title: HER2 signaling downregulation by trastuzumab and suppression of the PI3K/Akt pathway: an unexpected effect on TRAIL-induced apoptosis.
abstract: We investigated whether HER2 downregulation by trastuzumab modulates the responsiveness of breast cancer cells to TNF-related apoptosis-inducing ligand (TRAIL). Interestingly, in contrast to increased response to TRAIL in SKBr3 cells, trastuzumab decreased the susceptibility of BT474 cells to TRAIL. This decrease was also observed after exogenous inhibition of PI3-K/Akt kinase, but not MAPK/ERK kinase (MEK)/mitogen-activated protein kinase (MAPK). In BT474 cells, but not SKBr3 cells, inhibition of the HER2/phosphatidylinositol 3' kinase (PI3K)/Akt pathway resulted in downregulation of the pro-apoptotic receptors TRAIL-receptor 1 (TRAIL-R1) and TRAIL-R2. TRAIL-induced caspase-8 activation, Bid processing, drop of DeltaPsi(m), and poly ADP-ribose polymerase (PARP) cleavage but not in caspase-9 activation, and these events were inhibited in HER2/PI3K/Akt-suppressed BT474 cells, which on the other hand exhibited downregulation of Bcl-xL and increased response to mitomycin C. We show that HER2/PI3K/Akt pathway may play a specific pro-apoptotic role in certain cell type by inducing TRAIL-R1 and -R2 expression and thereby enhancing responsiveness to TRAIL.
authors: Department of Laboratory Medicine, Masaryk Memorial Cancer Institute, Zluty Kopec 7, 656 53 Brno, Czech Republic. dubska@mou.cz
authors: Lenka
authors: L
authors: Dubská
authors: Ladislav
authors: L
authors: Andera
authors: Michael Allen
authors: MA
authors: Sheard
mesh_terms: D000230:Adenocarcinoma / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D001943:Breast Neoplasms / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D015536:Down-Regulation; D005455:Fluorescent Antibody Technique; D018734:Genes, erbB-2; D006801:Humans; D008562:Membrane Glycoproteins / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction; D053221:TNF-Related Apoptosis-Inducing Ligand; D000068878:Trastuzumab; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D051017:Apoptosis Regulatory Proteins; D008562:Membrane Glycoproteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D053221:TNF-Related Apoptosis-Inducing Ligand; D000068878:Trastuzumab; D014409:Tumor Necrosis Factor-alpha; C505653:TNFSF10 protein, human; C494918:AKT1 protein, human