DIFFERENTIAL EXPRESSION OF COLLAGEN-BINDING RECEPTORS IN FETAL-RAT LUNG-CELLS

Interactions of cells with molecules of the extracellular matrix (ECM) are mediated via specific cell surface receptors. Because collagen is an important ECM component in the developing lung, we investigated th e expression of collagen receptors by distal fetal lung epithelial cel ls and fibroblasts. Cell attachment experiments revealed that fibrobla sts but not epithelial cells adhered to various types of collagen. Wit h the use of subunit-specific antibodies, we demonstrated the presence of the collagen integrins alpha(1) beta(1), alpha(2) beta(1), and alp ha(3) beta(1) at the fibroblast surface but only the integrin alpha(3) beta(1) on epithelial cells. Affinity chromatography on collagen-Seph arose identified only alpha(1) beta(1) and alpha(2) beta(1) as collage n-binding integrins in extracts of I-125 surface-labeled fibroblasts. No collagen-binding receptors were detected in extracts of surface-iod inated epithelial cells. Message for alpha(1)- and alpha(2)-integrin w as readily demonstrated for fibroblasts, but both mRNAs were hardly de tectable in epithelial cells. In contrast, epithelial cells expressed significantly greater as mRNA levels than fibroblasts. These data demo nstrate that alpha(1) beta(1)- and alpha(2) beta(1)-integrins function as collagen-binding receptors in fetal lung fibroblasts. Distal fetal lung epithelial cells do not express the alpha(1) beta(1)- and alpha( 2) beta(1)-integrins and do not adhere to collagen. The alpha(3) beta( 1)-integrin, which is expressed by both cell types, does not function as a collagen receptor.