c-fos mRNA levels are reduced in the presence of antipain and Bowman-Birk inhibitor.

We have studied whether the Bowman-Birk protease inhibitor (BBI) could affect the expression of c-fos in BALB/c/3T3 cells stimulated to divide with serum. Our results show that the levels of c-fos message are significantly decreased in the presence of antipain and BBI. When the cells were treated with cycloheximide after being grown in the presence of BBI, there was no significant decrease in mRNA levels. Our experiments suggest that a BBI-inhibitable protease may be necessary for c-fos expression in 3T3 cells and that new protein synthesis is required for this hypothesized protease to be active. As BBI is capable of affecting c-fos gene expression in cells without being present in the nucleus, our results suggest that a novel pathway could be involved in c-fos gene expression.