Accumulation of unglycosylated liver secretory glycoproteins in the rough endoplasmic reticulum

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Previous studies in this laboratory (1) have shown that tunicamycin-treatment inhibits the secretion of three secretory glycoproteins - α2-macroglobulin, ceruloplasmin, and α1-protease inhibitor in human hepatoma (Hep G2) cell cultures. In the present study, we have investigated (i) their site of accumulation within the endoplasmic reticulum/Golgi pathway, and (ii) the solubility characteristics of these unglycosylated proteins. Using percoll density gradient centrifugation, we found that tunicamycin-treatment markedly inhibited the transport of α2-macroglobulin, ceruloplasmin and α1-protease inhibitor from the rough endoplasmic reticulum. However, there was no detectable changes in their solubility properties as both the glycosylated and unglycosylated species were associated with the 100,000 xg supernatant fraction following disruption of the microsomal fraction (i) with 0.2% Triton X-100 and (ii) by repeated freeze-thaw cycles. Also no evidence of protein aggregation was detected by liquid chromatography of the unglycosylated proteins on Bio-Gel A-1.5 column. © 1989 Academic Press, Inc.

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