Characterization of the endopeptidase PC2 activity towards secretogranin II in stably transfected PC12 cells.
To study the processing of secretogranin II (SgII) by the prohormone convertase PC2 we have generated a stable PC12 cell line which expresses mouse PC2. We here present the characteristics of the PC12/PC2 cell line and demonstrate that the exogenous PC2 is sorted and stored in secretory granules in the PC12/PC2 cell line as efficiently as the endogenous granins. By indirect immunofluorescence with antibodies specific for chromogranin B (CgB) and PC2 we were able to establish that the PC2 is stored in secretory granules in the PC12/PC2 cell line. After subcellular fractionation, followed by immunoblotting, the mature 68 kDa form of PC2 was found co-sedimented with SgII in fractions containing secretory granules. Two-dimensional gel electrophoresis was used to characterize a secretory granule fraction obtained from the PC12/PC2 cells, and a comparison was done of the electrophoretic pattern obtained from the PC12/PC2 cells with the parent cell line PC12. The products derived from the processing of SgII by PC2 were identified by immunoblotting with a panel of antibodies directed against SgII. Using [35S]sulphate to label the newly synthesized SgII, we performed a time course to monitor the appearance of the lower-molecular-mass fragments of SgII: beginning 15 min after a 5 min pulse of [35S]sulphate we were able to detect the first proteolytic fragment of SgII. Our results demonstrate that SgII is proteolytically processed by PC2 in the immature secretory granule into several lower-molecular-mass proteins, the major ones being an 18 kDa sulphated fragment and a 28 kDa fragment.
Dittié
A S
AS
Imperial Cancer Research Fund, London, U.K.
Tooze
S A
SA
D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity; D001345:Autoradiography; D002458:Cell Fractionation; D002864:Chromogranins / Q000032:analysis / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000201:enzymology / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes / Q000032:analysis; D051379:Mice; D008969:Molecular Sequence Data; D016716:PC12 Cells; D045706:Proprotein Convertase 2; D014176:Protein Biosynthesis; D011506:Proteins / Q000032:analysis / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D013381:Subtilisins / Q000096:biosynthesis / Q000378:metabolism*; D013431:Sulfates / Q000378:metabolism; D013462:Sulfur Radioisotopes; D014162:Transfection
D002864:Chromogranins; D000939:Epitopes; D011506:Proteins; D011994:Recombinant Proteins; D013431:Sulfates; D013462:Sulfur Radioisotopes; D013381:Subtilisins; D045706:Proprotein Convertase 2