Initiation of growth inhibition by TGF beta 1 is unlikely to occur in G1.
Type beta transforming growth factors represent a family of polypeptides that modulate growth and differentiation. They exert their effect on target cells through interaction with multiple cell surface receptors. Transforming growth factor-beta 1 has a strong inhibitory action on cell division in mink lung CC164 cells, a process that is initiated by immediate induction of junB and phosphorylation of nuclear protein followed by a reduced expression of cdk4. However, its signal transduction pathways are still unresolved. In this study we report a detailed analysis of cell kinetic events following addition of transforming growth factor-beta 1 to mink lung CCL64 cells. We show that transforming growth factor-beta 1 reduces [3H]thymidine incorporation after a delay of 8 hours, which reaches its nadir at 16 hours. The reduced growth rate is maintained for at least 48 hours as shown by flow cytometric analysis of DNA content. Using time-lapse video microscopy it was shown that control cells double on average every 14.4 hours, whereas the transforming growth factor-beta 1-treated cells have a doubling time of on average 20.3 hours. The difference in intermitotic time is a consequence of a prolonged G1 phase (a shift from 7.5 to 13.5 hours on average). However, changes in intermitotic times occur only after cells have undergone division in the presence of transforming growth factor-beta 1 and treated cells finish the ongoing cell cycle exactly like control cells. From these findings we conclude that transforming growth factor-beta 1 may change cell cycle parameters by interfering with cellular events prior to G1.(ABSTRACT TRUNCATED AT 250 WORDS)
Kramer
I M
IM
Department of Pharmacology, University College London, UK.
Patel
R
R
Spargo
D
D
Riley
P
P
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects*; D002478:Cells, Cultured; D016213:Cyclins / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D005434:Flow Cytometry; D016193:G1 Phase / Q000187:drug effects; D006801:Humans; D008168:Lung / Q000166:cytology; D018715:Microscopy, Video; D008907:Mink; D008938:Mitosis / Q000187:drug effects; D011233:Precipitin Tests; D011485:Protein Binding; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D016213:Cyclins; D016212:Transforming Growth Factor beta; D004247:DNA