ABSTRACT
Neu differentiation factor (NDF)/heregulin activates ErbB2 via heterodimerization with the NDF receptors ErbB3 and ErbB4. Cells which express normal levels of these receptors are often growth stimulated by NDF, whereas SKBR3, and other ErbB2-overexpressing breast tumour cells are growth inhibited. We demonstrate here that in SKBR3 cells, NDF induces G1 progression but also causes a G2 delay from day 1 and apoptosis from days 2-3. G1 progression was associated with ErbB2 transactivation of ErbB3 and subsequent stimulation of the phosphatidylinositol 3-kinase (PI3K) pathway whereas apoptosis was dependent on p38 MAPK. Inhibition of ERK1/ERK2 had no effect on cell cycle progression or apoptosis. Activation of ErbB3 and PI3K was also seen with betacellulin (BTC) but not epidermal growth factor (EGF) and correlated with the growth effects of these ligands. All three ligands induced short-term activation of p38 MAPK in a c-Src-dependent manner. However, only NDF caused a second, c-Src-independent increase in p38 MAPK activity which was required for apoptosis.
Subject(s)
Antineoplastic Agents/pharmacology , Apoptosis/drug effects , Calcium-Calmodulin-Dependent Protein Kinases/physiology , Cell Cycle/drug effects , Glycoproteins/pharmacology , Mitogen-Activated Protein Kinases , Phosphatidylinositol 3-Kinases/physiology , Apoptosis/physiology , CSK Tyrosine-Protein Kinase , Cell Division/drug effects , Cell Division/physiology , Enzyme Activation , Epidermal Growth Factor/metabolism , ErbB Receptors/metabolism , G1 Phase/drug effects , G1 Phase/physiology , G2 Phase/drug effects , G2 Phase/physiology , Humans , Neuregulins , Protein-Tyrosine Kinases/metabolism , Proto-Oncogene Proteins/metabolism , Receptor, ErbB-2/metabolism , Receptor, ErbB-3 , Signal Transduction , Tumor Cells, Cultured , p38 Mitogen-Activated Protein Kinases , src-Family KinasesABSTRACT
Neu differentiation factor (NDF), a member of the epidermal growth factor (EGF)-related peptide family, activates ErbB2 via heterodimerization with the NDF receptors ErbB3 and ErbB4. In a similar fashion, EGF receptor (EGFR) agonists induce heterodimers of EGFR and ErbB2. In this paper, we show that the ErbB2-overexpressing breast tumor cells SKBR3, AU565, and MDA-MB453 are growth inhibited by NDF. Cells with elevated levels of ErbB2 but little or no NDF receptors (SKOV3 and MDA-MB361) or cells with low levels of ErbB2 (T47D and MCF7) are not growth inhibited. None of the EGFR agonists tested (EGF, beta-cellulin, or heparin-binding EGF) inhibited growth of ErbB2-overexpressing cells. These results suggest that formation of an ErbB2/NDF receptor heterodimer, but not of an ErbB2/EGFR heterodimer, promotes growth inhibition. In addition, NDF caused a down-regulation of ErbB2 but not of ErbB3. The mechanism underlying the inhibitory effect was examined further in SKBR3 cells, which are 95% growth inhibited by NDF. A G2-M arrest is seen 24 h after NDF treatment, and increased apoptosis is detectable from day 2 onward. The results demonstrate for the first time that NDF induces apoptosis of tumor cells overexpressing ErbB2.
