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Mitogenic growth factors regulate differentially early gene mRNA expression: a study on two clones of 3T3 fibroblasts
T Janet1, G Labourdette, M Sensenbrenner
1Laboratoire de Neurobiologie Ontogénique, CNRS UPR 417, Strasbourg, France.
Abstract:
The relationship between cell proliferation and mRNA levels of the immediate early genes c-fos, c-jun, and jun B has been investigated in two clones of 3T3 fibroblasts (D1-3T3 and N2-3T3) upon treatment with basic fibroblast growth factor (bFGF), thrombin, phorbol 12-myristate 13-acetate (PMA) and dibutyryl cyclic AMP (Bt2cAMP). The 3T3-derived clone D1-3T3 almost stops dividing upon serum deprivation, while the N2-3T3 clone does not. The proliferation of the two clones was stimulated by thrombin and PMA and inhibited by Bt2cAMP. Basic FGF stimulated the growth of D1-3T3 but partly inhibited that of N2-3T3 cells. In spite of variable mitogenic response, immediate early genes, c-fos, c-jun, jun B, and c-myc, were induced by the growth factors and by PMA in both cell clones. In our experimental conditions the early gene mRNAs were expressed independently; i.e., the expression of one protooncogene had no bearing on the expression of the other. The cell growth was not directly related to the expression of a particular protooncogene mRNA. Data are presented showing that early gene mRNA expression induced by bFGF or thrombin was not mediated by protein kinase C activation while thrombin-induced mitosis was. Basic FGF induced a part of c-jun mRNA expression, but not mitosis, through a pertussis toxin-sensitive mechanism.
Insights
Cell proliferation and immediate early gene expression (c-fos, c-jun, jun B) were studied in 3T3 fibroblast clones. Growth factors and PMA induced gene expression independently of cell growth, suggesting varied signaling pathways.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Understanding the molecular mechanisms regulating cell proliferation is crucial in cell biology.
- Immediate early genes (IEGs) like c-fos, c-jun, and jun B are rapidly induced by growth factors and play roles in cellular responses.
- Fibroblast growth factors (FGFs) and other mitogens are key regulators of cell division.
Purpose of the Study:
- To investigate the relationship between cell proliferation and the mRNA levels of immediate early genes (c-fos, c-jun, jun B) in response to various stimuli.
- To compare the mitogenic and gene expression responses in two distinct 3T3 fibroblast clones with different proliferative behaviors.
- To elucidate the signaling pathways involved in growth factor-induced gene expression and proliferation.
Main Methods:
- Utilized two 3T3 fibroblast clones (D1-3T3 and N2-3T3) with differential serum deprivation responses.
- Treated cells with basic fibroblast growth factor (bFGF), thrombin, phorbol 12-myristate 13-acetate (PMA), and dibutyryl cyclic AMP (Bt2cAMP).
- Quantified mRNA levels of immediate early genes (c-fos, c-jun, jun B, c-myc) and assessed cell proliferation.
Main Results:
- Both cell clones exhibited induction of c-fos, c-jun, and jun B mRNA upon stimulation with growth factors and PMA, irrespective of their proliferative response.
- Cell growth was not directly correlated with the expression levels of specific protooncogene mRNAs.
- Basic FGF and thrombin induced early gene mRNA expression independently of protein kinase C activation, although thrombin-induced mitosis involved this pathway.
Conclusions:
- Immediate early gene expression in response to mitogens can occur independently of direct cell proliferation.
- Distinct signaling pathways mediate growth factor-induced gene expression and mitogenesis.
- Basic FGF utilizes a pertussis toxin-sensitive pathway for partial c-jun mRNA induction, uncoupled from mitosis.