PRODUCTION OF FIBROBLAST-PNEUMOCYTE-LIKE FACTOR BY FETAL RABBIT LUNG FIBROBLASTS - ISOLATION AND EFFECTS OF IT AND RELATED FACTORS ON FETALTYPE-II CELLS IN-VITRO

Fetal lung fibroblasts interact with type II epithelial cells, inducin g their maturation. This interaction arises by secretion of factors wh ich alter fetal type II cell function. To analyze these factors, condi tioned medium (CM) was produced by exposing serum-free minimum essenti al medium, with [S-35]methionine (5 muCi/ml), to confluent cultures of fetal rabbit lung fibroblasts. This medium was tested for ability to stimulate [H-3]choline incorporation by fetal type II cells and subseq uently fractionated on molecular weight filtration columns P60 (2.5 cm x 90 cm; NMW cutoff, 60kd; 1 M acetic acid) and A 1.5m (2.5 cm x 90 c m; NMW cutoff, 1,500 kd; Tris-buffered saline) and a hydroxyapatite co lumn (HT) (1.5 cm x 30 cm; NaCl and 0.01 - 0.3M phosphate). Crude medi um stimulated choline incorporation into phosphatidylcholine. [S-35]me thionine was resolved in void volume material and in material of appar ent molecular weight of 6000 daltons on the P60 filtration column. Fil tration on the A1.5m column showed two major fractions with radiolabel incorporation. Each of these was resolved into two subfractions on HT chromatography. The high molecular mass fraction contained material w hich stimulated [H-3]choline incorporation by fetal type II cells. The low molecular mass fraction tended to inhibit [H-3]choline incorporat ion. The second subfractions of both the first and second primary frac tions inhibited [H-3]thymidine incorporation into DNA by fetal type II cells. SDS-PAGE electrophoresis and autoradiography showed that under reducing conditions, each peak contained several proteins. However fe w of these displayed radioactivity. These results indicate that protei n factors produced by fetal lung fibroblasts may be involved in regula ting both differentiation and replication of fetal type II cells.