title: Concomitant activation of MEK-1 and Rac-1 increases the proliferative potential of thyroid epithelial cells, without affecting their differentiation.
abstract: Activating point mutations in the Ras oncogene occur in a large number of human tumors, especially of epithelial origin. In thyroid follicular cells, ectopic expression of oncogenic H-Ras results in growth factor-independent proliferation, loss of differentiation and tumor formation in nude mice. In fibroblasts concomitant activation of the MAP kinase cascade and the small GTPase Rac-1 leads to full malignant transformation. We have tested the effects of these key downstream mediators of Ras in thyroid epithelial cells, by stably expressing either a constitutively active form of MEK-1 (MEK(deltaN3/S218E/S222D)), a constitutively active form of Rac-1 (Val12-Rac), or both. While the activation of one molecule or the other results in a weak phenotype, concomitant activation of both MEK-1 and Rac-1 in thyroid cells leads to growth factor-independent proliferation, morphological transformation and anchorage-independent growth. However, in contrast to Ras-transformed thyroid cells, the ones expressing the constitutively active forms of MEK-1 and Rac-1 maintain their differentiate phenotype and fail to form tumors when injected into nude mice. Thus, in thyroid epithelial cells, concomitant activation of MEK-1 and Rac-1 can reproduce only a subset of the Ras-induced effects and is not sufficient to cause full malignant transformation. Significantly, Ras-mediated increased proliferation and loss of differentiation can be dissociated in these cells.
authors.affiliation: Stazione Zoologica A. Dohrn Villa Comunale, Naples, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Cobellis
authors.forename: C
authors.initials: C
authors.lastname: Missero
authors.forename: R
authors.initials: R
authors.lastname: Di Lauro
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D051379:Mice; D008819:Mice, Nude; D020929:Mitogen-Activated Protein Kinase Kinases; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D013961:Thyroid Gland / Q000166:cytology* / Q000378:metabolism; D020744:rac GTP-Binding Proteins
chemical_list: D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins