Nuclear factor-kappa B binding to the HIV-1 LTR in kidney: implications for HIV-associated nephropathy

Abstract

Background: We have recently shown that renal epithelium is infected by HIV-1 and supports HIV-1 transcription in seropositive patients with renal disease. To investigate the regulation of HIV-1 gene expression in kidney, an HIV-1 transgenic mouse model was used to analyze the host transcriptional proteins that bind the 5' long-terminal repeat (LTR).

Methods: Viral gene expression was assessed in transgenic mouse tissue using Northern blotting and mRNA in situ hybridization. The transcription factors involved in LTR binding were determined using electrophoretic mobility shift assays. Cytoplasmic and nuclear extracts were prepared from tissues with varied levels of transgene expression. The binding of transcription factors to specific LTR fragments was determined using DNA competition experiments and supershifts with transcription factor-specific antibodies.

Results: Tissue-specific expression of the transgene was variable, with viral gene expression in the kidney at an intermediate level as compared with other tissues. Overall, the level of transgene expression directly correlated with abundance of nuclear factor-kappa B (NF-kappa B) in the nuclear extracts. High expressing tissue, however, had a constitutively active form of NF-kappa B. In contrast, the kidney contained an inducible NF-kappa B, which bound the LTR in combination with Sp1, suggesting a requirement for an activating event in renal HIV-1 expression of the LTR.

Conclusions: These studies indicate that the regulation of the HIV-1 LTR in the kidney is similar to lymphoid tissues, and may explain, in part, why the HIV-1 life cycle is supported in kidney.