title: Role of the integrin-binding protein osteopontin in lymphatic metastasis of breast cancer.
abstract: Although a primary route of breast cancer metastasis is believed to be via lymphatics, the molecular factors involved are poorly understood. We hypothesized that one such factor may be the integrin-binding protein osteopontin (OPN), and we investigated this clinically and experimentally. In breast cancer patients undergoing sentinel lymph node biopsy, OPN levels were significantly higher in lymph node metastases than in the primary tumor (P < 0.001). To test the functional contribution of OPN to lymphatic metastasis and to determine whether the RGD (Arg-Gly-Asp) integrin-binding sequence of OPN is important for this process, we transfected wild-type OPN or mutant OPN (lacking the RGD sequence) into MDA-MB-468 human breast cancer cells. In vitro, cells overexpressing OPN demonstrated increased anchorage-independent growth in soft agar (P = 0.001) and increased RGD-dependent adhesion (P = 0.045). Following mammary fat pad injection of nude mice, cells overexpressing OPN showed increased lymphovascular invasion, lymph node metastases, and lung micrometastases at earlier time points (P = 0.024). Loss of the RGD region partially abrogated this effect in the lymphatics (P = 0.038). These novel findings indicate that OPN is a key molecular player involved in lymphatic metastasis of breast cancer, potentially by affecting RGD-mediated adhesive interactions and by enhancing the establishment/persistence of tumor cells in the lymphatics.
authors.affiliation: Department of Oncology, Schulich School of Medicine and Dentistry, University of Western Ontario, London Regional Cancer Program, 790 Commissioners Road East, London, Ontario N6A 4L6, Canada. alison.allan@lhsc.on.ca
authors.forename: Alison L
authors.initials: AL
authors.lastname: Allan
authors.forename: Rosamma
authors.initials: R
authors.lastname: George
authors.forename: Sharon A
authors.initials: SA
authors.lastname: Vantyghem
authors.forename: Mark W
authors.initials: MW
authors.lastname: Lee
authors.forename: Nicole C
authors.initials: NC
authors.lastname: Hodgson
authors.forename: C Jay
authors.initials: CJ
authors.lastname: Engel
authors.forename: Ron L
authors.initials: RL
authors.lastname: Holliday
authors.forename: David P
authors.initials: DP
authors.lastname: Girvan
authors.forename: Leslie A
authors.initials: LA
authors.lastname: Scott
authors.forename: Carl O
authors.initials: CO
authors.lastname: Postenka
authors.forename: Waleed
authors.initials: W
authors.lastname: Al-Katib
authors.forename: Larry W
authors.initials: LW
authors.lastname: Stitt
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Uede
authors.forename: Ann F
authors.initials: AF
authors.lastname: Chambers
authors.forename: Alan B
authors.initials: AB
authors.lastname: Tuck
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism*; D002448:Cell Adhesion / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D007150:Immunohistochemistry; D016023:Integrins / Q000378:metabolism; D008207:Lymphatic Metastasis; D051379:Mice; D008819:Mice, Nude; D008875:Middle Aged; D016297:Mutagenesis, Site-Directed; D009368:Neoplasm Transplantation; D009842:Oligopeptides / Q000378:metabolism*; D053495:Osteopontin; D021701:Sentinel Lymph Node Biopsy; D012795:Sialoglycoproteins / Q000378:metabolism*; D014162:Transfection
chemical_list: D016023:Integrins; D009842:Oligopeptides; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; D053495:Osteopontin; C047981:arginyl-glycyl-aspartic acid