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

If the variant line had lost the regulated pathway, it should not be able to store, and secrete on stimulation the other soluble components of dense core secretory granules. These include chromogranin A (Iacangelo et al., 1988) , secretogranins (Rosa et ai., 1985) , sulfated proteins such as B15 (Moore et al., 1983a) , and the "sulfated staircase" which represent proteoglycans that are sulfated on glycosaminoglycan (GAG) side chains (Moore et al., 1983a; Burgess and Kelly, 1984) . Many of these components were not expressed by the HYA.15.6 variant. The sulfated proteoglycans and proteins, sorted into the regulated secretory pathway and released on stimulation of cells containing the regulated secretory pathway, HYA.15.10 ( Fig. 2 A, lanes I and 2), were not made or released into the medium by the HYA.15.6 variant ( Fig. 2 A, lanes 3 and 4) . The only sulfated material in extracts of HYA.15.6 cells was higher molecular weight material that did not enter the gel and some material that migrated as a diffuse band (Fig. 2 A, lanes 7 and 8) . Although some sulfated material migrating at 97 kD could be seen decreasing in the cell extracts after stimulation, a corresponding appearance in the stimulated medium could never be reproducibly detected. In addition, neither chromogranin A nor its mRNA could be easily detected in HYA.15.6 cells because expression was at such low levels (Grimes, M., and R. B. Kelly, unpublished results).