title: Cytosolic phospholipase A2 activation correlates with HER2 overexpression and mediates estrogen-dependent breast cancer cell growth.
abstract: Cytosolic phospholipase A(2)alpha (cPLA(2)alpha) catalyzes the hydrolysis of membrane glycerol-phospholipids to release arachidonic acid as the first step of the eicosanoid signaling pathway. This pathway contributes to proliferation in breast cancer, and numerous studies have demonstrated a crucial role of cyclooxygenase 2 and prostaglandin E(2) release in breast cancer progression. The role of cPLA(2)alpha activation is less clear, and we recently showed that 17beta-estradiol (E2) can rapidly activate cPLA(2)alpha in MCF-7 breast cancer cells. Overexpression or gene amplification of HER2 is found in approximately 30% of breast cancer patients and correlates with a poor clinical outcome and resistance to endocrine therapy. This study reports the first evidence for a correlation between cPLA(2)alpha enzymatic activity and overexpression of the HER2 receptor. The activation of cPLA(2)alpha in response to E2 treatment was biphasic with the first phase dependent on trans-activation through the matrix metalloproteinase-dependent release of heparin-bound epidermal growth factor. EGFR/HER2 heterodimerization resulted in downstream signaling through the ERK1/2 cascade to promote cPLA(2)alpha phosphorylation at Ser505. There was a correlation between HER2 and cPLA(2)alpha expression in six breast cancer cell lines examined, and inhibition of HER2 activation or expression in the SKBR3 cell line using herceptin or HER2-specific small interfering RNA, respectively, resulted in decreased activation and expression of cPLA(2)alpha. Pharmacological blockade of cPLA(2)alpha using a specific antagonist suppressed the growth of both MCF-7 and SKBR3 cells by reducing E2-induced proliferation and by stimulating cellular apoptosis and necrosis. This study highlights cPLAalpha(2) as a potential target for therapeutic intervention in endocrine-dependent and endocrine-independent breast cancer.
authors.affiliation: Department of Molecular Medicine, Royal College of Surgeons in Ireland, Education and Research Centre, Beaumont Hospital, Dublin 9, Ireland.
authors.forename: Francesco
authors.initials: F
authors.lastname: Caiazza
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Harvey
authors.forename: Warren
authors.initials: W
authors.lastname: Thomas
mesh_terms: D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology; D004967:Estrogens / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000235:genetics; D054513:Group IV Phospholipases A2 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics; D034622:RNA Interference; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics
chemical_list: D004958:Estradiol; D004967:Estrogens; D054513:Group IV Phospholipases A2; D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human