Progressive relaxation of Go-arrest controls and altered responsiveness to insulin, EGF and thrombin in CCL39 lung fibroblasts over-expressing myc and ras oncogenes.
Factor-dependent hamster lung fibroblasts (CCL39) were transfected with plasmid vectors expressing normal Ha-ras, T24 Ha-ras, V-Ki-ras or myc oncogenes placed under the transcriptional control of potent viral or inducible (metallothionein-I) promoters. The rate at which clonal isolates proliferated in monolayer cultures in serum-free medium or in response to progression (insulin, EGF) and competence growth factors (alpha-thrombin) was found to vary according to the level of oncogene expression. Low levels of T24 ras gene did not abrogate Go-arrest controls but rendered CCL39 cells responsive to both insulin and EGF. Moderate levels (3- to 10-fold) of T24 and Ki-ras genes induced autonomous growth in serum-free medium and attenuated the cell responsiveness to all three factors. Growth of highest ras expressors was enhanced by low (less than 100 microM) concentrations of suramin, and was partially or not inhibited at higher concentrations. In contrast, EGF but not insulin, was able to recruit quiescent cells expressing moderate (less than or equal to 5-fold) myc levels. Higher levels conferred growth autonomy as well as hypersensitivity to insulin, EGF and thrombin. Suramin abolished the self-replication of such myc cells, thus suggesting an autocrine mechanism of proliferation. Hence, both myc and ras genes provided CCL39 cells with distinct growth competence functions which enabled these cells to respond overall more efficiently to functionally distinct classes of mitogens, or to sustain a completely autonomous replication, depending on the abundance of their respective products. Negative autoregulatory mechanisms may additionally be set into motion in this system when activated ras oncogenes are excessively expressed.
Pichon
F
F
Division of Cancer and Cell Biology, Mount Sinai Research Institute, Toronto, Ontario, Canada.
Seuwen
K
K
Pouysségur
J
J
Lagarde
A E
AE
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002999:Clone Cells; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression; D011905:Genes, ras; D005822:Genetic Vectors; D007328:Insulin / Q000494:pharmacology*; D007399:Interphase; D008168:Lung; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016271:Proto-Oncogene Proteins c-myc; D011519:Proto-Oncogenes; D013917:Thrombin / Q000494:pharmacology*; D014158:Transcription, Genetic; D014162:Transfection
D007328:Insulin; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D004815:Epidermal Growth Factor; D013917:Thrombin