title: Septin oligomerization regulates persistent expression of ErbB2/HER2 in gastric cancer cells.
abstract: Septins are a family of cytoskeletal GTP-binding proteins that assemble into membrane-associated hetero-oligomers and organize scaffolds for recruitment of cytosolic proteins or stabilization of membrane proteins. Septins have been implicated in a diverse range of cancers, including gastric cancer, but the underlying mechanisms remain unclear. The hypothesis tested here is that septins contribute to cancer by stabilizing the receptor tyrosine kinase ErbB2, an important target for cancer treatment. Septins and ErbB2 were highly over-expressed in gastric cancer cells. Immunoprecipitation followed by MS analysis identified ErbB2 as a septin-interacting protein. Knockdown of septin-2 or cell exposure to forchlorfenuron (FCF), a well-established inhibitor of septin oligomerization, decreased surface and total levels of ErbB2. These treatments had no effect on epidermal growth factor receptor (EGFR), emphasizing the specificity and functionality of the septin-ErbB2 interaction. The level of ubiquitylated ErbB2 at the plasma membrane was elevated in cells treated with FCF, which was accompanied by a decrease in co-localization of ErbB2 with septins at the membrane. Cathepsin B inhibitor, but not bafilomycin or lactacystin, prevented FCF-induced decrease in total ErbB2 by increasing accumulation of ubiquitylated ErbB2 in lysosomes. Therefore, septins protect ErbB2 from ubiquitylation, endocytosis and lysosomal degradation. The FCF-induced degradation pathway is distinct from and additive with the degradation induced by inhibiting ErbB2 chaperone Hsp90. These results identify septins as novel regulators of ErbB2 expression that contribute to the remarkable stabilization of the receptor at the plasma membrane of cancer cells and may provide a basis for the development of new ErbB2-targeting anti-cancer therapies.
authors.affiliation: Department of Pediatrics, DGSOM at UCLA, Los Angeles, CA 90095, U.S.A. VA Greater Los Angeles Health Care System, Los Angeles, CA 90073, U.S.A.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Marcus
authors.affiliation: VA Greater Los Angeles Health Care System, Los Angeles, CA 90073, U.S.A. Department of Physiology, DGSOM at UCLA, Los Angeles, CA 90095, U.S.A.
authors.forename: Elmira
authors.initials: E
authors.lastname: Tokhtaeva
authors.affiliation: Center for High Technology, Academy of Science, Tashkent 700174, Republic of Uzbekistan.
authors.forename: Shahlo
authors.initials: S
authors.lastname: Turdikulova
authors.affiliation: Pasarow Mass Spectrometry Laboratory, The NPI-Semel Institute, UCLA, Los Angeles, CA 90024, U.S.A.
authors.forename: Joseph
authors.initials: J
authors.lastname: Capri
authors.affiliation: Pasarow Mass Spectrometry Laboratory, The NPI-Semel Institute, UCLA, Los Angeles, CA 90024, U.S.A.
authors.forename: Julian P
authors.initials: JP
authors.lastname: Whitelegge
authors.affiliation: VA Greater Los Angeles Health Care System, Los Angeles, CA 90073, U.S.A. Department of Physiology, DGSOM at UCLA, Los Angeles, CA 90095, U.S.A.
authors.forename: David R
authors.initials: DR
authors.lastname: Scott
authors.affiliation: VA Greater Los Angeles Health Care System, Los Angeles, CA 90073, U.S.A. Department of Physiology, DGSOM at UCLA, Los Angeles, CA 90095, U.S.A. Department of Medicine, DGSOM at UCLA, Los Angeles, CA 90095, U.S.A.
authors.forename: George
authors.initials: G
authors.lastname: Sachs
authors.affiliation: School of Cancer Sciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
authors.forename: Fedor
authors.initials: F
authors.lastname: Berditchevski
authors.affiliation: VA Greater Los Angeles Health Care System, Los Angeles, CA 90073, U.S.A. Department of Physiology, DGSOM at UCLA, Los Angeles, CA 90095, U.S.A. olgav@ucla.edu.
authors.forename: Olga
authors.initials: O
authors.lastname: Vagin
mesh_terms: D015153:Blotting, Western; D045744:Cell Line, Tumor; D002853:Chromatography, Liquid; D003599:Cytoskeleton / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D010671:Phenylurea Compounds / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011725:Pyridines / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics / Q000502:physiology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D058112:Septins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013274:Stomach Neoplasms / Q000378:metabolism*; D053719:Tandem Mass Spectrometry; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D010671:Phenylurea Compounds; D011725:Pyridines; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; D058112:Septins; C508053:ERBB2 protein, human; C116093:N-(2-chloro-4-pyridyl)-N'-phenylurea
keywords: ErbB2; endocytosis; gastric cancer; lysosomal degradation; septin; ubiquitylation