Cell-Surface Actin Binds Plasminogen and Modulates Neurotransmitter Release from Catecholaminergic Cells

Abstract

An emerging area of research has documented a novel role for the plasminogen activation system in the regulation of neurotransmitter release. Prohormones, secreted by cells within the sympathoadrenal system, are processed by plasmin to bioactive peptides that feed back to inhibit secretagogue-stimulated release. Catecholaminergic cells of the sympathoadrenal system are prototypic prohormone-secreting cells. Processing of prohormones by plasmin is enhanced in the presence of catecholaminergic cells, and the enhancement requires binding of plasmin(ogen) to cellular receptors. Consequently, modulation of the local cellular fibrinolytic system of catecholaminergic cells results in substantial changes in catecholamine release. However, mechanisms for enhancing prohormone processing and cellsurface molecules mediating the enhancement on catecholaminergic cells have not been investigated. Here we show that plasminogen activation was enhanced Ͼ6.5-fold on catecholaminergic cells. Carboxypeptidase B treatment decreased cell-dependent plasminogen activation by ϳ90%, suggesting that the binding of plasminogen to proteins exposing C-terminal lysines on the cell surface is required to promote plasminogen activation. We identified catecholaminergic plasminogen receptors required for enhancing plasminogen activation, using a novel strategy combining targeted specific proteolysis using carboxypeptidase B with a proteomics approach using twodimensional gel electrophoresis, radioligand blotting, and tandem mass spectrometry. Two major plasminogen-binding proteins that exposed C-terminal lysines on the cell surface contained amino acid sequences corresponding to ␤/␥-actin. An anti-actin monoclonal antibody inhibited cell-dependent plasminogen activation and also enhanced nicotine-dependent catecholamine release. Our results suggest that cell-surface-expressed forms of actin bind plasminogen, thereby promoting plasminogen activation and increased prohormone processing leading to inhibition of neurotransmitter release.

Inhibition of plasminogen activation by apo(a): role of carboxyl-terminal lysines and identification of inhibitory domains in apo(a)

“…For example, treatment of monocytoid cells with carboxypeptidase B (CpB), which removes carboxyl-terminal lysines, leads to a decrease of 64% for plasminogen binding and >95% for plasminogen activation ( 39 ). On catecholaminergic cells, binding of plasminogen decreased following CpB treatment by ‫ف‬ 70%, whereas a decrease of 90% was observed for plasminogen activation ( 40 ). In another study, binding of plasminogen to human umbilical vein endothelial cells (HUVECs) was also inhibited by -aminocaproic acid ( -ACA), a lysine analog, by 70-80% ( 29 ).…”

Expression profiles of genes regulating dairy cow fertility: recent findings, ongoing activities and future possibilities

“…g-actin influences cell growth and plays a role in the readout of genetic information (Fojo, 2006). Miles et al (2006) reported on plasminogen-binding proteins identified as rat b/g-actin on cell surfaces that, upon binding, increased prohormone processing, leading to inhibition of catecholamine release. Desmin plays a role in the structural as well as functional interaction of mitochondria and the cytoskeleton (Capetanaki, 2002) and is typically associated with mitochondrial function in muscle cells (Fountoulakis et al, 2005).…”

Review: Current and new generation pneumococcal vaccines

“…[91][92][93][94][95][96][97] In addition, PavB and PfbA, as well as PavA, promote the attachment of the pneumococcus to fibronectin, a component of the extracellular matrix.…”