Processing and expression of rat and human clotting factor-X-encoding cDNAs

Production of a self-activating CBM-factor X fusion protein in a stable transformed Sf9 insect cell line using high cell density perfusion culture

Factor Xa is a serine protease, whose high selectivity can be used to cleave protein tags from recombinant proteins. A fusion protein comprised of a self-activating form of factor X linked to a cellulose-binding module, saCBMFX, was produced in a stable transformed Sf9 insect cell line. The activity of the insect cell produced saCBMFX was higher than the equivalent mammalian cell produced material. A 1.5 l batch fermentation reached a maximum cell concentration of 1.6 x 10(7) cells ml(-1) and a final saCBMFX concentration of 4 mg l(-1). The production of saCBMFX by this cell line was also analyzed in a 1.5 l perfusion system using an ultrasonic filter as a cell-retention device for flow rates up to 3.5 l day(-1). The cell-retention efficiency of an air backflush mode of acoustic filter operation was greater than 95% and eliminated the need to pump the relatively shear sensitive insect cells. In the perfusion system over 4 x 10(7) Sf9 cells ml(-1) were obtained with a viability greater than 80%. With a doubling of viable cell concentration from 1.5 to 3 x 10(7) cells ml(-1) the saCBMFX production rate was doubled to 6 mg l(-1) day(-1). The saCBMFX volumetric productivity of the perfusion system was higher than the batch fermentations (0.6 mg l(-1) day(-1)) by an order of magnitude.

Self-activating factor X derivative fused to the C-terminus of a cellulose-binding module: Production and properties

In this work, a new derivative of FX was engineered. It comprises a cellulose-binding module (CBM) fused to the N-terminus of the truncated light chain (E2FX) of FX and a hexahistidine tag (H6) fused to the C-terminus of the heavy chain. The sequence LTR at the site of cleavage of the activation peptide from the N-terminus of the heavy chain is changed to IEGR to render the derivative self-activating. However, N-linked glycans on the CBM of the derivative blocked its binding to cellulose and those on the activation peptide slowed its activation. Therefore, the sites of N-linked glycosylation on the CBM and on the activation peptide were eliminated by mutation. The final derivative can be produced in good yield by cultured mammalian cells. It is purified easily with Ni(2+)-agarose, it is self-activating, and it can be immobilized on cellulose. When immobilized on a column of cellulose beads, the activated derivative retains approximately 80% of its initial activity after 30 days of continuous hydrolysis of a fusion protein substrate. Under these conditions of operation, the effective substrate:enzyme ratio is >10(4).

Recombinant human factor X: high yield expression and the role of furin in proteolytic maturation in vivo and in vitro

Factor X/Xa plays a pivotal role in the coagulation cascade and exhibits a therapeutic potential for the treatment of factor X-deficient as well as FVIII and FIX inhibitor patients. This report describes the establishment of Chinese hamster ovary cell clones expressing recombinant human factor X up to 120 microg/mL x day and 78 microg/10(6) cells x day, that is to 100-fold higher levels than reported previously. Although propeptide removal and single chain precursor to light and heavy chain processing as well as vitamin K-dependent gamma-carboxylation became impaired at these expression levels, up to 25% of the recombinant human factor X produced was active. This represents the highest functional activity ever reported for a vitamin K-dependent protein at such an expression level. Expression of recombinant human factor X in Chinese hamster ovary cells lacking the endoprotease Furin revealed that propeptide removal still occurred, whereas single chain precursor to light/heavy chain processing was abolished. This suggests that a protease different from Furin mediates propeptide removal, a unique finding compared with the other vitamin K-dependent coagulation factors. In contrast, exposure of incompletely processed rFX molecules to soluble recombinant Furin in vitro mediated both of these cleavage reactions despite the absence of a typical argP4-xP3-lys/argP2-argP1 Furin cleavage site in the propeptide, indicating relaxed specificity in vitro. Concomitantly with the degree of processing, the functional activity of recombinant human factor X increased. Interestingly, Furin was shown to even perform correct N-terminal proteolytic trimming of FX molecules truncated amino-terminal to the P3 residue in vitro. Depending on the absence or presence of warfarin in the culture media, as well as on the processing state, four distinct recombinant human factor X light chain isoforms were observed and their structure characterized. One of these light chain forms correlated with the functional activity. Finally, the distribution of the individual light chain isoforms suggests that gamma-carboxylation may be a prerequisite for propeptide removal.

Cloning and recombinant expression of mouse coagulation factor X

Engineering of recombinant coagulation factor X variants, which can be activated by tumor-associated proteinases may lead to the development of new therapeutic molecules. However, the evaluation of such variants requires an appropriate animal model. Therefore, we isolated the complete coding sequence of mouse coagulation factor X from mouse liver cDNA by polymerase chain reaction. The deduced amino acid sequence codes for a prepro protein of 481 amino acids homologous to factor X sequences from various species. Recombinant mouse factor X was expressed in human embryonic kidney cells and secreted into cell culture supernatant as zymogen, which could be converted to catalytically active factor Xa by Russell's viper venom. Purified recombinant mouse factor X restored coagulation in human factor X deficient plasma, demonstrating that mouse factor X is able to functionally interact with the human blood coagulation system. Recombinant mouse factor X opens the possibility to analyze therapeutically useful variants in the mouse system.

Thrombosis with outflow obstruction delays thrombolysis and results in chronic wall thickening of rat veins

PURPOSE

An in vivo model of acute deep venous thrombosis was developed in rats to assess the role of venous thrombosis and outflow obstruction in recanalization and development of secondary wall changes.

METHODS

The left femoral veins of male Sprague-Dawley rats were thrombosed either by means of proximal ligation (obstruction, group A, n = 38) or by means of temporary 24-hour occlusion with a microvascular clamp (unobstructed, group B, n = 20). Right femoral veins served as controls. The rats were killed at intervals over 5 weeks. Wall thickness was compared among groups by means of counting of cells on representative sections through the midvein area. Thrombi were indirectly quantitated with a radiolabeled fibrinogen assay in a parallel series of rats.

RESULTS

Control veins showed no evidence of cellular or structural changes. Early thrombus extension was seen in group A (peak at day 4) followed by recanalization after 2 weeks. Group A veins had marked wall thickening (27 +/- 7 vs 6 +/- 2 cells, p < 0.01, peak at 10 days) consisting of smooth muscle-type, neointimal, and medial cellular proliferations. Within 2 to 3 weeks, local neovascular channels had grown to bypass the outflow obstruction, and resumption of normal cephalad flow was seen. At the same time neointimal proliferation regressed, but medial cellular growth persisted, resulting in chronic wall thickening (11 +/- 3 vs 5 +/- 1 cells, p < 0.01, after 21 days). In contrast, group B veins exhibited no thrombus extension, had significantly less wall thickening (13 +/- 2 vs 5 +/- 1 cells, p < 0.01, peak at 4 days), and did not induce growth of local collateral blood vessels. Within 2 weeks, group B veins regained normal appearance and resumed normal flow.

CONCLUSIONS

Thrombosis of rat femoral veins without chronic obstruction results in rapid lysis of thrombus and transient proliferative changes. In contrast, thrombosis with chronic outflow obstruction results in delayed recanalization, early extension of thrombus, and development of vigorous and persistent proliferative cellular responses. Thrombus-induced chronic wall thickening may be an important factor in development of postthrombotic venous insufficiency.

Characterization of a full-length cDNA for rabbit factor X

A 300 bp probe generated by the PCR was derived from rabbit genomic DNA using primers from a highly conserved region of the DNA for human factor X (HFX). The probe was used in northern blot analysis of liver RNA to demonstrate an mRNA species of 1.6 kb for the rabbit factor X and subsequently for isolation and characterization of the cDNA for rabbit factor X (RFX) from a lambda Zap II cDNA library generated from rabbit liver mRNA. The cDNA contains 22 bases upstream from the 5'-translation initiation codon, 1470 nucleotides of open reading frame, a stop codon and a 3' poly (A) tail. The cDNA codes for a 40-residue signal/propeptide region, followed by a 447-residue mature protein. The deduced amino acid sequence shows a high degree of homology with the sequence of HFX. Inhibitory peptides derived from interactive sites of HFX for activators, cofactor and substrate exerted degrees of inhibition of RFX activation which showed a dependence on extent of homology with the corresponding regions of RFX.