SINGLE-CHAIN ANTIBODY-MEDIATED INTRACELLULAR RETENTION OF ERBB-2 IMPAIRS NEU DIFFERENTIATION FACTOR AND EPIDERMAL GROWTH-FACTOR SIGNALING

ErbB-2 becomes rapidly phosphorylated and activated following treatmen t of many cell lines with epidermal growth factor (EGF) or Neu differe ntiation factor (NDF). However, these factors do not directly bind Erb B-2, and its activation is likely to be mediated via transmodulation b y other members of the type I/EGF receptor (EGFR)-related family of re ceptor tyrosine kinases. The precise role of ErbB-2 in the transductio n of the signals elicited by EGF and NDF is unclear. We have used a no vel approach to study the role of ErbB-2 in signaling through this fam ily of receptors. An ErbB-2-specific single-chain antibody, designed t o prevent transit through the endoplasmic reticulum and cell surface l ocalization of ErbB-2, has been expressed in T47D mammary carcinoma ce lls, which express all four known members of the EGFR family. We show that cell surface expression of ErbB-2 was selectively suppressed in t hese cells and that the activation of the mitogen activated protein ki nase pathway and p70/p85(S6K), induction of c-fos expression, and stim ulation of growth by NDF were dramatically impaired. Activation of mit ogen-activated protein kinase and p70/p85(S6K) and induction of c-fos expression by EGF were also significantly reduced. We conclude that in T47D cells, ErbB-2 is a major NDF signal transducer and a potentiator of the EGF signal. Thus, our observations demonstrate that ErbB-2 pla ys a central role in the type I/EGFR-related family of receptors and t hat receptor transmodulation represents a crucial step in growth facto r signaling.