title: A critical role for ras-mediated, epidermal growth factor receptor-dependent angiogenesis in mouse skin carcinogenesis.
abstract: Epidermal growth factor receptor (EGFR) plays a critical role in epidermal biology. Abnormal EGFR function has been described in epithelial tumors including those induced by two-stage chemical carcinogenesis in mouse skin. A large body of evidence indicates that in this model, activation of Ha-ras is the critical event in papilloma formation, a process that involves epidermal proliferation and stroma remodeling, which includes angiogenesis. This study reports that activated Ha-ras results in a dramatic induction of EGFR in epidermal tumor cells and provides experimental evidence that EGFR signaling is responsible for Ha-ras-dependent vascular endothelial growth factor (VEGF) induction, as well as for the repression of other angiogenic factors such as angiopoietin 1. The pivotal role of functional EGFR in throwing the angiogenic switch necessary for tumor growth was confirmed by s.c. injection of immunodeficient mice with epidermal tumor cells carrying a dominant negative (dn) EGFR and by in vivo chemical skin carcinogenesis assays in transgenic mice expressing the same dn EGFR form in the epidermis. Immunohistochemical analysis of the tumors obtained by both ex vivo and in vivo approaches showed that dn EGFR expression abolished the changes in blood vessels that occurred during tumor progression. A strong reduction of VEGF expression in dn EGFR tumors appears to be the key event responsible for angiogenesis and tumor growth suppression. The apoptotic rate was increased, and Akt activity was decreased, suggesting that impaired nutrient and oxygen supply might contribute to diminished cell survival in dn EGFR tumors. Support for this mechanism is provided by the fact that the ectopic expression of VEGF in dn EGFR-expressing tumor cell lines restored tumor growth capacity. Although ras activation might suffice for epidermal transformation and the stroma-remodeling events of tumor induction, such effects may not be operative without a functional upstream EGFR. It is tempting to speculate that EGFR family members may function as angiogenic regulators in other epithelial tumors such as those of the colon, breast, and prostate, reinforcing their value as targets for therapeutic intervention.
authors.affiliation: Project on Cell and Molecular Biology and Gene Therapy, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, 28040 Madrid, Spain.
authors.forename: M Llanos
authors.initials: ML
authors.lastname: Casanova
authors.forename: Fernando
authors.initials: F
authors.lastname: Larcher
authors.forename: Benito
authors.initials: B
authors.lastname: Casanova
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Murillas
authors.forename: M Jesús
authors.initials: MJ
authors.lastname: Fernández-Aceñero
authors.forename: Concepción
authors.initials: C
authors.lastname: Villanueva
authors.forename: Jesús
authors.initials: J
authors.lastname: Martínez-Palacio
authors.forename: Axel
authors.initials: A
authors.lastname: Ullrich
authors.forename: Claudio J
authors.initials: CJ
authors.lastname: Conti
authors.forename: Jose Luis
authors.initials: JL
authors.lastname: Jorcano
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D011905:Genes, ras / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D009389:Neovascularization, Pathologic / Q000378:metabolism / Q000473:pathology*; D010212:Papilloma / Q000098:blood supply / Q000473:pathology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology; D012878:Skin Neoplasms / Q000098:blood supply* / Q000473:pathology
chemical_list: D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D066246:ErbB Receptors; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt