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.
Coyle-Rink
Jacquelyn
J
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.
Sweet
Thersa
T
Abraham
Selvajothi
S
Sawaya
Bassel
B
Batuman
Olcay
O
Khalili
Kamel
K
Amini
Shohreh
S
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