The heparin-binding domain of heparin-binding EGF-like growth factor can target Pseudomonas exotoxin to kill cells exclusively through heparan sulfate proteoglycans

Heparin-binding EGF-like growth factor (HB-EGF) is a smooth muscle cell mitogen composed of both EGF receptor and heparin-binding domains. To better understand the function of its domains, intact HB-EGF or its heparin-binding (HB) domain (amino acids 1–45) were fused to a mutant Pseudomonas exotoxin with an inactivated cell-binding domain. The resulting chimeric toxins, HB-EGF-PE* and HB-PE*, were tested on tumor cells, proliferating smooth muscle cells and a mutant Chinese hamster ovary cell line deficient in heparan sulfate proteoglycans (HSPGs). Two targets were found for HB-EGF-PE*. Cells were killed mainly through EGF receptors, but the HB domain was responsible for killing via HSPGs. HB-PE* did not bind to the EGF receptor and thus was cytotoxic by interacting exclusively with HSPGs. We conclude that the HB domain of HB-EGF is able to mediate internalization through HSPGs, without requiring the EGF receptor.