Serotonin N-acetyltransferase mRNA levels in photoreceptor-enriched chicken retinal cell cultures: elevation by...

Serotonin N-acetyltransferase (AA-NAT; arylalkylamine N-acetyltransferase; EC 2.3.1.87) is a key regulatory enzyme in the biosynthesis of melatonin. Previous studies have shown that the activity of this enzyme in the chicken retina is regulated by a cyclic AMP-dependent mechanism. In the present report, we investigated whether cyclic AMP can regulate the levels of AA-NAT mRNA in photoreceptor-enriched chick retinal cell cultures. AA-NAT mRNA levels were elevated by acute treatment with cyclic AMP protagonists, including forskolin; this response was blocked by H-89, a selective inhibitor of cyclic AMP-dependent protein kinase. Forskolin did not alter the rate of disappearance of AA-NAT mRNA in actinomycin D-treated cells, suggesting that cyclic AMP enhances transcription of the AA-NAT gene. Forskolin-induced elevation of AA-NAT mRNA levels was enhanced by cycloheximide, which decreased the degradation of the transcript in cells treated with actinomycin D. These studies indicate that the abundance of AA-NAT mRNA is regulated in part through a cyclic AMP-dependent mechanism.