Epidermal growth factor dependence and TGFα autocrine growth regulation in primary rat tracheal epithelial cells

Publisher Website
Google Scholar
Abstract
We have examined dependence of primary rat tracheal epithelial (RTE) on exogenous epidermal growth factor (EGF) and determined whether a TGFα autocrine pathway is operating in these cells. Primary RTE cells plated in serum free media (SFM) without EGF and bovine pituitary factor (BPE) show little proliferation compared to cultures propagated in media containing EGF/BPE (CSFM). Removal of EGF/BPE shortly after plating, however, results in significant proliferation, although plateau cell densities are reduced and cell morphology is significantly altered compared to cells propagated in CSFM. Addition of EGF and/or BPE to cultures propagated in SFM minus EGF/BPE restores maximum cell density. The concentration of TGFα peptide in media conditioned by cells propagated without EGF/BPE is lower than the concentration in the media of CSFM cultures. TGFα mRNA and protein levels are also significantly lower in cells late in culture compared to logarithmically growing cells regardless of the presence or absence of EGF/BPE. The proliferation of primary RTE cells propagated without EGF/BPE is inhibited by neutralizing TGFα antiserum and by a tyrphostin compound that blocks TGFα/EGF receptor tyrosine kinase activity. These results indicate that primary RTE cells utilize TGFα as an autocrine growth factor and that the autocrine pathway is regulated as a function of growth state of the cells. However, this pathway does not provide growth autonomy to primary RTE cells, since cultures remain dependent on exogenous EGF/BPE for sustained proliferation.