title: Flavopiridol induces phosphorylation of AKT in a human glioblastoma cell line, in contrast to siRNA-mediated silencing of Cdk9: Implications for drug design and development.
abstract: Cdk9 and Cdk7 are cdc2-like serine/threonine kinases that stabilize RNA transcript elongation through RNA polII carboxyl terminal domain (CTD) phosphorylation and are considered suitable targets for cancer therapy.   The effects of flavopiridol and of siRNA-mediated inhibition of Cdk9 and/or Cdk7 were analyzed in human glioblastoma and human prostate cancer cell lines.   One finding revealed that Cdk9 and Cdk7 could substitute each other in RNA polII CTD phosphorylation in contrast to the in vitro system. Thus, a simultaneous inhibition of Cdk9 and Cdk7 might be required both for targeting malignant cells and developing a platform for microarray analysis. However, these two pathways are not redundant, as indicated by differential effects observed in cell cycle regulation following siRNA-mediated inhibition of Cdk9 and/or Cdk7 in human PC3 prostate cancer cell line. Specifically, siRNA-mediated inhibition of Cdk9 caused a shift from G 0/G 1 to G 2/M phase in human PC3 prostate cancer cell line.   Another finding showed that flavopiridol treatment induced a substantial AKT-Ser473 phosphorylation in human glioblastoma T98G cell line in contrast to siRNA-mediated inhibition of Cdk9 and Cdk9 combined with Cdk7, whereas siRNA-mediated silencing of Cdk7 caused a minor increase in AKT-Ser473 phosphorylation. AKT-Ser473 is a hallmark of AKT pathway activation and may protect cells from apoptosis. This finding also shows that Cdk9 and Cdk7 pathways are not redundant and may have important implications in drug development and for studying the mechanism of chemoresistance in malignant cells.
authors.affiliation: Sbarro Institute for Cancer Research and Molecular Medicine, Center for Biotechnology, College of Science and Technology, Temple University, Philadelphia, PA, USA.
authors.forename: Valentina
authors.initials: V
authors.lastname: Caracciolo
authors.forename: Giulio
authors.initials: G
authors.lastname: Laurenti
authors.forename: Gaetano
authors.initials: G
authors.lastname: Romano
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Carnevale
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Cimini
authors.forename: Catena
authors.initials: C
authors.lastname: Crozier-Fitzgerald
authors.forename: Emilio
authors.initials: E
authors.lastname: Gentile Warschauer
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Russo
authors.forename: Antonio
authors.initials: A
authors.lastname: Giordano
mesh_terms: D015153:Blotting, Western; D002453:Cell Cycle; D045744:Cell Line, Tumor; D042863:Cyclin-Dependent Kinase 9 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015195:Drug Design; D004789:Enzyme Activation; D005419:Flavonoids / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D005909:Glioblastoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D006801:Humans; D010766:Phosphorylation; D010880:Piperidines / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D000095043:Cyclin-Dependent Kinase-Activating Kinase
chemical_list: D005419:Flavonoids; D010880:Piperidines; D034741:RNA, Small Interfering; D012694:Serine; C077990:alvocidib; D051057:Proto-Oncogene Proteins c-akt; C467969:CDK9 protein, human; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases; D012319:RNA Polymerase II; D000095043:Cyclin-Dependent Kinase-Activating Kinase; C000722416:CDK7 protein, human