Expression of transforming-growth-factor (TGF)-beta receptors and Smad proteins in glioblastoma cell lines with distinct responses to TGF-beta1.
A panel of 6 human glioma cell lines was examined for TGF-beta1 responsiveness. U-178 MG and U-251 MG AgCl1 were significantly inhibited by TGF-beta1, while U-343 MGa 31L and U-343 MGa 35L were potently stimulated to proliferate. TGF-beta1 induced endogenous PAI-1 protein synthesis, Smad binding element/(CAGA)12-luciferase-reporter activity, as well as mRNA expression of Smad6 and Smad7 in all gliomas. Interestingly, TGF-beta1 differentially stimulated or inhibited the expression of TbetaR-I and TbetaR-II mRNA in the gliomas. Affinity cross-linking studies using 125I-TGF-beta1 revealed that the gliomas expressed TGF-beta-type-I(TbetaR-I) and -type-II(TbetaR-II) receptors, although binding to TbetaR-II in U-343 MGa 31L and U-251 MG AgCl1 was low to undetectable. Smad2 protein was abundantly present in U-178 MG, U-343 MG, and U-343 MGa 35L, while Smad3 was readily detectable in U-178 MG, U-343 MG, U-343 MGa 35L and U-251 MG AgCl1. In all gliomas, TGF-beta1 induced phosphorylation of Smad2. The level to which TGF-beta1 could activate the pathway leading to induction of the (CAGA)12-luciferase reporter seemed to correlate to the expression levels of TGF-beta receptors, Smad3 and Smad4 proteins. However, despite the plethora of data regarding TGF-beta1 signalling in the different glioma cell lines, the mechanism underlying the differential growth effects mediated by TGF-beta1 is still unclear. The results suggest that a complex balance between several components in the TGF-beta signalling pathway controls glioma responsiveness to TGF-beta1, and extend reports indicating that distinct signal transduction pathways are involved in growth inhibition and other cellular responses.
Department of Cell Biology, University of Nijmegen, The Netherlands. Ester.Piek@LICR.uu.se
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Ten Dijke
D004273:DNA, Neoplasm / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000235:genetics*; D017930:Genes, Reporter; D005909:Glioblastoma; D005910:Glioma; D006801:Humans; D008156:Luciferases / Q000235:genetics; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000235:genetics; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D018125:Receptors, Transforming Growth Factor beta; D011993:Recombinant Fusion Proteins; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D008156:Luciferases