Plasminogen activators and inhibitors in the neuromuscular system: III. The serpin protease nexin I is synthesized by muscle and localized at neuromuscular synapses.
Recent studies suggest that the nature of events leading to the formation, maintenance, and elimination of synapses may be regulated by cascade-type, locally expressed proteases and protease inhibitors acting on adhesive extracellular matrix components. We have identified a molecule in conditioned medium of murine skeletal muscle cells that in molecular weight, target protease inhibition, heparin-binding and cross-reactivity with authenic antisera is similar to the human serine proteinase inhibitor, protease nexin I. Protease nexin I is a 43-50 kDa glycoprotein of the serpin superfamily (arg-serpin class). Purified anti-protease nexin I antibody (anti-47 kDa) stains adult mouse skeletal muscle in discrete foci that precisely superimpose on synaptic neuromuscular junctions. Protease nexin I appears in patches on surfaces of cultured mouse skeletal myotubes, but not on myoblasts. These patches co-localize with acetylcholine receptor clusters and acetylcholinesterase staining during cellular maturation in culture. Evidence that protease nexin I is a synaptic, extracellular antigen is particularly intriguing since it has been shown to be identical, in structure and activity, with a factor released by glial cells, called glia-derived nexin that stimulates mouse neuroblastoma cell neurite outgrowth and inhibits granule cell migration. Protease nexin I inhibits both tumor cell and myoblast plasminogen activator-mediated destruction of extracellular matrix. Thus, such observations as presented in this report provide further evidence for involvement of cascade proteolytic systems, and their post-translational regulation by specific serpins, in the remodeling that occurs in synapse formation and elimination.
Festoff
B W
BW
Neurobiology Research Laboratory, Veterans Affairs Medical Center, Kansas City, Missouri 64128.
Rao
J S
JS
Hantaï
D
D
D016564:Amyloid beta-Protein Precursor; D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000276:immunology / Q000378:metabolism*; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D009132:Muscles / Q000201:enzymology*; D009469:Neuromuscular Junction / Q000201:enzymology* / Q000648:ultrastructure; D010960:Plasminogen Activators / Q000502:physiology*; D015849:Plasminogen Inactivators / Q000378:metabolism*; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D011978:Receptors, Nicotinic / Q000276:immunology / Q000378:metabolism; D015843:Serpins / Q000378:metabolism*
D016564:Amyloid beta-Protein Precursor; D002352:Carrier Proteins; D015849:Plasminogen Inactivators; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D011978:Receptors, Nicotinic; D015843:Serpins; D010960:Plasminogen Activators