Plasminogen activator inhibitor 2 (PAI-2) is not inactivated by exposure to oxidants which can be released from activated neutrophils

A Novel Role for Plasminogen Activator Inhibitor Type-2 as a Hypochlorite-Resistant Serine Protease Inhibitor and Holdase Chaperone

Plasminogen activator inhibitor type-2 (PAI-2), a member of the serpin family, is dramatically upregulated during pregnancy and in response to inflammation. Although PAI-2 exists in glycosylated and non-glycosylated forms in vivo, the majority of in vitro studies of PAI-2 have exclusively involved the intracellular non-glycosylated form. This study shows that exposure to inflammation-associated hypochlorite induces the oligomerisation of PAI-2 via a mechanism involving dityrosine formation. Compared to plasminogen activator inhibitor type-1 (PAI-1), both forms of PAI-2 are more resistant to hypochlorite-induced inactivation of its protease inhibitory activity. Holdase-type extracellular chaperone activity plays a putative non-canonical role for PAI-2. Our data demonstrate that glycosylated PAI-2 more efficiently inhibits the aggregation of Alzheimer’s disease and preeclampsia-associated amyloid beta peptide (Aβ), compared to non-glycosylated PAI-2 in vitro. However, hypochlorite-induced modification of non-glycosylated PAI-2 dramatically enhances its holdase activity by promoting the formation of very high-molecular-mass chaperone-active PAI-2 oligomers. Both PAI-2 forms protect against Aβ-induced cytotoxicity in the SH-SY5Y neuroblastoma cell line in vitro. In the villous placenta, PAI-2 is localised primarily to syncytiotrophoblast with wide interpersonal variation in women with preeclampsia and in gestational-age-matched controls. Although intracellular PAI-2 and Aβ staining localised to different placental cell types, some PAI-2 co-localised with Aβ in the extracellular plaque-like aggregated deposits abundant in preeclamptic placenta. Thus, PAI-2 potentially contributes to controlling aberrant fibrinolysis and the accumulation of misfolded proteins in states characterised by oxidative and proteostasis stress, such as in Alzheimer’s disease and preeclampsia.

PZP and PAI-2: Structurally-diverse, functionally similar pregnancy proteins?

Pregnancy zone protein (PZP) and plasminogen activator inhibitor type 2 (PAI-2) are two multifunctional proteins that are elevated in normal pregnancy and numerous other inflammatory states. Both proteins were originally identified as protease inhibitors, but current evidence supports the notion that they may also function as modulators of T-helper cells and/or extracellular chaperones. Exacerbated inflammation, fibrinolytic disturbances and misfolded proteins are all implicated in the pathology of preeclampsia, a leading cause of maternal and foetal mortality and morbidity. Notably, reduced levels of PZP or PAI-2 are associated with preeclampsia and clarification of their diverse functions in normal pregnancy could provide much needed insight regarding the pathogenesis of this disorder. Given that inflammation and protein misfolding underlie the pathology of a very large number of disorders, the contributions of PZP and PAI-2 to extracellular proteostasis and immunoregulation could be broad-reaching.

Proteolytic-antiproteolytic balance and its regulation in carcinogenesis

Cancer development is essentially a tissue remodeling process in which normal tissue is substituted with cancer tissue. A crucial role in this process is attributed to proteolytic degradation of the extracellular matrix (ECM). Degradation of ECM is initiated by proteases, secreted by different cell types, participating in tumor cell invasion and increased expression or activity of every known class of proteases (metallo-, serine-, aspartyl-, and cysteine) has been linked to malignancy and invasion of tumor cells. Proteolytic enzymes can act directly by degrading ECM or indirectly by activating other proteases, which then degrade the ECM. They act in a determined order, resulting from the order of their activation. When proteases exert their action on other proteases, the end result is a cascade leading to proteolysis. Presumable order of events in this complicated cascade is that aspartyl protease (cathepsin D) activates cysteine proteases (e.g., cathepsin B) that can activate pro-uPA. Then active uPA can convert plasminogen into plasmin. Cathepsin B as well as plasmin are capable of degrading several components of tumor stroma and may activate zymogens of matrix metalloproteinases, the main family of ECM degrading proteases. The activities of these proteases are regulated by a complex array of activators, inhibitors and cellular receptors. In physiological conditions the balance exists between proteases and their inhibitors. Proteolytic-antiproteolytic balance may be of major significance in the cancer development. One of the reasons for such a situation is enhanced generation of free radicals observed in many pathological states. Free radicals react with main cellular components like proteins and lipids and in this way modify proteolytic-antiproteolytic balance and enable penetration damaging cellular membrane. All these lead to enhancement of proteolysis and destruction of ECM proteins and in consequence to invasion and metastasis.

Pro- and antifibrinolytic properties of human pulmonary microvascular versus artery endothelial cells: impact of endotoxin and tumor necrosis factor-alpha

OBJECTIVE

Microvascular thrombosis is a common feature of acute inflammatory lung injury, as occurs in sepsis and acute respiratory distress syndrome, but the underlying pathomechanisms are presently not fully understood.

DESIGN

Experimental.

SETTING

University laboratory.

SUBJECTS

Lung endothelial cells.

INTERVENTIONS

We characterized the expression of tissue-type and urokinase-type plasminogen activator (t-PA and u-PA) as well as plasminogen activator inhibitor (PAI)-1 and PAI-2 in human endothelial cells (EC) from the microvascular pulmonary circulation (HMVEC-L) and compared it with that of EC from pulmonary artery (HPAEC) and umbilical vein (HUVEC) under baseline conditions and upon stimulation with either tumor necrosis factor-alpha or lipopolysaccharide.

MEASUREMENTS AND MAIN RESULTS

Real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay were employed for quantification of messenger RNA and protein concentrations. Under baseline conditions, comparable PAI-1 expression was noted in all EC. HPAEC were characterized by significantly higher baseline expression of t-PA and PAI-2 compared with HUVEC and HMVEC-L. In contrast, u-PA messenger RNA concentrations were found to be significantly higher in nonstimulated HMVEC-L compared with HUVEC and HPAEC. In all EC, stimulation with tumor necrosis factor-alpha and lipopolysaccharide increased the expression of PAI-1, PAI-2, and u-PA and decreased t-PA expression. The changes in messenger RNA content were reflected by corresponding changes in the protein concentrations.

CONCLUSIONS

High baseline u-PA expression is a prominent feature of human lung microvascular EC, whereas pulmonary artery EC are characterized by high t-PA concentrations. Microbial and inflammatory challenge provokes up-regulation of PAI-1 and PAI-2 and down-regulation of t-PA in both macro- and microvascular pulmonary EC, which may favor local fibrin deposition.

Myeloperoxidase and plasminogen activator inhibitor 1 play a central role in ventricular remodeling after myocardial infarction

Left ventricular (LV) remodeling after myocardial infarction (MI) results in LV dilation, a major cause of congestive heart failure and sudden cardiac death. Ischemic injury and the ensuing inflammatory response participate in LV remodeling, leading to myocardial rupture and LV dilation. Myeloperoxidase (MPO), which accumulates in the infarct zone, is released from neutrophils and monocytes leading to the formation of reactive chlorinating species capable of oxidizing proteins and altering biological function. We studied acute myocardial infarction (AMI) in a chronic coronary artery ligation model in MPO null mice (MPO(-/-)). MPO(-/-) demonstrated decreased leukocyte infiltration, significant reduction in LV dilation, and marked preservation of LV function. The mechanism appears to be due to decreased oxidative inactivation of plasminogen activator inhibitor 1 (PAI-1) in the MPO(-/-), leading to decreased tissue plasmin activity. MPO and PAI-1 are shown to have a critical role in the LV response immediately after MI, as demonstrated by markedly delayed myocardial rupture in the MPO(-/-) and accelerated rupture in the PAI-1(-/-). These data offer a mechanistic link between inflammation and LV remodeling by demonstrating a heretofore unrecognized role for MPO and PAI-1 in orchestrating the myocardial response to AMI.

Retinoic acid stimulates plasminogen activator inhibitor 2 production by blood mononuclear cells and inhibits urokinase-induced extracellular proteolysis

Retinoids have been shown to modulate several functions of mononuclear phagocytes. We investigated the in vitro effect of all-trans-retinoic acid (ATRA) on the production of two major fibrinolytic components, urokinase-type plasminogen activator (u-PA) and PA inhibitor 2 (PAI-2), by human blood mononuclear cells (MNC). ATRA caused a dose-dependent (range 0.01-10 microM) accumulation of PAI-2 antigen and activity into the cell culture medium, with a maximal increase (about 5-fold over control) at a concentration of 1-10 microM. Similarly, a dose-dependent increase in PAI-2 antigen was observed in cell extracts upon ATRA stimulation. Northern blot analysis showed a parallel increase in the amount of PAI-2 mRNA in ATRA-treated cells. Time-course experiments with 1 microM ATRA showed enhanced PAI-2 mRNA expression as early as 2 h, reaching a maximum at 4-6 h and then declining at 18-24 h, and a time-dependent increase in PAI-2 antigen in the cell culture medium. At variance with PAI-2, u-PA was not influenced by the drug. To establish whether ATRA-induced changes influenced the fibrinolytic process, we evaluated the effect of MNC stimulated with ATRA on u-PA-induced degradation of diluted plasma clots. ATRA-treated cells markedly inhibited clot lysis induced by low concentrations of u-PA. The effect was due to enhanced extracellular PAI-2 accumulation since it was observed with conditioned medium from ATRA-treated cells; it was abolished by the addition of neutralizing anti-PAI-2 antibodies and was negligible when single-chain t-PA was used instead of u-PA. Since monocyte/macrophage-mediated, plasminogen-dependent extracellular proteolysis has been proposed as an important mechanism of tissue damage in several inflammatory states, our findings might contribute to better explain the anti-inflammatory properties of retinoids.

The insulin-like growth factor (IGF) binding site of bovine insulin-like growth factor binding protein-2 (bIGFBP-2) probed by iodination

The insulin-like growth factor (IGF) binding site of bovine insulin-like growth factor binding protein 2 (bIGFBP-2) has been probed by chemical iodination. Tyrosyl residues of bIGFBP-2 were reacted by chloramine T-mediated iodination. The modification patterns of free bIGFBP-2 and bIGFBP-2 associated with insulin-like growth factor II (IGF-II) were compared by tryptic mapping using electrospray mass spectrometry and N-terminal sequencing. The presence of bound IGF-II resulted in protection of tyrosine at position 60 from iodination measured by the relative loss of tyrosine specific fluorescence and the incorporation of the radioisotope 125I. In addition, the pattern of iodine incorporation of bIGFBP-2 was not different whether IGF-I or IGF-II was the protective ligand. bIGFBP-2, when iodinated alone sustained a 8-fold loss of binding affinity for IGF-I and a 4-fold loss in binding affinity for IGF-II. In contrast, bIGFBP-2 iodinated while complexed with either IGF-I or IGF-II retained the same binding affinity for IGF-I or IGF-II as non-iodinated bIGFBP-2. We conclude that tyrosine 60 lies either in a region of bIGFBP-2 which directly interacts with both IGF-I and IGF-II or lies in a region of bIGFBP-2 which undergoes a conformational change that is important for IGF binding. Furthermore, iodination of tyrosine residues at positions 71, 98, 213, 226, and 269 has no detectable impact on binding of bIGFBP-2 to the IGFs.

Aggravation of gingival inflammatory symptoms during pregnancy associated with the concentration of plasminogen activator inhibitor type 2 (PAI-2) in gingival fluid

Gingival inflammatory symptoms are aggravated during pregnancy. In vitro studies suggest a hormonal influence on the plasminogen activator inhibitor type 2 (PAI-2), and a disturbed balance of the fibrinolytic system could help to explain pregnancy gingivitis. Gingival crevicular fluid (GCF) was sampled in 14 women in pregnant and post-pregnant states. The gingival condition was assessed by the gingival index of Løe & Silness (GI) and the amount of bacterial plaque by the plaque index of Silness & Løe (PI). The ratio of sites with gingivitis to sites with bacterial plaque was calculated (G/P-ratio). Antigen levels of tissue plasminogen activator (t-PA), urokinase-type plasminogen activator (u-PA), plasminogen activator inhibitors type 1 (PAI-1) and PAI-2 in GCF were determined with ELISAs and 17 beta-oestradiol and progesterone in serum with radioimmunoassays. For each individual the differences (delta) in hormone levels and PAs and PAIs between pregnancy and post-pregnancy were calculated. Based on differences in G/P-ratio between pregnancy and post-pregnancy, subgrouping was done into a high-reacting and a low-reacting group. For the total group, the mean G/P-ratio was 2.0 during and 1.2 after pregnancy (p = 0.064). A statistically significant correlation between delta progesterone and delta PAI-2 was noted: the higher delta progesterone, the lower delta PAI-2. No other significant correlations between hormone levels and components of the fibrinolytic system were found. For the total group of women, the concentrations of PAI-2, PAI-1 and t-PA were significantly higher during than after pregnancy. The individuals in the high-reacting group, however, showed a lower or unchanged production of PAI-2 during pregnancy, while those in the low-reacting group showed a greatly increased production. The lower inhibitory capacity in terms of a low production of PAI-2 during pregnancy in women with a higher inflammatory reaction indicates that the components of the fibrinolytic system may be involved in the development of pregnancy gingivitis and implies that PAI-2 serves as an inhibitor of importance for tissue proteolysis. The present finding contributes to the explanation of pregnancy gingivitis.