Cell-mediated co-action of transforming growth factors: incubation of type beta with normal rat kidney cells produces a soluble activity that prolongs the ruffling response to type alpha.
Intense, continuous ruffling is a characteristic of many transformed cells, but untransformed cells ruffle intensely only briefly after exposure to growth factors. We reported previously that cells of a normal rat kidney (NRK) cell line transformed by Kirsten murine sarcoma virus secrete their own ruffle-inducing agent(s) that cause sustained ruffling in either themselves or untransformed NRK cells. In the present study, we examined the roles of the transforming growth factors TGF-alpha and TGF-beta in the induction and maintenance of ruffling in untransformed NRK cells and observed the following: TGF-alpha caused a transient epidermal growth factor (EGF)-like response, which could be blocked by prior exposure of cells to EGF or by antiserum directed against the COOH-terminus of TGF-alpha. TGF-beta caused no ruffling and did not itself prolong TGF-alpha ruffling. A new, buffer-soluble (transferable) mediator activity produced by incubation of TGF-beta with NRK cells for 6-h extended the duration of maximal TGF-alpha-induced ruffling by several-fold. This study demonstrates that TGF-alpha alone causes an EGF-like, transient ruffling response, but neither TGF-alpha or TGF-beta alone, nor the two together, cause transformation-associated sustained ruffling. Rather, TGF-alpha acts in concert with a new, TGF-beta-dependent activity. This new activity appears to inhibit normal cellular off-regulation of TGF-alpha-induced ruffling. Inhibition of the cellular off-regulation of a growth factor response could play a key role in the unregulated growth associated with malignancy.
D000818:Animals; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D003470:Culture Media; D004815:Epidermal Growth Factor / Q000494:pharmacology; D006133:Growth Substances / Q000494:pharmacology*; D007668:Kidney; D007700:Kinetics; D007708:Kirsten murine sarcoma virus / Q000235:genetics*; D010455:Peptides / Q000494:pharmacology*; D051381:Rats; D009053:Sarcoma Viruses, Murine / Q000235:genetics*; D013329:Structure-Activity Relationship; D015291:Transforming Growth Factors
D003470:Culture Media; D006133:Growth Substances; D010455:Peptides; D004815:Epidermal Growth Factor; D015291:Transforming Growth Factors