INDUCTION OF ANCHORAGE-INDEPENDENT GROWTH BY AMPHIREGULIN

We have previously shown that the epidermal growth factor receptor (EG FR) ligand, amphiregulin (AR) exhibits low potency as a result of its C-terminal truncation. This led us to investigate whether its inabilit y to promote anchorage-independent growth (AIG) of normal cells arose because of its compromised interaction with EGFR. Wild type AR(1-84) w as tested in AIG and mitogenesis assays using NRK-49F or NRG/HER fibro blasts. In contrast to NRG/HER cells, the response of NRK-49F fibrobla sts to AR was much lower than expected. As the effect of AR was hepari n-insensitive, contributions from heparan sulphate proteoglycan intera ctions could not explain the differing sensitivities of the cells. Com parison of the effects of AR on two additional cell lines indicated th at low EGFR number correlated with AR insensitivity: this suggested th at the low potency of AR precluded activation of sufficient receptors to elicit a response. Consistent with this proposal, a modified form o f AR (AR(1-90(leu86))) with enhanced potency was able to induce AIG of NRK-49F fibroblasts. Thus, the ability of AR to promote AIG is determ ined both by ligand potency and the EGFR complement of cells.