Enhancement of protein glycosylation in tissue slices by dolichylphosphate.

Abstract

Glycosylation of N-linked glycoproteins has been stimulated in hen oviduct and bovine pancreas tissue slices by supplementing the tissue culture media with concentrations of dolichylphosphate from 1-100 micrograms/ml. In oviduct, overall incorporation of radioactive sugars into alkali-stable, hot trichloroacetic acid-precipitable material (N-linked glycoproteins) is stimulated approximately 2-fold in dolichylphosphate-supplemented tissues although no stimulation in protein synthesis is observed. Rather, the elevation in glycosylation seems to be a general one involving many protein acceptors. In vitro analysis of microsomal preparations derived from control or dolichylphosphate-supplemented oviduct tissue slices demonstrated a similar enhancement in glycosylation activities that appears to be attributable to an enhanced level of endogenous dolichylphosphate in the microsomes from supplemented tissues. Additionally, when bovine pancreas tissue slices are preincubated with dolichylphosphate and then doubly labeled with [3H]mannose and 14C-labeled amino acids, a 4-fold increase in the ratio of [3H-mannose to 14C-amino acids in secreted ribonuclease is observed relative to the nonsupplemented control. Furthermore, while only 12% of the ribonuclease secreted from control tissue slices specifically binds to concanavalin A-Sepharose, more than 90% of that secreted by dolichylphosphate-supplemented tissue slices binds to the lectin. These data support the notion that dolichylphosphate availability is a limiting factor in the in vivo glycosylation of proteins in these systems.