Transcription of krox-20/egr-2 is upregulated after exposure to fibrous particles and adhesion in rat alveolar macrophages

Alveolar macrophages meet various types of particulate substances deposited deep in the lung. We report differences in biologic responses of alveolar macrophages between phagocytosis of fine spherical and fibrous particles. Although titanium dioxide (TiO2) is thought to be biologically inert, the cytotoxicity of fibrous TiO2 (F-TiO2 was much higher than spherical TiO2 (S-TiO2). Differential display and the subsequent Northern blot analysis indicated that transcription of krox-20/egr-2 gene was slightly and greatly upregulated in Sand F-TiO2-exposed alveolar macrophages, respectively. The messenger RNA (mRNA) level of krox-20/egr-2 increased up to 8 h in F-TiO2-exposed alveolar macrophages, whereas krox-20/egr-2 mRNA level was transiently increased in response to adhesion to the culture dish. Stimulation with lipopolysaccharide also increased krox-20/egr-2 mRNA level transiently, although the mRNA level rebounded after 8 h, The analysis with 5' rapid amplification of complementary DNA ends suggested that there is a heterogeneity in the upstream region of this gene (krox-20/egr-2 and krox-20H1; accession numbers AB032420 and AB032419, respectively). The polymerase chain reaction analysis with specific primers for krox-20/egr-2 and krox-20H1 indicated that both genes were almost equally upregulated after either adhesion to the plastic dish or phagocytosis of F-TIO,, These results suggest that both krox-20/egr-2 and krox-20H1 are implicated in adhesion and phagocytosis, and that the expression of krox-20 may reflect interaction with foreign substances and adhesion in alveolar macrophages.