Plasminogen activator inhibitor-2

Last updated
SERPINB2
Protein SERPINB2 PDB 1by7.png
Available structures
PDB Ortholog search: PDBe RCSB
Identifiers
Aliases SERPINB2 , HsT1201, PAI, PAI-2, PAI2, PLANH2, serpin family B member 2
External IDs OMIM: 173390; MGI: 97609; HomoloGene: 20571; GeneCards: SERPINB2; OMA:SERPINB2 - orthologs
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_002575
NM_001143818

NM_001174170
NM_011111

RefSeq (protein)

NP_001137290
NP_002566

NP_001167641
NP_035241

Location (UCSC) Chr 18: 63.87 – 63.9 Mb Chr 1: 107.44 – 107.46 Mb
PubMed search [3] [4]
Wikidata
View/Edit Human View/Edit Mouse

Plasminogen activator inhibitor-2 (placental PAI, SerpinB2, PAI-2), a serine protease inhibitor of the serpin superfamily, is a coagulation factor that inactivates tissue plasminogen activator and urokinase. It is present in most cells, especially monocytes/macrophages. PAI-2 exists in two forms, a 60-kDa extracellular glycosylated form and a 43-kDa intracellular form.

Contents

Fibrinolysis (simplified). Blue arrows denote stimulation, and red arrows inhibition. Fibrinolysis.svg
Fibrinolysis (simplified). Blue arrows denote stimulation, and red arrows inhibition.

It is present only at detectable quantities in blood during pregnancy, as it is produced by the placenta, and may explain partially the increased rate of thrombosis during pregnancy. The majority of expressed PAI-2 remains unsecreted due to the presence of an inefficient internal signal peptide.

Interactions

PAI-2 has been reported to bind a series of intracellular and extracellular proteins. Whether PAI-2's physiological function is inhibition of the extracellular protease urokinase and/or whether PAI-2 has intracellular activities remains controversial. At least one of PAI-2's physiological functions may involve regulation of adaptive immunity. [5]

Structure and polymerization

Like other serpins, PAI-2 has three beta sheets (A, B, C) and nine alpha helices (hA-hI). [6] [7] The structure of PAI-2 mutants have been solved, in which the 33-amino acid loop connecting helices C and D is deleted. This CD-loop is particularly flexible and difficult to stabilize, as the loop is known to translocate up to 54 Å during the formation of intramolecular disulfide bonds. [8] In addition to the CD-loop, notable motifs include the reactive center loop (RCL) spanning amino acids 379-383 and an N-terminal hydrophobic signal sequence.

Reactive center loop (RCL) of plasminogen activator inhibitor-2. PyMol rendering of PDB 2ARR. Reactive center loop (RCL) of plasminogen activator inhibitor-2. PyMol rendering of PDB 2ARR.png
Reactive center loop (RCL) of plasminogen activator inhibitor-2. PyMol rendering of PDB 2ARR.

Despite their similar inhibitory targets, PAI-2 is phylogenetically distant from its counterpart plasminogen activator inhibitor-1 (PAI-1). As a member of the ovalbumin-related serpin family, PAI-2 is genetically similar to chicken ovalbumin (Gallus gallus), and is a close mammalian homolog. [9] Both ovalbumin and PAI-2 undergo secretion via uncleaved secretory signal peptides, although PAI-2 secretion is relatively much less efficient. [10]

PAI-2 exists in three polymeric states: monomeric, polymerigenic, and polymer (inactive state). Polymerization occurs by a so-called "loop-sheet" mechanism, in which the RCL of one molecule sequentially inserts into the A-beta-sheet of the next molecule. This process occurs preferentially when PAI-2 is in its polymerigenic form, which is stabilized by a disulfide bond between Cys-79 (located in the CD-loop) and Cys-161. [11] When PAI-2 is in its monomeric form, the CD-loop is vastly out-of-position for this disulfide linkage, and it must translocate a distance of 54 Å to become sufficiently close to Cys-161. Nevertheless, since the CD-loop is quite flexible, the monomeric and polymerigenic forms are fully interconvertible, and one state can be favored over the other by altering the redox environment of the protein. [8] Polymerization of PAI-2 occurs spontaneously under physiological conditions, for instance in the cytosol of placental cells. [12] Cytosolic PAI-2 tends to be monomeric, while PAI-2 in secretory organelles (which tend to be more oxidizing than the cytosol) is more prone to polymerization. [11] For these combined reasons, it is thought that PAI-2 may sense and respond to environmental redox potential. [8]

Mechanism

PAI-2 uses a suicide inhibition mechanism (a common mechanism for serpins) to irreversibly inactivate tissue plasminogen activator and urokinase. [6] First, the target serine protease docks to PAI-2 and catalyzes cleavage of the RCL, between residues Arg-380 and Thr-381. At this point, two outcomes are possible: the protease escapes, leaving an inactive PAI-2; or the protease forms a permanent, covalently-bonded complex with PAI-2, in which the protease is significantly distorted.

Biological Functions

Although extracellular (glycosylated) PAI-2 functions to regulate fibrinolysis, it remains unclear whether this inhibitory role is the main function of PAI-2. PAI-2 is predominantly intracellular. The secretory signal peptide of PAI-2 is relatively inefficient, perhaps by evolutionary design, as various mutations to the signal sequence can significantly enhance secretion efficiency. [10] PAI-2 is undetectable in adult plasma, and is typically only detectable during pregnancy, in myelomonocytic leukemias, or in gingival crevicular fluid; moreover, PAI-2 is a slower inhibitor than its counterpart PAI-1 by orders of magnitude (based on second order rate constants). [13] On the other hand, detailed intracellular roles for PAI-2 have not yet been conclusively established.

PAI-2 is upregulated during both pregnancy and immune responses. During pregnancy, PAI-2 is particularly present in the decidua and amniotic fluid, where it may protect membranes from digestion and aid in remodeling fetal and uterine tissues. [14] PAI-2 assists PAI-1 in regulating fibrinolysis and may help prevent overexpression of PAI-1, which increases risk of thrombosis. [14] [15] Over the course of a pregnancy, PAI-2 plasma concentration rises from nearly-undetectable levels to 250 ng/mL (mostly in glycosylated form). [13]

Among immune cells, macrophages are the main producers of PAI-2, as both B-cells and T-cells do not produce significant amounts. [16] PAI-2 plays a role in inflammatory responses and infections, potentially in downregulating T cells that secrete IgG2c and interferon type II. [16]

Due to its position on chromosome 18 close to the bcl-2 protooncogene and several other serpins, PAI-2's role in apoptosis has been investigated, but current evidence remains inconclusive. [13] [17] A recent study suggests PAI-2 may be a direct downstream target and activator of p53, and may directly stabilize p21; in addition, PAI-2 expression is increased in senescent fibroblasts and may arrest growth of young fibroplasts. [18]

Potential roles in cancer

The role of PAI-2 in cancer growth and metastasis is complex, as PAI-2 may have tumor-promoting and tumor-inhibiting effects. Notably, it is high expression of PAI-2 by tumor cells, not the host organism, which influences cancer growth. [19] Cancer cells may facilitate export of PAI-2 via microparticles. [19]

PAI-2 provides protection for cancer cells against plasmin-induced cell death, which can exert a lethal effect on tumors. This protection is particularly salient in brain metastases, which tend to express high levels of PAI-2 and neuroserpin, and whose growth may be partially inhibited by knockout of PAI-2. [20] Due to its high expression in tumor cells, PAI-2 has been used to track and study the spread of angiotropic melanoma cells. [21]

Although PAI-2 expression can promote metastasis to the brain, in other cases high PAI-2 expression significantly decreases metastasis to the lungs and other organs. [19] [22] The particular effects of PAI-2 on metastasis may depend on cancer type and location in the body.

See also

Related Research Articles

<span class="mw-page-title-main">Antithrombin</span> Mammalian protein found in Homo sapiens

Antithrombin (AT) is a small glycoprotein that inactivates several enzymes of the coagulation system. It is a 464-amino-acid protein produced by the liver. It contains three disulfide bonds and a total of four possible glycosylation sites. α-Antithrombin is the dominant form of antithrombin found in blood plasma and has an oligosaccharide occupying each of its four glycosylation sites. A single glycosylation site remains consistently un-occupied in the minor form of antithrombin, β-antithrombin. Its activity is increased manyfold by the anticoagulant drug heparin, which enhances the binding of antithrombin to factor IIa (thrombin) and factor Xa.

<span class="mw-page-title-main">Serpin</span> Superfamily of proteins with similar structures and diverse functions

Serpins are a superfamily of proteins with similar structures that were first identified for their protease inhibition activity and are found in all kingdoms of life. The acronym serpin was originally coined because the first serpins to be identified act on chymotrypsin-like serine proteases. They are notable for their unusual mechanism of action, in which they irreversibly inhibit their target protease by undergoing a large conformational change to disrupt the target's active site. This contrasts with the more common competitive mechanism for protease inhibitors that bind to and block access to the protease active site.

<span class="mw-page-title-main">Urokinase</span> Human protein

Urokinase, also known as urokinase-type plasminogen activator (uPA), is a serine protease present in humans and other animals. The human urokinase protein was discovered, but not named, by McFarlane and Pilling in 1947. Urokinase was originally isolated from human urine, and it is also present in the blood and in the extracellular matrix of many tissues. The primary physiological substrate of this enzyme is plasminogen, which is an inactive form (zymogen) of the serine protease plasmin. Activation of plasmin triggers a proteolytic cascade that, depending on the physiological environment, participates in thrombolysis or extracellular matrix degradation. This cascade had been involved in vascular diseases and cancer progression.

<span class="mw-page-title-main">Plasminogen activator inhibitor-1</span> Human protein

Plasminogen activator inhibitor-1 (PAI-1) also known as endothelial plasminogen activator inhibitor is a protein that in humans is encoded by the SERPINE1 gene. Elevated PAI-1 is a risk factor for thrombosis and atherosclerosis.

<span class="mw-page-title-main">Plasminogen activator</span> Type of protein

Plasminogen activators are serine proteases that catalyze the activation of plasmin via proteolytic cleavage of its zymogen form plasminogen. Plasmin is an important factor in fibrinolysis, the breakdown of fibrin polymers formed during blood clotting. There are two main plasminogen activators: urokinase (uPA) and tissue plasminogen activator (tPA). Tissue plasminogen activators are used to treat medical conditions related to blood clotting including embolic or thrombotic stroke, myocardial infarction, and pulmonary embolism.

<span class="mw-page-title-main">P-selectin</span> Type-1 transmembrane protein

P-selectin is a type-1 transmembrane protein that in humans is encoded by the SELP gene.

<span class="mw-page-title-main">Urokinase receptor</span> Mammalian protein found in Homo sapiens

The Urokinase receptor, also known as urokinase plasminogen activator surface receptor (uPAR) or CD87, is a protein encoded in humans by the PLAUR gene. It is a multidomain glycoprotein tethered to the cell membrane with a glycosylphosphotidylinositol (GPI) anchor. uPAR was originally identified as a saturable binding site for urokinase on the cell surface.

<span class="mw-page-title-main">Vitronectin</span> Protein

Vitronectin is a glycoprotein of the hemopexin family which is synthesized and excreted by the liver, and abundantly found in serum, the extracellular matrix and bone. In humans it is encoded by the VTN gene.

<span class="mw-page-title-main">Protein C inhibitor</span> Human protein

Protein C inhibitor is a serine protease inhibitor (serpin) that limits the activity of protein C.

<span class="mw-page-title-main">Cathepsin B</span> Protein-coding gene in the species Homo sapiens

Cathepsin B belongs to a family of lysosomal cysteine proteases known as the cysteine cathepsins and plays an important role in intracellular proteolysis. In humans, cathepsin B is encoded by the CTSB gene. Cathepsin B is upregulated in certain cancers, in pre-malignant lesions, and in various other pathological conditions.

<span class="mw-page-title-main">Maspin</span> Protein-coding gene in the species Homo sapiens

Maspin is a protein that in humans is encoded by the SERPINB5 gene. This protein belongs to the serpin superfamily. SERPINB5 was originally reported to function as a tumor suppressor gene in epithelial cells, suppressing the ability of cancer cells to invade and metastasize to other tissues. Furthermore, and consistent with an important biological function, Maspin knockout mice were reported to be non-viable, dying in early embryogenesis. However, a subsequent study using viral transduction as a method of gene transfer was not able to reproduce the original findings and found no role for maspin in tumour biology. Furthermore, the latter study demonstrated that maspin knockout mice are viable and display no obvious phenotype. These data are consistent with the observation that maspin is not expressed in early embryogenesis. The precise molecular function of maspin is thus currently unknown.

<span class="mw-page-title-main">LRP1</span> Mammalian protein found in Homo sapiens

Low density lipoprotein receptor-related protein 1 (LRP1), also known as alpha-2-macroglobulin receptor (A2MR), apolipoprotein E receptor (APOER) or cluster of differentiation 91 (CD91), is a protein forming a receptor found in the plasma membrane of cells involved in receptor-mediated endocytosis. In humans, the LRP1 protein is encoded by the LRP1 gene. LRP1 is also a key signalling protein and, thus, involved in various biological processes, such as lipoprotein metabolism and cell motility, and diseases, such as neurodegenerative diseases, atherosclerosis, and cancer.

<span class="mw-page-title-main">PEDF</span> Protein-coding gene in the species Homo sapiens

Pigment epithelium-derived factor (PEDF) also known as serpin F1 (SERPINF1), is a multifunctional secreted protein that has anti-angiogenic, anti-tumorigenic, and neurotrophic functions. Found in vertebrates, this 50 kDa protein is being researched as a therapeutic candidate for treatment of such conditions as choroidal neovascularization, heart disease, and cancer. In humans, pigment epithelium-derived factor is encoded by the SERPINF1 gene.

<span class="mw-page-title-main">ST14</span> Protein-coding gene in the species Homo sapiens

Suppressor of tumorigenicity 14 protein, also known as matriptase, is a protein that in humans is encoded by the ST14 gene. ST14 orthologs have been identified in most mammals for which complete genome data are available.

<span class="mw-page-title-main">SPINT2</span> Protein-coding gene in the species Homo sapiens

Kunitz-type protease inhibitor 2 is an enzyme inhibitor that in humans is encoded by the SPINT2 gene. SPINT2 is a transmembrane protein with two extracellular Kunitz domains to inhibit serine proteases. This gene is a presumed tumor suppressor by inhibiting HGF activator which prevents the formation of active hepatocyte growth factor. Mutations in SPINT2 could result in congenital sodium diarrhea (CSD).

<span class="mw-page-title-main">SERPINE2</span> Protein-coding gene in the species Homo sapiens

Glia-derived nexin is a protein that in humans is encoded by the SERPINE2 gene.

<span class="mw-page-title-main">SERPINB6</span> Protein-coding gene in the species Homo sapiens

Serpin B6 is a protein that in humans is encoded by the SERPINB6 gene.

<span class="mw-page-title-main">SERPINB1</span> Protein-coding gene in the species Homo sapiens

Leukocyte elastase inhibitor (LEI) also known as serpin B1 is a protein that in humans is encoded by the SERPINB1 gene. It is a member of the clade B serpins or ov-serpins founded by ovalbumin.

Angiogenesis is the process of forming new blood vessels from existing blood vessels, formed in vasculogenesis. It is a highly complex process involving extensive interplay between cells, soluble factors, and the extracellular matrix (ECM). Angiogenesis is critical during normal physiological development, but it also occurs in adults during inflammation, wound healing, ischemia, and in pathological conditions such as rheumatoid arthritis, hemangioma, and tumor growth. Proteolysis has been indicated as one of the first and most sustained activities involved in the formation of new blood vessels. Numerous proteases including matrix metalloproteinases (MMPs), a disintegrin and metalloproteinase domain (ADAM), a disintegrin and metalloproteinase domain with throbospondin motifs (ADAMTS), and cysteine and serine proteases are involved in angiogenesis. This article focuses on the important and diverse roles that these proteases play in the regulation of angiogenesis.

<span class="mw-page-title-main">SERPINB10</span> Protein-coding gene in the species Homo sapiens

Serpin peptidase inhibitor, clade B (ovalbumin), member 10 is a protein that in humans is encoded by the SERPINB10 gene.

References

  1. 1 2 3 GRCh38: Ensembl release 89: ENSG00000197632 Ensembl, May 2017
  2. 1 2 3 GRCm38: Ensembl release 89: ENSMUSG00000062345 Ensembl, May 2017
  3. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. Schroder WA, Major L, Suhrbier A (2011). "The role of SerpinB2 in immunity". Critical Reviews in Immunology . 31 (1): 15–30. doi:10.1615/critrevimmunol.v31.i1.20. PMID   21395508.
  6. 1 2 Law RH, Zhang Q, McGowan S, Buckle AM, Silverman GA, Wong W, Rosado CJ, Langendorf CG, Pike RN, Bird PI, Whisstock JC (2006). "An overview of the serpin superfamily". Genome Biology. 7 (5): 216. doi: 10.1186/gb-2006-7-5-216 . PMC   1779521 . PMID   16737556.
  7. Di Giusto DA, Sutherland AP, Jankova L, Harrop SJ, Curmi PM, King GC (November 2005). "Plasminogen activator inhibitor-2 is highly tolerant to P8 residue substitution--implications for serpin mechanistic model and prediction of nsSNP activities". Journal of Molecular Biology. 353 (5): 1069–80. doi:10.1016/j.jmb.2005.09.008. PMID   16214170.
  8. 1 2 3 Lobov S, Wilczynska M, Bergström F, Johansson LB, Ny T (December 2004). "Structural bases of the redox-dependent conformational switch in the serpin PAI-2". Journal of Molecular Biology. 344 (5): 1359–68. doi:10.1016/j.jmb.2004.10.010. PMID   15561148.
  9. Ye RD, Ahern SM, Le Beau MM, Lebo RV, Sadler JE (April 1989). "Structure of the gene for human plasminogen activator inhibitor-2. The nearest mammalian homologue of chicken ovalbumin". The Journal of Biological Chemistry. 264 (10): 5495–502. doi: 10.1016/S0021-9258(18)83572-4 . PMID   2494165.
  10. 1 2 Belin D, Guzman LM, Bost S, Konakova M, Silva F, Beckwith J (January 2004). "Functional activity of eukaryotic signal sequences in Escherichia coli: the ovalbumin family of serine protease inhibitors". Journal of Molecular Biology. 335 (2): 437–53. doi:10.1016/j.jmb.2003.10.076. PMID   14672654.
  11. 1 2 Wilczynska M, Lobov S, Ohlsson PI, Ny T (April 2003). "A redox-sensitive loop regulates plasminogen activator inhibitor type 2 (PAI-2) polymerization". The EMBO Journal. 22 (8): 1753–61. doi:10.1093/emboj/cdg178. PMC   154470 . PMID   12682008.
  12. Mikus P, Ny T (April 1996). "Intracellular polymerization of the serpin plasminogen activator inhibitor type 2". The Journal of Biological Chemistry. 271 (17): 10048–53. doi: 10.1074/jbc.271.17.10048 . PMID   8626560.
  13. 1 2 3 Kruithof EK, Baker MS, Bunn CL (December 1995). "Biological and clinical aspects of plasminogen activator inhibitor type 2". Blood. 86 (11): 4007–24. doi: 10.1182/blood.v86.11.4007.bloodjournal86114007 . PMID   7492756.
  14. 1 2 Astedt B, Lindoff C, Lecander I (1998). "Significance of the plasminogen activator inhibitor of placental type (PAI-2) in pregnancy". Seminars in Thrombosis and Hemostasis. 24 (5): 431–5. doi:10.1055/s-2007-996035. PMID   9834009. S2CID   39347062.
  15. Thompson PN, Cho E, Blumenstock FA, Shah DM, Saba TM (October 1992). "Rebound elevation of fibronectin after tissue injury and ischemia: role of fibronectin synthesis". The American Journal of Physiology. 263 (4 Pt 1): G437–45. doi:10.1152/ajpgi.1992.263.4.G437. PMID   1415704.
  16. 1 2 Schroder WA, Le TT, Major L, Street S, Gardner J, Lambley E, Markey K, MacDonald KP, Fish RJ, Thomas R, Suhrbier A (March 2010). "A physiological function of inflammation-associated SerpinB2 is regulation of adaptive immunity". Journal of Immunology. 184 (5): 2663–70. doi: 10.4049/jimmunol.0902187 . PMID   20130210.
  17. Lee JA, Cochran BJ, Lobov S, Ranson M (June 2011). "Forty years later and the role of plasminogen activator inhibitor type 2/SERPINB2 is still an enigma". Seminars in Thrombosis and Hemostasis. 37 (4): 395–407. doi:10.1055/s-0031-1276589. PMID   21805446. S2CID   260316614.
  18. Hsieh HH, Chen YC, Jhan JR, Lin JJ (October 2017). "The serine protease inhibitor serpinB2 binds and stabilizes p21 in senescent cells". Journal of Cell Science. 130 (19): 3272–3281. doi: 10.1242/jcs.204974 . PMID   28794016.
  19. 1 2 3 Schroder WA, Major LD, Le TT, Gardner J, Sweet MJ, Janciauskiene S, Suhrbier A (June 2014). "Tumor cell-expressed SerpinB2 is present on microparticles and inhibits metastasis". Cancer Medicine. 3 (3): 500–13. doi:10.1002/cam4.229. PMC   4101741 . PMID   24644264.
  20. Valiente M, Obenauf AC, Jin X, Chen Q, Zhang XH, Lee DJ, Chaft JE, Kris MG, Huse JT, Brogi E, Massagué J (February 2014). "Serpins promote cancer cell survival and vascular co-option in brain metastasis". Cell. 156 (5): 1002–16. doi:10.1016/j.cell.2014.01.040. PMC   3988473 . PMID   24581498.
  21. Bentolila LA, Prakash R, Mihic-Probst D, Wadehra M, Kleinman HK, Carmichael TS, Péault B, Barnhill RL, Lugassy C (April 2016). "Imaging of Angiotropism/Vascular Co-Option in a Murine Model of Brain Melanoma: Implications for Melanoma Progression along Extravascular Pathways". Scientific Reports. 6: 23834. Bibcode:2016NatSR...623834B. doi:10.1038/srep23834. PMC   4822155 . PMID   27048955.
  22. Mueller BM, Yu YB, Laug WE (January 1995). "Overexpression of plasminogen activator inhibitor 2 in human melanoma cells inhibits spontaneous metastasis in scid/scid mice". Proceedings of the National Academy of Sciences of the United States of America. 92 (1): 205–9. Bibcode:1995PNAS...92..205M. doi: 10.1073/pnas.92.1.205 . PMC   42846 . PMID   7816818.

Further reading