ErbB-2 expression is rate-limiting for epidermal growth factor-mediated stimulation of ovarian cancer cell proliferation

Over-expression of the ErbB-2 proto-oncogene frequently coincides with an a ggressive clinical course of certain human adenocarcinomas. The ErbB-2 rece ptor is a member of the ErbB family of growth factor receptors, and within this complex signaling network, ErbB-2-containing heterodimers are preferen tially formed. To assess whether ErbB-2 is a critical component in epiderma l growth factor (EGF)-mediated stimulation of tumor cell proliferation, we used as a model SK-OV-3 ovarian cancer cells, which over-express EGF recept or (EGFR) and ErbB-2 receptors. In these cells, we reduced ErbB-2 mRNA and protein expression by transfection with ErbB-2-targeted hammerhead ribozyme s and generated cell lines expressing different levels of ErbB-2, In SK-OV- 3 cells, ErbB-2 expression conferred a growth advantage and soft agar exper iments revealed that ErbB-2 was rate-limiting for anchorage-independent gro wth. The induction of colony formation by EGF was completely abrogated in E rbB-2-depleted cells, despite unchanged expression levels and tyrosine phos phorylation of the EGFR, The duration of EGF-mediated c-Fos mRNA up-regulat ion was decreased in parallel with loss of ErbB-2 expression. Furthermore, the rate of spontaneous apoptosis was increased in ErbB-2-depleted cells. O ur results demonstrate that in human ovarian cancer cells the EGFR-ErbB-2 h eterodimer, and not the EGFR homodimer, can be rate-limiting for EGF-mediat ed proliferation, thus suggesting that the oncogenic activity of ErbB-2 in human tumors is due in part to its ability to increase the growth response to stroma-derived EGF-like growth factors. (C) 2000 Wiley-Liss, Inc.