Heterologous protein expression affects the death kinetics of baculovirus-infected insect cell cultures: a quantitative study by use of n-target theory.
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 beta-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.(ABSTRACT TRUNCATED AT 250 WORDS)
Wu
S C
SC
Department of Chemical Engineering, Texas A&M University, College Station 77843.
Jarvis
D L
DL
Dale
B E
BE
Liao
J C
JC
D000818:Animals; D016367:Baculoviridae / Q000235:genetics*; D016923:Cell Death; D002470:Cell Survival; D002478:Cells, Cultured; D007376:Interleukin-2 / Q000096:biosynthesis*; D009036:Moths; D000077183:Occlusion Body Matrix Proteins; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000096:biosynthesis*; D010959:Tissue Plasminogen Activator / Q000096:biosynthesis*; D014764:Viral Proteins / Q000235:genetics; D015678:Viral Structural Proteins; D001616:beta-Galactosidase / Q000096:biosynthesis*
D007376:Interleukin-2; D000077183:Occlusion Body Matrix Proteins; D011994:Recombinant Proteins; D014764:Viral Proteins; D015678:Viral Structural Proteins; C009829:polyhedrin protein, Nucleopolyhedrovirus; D001616:beta-Galactosidase; D010959:Tissue Plasminogen Activator