O6-methylguanine-DNA methyltransferase activity in tissues and cells of the rat respiratory tract.
A product of alkylating agents and DNA, O6-methylguanine (O6-MG), can mispair with thymine, resulting in initiation of a carcinogenic tissue response. O6-alkylguanine-DNA alkyltransferase (AGT) is an acceptor protein responsible for repairing O6-MG. The purpose of our experiments was to characterize in vitro AGT activity in tissues and cells in the respiratory tract, a target tissue for inhaled alkylating agents. Anatomically defined regions throughout the respiratory tract of male F344 rats were obtained. These included two regions of the lateral wall of the left and right nasal airway (maxilloturbinates and ethmoturbinates), trachea, extrapulmonary bronchi and peripheral lung. Alveolar type II cells were also used in these studies. Radioactive 3H-methylated DNA was synthesized for use in all experiments. Removal of [3H]methyl from O6-MG was measured by high-pressure liquid chromatography after incubation for up to 30 min of tissue and cell extracts with the [3H]DNA. With the exception of tracheal and bronchial extracts, all tissues and cells analyzed contained AGT activity, which was found to increase proportionally to the amount of protein added to reaction flasks. AGT activity in tracheal and bronchial extracts was only detected at the highest protein concentration used (1.5 mg protein/ml) and ranged from 10-15 fmol/mg protein. AGT activity was highest in the lung (integral of 75 fmol/mg protein) and a region of the nasal tissue, the ethmoturbinates (integral of 45 fmol/mg protein). AGT activity in the maxilloturbinates was about 50% less than the AGT activity measured in the ethmoturbinates. These data suggest that methylated DNA in specific regions of the rat respiratory tract should be readily repaired, albeit to different extents.
Bond
J A
JA
Lovelace Biomedical and Environmental Research Institute, Albuquerque, NM 87185.
Gubin
J M
JM
Johnson
N F
NF
D000818:Animals; D001980:Bronchi / Q000201:enzymology; D007700:Kinetics; D008168:Lung / Q000201:enzymology; D008297:Male; D008780:Methyltransferases / Q000378:metabolism*; D019853:O(6)-Methylguanine-DNA Methyltransferase; D009928:Organ Specificity; D051381:Rats; D011916:Rats, Inbred F344; D012137:Respiratory System / Q000201:enzymology*; D014132:Trachea / Q000201:enzymology; D014420:Turbinates / Q000201:enzymology
D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase