Transforming Growth Factor β1: Importance of Glycosylaytion and Acidic Proteases for Processing and Secretion

The role of glycosylation of the transforming growth factor-β1 (TGF-β1) precursor was investigated by treating a transfected Chinese hamster ovary (CHO) cell line expressing high levels of recombinant TGF-β1 (TGF-β3-2000 cells) with a series of glycosylational inhibitors. Tunicamycin, a nucleoside anti-biotic which prevents the formation of the dolichol intermediate necessary for oligosaccharide addition of the nascent polypeptide chain, appeared to block secretory exit and led to an increase in the cellular associated, nonglycosylated pro-TGF-β1 form. 1-Deoxymannojirimycin and swainsonine, inhibitors of the mannosidases I and II, respectively, blocked complete glycoprotein processing of the TGF-β1 precursor as judged by sodium dodecyl sulfatepolyacrylamide gel electrophoresis and by sensitivity to glycosidases. However, the abnormal TGF-β1 polypeptides containing the altered carbohydrate side chains were secreted readily by the CHO cells. In contrast, inhibitors of the glucosidases at the first step in g...