Expression of asparagine synthetase mRNA through asparagine independent signal transduction pathway that might involve protein kinase C in BALB3T3 cells.

ABSTRACT

Basal level of asparagine synthetase mRNA in BALB3T3 cells was elevated when the cells were shifted from medium containing a high concentration (3.3 mM) of asparagine to one lacking asparagine. We then studied whether the expression of asparagine synthetase mRNA is also mediated through other asparagine-independent signaling pathways. BALB3T3 cells grown to near confluence were quiesced by serum-starvation, and various agents were then added to the culture to examine the enzyme activity and mRNA level of asparagine synthetase. 12-O-tetradecanoylphorbol-13-acetate (TPA), a direct activator of protein kinase C (PKC), elevated dose and time dependently the level of asparagine synthetase mRNA even in Eagle's minimum essential medium with alpha modification (MEM alpha) that contains protein-constituting 20 amino acids and is supplemented with 3.3 mM asparagine. Staurosporine and H-7, PKC inhibitors, strongly blocked the fetal bovine serum-dependent accumulation of asparagine synthetase mRNA. TPA could also enhance the activity of asparagine synthetase within 24 h at concentrations of more than 10 nM. These results suggest that expression of asparagine synthetase gene can be induced both through a pathway that involves PKC and through a pathway the origin of which is a reduced concentration of asparagine in BALB3T3 cells.