title: Herceptin-induced inhibition of ErbB2 signaling involves reduced phosphorylation of Akt but not endocytic down-regulation of ErbB2.
abstract: The anti-proliferative effect of the ErbB2 specific antibody Herceptin in cells overexpressing ErbB2 has previously been explained by endocytic downregulation of ErbB2. However, in the following, we demonstrate that Herceptin inhibited proliferation of ErbB2 overexpressing cells without downregulating ErbB2. Herceptin did also not induce endocytosis of ErbB2. Herceptin was found to blunt proliferation of SKBr3 cells overexpressing EGFR, ErbB2, and ErbB3 and expressing functional PTEN, probably by recruiting PTEN to the plasma membrane. Akt was found to be constitutively phosphorylated both in SKBr3 cells overexpressing EGFR, ErbB2 and ErbB3, and in SKOv3 cells, overexpressing EGFR and ErbB2. However, phosphorylation of Akt was inhibited by Herceptin only in SKBr3 cells. SKOv3 cells, which lack the tumour suppressor protein Ras homolog member I, was found to have constitutively phosphorylated mitogen activated protein kinase and functionally increased Ras activity. SKOv3 cells further had low expression levels of PTEN. We thus confirm that the anti-proliferative effect of Herceptin in SKBr3 cells is due to recruitment of PTEN to the plasma membrane and conclude that Herceptin does not blunt phosphatidyl inositol 3 kinase-induced growth in cells with constitutive Ras activity. We further conclude that endocytic downregulation of ErbB2 does not contribute to Herceptin's antiproliferative effect.
authors.affiliation: Institute of Pathology, The University of Oslo, Rikshospitalet, Oslo, Norway.
authors.forename: Karianne E
authors.initials: KE
authors.lastname: Longva
authors.forename: Nina Marie
authors.initials: NM
authors.lastname: Pedersen
authors.forename: Camilla
authors.initials: C
authors.lastname: Haslekås
authors.forename: Espen
authors.initials: E
authors.lastname: Stang
authors.forename: Inger H
authors.initials: IH
authors.lastname: Madshus
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000473:pathology; D002277:Carcinoma / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects*; D015536:Down-Regulation; D004705:Endocytosis; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007822:Laryngeal Neoplasms / Q000473:pathology; D010051:Ovarian Neoplasms / Q000473:pathology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis* / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D000068878:Trastuzumab; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; C494918:AKT1 protein, human