p21 selectively delays the loss of Mcl-1 and Bcl-XL during hyperoxia. EGFp21 cells were cultured with or without 2μg/ml doxycycline (Dox) for 24 hours (day 0) then exposed to hyperoxia for 2 and 4 days. (A) Repersentative western blot of p21, Mcl-1, Bcl-XL, Bcl-2, A1, and actin. Band intensities were quantified, normalized to actin, and graphed for (B) Mcl-1, (C) Bcl-XL and (D) Bcl-2. Values represent mean +/− SD of triplicate experiments (* P<0.05 relative to day 0, # P<0.05 between − p21 and + p21).