Analysis of nuclear transport signals of the human apurinic/apurimidinic endonuclease (APE1/REF1)

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The nuclear localization signal (NLS) in human apurinic/apyrimidinic endonuclease (APE1), a key protein in both DNA base excision repair and transcriptional regulation, has not been analyzed in detail. We examined the role of specific residues in nuclear translocation of APE1, using green fluorescent protein (EGFP) fused to APE1 as a reporter. Nuclear localization (NL) of ectopic APE1 was abrogated for the mutant lacking 20 N-terminal aa residues (ND20). Fusion of these 20 residues directed nuclear localization of EGFP. While an APE1 mutant lacking N-terminal 7 residues (ND7 APE1) showed normal nuclear localization, ND7 APE1 with E12A/D13A double mutation resulted in drastic decrease of nuclear localization, indicating that E12 and D13 are critical components of the NLS. \r\n On the other hand, nuclear localization of the full-length APE1 containing the E12A/D13A mutations suggests that the putative NLS and residues 8-13 contribute independently to nuclear import. Nuclear accumulation of the ND7 APE1(E12A/D13A), but not EGFP alone, after treatment with leptomycin B or after oxidative stress suggests the presence of a previously unidentified nuclear export signal in APE1. Together, these results indicate that the mechanism of nuclear localization of APE1 is complex and regulated via import and export.\r\n In addition increase DNA damage occurs in astronauts during space flight. Humans in space are exposed both to radiation and microgravity. It is clear that the increased exposure to radiation influences DNA damage however it is not clear as to the role that microgravity plays in this increase in damage. \r\n Our investigation on the effects of microgravity on the nuclear translocation of DNA repair enzyme APE1 has revealed that microgravity interferes with the normal trafficking of APE1. \r\n

apurinic/apyrimidinic endonuclease 1, APE1