Changes in response to, and production of, transforming growth factor type beta during neoplastic progression in cultured rat tracheal epithelial cells.

As rat tracheal epithelial cells progress from a normal to a neoplastic phenotype there are systematic changes in their ability to produce and activate latent transforming growth factor type beta (TGF-beta) as well as systematic changes in their response to this growth factor. Using a TGF-beta radioreceptor binding competition assay it was found that normal proliferating rat tracheal cells in early primary culture produced latent TGF-beta. With the emergence of terminally differentiated cell populations active TGF-beta was also detected in the conditioned medium. When normal cells were cultured under conditions allowing for continued proliferation, no active TGF-beta was detected in the conditioned medium. Colonies of proliferating epithelial cells in 4-6 week primary cultures or subculturable tracheal cell lines did not produce detectable levels of active or latent growth factor. With neoplastic progression there was likewise a change in response to active TGF-beta. Normal tracheal cells in primary culture were highly sensitive to growth-factor-induced decreases in thymidine uptake as well as to the induction of terminal differentiation. Proliferating epithelial cells in late (4-6 week) primary cultures and preneoplastic, subculturable cell lines were often as sensitive as normal cells to the growth factor-induced decline in thymidine uptake. None of these altered populations, however, was induced to differentiate (to form cornified, cross-linked envelopes) in the presence of TGF-beta.