Characterization of a neu/c-erbB-2 protein-specific activating factor.

Abstract

The neu oncogene encodes a tyrosine kinase with growth factor receptor-like properties. A neu proteinspecific activating factor (NAF) was partially purified from medium conditioned by the transformed human T-cefl line ATL-2. NAF was able to stimulate the tyrosine-specific kinase activity of the neu protein (p185"), induce dimerization and internalization, and increase the growth ofcells bearing the neu protein. The effects of NAF were mediated by an interaction with the pl85" extracellular domain. NAF had no effect on the epidermal growth factor receptor kinase activity and no effect on cells that express that receptor. Further analysis of NAF and of other recently described neu protein-activating activities should help clarify the role of the neu protein in cell growth and transformation.The rat neu gene encodes a 185-kDa transmembrane tyrosine kinase that shows significant structural similarity to the epidermal growth factor receptor (EGFR) (1-3). The rat neu gene product has been identified in two forms: the protooncogenic form is termed pl85-cneu and the oncogenic form is termed p185neu. pl8Snu becomes activated in chemically induced neuroglioblastomas by a point mutation in the transmembrane region that results in constitutively increased neu tyrosine kinase activity (4-7). The c-erbB-2 gene (8, 9) is the human homologue of the rat neu gene, and aberrant c-erbB-2 protein expression has been implicated in a number of human adenocarcinomas, including those of the breast (10-12), ovaries (12), salivary gland and digestive tract (13), skin (14), kidney (13), pancreas (15), and lung (16). Its growth factor receptor-like attributes, tissue-specific and developmentally regulated expression pattern (17,18), and involvement in neoplasia suggest that the pl85/c-erbB-2 protein plays a role in normal and abnormal growth and differentiation ofthe cells in which it is expressed and that a cognate ligand exists for this protein.Although the neu gene has been studied for nearly 10 years now, identification of candidate ligands for p185 have only been reported in the last 2 years. Though several endogenous p185 modulatory factors may exist, the effects of the ligand for p185 might be most comparable to those of EGF and platelet-derived growth factor (PDGF) on their receptors, since these receptors are the transmembrane tyrosine kinases most closely related to p185 (19,20). According to these criteria, the primary ligand for p185 should increase the autophosphorylation/kinase activity of p185, induce p185 dimerization and internalization, and affect the growth of cells that express p185. Several reports have described preparations that contain p185-activating activity (21-23). Each of these activities/factors conforms to these criteria to a different extent. We report here the characterization of a purified neu protein-specific activating factor (NAF) secreted by the transformed human T-cell line ATL-2 (24) that meets all of these expected criteria. MATERIALS AND METHODSCells. PN-NR6 and PT-NR6 cells express high lev...

Ligand and p185c-neu density govern receptorinteractions and tyrosine kinase activation.

“…We propose that overexpression of the neu receptor causes the formation of multimeric receptors resulting in constitutive activation that ultimately leads to transformation. Since overexpression of the c-erbB2 protein has been observed in several human cancers (1,11,21,30), these studies provide a physicochemical explanation for the activated forms of amplified receptor species. The conversion of monomeric p185c-neu to the multimeric form also develops as a consequence of specific binding of the ligand to its extracellular ligand-binding domain of the receptor.…”

“…A factor of 25 kDa has been isolated from bovine kidney and is mitogenic for NIH 3T3, DHFR-G8, and A431 cells (10). We have isolated and characterized a neuactivating factor (NAF) from a transformed human T-cell line (11). The NAF ligand specifically interacts with the neu extracellular domain, resulting in neu-specific tyrosine kinase activation, receptor dimerization, internalization, and concomitant potentiation of the growth of neu receptorexpressing cell lines.…”

Loss of heterozygosity at theTP53 gene: Independent occurrence from genetic instability events in node-negative breast cancer

“…Because the c-ras and c-myc oncogenes were both involved in cellular transformation and/or apoptosis pathway in cooperation with TP53 (Finlay et al, 1989), we analyzed these 2 genes in the N 2 breast tumors. The c-erbB-2/neu gene, which encodes a transmembrane protein with extensive homology with the epidermal-growth-factor receptor (Dobashi et al, 1991), has been found to be amplified and over-expressed in 10-to 50% of N 1 breast cancers. In N 2 breast cancer, the prevalence is somewhat lower (10 to 20%), but the prognostic value of c-erbB-2/neu is now well established in this group of patients (Press et al, 1993).…”

Signal transduction in mammary tumorigenesis: a transgenic perspective

“…Similarly, ErbB-2 can be transphorylated by either ErbB-3 and ErbB-4 following the stimulation of mammary tumor cell lines with Neuregulins which are speci®c ligands for ErbB-2 and ErbB-4. By contrast, no direct ligand has been cloned for ErbB-2 although several activities have been puri®ed for some time (Dobashi et al, 1991;Lupu et al, 1992;Samanta et al, 1994;Wu et al, 1994;Heldin, 1995;Tzahar and Yarden, 1998).…”