Constitutive and basal secretion from the endocrine cell line, AtT-20

Although the dense core vesicle-specific proteoglycans and other sulfated molecules were absent in the HYA.15.6 variant cells, the machinery to synthesize the glycosaminoglycan side chains of proteoglycans was still intact. This was shown by preincubating cells in medium containing 0.5 mM 4-methyl-umbelliferyl xyloside and labeling cells, in the continued presence of xyloside, with [35S]sulfate. Xylosides compete with the protein core of proteoglycans for attachment of free GAG chains. The 35S-labeled free GAG chain xyloside conjugates in cell extracts and media were recovered and analyzed on SDS-polyacrylamide gels. Wild type ART-20 cells, grown in the xyloside analogue, secreted into the medium a ladder of GAG chains, migrating between the protein molecular weight markers of 2 and 18 kD (Fig. 2 B , lane/). The HYA.15.6 variant cells, grown under the same conditions, secreted a ladder of sulfated GAG chains of roughly the same molecular weight although the ladder was less discrete (Fig. 2 B, lane 2) .