title: Activin A suppresses neuroblastoma xenograft tumor growth via antimitotic and antiangiogenic mechanisms.
abstract: The tumor suppressor function of activin A, together with our findings that activin A is an inhibitor of angiogenesis, which is down-regulated by the N-MYC oncogene, prompted us to investigate in more detail its role in the malignant transformation process of neuroblastomas. Indeed, neuroblastoma cells with restored activin A expression exhibited a diminished proliferation rate and formed smaller xenograft tumors with reduced vascularity, whereas lung metastasis rate remained unchanged. In agreement with the decreased vascularity of the xenograft tumors, activin A inhibited several crucial angiogenic responses of cultured endothelial cells, such as proteolytic activity, migration, and proliferation. Endothelial cell proliferation, activin A, or its constitutively active activin receptor-like kinase 4 receptor (ALK4T206D), increased the expression of CDKN1A (p21), CDKN2B (p15), and CDKN1B (p27) CDK inhibitors and down-regulated the expression of vascular endothelial growth factor receptor-2, the receptor of a key angiogenic factor in cancer. The constitutively active forms of SMAD2 and SMAD3 were both capable of inhibiting endothelial cell proliferation, whereas the dominant-negative forms of SMAD3 and SMAD4 released the inhibitory effect of activin A on endothelial cell proliferation by only 20%. Thus, the effects of activin A on endothelial cell proliferation seem to be conveyed via the ALK4/SMAD2-SMAD3 pathways, however, non-SMAD cascades may also contribute. These results provide novel information regarding the role of activin A in the malignant transformation process of neuroblastomas and the molecular mechanisms involved in regulating angiogenesis thereof.
authors.affiliation: Laboratory of Biological Chemistry, Medical School, University of Ioannina, Greece.
authors.forename: Ekaterini
authors.initials: E
authors.lastname: Panopoulou
authors.forename: Carol
authors.initials: C
authors.lastname: Murphy
authors.forename: Heidi
authors.initials: H
authors.lastname: Rasmussen
authors.forename: Eleni
authors.initials: E
authors.lastname: Bagli
authors.forename: Einar K
authors.initials: EK
authors.lastname: Rofstad
authors.forename: Theodore
authors.initials: T
authors.lastname: Fotsis
mesh_terms: D029404:Activin Receptors / Q000378:metabolism; D028341:Activins / Q000627:therapeutic use*; D020533:Angiogenesis Inhibitors / Q000627:therapeutic use*; D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D018797:Cell Cycle Proteins / Q000378:metabolism; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D050762:Cyclin-Dependent Kinase Inhibitor p15; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004268:DNA-Binding Proteins / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D028322:Inhibin-beta Subunits / Q000627:therapeutic use*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009389:Neovascularization, Pathologic; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D015398:Signal Transduction; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators / Q000378:metabolism; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D020533:Angiogenesis Inhibitors; D000970:Antineoplastic Agents; C493956:CDKN1A protein, human; C493966:CDKN2B protein, human; C493957:Cdkn1a protein, mouse; C493961:Cdkn1b protein, mouse; C493968:Cdkn2b protein, mouse; D018797:Cell Cycle Proteins; D050762:Cyclin-Dependent Kinase Inhibitor p15; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D015534:Trans-Activators; D025521:Tumor Suppressor Proteins; C422405:activin A; D028341:Activins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D028322:Inhibin-beta Subunits; D040301:Vascular Endothelial Growth Factor Receptor-2; D029404:Activin Receptors