Interaction between TGFbeta signaling proteins and C/EBP controls basal and Tat-mediated transcription of HIV-1 LTR in astrocytes.
Signal transduction pathways induced by cytokines can modulate the level of HIV-1 gene transcription and replication in a variety of cells including those from the central nervous system. Here, we investigated the effect of TGFbeta-1 signaling the factors, including Smads, on transcription of the viral LTR in human astrocytic cells. Ectopic expression of Smad-3 increased activity of the viral promoter, while its partner protein, Smad-4, caused a slight decrease in viral gene transcription. Further, Smad-4 was able to suppress transcriptional activation of the LTR by Smad-3 as well as by C/EBPbeta, another activator of LTR transcription in these cells. Results from promoter deletion experiments identified the C/EBP-binding site, which is positioned between nucleotides -114 and -102 as one of the targets for Smad-mediated regulation of the LTR. Band-shift studies showed inhibition of C/EBP binding to its target DNA in protein extract from cells overexpressing Smad-3 and Smad-4. Results from GST pull-down assay and combined immunoprecipitation/Western blot of protein extracts from human astrocytes verified the association of Smad-3 and Smad-4 with C/EBPbeta, suggesting that interaction of C/EBPbeta with Smad-3 and Smad-4 may have a negative impact upon C/EBPbeta-mediated activation of the LTR. Interestingly, Smad-4 showed no inhibitory effect on viral gene transcription in cells expressing Tat protein. However, in the presence of Smad-3, expression of Smad-4 exerted a negative effect on Tat-mediated activation of the LTR promoter. These observations pointed to the functional interplay between viral and cellular proteins in modulating LTR transcription.
Center for Neurovirology and Cancer Biology, College of Science and Technology, Temple University, 1900 North 12th Street, 015-96, Room 203, Philadelphia, PA 19122, USA.
Jacquelyn
J
Coyle-Rink
Thersa
T
Sweet
Selvajothi
S
Abraham
Bassel
B
Sawaya
Olcay
O
Batuman
Kamel
K
Khalili
Shohreh
S
Amini
D001253:Astrocytes / Q000821:virology*; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology; D015696:Gene Products, tat / Q000502:physiology*; D016325:HIV Long Terminal Repeat / Q000235:genetics*; D015497:HIV-1 / Q000235:genetics*; D006801:Humans; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000502:physiology; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000502:physiology*; D054322:tat Gene Products, Human Immunodeficiency Virus
D022782:CCAAT-Enhancer-Binding Protein-beta; D004268:DNA-Binding Proteins; D015696:Gene Products, tat; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D054322:tat Gene Products, Human Immunodeficiency Virus