Modulation of c-myc and c-fos gene expression in regenerating rat liver by 2-mercaptopropionylglycine

Expression of the two proto-oncogenes, c- myc and c- fos, in proliferating liver, and the modulation of their expression by 2-mercaptopropionylglycine (MPG) has been investigated. A significant increase in the expression of both c-myc and c-fos was observed, attaining a peak at 30 min, followed by a gradual decline for 8h after partial hepatectomy. Treatment of partially hepatectomized animals with MPG resulted in a significant decrease in the expression of both genes, the decrease being more marked in c- myc mRNA levels. At later time points, there was a very small rise in the mRNA levels of these genes in MPG-treated animals but they still remained much lower than the peak levels observed in both genes 30 min after surgery. A decline in the recovery of liver weight in MPG-treated animals was also observed.     

c-fos and c-myc gene activation, ionic signals, and DNA synthesis in thymocytes

Among the earliest responses to mitogens that have been detected in normal quiescent cells are ionic changes: we have described rapid increases in the cytosolic free Ca2+ concentration ([Ca]i) and in the intracellular pH (pHi) in mitogen-stimulated thymocytes and fibroblasts (Hesketh, T. R., Moore, J. P., Morris, J. D. H., Taylor, M. V., Rogers, J., Smith, G. A., and Metcalfe, J. C. (1985) Nature 313, 482-484). Here we investigate the relationship between these ionic signals and the subsequent expression of the c-fos and c-myc proto-oncogenes in murine thymocytes. We show that the plant lectin concanavalin A (ConA), the phorbol ester 12-O-tetradecanoyl phorbol 13-acetate (TPA) and the Ca2+-ionophore A23187 each causes a rapid increase in both c-fos and c-myc mRNAs. The activation of both genes is completely dependent on the extracellular Ca2+ concentration ([Ca]o) for A23187 and independent of [Ca]o for TPA. Activation of c-myc, but not c-fos, by ConA is partially dependent on [Ca]o. The pHi increases generated by ConA or TPA are not necessary for expression of mRNA from either gene in response to these mitogens. Exogenous 8-bromo-cyclic AMP (but not 8-bromo-cyclic GMP) inhibits the c-myc responses to ConA and TPA. The data also show that neither early c-fos nor c-myc expression is sufficient to commit the cells to DNA synthesis.     

c-fos antisense RNA blocks expression of c-fos gene in F9 embryonal carcinoma cells

To study the function of proto-oncogene c-fos, we prepared an antisense plasmid that expresses in mammalian cells c-fos antisense RNA which is complementary to the endogenous c-fos mRNA. Upon transfection into undifferentiated F9 EC cells, the antisense plasmid directed constitutive expression of a large amount of c-fos antisense RNA. These cells were very low in the basal level of c-fos message and were unable to induce c-fos message when stimulated with interferon or phorbol ester. The failure to induce c-fos message led to the blockade of c-fos protein expression in these cells. Thus, these cells represented a c-fos defective phenotype. The blockade of c-fos gene expression seen in antisense-cells could be caused by rapid degradation of the c-fos message, since c-fos mRNA expression was rescued in these cells when treated with protein synthesis inhibitor, cycloheximide. We found that expression of c-myc gene was down-regulated in c-fos antisense-cells: Although control undifferentiated F9 cells constitutively expressed a high level of c-myc message, the antisense cells had a much lower amount of c-myc mRNA. Since p53 and heat shock gene 70 were expressed at comparable levels in control and antisense cells, c-myc gene expression appears to be regulated by c-fos gene in F9 EC cells. Lastly, these antisense cells grew as rapidly as control F9 cells and underwent differentiation after retinoic acid treatment, indicating that c-fos expression is not a prerequisite for differentiation of F9 cells.     

Changes in polyamines, c-myc and c-fos gene expression in osteoblast-like cells exposed to pulsed electromagnetic fields

Pulsed electromagnetic field (PEMF) stimulation promotes the healing of fractures in humans, though its effect is little known. The processes of tissue repair include protein synthesis and cell differentiation. The polyamines (PA) are compounds playing a relevant role in both protein synthesis processes and cell differentiation through c-myc and c-fos gene activation. Since several studies have demonstrated that PEMF acts on embryonic bone cells, human osteoblast-like cells and osteosarcoma TE-85 cell line, in this study we analyzed the effect on cell PAs, proliferation, and c-myc and c-fos gene expression of MG-63 human osteoblast-like cell cultures exposed to a clinically useful PEMF. The cells were grown in medium with 0.5 or 10% fetal calf serum (FCS). c-myc and c-fos gene expressions were determined by RT-PCR. Putrescine (PUT), spermidine (SPD), or spermine (SPM) levels were evaluated by HPLC. [(3)H]-thymidine was added to cultures for DNA analysis. The PEMF increased [(3)H]-thymidine incorporation (P < or = .01), while PUT decreased after treatment (P < or = .01); SPM and SPD were not significantly affected. c-myc was activated after 1 h and downregulated thereafter, while c-fos mRNA levels increased after 0.5 h and then decreased. PUT, SPD, SPM trends, and [(3)H]-thymidine incorporation were significantly related to PEMF treatment. These results indicate that exposure to PEMF exerts biological effects on the intracellular PUT of MG-63 cells and DNA synthesis, influencing the genes encoding c-myc and c-fos gene expression. These observations provide evidence that in vitro PEMF affects the mechanisms involved in cell proliferation and differentiation.     

c-myc and c-fos expression in differentiating mouse primary keratinocytes.

Expression of the myc and fos genes has been monitored in mouse primary keratinocytes after induction of terminal differentiation by calcium or tetradecanoylphorbol acetate (TPA). myc RNA levels in growing cells are very high and remain elevated even at late times after calcium-induced differentiation. Thus, keratinocytes provide the first example of normal primary cells with persistent c-myc expression irrespective of their proliferative or differentiated state. fos expression is also relatively unaffected by addition of calcium. In contrast to calcium, TPA-induced differentiation is accompanied by dramatic changes in proto-oncogene expression: marked c-fos induction and considerable although transient decrease in c-myc expression. These effects might be important for the keratinocyte response to TPA: TPA treatment of a keratinocyte cell line (RBK) resistant to this substance has no effect on c-myc expression and leads only to minimal c-fos induction. In these cells full fos induction can still be triggered by addition of fresh medium. Thus, the fos gene in normal keratinocytes is inducible through at least two independent mechanisms, only one of which has been lost during derivation of the TPA-resistant cell line.     

Increased levels of c-fos and c-myc mRNA in ATP-stimulated endothelial cells

In bovine aortic endothelial cells, ATP induced a transient and sequential accumulation of c-fos and c-myc mRNA, which was detected after 1 hour and 3 hours, respectively. The effect of ATP on c-fos mRNA was stronger than that of TNF and bFGF. Both ATP and bFGF increased c-myc mRNA after a 3 hour treatment, whereas TNF did not. If none of the 3 agonists tested induced a selective expression of c-fos or c-myc, each of them was associated with a different quantitative combination of the 2 signals, which might be related to the distinct responses that they trigger in endothelial cells.     

c-fos和c-myc在北方山溪鲵精子发生中的表达

用免疫组织化学方法检测原癌基因cf-os和c-myc蛋白在北方山溪鲵(Batrachuperus tibetanus)精子发生中的表达定位。结果显示,在精原细胞缓慢增殖期,8、9月,FOS阳性反应物出现在精原细胞的胞质及核膜外,10、11月,FOS在少量精原细胞的胞核中表达。在精原细胞快速增殖期,即翌年4月,FOS定位在精原细胞的胞质中;5月,FOS在大量的胞核中强阳性表达;6月,FOS定位于部分精母细胞核质和核膜下;7月,FOS在一些精子细胞的核质和核膜下表达。MYC在8、9月的部分精原细胞胞质中表达较弱,在101、1月阳性反应出现在个别精原细胞的核质中。翌年4月,MYC在精原细胞核周围的胞质中表达;5月在大量的精原细胞核膜下有强表达;6月,MYC在一些精母细胞核膜下表达;7月,MYC在部分精子细胞的核膜下弱表达。结果表明,北方山溪鲵的原癌基因cf-os和c-myc表达大强度在生精细胞发育中呈阶段性,表达的强度和细胞数量与细胞增殖的速度相一致。FOS和MYC在精原细胞内从胞质向胞核的转移与细胞快速增殖的时期相吻合。说明cf-os和c-myc对精原细胞有丝分裂有促进作用,并参与精母细胞成熟分裂的调控。     

Differential control of proto-oncogene c-myc and c-fos expression in lymphocytes and fibroblasts.

In lymphocytes stimulated with the mitogen phytohaemagglutinin, an inhibitor of the enzyme ADP-ribosyltransferase (ADPRT) completely blocks the proliferative response and the increase in expression of the proto-oncogene c-myc without affecting c-fos significantly. Conversely, in fibroblasts the serum-induced growth is not affected by the ADPRT inhibitor, and both oncogenes are dramatically super-induced. Hence there are differences between lymphocyte and fibroblast early responses to mitogenic stimulation and also between regulation of c-fos and c-myc gene expression.     

Regulation of expression of c-fos and c-myc in rat lymphoma Nb-2 cells

This study examined the effects of the mitogen, prolactin and the cell cycle inhibitors, cyclosporin A and neomycin sulfate, on expression of the proto-oncogenes c-fos and c-myc in the rat lymphoma Nb-2 cell line. Stimulation of quiescent cultures with prolactin resulted in a 2-3-fold increase in the constitutive levels of c-myc mRNA which peaked at 4 h and declined thereafter. c-Fos mRNA was not detected in quiescent or prolactin-stimulated cultures. Cyclosporin A or neomycin sulfate reversibly blocked the mitogenic effect of prolactin on Nb-2 cells, but had little effect on constitutive levels of c-myc. However, the release of Nb-2 cells from a cyclosporin A or a neomycin sulfate block resulted in a rapid transient induction of c-fos which peaked at 0.5-1 h and declined rapidly thereafter. These results indicate that the rapid transient expression of c-fos following release from cell cycle blockage was not sufficient to elicit cell division, but these cells were competent to respond to prolactin. Prolactin allows progression through the cell cycle and enhances c-myc mRNA levels.