title: Fatty acid synthase phosphorylation: a novel therapeutic target in HER2-overexpressing breast cancer cells.
abstract: BACKGROUND
  The human epidermal growth factor receptor 2 (HER2) is a validated therapeutic target in breast cancer. Heterodimerization of HER2 with other HER family members results in enhanced tyrosine phosphorylation and activation of signal transduction pathways. HER2 overexpression increases the translation of fatty acid synthase (FASN), and FASN overexpression markedly increases HER2 signaling, which results in enhanced cell growth. However, the molecular mechanism and regulation of HER2 and FASN interaction are not well defined. Lapatinib is a small-molecule tyrosine kinase inhibitor that blocks phosphorylation of the epidermal growth factor receptor and HER2 in breast cancer cells, resulting in apoptosis. We hypothesized that FASN is directly phosphorylated by HER2, resulting in enhanced signaling and tumor progression in breast cancer cells.
  
  
  METHODS
  Using mass spectrometry, we identified FASN as one of the proteins that is dephosphorylated by lapatinib in SKBR3 breast cancer cells. Immunofluorescence, immunoprecipitation, Western blotting, a kinase assay, a FASN enzymatic activity assay, an invasion assay, a cell viability assay and zymography were used to determine the role of FASN phosphorylation in invasion of SKBR3 and BT474 cells. The FASN inhibitor C75 and small interfering RNA were used to downregulate FASN expression and/or activity.
  
  
  RESULTS
  Our data demonstrated that FASN is phosphorylated when it is in complex with HER2. FASN phosphorylation was induced by heregulin in HER2-overexpressing SKBR3 and BT474 breast cancer cells. Heregulin-induced FASN phosphorylation resulted in increased FASN enzymatic activity, which was inhibited by lapatinib. The FASN inhibitor C75 suppressed FASN activity by directly inhibiting HER2 and FASN phosphorylation. Blocking FASN phosphorylation and activity by lapatinib or C75 suppressed the activity of matrix metallopeptidase 9 and inhibited invasion of SKBR3 and BT474 cells.
  
  
  CONCLUSIONS
  FASN phosphorylation by HER2 plays an important role in breast cancer progression and may be a novel therapeutic target in HER2-overexpressing breast cancer cells.
authors.affiliation: Department of Breast Medical Oncology, The University of Texas M, D, Anderson Cancer Center, Houston, TX 77030, USA. qjin@mdanderson.org
authors.forename: Quanri
authors.initials: Q
authors.lastname: Jin
authors.forename: Linda X
authors.initials: LX
authors.lastname: Yuan
authors.forename: Delphine
authors.initials: D
authors.lastname: Boulbes
authors.forename: Jong Min
authors.initials: JM
authors.lastname: Baek
authors.forename: Ying Nai
authors.initials: YN
authors.lastname: Wang
authors.forename: Daniel
authors.initials: D
authors.lastname: Gomez-Cabello
authors.forename: David H
authors.initials: DH
authors.lastname: Hawke
authors.forename: Sai Ching
authors.initials: SC
authors.lastname: Yeung
authors.forename: Mong Hong
authors.initials: MH
authors.lastname: Lee
authors.forename: Gabriel N
authors.initials: GN
authors.lastname: Hortobagyi
authors.forename: Mien Chie
authors.initials: MC
authors.lastname: Hung
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Esteva
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D064429:Fatty Acid Synthases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005260:Female; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D006801:Humans; D000077341:Lapatinib; D013058:Mass Spectrometry; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D061965:Matrix Metalloproteinase Inhibitors; D020890:Neuregulin-1 / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011799:Quinazolines / Q000378:metabolism / Q000494:pharmacology*; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D015107:4-Butyrolactone; D000970:Antineoplastic Agents; D064429:Fatty Acid Synthases; D000077341:Lapatinib; D020780:Matrix Metalloproteinase 9; D061965:Matrix Metalloproteinase Inhibitors; D020890:Neuregulin-1; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; C406734:4-methylene-2-octyl-5-oxofuran-3-carboxylic acid; C508053:ERBB2 protein, human