Abstract
Previous studies have demonstrated a robust pulmonary expression of hypoxia-induced mitogenic factor (HIMF) during the perinatal period, when surfactant protein (SP) synthesis begins. We hypothesized that HIMF modulates SP expression and participates in lung development and maturation. The temporal-spatial expression of HIMF, SP-B, and SP-C in developing mouse lungs was examined by immunohistochemical staining, Western blot, and RT-PCR. The expression and localization of SP-B and SP-C were investigated in mouse lungs after intratracheal instillation of HIMF in adult mice. The effects of HIMF on SP-B and SP-C transcription activity, and on mRNA degradation, were investigated in mouse lung epithelial (MLE)-12 and C10 cells using the promoter-luciferase reporter assay and actinomycin D incubation. The activation of Akt, extracellular signal-regulated kinase (ERK)1/2, and p38 mitogen-activated protein kinase was explored by Western blot. Intratracheal instillation of HIMF resulted in significant increases of SP-B and SP-C production, predominantly localized to alveolar type II cells. In MLE-12 and C10 cells, HIMF enhanced SP-B and SP-C mRNA levels in a dose-dependent manner. Meanwhile, HIMF increased transcription activity and prevented actinomycin D-facilitated SP-B and SP-C mRNA degradation in MLE-12 cells. Incubation of cells with LY294002, PD098059, or U0126 abolished HIMF-induced Akt and ERK1/2 phosphorylation and suppressed HIMF-induced SP-B and SP-C production, whereas SB203580 had no effect. These results indicate that HIMF induces SP-B and SP-C production in mouse lungs and alveolar type II-like cell lines via activations of phosphatidylinositol 3-kinase/Akt and ERK1/2 mitogen-activated protein kinase, suggesting that HIMF plays critical roles in lung development and maturation.