M. Konrad et We. Merz, LONG-TERM EFFECT OF CYCLIC-AMP ON N-GLYCOSYLATION IS CAUSED BY AN INCREASE IN THE ACTIVITY OF THE CIS-PRENYLTRANSFERASE, Biochemical journal, 316, 1996, pp. 575-581
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.