PROCESSING AND ROUTING OF A MEMBRANE-ANCHORED FORM OF PRONEUROPEPTIDE-Y

To investigate factors governing proteolytic processing and routing of biologically active peptides in the secretory pathway, cDNAs for prep roneuropeptide Y (preproNPY) and preproneuropeptide Y fused to a membr ane anchor were transfected into pituitary cells, The anchor was the t ransmembrane and COOH-terminal cytoplasmic domain of peptidylglycine a lpha-amidating monooxygenase (PAM); these domains are essential for co rrect routing of integral membrane forms of PAM, Like proneuropeptide Y (proNPY), the integral membrane form of proNPY was a good substrate for the endogenous prohormone convertases, yielding soluble NPY stored in regulated secretory granules, Tethering of proNPY to the membrane resulted in only a small delay in the rate of cleavage to produce matu re NPY and in the arrival of NPY in regulated secretory granules. In c ontrast, the COOH-terminal region of proNPY remained attached to the t ransmembrane/COOH-terminal domain of PAM and was rerouted to the vicin ity of the trans-Golgi network, where integral membrane forms of PAM a re concentrated, Thus, the COOH-terminal of proNPY cannot override the signals in the PAM membrane anchor.