Involvement of MEK/ERK1/2 and PI3K/Akt pathways in the refractory behavior of GH3B6 pituitary tumor cells to the inhibitory effect of TGFβ1.
Pituitary tumor cells have a poor response to the growth inhibitory effect of TGFβ1, possibly resulting from the cross talk of TGFβ/Smads signal with other signaling pathways, an undescribed mechanism in these tumoral cells. To address this hypothesis, we investigated whether the mitogen-activated extracellular signal-regulated kinase (MEK)/ERK1/2 and phosphoinositide-3 kinase/protein kinase B (PI3K/Akt) pathways were able to regulate the antimitogenic effect of TGFβ1 on GH3B6 cells. TGFβ1 treatment decreased the cell proliferation and induced an activation of mothers against decapentaplegic homolog 2/3 (Smad2/3), effects that were potentiated by MEK and PI3K inhibitors, thus indicating the existence of a cross talk between TGFβ1/Smad with the MEK/ERK1/2 or PI3K/Akt pathways. In addition, through immunoprecipitation assays, a direct interaction was observed between Smad2/3-ERK1/2 and Smad2/3-Akt, which decreased when the GH3B6 cells were incubated with TGFβ1 in the presence of MEK or PI3K inhibitors, thereby suggesting that the ERK1/2- and Akt-activated states were involved. These Smad2/3-ERK1/2 and Smad2/3-Akt associations were also confirmed by confocal and transmission electron microscopy. These findings indicate that the TGFβ1-antimitogenic effect in GH3B6 cells was attenuated by the MEK/ERK1/2 and PI3K/Akt pathways via modulating Smad2/3 phosphorylation. This molecular mechanism could explain in part the refractory behavior of pituitary tumor cells to the inhibitory effect of TGFβ1.
Centro de Microscopía Electrónica, Instituto de Investigaciones en Ciencias de la Salud-Consejo Nacional de Investigaciones Científicas y Técnicas and Facultad de Ciencias Médicas, Universidad Nacional de Córdoba, 5000-Córdoba, Argentina.
Juan Pablo
JP
Petiti
Liliana del Valle
Ldel V
Sosa
María Eugenia
ME
Sabatino
Alicia Maldré
AM
Vaca
Silvina
S
Gutiérrez
Ana Lucía
AL
De Paul
Alicia Inés
AI
Torres
D000236:Adenoma / Q000378:metabolism*; D000818:Animals; D063646:Carcinogenesis; D045744:Cell Line, Tumor; D020935:MAP Kinase Signaling System; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010911:Pituitary Neoplasms / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D051785:Smad Proteins / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
D051785:Smad Proteins; C508962:Tgfb1 protein, rat; D053773:Transforming Growth Factor beta1; D011388:Prolactin; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt