Transient increase in the c-fos mRNA level after change of culture condition from serum absence to serum presence and after cycloheximide addition in rat 3Y1 fibroblasts

When 3Y1 cells resting at a saturation density were mitotically stimulated with serum, the c-fos mRNA level markedly increased in a short period of time and then decreased rapidly to an undetectable level. Subsequent serum deprivation followed by serum re-addition or subsequent cycloheximide addition caused a transient re-increase in the c-fos mRNA level. These results can be explained by assuming that the continuous expression of the c-fos gene at a minimum level is necessary for the eventual initiation of S phase, and that the over-expression of the c-fos gene occurs when the control of the gene expression is transiently disturbed by the change of the culture condition.     

Tumor necrosis factor and interleukin-1 cause a rapid and transient stimulation of c-fos and c-myc mRNA levels in human fibroblasts

Tumor necrosis factor (TNF) and interleukin-1 (IL-1) were shown previously to be mitogenic for human fibroblasts. Here we show that recombinant human TNF and recombinant human IL-1 alpha increase steady state levels of c-fos and c-myc proto-oncogene mRNAs in quiescent human FS-4 fibroblasts. Proto-oncogene mRNA levels were enhanced within 20 min of TNF or IL-1 addition, peaked at 30 min, and declined to undetectable levels (c-fos) or basal levels (c-myc) by 60 or 90 min. A similar rapid increase in c-fos and c-myc mRNA was seen in quiescent FS-4 cells exposed to cycloheximide. However, in the presence of cycloheximide, both proto-oncogene mRNA levels continued to rise for at least 90 min. The transient nature of the increase in c-myc mRNA levels appears to be a response characteristic for TNF and IL-1 because in quiescent FS-4 cells exposed to 10% fetal bovine serum, steady state levels of c-myc mRNA remained elevated for at least 4 h.