LONG-TERM EFFECT OF CYCLIC-AMP ON N-GLYCOSYLATION IS CAUSED BY AN INCREASE IN THE ACTIVITY OF THE CIS-PRENYLTRANSFERASE

Previously we have shown that long-term pretreatment of JEG-3 chorioca rcinoma cells with 8-bromo-cAMP increases the capacity for N-glycosyla tion that was caused by an 8-10-fold enlargement of the dolichol pyrop hosphoryl oligosaccharide (Dol-PP-oligosaccharide) pool [Konrad and Me rz (1994) J. Biol. Chem. 269, 8659-8666]. The factors involved in the effect of cAMP on synthesis of Dol-PP-oligosaccharide are investigated here. The GlcNAc transfer to dolichol phosphate (Dol-P) was found to be unaffected by pretreatment with 8-bromo-cAMP. By measuring the upta ke of [H-3]mevalonate, a 20-fold increase in the incorporation of the label into Dol-P was observed in the cells treated with 8-bromo-cAMP. Under the same conditions, the synthesis of dolichol was enhanced 60-f old. However, the incorporation of the radioactivity into cholesterol was not increased in the JEG-3 cells pretreated with 8-bromo-cAMP, whi ch suggests a specific stimulation of the dolichol/Dol-P pathway by cA MP. The cis-prenyltransferase activity was found to be increased 10-fo ld in cells pretreated with 8-bromo-cAMP. Dolichol kinase activity was unaffected by stimulation with 8-bromo-cAMP. The present study sugges ts that the larger glycosylation capacity in JEG-3 cells treated with 8-bromo-cAMP is caused by an increase in the microsomal cis-prenyltran sferase activity.