The glioma cell‐derived neurite promoting activity protein is functionally and immunologically related to human protease nexin‐I

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Abstract
Protease nexin‐I (PN‐I, Mr ∼ 43,000) is representative of a newly described class of cell‐secreted protease inhibitors. PN‐I has been purified to apparent homogeneity, partially sequenced, and monospecific antibodies have been raised against it. PN‐I is a potent inhibitor of urokinase, thombin, plasmin, and trypsin. In addition, cells have specific receptors that mediate the uptake of covalently linked complexes formed between PN‐I and its protease substrates. In the present studies, we have investigated the relationship between human PN‐I and a protease inhibitor derived from C6 glioma cells in culture that has neurite‐promoting activity. On the basis of co‐purification on heparin‐Sepharose, identical molecular weight, antibody cross‐reactivity, and receptor cross‐reactivity, we conclude that PN‐I and the glioma‐cell‐derived inhibitor are equivalent molecules.