The CD-loop of PAI-2 (SERPINB2) is redundant in the targeting, inhibition and clearance of cell surface uPA activity

<p>Abstract</p> <p>Background</p> <p>Plasminogen activator inhibitor type-2 (PAI-2, SERPINB2) is an irreversible, specific inhibitor of the urokinase plasminogen activator (uPA). Since overexpression of uPA at the surface of cancer cells is linked to malignancy, targeting of uPA by exogenous recombinant PAI-2 has been proposed as the basis of potential cancer therapies. To this end, reproducible yields of high purity protein that maintains this targeting ability is required. Herein we validate the use <it>in vitro </it>of recombinant 6 × His-tagged-PAI-2 lacking the intrahelical loop between C and D alpha-helices (PAI-2 ΔCD-loop) for these purposes.</p> <p>Results</p> <p>We show that PAI-2 ΔCD-loop expressed and purified from the pQE9 vector system presents an easier purification target than the previously used pET15b system. Additionally, PAI-2 ΔCD-loop gave both higher yield and purity than wild-type PAI-2 expressed and purified under identical conditions. Importantly, absence of the CD-loop had no impact on the inhibition of both solution phase and cell surface uPA or on the clearance of receptor bound uPA from the cell surface. Furthermore, uPA:PAI-2 ΔCD-loop complexes had similar binding kinetics (K_D~5 nM) with the endocytosis receptor Very Low Density Lipoprotein Receptor (VLDLR) to that previously published for uPA:PAI-2 complexes.</p> <p>Conclusion</p> <p>We demonstrate that the CD-loop is redundant for the purposes of cellular uPA inhibition and cell surface clearance (endocytosis) and is thus suitable for the development of anti-uPA targeted cancer therapeutics.</p

Spatial memory based on an STDP driven neural network

We propose a model of spatial memory implemented in a Spiking Neural Network (SNN) and test it on a robot moving in an environment with neutral and harmful regions. Neurons in the SNN play the role of place cells, and their population dynamics determines the robot movements. We show that STDP rearranges the couplings in the SNN and forms spatial memory similar to cognitive maps associated with the negative experience. Then, the robot learns to avoid harmful zones

Plasminogen activator inhibitor type 2 : a unique serpin with two mobile loops

The superfamily of serine protease inhibitors (serpins) is a large group of proteins with diverse functions but a common tertiary structure. Active serpins are highly metastable molecules. Metastability is the property underlying the success and ubiquitousness of serpins. However, serpin metastability also accounts for improper conformational changes in serpin mutants which may result in pathological serpin polymerization. Plasminogen activator inhibitor type 2 (PAI-2) is a member of the subfamily of ov-serpins. It is the only wild-type (wt) serpin that spontaneously polymerizes under physiological conditions. Another unique feature of PAI-2 is the loop connecting helices C and D (the CD-loop), which is the longest among known serpins and is involved in interactions with the environment. Two partially overlapping goals were achieved during this thesis. The first was to study the molecular determinants involved in PAI-2 polymerization. By using in vitro mutagenesis in combination with biochemical and fluorescence methods, we have shown that wt PAI-2 exists both in stable monomeric and in polymerogenic conformations. The polymerogenic conformation can spontaneously form loop-sheet polymers and does not require conformational rearrangements prior to polymerization. The polymerogenic conformation of PAI-2 has an open β-sheet A, and it is stabilized by a disulfide bond formed between the unique CD-loop of PAI-2 and the bottom of the molecule. Under reducing conditions, the polymerogenic conformation of PAI-2 converts to the stable monomeric form. The polymerogenic and the stable monomeric forms are fully interconvertible, depending on the redox status of the environment. The stable monomeric conformation can be stabilized by vitronectin disulfide-bound to the CD-loop of PAI-2. The most populated conformation of the stable monomeric form of PAI-2 is that with the CD-loop folded on the side of the molecule. However, a mall fraction of stable monomeric PAI-2 can also exist with the CD-loop oriented toward the bottom of the molecule. Thus, the CD-loop of PAI-2 is a mobile molecular switch that regulates PAI-2 conformation. The second goal of the thesis was to use PAI-2 as a model protein to develop methods for intramolecular distance measurements. An improved purification procedure, the stability of the protein and our understanding of its structure make PAI-2 an attractive candidate for use as a model protein. In this context, we have used PAI-2 successfully to measure distances by the previously used DDEM and newly developed PDDEM methods

Molecular competition between plasminogen activator inhibitors type -1 and -2 for urokinase: implications for cellular proteolysis and adhesion in cancer

Up-regulation of the urokinase plasminogen activation (uPA) system leads to increased cancer invasion and metastasis. Plasminogen activator inhibitors type-1 (PAI-1/SERPINE1) and type-2 (PAI-2/SERPINB2) have similar uPA inhibitory properties yet PAI-1 promotes cell invasion by modulating cell adhesion and migration. High tumour PAI-2 levels are associated with improved prognoses. Herein we show that PAI-2 is capable of inhibiting uPA in the presence of PAI-1, particularly on adherent cells in the presence of vitronectin. This suggests that elevated levels of PAI-2 in the tumour microenvironment could outcompete PAI-1 for uPA inhibition through its inhibitory serpin function. However, PAI-1 modulated cell adhesion in a largely uPA-independent manner consequently PAI-2 could not counteract the effects of PAI-1 on adhesion/migration. Thus studies aimed at further characterising the interplay between PAI-1 and PAI-2 on uPA-dependent pro-invasive processes are warranted

Revisiting the biological roles of PAI2 (SERPINB2) in cancer

Tumour expression of the urokinase plasminogen activator correlates with invasive capacity. Consequently, inhibition of this serine protease by physiological inhibitors should decrease invasion and metastasis. However, of the two main urokinase inhibitors, high tumour levels of the type-1 inhibitor actually promote tumour progression, whereas high levels of the type-2 inhibitor decrease tumour growth and metastasis. We propose that the basis of this apparently paradoxical action of two similar serine protease inhibitors lies in key structural differences controlling interactions with components of the extracellular matrix and endocytosis/signalling co-receptors

Spatial memory based on an STDP driven neural network

We propose a model of spatial memory implemented in a Spiking Neural Network (SNN) and test it on a robot moving in an environment with neutral and harmful regions. Neurons in the SNN play the role of place cells, and their population dynamics determines the robot movements. We show that STDP rearranges the couplings in the SNN and forms spatial memory similar to cognitive maps associated with the negative experience. Then, the robot learns to avoid harmful zones.Depto. de Análisis Matemático y Matemática AplicadaFac. de Ciencias MatemáticasFALSEpu

Forty Years Later and the Role of Plasminogen Activator Inhibitor Type 2/SERPINB2 Is Still an Enigma

Plasminogen activator inhibitor (PAI)-2 expression is acutely upregulated in pregnancy, inflammation, infection, and other pathophysiological conditions. Circumstances that prevent PAI-2 upregulation are associated with chronic pathology. Altogether this strongly suggests that PAI-2 is one of the many proteins that maintain homeostasis during damage or stress. However, several functions ranging from a classical serpin to various intracellular roles have been ascribed to PAI-2 and, because none of these have been definitively proven in vivo, to this day its precise role or roles remains an enigma. This review readdresses the evidence supporting a role for PAI-2 in fibrinolysis and proteolysis within extracellular environments and includes a review of the many potential intracellular functions attributed to PAI-2

Improved pharmacokinetic and biodistribution properties of the selective urokinase inhibitor PAI-2 (SerpinB2) by site-specific PEGylation: implications for drug delivery

Purpose Overexpression of the serine protease urokinase (uPA) is recognised as an important biomarker of metastatic disease and a druggable anticancer target. Plasminogen activator inhibitor type-2 (PAI-2/SerpinB2) is a specific uPA inhibitor with proven potential for use in targeted therapy. However, PAI-2 is rapidly cleared via the renal system which impairs tumor uptake and efficacy. Here we aimed to improve the pharmacological properties of PAI-2 by site-specific PEGylation. Methods Several cysteine to serine substitution mutants were generated for PEGylation with PEG-maleimide (size range 12-30 kDa) and the physico-chemical and biochemical properties of the PEG-PAI-2 conjugates characterised. Radiolabeled proteins were used for evaluation of blood clearance and tissue uptake profiles in an orthotopic breast tumor xenograft mouse model. Results PEGylation of the PAI-2C161S mutant gave a predominant mono-PEGylated-PAI-2 product (~90%) with full uPA inhibitory activity, despite a significant increase in hydrodynamic radius. Compared to un-PEGylated protein the plasma half-life and AUC for PEG20-PAI-2C161S were significantly increased. This translated to a 10-fold increase in tumor retention after 24 h compared to PAI-2C161S, an effect not seen in non-target organs. Conclusions Our data underscores the potential for PEG20-PAI-2C161S drug conjugates to be further developed as anti-uPA targeted therapeutics with enhanced tumor retention