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Abstract
To determine whether manipulation of time, temperature and intragranular pH could
be used to distinguish the actions of two subtilisin-related endoproteases, PC1 and
PC2, in peptide biosynthesis, the biosynthetic processing of proneuropeptide Y (proNPY)
and proopiomelanocortin (POMC) was examined in pituitary cell lines. AtT-20 cells
express PC1 and POMC endogenously; stably transfected AtT-20 lines expressing NPY
or PC2 were studied. GH3 cells express PC2 endogenously; NPY-expressing GH3 transfectants
were investigated. PC1 mediated rapid processing of NPY and POMC; PC1-dependent cleavages
were relatively insensitive to 20 degrees C blockade (which arrests secretory pathway
transport at the trans-Golgi network) and do not require an acidic intracellular compartment
(as in secretory granules). PC2 mediated much slower processing of proNPY and POMC
which was totally blocked at 20 degrees C and required an acidic intracellular compartment.
Thus, kinetics, abolition of intracellular pH gradients, and incubation at reduced
temperatures can be used to distinguish PC1 and PC2 actions in neuroendocrine cells.