Protection of hybridoma cells against apoptosis by a loop domain-deficient Bcl-xL protein

The ectopic expression of several members of the Bcl-2 family of anti-apoptotic proteins is a promising strategy to improve the viability of hybridoma cells in culture. However, the impact of post-translational modifications on the function of these proteins in murine hybridomas is unknown. To address this issue, the anti-apoptotic properties of a mutant of Bcl-xL devoid of the so-called "loop domain" (Bcl-xLtriangle up 46-83) were investigated using the Sp2/ O-Ag14 hybridoma model. Clones of Sp2/ O-Ag14 cells expressing Bcl-xLtriangle up 46-83 exhibited resistance against L-glutamine deprivation to similar levels than cells expressing the wild type protein. In contrast, protection against the cytotoxic effects of cycloheximide (CHX) was highly dependent on the level of expression of the Bcl-xLtriangle up 46-83 mutant. Analysis of the growth behaviour of the transfected cells showed that Bcl-xLtriangle up 46-83 was superior to the wild type protein in prolonging Sp2/ O-Agl4 cell viability in stationary batch culture. Furthermore, the prolongation of cell viability in batch culture was directly proportional to the level of expression of the mutated protein. Our results indicate that removal of the loop domain improves the anti-apoptotic activity of Bcl-xL in hybridoma cells grown in stationary batch culture.