title: Targeting p70S6K prevented lung metastasis in a breast cancer xenograft model.
abstract: Overexpression of p70S6K in breast cancer patients is associated with aggressive disease and poor prognosis. Recent studies showed that patients with breast cancer with increased p70S6K phosphorylation had poor survival and increased metastasis. The purpose of our study was to determine whether knockdown of p70S6K would inhibit cell growth, invasion, and metastasis in breast cancer. We therefore stably knocked down p70S6K expression in MDA-231, a highly metastatic breast cancer cell line, using a lentiviral short hairpin RNA (shRNA) based approach. Inhibition of p70S6K led to inhibition of cell growth, migration, and invasion in vitro. To determine the role of p70S6K in breast cancer tumorigenesis and metastasis, we used an MDA-231 orthotopic and metastatic animal model. In the orthotopic model, mice injected with MDA-231-p70S6K shRNA cells developed significantly smaller tumors than control mice injected with MDA-231 control shRNA cells (P < 0.01). No metastasis was observed in the p70S6K downregulated group, whereas lung metastasis was detected in all mice in the control group. To determine the role of p70S6K on growth and invasion, we tested downstream signaling targets by Western blot analysis. Knockdown of p70S6K inhibited phosphorylation of focal adhesion kinase, tissue transglutaminase 2, and cyclin D1 proteins, which promote cell growth, survival, and invasion. In addition, downregulation of p70S6K induced expression of PDCD4, a tumor-suppressor protein. In conclusion, we showed that p70S6K plays an important role in metastasis by regulating key proteins like cyclin D1, PDCD4, focal adhesion kinase, E-cadherin, beta-catenin, and tissue transglutaminase 2, which are essential for cell attachment, survival, invasion, and metastasis in breast cancer.
authors.affiliation: Department of Breast Medical Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA. ugurakar@mdanderson.org
authors.forename: Ugur
authors.initials: U
authors.lastname: Akar
authors.forename: Bulent
authors.initials: B
authors.lastname: Ozpolat
authors.forename: Kapil
authors.initials: K
authors.lastname: Mehta
authors.forename: Gabriel
authors.initials: G
authors.lastname: Lopez-Berestein
authors.forename: Dongwei
authors.initials: D
authors.lastname: Zhang
authors.forename: Naoto T
authors.initials: NT
authors.lastname: Ueno
authors.forename: Gabriel N
authors.initials: GN
authors.lastname: Hortobagyi
authors.forename: Banu
authors.initials: B
authors.lastname: Arun
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D015820:Cadherins / Q000235:genetics; D002277:Carcinoma / Q000188:drug therapy* / Q000473:pathology; D019938:Cyclin D1 / Q000235:genetics; D016503:Drug Delivery Systems; D005260:Female; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008175:Lung Neoplasms / Q000517:prevention & control* / Q000556:secondary; D051379:Mice; D008819:Mice, Nude; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage* / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000008:administration & dosage* / Q000494:pharmacology; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000502:physiology; D023041:Xenograft Model Antitumor Assays; D051176:beta Catenin / Q000235:genetics
chemical_list: D000970:Antineoplastic Agents; D015820:Cadherins; D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; C000717608:TGM2 protein, human; D051176:beta Catenin; D019938:Cyclin D1; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D051416:Focal Adhesion Protein-Tyrosine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa