Figure 4

Differential involvement of various APE1 functions in melphalan-resistanct MM cells. (A) The protein expression levels of APE1 mutants were assayed by Western blot and the results indicated that the exogenous protein levels were comparable in APE1 ^WT, APE1^H309N, APE1^C65S and APE1^K6R/K7R cell lines. (B) The AP endonuclease activities of the whole cell extracts from APE1^shRNA and exogenous APE1-expressing cells were measured by oligo incision assay. The representative image out of three experimental repeats was shown. (C) Cell survival of different APE1 mutant-transfected groups was measured by CCK-8 assay after various doses of melphalan treatment. All results were from three independent experiments and * represents that the difference between the indicated group and the APE1 ^WT group is statistically significant (p < 0.01), # represents that the difference between the indicated group and APE1^shRNA group is statistically significant (p < 0.01), and & represents that the difference between the indicated group and the APE1 ^H309 group is statistically significant (p < 0.01).