Cells which line the airway provide defense against airborne particles and chemicals. They are also the site of certain major diseases including chronic bronchitis, cystic fibrosis and carcinoma. Unfortunately, we know little about how these airway epithelial cells control their differentiated functions. This is due in part to lack of a suitable in vitro model. Hamster tracheal epithelial cells (HTE) offer such a model. In contrast to other tracheal epithelial cells in culture, HTE cells redifferentiate when the cells reach confluence. Using this HTE cell culture system, we have found that retinoic acid (RA) has a profound influence on the growth and differentiation of these cells. We will examine the possibility that RA alters cell growth by modulating the production of TGF-alpha, TGF-beta, or their respective receptors. These factors have been shown to be produced by many normal cells, and may play a role in regulating their growth. In addition to its effect on cell growth, RA also changes cell configuration, ie it converts HTE from flat to cuboidal cells. We will determine whether this shape change might be related to the extracellular matrix. Therefore, we will investigate whether RA induces the production of the basement membrane proteins type IV collagen, laminin or fibronectin. Another possibility is that the shape change might be related to alteration in either the amount of distribution of cytoskeletal elements. Thus we will measure the levels of actin, tubulin, and cytokeratins in control and RA- treated HTE cells. The intracellular distribution of these elements will be analyzed by immunofluoesence, using specific antibodies. The third major effect of RA on these cells is to increase the release of mucus-like glycoprotein (MLGP). We will investigate whether RA stimulates synthesis of the protein moiety, or increases glycosylation of pre-existing protein cores. Finally we will determine if these RA-induced effects are mediated through the newly discovered nuclear retinoic acid receptors (RAR- alpha&beta). We will characterize the nuclear receptors in these cells using anti-peptide antibodies developed in our laboratory. HTE cells will be depleted of RAR-alpha & beta by using the appropriate anti-sense oligonucleotide and the ability of these depleted cells to respond to RA determined. These studies should provide new insights into the mechanism(s) by which the essential element retinoic acid control the differentiated phenotype of airway epithelial cells.