GADD153 expression does not necessarily correlate with changes in culture behavior of hybridoma cells

The expression of Gadd153 was found to increase in Sp2/0-Ag14 cells in a manner which coincided with the decline in cell viability. L-glutamine supplementation prolonged Sp2/0-Ag14 cell survival and greatly suppressed Gadd153 expression both at the mRNA and protein level. However, Gadd153 levels remained low after L-glutamine supplementation even as cell viability declined. Bcl-xL overexpression also extended Sp2/0-Ag14 cell viability, initially delayed the induction of Gadd153, but did not prevent the increase in Gadd153 protein levels during the later phase of the culture, when cell viability was declining. Interestingly, L-glutamine supplementation prevented Gadd153 up-regulation in cells ectopically expressing Bcl-xL, but had no effect on cell viability.This study highlights important limitations to the use of Gadd153 as an indicator of cell stress in hybridoma cells.Mammalian cell lines provide several advantages over other cellular systems for the production of recombinant proteins, most notably the correct processing and modification of mammalian proteins [1]. Unfortunately, several mammalian cell lines undergo apoptotic death upon exposure to stresses originating from large scale cultures (nutrient starvation, hypoxia, shear stress, osmotic stress), severely limiting their productivity [2]. Therefore, substantial efforts have been made in the past few years to devise strategies that reduce the loss of cell viability and increase the productive life of the cells. This includes 1) culture supplementation with limiting nutrients [3] and 2) cellular engineering by transfecting cell lines with cDNA molecules encoding anti-apoptotic proteins (e.g. Bcl-2 family proteins) [4].Recent efforts have also focused on the characterization of the stress-induced signaling pathways leading to changes in the cellular phenotype [5,6]. Of particular interest is the identification of stress-related markers that would facilitate the optimization of mammalian cell culture processes