Functional expression of the human coagulation factor IX using heterologous signal peptide and propeptide sequences in mammalian cell line

Improvement of recombinant ADAMTS13 production through a more optimal signal peptide or an N-terminal fusion protein

BACKGROUND

Recombinant human ADAMTS13 (rADAMTS13) is a key protein in fundamental research for investigating its mode of action and the pathophysiology of thrombotic thrombocytopenic purpura (TTP). However, the expression of rADAMTS13 is quite low in mammalian cells, which makes the production of the protein time-consuming and labor-intensive.

OBJECTIVES

We aimed at increasing the yield of rADAMTS13 by (1) using a more optimal signal peptide (SP) and (2) constructing an N-terminal fusion protein of ADAMTS13 with human serum albumin domain 1 (AD1-ADAMTS13).

METHODS

Six SPs were investigated to select the most optimal SP. Expression plasmids containing the most optimal SP and ADAMTS13 cDNA or the fusion construct AD1-ADAMTS13 were generated and transiently transfected into CHOEBNALT85 cell-line. Expression levels of rADAMTS13 in expression medium were analyzed and compared with the expression level of rADAMTS13 with native SP (nat-SP).

RESULTS

Expression of rADAMTS13 with coagulation factor VII (FVII) SP was 3-fold higher (16.00 μg/ml) compared with the expression with nat-SP (5.03 μg/ml). The highest yields were obtained with AD1-ADAMTS13 protein with a 15-fold higher concentration (78.22 μg/ml) compared with the expression with nat-SP. The rADAMTS13 expressed with FVII-SP retained its activity (104.0%) to cleave von Willebrand factor, whereas AD1-ADAMTS13 demonstrated even higher activity (144.3%).

CONCLUSION

We succeeded in generating expression vectors that yield (1) rADAMTS13 at higher levels because of more optimal FVII-SP and (2) high levels of AD1-ADAMTS13 N-terminal fusion protein. The highest expression levels were obtained with AD1-ADAMTS13 N-terminal fusion protein, which is paving the way for highly efficient protein production.

Effect of prepropeptide replacement on γ-carboxylation and activity of recombinant coagulation factor IX

Based on observations indicating that the γ-carboxylase enzyme has a lower affinity for the protein C (PC) propeptide and that the γ-carboxylase region in the PC propeptide has a higher net charge, expression of recombinant chimeric factor IX (FIX) equipped with the PC propeptide was studied. The prepropeptide of FIX was replaced with that of PC by SOEing PCR and after cloning, recombinant pMT-prepro PC/FIX was transfected into insect Drosophila S2 cells. The expression and activity of expressed FIX were analyzed employing antigen and activity analyses 72 h of post-induction with copper. Higher secretion (1.2 fold) and activity (1.6 fold) levels were observed for chimeric prepro- PC/FIX in relation to wild-type FIX. Furthermore, after barium citrate precipitation, the evaluation of fully γ-carboxylated FIX indicated that more than 51% of the total FIX produced with the PC prepropeptide was fully γ-carboxylated, representing a substantial improvement (twofold) over a system employing the native FIX propeptide in which 25% of the protein is fully γ-carboxylated. The data illustrated that the expression of FIX using the PC propeptide led to much higher fully γ-carboxylated material, which is preferred to FIX constructs tolerating the sequence for the native FIX propeptide expressed in heterologous S2 systems.

Recent advances in the production of recombinant factor IX: bioprocessing and cell engineering

Appropriate treatment of Hemophilia B is vital for patients' quality of life. Historically, the treatment used was the administration of coagulation Factor IX derived from human plasma. Advancements in recombinant technologies allowed Factor IX to be produced recombinantly. Successful recombinant production has triggered a gradual shift from the plasma derived origins of Factor IX, as it provides extended half-life and expanded production capacity. However, the complex post-translational modifications of Factor IX have made recombinant production at scale difficult. Considerable research has therefore been invested into understanding and optimizing the recombinant production of Factor IX. Here, we review the evolution of recombinant Factor IX production, focusing on recent developments in bioprocessing and cell engineering to control its post-translational modifications in its expression from Chinese Hamster Ovary (CHO) cells.

Calumenin knockdown, by intronic artificial microRNA, to improve expression efficiency of the recombinant human coagulation factor IX

OBJECTIVES

To improve the expression efficiency of recombinant hFIX, by enhancing its γ-carboxylation, which is inhibited by Calumenin (CALU), we used intronic artificial microRNAs (amiRNAs) for the CALU downregulation.

METHODS

Two human CALU (hCALU)-specific amiRNAs were designed, validated and inserted within a truncated form of the hFIX intron 1, in either 3'- or 5'-untranslated regions of the hFIX cDNA, in an expression vector. After transfections of a human cell line with the recombinant constructs, processing of the miRNAs confirmed by RT-PCR, using stem-loop primers. The hFIX and hCALU expression assessments were done based on RT-PCR results. The Gamma(γ)-carboxylation of the expressed hFIX was examined by a barium citrate precipitation method, followed by Enzyme-Linked Immunosorbent Assay.

RESULTS

Efficient CALU down regulations, with more than 30-fold decrease, occurred in the cells carrying either of the two examined the 3'-located amiRNAs. The CALU downregulation in the same cells doubled the FIX γ-carboxylation, although the transcription of the FIX decreased significantly. On the other hand, while the expression of the amiRNAs from the 5'-located intron had no decreasing effect on the expression level of CALU, the level of hFIX transcription in these cells increased almost twofold compared to the construct without amiRNA.

CONCLUSION

The CALU downregulation, consistent with efficient hFIX γ-carboxylation, occurred in the cells carrying either of the two amiRNAs containing constructs, although it was affected by the locations of the amiRNA carrying introns, suggesting a possible need to optimize the conditions for the amiRNAs expression.

Improved activity and expression of recombinant human factor IX by propeptide engineering

PURPOSE

The main therapeutic strategy for Hemophilia B patients involves the administration of recombinant coagulation factors IX (rFIX). Although there are various approaches to increasing the activity of rFIX, targeted protein engineering of specific residues could result in increased rFIX activity through enhanced γ-carboxylation. Specific amino acids in the propeptide sequence of vitamin K-dependent proteins are known to play a role in the interaction with the enzyme γ-carboxylase. The net hydrophobicity and charge of the γ-carboxylic recognition site (γ-CRS) region in the propeptide are important determinants of γ-carboxylase binding. So the contribution of individual γ-CRS residues to the expression of fully γ-carboxylated and active FIX was studied.

METHODS

Propeptide residues at positions -14, -13, or - 12 were substituted for equivalent prothrombin amino acids by SEOing PCR. The recombinant FIX variants were transfected and stably expressed in Drosophila S2 cells, and the expression of both total FIX protein and active FIX was assessed.

RESULTS

While overall the substitutions resulted in an increase of both total FIX protein expression as well as an increase in the portion of active FIX, the highest increase in FIX protein expression, FIX activity, and specific FIX activity was observed following the simultaneous substitution of residues at positions -12, -13, and - 14. The enhanced rFIX activity was further confirmed by enrichment for functional, fully γ-carboxylated rFIX species via barium citrate adsorption.

CONCLUSION

Our findings indicate that by increasing both the net charge and the net hydrophobicity of the FIX γ-CRS region, the expression of fully γ-carboxylated and as such active FIX is enhanced. Graphical abstract .

Production of recombinant human factor IX by propeptide modification in Drosophila S2 cell line

OBJECTIVE

To compare the effect of pre-propeptide (pre-pro) of the human prothrombin (hPT), with both the native and an R-9N mutant forms of the human factor IX (hFIX) pre-pro on the hFIX carboxylation, in Drosophila cell.

RESULTS

The three different pre-pro sequences, equipped with Drosophila Kozak, were joined to the mature hFIX cDNA and were subjected to transient expression analysis of hFIX in the S2 Drosophila cells, compared to that of a native hFIX cDNA, with its native Kozak. Replacement of the hFIX pre-pro sequence with that of hPT increased the biological activity of hFIX, significantly. The highest total level of hFIX expression occurred for the native hFIX with the Drosophila Kozak. However, the hFIX secretion efficiency with this construct was less than that of the native hFIX with its native Kozak. The R-9N substitution, in the hFIX propeptide, with no apparent effect on the FIX γ-carboxylation, reduced the FIX expression efficiency.

CONCLUSION

Potential of the hPT pre-pro sequence for FIX expression in Drosophila cells, was confronted by γ-glutamyl carboxylase (GGCX) saturation in ER, besides the functional importance of -9 amino acid in propeptide is described; these are noteworthy for production of γ-carboxylated proteins.

Effect of propeptide amino acid substitution in γ-carboxylation, activity and expression of recombinant human coagulation factor IX

The production of recombinant vitamin K dependent (VKD) proteins for therapeutic purposes is an important challenge in the pharmaceutical industry. These proteins are primarily synthesized as precursor molecules and contain pre-propeptide sequences. The propeptide is connected to γ-carboxylase enzyme through the γ-carboxylase recognition site for the direct γ-carboxylation of VKD proteins that has a significant impact on their biological activity. Propeptides have different attitudes toward γ-carboxylase and certain amino acids in propeptide sequences are responsible for the differences in γ-carboxylase affinity. By aiming to replace amino acids in hFIX propeptide domain based on the prothrombin propeptide, pMT-hFIX-M14 expression cassette, containing cDNA of hFIX with substituted -14 residues (Asp to Ala) was made. After transfection of Drosophila S2 cells, expression of the active hFIX was analyzed by performing ELISA and coagulation test. A 1.4-fold increase in the mutant recombinant hFIX expression level was observed in comparison with that of a native recombinant hFIX. The enhanced hFIX activity and specific activity of the hFIXD-14A (2.2 and 1.6 times, respectively) were further confirmed by comparing coagulation activity levels of substituted and native hFIX. Enrichment for functional, fully γ-carboxylated hFIX species via barium citrate adsorption demonstrated 2-fold enhanced recovery in the S2-expressing hFIXD-14A relative to that expressed native hFIX. These results show that changing -14 residues leads to a decrease in the binding affinity to substrate, increase in γ-carboxylation and activity of recombinant hFIX. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:515-520, 2018.