HYPEROXIC STRESS ELEVATES P52(PAI-1) MESSENGER-RNA ABUNDANCE IN CULTURED-CELLS AND ADULT-RAT PULMONARY TISSUE

Hyperoxic stress alters expression of genes involved in extracellular matrix (ECM) remodeling. To identify novel ECM-associated gene product s positively regulated by hyperoxia, rat kidney cells were exposed to 95% O2, and the complement of [S-35]methionine-labeled, saponin-resist ant, ECM-associated proteins was compared with normoxic controls. O2-s tressed cells accumulated significantly greater ECM levels (approximat ely 3- to 4-fold that of control cells) of a 52-kDa glycoprotein (p52) , recently identified as the matrix form of plasminogen activator inhi bitor type 1 (PAI-1) (P. J. Higgins, P. Chaudhari, and M. P. Ryan. Bio chem. J. 273: 651-658, 1991; P. J. Higgins, M. P. Ryan, R. Zeheb, T. D . Gelehrter, P. Chaudhari. J. Cell. Physiol. 143: 321-329, 1990), whic h peaked at 48 h of exposure. Hyperoxia-associated increases in ECM p5 2 (PAI-1) content reflected parallel elevations in p52(PAI-1) mRNA abu ndance. Similar results were obtained using secondary cultures of rat pulmonary fibroblasts. This 48-h period of maximal hyperoxia-induced p 52(PAI-1) expression in vitro was used to design subsequent in vivo st udies. Adult rats were exposed to 99% 02 for 24-50 h, and RNA was extr acted from the pulmonary tissue of stressed and control animals. A 5- to 8-fold and 6- to 15-fold increase in lung p52(PAI-1) mRNA content w as evident in hyperoxia-treated rats at 24 and 50 h, respectively. All of this increase occurred in the defined 3.2-kb species of rat p52(PA I-1) mRNA. Actin mRNA levels increased three- to sevenfold as a functi on of hyperoxic stress, whereas catalase and glyceraldehyde-3-phosphat e dehydrogenase mRNA abundance was unchanged. Because p52(PAI-1) is a major regulator of the pericellular proteolytic environment, elevated p52(PAI-1) expression may be important in the reparative phase of O2-m ediated pulmonary injury.