Improvement of the Recombinant Human Coagulation Factor IX Expression by Co-Expression of a Novel Transcript of Drosophila Γ Carboxylase in a Human Cell Line

Mammalian cells as the main host for production of human proteins are incapable of complete γ-carboxylation of over-expressed Vitamin K Dependent (VKD) proteins. The Drosophila γ-glutamyl carboxylase (DγC) has been shown to be more efficient than its human counterpart in γ-carboxylation of human substrates, in vitro. Considering the Drosophila γ-carboxylase (DγC) efficiency, in comparison with its human counterpart, for recognition and γ-carboxylation of a human substrate in vitro, we were determined to study the effect of the DγC on the hFIX expression in a mammalian cell line. With this aim, we examined co-expression of the DγC with the hFIX, in a human cell line. While the co-expression of a complete DγC cDNA reduced the hFIX expression, a truncated form of DγC could improve both the expression level (up to 1211 ng/106 cells/ml on the 4th day of post-transfection) and carboxylation of the expressed hFIX, significantly (p < 0.009). Our findings provided evidences for potential of a partial fragment of the DγC for improvement of the γ-carboxylation of a human substrate in a mammalian cell. Our experimental data, in accordance with in silico analysis suggested that the DγC C-terminal fragment, with the advantage of a Kozak-like element has the potential of being expressed as a separate internal translation unit, to generate a peptide with appropriate γ-carboxylase activity.