title: Tyr phosphatase-mediated P-ERK inhibition suppresses senescence in EIA + v-raf transformed cells, which, paradoxically, are apoptosis-protected in a MEK-dependent manner.
abstract: Activation of the Ras-Raf-extracellular signal-regulated kinase (ERK) pathway causes not only proliferation and suppression of apoptosis but also the antioncogenic response of senescence. How these contrasting effects are reconciled to achieve cell transformation and cancer formation is poorly understood. In a system of two-step carcinogenesis (dedifferentiated PC EIA, transformed PC EIA-polyoma-middle T [PC EIA + Py] and PC EIA-v-raf [PC EIA + raf] cells], v-raf cooperated with EIA by virtue of a strong prosurvival effect, not elicited by Py-middle T, evident toward serum-deprivation-and H(2)O(2)-induced apoptosis. Apoptosis was detected by DNA fragmentation and annexin V staining. The prosurvival function of v-raf was, in part, mitogen-activated protein kinase/ERK kinase (MEK)-dependent, as shown by pharmacological MEK inhibition. The MEK-dependent antiapoptotic effect of v-raf was exerted despite a lower level of P-ERK1/2 in EIA + raf cells with respect to EIA + Py/EIA cells, which was dependent on a high tyrosine phosphatase activity, as shown by orthovanadate blockade. An ERK1/2 tyrosine phosphatase was likely involved. The high tyrosine phosphatase activity was instrumental to the complete suppression of senescence, detected by β-galactosidase activity, because tyrosine phosphatase blockade induced senescence in EIA + raf but not in EIA + Py cells. High tyrosine phosphatase activity and evasion from senescence were confirmed in an anaplastic thyroid cancer cell line. Therefore, besides EIA, EIA + raf cells suppress senescence through a new mechanism, namely, phosphatase-mediated P-ERK1/2 inhibition, but, paradoxically, retain the oncogenic effects of the Raf-ERK pathway. We propose that the survival effect of Raf is not a function of absolute P-ERK1/2 levels at a given time but is rather dynamically dependent on greater variations after an apoptotic stimulus.
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Facoltà di Scienze Matematiche Fisiche e Naturali, Università degli Studi del Salento, Lecce, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: De Vitis
authors.forename: Antonella
authors.initials: A
authors.lastname: Sonia Treglia
authors.forename: Luca
authors.initials: L
authors.lastname: Ulianich
authors.forename: Stefano
authors.initials: S
authors.lastname: Turco
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Terrazzano
authors.forename: Angela
authors.initials: A
authors.lastname: Lombardi
authors.forename: Claudia
authors.initials: C
authors.lastname: Miele
authors.forename: Corrado
authors.initials: C
authors.lastname: Garbi
authors.forename: Francesco
authors.initials: F
authors.lastname: Beguinot
authors.forename: Bruno
authors.initials: B
authors.lastname: Di Jeso
mesh_terms: D017209:Apoptosis / Q000235:genetics; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism*; D016922:Cellular Senescence; D005786:Gene Expression Regulation; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D027384:Oncogene Proteins v-raf / Q000235:genetics / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000201:enzymology*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D006861:Hydrogen Peroxide; D027384:Oncogene Proteins v-raf; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases; D017027:Protein Tyrosine Phosphatases; D001616:beta-Galactosidase