Heterologous Protein Expression Affects the Death Kinetics of Baculovirus-Infected Insect Cell Cultures: A Quantitative Study by Use of n-Target Theory

Authors

  • Suh-Chin Wu,

    1. Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843
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    • On leave to the Virus Biology Unit, Laboratory of Tumor Cell Biology, NCI-FCRDC, Frederick, MD 21702.

  • Donald L. Jarvis,

    1. Department of Entomology, Texas A&M University, College Station, Texas 77843
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  • Bruce E. Dale,

    1. Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843
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  • James C. Liao

    Corresponding author
    1. Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843
    • Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843
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Abstract

The death of cultured insect cells after baculovirus infection is a time-dependent event. Without a quantitative model, it is difficult to characterize its kinetics. Our group has shown that the cell survival rate can be characterized by use of the n-target theory, which involves only two parameters: the number of hypothetical inactivation targets (n) and the first-order death rate (k). In this study, we used different recombinant viruses to examine the effect of heterologous protein expression on the cell survival rate. The proteins expressed were β-galactosidase, human T-cell leukemia virus type I p40x, human interleukin-2, and human tissue plasminogen activator (tPA). The survival rate was affected by protein expression, but the n value remained constant if the protein expression level was high (above 30 mg/L). Low-level expression of secreted, glycosylated tPA resulted in a reduced n value, which was restored to the normal value when the tPA signal peptide and prosequence were deleted. In addition, if the n value was normal (10–11), the level of protein expression correlated negatively with the death rate. However, if the n value was reduced by unfavorable culture conditions or foreign protein expression, the expression level correlated positively with the death rate. A dimensionless plot with kt as the dimensionless time shows that alteration of the k value while retaining constant n is equivalent to a rescaling of time. Therefore, the survival curves with constant n reduce to a single curve on the dimensionless plot. Although the underlying mechanisms affecting n and k are still unknown, this study shows that they can serve as convenient phenotypes for investigating virus—host interactions.

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