RAT ANGIOTENSINOGEN IS SECRETED ONLY CONSTITUTIVELY WHEN TRANSFECTED INTO ATT-20 CELLS

To test whether angiotensinogen might be targeted to dense core secretory granules in cells containing a regulated secretory pathway, we expressed rat angiotensinogen in AtT-20 cells, a mouse pituitary cell line that has the demonstrated ability to correctly sort proteins to the constitutive or regulated pathway. We compared the pattern of secretion of angiotensinogen with that of endogenous adrenocorticotropin hormone, which is secreted by AtT-20 cells through the regulated pathway. When cells were incubated for 5 hours with dibutyryladenosine cyclic monophosphate or KCl, adrenocorticotropin hormone secretion was significantly higher than control, whereas monensin had no effect. In contrast, angiotensinogen secretion was markedly reduced by monensin, but no stimulation was observed with dibutyryladenosine cyclic monophosphate or KCl. These results make it unlikely that angiotensinogen could be cotargeted with active renin in the dense core granules of the regulated pathway. Alternative mechanisms must explain how angiotensin II is synthesized locally by tissue renin-angiotensin systems.