Engineering of the Human Cell Line HEK-293 to Enhance Recombinant Protein Production

A human HEK293 cell line producing a recombinant interferon was further engineered to express a yeast pyruvate carboxylase (PYC) gene. In batch culture, the transformed cells exhibited marked reductions in both nutrient consumption and toxic metabolites formation. This altered metabolism led to a 2-fold increase in the maximum cell density and a 25 % increase in recombinant protein production. To further characterize the underlying metabolic changes of the PYC-expressing cells, we have conducted isotopic tracer studies using various singly and uniformly labeled13C tracers. The resulting mass distributions of extracellular lactate determined by LC/MS analysis were used as inputs to a comprehensive metabolic model to calculate the intracellular flux distributions. Our results suggest that the transformed cells convert a significant amount of pyruvate via the pyruvate carboxylase, whereas no activity in this pathway could be detected for the parental cells. The malic enzyme is also significantly enhanced in the PYC-expressing cells, likely to compensate for the reduced pentose shunt activity observed. By allowing to quantify important intracellular pathways,13C-metabolic flux analysis can provide invaluable information to guide the design of efficient fed-batch strategies.