Biologic effects of heregulin/neu differentiation factor on normal and malignant human breast and ovarian epithelial cells

The heregulins are a family of ligands with ability to induce phosphorylati on of the p185(HER-2/neu) receptor. Various investigators have reported a v ariety of responses of mouse and human breast and ovarian cells to this fam ily of ligands including growth stimulation, growth inhibition, apoptosis a nd induction of differentiation in cells expressing the HER-2/neu receptor. Some of the disparity in the literature has been attributed to variations in the cell lines studied, ligand dose applied, methodologies utilized or m odel system evaluated (i.e. in vitro or in vivo). To evaluate the effects o f heregulin on normal and malignant human breast and ovarian epithelial cel ls expressing known levels of the HER-2/ neu receptor, this report presents the use of several different assays, performed both in vitro and in vivo, in vitro proliferation assays, direct cell counts, clonogenicity under anch orage-dependent and aochorage-independent conditions, as well as the in viv o effects of heregulin on human cells growing in nude mice to address hereg ulin activity. Using a total of five different biologic assays in nine diff erent cell lines, across two different epithelia and over a one log heregul in dose range, we obtained results that clearly indicate a growth-stimulato ry role for this ligand in human breast and ovarian epithelial cells, We fi nd no evidence that heregulin has any growth-inhibitory effects in human ep ithelial cells. We also quantitated the amount of each member of the type I receptor tyrosine kinase family (RTK I, i.e. HER-1, HER-2, HER-3 and HER-4 ) in the cell lines employed and correlated this to their respective heregu lin responses. These data demonstrate that HER-2/neu overexpression itself affects the expression of other RTK I members and that cells expressing the highest levels of HER-2/neu have the greatest response to HRG.