EXPOSURE TO HYPEROXIA INDUCES P53 EXPRESSION IN MOUSE LUNG EPITHELIUM

Cells that are exposed to free radicals have increased levels of DNA s trand breaks with accumulation of the tumor suppressor protein p53, wh ich induces cell cycle arrest and/or apoptosis, Because oxidants injur e pulmonary epithelial cells, it was hypothesized that exposure to hyp eroxia promotes DNA strand breaks in lung epithelium, resulting in inc reased expression of p53 and loss of epithelial cell function. Adult m ale C57B1/6J mice were exposed to > 95% oxygen for 72 h and DNA integr ity was determined in their lungs by terminal transferase immunoreacti vity. Both nonimmunoreactive and lightly stained nuclei were observed in cells comprising the airway and parenchyma. Exposure to hyperoxia r esulted in a marked increase in the intensity of nuclear staining in d istal bronchiolar epithelium and alveolar epithelial and endothelial c ells. Airway epithelial cells from control lungs contained detectable levels of p53 protein, which markedly increased in both nuclei and cyt oplasm of distal bronchiolar epithelial cells and to a lesser extent i n alveolar epithelial cells that were morphologically consistent with type II cells, Western and Northern blot analyses revealed that hypero xia increased total lung p53 protein expression but not levels of mRNA . Changes in terminal transferase immunoreactivity and p53 expression were not observed in large airway cells, fibroblasts underlying distal airway, or smooth muscle cells. Expression of SP-B mRNA modestly incr eased and Clara cell secretory protein and cytochrome P-450 2F2 mRNAs decreased, providing additional evidence that hyperoxia injured pulmon ary epithelial cells. These findings support the concept that hyperoxi a damages DNA of pulmonary epithelial cells, which respond by accumula ting p53 and changes in epithelial cell-specific gene expression.