title: A Switch in Akt Isoforms Is Required for Notch-Induced Snail1 Expression and Protection from Cell Death.
abstract: Notch activation in aortic endothelial cells (ECs) takes place at embryonic stages during cardiac valve formation and induces endothelial-to-mesenchymal transition (EndMT). Using aortic ECs, we show here that active Notch expression promotes EndMT, resulting in downregulation of vascular endothelial cadherin (VE-cadherin) and upregulation of mesenchymal genes such as those for fibronectin and Snail1/2. In these cells, transforming growth factor β1 exacerbates Notch effects by increasing Snail1 and fibronectin activation. When Notch-downstream pathways were analyzed, we detected an increase in glycogen synthase kinase 3β (GSK-3β) phosphorylation and inactivation that facilitates Snail1 nuclear retention and protein stabilization. However, the total activity of Akt was downregulated. The discrepancy between Akt activity and GSK-3β phosphorylation is explained by a Notch-induced switch in the Akt isoforms, whereby Akt1, the predominant isoform expressed in ECs, is decreased and Akt2 transcription is upregulated. Mechanistically, Akt2 induction requires the stimulation of the β-catenin/TCF4 transcriptional complex, which activates the Akt2 promoter. Active, phosphorylated Akt2 translocates to the nucleus in Notch-expressing cells, resulting in GSK-3β inactivation in this compartment. Akt2, but not Akt1, colocalizes in the nucleus with lamin B in the nuclear envelope. In addition to promoting GSK-3β inactivation, Notch downregulates Forkhead box O1 (FoxO1), another Akt2 nuclear substrate. Moreover, Notch protects ECs from oxidative stress-induced apoptosis through an Akt2- and Snail1-dependent mechanism.
authors.affiliation: Programa de Recerca en Càncer, Institut Hospital del Mar d'Investigacions Mèdiques, Barcelona, Spain Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Barcelona, Spain.
authors.forename: Alex
authors.initials: A
authors.lastname: Frías
authors.affiliation: Programa de Recerca en Càncer, Institut Hospital del Mar d'Investigacions Mèdiques, Barcelona, Spain.
authors.forename: Guillem
authors.initials: G
authors.lastname: Lambies
authors.affiliation: Programa de Recerca en Càncer, Institut Hospital del Mar d'Investigacions Mèdiques, Barcelona, Spain.
authors.forename: Rosa
authors.initials: R
authors.lastname: Viñas-Castells
authors.affiliation: Programa de Recerca en Càncer, Institut Hospital del Mar d'Investigacions Mèdiques, Barcelona, Spain.
authors.forename: Catalina
authors.initials: C
authors.lastname: Martínez-Guillamon
authors.affiliation: Programa de Recerca en Càncer, Institut Hospital del Mar d'Investigacions Mèdiques, Barcelona, Spain.
authors.forename: Natàlia
authors.initials: N
authors.lastname: Dave
authors.affiliation: Programa de Recerca en Càncer, Institut Hospital del Mar d'Investigacions Mèdiques, Barcelona, Spain Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Barcelona, Spain agarcia@imim.es victor.diaz@upf.edu.
authors.forename: Antonio
authors.initials: A
authors.lastname: García de Herreros
authors.affiliation: Programa de Recerca en Càncer, Institut Hospital del Mar d'Investigacions Mèdiques, Barcelona, Spain Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Barcelona, Spain agarcia@imim.es victor.diaz@upf.edu.
authors.forename: Víctor M
authors.initials: VM
authors.lastname: Díaz
mesh_terms: D000818:Animals; D001011:Aorta / Q000166:cytology; D016923:Cell Death; D002460:Cell Line; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism; D058750:Epithelial-Mesenchymal Transition; D005786:Gene Expression Regulation; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D018384:Oxidative Stress; D020033:Protein Isoforms / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D055550:Protein Stability; D051057:Proto-Oncogene Proteins c-akt / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D051880:Receptors, Notch / Q000378:metabolism*; D000071250:Snail Family Transcription Factors; D013552:Swine; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation; D051176:beta Catenin / Q000378:metabolism
chemical_list: D020033:Protein Isoforms; D051880:Receptors, Notch; C000604407:SNAI1 protein, human; C000604429:Snai1 protein, mouse; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors; D051176:beta Catenin; C494918:AKT1 protein, human; C494921:AKT2 protein, human; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3