A study of ErbB receptor signal transduction pathways in a human breast cancer cell line

Abstract

Growth factor receptors of the tyrosine kinase subfamily I, ECFR/ErbB receptor family members, EGF receptor, erbB2, erbB3, and erbB4, mediate specific biological signals via heterodimerization among family members after ligand stimulation. The overall aim of this study was to examine erbB family member interaction mediating the biological effect of Heregulin (HRG), an erbB3 ligand. C-erbB2, an orphan receptor, was involved in the concentration-dependent pleiotropic responses of a breast cancer cell line to HRG, via heterodimerization with erbB3. HRG-mediated proliferation was maintained in erbB2-nonexpressing, antisense-erbB2 stable transfectants. In contrast, c-erbB2 was required for induction of HRC-mediated differentiation at high concentrations of HRG. To further study proteins that modulate the actions of erbB3, a receptor for HRG with an impaired tyrosine kinase activity, we isolated interacting proteins using a yeast two hybrid system screening. EBP1 and EBP2 have been identified as erbB3 interacting proteins using the yeast two hybrid system. EBP1 and EBP2 interacted with the juxtamembrane domain of erbB3 in the absence of ligand activation or intrinsic tyrosine kinase activity, in vitro. EBP1 and EBP2 mRNA was expressed in normal human epithelial tissues including brain, heart, and skeletal muscle, and in human carcinomas including breast, lung, and sarcoma. Overexpression of EBP1 or EBP2 suppressed colony growth and induced differentiation in a human breast carcinoma cell line, AU565. Treatment with HRG, but not with EGF, caused dissociation of EBP1 from erbB3 in vivo. EBP1 translocated from the cytoplasm into the nucleus following HRG stimulation. These findings suggest that HRG may regulate erbB3 function in part by directly linking receptor activation to nuclear activation through the translocation of an erbB3 interacting proteins. C-erbB2 was also partly involved in 17beta-estradiol-HRG induced cell growth inhibition of ER-negative erbB2-expressing breast carcinoma cell lines.