NEGATIVE REGULATION OF THE MAJOR HUMAN AP-ENDONUCLEASE, A MULTIFUNCTIONAL PROTEIN

Abasic sites in DNA are generated either spontaneously or after remova l of altered bases during the base excision repair process. These as w ell as 3' damaged ends of DNA at single-strand breaks induced by react ive oxygen species are repaired by AP-endonucleases. The major human A P-endonuclease (named APE-1) has two unrelated activities. It may func tion as an activator of c-Fos and c-Jun transcription factors and as a repressor of the parathyroid hormone (PTH) gene by binding to the neg ative Ca2+-response elements (nCaRE) in its promoter. Preliminary stud ies indicate that the h-APE-1 gene is highly regulated. Analysis of it s promoter activity by transient expression of the luciferase reporter gene in human, HeLa and TK6 cells suggested the presence of a negativ e regulatory element in the promoter. Two nCaRE-like sequences were id entified in the promoter segment responsible for inhibiting reporter g ene expression. Competitive electrophoretic mobility shift assay with HeLa nuclear extract indicated that the nCaRE sequences of the APE-1 a nd PTH genes are recognized by the APE-1 polypeptide. These results su ggest that the APE-1 gene may be down-regulated by its own product.