Hypoxia‐induced proliferation via epidermal growth factor receptor signaling in pulmonary endothelial cells

Abstract

Arginase activity is involved in cellular proliferation via ornithine production and its subsequent metabolism to proline and/or polyamines. Ornithine decarboxylase (ODC) is the rate‐controlling enzyme in polyamine biosynthesis. We have previously shown that epidermal growth factor receptor (EGFR) is important in hypoxia‐induced cellular proliferation in endothelial cells. We hypothesized that hypoxia would activate EGFR which would in turn up‐regulate arginase expression and thereby promote cellular proliferation. We studied human pulmonary microvascular endothelial cells (hPMVEC) kept in either normoxia (20% O2 , 5% CO2) or hypoxia (1% O2, 5% CO2) for 24 hours. Arginase II protein expression was ~3 fold greater in hypoxia than in normoxia, and this hypoxia‐induced increase was attenuated by inhibition of EGFR using AG1478 (30nM). Urea production was also greater in hypoxia than in normoxia, and this hypoxia‐induced increase was completely prevented by EGFR inhibition. The mRNA levels of ODC were ~2.5 fold greater in hypoxia than in normoxia, and treatment with AG1478 prevented the hypoxia‐induced increase in ODC mRNA. Pharmacological inhibition of either arginase or ODC prevented hypoxia‐induced cellular proliferation. Our data demonstrate that EGFR tyrosine kinase activity is critical for hypoxia‐induced hPMVEC proliferation via up‐regulation of arginase and ODC.