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

The Wnt/beta-catenin pathway is involved in diverse cell functions governing development and disease. beta-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/beta-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 beta-catenin/TCF-4 leads to inhibition of HIV replication, we knocked down beta-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 beta-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 beta-catenin/TCF-4 also impacted tethering of other transcription factors on the HIV promoter. Specifically, knockdown of TCF-4 enhanced binding of C/EBP beta, C/EBP delta, and NF-kappa B to the HIV LTR, while beta-catenin knockdown increased binding of C/EBP beta and C/EBP delta but had no effect on NF-kappa B. Approximately 150 genes in astrocytes were impacted by beta-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 beta-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.