The class of mammalian biologically active polypeptides called growth factors influence the proliferation, differentiation, motility, maintenance and apoptosis of target cells. On-going studies in my laboratory are directed towards understanding the mechanism of action and biological role of growth factors which signal through the epidermal growth factor receptor (EGFR). To address these issues, we utilize techniques common to protein biochemistry, cell biology and molecular biology. We have demonstrated that one of the growth factors which signals via the EGFR, called amphiregulin, requires the presence of heparan sulfate proteoglycan to activate the EGFR. The heparan sulfate binding region of amphiregulin has been localized to an approximately 20 amino acid residue region which lies just adjacent to the epidermal growth factor-like domain. We found that the mitogenic action of amphiregulin could be specifically inhibited by the soluble glycosaminoglycans, heparin and heparan sulfate, but not by chondroitin sulfate. When target cells were grown in the presence of chlorate, an inhibitor of sulfation, amphiregulin was no longer able to elicit activation of the EGFR or mitogenesis in the target cells. Furthermore, treatment of these cells with the glycosaminoglycan-degrading enzymes, heparinase or heparitinase, inhibited amphiregulin-induced mitogenic signaling by the EGFR. Based upon this data and other findings, we have proposed a mechanism for amphiregulin action in which the heparan sulfate proteoglycan is an integral membrane protein which either functions to present amphiregulin to the EGFR or stabilizes the bivalent binding of one molecule of aqmphiregulin to the activated receptor dimer. Collaborative studies with other investigators have demonstrated an important role for amphiregulin in normal physiological processes such as development of the human placenta and mouse mammary gland. Additionally, amphiregulin has been found to be commonly overexpressed in human breast, gastric and pancreatic cancer. Expression of amphiregulin in pancreatic cancer has been shown to predict a poor prognosis for the patient. Current studies are focusing on the identification of the signals which emanate from the amphiregulin- and epidermal growth factor-activated EGFR and how these signals relate to specific biological responses in target cells.
