j.1432-1033.1996.0088q.x. PMID 8665956.
  19. 19.0 19.1 España F, Berrettini M, Griffin JH (August 1989). "Purification and characterization of plasma protein C inhibitor". Thrombosis Research. 55 (3): 369–84. doi:10.1016/0049-3848(89)90069-8. PMID 2551064.
  20. Strandberg K, Kjellberg M, Erb EM, Persson U, Mosher DF, Villoutreix BO, Stenflo J (December 2000). "Activated protein C-protein C inhibitor complex formation: characterization of a neoepitope provides evidence for extensive insertion of the reactive center loop". Biochemistry. 39 (51): 15713–20. doi:10.1021/bi001640h. PMID 11123896.
  21. Geiger M, Huber K, Wojta J, Stingl L, Espana F, Griffin JH, Binder BR (August 1989). "Complex formation between urokinase and plasma protein C inhibitor in vitro and in vivo". Blood. 74 (2): 722–8. PMID 2752144.

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