Objective: To study the effects of nitric oxide (NO) on surfactant protein A (SP-A) gene expression.
Design: In vitro study.
Subjects: A human lung tumor cell line (H441) representative of distal respiratory epithelium.
Interventions: Cells were treated with the NO donor S-nitroso-N-acetyl penicillamine (SNAP) at concentrations ranging from 0.3 to 3.0 mM for 24 hrs.
Measurements and main results: Northern blot analyses using a radiolabeled cDNA probe for human SP-A demonstrated that SNAP modestly (approximately 30%) decreased SP-A mRNA expression in a dose-dependent manner. Western blot analyses using a polyclonal anti-human SP-A antibody demonstrated that SNAP also decreased SP-A peptide expression. mRNA stability assays demonstrated that SNAP did not affect the half-life of SP-A mRNA. Cell viability assays demonstrated that SNAP slightly decreased cell viability compared with control cells. There were no significant differences in cell viability among cells treated with the different concentrations of SNAP.
Conclusions: NO decreases in vitro SP-A gene expression by approximately 30% in a human lung tumor cell line representative of distal respiratory epithelium. This effect does not occur at the posttranscriptional level and cannot be entirely accounted for by changes in cell viability. The inhibitory effect of NO demonstrated in this study is of relatively small magnitude and it is therefore difficult to make strong conclusions regarding biological relevance. However, these data, coupled with previous data demonstrating that NO negatively affects surfactant function, suggest that NO has the potential to negatively impact surfactant homeostasis.