text: Foxp3 Suppresses HIV-1 Gene Expression in Part through Blocking Activation of NF-kappaB
  If Foxp3 functions as a repressor of NF-kappaB-dependent gene expression, then we hypothesized that Foxp3 overexpression could selectively down-regulate transcription from promoters previously shown to be responsive to NF-kappaB. To address this question, we examined the transcriptional activation of the HIV-1 LTR, which contains two tandem cis-acting NF-kappaB binding sites located between positions -102 and -81 with respect to the transcription initiation site [21]. NF-kappaB plays a crucial role in regulating gene expression directed from the HIV-1 LTR in CD4+ T cells [21]. Overexpression of full-length Foxp3, but not DeltaFKH, in HEK 293T cells was able to inhibit basal activation of the HIV-1 LTR (Figure 3A), similar to what was previously demonstrated with the synthetic NF-kappaB reporter vector (Figure 2B). Furthermore, HIV-1 LTR activation was suppressed by full-length Foxp3 and DeltaFKH in Jurkat T cells (Figure 3B). To demonstrate that Foxp3-mediated HIV-1 LTR repression was associated with interactions with NF-kappaB bound to the HIV-1 LTR, we compared basal activation of the HIV-1 LTR or an identical HIV-1 LTR lacking the NF-kappaB sites located between -102 and -81 (HIV-1 Delta-kappaB LTR) (Figure 3C). This mutant HIV-1 LTR construct exhibited reduced levels of transcription compared to the parental HIV-1 LTR in purified healthy donor CD4+ T cells (unpublished data). However, directly comparing the effect of Foxp3 overexpression on the activation of these two viral promoters demonstrated that Foxp3 was more capable of suppressing transcriptional activation of the HIV-1 LTR (Figure 3D) compared to the mutated HIV-1 LTR (Figure 3E). These results suggest that Foxp3 down-regulation of HIV-1 LTR activation was mediated at least in part by cis-acting NF-kappaB binding sites. Residual levels of inhibition of the HIV-1 Delta-kappaB LTR by Foxp3 may be due to NF-AT binding sites located upstream of the NF-kappaB sites within the HIV-1 LTR [22,23]. 
  