Analysis of Mcl-1 expression under different cell culture conditions. (A) Immunoblot analysis of Mcl-1 expression after 36 h incubation in the presence of 0.1% or 10% serum. (B) Betulinic acid stimulated Mcl-1 expression in under different cell culture conditions in the presence of 10% serum. Determination of protein levels was performed 1, 2 and 3 days after addition of betulinic acid (+) or in untreated controls (−) to either confluent (confl.) or to subconfluent (subc.) cell cultures. Cell culture medium was not changed during the course of the experiment.