Objective        To investigate the endogenous and exogenous interaction between apurinic/apyrimidinic endonuclease 1 (APE1) and p53 in A549 and HeLa cells.       Methods        Recombinant plasmid pET42a-APE1 was transformed into

E. coli

BL21(DE3)

and the expression of APE1was induced and identified with IPTG. The expressed GST-APE1 fusion protein was purified by affinity chromatography with Ni

2+

column and identified by We

stern blotting. The interaction between APE1 and p53 protein was identified by co-immunoprecipitation (Co-IP) and GST pull down assay. Immunofluorescence assay and laser scanning confocal microscopy was used to observe the subcellular localization of the 2 proteins.       Results        Highly expressed hAPE1 fusion protein by pET42a-hAPE1 was obtained in

E.coli

BL21(DE3) after IPTG induction. The GST-APE1 fusion protein with molecular weight of 64×10

3

by SDS-PAGE was purified by affinity chromatography with Ni

2+

column and identified by Western blotting. Through Co-IP and GST pull down assay

APE1 was confirmed to interact with p53 endogenously and exogenously. Immunofluorescence assay and laser scanning confocal microscopy indicated that the 2 proteins were located in the nuclear and cytoplasm

and then transformed from the cytoplasm to the nuclear membrane after oxidative stress.        Conclusion        There are endogenous and exogenous interaction between APE1 and p53 protein in A549 and HeLa cells

which might be associated with transcriptional regulation and efficiency of tumor radiotherapy and chemotherapy.