A conjugate between human urokinase and saporin, a type-1 ribosome-inactivating protein, is selectively cytotoxic to urokinase receptor-expressing cells.
Urokinase-type plasminogen activator (uPA) confers invasive potential to transformed cells. Cancer cells express high numbers of uPA receptors (uPARs), which concentrate uPA activity at the invasive edge of cancer cells and the tumor mass. We synthesized a conjugate between human uPA and saporin (SAP), a ribosome-inactivating protein produced by Saponaria officinalis. Results of cell-killing assays showed that uPA is very effective at targeting saporin specifically to uPAR-expressing cells, whereas cell lines devoid of uPARs were not affected by the conjugate. Receptor-bound uPA is internalized only upon formation of a complex with one of its inhibitors (PAIs). However, our conjugate was highly cytotoxic even when the interaction between uPA and PAIs was prevented. Moreover, the alpha 2-macroglobulin receptor, which has been reported to mediate the internalization of uPA.PAI complexes, seems not to be involved in cell killing caused by the uPA.SAP conjugate. Thus, uPA.SAP might follow a mechanism of internalization different from that of unconjugated uPA complexed to PAIs, although still uPAR-mediated. Our results also suggest that alpha 2-macroglobulin and/or its receptor could mediate the internalization and cytotoxicity of unconjugated saporin, as it has been shown for other toxins.
Cavallaro
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Department of Biological and Technological Research, San Raffeaele Research Institute, Milano, Italy.
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D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003603:Cytotoxins / Q000008:administration & dosage / Q000737:chemistry*; D000922:Immunotoxins; D066298:In Vitro Techniques; D009699:N-Glycosyl Hydrolases; D010940:Plant Proteins / Q000008:administration & dosage*; D011500:Protein Synthesis Inhibitors / Q000008:administration & dosage*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D055293:Receptors, Urokinase Plasminogen Activator; D054789:Ribosome Inactivating Proteins, Type 1; D000076985:Saporins; D013997:Time Factors; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism*
D003603:Cytotoxins; D000922:Immunotoxins; C524898:PLAUR protein, human; D010940:Plant Proteins; D011500:Protein Synthesis Inhibitors; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D054789:Ribosome Inactivating Proteins, Type 1; D009699:N-Glycosyl Hydrolases; D000076985:Saporins; D014568:Urokinase-Type Plasminogen Activator