Effect of Bcl-xL overexpression on apoptosis and autophagy in recombinant Chinese hamster ovary cells under nutrient-deprived condition.

Upon nutrient deprivation during culture, recombinant Chinese hamster ovary (rCHO) cells are subjected to two types of programmed cell death (PCD), apoptosis and autophagy. To investigate the effect of Bcl-x(L) overexpression on apoptosis and autophagy in rCHO cells, an erythropoietin (EPO)-producing rCHO cell line with regulated Bcl-x(L) overexpression (EPO-off-Bcl-x(L)) was established using the Tet-off system. The expression level of Bcl-x(L) in EPO-off-Bcl-x(L) cells was tightly regulated by doxycycline in a dose-dependent manner. Bcl-x(L) overexpression enhanced cell viability and extended culture longevity in batch culture. Upon nutrient depletion in the later stage of batch culture, Bcl-x(L) overexpression suppressed apoptosis by inhibiting the activation of caspase-3 and -7. Simultaneously, Bcl-x(L) overexpression also delayed autophagy, characterized by LC3-II accumulation. Immunoprecipitation analysis with a Flag-tagged Bcl-x(L) revealed that Bcl-x(L) interacts with Bax and Bak, essential mediators of caspase-dependent apoptosis, as well as with Beclin-1, an essential mediator of autophagy, and may inhibit their pro-cell death function. Taken together, it was found that Bcl-x(L) overexpression inhibits both apoptosis and autophagy in rCHO cell culture.