Role of the heparin-binding domain in intracellular trafficking of sHB-EGF

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the epidermal growth factor fami­ly that was proven as a potent mitogen and chemoattractant. HB-EGF mediated EGFR activation is a key event in the stimulation of gene expression, cell migration and proliferation during both normal and pathogenic physiological processes. The main goal of this research was to reveal the role of the heparin-binding domain of HB-EGF in the ligand-receptor formation and its further internalization to the cytoplasm. We used fluorescently-labeled recombinant derivative of soluble HB-EGF and its truncated form (sHB-EGFΔ84–106) with deletion of the heparin-binding domain. Firstly, the binding kinetics of two forms of sHB-EGF to its cell surface receptors was determined using flow cytometry. To determine how the absence of heparin-binding domain in the structure of HB-EGF affects its internalization, we analyzed the endocytosis process of EGFP-sHB-EGFΔ84–106 and EGFP-sHB-EGF complexes by confocal microscopy. It was found that the full-size form of HB-EGF is characterized by a lower intensity of translocation to the cytoplasm in comparison to HBD-deleted form. Thus, differences in the trafficking of the full-size or truncated forms of sHB-EGF in the cell cytoplasm may reflect the mechanisms of extracellular matrix influence on the biological activity of sHB‑EGF.