Tissue-type plasminogen activator domain-deletion mutant BM 06.022: modular stability, inhibitor binding, and activation cleavage

Comparison of the cytoplasmic and periplasmic production of reteplase in Escherichia coli

Reteplase is the recombinant type of tissue plasminogen activator variant. In this study, preplasmic and cytoplasmic (as inclusion body: IBs) production and activity of recombinant reteplase in E. coli were investigated and compared using a pET system (pET22b and pET15b). The cDNA of reteplase was cloned by polymerase chain reaction (PCR) amplification, sequenced, inserted into the vector pET 22b and pET15b, and expressed using isopropyl β-D-1-thiogalactopyranoside (IPTG). The recombinant plasmid was expressed in the form of inclusion body in pET 15b and in periplasmic space in pET22b. The obtained results of inclusion body extraction from recombinant pET22b (rpET22b) and recombinant pET15b (rpET15b) plasmids using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed a band of ~39 kD. However, the obtained results of periplasmic space extraction from rpET22b plasmid showed a very weak band, while cytoplasmic expression of reteplase (pET15b) produced a strong protein band confirmed with Western blotting. Consequently, our results demonstrated that the cytoplasmic expression system is efficient for the production of reteplase protein in prokaryote systems and a high amount of reteplase was obtained from the expressed proteins in the form of IBs. The obtained activity of rpET15b plasmid showed a higher enzyme absorbance in comparison to rpET22b plasmid. This suggests rpET15b as an appropriate candidate for reteplase production.

Defensins and cathelicidins: neutrophil peptides with roles in inflammation, hyperlipidemia and atherosclerosis

Atherosclerosis is a disease that begins in fetal life and represents a leading cause of morbidity and mortality associated with significant socioeconomic consequences. A central concept with regard to its pathogenesis is that of endothelial cell dysfunction, which is associated with the release of a large number of mediators secreted by leukocytes that are present in large numbers at the sites of atheroma formation. Neutrophil peptides defensins and cathelicidins are essential elements of the innate immunity and have been present in high concentrations in atherosclerotic plaques in humans. Recently, their role as potential mediators of vascular disease was investigated. Defensins are involved in the lipoprotein metabolism in the vessel wall, favoring LDL and lipoprotein (a) accumulation and modification in the endothelium and the extracellular matrix. They also interfere with the vascular smooth muscle cell function, exhibit prothrombotic activity, and play an inhibitory role in various phases of angiogenesis. Cathelicidins were recently found to enhance endothelial proliferation in cultures, induce functionally significant angiogenesis in animal models, and regulate endothelial cell apoptosis. Further study of these peptides could provide useful insight in the relationship between inflammation and atherosclerosis and is anticipated to have therapeutic and prognostic ramifications.

Antiangiogenic activity of a domain deletion mutant of tissue plasminogen activator containing kringle 2

OBJECTIVE

The thrombolytic therapy drug, Reteplase, is a domain deletion mutant of tissue plasminogen activator (tPA), comprising the kringle 2 and protease (K2P) domains. Some kringle domains of hemostatic proteins are antiangiogenic and promote apoptosis. The objective of this study was to investigate whether K2P is an angiogenesis inhibitor because of the presence of kringle 2.

METHODS AND RESULTS

K2P inhibited basic fibroblast growth factor-induced human endothelial cell proliferation and migration. Inhibition was not dependent on the protease activity of K2P because similar results were obtained with catalytically inactivated K2P. Purification of the kringle 2 domain derived from elastase cleavage of K2P at the Arg275-Ile276 bond revealed that inhibition was mediated by this domain. In addition, K2P inhibited angiogenesis in vivo and increased endothelial cell apoptosis.

CONCLUSIONS

Wound healing and angiogenesis are severely compromised by K2P. These data provide new mechanistic insights into the bleeding complications observed in some patients while undergoing thrombolytic therapy with this drug. In addition, we identify the kringle 2 domain of tPA as a novel target for antiangiogenic therapy.

Secretion of active recombinant human tissue plasminogen activator derivatives in Escherichia coli

The DNA fragment coding for kringle 2 plus serine protease domains (K2S) of tissue plasminogen activator (tPA) was inserted into a phagemid vector, pComb3HSS. In the recombinant vector, pComb3H-K2S, the K2S gene was fused to gpIII of PhiM13 and linked to the OmpA signal sequence. The resulting gene, rK2S-gpIII, was inducibly expressed in Escherichia coli XL-1 Blue. The protein was presented on the phage particle. To stop the expression of gpIII, a stop codon between K2S and the gpIII gene was inserted by site-directed mutagenesis. This mutated vector, MpComb3H-K2S, was transformed in XL-1 Blue. After induction with IPTG (isopropyl-beta-D-thiogalactopyranoside), rK2S was found both in the periplasm as an inactive form of approximately 32% and in the culture supernatant as an active form of approximately 68%. The secreted form of rK2S was partially purified by ammonium sulfate (55%) precipitation. The periplasmic form was isolated from whole cells by chloroform extraction. The fibrin binding site of kringle 2 was demonstrated in all expressed versions (phage-bound, periplasmic, and secreted forms) using the monoclonal anti-kringle 2 antibody (16/B). Only the secreted form of rK2S revealed a fibrinogen-dependent amidolytic activity with the specific activity of 236 IU/microg. No amidolytic activity of rK2S was observed in either the periplasmic or the phage-bound form. The secretion of rK2S as an active enzyme offers a novel approach for the production of the active-domain deletion mutant tPA, rK2S, without any requirements for bacterial compartment preparation and in vitro refolding processes. This finding is an important technological advance in the development of large-scale, bacterium-based tPA production systems.

Defensin modulates tissue-type plasminogen activator and plasminogen binding to fibrin and endothelial cells

Defensins are naturally occurring antimicrobial peptides that may participate in host defense against microorganisms. We previously reported that the amino acid sequence of leukocyte defensins resembles the lysine-binding site in the kringles of plasminogen and that defensin inhibits fibrinolysis mediated by tissue-type plasminogen activator (tPA) and plasminogen. In the present paper we analyze the mechanisms of this inhibition. Defensin binds specifically to cultured human umbilical vein endothelial cells (HUVEC) (half-maximal binding = 3 microM) as well as to fibrin. At saturating concentrations (5-10 microM), defensin stimulates the maximum binding of plasminogen to HUVEC and to fibrin approximately 10-fold. However, defensin inhibits plasminogen binding to both surfaces at concentrations >10 microM. Defensin also inhibits tPA and plasminogen-mediated fibrinolysis in a dose-dependent manner at all concentrations tested. Fibrinolysis is almost totally inhibited by 6 microM defensin, a concentration that stimulates the binding of plasminogen to fibrin. Discordance between the enhancement of plasminogen binding and its activation cannot be explained by an inhibitory effect of defensin on tPA binding nor by inhibition of plasmin activity, each of which occur only at higher concentrations. Rather, these results suggest that plasminogen bound to fibrin in the presence of defensin is less susceptible to activation by tPA.