ErbB2-dependent downregulation of a pro-apoptotic protein Perp is required for oncogenic transformation of breast epithelial cells.
The ability of breast cancer cells to resist anoikis, apoptosis caused by detachment of the non-malignant epithelial cells from the extracellular matrix (ECM), is thought to be critical for breast tumor growth, invasion and metastasis. ErbB2, an oncoprotein that is often overproduced in breast tumors, can block breast cancer cell anoikis via mechanisms that are understood only in part. In an effort to understand them better we found that detachment of the non-malignant human breast epithelial cells from the ECM upregulates a protein Perp in these cells. Perp is a component of the desmosomes, multiprotein complexes involved in cell-to-cell adhesion. Perp can cause apoptosis via unknown mechanisms. We demonstrated that Perp upregulation by cell detachment is driven by detachment-induced loss of epidermal growth factor receptor (EGFR). We also found that Perp knockdown by RNA interference (RNAi) rescues detached cells from death which indicates that Perp contributes to their anoikis. We observed that ErbB2, when overexpressed in detached breast epithelial cells, causes Perp downregulation. Furthermore, ErbB2-directed RNAi or treatment with lapatinib, an ErbB2/EGFR small-molecule inhibitor used for breast cancer therapy, upregulated Perp in ErbB2-positive human breast and ovarian carcinoma cells. We established that ErbB2 downregulates Perp by activating an ErbB2 effector protein kinase Mek that blocks detachment-induced EGFR loss in a manner that requires the presence of a signaling protein Sprouty-2. Finally, we observed that restoration of the wild-type Perp levels in ErbB2-overproducing breast epithelial cells increases their anoikis susceptibility and blocks their clonogenicity in the absence of adhesion to the ECM. In summary, we have identified a novel mechanism of ErbB2-mediated mechanism of anoikis resistance of ErbB2-overproducing breast epithelial cells. This mechanism allows such cells to grow without adhesion to the ECM and is driven by ErbB2-induced activation of Mek, subsequent EGFR upregulation and further EGFR-dependent Perp loss.
Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada.|Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
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Khan
Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada.|Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
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Yoo
Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada.|Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
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Masson
Department of Radiation and Cancer Biology, Stanford University School of Medicine, Stanford, CA, USA.
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Baron
Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.|Department of Pathology, Dalhousie University, Halifax, Nova Scotia, Canada.
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Corkery
Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.|Department of Pathology, Dalhousie University, Halifax, Nova Scotia, Canada.
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Dellaire
Department of Radiation and Cancer Biology, Stanford University School of Medicine, Stanford, CA, USA.
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Attardi
Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada.|Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
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Rosen
D023102:Anoikis / Q000235:genetics; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000378:metabolism*; D015536:Down-Regulation; D058750:Epithelial-Mesenchymal Transition / Q000235:genetics*; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor; D006801:Humans; D020935:MAP Kinase Signaling System; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*
D066246:ErbB Receptors; D008565:Membrane Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases; C416404:PERP protein, human