Two Activation States of the Prohormone Convertase PC1 in the Secretory Pathway

Isabelle Jutras,Nabil G Seidah,Timothy L Reudelhuber,Véronique Brechler

doi:10.1074/jbc.272.24.15184

Abstract

PC1, a neuroendocrine member of the prohormone convertase family of serine proteinases, is implicated in the processing of proproteins in the secretory pathway. PC1 is synthesized as a zymogen and cleaves not only its own profragment in the endoplasmic reticulum, but a subset of protein substrates in the Golgi apparatus and in the Golgi-distal compartments of the regulated secretory pathway. Likewise, mouse PC1 (mPC1) has previously been shown to cleave human prorenin in GH4 cells (that contain secretory granules) while being unable to cleave prorenin in cells, such as Chinese hamster ovary (CHO) or BSC-40, which are devoid of secretory granules. In the current study, we show that removal of a C-terminal tail of mPC1 allows the efficient cleavage of prorenin in the constitutive secretory pathway of CHO cells. The C-terminal tail thus appears to act as an inhibitor of PC1 activity against certain substrates in the endoplasmic reticulum and Golgi apparatus, and its removal, which occurs naturally in secretory granules, may explain the observed granule-specific processing of certain proproteins. These results also demonstrate that PC1 is present in a partially active state prior to the secretory granules where it is processed to a maximally active state.

Highlights

Proprotein convertases are serine proteinases that cleave their substrates at specific basic amino acids [1, 2]
We show that truncation of the C-terminal tail of mouse PC1 (mPC1) greatly augments the cleavage of prorenin in GH4 cells and allows PC1 to cleave prorenin in Chinese hamster ovary (CHO) cells, which are devoid of secretory granules
Pulse-chase experiments in GH4 cells indicate that processed renin is secreted more rapidly when mPC1-⌬C is coexpressed compared with native mPC1, consistent with processing in the rapidly secreting constitutive secretory compartment

Summary

Introduction

Proprotein convertases are serine proteinases that cleave their substrates at specific basic amino acids [1, 2]. Cotransfection of expression vectors for mouse PC1 (mPC1) and human prorenin in cells that contain secretory granules (GH4 cells) leads to the secretion of active renin in the medium [21].

Results

Conclusion