Glucocorticoids increase insulin-like growth factor-II mRNA accumulation in cultured human phaeochromocytoma cells

Human phaeochromocytomas abundantly express insulin-like growth factor-II (IGF-II), but its regulation and biological role in these neoplasms is not known at present. To clarify the regulation of IGF-II gene expression in phaeochromocytomas, we studied the effects of glucocorticoids, nerve growth factor (NGF), and protein kinase A and C regulators in primary cultures of human phaeochromocytoma cells. Cytoplasmic RNA was extracted and analysed by Northern and dot blotting with a 32P-labelled cDNA probe for IGF-II. Dexamethasone treatment (500 ng/ml) for 3 and 7 days resulted in a 260% and 515% increase in the accumulation of IGF-II mRNA respectively. The stimulatory effect of dexamethasone was time- and dose-dependent. The increases in the 6.0 and 2.2 kb species of IGF-II mRNAs were the most apparent. Cortisol (1 microgram/ml) increased the amount of IGF-II mRNA by threefold compared with the control. NGF (200 ng/ml), dibutyryl cyclic AMP (1 mM) and 12-O-tetradecanoyl phorbol-13-acetate (a protein kinase C activator; 100 ng/ml) had no significant effect on IGF-II mRNA levels. These data suggest that IGF-II gene expression in human phaeochromocytomas may be regulated by microenvironmental glucocorticoids.