Processing of chromogranin A by plasmin provides a novel mechanism for regulating catecholamine secretion
Robert J. Parmer, … , Xiao-Ping Xi, Lindsey A. Miles
Robert J. Parmer, … , Xiao-Ping Xi, Lindsey A. Miles
Published October 1, 2000
Citation Information: J Clin Invest. 2000;106(7):907-915. https://doi.org/10.1172/JCI7394.
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Article

Processing of chromogranin A by plasmin provides a novel mechanism for regulating catecholamine secretion

Abstract

Chromogranin A (CgA) is the major soluble protein in the core of catecholamine-storage vesicles and is also distributed widely in secretory vesicles throughout the neuroendocrine system. CgA contains the sequences for peptides that modulate catecholamine release, but the proteases responsible for the release of these bioactive peptides from CgA have not been established. We show here that the major fibrinolytic enzyme, plasmin, can cleave CgA to form a series of large fragments as well as small trichloroacetic acid-soluble peptides. Peptides generated by plasmin-mediated cleavage of CgA significantly inhibited nicotinic cholinergic stimulation of catecholamine release from PC12 cells and primary bovine adrenal chromaffin cells. We also show that the zymogen, plasminogen, as well as tissue plasminogen activator bind saturably and with high capacity to catecholaminergic (PC12) cells. Occupancy of cell surface binding sites promoted the cleavage of CgA by plasmin. Positive and negative modulation of the local cellular fibrinolytic system resulted in substantial alterations in catecholamine release. These results suggest that catecholaminergic cells express binding sites that localize fibrinolytic molecules on their surfaces to promote plasminogen activation and proteolytic processing of CgA in the environment into which CgA is secreted to generate peptides which may regulate neuroendocrine secretion. Interactions between CgA and plasmin(ogen) define a previously unrecognized autocrine/paracrine system that may have a dramatic impact upon catecholamine secretion.

Authors

Robert J. Parmer, Manjula Mahata, Yun Gong, Sushil K. Mahata, Qijiao Jiang, Daniel T. O’Connor, Xiao-Ping Xi, Lindsey A. Miles

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Figure 1

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Cleavage of CgA by plasmin. Human 125I-CgA (1.5 nM) was incubated with e...
Cleavage of CgA by plasmin. Human 125I-CgA (1.5 nM) was incubated with either buffer (PBS) or streptokinase (100 U/ml) plus 2 μM plasminogen (a), 0.2 μM plasminogen (b), or 0.02 μM plasminogen (c) in 0.01 M Tris Cl, pH 8.0, 0.15 M NaCl, at 37°C for the indicated times in the presence or absence of 0.2 μM α2-antiplasmin. The generation of active plasmin was verified spectrophotometrically as cleavage of the chromogenic substrate, S-2251, D-Val-Leu-Lys-paranitroanilide. Samples were electrophoresed on 8% SDS-PAGE under nonreducing conditions. Mr size standards (in thousands) are indicated on the right. In controls, neither plasminogen alone nor streptokinase alone cleaved the parent CgA molecule (data not shown).