Expression of Epidermal Growth Factor Receptor or ErbB3 Facilitates Geldanamycin-Induced Down-Regulation of ErbB2

Nina Marie Pedersen,Espen Stang,Camilla HaslekåS,Inger Helene Madshus,Kamilla Breen,Marianne Skeie Rødland

doi:10.1158/1541-7786.mcr-07-2183

Nina Marie Pedersen, Espen Stang + Show 4 more

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https://doi.org/10.1158/1541-7786.mcr-07-2183

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Abstract

Overexpression of the epidermal growth factor receptor (EGFR), ErbB2, and ErbB3 promotes growth and antiapoptotic signaling. Overexpression of ErbB2 in breast cancer is associated with poor clinical outcome, and ways of down-regulating ErbB2 are important as therapeutic approaches. In contrast to EGFR, ErbB2 has been shown to be endocytosis deficient. However, down-regulation of ErbB2 can be induced by incubation of cells with geldanamycin and geldanamycin derivatives, counteracting the stabilizing function of heat shock protein 90 on ErbB2. In the present study, we have made use of stably transfected isogenic cell lines expressing ErbB2 only or ErbB2 together with EGFR and/or ErbB3. We now show that whereas ErbB2 can be down-regulated by incubation with geldanamycin in cells expressing ErbB2 only, the rate of geldanamycin-induced down-regulation increases significantly when the cells additionally express EGFR and/or ErbB3. This increase does, however, not correlate with activation/phosphorylation of ErbB2. The potential of heterodimer formation in ErbB2-positive breast cancer cells could thus turn out to be prognostically predictive with respect to outcome of treatment with geldanamycin derivatives.

Highlights

The epidermal growth factor (EGF) receptor (EGFR) family includes four members: epidermal growth factor receptor (EGFR)/ErbB1, ErbB2, ErbB3, and ErbB4
In contrast to EGFR and ErbB2, ErbB3 was shown to have a rapid turnover at the plasma membrane, and this turnover was reported to depend on the ubiquitin ligase Nrdp1 and on proteasomal activity [24, 25]
To investigate to what extent ErbB2 undergoes geldanamycininduced down-regulation in cells not expressing other ErbB proteins, we used porcine aortic endothelial (PAE) cells stably transfected with a plasmid encoding ErbB2 (PAE.ErbB2 cells; see Table 1 for overview of PAE cells used in the current study and Supplementary Fig. S1 for Western blots showing the expression of ErbB proteins in each cell line)

Summary

Introduction

The epidermal growth factor (EGF) receptor (EGFR) family includes four members: EGFR/ErbB1, ErbB2, ErbB3, and ErbB4. The ErbB proteins share a common structural organization with an extracellular ligand-binding domain, a single-membrane spanning region and a cytoplasmic tyrosine kinase domain EGFR, ErbB3, and ErbB4 bind multiple ligands Ligand binding induces conformational changes causing exposure of the extracellular dimerization arm allowing formation of homodimers and/or heterodimers Heterodimers containing ErbB2 have enhanced and prolonged signaling [10], which is induced by phosphorylation of COOH-terminal tyrosine residues serving as docking sites for adaptor and effector proteins. Each ErbB protein exhibits a unique phosphotyrosine profile that allows binding of different enzymes and adaptors Phosphorylation of ErbB3 depends on dimerization with other ErbB proteins [14, 15], and the ErbB2-ErbB3 complex is reportedly the most potent in oncogenic signaling [7, 10, 16]. In contrast to EGFR and ErbB2, ErbB3 was shown to have a rapid turnover at the plasma membrane, and this turnover was reported to depend on the ubiquitin ligase Nrdp and on proteasomal activity [24, 25]

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