Spatiotemporal visualization of proHB-EGF ectodomain shedding in living cells

Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) is a member of the EGF family, each of which is produced as a type I transmembrane precursor. The juxtamembrane domain of proHB-EGF, a precursor of HB-EGF, is cleaved by a disintegrin and metalloproteases. HB-EGF is released into the extracellular space and strongly activates EGF receptor. The relevance of better understanding proHB-EGF shedding relates to the importance of the process in the proliferation, differentiation and survival of various types of cells. Shedding of proHB-EGF is normally evaluated using an alkaline phosphatase-tagged proHB-EGF assay or a western blotting assay that involves multiple cells, which makes it difficult to observe spatiotemporal differences in the activities of the individual cells. In this study, we developed a fluorescent proHB-EGF-based metalloprotease biosensor, named Fluhemb, to visualize spatiotemporal regulation of proHB-EGF shedding in individual cells using a simple method that measures changes in fluorescence ratios. Fluhemb might be very useful for detecting the activity of proHB-EGF shedding in various types of cells under different conditions in vitro and in vivo.