title: Smad4-independent, PP2A-dependent apoptotic effect of exogenous transforming growth factor beta 1 in lymphoma cells.
abstract: B-lymphoid tumor cells are often less sensitive than their normal counterparts or insensitive to transforming growth factor beta1 (TGFb) effects. We studied the apoptotic effect of exogenous TGFb in B-lymphoma cells, focusing on the activity and the role of Smad and protein phosphatase/kinase signals. Recombinant TGFb treatment and Smad4 siRNA transfection were used in HT58 B-NHL lymphoma cells in vitro. Gene expression and apoptosis were detected by RT-PCR, Western blot analysis and flow cytometry. The role of MEK1 kinase and PP2A activity--measured with a phosphatase assay--were assessed with the help of specific inhibitors. Smad4 siRNA treatment completely abolished TGFb-induced early gene upregulation, indicating the absence of the rapid activation of Smad signaling. Moreover, functional inhibition of Smad4 had no influence on TGFb-induced apoptosis, but it was dependent on PP2A phosphatase activation, ERK1/2 and JNK inactivation in lymphoma cells. The results prove that exogenous TGFb uses Smad4-independent, alternative (PP2A/PP2A-like dependent) signaling pathways for apoptosis induction in lymphoma cells. Further studies are needed to clarify the possible role and involvement of Smad4-independent effects of TGFb in normal and malignant lymphoid cells and in cells of the tumor microenvironment.
authors.affiliation: Semmelweis University, I. Department of Pathology and Experimental Cancer Research, 1085 Budapest, Ulloi út 26, Hungary. anna@korb1.sote.hu
authors.forename: Anna
authors.initials: A
authors.lastname: Sebestyén
authors.forename: Melinda
authors.initials: M
authors.lastname: Hajdu
authors.forename: Lilla
authors.initials: L
authors.lastname: Kis
authors.forename: Gábor
authors.initials: G
authors.lastname: Barna
authors.forename: László
authors.initials: L
authors.lastname: Kopper
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D016393:Lymphoma, B-Cell / Q000378:metabolism* / Q000473:pathology; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction; D051901:Smad4 Protein / Q000502:physiology*; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology* / Q000502:physiology
chemical_list: D005419:Flavonoids; D034741:RNA, Small Interfering; D051901:Smad4 Protein; D053773:Transforming Growth Factor beta1; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1; D048670:MAP Kinase Kinase 4; C482125:MAP2K1 protein, human; D010749:Phosphoprotein Phosphatases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one