Polyamine regulation of the rat pro-opiomelanocortin gene expression in AtT-20 cells

Polyamines are a ubiquitous group of amines that play diverse biological ro les. In the anterior pituitary, intracellular polyamine levels are reported to show diurnal changes, although the biological significance remains to b e elucidated. In this study, we examined the effects of polyamines on the t ranscriptional activity of the rat pro-opiomelanocortin (POMC) gene using A tT20PL, a clone of the AtT20 cell line in which an approximately 0.7 kb of the rat POMC 5' promoter-luciferase fusion gene was stably incorporated. Th e results showed that three representative polyamines (putrescine, spermidi ne and spermine) all stimulated POMC promoter activity in a time- and dose- related manner, spermine showing the most potent effect (maximum approximat e three-fold increase). This effect was not observed under treatment with a ctinomycin D, suggesting the effect of polyamine at the transcriptional lev el. On the other hand, methylglyoxal bis (guanylhydrazone), an inhibitor of polyamine synthesis, showed the opposite effect, further supporting the po sitive role of intracellular polyamines. Taken together, our findings sugge st that polyamines are involved in the regulation of POMC gene expression ( especially in terms of diurnal changes) in corticotroph cells. The precise molecular mechanisms of polyamine effects await further research.