[cAMP cascade in regulation of protein glycosylation]

O- and N-glycosylation are the most common and complex of the post-translational modifications. Both are enzymatic processes and it was suggested that both could be regulated by cAMP cascade at the early stages. N-glycosylation starts with the formation of lipid-linked oligosaccharides and this process is catalysed by crucial glycosyltransferase - dolichol phosphate mannose synthase. The results of several studies strongly suggest that the cAMP acting through a cAMP-dependent protein kinase A-mediated protein phosphorylation/dephosphorylation cycle may modulate activation of this enzyme. It was shown that cAMP can also up regulate another enzyme involved in phosphodolichole synthesis - cis-prenyltransferase. The mechanism acting here is the alteration of the rate of its gene expression. cAMP cascade is also involved in regulation of O-glycosylation since phosphorylation of human glutamine:fructose-6-phosphate amidotransferase results in depletion of O-GlcNAc structure formation. These observation suggested an important role of GPCRs and their ligand in regulation of N- and O-glycan synthesis.