The production of pulmonary surfactant, a complex of phospholipids and lung-specific surfactant proteins, is a primary function of alveolar type II cells. Although previous studies have demonstrated a role for cell-extracellular matrix interactions and normal cell shape in the maintenance of differentiated function in primary cultures of adult rat type II cells, a positive role for growth factors in surfactant protein gene expression in isolated normal adult type II cells has not been reported. In the present study, we have examined the effects of a panel of hormones, growth factors, and cytokines on the expression of mRNAs for surfactant proteins A, B, and C (SP-A, SP-B, and SP-C). Our results show that keratinocyte growth factor (KGF) induced a two- to threefold increase in steady-state levels of mRNAs for SP-A and SP-B, but had no effect on or decreased SP-C mRNA. The increase in SP-A mRNA was accompanied by an increase in SP-A protein. The effects of KGF were both dose and time dependent, and they could be neutralized by a monoclonal antibody against KGF. The effects of KGF were mimicked by acidic fibroblast growth factor, which will bind the KGF receptor. We conclude that KGF can support differentiation of alveolar type II cells as well as act as a mitogen, thus suggesting an important role for KGF in maintenance of the alveolar epithelium.
Effects of cortisol and thyroxine on phosphatidylcholine and phosphatidylglycerol synthesis by adult rat lung alveolar type II cells in primary culture
