Fig. 2.

Effects of Bcl-2 overexpression on cisplatin resistance of cell lines derived from HNSCC. A, cisplatin treatment led to loss of ΔNp63 and activation of upstream proapoptotic targets regardless of Bcl-2 expression, whereas Bcl-2 inhibited the downstream apoptotic program. Western blots of protein extracts taken after 21h exposure of vector-control JHU029 cells (left) or cells overexpressing Bcl-2 (right) to 5 μg/mL cisplatin. The p73 target gene NOXA is induced by cisplatin in both cases, whereas the apoptotic program, illustrated by cleavage (two bands) of poly-ADP ribose polymerase, was inhibited by Bcl-2 overexpression. B, Bcl-2 overexpression increased cisplatin resistance of JHU029 cells as assessed by MTT viability assay. MTT absorbance, normalized to vehicle-only control absorbance, in vector-control cells or cells overexpressing Bcl-2, treated with the indicated concentrations of cisplatin for 48 h; mean ± SE of four observations at each concentration. Dashed lines, shift in IC₅₀, the concentration of cisplatin required to reduce viability to 50% of control. C, Bcl-2 overexpression increased cisplatin resistance of all cell lines examined. For each of nine cell lines, mean cisplatin IC₅₀ in cells overexpressing Bcl-2 is plotted against mean IC₅₀ in vector-control cells examined in parallel. Dashed line, line of identity, expected if Bcl-2 expression did not affect IC₅₀; solid line, observed linear regression of IC₅₀ for cells expressing Bcl-2 versus IC₅₀ for control cells, indicating a 54% increase in resistance following Bcl-2 overexpression; P value is for difference of observed slope from line of identity.