Changes in responsiveness of rat tracheal epithelial cells to transforming growth factor-beta 1 with time in culture.
Primary rat tracheal epithelial (RTE) cell cultures have previously been shown to be highly sensitive to growth inhibition by transforming growth factor-beta 1 (TGF beta 1) when treated within 1-2 days after plating. The purpose of the present studies was to examine the effects of TGF beta 1 on the growth of RTE cells as a function of time in culture. We found that the sensitivity of RTE cells to growth inhibition by TGF beta 1 decreased dramatically as the cultures aged. The IC50 for inhibition of colony forming efficiency was 0.18 pM when TGF beta 1 was added 24 h after cell plating. When TGF beta 1 treatment was begun on day 5 of culture, the IC50 was 3-4 pM as measured by inhibition of growth (cell number) and DNA synthesis. However, when TGF beta 1 was begun on day 19, the IC50 was 65 pM or greater than 500 pM, depending on whether inhibition of growth or DNA synthesis, respectively, was measured. TGF beta 1 accelerated cell death, as measured by exfoliation of cells, and inhibited cell proliferation. The decrease in responsiveness to TGF beta 1 in late cultures was shown to be dependent on culture age as well as on cell density. No evidence was found for inactivation or degradation of the added TGF beta 1 by the late stage cultures. Cells subcultured from late stage primary cultures remained less responsive to TGF beta 1 than subcultured cells from early cultures. Similar to its effect on proliferation, TGF beta 1 down-regulated the expression of two proliferation-related genes, c-myc and transforming growth factor-alpha, in early but not late RTE cell cultures. On the other hand, fibronectin expression was increased by TGF beta 1 by about twofold at both early and late times in culture. This indicates that the changes in TGF beta 1 responsiveness with time in culture are selective, apparently affecting primarily proliferation-related events.
Rundhaug
J E
JE
Laboratory of Pulmonary Pathobiology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Gray
T
T
Steigerwalt
R W
RW
Nettesheim
P
P
D000818:Animals; D002452:Cell Count; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003584:Cytological Techniques; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D051381:Rats; D013234:Stem Cells / Q000502:physiology; D013997:Time Factors; D014132:Trachea / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology*
D016212:Transforming Growth Factor beta