title: Evidence for regulation of long terminal repeat transcription by Wnt transcription factor TCF-4 in human astrocytic cells.
abstract: The Wnt signaling pathway plays an important role in neural cell development and function. The key components of this pathway, beta-catenin and its partner TCF-4/LEF-1, exert their effects on transcription by entering the nuclei, where they associate with the TCF-4/LEF-1 DNA motif positioned in the promoters of several important genes. Here we examined the role of TCF-4 upon transcription of the human immunodeficiency virus type 1 (HIV-1) promoter in human astrocytic cells. Our results showed that expression of TCF-4 in human astrocytic cells (U-87MG cells) decreased the basal and Tat-mediated transcription of the HIV-1 long terminal repeat (LTR). Results from promoter deletion studies revealed that the promoter sequence of the LTR with no classical binding motif for TCF-4/LEF-1, which spans positions -80 to +80 of the LTR, remained responsive to down-regulation by TCF-4. Noticeably, removal of the sequences between positions -80 and -68 decreased the negative effect of TCF-4 on viral gene transcription. A mutant variant of TCF-4 with no binding site for beta-catenin was able to down-regulate LTR transcription, suggesting that beta-catenin may not be directly involved in the observed regulatory events. Results from the glutathione S-transferase pull-down assay as well as the combined immunoprecipitation and Western blot analysis of protein extract from U-87MG cells revealed an interaction of Tat with TCF-4. Subcellular examination of TCF-4 and Tat in cells expressing either protein alone showed a predominantly nuclear accumulation of these proteins. However, in cells which coexpressed both TCF-4 and Tat, significant levels of these proteins were found in the cytoplasm. All together, these observations provide evidence for the cooperative interaction of TCF-4, the important transcription factor of the Wnt pathway, with Tat; this interaction may determine the level of viral gene transcription in human astrocytic cells.
mesh_terms: D001253:Astrocytes / Q000166:cytology / Q000378:metabolism; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D015696:Gene Products, tat / Q000378:metabolism; D016325:HIV Long Terminal Repeat; D015497:HIV-1 / Q000235:genetics*; D006801:Humans; D051820:TCF Transcription Factors; D015534:Trans-Activators / Q000378:metabolism; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D051176:beta Catenin; D054322:tat Gene Products, Human Immunodeficiency Virus
chemical_list: C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D015696:Gene Products, tat; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D015534:Trans-Activators; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors; D051176:beta Catenin; D054322:tat Gene Products, Human Immunodeficiency Virus