Deletion of Mcl-1 in MEFs modifies FBS-induced proliferation. (A) Deletion of Mcl-1 in MEFs reduces FBS-induced proliferation. Mcl-1^wt/wt and Mcl-1^Δ/null MEFs were cultured in 96-well plates overnight in DMEM with 0.25% FBS. They were then cultured without or with the indicated percentages of FBS for 48 hours; proliferation was determined by ³H-thymidine uptake during the last 8 hours. Data represent mean ± SD for quadruplicate samples. Shown is 1 representative experiment of 3. CPM indicates counts per minute. (B) Mcl-1 is required for m-rIL-6- or m-rVEGF-induced proliferation. Mcl-1^wt/wt and Mcl-1^Δ/null MEFs were starved overnight in DMEM with 0.25% FBS followed by culture with or without m-rIL-6 or m-rVEGF (25 ng/mL) for 48 hours; cell growth was assessed as described in “Materials and methods.” Proliferation index is defined as the number of CPM in the stimulated cell divided by the CPM in the control unstimulated cells. Data represent mean ± SD of 3 different experiments.