Cytosolic immunization allows the expression of preATF-saporin chimeric toxin in eukaryotic cells

In this work, we have devised an intracellular immunization strategy for th e expression in high amounts of ATF-saporin, a targeted chimeric toxin cons tituted by the ATF receptor binding domain of human urokinase and the plant ribosome-inactivating protein saporin, which has been shown to be highly c ytotoxic to target cells. This strategy may allow the production of highly toxic secretory proteins in eukaryotic cells, avoiding cell suicide caused by autointoxication. The procedure consists of equipping host cells with cy tosolic neutralizing antibodies directed toward the toxic domain of the het erologous polypeptide, We show that this intracellular immunization is esse ntial for the synthesis of correctly folded, biologically active ATF-SAP in the high amounts needed to investigate its in vivo antimetastatic potentia l. Such a strategy should be generally useful for the production of toxic m olecules of therapeutic value whose folding and maturation require transit through the eukaryotic secretory pathway.