Differential effects of reactive nitrogen species on DNA base excision repair initiated by the alkyladenine DNA glycosylase.
Chronic generation of reactive nitrogen species (RNS) can cause DNA damage and may also directly modify DNA repair proteins. RNS-modified DNA is repaired predominantly by the base excision repair (BER) pathway, which includes the alkyladenine DNA glycosylase (AAG). The AAG active site contains several tyrosines and cysteines that are potential sites for modification by RNS. In vitro, we demonstrate that RNS differentially alter AAG activity depending on the site and type of modification. Nitration of tyrosine 162 impaired 1,N(6)-ethenoadenine (epsilonA)-excision activity, whereas nitrosation of cysteine 167 increased epsilonA excision. To understand the effects of RNS on BER in vivo, we examined intestinal adenomas for levels of inducible nitric oxide synthase (iNOS) and AAG. A striking correlation between AAG and iNOS expression was observed (r = 0.76, P = 0.00002). Interestingly, there was no correlation between changes in AAG levels and enzymatic activity. We found AAG to be nitrated in human adenomas, suggesting that this RNS modification is relevant in the human disease. Expression of key downstream components of BER, apurinic/apyrimidinic endonuclease 1 (APE1) and DNA polymerase beta (POLbeta), was also examined. POLbeta protein was increased in nearly all adenomas compared with adjacent non-tumor tissues, whereas APE1 expression was only increased in approximately half of the adenomas and also was relocalized to the cytoplasm in adenomas. Collectively, the results suggest that BER is dysregulated in colon adenomas. RNS-induced posttranslational modification of AAG is one mechanism of BER dysregulation, and the type of modification may define the role of AAG during carcinogenesis.
Jones
Larry E
LE
Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208, USA.
Ying
Lei
L
Hofseth
Anne B
AB
Jelezcova
Elena
E
Sobol
Robert W
RW
Ambs
Stefan
S
Harris
Curtis C
CC
Espey
Michael Graham
MG
Hofseth
Lorne J
LJ
Wyatt
Michael D
MD
D000236:Adenoma / Q000235:genetics; D000818:Animals; D020134:Catalytic Domain; D045744:Cell Line, Tumor; D045647:DNA Glycosylases / Q000235:genetics*; D019951:DNA Polymerase beta / Q000235:genetics; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000235:genetics; D006801:Humans; D007414:Intestinal Neoplasms / Q000235:genetics; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D026361:Reactive Nitrogen Species
D026361:Reactive Nitrogen Species; D019951:DNA Polymerase beta; C021565:3-methyladenine-DNA glycosylase; D045647:DNA Glycosylases; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase