Epiregulin is a member of the epidermal growth factor (EGF) family, and has certain characteristics that are di erent from that of EGF, including mitogenic responses and binding to EGF receptor (EGFR). Epiregulin may also have another cell surface receptor and/or induces di erent receptor heterodimerizations for intracellular signaling. We investigated the binding ability of epiregulin to four ErbB family receptors using four human breast carcinoma cell lines that expressed di erent subsets of receptors. Chemical cross-linking experiments showed that [ 125 I]epiregulin directly bound to each of EGFR and ErbB-4 but not to ErbB-2 and ErbB-3. Furthermore, although epiregulin stimulated tyrosine phosphorylation of all four ErbB receptors, the main intracellular signal was mediated by ErbB-4 and/or EGFR. The pattern of activation of ErbB family receptors was di erent from that of other EGF-related ligands. Our ®ndings indicate that ErbB-4 and EGFR are receptors for epiregulin, and suggest that EGFrelated ligands transduce signals for di erent biological responses by the hierarchical mechanism.

Rev i ew o f P ri m a ry P r eve n t i o n o fTy p e 2 D i a b ete s i n We s te rn Au s t r a l i a E xe c u t i ve S u m m a ry R E V I E W O F P R I M A RY P R E V E N T I O N O F T Y P E 2 D I A B E T E S I N W E S T E R N A U S T R A L I R E V I E W O F P R I M A RY P R E V E

We have recently identified epiregulin as a new growth regulator and a member of the epidermal growth factor (EGF) family. Epiregulin has certain characteristics that are different from those of the classical members of the EGF family, EGF and transforming growth factor alpha, including mitogenic responses on several normal cells and binding to EGF receptors on epidermoid carcinoma A431 cells. In the present study we cloned and identified the expression of human epiregulin transcript. The human epiregulin gene encoded a 163-residue putative transmembrane precursor containing an EGF-like domain in the internal segment, and the structural organization was similar to that of other members of the EGF family that bind to EGF receptors. Northern blot analysis showed the expression of human epiregulin to be mainly on peripheral blood macrophages and the placenta in normal tissues, and was highest on epithelial tumour cell lines in various types of tumour cell lines. The expression profile was quite different from that of other members of the EGF family in normal and tumour cells. Recombinant expression in mammalian cells also showed that human epiregulin was secreted as a soluble form of approx. 5 kDa that is biologically active on the basis of the stimulation of DNA synthesis. Our findings suggest that epiregulin is involved in certain physiological processes such as maintenance or development of normal cell growth, and the progression of carcinomas.

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