Role of β-Catenin and TCF/LEF Family Members in Transcriptional Activity of HIV in Astrocytes

Abstract

The Wnt/␤-catenin pathway is involved in diverse cell functions governing development and disease. ␤-Catenin, a central mediator of this pathway, binds to members of the TCF/LEF family of transcription factors to modulate hundreds of genes. Active Wnt/␤-catenin/TCF-4 signaling plays a significant role in repression of HIV-1 replication in multiple cell targets, including astrocytes. To determine the mechanism by which active ␤-catenin/TCF-4 leads to inhibition of HIV replication, we knocked down ␤-catenin or TCF/LEF members in primary astrocytes and astrocytomas transiently transfected with an HIV long terminal repeat (LTR)-luciferase reporter that contained an integrated copy of the HIV LTR-luciferase construct. Knockdown of either ␤-catenin or TCF-4 induced LTR activity by 2-to 3-fold under both the episomal and integrated conditions. This knockdown also increased presence of serine 2-phosphorylated RNA polymerase II (Pol II) on the HIV LTR as well as enhanced its processivity. Knockdown of ␤-catenin/TCF-4 also impacted tethering of other transcription factors on the HIV promoter. Specifically, knockdown of TCF-4 enhanced binding of C/EBP␤, C/EBP␦, and NF-B to the HIV LTR, while ␤-catenin knockdown increased binding of C/EBP␤ and C/EBP␦ but had no effect on NF-B. Approximately 150 genes in astrocytes were impacted by ␤-catenin knockdown, including genes involved in inflammation/immunity, uptake/transport, vesicular transport/exocytosis, apoptosis/ cellular stress, and cytoskeleton/trafficking. These findings indicate that modulation of the ␤-catenin/TCF-4 axis impacts the basal level of HIV transcription in astrocytes, which may drive low level/persistent HIV in astrocytes that can contribute to ongoing neuroinflammation, and this axis also has profound effects on astrocyte biology.

TCF1 and LEF1 act as T-cell intrinsic HTLV-1 antagonists by targeting Tax

“…TCF family members have been recently reported to inhibit HIV type 1 (HIV-1) basal transcription (17). Therefore, we analyzed effects of TCF1 and LEF1 on transcription from the HTLV-1 LTR.…”

Epigenetic Regulation of HIV-1 Latency in Astrocytes

“…In vitro, astrocytes support low-level HIV replication, which is inducible in response to proinflammatory signals (11)(12)(13). Through a series of publications, we also demonstrated that robust/productive HIV replication in astrocytes is restricted but can be supported under inflammatory signals, such as gamma interferon (IFN-␥) (13)(14)(15)(16)(17). Priming astrocytes with IFN-␥, in particular, facilitates HIV replication in astrocytes (13)(14)(15)(16)(17).…”

“…Through a series of publications, we also demonstrated that robust/productive HIV replication in astrocytes is restricted but can be supported under inflammatory signals, such as gamma interferon (IFN-␥) (13)(14)(15)(16)(17). Priming astrocytes with IFN-␥, in particular, facilitates HIV replication in astrocytes (13)(14)(15)(16)(17). We used primary human progenitor-derived astrocytes (PDAs) and two astrocytoma cell lines (U87MG and U138) in this study to define the role of astrocytes in HIV latency.…”

“…(ii) We generated astrocytic cell lines that stably harbor the HIV LTRLuc construct. We generated two astrocytic cell lines (U87MG and U251MG) expressing chromosomally integrated HIV LTR luciferase and selected by neomycin resistance, as previously described (16).…”

Identification of Novel T Cell Factor 4 (TCF-4) Binding Sites on the HIV Long Terminal Repeat Which Associate with TCF-4, β-Catenin, and SMAR1 To Repress HIV Transcription

“…These transcriptional factors negatively regulate the HIV LTR by recruiting histone deacetylases (HDACs) and methyltransferases to alter the chromatin structure to render it inaccessible to the transcriptional machinery and hence play a significant role in repression of HIV transcription. We and others have identified an additional transcriptional factor (T cell factor 4 ) that inhibits HIV replication (3,26,28,38). The mechanism by which TCF-4 mediates HIV repression is not entirely clear and is the focus of this study.…”