title: Osteopontin promotes the invasive growth of melanoma cells by activating integrin αvβ3 and down-regulating tetraspanin CD9.
abstract: Overexpression of osteopontin (OPN) is strongly associated with the invasiveness/metastasis of many cancers, including melanomas. However, the molecular mechanisms of OPN in these processes remain poorly understood. We found that forced expression of OPN in early vertical-growth-phase melanoma cells dramatically increased their migration/invasion and growth/survival in a three-dimensional collagen I gel. Neutralizing antibodies to OPN, integrin β1, and integrin αvβ3, but not to CD44, negated the effects of OPN. Conversely, knocking down OPN in metastatic melanoma cells abrogated the invasive growth. OPN overexpression activated and OPN knockdown inactivated αvβ3 and αvβ5 integrins, negligibly affecting their expression. We further found OPN expression to inversely correlate with tetraspanin CD9 expression. Early-stage melanoma cells displayed low OPN and high CD9 expression, and conversely, metastatic cells displayed high OPN and low CD9 expression. Overexpression of OPN in vertical-growth-phase melanoma cells induced down-regulation of CD9, and knockdown of OPN in metastatic melanoma cells up-regulated CD9. Reversion of these CD9 changes abolished the effects of OPN. Furthermore, knockdown of CD9 in early-stage melanoma cells stimulated their invasive capacity in three-dimensional collagen. Similarly, microarray analyses of benign nevi and primary melanomas from different stages revealed an inverse correlation between OPN and CD9. These data suggest that OPN promotes melanoma cell invasion by activating integrin αvβ3 and down-regulating CD9, a putative metastasis suppressor.
authors.affiliation: Department of Pathology, Haartman Institute, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Miao
authors.initials: M
authors.lastname: Yin
authors.affiliation: Department of Pathology, Haartman Institute, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Johanna
authors.initials: J
authors.lastname: Soikkeli
authors.affiliation: Department of Plastic Surgery, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Tiina
authors.initials: T
authors.lastname: Jahkola
authors.affiliation: Department of Pathology, Haartman Institute, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Susanna
authors.initials: S
authors.lastname: Virolainen
authors.affiliation: Department of Dermatology, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Olli
authors.initials: O
authors.lastname: Saksela
authors.affiliation: Department of Pathology, Haartman Institute, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland. Electronic address: erkki.holtta@helsinki.fi.
authors.forename: Erkki
authors.initials: E
authors.lastname: Hölttä
mesh_terms: D045744:Cell Line, Tumor; D002465:Cell Movement; D015536:Down-Regulation; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000235:genetics / Q000378:metabolism*; D008545:Melanoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D009361:Neoplasm Invasiveness; D020411:Oligonucleotide Array Sequence Analysis; D053495:Osteopontin / Q000235:genetics / Q000378:metabolism*; D019030:Receptors, Vitronectin / Q000235:genetics / Q000378:metabolism*; D060245:Tetraspanin 29 / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D039302:Integrin alphaVbeta3; D019030:Receptors, Vitronectin; D060245:Tetraspanin 29; C064660:integrin alphaVbeta5; D053495:Osteopontin