The isoforms of proprotein convertase PC5 are sorted to different subcellular compartments.
The proprotein convertase PC5 is encoded by multiple mRNAs, two of which give rise to the COOH-terminal variant isoforms PC5-A (915 amino acids [aa]) and PC5-B (1877 aa). To investigate the differences in biosynthesis and sorting between these two proteins, we generated stably transfected AtT-20 cell lines expressing each enzyme individually and examined their respective processing pattern and subcellular localization. Biosynthetic analyses coupled to immunofluorescence studies demonstrated that the shorter and soluble PC5-A is sorted to regulated secretory granules. In contrast, the COOH-terminally extended and membrane-bound PC5-B is located in the Golgi. The presence of a sorting signal in the COOH-terminal 38 amino acids unique to PC5-A was demonstrated by the inefficient entry into the regulated secretory pathway of a mutant lacking this segment. EM of pancreatic cells established the presence of immunoreactive PC5 in glucagon-containing granules, demonstrating the sorting of this protein to dense core secretory granules in endocrine cells. Thus, a single PC5 gene generates COOH-terminally modified isoforms with different sorting signals directing these proteins to distinct subcellular localization, thereby allowing them to process their appropriate substrates.
De Bie
I
I
J.A. De Sève Laboraotry of Biochemical Neuroendocrinology, Clinical Research Institute of Montréal, QC, Canada.
Marcinkiewicz
M
M
Malide
D
D
Lazure
C
C
Nakayama
K
K
Bendayan
M
M
Seidah
N G
NG
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D020126:Brefeldin A; D002451:Cell Compartmentation; D003517:Cyclopentanes / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000201:enzymology*; D004792:Enzyme Precursors / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D005934:Glucagon / Q000032:analysis; D006056:Golgi Apparatus / Q000201:enzymology*; D007527:Isoenzymes / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D010179:Pancreas / Q000378:metabolism / Q000648:ultrastructure; D045702:Proprotein Convertase 5; D011499:Protein Processing, Post-Translational; D051381:Rats; D017207:Rats, Sprague-Dawley; D012697:Serine Endopeptidases / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D012995:Solubility; D014162:Transfection; D014407:Tumor Cells, Cultured
D003517:Cyclopentanes; D004792:Enzyme Precursors; D007527:Isoenzymes; D020126:Brefeldin A; D015124:8-Bromo Cyclic Adenosine Monophosphate; D005934:Glucagon; D045702:Proprotein Convertase 5; D012697:Serine Endopeptidases; C473805:propeptide convertase 5, mouse; C473807:propeptide convertase 5, rat